Indiabix With Explanations

MICROWAVE COMMS INDIABIX SECTION 1 1. The velocity factor of a t ransmission line depends on A. temperature B.skin B. skin effect C.relative C. relative permittivity of dielectric D.none D.none of the above C

Answer: Option C Explanation: ∈r of of a dielectric c hanges with humidity. 2. A loss less line of characteristic impedance Z0 is terminated in pure reactance of - jZ jZ 0 value. VSWR is A.10 A. 10 B.2 B. 2 C.1 C. 1 D.i D.infinity D

Answer: Option D Explanation: A pure reactance does not absorb any power. Therefore VSWR is infinite because |rv | = 1. 3. In a klystron amplifier the input cavity is c alled A.buncher A. buncher B.catcher B. catcher C.Pierce C. Pierce gun D.c D.collector A

Answer: Option A Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode. This beam is transmitted through a glass tube. The input cavity where the beam enters e nters the glass tube is called buncher. As electrons move ahead they see an accelerating field for half cycle and retarding field for t he other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation. The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam. The input is fed at buncher cavity and output is take n at catcher cavity. In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used. The features of a multicavity klystron are : 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 3. Power gain - 60 dB (nominal value) 4. Efficiency - about 40%. A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication. 4. In a circular waveguide the dominant mode is A.TE A. TE01 B.TE B. TE11 C.TE C. TE20 D.T D.TE21 B

Answer: Option B Explanation: Some applications require dual polarization capability. Circular waveguide has this capability. These analysis uses cylindrical coordinates. In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode. If D is diameter of w aveguide λc = 1.706 D for TE11 mode λc = 1.029 D for TE21 mode λc = 0.82 D for TE01 mode λc = 1.306 D for TM01 mode. 5. The reflection coefficient on a line is 0.2 ∠45°. The SWR is A.0.8 A. 0.8 B.1.1 B. 1.1 C.1.2 C. 1.2 D.1 D.1.5 D

Answer: Option D Explanation:

6. Microwave resonators are used in A.microwave A. microwave oscillators B.microwave B. microwave narrow band amplifier C.microwave C. microwave frequency metres D.all D.all of the above D

Answer: Option D Explanation: They are used in all the devices. 7. Assertion (A): TWT uses a focussing mechanism to prevent the electron beam from spreading. Reason (R): In a TWT the electron e lectron beam has to travel a much longer distance than in klystron. Both A and R are correct and R is correct explanation A. of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct A

Answer: Option A Explanation: In a klystron the resonant structure limits the bandwidth. A TWT is a broadband device. Its main components are electron gun (to produce the ele ctron beam) and a structure supporting the slow electromagnetic wave. The velocity of wave propagation along the helix structure is less than velocity of light. The beam and wave travel along the structure at the same speed. Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave. Therefore the signal gets strengthened and amplified output is delivered at the other end of tube. The main features of TWT are : 1. Frequency range - 0.5 GHz to 90 GHz 2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz 3. Efficiency - about 5 to 20%

4. Noise - about 5 dB for low power TWT 25 dB for high power TWT TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc. 8. In a TWT the amplitude of resultant wave travelling down the helix A. increases exponentially B. increases linearly C.decreases C. decreases exponentially D.i D.is almost constant A

Answer: Option A Explanation: In a klystron the resonant structure limits the bandwidth. A TWT is a broadband device. Its main components are electron gun (to produce the electr on beam) and a structure supporting the slow electromagnetic wave. The velocity of wave propagation along the helix structure is less than velocity of light. The beam and wave travel along the struc ture at the same speed. Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave. Therefore the signal gets strengthened and amplified output is delivered at the other end of tube. The main features of TWT are : 1. Frequency range - 0.5 GHz to 90 GHz 2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz 3. Efficiency - about 5 to 20% 4. Noise - about 5 dB for low power TWT 25 dB for high power TWT TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc. 9. Which of the following is not a tr avelling wave? A.e A. e = Em sin (β x - ωt ) B.e B. e = Em cos (β x - ωt ) C.e C. e = Em sin (ωt (ωt - β x ) D.e D.e = Em sin (β x ) D

Answer: Option D

Explanation: In a travelling wave both x both x and and t increase increase simultaneously so that a constant phase point moves in the direction of positive (or negative) x negative) x .

10. Both Impatt and Trapatt devices use avalanche effect A.True A.True B.False B. False A

Answer: Option A Explanation: An Impatt diode has n+ - p - p - i - p - p + structure and is used with reverse bias. It exhibits negative resistance and operates on the principle of avalanche breakdown. Impatt diode circuits are classified c lassified as broadly tunable circuit, low Q circuit and high Q circuit. The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode. The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%. Its applications include police radar systems, low power microwave transmitter etc. Avalanche diode can also be operated in large signal high efficiency mode called Trapped Avalanche Transit Time mode. The Trapatt oscillations depend on the delay in the current caused by avalanche process. The avalanche delay makes it possible to increase the diode voltage well above the breakdown voltage. Therefore a very rapid multiplication of charge carriers occurs. A Trapatt diode is also a negative resistance device. The features of Trapatt diode oscillator are : Frequency 3 to 50 GHz, Power output 1-3 W, efficiency about 25%. Its applications are low power doppler radar, microwave beacon landing system etc. 11. In a directional coupler A. isolation (dB) equals coupling plus directivity B.coupling B. coupling (dB) equals isolation plus directivity

C.directivity C. directivity (dB) equals isolation plus coupling D.i D.isolation (dB) equals (coupling) (directivity) A

Answer: Option A Explanation: Isolation equals coupling plus directivity. 12. As the frequency is increased, incre ased, the charging MVAR in a cable A.decreases A.decreases B. increases C.remain C. remain the same D.decreases D.decreases or remains the scheme B

Answer: Option B Explanation: Charging current and MVAR are proportional to frequency. 13. Loss angle of a good quality cable is about A.1° A. 1° B.30° B. 30° C.70° C. 70° D.90° D.90° A

Answer: Option A Explanation: For ideal dielectric loss angle is ze ro. For good quality cables, loss angle is very small, about 1° only. 14. In a three cavity klystron amplifier, the oscillations are excited in A. input cavity B.output B. output cavity C. intermediate cavity D.both D.both (a) and (b) C

Answer: Option C Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by ox ide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher. As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle. Therefore, some electrons are accelerated and some are retarded. This process is called ve locity modulation. The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam. The input is fed at buncher cavity and output is taken at catcher cavity. In a two cavity klystron only buncher and c atcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used. The features of a multicavity klystron are : 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 3. Power gain - 60 dB (nominal value) 4. Efficiency - about 40%. A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication. 15. In the given figure reflection coefficient at load is

B.Coaxial B. Coaxial C.Both C. Both D.None D.None of the above B

Answer: Option B Explanation: Since fields are confirmed within a coaxial cable it is non-radiating. 17. Assertion (A): The impedance of a matched load is equal to characteristic impedance of line. Reason (R): A matched termination absorbs all the power incident on it. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct A

Answer: Option A Explanation: Matched load means no reflections. 18. Skin effect is more pronounced at high frequencies. A.T A.True B.False B.False A

Answer: Option A Explanation: Skin effect increases as frequency increases.

A.0.6 A. 0.6 B. - 0.6 C.0.4 C. 0.4 D.D.- 0.4 B

Answer: Option B Explanation:

19. Assertion (A): The phenomenon of differential mobility is called transferred electron effect. Reason (R): GaAs exhibits transferred electron effect . Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct B

16. Which of the following lines is non-radiating? A.Open A. Open two wire


A Gunn diode uses GaAs which has a negative differential mobility, i .e., a decrease in carrier velocity with increase in electric field. This effects is called transferred electron effect. The impedance of a Gunn diode is tens of o hms. A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement t o couple RF power to load. Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers. 20. Which of the following devices uses a helix? A.Klystron A. Klystron amplifier B.Klystron B. Klystron oscillator C.TWT C. TWT D.Both D.Both (a) and (b) C

Answer: Option C Explanation: In a klystron the resonant structure limits the bandwidth. A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave. The velocity of wave propagation along the helix structure is less than velocity of light. The beam and wave travel along the structure at the same speed. Thus interaction occurs between beam and w ave and the beam delivers energy to the RF wave. Therefore the signal gets strengthened and amplified output is delivered at the other end of tube. The main features of TWT are : 1. Frequency range - 0.5 GHz to 90 GHz 2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz 3. Efficiency - about 5 to 20% 4. Noise - about 5 dB for low power TWT 25 dB for high power TWT TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

21. Which of the following parameters is negligible in transmission lines? A.R A. R B.L B. L C.C C. C D.G D.G D

Answer: Option D Explanation: Shunt conductance can be neglected in most of calculations. 22. The width of a radio beam from a 1 m diameter parabolic antenna at 10 GHz is about A.100° A. 100° B.50° B. 50° C.5° C. 5° D.1° D.1° C

Answer: Option C Explanation:

. 23. The diagram to show distance time history of electrons in klystron amplifier is called A.apple A.apple gate diagram B.asynchronous B. asynchronous diagram C.bunching C. bunching diagram D.velocity D.velocity modulation diagram A

Answer: Option A Explanation: Applegate diagram is distance time plot. 24. Impedance level of Impatt diodes is generally lower than that of Gunn diodes A.T A.True B.False B.False A

Answer: Option A Explanation: An Impatt diode has n+ - p - p - i - p - p + structure and is used with reverse bias.

