Objective Questions
1. TheL The L ore orentzg tz gauge con condition is given iven by A =: (a) µεd 2/dt 2 (b) µεd/dt
(c) (c)
(d) (d) 0
2. TheCou The Coulom lomb b gauge con condition is given iven by (a) µεd 2/dt 2 (b) µεd/dt
− µε
(c) (c)
(d) (d) 0
3. Thefree hefreesp spacewa ce wavenu ve number k0 is define fined as (a) k0 ω0 (µ0ε0)
− µε
(b) (b) k0
−
−
−
−
∇•
∇ • A =:
= √ √ (c) k0 = ω0 (µ0/ε0)
= ω0/√ (µ0ε0) √ (d) (d) k0 = ω0/ (ε0/µ0)
4. If Es is the field field inte intensity vector ctor identified tified as a phasor by its subscript cript s an and k0 is the the wavenu ve num mber, 2 2 k0Es is equation Es is kno knowna wn as: (a) Poiss isson’s equation ion (b) Coulom lombs gaugeeq eequation ion
∇ = −
(c) Vector Helmholtz ltz equation ion
(d) Diffu iffus sion ion equation ion
5. Thei The inducti ctiona on and rad radiationfie tion fiellds of an oscil oscilllatingd ting dipole becom comes approxi roximately equal at a dista distance when r =: r , whe (a) λ/6 (b) λ/4 (c) λ/3 (d) λ/2 6. Radi Radiationre tion res sista stanceof ce of a hypot ypoth hetical tical curre curren nt element of length d l is: is: 2 2 (a) (a) 800 (dl/λ) (b) (b) 400 (dl/λ) (c) (c) 800 (dl/λ)
(d) 400 (dl/λ)
7. Thera The ratio tio of effective ffectivea apertu rtureto re toth the e actu ctual aperture rtureiis a direct rectm measureof re of antenna effe ffective ctiven nessi ss in rad radiating/re ting/rece ceivin iving the the power toor to or fromth from the e desired red direct rectiion. on. Dep Depending onth on the e typ type and design, the the norm normal valueof ueof thi this ratio ratio for refle reflect ctor or ante ntenna rang range es between: (a) 25–45% (b) 35–65% (c) 45–75% (d) 75–95% 8. I n a plane con containing an isol solated Hertz Hertziian dipole, ole, the the rad radiationp tion patte tternof rn of the the antenna is a: (a) (a) Circ Circle le and the radiation iation is circu circularly larly polarize olarized d (b) (b) Circ Circle le and the radiation iation is lin li nearly polarize olarized d (c) Fig Figureof re of eight ight and the radiation iation is circu circularly larly polarize olarized d (d) (d) Figu Figure reof of eight ight and the radiation iation is lin li nearly polarize olarized d
876
Appendix G
Objective Questions
877
9. Theboundary between thenear fieldand far field may bearbitrarily taken tobeat aradius R , whichis related to thewavelength λ and maximumdimension L (in meters) of theantennaas: (a) R 2L2/λ (b) 2L/λ (c) 2λ/L (d) 2λ/L2
=
10. Thefollowingterms spell thesamemeaning in referencetoan antenna: (a) Near field and Principal zone (b) Near field and Fresnel zone (c) Near field and Fraunhafer zone
(d) Far field and Fresnel zone
11. Thestandard referenceantennafor thedirective gain is: (a) infinitesimal dipole (b) elementary doublet (c) half wave dipole
(d) none of the above
12. Theantennaused as standard referencefor directive gain is: (a) quarter wavedipole (b) isotropicantenna (c) elementary double
(d) half wavedipole
13. Therearefour antennaconfigurations (i) asimple λ/2 dipole (ii) aflat sheet placed in front of simple λ/2 dipole (iii) aflat sheet placed in front of an array of two λ/2 dipoles and (iv) aflat sheet folded into to a90◦ squarecorner and is placed in front of simple λ/2 dipole. Thedirectivitiesof theabove four configurations will bein theorder of: (a) 1.64:3:6:9 (b) 1.64:4:8:12 (c) 1.64:5:10:15 (d) 1.64:5:10:20 14. Theinput impedanceof adipoleantennahavingtip-to-tipphysical lengthequal tohalf wavelength, is: (a) Pureresistance (b) Purecapacitance (c) Inductiveimpedance
(d) capacitiveimpedance
15. Theinput impedanceof ashort dipole withlengthnearer to0.23 λ containsareactance, whichis normally: (a) largeand capacitive (b) small andcapacitive (c) largeandinductive
(d) small andinductive
