Antenna Tutorials question & answers

Radharaman Institute of Research and Technology, Bhopal Department of Electronics and Communication Engineering BE VI Semester Antenna and Wae !ropagation "EC#$%&'

Assignment( )nit#I( Radiation Radiation 1 What is retarded potential? Derive the expression for it.***** 2 Derive the expression for the radiative eld due to small or elementary current element.***** 1

3 Prove that the eld of a simple antenna consists of three terms involving

,

1

r r 2  and

1

r

3

 terms. xplain the nature of these terms.*****

! What is the signicance of the electros electrostatic tatic eld" induction eld and radiation eld of  the antenna? # What is the radiation resistance resistance of an antenna? $ho% that the radiation resistance of  a half %ave dipole antenna is &3 ohms. ***** ' ()tain the expression for the Po%er radiated )y a current element and its adiation resistance.***** & Derive the expression for the eld variation due to linear current and sinusoidal current distri)ution on e+ective length of linear antennas. , Derive the po%er radiated )y and radiation resistance )y half %ave dipole antenna or -uarter %ave monopole antenna.*****  /t %hat distance" in %avelength" the radiation component of magnetic eld %ill )e three times of the induction component. /t %hat distance is it #0 times. 10 /n antenna operating at 20 fre-uency has directional gain of 1' d4. / minimum electr ele ctric ic el eld d int intens ensity ity of 100 100m5 m56m 6mete eterr is re re-ui -uire red d at a dis distan tance ce of 20 7m fr from om antenna in free space. Determine the minimum po%er to )e radiated )y the antenna. 8int9 Erms =

90 Pr √ 90

 R

v / m :.

11 ;ind out the eld strength at 30 7m a%ay from a transmitting antenna of '2#
90 Pr √ 90 v / m :.  R

12 valuate the radiation resistance of a circular loop %ith a circumference of a -uarter

 λ

( )

 A   Circumference =2 π r ∴ =2 π r , A =π r , ∴ R r=320 π  2 of a %avelength. 8int9 4  λ 2

4

2

:.

1

13 Determine the radiation resistance of a dipole antenna of

( )

2

dl  R =80 π  r 8int9  λ 2

 %avelength long.

12

:.

 λ 1! =alculate the radiation resistance of dipole antenna

8

 long. >f the e-uivalent loss

resistance in the antenna due to dielectric structure is 0.&# (hms" What is the

( )

2  Rr dl 80  R = π  , η = × 100 :. r eciency of the antenna? 8int9  λ  Rr + R l 2

1# /n electric field strength 10@56m is to )e measured at a point ABC62" #007m from a half %ave dipole antenna operating in air at #0. =alculate the current ErmsF that

must )e fed to the antenna. 8int9 ;or half %ave dipole"  E θ

=

60 I m

r

{

cos

(

π  2

cosθ

sinθ

)

}

:.

1' / rounded vertical half %ave dipole radiating at #00 7 produces a maximum r.m.s electric field of 20@56m at distance of !0 7m. Determine the total po%er radiated )y dipole. 8int9 for rounded vertical antenna"

Erms

120 π =

I rms l e

 λ r

:.

1& Ghe current at the )ase of an earthed antenna &0m high is 2# /mp" at a fre-uency of  10. =alculate the eld strength at a distance of 2#
120 π

2 =

 l , E π  rms

=

I rms l e

 λ r

:.

1, / half %ave dipole is driven )y r.m.s current of 10 /mp" at 100  in free space. =alculate the pointing vector at a distance of 20 cm in the direction of maximum radiation. 8int9  Erms =

120 π I rms l e

 λ r

:.

1 / $hort dipole antenna of length #m is centre feed %ith r.m.s current of 2#/mp at fre-uency of 10. =alculate the po%er radiated )y the antenna. 8int9

()

le  Rrad =160 π   λ 2

2

:.

20 /n antenna of e+ective height of 100m and the current at the )ase is !#0/mp Er.m.sF at !0. What is the po%er radiated? >f the total resistance of antenna

()

2

le Rr Rrad =160 π  , η= × 100 :.  λ  Rr + R l 2

circuit is 1.12 (hms. What is its eciency? 8int9

 λ 21 =alculate the po%er radiated )y 100

=osHt

/mp. 2

What

( )

π   I m dl 2 dl ⌋ , Rr =80 π   Prad =η o ⌊ 3  λ  λ

 dipole" if it carries a uniform current of > B

16

is

its

radiation

resistance?

2

:.

Iote9 ***** mar
Radharaman Institute of Research and Technology, Bhopal Department of Electronics and Communication Engineering BE VI Semester Antenna and Wae !ropagation "EC#$%&'

Assignment( )nit#II( Antenna *undamentals J1. J2. J3.

$tate eciprocity theorem and prove it for antenna systems. Write application of eciprocity theorem in antenna systems Write short note on the follo%ing9 EaF adiation Pattern

8int9

J!. J#.

E)F $teradian and $olid angle EcF adiation intensity EdF Directivity EeF /ntenna ain EfF /ntenna ciency EgF /ntenna 4eamK%idth EhF +ective aperture EiF ;ront to )ac< ratio Derive the relation )et%een the e+ective area and gain of antenna. /n antenna has a loss resistance 10 (hms" po%er gain of 20 and directivity 22.

=alculate its radiation resistance. 8int9

η=

G p Gd

=

 Rr  Rr + Rl :.

J'. >n a micro%ave communication lin<" t%o identical antennas operating at 10  are used %ith po%er gain of !0d4. >f the transmitter po%er id 1 W" nd the received po%er" if the range of the lin< is 30 7m. 8int9 E;eriiLs formulaF J&.

 Pr= P t  A t  A r

( ) λ 4 πr

2

:.

/n antenna having directivity of 0 is operating at a %avelength of 2m. =alculate 2

λ  A =  × D :. ( ) e max the maximum e+ective aperture of the antenna. 8int9 4 π  J,. G%o short dipoles are placed at distance of # 7m in free space. (ne dipole is supplied %ith po%er of #7W at fre-uency of 1#0. =alculate the maximum po%er %hich can )e received at the second dipole. 8int9 E;eriiLs formulaF

 Pr= P t 

 A et  A er 2

r  λ

2

2

λ , A et = A er= A e , A e =  × D :. 4 π 

J. / directional antenna has an e+ective radiated po%er of 1.1
η=

What is its directivity" if po%er gain is 22. 8int9

G p Gd

=

 Rr  Rr + Rl :.

J11. /n antenna is feed )y current of !.# /mp %ith a resistance of 300 (hm radiates po%er in its optimum direction" then =alculate the ;4 E;ront to 4ac< atioF of an antenna in d4" if po%er of #00 Watts is radiated in the opposite direction. J12. =alculate the approximate gain and )eamK%idth of a para)olic reNector antenna at operating fre-uency ! " diameter 20m and illumination eciency ##O. 8int9

 D=

4 π  2

 λ

× ( A e )max , ( A e ) max= A, A=

πD 4

2

,!P"# =

70 λ

140 λ

 D

 D

  ,"#$% =

Iote9 ust su)mit the assignment on or )efore 0# arch 201!.

:.