It exhibits negative resistance and operates on the principle of avalanche breakdown. Impatt diode circuits are classified c lassified as broadly tunable circuit, low Q circuit and high Q circuit. The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode. The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%. Its applications include police radar systems, low power microwave transmitter etc. 25. A quarter wave line open circuited at far end behaves as A. inductance B.L B. L and C in parallel C.capacitance C. capacitance D.L D.L and C in series D

Answer: Option D Explanation: A quarter wave line o.c. at far end behaves as a series tuned circuit. 26. A line has Z0 = 300 ∠ 0° Ω. If Z If Z L = 150 ∠ 0° Ω, reflection coefficient is A.0.5 A. 0.5 B.0.3333 B. 0.3333 C. -0.3333 D.D.-0.5 C

Answer: Option C Explanation: Reflection coefficient

27. Assertion (A): A backward wave oscillator has an internal positive feedback. Reason (R): A positive feedback is necessary for sustained oscillations. Both A and R are correct and R is correct A. explanation of A

Both A and R are correct but R is not correct explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct

B.

B

Answer: Option B Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide fre quency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT. The growing RF wave travels tr avels in opposite direction to the electron beam. The frequency of wave can be changed by changing the voltage which controls the beam velocity. Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are: 1. Frequency range - 1 GHz to 1000 GHz. 2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed). It is used as signal source in transmitters and instruments. 28. In a microstrip transmission the signal can be easily redirected by changing the centre strip. A.T A.True B.False B.False A

Answer: Option A Explanation: A Microstrip line has a single dielectric substratc with ground plane on one side and a strip on the other face. Its special feature is easy access to top surface so that minor adjustments can be made after circuit fabrication. The high dielectric constant of the substrate reduces guide wavelength and circuit dimensions. A microstrip line is the most commomly used transmission structure for microwave integrated circuits. 29. The frequency of oscillation in a backward wave oscillator can be changed by

A.varying A. varying the voltage which controls beam velocity B.varying B. varying the beam current both by varying the beam current and by light C. varying the voltage which controls beam velocity D.c D.changing the rate of thermionic emission

31. In the given figure the time taken by the wave to make one ro

A

Answer: Option A Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide frequency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT. The growing RF wave travels t ravels in opposite direction to the electron beam. The frequency of wave can be changed by changing the voltage which controls the beam ve locity. Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are: 1. Frequency range - 1 GHz to 1000 GHz. 2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed). It is used as signal source in transmitters and instruments.

A.10 A. 10 ns B.20 B. 20 ns C.30 C. 30 ns D.40 D.40 ns D


32. For a 50 Ω resistor for 3 GHz application, the stray capacitance should be less than A.1 A. 1 μF μF B.1 B. 1 nF C.1 C. 1 pF D.0.1 D.0.1 pF pF D

30. A line has a phase constant of 29.8 rad/m rad/m. At 1000 MHz the wavelength is Answer: Option D A.29.8 A. 29.8 m Explanation: B.2.98 B. 2.98 m XC should be at least ten times greater than R. C.2.1 C. 2.1 m Therefore for 50 Ω resistor at 3 GHz, C should be less D.0 D.0.21 m than 0.1 pF. D Answer: Option D Explanation: .

33. In a travelling wave tube distributed interaction between an electron beam and a travelling wave takes place A.T A.True B.False B.False A

Answer: Option A Explanation: In a klystron the resonant structure limits the bandwidth. A TWT is a broadband device. Its m ain components are electron gun (to produce the electron beam) and

a structure supporting the slow electromagnetic wave. The velocity of wave propagation along the helix structure is less than velocity of light. The beam and wave travel along the structure at the same speed. Thus interaction occurs between beam and w ave and the beam delivers energy to the RF wave. Therefore the signal gets strengthened and amplified output is delivered at the other end of tube. The main features of TWT are : 1. Frequency range - 0.5 GHz to 90 GHz 2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz 3. Efficiency - about 5 to 20% 4. Noise - about 5 dB for low power TWT 25 dB for high power TWT TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc. 34. The fabrication of microstrip line is done by A.photo A. photo etching B.printed B. printed circuit technique C.oxidation C. oxidation D.c D.cladding B

Answer: Option B Explanation: Printed circuit techniques is used for micro strip line. 35. The condition of minimum distortion in a transmission line is

A.RL A.RL = 1 B.R B. R = 0 C. D. D

Answer: Option D Explanation: The condition for minimum distortion is found by equating

The result is

.

36. The action of backward wave oscillator is similar to that of A.klystron A.klystron amplifier B.reflex B. reflex klystron oscillator C.TWT C. TWT D.magnetron D.magnetron C

Answer: Option C Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide frequency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT. The growing RF wave travels in o pposite direction to the electron beam. The frequency of wave can be changed by changing the voltage which controls the beam velocity. Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are: 1. Frequency range - 1 GHz to 1000 GHz. 2. Power output - 10 mV m V to 150 mW (continuous wave) 250kW (pulsed). It is used as signal source in transmitters and instruments.

37. In the given figure the reflection coefficient at source end is

A.1 A. 1 B. -1 C.1/3 C. 1/3 D.D.-1/3 C

Answer: Option C Explanation: . 38. Assertion (A): Artificial transmission lines are frequently used in laboratories. Reason (R): An artificial transmission line can be used to represent an actual line and can also be used as a delay circuit, as attenuator, as filter network etc. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct A

Answer: Option A Explanation: Artificial transmission lines have many applications. One of the applications is to simulate an ac tual line in the laboratory. 39. In a backward wave oscillator the wave travelling along the line winds itself back and forth A.True A.True B.False B. False A

Answer: Option A

Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide fre quency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT. The growing RF wave travels tr avels in opposite direction to the electron beam. The frequency of wave can be changed by changing the voltage which controls the beam velocity. Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are: 1. Frequency range - 1 GHz to 1000 GHz. 2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed). It is used as signal source in transmitters and instruments. 40. A line is excited by a 100 V dc source. If reflection coefficients at both ends are 1 each then A. there will be no oscillations on line B.there B. there will be only 1 or 2 oscillations on line C.there C. there will be a finite number of oscillations on line D.t D.the oscillations will continue indefinitely D

Answer: Option D Explanation: Because rv = = 1 at each end, the line voltage will not reach a steady value and oscillations will continue indefinitely. 41. Assertion (A): A coaxial line is a non-radiating line. Reason (R): In a coaxial line the electric and magnetic fields are confined to the region between the concentric conductors. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct A

Answer: Option A Explanation: Since the fields are confined, there is no radiation.

42. Reflex klystron oscillator is essentially a low power device A.True A.True B.False B. False A

Answer: Option A Explanation: It uses a single cavity resonator for generating microwave oscillations. Its parts are electron gun, resonator, repeller and output coupling. It operates on the principle of positive feed back. The repeller electrode is at negative potential and sends the partially bunched electron beam back to resonator cavity. This positive feedback supports oscillations. Its feature are: 1. Frequency range - 2 to 100 GHz 2. Power output - 10 MW to about 2 W 3. Efficiency - 10 - 20 % Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc. 43. A 10 km long line has a characteristic impedance of 400 ohms. If line length is 100 km, the characteristic impedance is A.4000 A. 4000 Ω B.400 B. 400 Ω C.40 C. 40 Ω D.4 D.4 Ω B

Answer: Option B Explanation: and is independent of line length. 44. A matched generator (Zg = Z0) with 1 Ω available. If all ports are matched, the power delivered at ports 1, 2, 3 respectively are A.0.5 A. 0.5 W, 0.5 W, 0 W B.0 B. 0 W, 0 W, 1 W C.0.33 C. 0.33 W each D.0 D.0 W, 0.25 W, 0.25 W A

Answer: Option A Explanation: Since all ports matched, input SWR = 1. No power is reflected and Pin = P4 = 1 W. This power splits between ports 1 and 2. Therefore P1 = P2 = 0.5 Ω, P 3 = 0. 45. Which TM mode in rectangular waveguide has lowest cutoff frequency? A.TM A. TM11 B.TM B. TM01 C.TM C. TM10 D.TM D.TM21 A

Answer: Option A Explanation: Hz = 0

E x = = ± ZTM Hy Ey = = ± ZTM H x where E0 is the amplitude of the wave. The expressions for β, λc, f c, λg, a are the same as for TE waves. For TM wave the lowest cut c ut off frequency in rectangular wave guide is for TM 11 mode. If , the cutoff frequency for TM11 mode is about 12% more than that for TE20 mode. 46. A resistive microwave load with Z L = 150 Ω is connected to 50 Ω coaxial line. SWR is A.more A.more than 3 B. less than 3 C.equal C. equal to 3 D.either D.either (a) or (c) C


47. Which of the following devices uses a slow wave structure? A.Klystron A. Klystron two cavity amplifier B.Klystron B. Klystron multicavity amplifier C.Reflex C. Reflex klystron oscillator D.T D.TWT D

Answer: Option D Explanation: In a klystron the resonant structure limits the bandwidth. A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave. The velocity of wave propagation along the helix structure is less than velocity of light. The beam and wave travel along the structure at the same speed. Thus interaction occurs between beam and w ave and the beam delivers energy to the RF wave. Therefore the signal gets strengthened and amplified output is delivered at the other end of tube. The main features of TWT are : 1. Frequency range - 0.5 GHz to 90 GHz 2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz 3. Efficiency - about 5 to 20% 4. Noise - about 5 dB for low power TWT 25 dB for high power TWT TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc. 48. In a turnstile antenna two-half two -half wave resonant wire radiators are placed at 90° to each other in the same plane and are excited A. in phase B. in phase opposition C.90° C. 90° out of phase with each other D.4 D.45° out of phase with each other C


Since the two wire radiators are at 90° to each other, they have to be exc ited 90° out of phase with each other. 49. A waveguide section in a microwave circuit acts as A. LP filter B.Bandpass B. Bandpass filter C.HP C. HP filter D.Band D.Band stop filter C

Answer: Option C Explanation: It allows high frequencies. 50. In a klystron amplifier dc e lectron velocity is v 0 and dc electron charge density is r0 the dc beam current is A. r0v 0 B.r B. r0/v 0 C.v C. v 0/r0 D.( D.(v 0/r0)2 A

Answer: Option A Explanation:

= coulomb |sec|m2 = current density.