16. Thenear zonefieldsof an oscillatingtimevarying dipole are: (a) dynamic (b) static (c) quasi-static
(d) noneof theabove
17. For half wavedipole thedirectivity D (in dB’s) is obtained to be: (a) 1.76 (b) 2.15 (c) 3.14
(d) 1.64
18. Thedirectivity of ahalf wavedipole is given by: (a) 1.51 (b) 1.64
(d) 2.54
(c) 2.03
19. If an antennais at aheight h, abovetheearth(radiusR ) simplegeometry gives line-of-sight distance (d ) to thehorizon: (a) d 2Rh (b) 2 2Rh (c) 3 2Rh (d) 4 4Rh
=
√
√
√
20. In relationtothedirectional characteristicsof thedipole antennas theterms θ and φ polarization are synonymous with and may beused for thefollowingterms in that order: (a) Horizontal andVertical Polarization
(b) Vertical and Horizontal Polarization
(c) Circular and Elliptic Polarization
(d) Elliptic and Circular Polarization
Appendix G
878
Objective Questions
21. When thecurrent ratiosand phasings areproperly chosen sharpdirectivity withan array of fixed lengthbutsufficiently largenumber of elements can beobtained.Withthis phasingandclosespacings between elementstheradiation resistance: (a) Reduces to very low value (b) Increases to very high value (c) Remains unaffected
(d) Changes only slightly
22. TheTchebycheff polynomial T m(x) is commonly used in design and synthesis problems. For m and m 1 its values are: (a) 1 and 0 (b) 1 and (c) 0 and 1 (d) and 1
=
∞
=0
∞
23. A straight dipole radiator fedin thecenter will causemaximumradiation: (a) intheplaneparallel to its axis: (b) intheplanenormal to its axis (c) attheplaceof feed
(d) atitsextremeends
24. Theimpedanceof half wavedipoleantennamounted andradiatinginto an unbounded ideal dielectric mediumis: (a) apureresistance (b) apurecapacitance (c) an impedancewith capacitivereactance
(d) an impedancewith inductivereactance
25. If Z is theinput impedanceof asimpledipole, theimpedanceof n fold dipole is (a) nZ (b) n2Z (c) Z/n (d) Z/ n2 26. A dipole antennafed at theextremeleft end will produceabeam, which will be: (a) tiltedtowardleft (b) tiltedtowardright (c) perpendicular to thedipole
(d) parallel to thedipole
27. Theradiationresistanceof aquarter wavemonopole (if h 1/2) is given by: (a) 100 (l/λ)2 (b) 200 (h/λ)2 (c) 300 (l/λ)2 (d) 400 (h/λ)2
=
28. If theradiated power of aquarter wavemonopoleis given by (1/2π ) resistance(in Ohms) of ahalf wavedipole is obtained tobe: (a) 36.5
(b) 18.25
(c) 73
• 0.609ηI m2eff/2π theradiation (d) 146
29. Theunit patternof thefollowingwill beafigureof eight shape: (a) two elements with λ spacing (b) two elementswith λ/2 spacing (c) two elementswith λ/4 spacing
(d) two elements with 3λ/4 spacing
30. At 450 MHz thehalf power beamwidth of a3-element array is: (a) 10◦ (b) 12◦ (c) 8◦
(d) 28◦
31. At 450 MHz thehalf power beamwidth of a7-element array is: (a) 8◦ (b) 10◦ (c) 12◦
(d) 28◦
32. Anarray consisting anumber of radiatorsequally spacedalongalineand carryingcurrent of thesame phase, shall mainly radiate: (a) (b) (c) (d)
in aplaneparallel to thelineof array in aplaneperpendicular tothelineof array at 30◦ angle fromthelineof array at 60◦ angle fromthelineof array
Appendix G
Objective Questions
879
33. An array consistingof anumber of dipolesof equal size, equally spaced along astraight line, withall dipoles fedin thesamephasefromthesamesourceis called: (a) End-firearray
(b) Back firearray
(c) Broadside array
(d) Binomial array
34. An array consisting anumber of equidistant dipoles of equal size, fedwith thesamecurrentsand phaseis called: (a) End-firearray
(b) Back firearray
(c) Broadsidearray
(d) Binomial array
35. Thefollowingantennaarray has no sidelobes: (a) End-firearray (b) Back-firearray
(c) Broadsidearray
(d) Binomial array
36. Thesidelobeless broadsidearraysarecalled: (a) Uniformarray
(b) End-firearray
(c) L og periodic array
(d) Binomial array