SECTION 2 1. The directivity in a receiving antenna increases the intercept area in forward direction reduces the noise picked up from other sources provides a means of discriminating against undesired signals originating in directions other than in which the desired transmitter lies. Which of the above statements are correct? A.1 A. 1 only B.1 B. 1 and 2 only C.1, C. 1, 2 and 3 D.2 D.2 and 3 only C

2. Assertion (A): PIN diode can be used as attenuator and limiter. Reason (R): PIN diode has a thin intrinsic layer. Both A and R are correct and R is correct explanation A. of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct B

3. The bunching action which occurs in multicavity klystron amplifier can be represented by Applegate diagram A.True B.False B. False A

Answer: Option A Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode. This beam is transmitted through a glass tube. The input cavity where the beam enters e nters the glass tube is called buncher.

As electrons move ahead they see an accelerating field for half cycle and retarding field for t he other half cycle. Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation. The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam. The input is fed at buncher cavity and output is take n at catcher cavity. In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or m ore intermediate cavities are also used. The features of a multicavity klystron are : 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 3. Power gain - 60 dB (nominal value) 4. Efficiency - about 40%. A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication. 4. The cut off wavelength in circular waveguide A.guide A.guide diameter B.square B. square of guide diameter C.cube C. cube of guide diameter D.s D.square root of guide diameter A

Answer: Option A Explanation: Some applications require dual polarization capability. Circular waveguide has this capability. These analysis uses cylindrical coordinates. In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode. If D is diameter of w aveguide λc = 1.706 D for TE11 mode λc = 1.029 D for TE21 mode λc = 0.82 D for TE01 mode λc = 1.306 D for TM01 mode. 5. In Reflex Klystron Klystron oscillator the focussing focussing electrode is is at a high potential A. True B. False B

Answer: Option B

Explanation: It uses a single cavity resonator for generating microwave oscillations. Its parts are electron gun, resonator, repeller and output coupling. It operates on the principle of positive feed back. The repeller electrode is at neg ative potential and sends the partially bunched electron beam back to resonator cavity. This positive feedback supports oscillations. Its feature are: 1. Frequency range - 2 to 100 GHz 2. Power output - 10 MW to about 2 W 3. Efficiency - 10 - 20 % Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc. 6. Consider the following statements Impedance of Gunn diode is about tens of ohms. Impedance of Impatt diode is a few ohms. Impedance of Impatt diode are of the same order. Impedance of Impatt diode is more than that of Gunn diode. Which of the above statement are correct? A. all B. 1 and 2 only C. 1, 2 and 3 D. 1, 2 and 4 B

Answer: Option B Explanation: A Gunn diode uses GaAs which has a negative differential mobility, i .e., a decrease in carrier velocity with increase in electric field. This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms. A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to c avity, biasing arrangement for Gunn diode and arrangement to couple RF power to load. Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers. An Impatt diode has n+ - p - p - i - p - p + structure and is used with reverse bias.

It exhibits negative resistance and operates on the principle of avalanche breakdown. Impatt diode circuits are classified as broadly tunable circuit, low Q circuit and high Q circuit. The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode. The features of Impatt diode oscillator are : Frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%. Its applications include police radar systems, low power microwave transmitter etc. 7. In high frequency circuits impedance matching can be done by open circuited stubs short circuited stubs transformer Which of the above correct? A. 1, 2 and 3 B. 1 and 2 only C. 1 and 3 only D. 2 and 3 only A

Answer: Option A Explanation: All the three can be used for impedance matching in high frequency circuits. 8. The directive gain of a transmitting antenna is proportional to A. its cross-sectional area B. square of cross-sectional area C. square root of cross-sectional area D. cube root of cross-sectional area A


and is thus proportional to cross sectional area.

9. In a loss line line RL < Z0, then A. Reflection coefficient is zero B. Reflection coefficient is ∞ C. Reflection coefficient is negative D. Reflection coefficient is positive C


11. If a line having Z0 = 300 ∠ 0 W is open circuited at far end, VSWR is A. 0 B. 1 C. ∞ D. 2 C


Since RL < Z0, rv is is negative. If line is o.c. |r v | = 1 and VSWR 10. Assertion (A): A backward wave oscillator can be used as a sweep generator. Reason (R): The frequency of oscillation of a backward wave oscillator can be changed by varying the voltage which controls the beam velocity. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C. A is correct but R is wrong D. A is wrong but R is correct A

Answer: Option A Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide fre quency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT. The growing RF wave travels tr avels in opposite direction to the electron beam. The frequency of wave can be changed by changing the voltage which controls the beam velocity. Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are: 1. Frequency range - 1 GHz to 1000 GHz. 2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed). It is used as signal source in transmitters and instruments.

= ∞.

12. If f If f is is the frequency of electromagnetic wave, f wave, f c is cutoff frequency, then in a rect angular waveguide A.attenuation A. attenuation is low when f when f > f > f c B.attenuation B. attenuation is low when f when f < f < f c C.attenuation C. attenuation is high when f when f < f < f c D.either D.either (b) or (c) A

Answer: Option A Explanation: Wavelength should be less than cutoff wavelengths. Therefore frequency should be higher than cutoff frequency for minimum attenuation. 13. Assertion (A): The condition of minimum distortion in a transmission line is L = RC/G. RC/G . Reason (R): Line loading means addition of inductance to satisfy the condition L = RC/G. RC/G. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct B

Answer: Option B Explanation: Oscillator circuits using vacuum tubes (triodes, pentodes) have the following limitations at very high frequencies (microwave region). The stray capacitances and inductances become important and affect the operation of the circuit. At low frequencies the transit time between cathode and anode is a small fraction of period of osc illation.

However, at microwave frequencies this transit time becomes comparable to time period of osc illations. 14. A magnetron has a cylindrical cathode surrounded by an anode structure having cavities opening into interaction space by means of slots A.True A.True B.False B. False A

Answer: Option A Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide frequency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT. The growing RF wave travels t ravels in opposite direction to the electron beam. The frequency of wave can be changed by changing the voltage which controls the beam ve locity. Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are: 1. Frequency range - 1 GHz to 1000 GHz. 2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed). It is used as signal source in transmitters and instruments. 15. The correct sequence of parts parts in klystron amplifier are A. anode, catcher cavity, cathode, buncher cavity B. athode, buncher cavity, catcher cavity, c avity C. anode, buncher cavity, catcher cavity, cathode D. cathode, catcher cavity, anode, buncher cavity B

Answer: Option B Explanation: Cathode is the first part and anode is t he last. 11. If a line having Z0 = 300 ∠ 0 W is open circuited at far end, VSWR is A. 0 B. 1 C. ∞ D. 2

C

Answ er: Option C Explanation:

If line is o.c. |rv | = 1 and VSWR

= ∞.

12. If f If f is is the frequency of electromagnetic wave, f wave, f c is cutoff frequency, then in a rect angular waveguide A.attenuation A. attenuation is low when f when f > f > f c B.attenuation B. attenuation is low when f when f < f < f c C.attenuation C. attenuation is high when f when f < f < f c D.either D.either (b) or (c) A

Answer: Option A Explanation: Wavelength should be less than cutoff wavelengths. Therefore frequency should be higher than cutoff frequency for minimum attenuation. 13. Assertion (A): The condition of minimum distortion in a transmission line is L = RC/G. RC/G . Reason (R): Line loading means addition of inductance to satisfy the condition L = RC/G. RC/G. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct B

Answer: Option B Explanation: Oscillator circuits using vacuum tubes (triodes, pentodes) have the following limitations at very high frequencies (microwave region). The stray capacitances and inductances become important and affect the operation of the circuit. At low frequencies the transit time between cathode and anode is a small fraction of per iod of oscillation. However, at microwave frequencies this transit t ime becomes comparable to time period of oscillations. 14. A magnetron has a cylindrical cathode surrounded by an anode structure having cavities opening into interaction space by means of slots

A.True A.True B.False B. False A

Answer: Option A Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide frequency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT. The growing RF wave travels t ravels in opposite direction to the electron beam. The frequency of wave can be changed by changing the voltage which controls the beam ve locity. Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are: 1. Frequency range - 1 GHz to 1000 GHz. 2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed). It is used as signal source in transmitters and instruments. 15. The correct sequence of parts in klystron klystron amplifier are A. anode, catcher cavity, cathode, buncher cavity B. cathode, buncher cavity, catcher cavity, c avity C. anode, buncher cavity, catcher cavity, cathode D. cathode, catcher cavity, anode, buncher cavity B

Answer: Option B Explanation: Cathode is the first part and anode is the last. 16. A transmission line has Z has Z 0 = 300 Ω and Z and Z L = (300 300) ohm. The transmission coefficient is

A. B. C. D.

1.265 ∠ - 18.43° 1.01 ∠ - 10° 1.14 ∠ 66.68° 1.09 ∠ 66.68°

A


Transmission coefficient = 1.265 ∠- 18.43°. 17. In a reflex klystron oscillator, oscillator, repeller electrode is at low positive potential . high positive potential . negative potential . zero potential . C

Answer: Option C Explanation: It uses a single cavity resonator for generating microwave oscillations. Its parts are electron gun, resonator, repeller and output coupling. It operates on the pr inciple of positive feed back. The repeller electrode is at neg ative potential and sends the partially bunched electron beam back to resonator cavity. This positive feedback supports oscillations. Its feature are: 1. Frequency range - 2 to 100 GHz 2. Power output - 10 MW to about 2 W 3. Efficiency - 10 - 20 % Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.

18. A quarter wave line short circuited at load end behaves as A.an A.an inductance B.an B. an inductance and capacitance in series

C.a C. a capacitance D.a D.an inductance and capacitance in parallel

C

D

Answer: Option D Explanation: A quarter wave line short-circuited at far end behaves as a parallel tuned circuit. 19. A (75 - J - J50) 50) ohm load is connected to a coaxial of Z0 = 75 ohm at 10 GHz. G Hz. The best method of matching is to connect A.an A. an inductance at load B.a B. a short circuited stub at load C.a C. a short circuited stub at specific distance from load D.a D.a capacitance at specific distance from load

Answer: Option C Explanation: A Gunn diode uses GaAs which has a negative differential mobility, i .e., a decrease in carrier velocity with increase in electric field. This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms. A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to c avity, biasing arrangement for Gunn diode and arrangement to couple RF power to load. Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers.

C

22. A magnetron requires an ext ernal magnetic field with flux lines parallel to axis of cathode A.T A.True B.False B.False

Answer: Option C Explanation: A short-circuited stub is a suitable method of matching.

A

20. The width of a radio beam from a 1 m diameter parabolic antenna at 1 GHz is about 100° . 50° . 5° . 2° . B

Answer: Option B Explanation: Beam width between nulls of a parabolic antenna

. Therefore 50° is the nearest value. 21. Which one of the following following is transferred locking electron device C antenna? antenna? A. BARITT diode B. IMPATT diode C. Gunn diode D. Step recovery diode

Answer: Option A Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide fre quency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT. The growing RF wave travels tr avels in opposite direction to the electron beam. The frequency of wave can be changed by changing the voltage which controls the beam velocity. Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are: 1. Frequency range - 1 GHz to 1000 GHz. 2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed). It is used as signal source in transmitters and instruments. View Answer Discuss Answer Discuss in Forum Workspace Forum Workspace Report 23. When a line short circuited cir cuited at far end, the minimum voltage occurs at A. f ar ar end B.source B. source end

C.midway C. midway between source and far end D.n D.none of the above A

Answer: Option A Explanation: When a line is short-circuited at far end, the voltage at far end is zero. 24. In a TWT the axial component of electric field advances along the tube A.at A. at a velocity that is almost equal to speed of light B.at B. at a velocity that is a small fraction of speed of light C.at C. at a velocity that is about 50% of speed of light at a velocity that may be even more than speed of D. light B

Answer: Option B Explanation: In a klystron the resonant structure limits the bandwidth. A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave. The velocity of wave propagation along the helix structure is less than velocity of light. The beam and wave travel along the structure at the same speed. Thus interaction occurs between beam and w ave and the beam delivers energy to the RF wave. Therefore the signal gets strengthened and amplified output is delivered at the other end of tube. The main features of TWT are : 1. Frequency range - 0.5 GHz to 90 GHz 2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz 3. Efficiency - about 5 to 20% 4. Noise - about 5 dB for low power TWT 25 dB for high power TWT TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc. 25. If other parameter are constant, transmission loss at 5 GHz as compared to that at 0.5 GHz is

A.20 A.20 dB more B.20 B. 20 dB less C.700 C. 700 dB more D.1 D.100 dB less A

Answer: Option A Explanation: As frequency increases, transmission loss increases slightly. Workspace 26. For a circular wave guide A.cutoff A. cutoff frequency for TE10 and TE01 modes are same cutoff frequency for TE10 and TE01 modes are B. different cutoff frequency for TE10 mode = twice the cutoff C. frequency for TE20 mode cutoff frequency for TE 10 mode = haf the cutoff D. frequency for TE20 mode A

Answer: Option A Explanation: When a circular waveguide is rotated by 90°, the configuration remain the same. 27. In the given figure the reflected voltage wave after first reflection is

A.18 A.18 V B.-18 B. -18 V C.30 C. 30 V D.D.-30 V B


.

28. Assertion (A): A half wavelength line can be used as a 1 : 1 transformer. Reason (R): The input impedance of a half wavelength line is equal to load impedance. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct A

Answer: Option A Explanation: Since a half wavelength line has an input impedance equal to load impedance, the impedance transformation ratio is 1:1. 29. The magnitudes of OC and SC input impedances of a transmission line an 100 Ω and 25 Ω. The characteristic impedance is A.25 A. 25 Ω B.50 B. 50 Ω C.75 C. 75 Ω D.1 D.100 Ω B


31. Which of the following terminations makes the input impedance of a line equal to characteristic impedance Z0? A. line open circuited at far end B. line terminated in Z 0 C. line short circuited at far end D. line terminated in inductance B

Answer: Option B Explanation: If ZL is load impedance and Z 0 is characteristic impedance.

Input impedance = . If ZL = Z0 the input impedance = Z 0. 32. In microwave system the function of mode filter is A. to suppress modes with lower cut o ff frequencies B.to B. to suppress modes with higher cut off frequencies C.to C. to change mode of wave transmission D.both D.both (b) and (c) D

Answer: Option D Explanation: Mode filter suppress modes with lower cutoff frequencies. 33. For the strip line in the given figure the capacitance per unit length =

30. A loss less line is terminated in a circular lines are E lines A. SWR = 0 B. SWE = 0 C. SWR is finite D. SWR = ∞ C

Answer: Option C Explanation: A. = finite number and VSWR

= finite number.

B. C.

D. A

Answer: Option A Explanation: frads/unit length.

Reason (R): A quarter wave transformer is a transmission line of quarter wave length. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct B

34. The total field developed by an antenna arr ay at a distant point is phasor sum of fields produced by individual A. antennas of the array algebraic sum of fields produced by individual B. antennas of the array C.either C. either (a) or (b) depending on type of array D.n D.neither (a) nor (b)

Answer: Option B Explanation: A line of length is called quarter wavelength line. Such a line is used for impedance matching. If

A

Answer: Option A Explanation: Since field is a phasor quantity we have to take phasor sum.

A quarter wave line can match a source impedance Zin with load impedance Z impedance Z L by selecting a proper value of Z0 so as to satisfy equation. Such a line is also called

transformer.

35. High speed logic circuits use A.pulses A. pulses with very small width B.pulses B. pulses with very large width C.pulses C. pulses whose width is neither small nor large D.e D.either (b) or (c)

38. Assertion (A): Magnetron is generally used in n mode. Reason (R): Frequency for p mode can be easily separated from adjacent modes. Both A and R are correct and R is correct A. explanation of A A Both A and R are correct but R is not correct Answer: Option A B. explanation of A Explanation: C.A C. A is correct but R is wrong High speed means time period is small. Therefore pulses should should also have small width. D.A D.A is wrong but R is correct

36. To couple a coaxial line to a parallel wire line it is best t o use A.slotted A. slotted line B.balun B. balun C.directional C. directional coupler D.λ D.λ/4 transformer B

Answer: Option B Explanation: A balun gives 4 : 1 impedance transformation. 37. Assertion (A): A quarter wave transformer is used to match a resistive load to a transmission line.

A

Answer: Option A Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide fre quency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT. The growing RF wave travels tr avels in opposite direction to the electron beam. The frequency of wave can be changed by changing the voltage which controls the beam velocity.

Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are: 1. Frequency range - 1 GHz to 1000 GHz. 2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed). It is used as signal source in transmitters and instruments.

Explanation: TE01 mode is unaffected because its horizontally oriented elec to the conducting strips. 42. The directive gain of a transmitting antenna is A. proportional to wavelength B. inversely proportional to wavelength C. proportional to square of wavelength D. inversely proportional to square of wavelength D

39. A balun should have A. low SWR at both ports B.high B. high SWR at both ports C.high C. high SWR at input port and low SWR at output port D.l D.low SWR at input port and high SWR at output


A

Answer: Option A Explanation: Turn ratio is so selected as to give low SWR at both ports.

43. A duplexer is used to A. couple two antennas to a transmitter B. isolate the antenna from the local oscillator prevent interference between two antennas C. connected to receiver use an antenna for reception or transmission D. 40. Assertion (A): The velocity factor of a line is the ratio of wave velocity vewithout locity oninterference the line to speed of light. Reason (R): If the conductors of a line are immersed in a non magnetic insulating liquid, the wave D velocity increases. A.Both A. Both A and R are correct and R is correct explanation of A Answer: Option D B.Both B. Both A and R are correct but R is not correct explanation of Explanation: A Same antenna is used for transmission and reception. C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct 44. A branched duplexer requires C A.TR A.TR tubes Answer: Option C B.ATR B. ATR tube Explanation: C.both C. both TR and ATR tube R is wrong because wave velocity decreases. D.none D.none of the above C

41. In mode filter of the given figure which of the following modes is unaffected Answer: Option C Explanation: A branched duplexer funds use in narrow bandwidth applications. TR tube stands for transmit-receive t ube and ATR tube stands for antitransmit receive tube. A.TE A. TE01 Both these tubes are used in branched duplexer. B.TE B. TE10 C.TE C. TE11 D.a D.all TM A

Answer: Option A

45. In a backward wave oscillator o scillator the wave A. travelling along the line winds itself back and forth B.progresses B. progresses only in forward direction C.progresses C. progresses only in backward direction

D.e D.either (a) or (c)

Both A and R are correct but R is not correct explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct

B.