37. Thewidth of themajor lobeis almost exactly inversely proportional tothearray lengthif: (a) l λ (b) λ < l 3λ/2 (c) 3λ/2 < l 2λ (d) l > 2λ
≤
≤
≤
38. Sidelobes in abroadsidearray will beentirely eliminated provided thespacingbetween adjacent antennasdoes notexceed: (a) λ/2 (b) λ (c) λ/4 (d) 3λ/4 39. Thedirectional patternof an end firearray using isotropic radiators is substantially independent of the spacing of theantennaradiators provided this spacing does not exceed: (a) λ/8
(b) λ/4
(c) 3λ/8
(d) λ/2
40. Thevertical radiationpatternof acenter fed vertical dipole shownin Fig. G–1(B) is for thedipole length (of Fig. G–1(A)): (a) 2λ
(b) 3λ/2
(c) λ
(d) 3λ/4
41. Theradiationpatternof two non-directional radiators fedwithequal currents(with α phaseshift) shownin Fig. G–2 belongs to:
= λ/2, α = 0◦ (c) d = λ/4, α = −90◦
= λ/2, α = −90◦ (d) d = λ/4, α = 0◦
(a) d
(b) d
42. In an optimumhorn shownin Fig. G–3 thedifferencein thepathlength δ along theedgeandthe center of thehorn in E planeis made: (a)
≤ λ/10
(b)
≤ λ/8
(c)
≤ λ/7
(d)
≤ λ/4
43. If thedistributionof amplitudeof element excitationof acenter-symmetric linear array with L << λ is suchthat thefarther theelement fromthecenter, thelower is theexcitation, than compared tothe uniformly excited array, theradiationpatternof suchagraded array will have: (a) widebeamwidth (b) narrowbeamwidth (c) almost thesamebeamwidth (d) beamwidth related withgradingfunction
Appendix G
880
Objective Questions
(a) L a
(b) d
(c)
Figure G–2
(d) (A)
Figure G–3
(B)
Figure G–1
44. Identify theincorrect statement. (a) Dipole antennas arebalanced antennas if fedby two conductor transmissionline (b) Dipole antennas areun-balanced antennas if fedbytwo conductor transmissionline (c) Dipoleantennas arenarrowestbandwidth antenna (d) Short dipole has thesamedirectivity as that of asmall loop 45. Thedirectivity of thesmall loopand short dipole has thefollowing ratio: (a) 1:2 (b) 2:1 (c) 1:1
(d) 1:4
46. To qualify as asmall loopor short dipole their dimensions should be λ/10 λ/8 λ/4 (a) (b) (c)
(d)
≤
≤
≤
≤ λ/2
47. If adipole has been cut fromametal sheet, leaving aslot, thedipole and slot aresaid to be complimentary. Theterminal impedanceof dipole Zd and that of slot Zs arerelated totheintrinsic impedanceof space Z0 by Zs =: (a) Zd 2/4Z0
(b) 4Z02/Zd
(c) Z02/4Zd
(d) 4Zd 2/Z0
48. Theradiation resistance Rrad of acircular loop with N number of turnsanddiameter D is (a) 19000 N(D/λ)4
(b) 19000 N 2(D/λ)4
(c) 19000 N 2(D/λ)2
(d) 19000 N 4(D/λ)4
49. Patch is a: (a) High gain wideband antenna (c) Low gain narrow band antenna
(b) High gain narrow band antenna (d) Low gain wideband antenna
50. Thefield patterns for thefollowingantennas areidentical provided E and H fieldsareinterchanged: (a) Dipoleand Patch antenna (b) Dipoleand Horn antenna (c) Dipoleand Loop antenna (d) DipoleandYagi antenna 51. Themaximumgain for H -planesectoral horn withslant lengthof 12λ occurswhen aperturewidthis: (a) λ (b) 3λ (c) 6λ (d) 12λ
Appendix G
Objective Questions
881
52. Maximumbeamwidth for E -planesectoral horn is about: (a) 10◦ (b) 20◦ (c) 30◦
(d) 45◦
53. Thesharpest beamand highest gain for agiven mouthsize of ahorn areobtained by aflareangle which is: (a) very small (b) small (c) large (d) very large 54. In view of thesimilarity of directional pattern withelementary doublet theantenna, whichis referred toas amagnetic doublet is: (a) Yagi array (b) Turnstileantenna (c) Helical antenna
(d) Small loop antenna