A

Answer: Option A Explanation: It is somewhat similar to TWT and can deliver microwave powerBover a wide w ide frequency band. It has an electron gun and a helix structure. However the interaction Answer:between Option Belectron beam and RF wave is different than in TWT. Explanation: The growing RF wave travels t ravels in opposite direction to the electron A PINbeam. diode has an intrinsic (i ( i ) layer between p between p and and n The frequency of wave can be changed by changing the voltage layers. which When controls reverse the beam bias isve applied locity.depletion layers Moreover the amplitude of oscillations can be decreased continuously are formed toat p-i at zero p-i and by and changing i-n junctions. i-n junctions. the beam current. The effective/width of depletion layer increases by It features are: the width of i layer. layer. It can be used as a voltage 1. Frequency range - 1 GHz to 1000 GHz. controlled attenuator. 2. Power output - 10 mV to 150 mW (continuous wave) 250kW At(pulsed). high frequencies the rectification effect ceases It is used as signal source in transmitters and instruments. and impedance of diode is effectively that of i layer. layer. This impedance varies with the applied bias. It is used 46. A coaxial line has L = 500 nH/m and C = 50 p 50 pF/m. F/m. The characteristic in highimpedance frequency is switching circuits, limiters, A.500 A. 500 Ω modulators etc. B.250 B. 250 Ω C.100 C. 100 Ω 49. In a vacuum tube, the transit time of electron D.5 D.50 Ω between cathode and anode is important at A. low frequencies C B.high B. high frequencies Answer: Option C C.both C. both (a) and (b) Explanation: f requencies requencies which are neither very low nor very D. high B

. 47. The main feature of a parametric amplifier is A. low noise B.very B. very high gain C.broad C. broad bandwidth D.b D.both (b) and (c) C

Answer: Option C Explanation: Since reactance does not contribute thermal noise to the circuit, it is a low noise device. 48. Assertion (A): PIN diode is commonly used for microwave control. Reason (R): A PIN diode uses heavily doped p doped p and and n materials. Both A and R are correct and R is correct A. explanation of A

Answer: Option B Explanation: At high frequencies transit time is large as compared to the period of microwave signal. 50. Assertion (A): A line of length and short circuited at far end has an input impedance of infinity. Reason (R): A line of length and short circuited at far end behaves as a parallel re sonant circuit. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D.A is wrong but R is correct A

Answer: Option A Explanation: A parallel tuned circuit has an infinite impedance if R is zero.

1. A cavity resonator is A.a A. a hollow metallic enclosure a hollow enclosure having magnetic material as its B. walls a hollow enclosure having dielectric material as its C. walls D.e D. either (b) or (c) A

Answer: Option A Explanation: Hollow metallic enclosures exhibit resonance behaviour when excited by electromagnetic field. These enclosures are called cavity resonators. 2. If antenna diameter is increased four times, the maximum range is increased by a factor o f A.2 A. 2 B.2 B. 2 C.4 C. 4 D.0 D. 0.2 C

Answer: Option C Explanation: Range of radar is proportional to antenna diameter. 3. Assertion (A): Gunn diode is a transferred electron device.

MICROWAVE COMMS INDIABIX SECTION 3

Reason (R): A Gunn oscillator uses the phenomenon of transferred electron effect. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D. A is wrong but R is correct B

5. The component in the given given figure is Answer: Option B Explanation: A Gunn diode uses GaAs which has a negative differential mobility, i .e., a decrease in carrier velocity with increase in electric field. This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms. A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to c avity, biasing arrangement for Gunn diode and arrangement to couple RF power to load. Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers. 4. Atomic and molecular resonance is observed in many substances A.at A. at microwave frequencies B.at B. at low frequencies C.at C. at frequencies used in AM broadcast D.at D. at both (b) and (c) A

Answer: Option A Explanation: Atomic and molecular distances are very small. Therefore resonance can occur only at microwave frequencies.

A. B. C. D.

attenuator T type low pass filter T type high pass filter phase shifter

B

Answer: Option B Explanation: Z01 provides series inductances and teflon filled low impedanc line Z02 provides shunt capacitance.

6. The semiconductor diode diode which can be used in switching switching circu microwave range is A. PIN diode B. Varactor diode C. Tunnel diode D. Gunn diode A

Answer: Option A Explanation: A PIN diode has an intrinsic (i ( i ) layer between p between p and and n layers. When reverse bias is applied depletion layers are formed at pat pand i-n junctions. i-n junctions. The effective/width of depletion layer increases by t he width layer. It can be used as a voltage controlled attenuator.

At high frequencies the rectification effect ceases and impedan impe dance B.False B. False ce of diode is effectively that of i layer. layer. B This impedance varies with the applied bias. It is used in high Answer: Option B frequency switching circuits, limiters, modulators etc. 7. In the given figure the reflected current wave after first reflection is

Explanation: The quantities required to be measured in microwave circuits are frequency, power and impedance. Microwave frequency measurement is done by slotted line, resonant cavities and transfer oscillator. Microwave power measurement uses bolometers and micromave power meters.

A. 0.18 A A.0.18 B.-0.18 B. -0.18 A C.0.3 C. 0.3 A D.--0.3 A D. B


8. A line has an attenuation of 0.054 Np/m. The attenuation in decibels is A.4.7 A. 4.7 dB/m B.0.47 B. 0.47 dB/m C.0.54 C. 0.54 dB/m D.5.4 D. 5.4 dB/m B

A self balancing bridge working on the principle of power substitution is commomly used. Microwave impedance measurement is done by measurement of reflection coefficient and VSWR. A slotted line and probe is a basic tool for these measurements.' Network analyser enables rapid impedance measurement over a broad frequency range. 10. A reflex klystron oscillator uses A.one A. one cavity resonator B.two B. two cavity resonators C.three C. three cavity resonators D.none D. none of the above A


Answer: Option B

It uses a single cavity resonator for generating microwave osci

Explanation:

Its parts are electron gun, resonator, repeller and output cou

0.054 x 8.68 = 0.47 dB/m.

It operates on the principle of positive feed back.

9. If a line is open circuited Zin = Z0 tanh (gl (gl ). ). A.T A. True

The repeller electrode is at negative potential and sends the p

This positive feedback supports oscillations. Its feature are: Explanation: Power handling capacity μ (voltage) 2 and is inversely proportional to f to f 2 max.

1. Frequency range - 2 to 100 GHz 2. Power output - 10 MW to about 2 W

13. To couple a coaxial line to a parallel wire line it is best to use 3. Efficiency - 10 - 20 % A.sslotted line A. B.balun B. balun Its applications include radar receivers, local oscillator in microw mic rowave ave devices, oscillator for microwave measurements in C.directional C. directional coupler laboratories etc. D.λ/4 D. λ/4 transformer B

11. A coaxial RF cable has a characteristic impedance of 50 Ω and C equal to 40 pF/m. The inductance is A.1 A. 1 μ H/m Answer: Option B B.10 B. 10 μ H/m C.0.1 C. 0.1 μ H/m Explanation: D.0 D. 0.01 μ H/m C

A balun gives 4 : 1 impedance transformation. 14. In a multicavity klystron amplifier the signal to be amplified develops an ac voltage of signal frequency across the gap in buncher cavity A.T A. True B.False B. False


. 12. In a microwave coaxial line, the maximum operating frequency is f is f max and breakdown strength of dielectric is Ed ' Then maximum power handling capacity is proportional to A.

A

Answer: Option A Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by ox ide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

B. C. D. B

Answer: Option B

This beam is transmitted through a glass tube. The input cavity where the beam enters e nters the glass tube is called buncher. As electrons move ahead they see an accelerating field for half cycle and retarding field for t he other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called ve locity modulation. The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam. The input is fed at buncher cavity and output is taken at catcher cavity. In a two cavity klystron only buncher and c atcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used. The features of a multicavity klystron are : 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 3. Power gain - 60 dB (nominal value) 4. Efficiency - about 40%. A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication. 15. If VSWR is infinite, the transmission line is terminated in A.short A. short circuit B.complex B. complex impedance C.open C. open circuit D.e D. either (a) or (c) D

16. In a circular waveguide TE21 mode has lowest cutoff frequency A.T A. True B.False B. False B

Answer: Option B Explanation: Some applications require dual polarization capability. Circular waveguide has this capability. These analysis uses cylindrical coordinates. In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode. If D is diameter of waveguide λc = 1.706 D for TE 11 mode λc = 1.029 D for TE 21 mode λc = 0.82 D for TE01 mode λc = 1.306 D for TM 01 mode. 17. The number of TV channels which can be accommodated in a spectrum of 300 MHz is about A.5 A. 5 B.10 B. 10 C.50 C. 50 D.200 D. 200 C


and . Since VSWR = ∞, |rv | = 1. This can happen if Z L = 0 or ZL = ∞, i .e., line is o.c or s.c.

Answer: Option C Explanation: A TV channel has a bandwidth about 5 MHz. Hence 300 MHz spectrum can accommodate about 50 channels. 18. The noise figure of multicavity klystron amplifier is very low

A.True A.True B.False B. False B

Answer: Option B Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by o xide coated indirectly heated cathode and is focussed and accelerated by focussing electrode. This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.

4. Efficiency - about 40%. A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication. 19. Assertion (A): The velocity of electromagnetic waves on overhead lines and coaxial cables is the same. Reason (R): Free space has an intrinsic impedance o f 377 ohms. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D. A is wrong but R is correct D

Answer: Option D As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle. Therefore, some electrons are accelerated and some are retarded. This process is called ve locity modulation.

Explanation: Velocity of em waves on caoxial cables is less than that on overhead lines. 20. In the given figure the E and H lines in a coaxial co axial cable

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam. The input is fed at buncher cavity and output is taken at catcher cavity. In a two cavity klystron only buncher and c atcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used. The features of a multicavity klystron are : 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 3. Power gain - 60 dB (nominal value)

A. The radial lines are E lines and circular lines are H lines A.The B.Radial B. Radial lines are H lines and circular lines are E lines C.The C. The directions of E and H lines are wrong D.Radial D. Radial lines may be E and H lines depending an direction of A

Answer: Option A Explanation: H lines are concentric circles circ les around conductor and E lines are

In circular waveguide TE11 mode has the lowest cut 21. Roughly the time required for m icrowave cooking as compared offtofrequency conventional and is cooking the dominant is mode. A.about A. about twice B.about B. about half If D is diameter of waveguide C.about C. about 10 times D.a D. about one-tenth λc = 1.706 D for TE11 mode D

λc = 1.029 D for TE21 mode Answer: Option D Explanation:

λc = 0.82 D for TE01 mode λc = 1.306 D for TM01 mode.

Time required for microwave cooking is much less than the time required for conventional cooking. 24. Assertion (A): Klystron amplifiers use one or more intermediate cavities in addition to buncher and 22. If the minimum range of a radar is to be doubled, the catcher cavity. peak power has to be increased by a factor of A.2 A. 2 Reason (R): When one or more intermediate cavities B.4 B. 4 are used the bandwidth can be increased. C.8 C. 8 Both A and R are correct and R is correct D.1 D. 16 A. explanation of A D Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong Answer: Option D D.A D. A is wrong but R is correct Explanation: Range = (power)025. 23. Which mode has the lowest cut off frequency in circular wave guides? A.TE A. TE01 B.TE B. TE11 C.TE C. TE20 D.T D. TE21 B

A

Answer: Option A Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by ox ide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

Answer: Option B Explanation: Some applications require dual polarization capability. Circular waveguide has this capability. These analysis uses cylindrical coordinates.

This beam is transmitted through a glass tube. The input cavity where the beam enters e nters the glass tube is called buncher. As electrons move ahead they see an accelerating field for half cycle and retarding field for t he other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called ve locity modulation.


The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

It uses a single cavity resonator for generating microwave osci Its parts are electron gun, resonator, repeller and output cou

The input is fed at buncher cavity and output is taken at catcher cavity.

It operates on the principle of positive feed back.

In a two cavity klystron only buncher and c atcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.

The repeller electrode is at negative potential and sends the p

The features of a multicavity klystron are :

1. Frequency range - 2 to 100 GHz

1. Frequency range - 0.25 GHz to 100 GHz

2. Power output - 10 MW to about 2 W

2. Power output - 10 kW to several hundred kW

3. Efficiency - 10 - 20 %

3. Power gain - 60 dB (nominal value)

Its applications include radar receivers, local oscillator in micr laboratories etc.

This positive feedback supports oscillations. Its feature are:

4. Efficiency - about 40%. 27. Consider the following applications A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication. 25. A wave Em cos (b x - ωt ) is a backward wave. A.True A. True B.False B. False B

Answer: Option B Explanation: It is a forward wave because as t increases, x increases, x increases. increases.

1. TV tuning 2. Active filter 3. Microwave frequency multiplication In which of above can a varacto r diode be used? A.1 A. 1 2 and 3 B.ll and 2 only B. C.1 C. 1 and 3 only D.2 D. 2 and 3 only A


26. A reflex klystron oscillator is a A.llow power device A. B.high B. high power device C.high C. high efficiency device D.b D. both (a) and (b) A

Varactor diode is used in all the three applications. 28. Consider the following statements

1. Dissipative attenuator has a fixed value of attenuation. 2. Reflective attenuator has a fixed value of attenuation. 3. Both dissipative and reflective attenuators are available only with fixed attenuation. 4. Both dissipative and reflective attenuators are available with either fixed or v ariable attenuation. Which of the above are correct? A.1 A. 1 only B.1 B. 1 and 2 C.1, C. 1, 2 and 3 D.4 D. 4 only

Answer: Option A Explanation: A Klystron is a vacuum tube used for generation/amplification An electron beam is produced by ox ide coated indirectly heat electrode. This beam is transmitted through a glass tube. The input cavit As electrons move ahead they see an accelerating field for hal Therefore, some electrons are accelerated and some are reta

D

Answer: Option D

The velocity modulation causes bunching of electrons. This bu modulation of beam.

Explanation:

The input is fed at buncher cavity and output is t aken at catch

Both dissipative and reflective attenuators are available with either fixed or variable attenuation.

In a two cavity klystron only buncher and catcher cavity are u cavities are also used.

29. Impedance inversion may be obtained with A.a A. a short circuited stub B.a B. a quarter wave line C.an C. an open circuited stub D.a D. a half wave line B

The features of a multicavity klystron are : 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 3. Power gain - 60 dB (nominal value)

Answer: Option B

4. Efficiency - about 40%.

Explanation:

A multicavity klystron is used in UHF TV transmitters, Radar tr

Impedance inversion occurs when load impedance is not matched with characteristic impedance of line.

31. If a short line is terminated in characteristic impedance it beh A.T A. True B.False B. False

30. Power gain of a multicavity klystron amplifier is A.more A. more than 30 dB A B.causes B. causes retardation of all electrons C.causes C. causes acceleration of some electrons and retardation of others Answer: Option A D.n D. none of the above A

Explanation:

In a line terminated by Z0, there are no reflections. 32. Ga As exhibits negative differential mobility A.True A. True B.False B. False A

Answer: Option A Explanation: A Gunn diode uses GaAs which has a negative differential mobility, i .e., a decrease in carrier velocity with increase in electric field. This effects is called transferred electron effect. The impedance of a Gunn diode is tens of o hms. A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement t o couple RF power to load. Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers. 33. Consider the following statements 1. Bunching of electrons occurs in two cavity klystron amplifier. 2. Bunching of electrons occurs in multi cavity klystron amplifier. 3. Bunching of electrons occurs in reflex cavity klystron amplifier. Which of the above statements are correct? A.1, A. 1, 2, and only B.1, B. 1, 2 and 3 only o nly C.1 C. 1 and 3 only D.2 D. 2 and 3 only B

Answer: Option B

Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by ox ide coated indirectly heated cathode and is focussed and accelerated by focussing electrode. This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher. As electrons move ahead they see an accelerating field for half cycle and retarding field for t he other half cycle. Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation. The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam. The input is fed at buncher cavity and output is t aken at catcher cavity. In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or m ore intermediate cavities are also used. The features of a multicavity klystron are : 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 3. Power gain - 60 dB (nominal value) 4. Efficiency - about 40%. A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

34. Assertion (A): For high frequency lines inductive reactance is very high as compared to ac resistance. Reason (R): Due to skin effect ac resistance of line is higher than dc resistance. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D. A is wrong but R is correct B

36. Which one of the following is not a negative resistance devic devic A. Gunn diode B. Tunnel diode C. Impatt diode D. Varactor diode D

Answer: Option D Explanation: Gunn diode, Tunnel diode and Impatt diodes are negative resistance devices.


The limitation of solid state devices at high frequencies inclu those associated with transit time and junction capacitances.

XL = ωL. As frequency increases line resistance increases slightly but XL increases directly as per frequency.

The devices used are : Transferred Tr ansferred electron oscillators (Gunn diode), Avalanche diode oscillators (Impatt diode, Trapatt di Masters, Lasers, Tunnel diode, Varactor etc ).

35. Consider the following applications 1. 2. 3. 4.

Switch Attenuator Phase shifter Oscillator

In which of the above can a PIN diode be used? . . . .

37. Microwave links are typically 50 km apart A.because A. because of atmospheric attenuation B.because B. because of output tube power limitation C.because C. because of earth's curvature D.tto ensure that applied dc voltage D. dc voltage is not excessive C

Answer: Option C

1 2 3 and 4 Explanation: 1 2 and 3 only 1 and 2 only 2, 3 and 4 only B

Answer: Option B Explanation: PIN diode is not used in oscillators.

Earth's curvature limits the distance between microwave links. 38. For matching over a range of frequencies in a transmission line it is best to use A.a A. a balun B.a B. a broad band directional coupler C.double C. double stub D.a D. a single stub of adjustable position C

Answer: Option C

Explanation:

1. Frequency range - 1 GHz to 1000 GHz.

Double stub is useful for matching over a range of frequencies.

2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).

39. Assertion (A): In the interaction region of magnetron an electron is subjected to three forces: force due to electric field, force due to magnetic field and centrifugal force. Reason (R): The mechanism of generation of microwaves, in a magnetron, involves interaction of electromagnetic fields with electrons moving in static electric and magnetic fields oriented at right angles to each other. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D. A is wrong but R is correct A

Answer: Option A Explanation: It is somewhat similar to TWT and can deliver microwave power over a wide frequency band. It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.

It is used as signal source in transmitters and instruments. 40. Which of the following is wrong for a magic used to tee? A.E A. E and H arms are decoupled B.coplanar B. coplanar arms are coupled C.all C. all ports are perfectly matched D.A D. A signal into coplanar arm splits equally between E and H ar B

Answer: Option B Explanation: Coplanar arms are decoupled. 41. The expression HZ = C cos(B x ) cos(Ay cos(Ay )yz is yz is for A.TE A. TE wave B.TM B. TM waves C.both C. both TE and TM waves D.ssome TE and some TM waves D. A

Answer: Option A Explanation: In TM mode TM mode Hz = 0.

The growing RF wave travels t ravels in opposite direction to the electron beam.

42. Assertion (A): Impedance matching can be done by using stubs.

The frequency of wave can be changed by changing the voltage which controls the beam ve locity.

Reason (R): A double stub is used for impedance matching when frequency of signal varies. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D. A is wrong but R is correct

Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current. It features are:

A

Answer: Option A

Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.

Explanation:

The main features of TWT are :

Hollow metallic enclosures exhibit resonance behaviour when excited by electromagnetic field.

1. Frequency range - 0.5 GHz to 90 GHz

These enclosures are called cavity resonators.

2. Power output - 5 m W at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz

43. Read the following statements about TWT 3. Efficiency - about 5 to 20% 1. 2. 3. 4.

It uses thermionic emission. It uses an attenuater. It is inherently a resonant device. It has broad bandwidth.

Which of the above are correct? A.1, A. 1, 2, 3 and 4 B.1, B. 1, 2 and 3 C.1, C. 1, 3 and 4 D.1 D. 1, 2 and 4 D

Answer: Option D Explanation: In a klystron the resonant structure limits the bandwidth. A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave. The velocity of wave propagation along the helix structure is less than velocity of light.

4. Noise - about 5 dB for low power TWT 25 dB for high power TWT TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc. 44. If a line having Z 0 = 300 ∠ 0 W is short circuited at far end, VSWR is A.0 A. 0 B.1 B. 1 C.∞ C. ∞ D.2 D. 2 C

Answer: Option C Explanation: If line is s.c |rv | = 1 and VSWR = ∞. 45. A klystron amplifier generally uses Pierce gun A.T A. True B.False B. False A

The beam and wave travel along the structure at the same speed. Thus interaction occurs between beam and w ave and the beam delivers energy to the RF wave.