55. A helical antennais used for satellitetrackingbecauseof its: (a) Circular polarization (b) Maneuverability (c) Broadbandwidth (d) Goodfronttoback ratio 56. Helical antennas areoften used for satellitetrackingatVHF rangebecauseof: (a) Troposcatter (b) super refraction (c) Ionospheric refraction (d) theFaraday effect 57. When amono-filar helical antennais operated in normal mode, themaximumradiationoccurs in the plane: (a) parallel to thehelix axis (b) perpendicular tothehelix axis (c) located at 45◦ to thehelix axis (d) arbitrarily located in respecttothehelix axis 58. In mono-filar helices, thetermtransmissionmodeis used todescribethemanner in whichthe electromagnetic waveis propagated along: (a) avery shorthelix (b) amediumlengthhelix (c) along helix (d) an infinitehelix 59. Reflector antennas arepreferred for gainsgreater than: (a) 50 dB (b) 40 dB (c) 30 dB
(d) 20 dB
60. Theradiationpatternof aParaboloidal reflector antennawith ahornantennaas itsprimary feed is: (a) thesameas that of horn antenna (b) thesquareof thehorn antennapattern (c) thesquareroot of thehorn antennapattern (d) noneof theabove 61. Whenthefieldacrossthemouthof theparabolaiseverywhereof thesamephasethebeamgeneratedis: (a) omni directional (b) sharply unidirectional (c) main beamaccompanied by two minor sidelobes (d) bifurcated in two major lobes 62. Cassgrain feed is used with aparabolic reflector to: (a) increasethegain of thesystem (b) increasethebeamwidth of thesystem
Appendix G
882
Objective Questions
(c) reducethesizeof themain reflector (d) allow thefeed tobeplaced at aconvenient point 63. Beamwidths for corner reflectorsareapproximately equal in both principal planes, provided θ =: (a) 120◦ (b) 90◦ (c) 60◦ (d) 45◦ 64. A parabola reflects thewaveoriginatingfromasourceat thefocus and transforms: (a) aplanewavefront fromfeed at focus intospherical wave-front (b) aplanewavefront fromfeed at focus into cylindrical wave-front (c) any curved wavefront fromfeed at focus intoplanewave-front (d) acylindrical wavefront fromfeed at focus into spherical wave-front 65. For largeparabolaof many wavelengthapertureapractical choicefor feed can becorner reflector withacorner angle (dependingonF/D ratio of parabola) of (a) 0◦ –45◦ (b) 45◦ –90◦ (c) 60◦ –90◦ (d) (a) 90◦ –18◦ 66. Zoningis mainly used in dielectric lens antennas in order to: (a) reducethebulk of thelens (b) increasetheband width of thelenses (c) Permit pin point focusing (d) correctthecurvatureof wavefront froma horn that is too short 67. InYagi antennas thegain per element approaches unity when thenumber of directorsis: (a) 33 (b) 23 (c) 13 (d) 9 68. InYagi Udaantennathespacing between elements is normally keptbetween: (a) 0.15λ–0.3λ (b) 0.3λ–0.5λ (c) 0.5λ–λ (d) λ–2λ 69. Which of thefollowingterms does notapply totheYagi Udaarray: (a) goodbandwidth (b) parasiticelements (c) folded dipole (d) fixed frequency antenna 70. Let thefrequency of transmissionassigned tothedriven element and thefrequencies towhich reflectorsanddirectorsareresonantbef 0, f 1 and f 2 respectively. Thesefrequencies bear the relationship: (a) f 1 < f 0 but f 2 f 0 (b) f 1 > f 0 but f 2 f 0 (c) f 1 < f 0 and f 2 > f 0 (d) f 1 > f 0 and f 2 < f 0
=
=
71. Thebi-conical antennawill havebroadbandimpedancecharacteristic provided theflareanglelies between: (a) 30◦ –60◦ (b) 60◦ –90◦ (c) 60◦ –120◦ (d) 90◦ –120◦ 72. Bestbroadbandimpedancecharacteristicsof adisconeantennaareobtained at θ =: (a) 30◦ (b) 45◦ (c) 60◦ (d) 75◦ 73. Theheightof thedisconeat thelowest operatingfrequencyshould beat least: (a) λ/4 (b) λ/3 (c) λ/2 (d) λ 74. Thedisconeantennais: (a) auseful directionfinding antenna (b) used as aradar receivingantenna (c) circularly polarized likeother circular antennas (d) useful asVHF receiving antenna
Appendix G
Objective Questions
883
75. Thelower frequency limit of theconical spiral occurswhen thebasediameter is: (a) λ/8 (b) λ/4 (c) 3λ/8 (d) λ/2 76. Thehigher frequency limit of theconical spiral occurswhen theapex diameter is: (a) λ/8 (b) λ/4 (c) 3λ/8 (d) λ/2 77. Theconical spiral is fed by: (a) Two wiretransmission line (c) A hornantenna