It uses a single cavity resonator for generating microwave oscillations.

This impedance varies with the applied bias. It is used in high frequency switching circuits, limiters, modulators etc.

Its parts are electron gun, resonator, repeller and output47. A pulsed radar produces 1 μ sec pulses at a rate of 1000 per second. The duty cycle is coupling. A.0.001 A. 0.001 B.0.01 B. 0.01 It operates on the pr inciple of positive feed back. C.0.1 C. 0.1 D.1 1 The repeller electrode is at neg ative potential and sends the D. partially bunched electron beam back to resonator cavity. This positive feedback supports oscillations. Its feature are: 1. Frequency range - 2 to 100 GHz 2. Power output - 10 MW to about 2 W 3. Efficiency - 10 - 20 %

A

Answer: Option A Explanation: 1 x 10-6 x 1000 = 0.001.

48. Assertion (A): Impedance measurement at microwave frequencies is done by finding SWR.

Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in Reason (R): SWR and reflection coefficient depend laboratories etc. on the characteristic impedance and load impedance. 46. Assertion (A): PIN diode is used as a fast switch. Both A and R are correct and R is correct A. explanation of A Reason (R): PIN diode has very high resistance whe n reverse Both A and R are correct but R is not correct B. biased and very low resistance when forward biased. explanation of A A.Both A. Both A and R are correct and R is correct explanation of A C.A C. A is correct but R is wrong B.Both B. Both A and R are correct but R is not correct explanation of A D.A D. A is wrong but R is correct C.A C. A is correct but R is wrong B D.A D. A is wrong but R is correct A

Answer: Option B Answer: Option A

Explanation:

Explanation: A PIN diode has an intrinsic (i ( i ) layer between p between p and and n layers. When reverse bias is applied depletion layers are fo rmed at p-i at p-i 49. When a line is loaded the characteristic impedance is and i-n junctions. i-n junctions. equal to A.((R + j + j ωL)(G ωL)(G + j + j ωC) ωC) The effective/width of depletion layer increases by the width widthA. of i layer. layer. It can be used as a voltage controlled attenuator. B. At high frequencies the rectification effect ceases and impedance of diode is effectively that of i layer. layer.

C. D.LLC D.

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

B

Answer: Option B

The input is fed at buncher cavity and output is t aken at catcher cavity.

Explanation:

In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or m ore intermediate cavities are also used.

or

The features of a multicavity klystron are : . 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 50. Which device has internal positive feedback? A.Two A. Two cavity klystron amplifier B.Multi-cavity B. Multi-cavity klystron amplifier C.Reflex C. Reflex klystron amplifier D.All D. All of the above C

3. Power gain - 60 dB (nominal value) 4. Efficiency - about 40%. A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

Answer: Option C Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by o xide coated indirectly heated cathode and is focussed and accelerated by focussing electrode. This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher. As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle. Therefore, some electrons are accelerated and some are retarded. This process is called ve locity modulation.

MICROWAVE COMMS INDIABIX SECTION 4 1. The domain mode in rectangular waveguide is A.TE A. TE01 B.TE B. TE02 C.TE C. TE10 D.T D. TM11 C

Answer: Option C 2. The reverse voltage applied to a varactor diode A.iis less than avalanche breakdown voltage A. B.iis more than avalanche breakdown voltage B.

may be more or less than a avalanche breakdown voltage is very high as compared to avalanche bre akdown D. voltage C.

A

Answer: Option A Explanation: The action of varactor diode is due to the capacitance of depletion layer. The thickness of depletion layer depends on the reverse bias which should not cause breakdown.

Answer: Option D 6. In a TWT the amplitude of resultant wave travelling down the helix remains constant A.True A. True B.False B. False B

Answer: Option B Explanation: The signal gets strengthened. 7. In the given figure forward current wave has a magnitude of

3. To ensure that only dominant mode TE 10 is allowed to propagate in an air filled rectangular waveguide, the lower frequency limit and upper frequency limit are about 25% above f above f c for TE10 and 5% below f below f c for TE20 A. mode respectively about 50% above f above f c for TE10 and 25% below f below f c for B. TE20 mode respectively about 25% above f above f c for TE10 and 25% below f below f c for C. TE20 mode respectively D.none D. none of the above A

Answer: Option A

A.0.45 A A.0.45 B.0.3 B. 0.3 A C.0.2 C. 0.2 A D.0 D. 0.1 A B

4. The skin depth at 1000 MHz as compared to that at 500 MHz is A.2 A. 2 B.12 B. 12 C.0.707 C. 0.707 D.0.5 D. 0.5 C

Answer: Option C 5. The transit time (in cycles) for electrons in repeller space of reflex klystron oscillator for sustaining oscillations is (n ( n is any integer) A.2( A. 2(n n - 1) B.2 B. 2n - 1 C. D. D


8. In an infinite line the input impedance at e very point is equal to characteristic impedance. A.True A. True B.False B. False A

Answer: Option A 9. Consider the following time parameters Domain growth time constant. Transit time. Dielectric relaxation time in positive mobility regime. Which of the above are used in connection width transferred electron device? A.1, A. 1, 2, and 3

B. 1 and 2 only B.1 C.1 C. 1 and 3 only D.2 D. 2 and 3 only

14. In the given figure shows the equivalent circuit of a magic tee. If all ports are matched

A

Answer: Option A 10. PIN diode has A. p p+ and n layers separated by i layer layer + + B. p B. p and n layers separated by i layer layer C. p C. p and n layers separated by i layer layer D.n D. none of the above B

Answer: Option B 11. The two terms used to describe performance of a directional coupler are A.coupling A. coupling and directivity B.gain B. gain and coupling C.gain C. gain and directivity D.g D. gain and isolation A

Answer: Option A 12. The number of PM radio channels which c an be accommodated in a spectrum of 300 MHz is about A.10 A. 10 B.100 B. 100 C.500 C. 500 D.1 D. 1500 D

Answer: Option D 13. Consider the following statements Gunn diode can be used in combinational logic circuits. Gunn diode can be used in sequential logic c ircuits. Both Gunn diode and GaAs Mesfet can be used in logic circuits. Which of the above statements are correct? A.1, A. 1, 2, and 3 B.1 B. 1 and 2 only C.2 C. 2 and 3 only D.1 D. 1 and 3 only A

Answer: Option A

A. nE = nH = 2 A.n B.n B. nE = nH = 0.707 C.n C. nE = 2, nH = 0.707 D.n D. nH = 0.707, nH = 2 A

Answer: Option A

15. Assertion (A): Microstrip is very commonly used in microwave integrated circuits. Reason (R): Microstrip has an easy access to the topsurface so that active and passive discrete components can be easily mounted. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D. A is wrong but R is correct A

Answer: Option A Explanation: A Microstrip line has a single dielectric substratc with ground plane on one side and a strip on the other face. Its special feature is easy access to top surface so that minor adjustments can be made after circuit fabrication. The high dielectric constant of the substrate reduces guide wavelength and circuit dimensions. A microstrip line is the most commomly used transmission structure for microwave integrated circuits.

16. A 75 ohm line is first short terminated and minima locations are noted. Then the short is replaced by resistive load and minima location are again noted. If minima location are not altered and VSWR is 3, the value of resistive load is A.25 A. 25 Ω B.50 B. 50 Ω C.225 C. 225 Ω D.2 D. 250 Ω C


rv

and VSWR

D.((pulse width) + (PRF) D. A

Answer: Option A 20. In a klystron amplifier the bunching effect converts velocity modulation into current A. modulation of beam converts current modulation into velocity B. modulation of beam C.both C. both (c) and (b) D.neither D. neither (a) nor (b) A

.

17. The word 'LORAN' means A.llong range navigation A. B.llong range TV transmission B. C. long range cable transmission D.e D. either (b) or (c) A

Answer: Option A 18. In the given figure forward voltage wave has a magnitude

A. 90 V A.90 B.60 B. 60 V C.30 C. 30 V D.1 D. 10 V C

Answer: Option C 19. The duty cycle of a radar transmitter is equal to A.((PRF) (pulse width) A. B.((PRF)/(pulse width) B. C. (pulse width)/(PRF)

Answer: Option A Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by ox ide coated indirectly heated cathode and is focussed and accelerated by focussing electrode. This beam is transmitted through a glass tube. The input cavity where the beam enters e nters the glass tube is called buncher. As electrons move ahead they see an accelerating field for half cycle and retarding field for t he other half cycle. Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation. The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam. The input is fed at buncher cavity and output is t aken at catcher cavity. In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or m ore intermediate cavities are also used. The features of a multicavity klystron are : 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 3. Power gain - 60 dB (nominal value) 4. Efficiency - about 40%. A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication. 21. Out of modes TE 20 and TE30 of propagation of electromagnetic engery A.both A. both have the same cutoff frequency

TE20 has lower cut off frequency as compared to TE30 TE30 has lower cutoff frequency as compared to C. TE20 D.e D. either (a) or (c) B.

B

Answer: Option B 22. A TE10 rectangular waveguide is to be designed for operation over 25-35 GHz and the band centre is 1.5 times the cutoff frequency. The dimension of broadside is A.15 A. 15 mm B.10 B. 10 mm C.9 C. 9 mm D.7 D. 7.5 mm D

Answer: Option D 23. In a klystron amplifier the force on all electrons A.causes A. causes acceleration of all electrons B.causes B. causes retardation of all electrons causes acceleration of some electrons and C. retardation of others D.n D. none of the above C

Answer: Option C Explanation: A Klystron is a vacuum tube used for generation/amplification of microwaves. An electron beam is produced by o xide coated indirectly heated cathode and is focussed and accelerated by focussing electrode. This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher. As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle. Therefore, some electrons are accelerated and some are retarded. This process is called ve locity modulation. The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

The input is fed at buncher cavity and output is taken at catcher cavity. In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or m ore intermediate cavities are also used. The features of a multicavity klystron are : 1. Frequency range - 0.25 GHz to 100 GHz 2. Power output - 10 kW to several hundred kW 3. Power gain - 60 dB (nominal value) 4. Efficiency - about 40%. A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication. 24. If load impedance Z L >> Z0, then A.Z A. Z0 = ZL (VSWR) B.Z B. ZL = Z0 (VSWR) C.Z C. ZL = Z0 (VSWR - 1) D.Z D. ZL = Z0 VSWR B


If ZL >> Z0, |rv | and VSWR Therefore ZL = Z0(VSWR).

.

25. The inductance of a twin feeder used to connect antenna to TV receiver is about A.0.2 A. 0.2 μ H/m B.0.6 B. 0.6 μ H/m C.1.6 C. 1.6 μ H/m D.10 D. 10 μ H/m C

Answer: Option C 26. When resonant cavities are coupled together the result is A.one A. one resonant frequency B.n B. n resonant frequencies C. resonant frequencies D.either D. either (b) or (c) B

Answer: Option B

27. For a rectangular rec tangular waveguide having width a and height b, the cutoff wavelength for TM 11 mode is equal to A.

B. 0.01 Ω B.0.01 C.0.05 C. 0.05 Ω D.0.25 D. 0.25 Ω D

Answer: Option D B. C. D. B

Answer: Option B 28. The path length between ports 1 and 2 for the two waves in a hybrid ring is A.1 A. 1 B. C. D. C

Answer: Option C Explanation: The quantities required to be measured in microwave circuits are frequency, power and impedance. Microwave frequency measurement is done by slotted line, resonant cavities and transfer oscillator. Microwave power measurement uses bolometers and microwave power meters. A self balancing bridge working on the principle of power substitution is commonly used. Microwave impedance measurement is done by measurement of reflection coefficient and VSWR. A slotted line and probe is a basic tool for these measurements.' Network analyser enables rapid impedance measurement over a broad frequency range. 29. The radiation resistance of a circular loop of one turn is 0.01 ohm. For 5 t urn loop the radiation resistance is A.0.002 A. 0.002 Ω

30. As wavelength decrease the size of high directivity antenna A.decreases A. decreases B.iincreases B. C.iis not affected C. D.either D. either (b (b) or (c ( c) A

Answer: Option A 31. Which of the following modes of transmission will not be supported by a rectangular waveguide? A.TE A. TE15 B.TE B. TE12 C.TM C. TM11 D.TM D. TM10 D

Answer: Option D 32. In a circular waveguide w ith radius r , the dominant mode is A.TM A. TM01 B.TE B. TE01 C.TM C. TM11 D.TE D. TE11 B

Answer: Option B Explanation: Some applications require dual polarization capability. Circular waveguide has this capability. These analysis uses cylindrical coordinates. In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode. If D is diameter of waveguide λc = 1.706 D for TE11 mode λc = 1.029 D for TE21 mode λc = 0.82 D for TE01 mode λc = 1.306 D for TM01 mode.

33. If 'a 'a' is the width of re ctangular wave guide and 'λ' is the wave length, then A. B. C. D. B

Answer: Option B 34. A parametric amplifier uses A.non A. non linear resistance B.non B. non linear reactance C.either C. either (a) or (b) D.n D. neither (a) nor (b) B

Answer: Option B Explanation: In a parametric amplifier the non-linear e lement is varactor diode or inductor. 35. Assertion (A): Impatt diode can be used in both amplifiers and oscillators. Reason (R): Impatt diode has a low resistance. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D. A is wrong but R is correct B

Answer: Option B Explanation: An Impatt diode has n+ - p - p - i - p - p + structure and is used with reverse bias. It exhibits negative resistance and operates on the principle of avalanche breakdown. Impatt diode circuits are classified c lassified as broadly tunable circuit, low Q circuit and high Q circuit. The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode. The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W

for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%. Its applications include police radar systems, low power microwave transmitter etc. 36. Which one of the following can be used for amplification of microwave energy? A.TWT A. TWT B.Magnetron B. Magnetron C.Reflex C. Reflex klystron D.Gunn D. Gunn diode A

Answer: Option A 37. If ZTE is wave impedance for TE waves, Ed is maximum dielectric strength of insulating material, a and b are the width and height of a rectangular wave guide, the maximum power handling capability P max for TE10 mode is A. B. C. D. B

Answer: Option B 38. At frequencies of 10 MHz and higher the impedance represented by ground is primarity A.rresistive A. B.iinductive B. C.capacitive C. capacitive D.partly D. partly resistive and partly capacitive C

Answer: Option C 39. A disadvantage of microstrip line as the connect ions of compared to strip line is that former A.do A. do not lend themselves to printed circuit B.are B. are more likely to radiate C.are C. are bulky D.are D. are more expensive and complex

B

Answer: Option B 40. As frequency increases, the transmission efficiency A.decreases A. decreases B.iincreases B. C. is not affected D.e D. either (a) or (c) B

Answer: Option B 41. A circular polarizer converts a linearly polarized wave into a circularly polarised wave. A.True A. True B.False B. False A

Answer: Option A 42. If D is diameter of circ ular waveguide the cutoff wave-length for TE11 mode is equal to A.1.706 A. 1.706 D B.2.11 B. 2.11 D C.0.82 C. 0.82 D D.0 D. 0.41 D A

Answer: Option A Explanation: Some applications require dual polarization capability. Circular waveguide has this capability. These analysis uses cylindrical coordinates. In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode. If D is diameter of w aveguide λc = 1.706 D for TE11 mode λc = 1.029 D for TE21 mode λc = 0.82 D for TE01 mode λc = 1.306 D for TM01 mode.

Answer: Option A Explanation: The operation of magnetron is based on interaction of electromagnetic fields with electrons moving in static electric and magnetic fields oriented at 90° with respect to each other. In a magnetron three forces act on electron viz. force due to electric field (equal to - eE), force due to magnetic field [equal to - e (v (v x x B)] and centrifugal 2 force (equal to mv /r ). ). The path of the electron can c an be found by balancing these three forces. Magnetron can be of three types i.e., negative resistance device, cyclotron frequency device and travelling wave or cavity device. In negative resistance magnetron use is made of the negative resistance between two anode segments. It has low efficiency and is used at frequencies less than 0.5 GHz. In cyclotron magnetron a synchronism exists between ac component of electric field and periodic oscillation of electrons in a direction parallel to the field. It is used for frequencies higher than 100 MHz. A cavity magnetron has a number of cylindrical cavities in the interaction region. The cavity magnetron is the most common type of magnetron. Its features are : 1. Frequency range - 500 MHz to 10 GHz 2. Power output - 250 kW (pulses) 3. Efficiency - about 50% It is used in radar systems, industrial heating systems and microwave ovens. 44. Varactor diodes use A.ssilicon A. B.GaAs B. GaAs C.either C. either (a) or (b) D.neither D. neither (a) nor (b) C

Answer: Option C 43. The external magnetic field fie ld in a magnetron is such that lines are A.parallel A. parallel to the axis of cathode B.perpendicular B. perpendicular to the axis of cathode C. inclined to the axis of cathode D.e D. either (b) or (c) A

45. A circular waveguide carries TE11 mode whole radial electric field is given by Er = = E0 j 1(r ) sin Φ V/m V/m where r is is radial distance in cm from the ax is The cut off wavelength is A.10 A. 10 cm

B. 3 p cm B.3 C.2 C. 2 p cm D.8 D. 8 cm A

Answer: Option A 46. Assertion (A): Impatt diode is an avalanche diode. Reason (R): Avalanche breakdown phenomenon occurs when a p a p--n junction is reverse biased. Both A and R are correct and R is correct A. explanation of A Both A and R are correct but R is not correct B. explanation of A C.A C. A is correct but R is wrong D.A D. A is wrong but R is correct

power transmission is least efficient when there are no standing waves on the line power transmission is most efficient when there B. are no standing waves on line C.Load C. Load power depends on phase constant D.sstanding waves will always exist on the line D. A.

B

Answer: Option B Explanation: If standing waves are not there, whole of the power is absorbed by load. 49. In the given figure a short circuited transmission line resonator If n = 1, 2, 3...

B

Answer: Option B Explanation: An Impatt diode has n+ - p - p - i - p - p + structure and is used with reverse bias. It exhibits negative resistance and operates on the principle of avalanche breakdown. Impatt diode circuits are classified c lassified as broadly tunable circuit, low Q circuit and high Q circuit. The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode. The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%. Its applications include police radar systems, low power microwave transmitter etc.

For series reasonance βl βl = = np and for parallel A. resonance B. For series resonance

and for

parallel resonance βl βl = = np C.β C. βl = = np for both series and parallel resonance D.

for both series and parallel

resonance A

Answer: Option A 47. A radar has a maximum range of 120 km. The maximum allowable pulse repetition frequency for unambiguous reception is A.1250 A. 1250 B.330 B. 330 C.2500 C. 2500 D.8 D. 8330 A

Answer: Option A

48. In a line with finite attenuation

50. The electric field in a TWT due to applied signal A.iis directed along the helix axis A. B.iis directed radially from helix axis B. C.iis inclined to the helix axis by about 60° C. D.iis inclined to the helix axis by about 45 ° D. A

Answer: Option A Explanation: In a klystron the resonant structure limits the bandwidth.

A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave. The velocity of wave propagation along the helix structure is less than velocity of light. The beam and wave travel along the structure at the same speed. Thus interaction occurs between beam and w ave and the beam delivers energy to the RF wave. Therefore the signal gets strengthened and amplified output is delivered at the other end of tube. The main features of TWT are : 1. Frequency range - 0.5 GHz to 90 GHz 2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz 3. Efficiency - about 5 to 20% 4. Noise - about 5 dB for low power TWT 25 dB for high power TWT TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

Indiabix With Explanations

Recommend Documents