(b) A waveguide (d) A coaxial cablebonded to oneconducting strip
78. A longitudinal slot in acylinder has aradiation pattern, which is practically in aplaneperpendicular to theaxis provided thecylinder diameter in terms of wavelengthis of theorder of: (a) λ/2 (b) λ/4 (c) λ/8 (d) λ/10 79. At theoperatingwavelength λ theactiveregion of alog periodic dipole array consists mainly of several dipoles whoselengths areapproximately equal to (a) λ/2 (b) λ (c) 3λ/2 (d) several λ 80. Normally theVLF horizontal antennas havetheefficiency of theorder of: (a) <1 % (b) 10 % (c) 20 % (d) >2 0 % 81. Normally theVLF vertical antennas havetheefficiency of theorder of: (a) <10 % (b) 20 % (c) 50 % (d) >70 % 82. As per theclassificationof broadcastingstations for class1 stationtheminimum) and maximum power in kW is: (a) 0.1 and l (b) 0.5 and 5 (c) 0.25 and 50 (d) 10 and 50 83. MF broadcastingtransmittingantennas aregenerally vertical radiators with their heightsranging between: (a) λ/6 λ/4 (b) λ/4–5λ/8 (c) λ/6–5λ/8 (d) λ/4–3λ/8 84. Toploading is sometimes used with an antennain order toincreaseits: (a) effectiveheight (b) band width (c) beamwidth (d) input capacitance 85. An ungrounded antennanear theground: (a) acts as asingle antennaof twicetheheight (b) is unliketo need aground screen (c) act as an antennaarray (d) must behorizontally polarized
−
86. An ungrounded antennanear thegroundactsas: (a) asingle antennaof twiceof its actual length (b) asingle antennaof half of itsactual length (c) an antennaarray (d) apoint source 87. In caseof thewireantennas theaerodynamic considerations limit theanglebetween afixed wire and theair streamtoabout: (a) 10◦ (b) 15◦ (c) 30◦ (d) 45◦ 88. Therelativegain of aglass-mounted antennain comparison to theroof-mounted antennais: (a) Lessby 3dB (b) Lessby 5dB (c) Moreby 3dB (d) Moreby 6dB
Appendix G
884
89. Identify thecorrect answer. (a) only length λ/2 is theresonant length. (c) both λ/2 and λ aretheresonant length.
Objective Questions
(b) only length λ is theresonantlength. (d) noneof theseis aresonant length.
90. Oneof thefollowingconsists of non-resonant antennas: (a) Rhombic antenna (c) End-firearray
(b) Folded dipole (d) Broad side array
91. Oneof thevery useful multi-band HF receivingantennais: (a) Conical horn (b) Folded dipole (c) Log-periodic
(d) Squareloop
92. Whichof thefollowingantennas is best excited fromawaveguide: (a) Biconical (b) Horn (c) Helical
(d) Discone
93. Indicatetheantennathat is notwideband: (a) Foldeddipole
(b) Discone
(c) Helical
(d) Marconi
94. An antennathat is circularly polarized is the: (a) Helical
(b) Small circular loop
(c) Parabolic reflector
(d) Yagi Uda
95. Indicatewhich of thefollowing reasons for usingcounter poisewithantennas is false: (a) Impossibility of agood ground connection (b) Provisionof an earth for theantennas (c) Rockiness of theground itself (d) Protectionof personnel workingunderneath 96. In aRhombic antennatheangle of elevationof themain beamis controlledmainly by: (a) Height of antennaabovetheground (b) Lengthof thesidewires formingtherhombic (c) Tilt angle (d) Theterminatingresistance 97. Theinput and terminatingimpedances in arhombic antennaareusually about equal and of theorder of: (a) 150–200 (b) 200–400 (c) 300–600 (d) 600–800 98. Oneof thefollowing is very useful as multi-band HF receivingantenna: (a) Half wavedipole (b) Quarter wavemono-pole (c) Two-element array
(d) Logperiodicantenna
99. Radio transmission at frequencies aboveabout 30 MHz used for TV, FM Radar, etc. is normally by: (a) Ground waves
(b) Spacewaves
(c) Sky waves
(d) Direct waves
100. Identify theresonant antennaillustrated by Fig. G–4 below along withtheir lengths and current distributions: (a) Only(a)
(b) Only (b)
(c) Both(a) and(b)
(d) None
Appendix G
Objective Questions
885
λ
λ
(a)
(b)
Figure G–4