Antennas: Assignment 12:

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1. If the corner angle ‘a’  of a reflector antenna is reduced, it provides:

(i) High gain (ii) More number of images

(iii) Wider half power beam width (iv) Less number of images

(i) and (ii)

(i) and (iv)

(ii) and (iii)

(iii) and (iv)

Ans: a

2. For a corner reflector antenna with corner reflector angle ‘a’ = 40°, number of images will be:

7

8

9

10

Ans: b

3. If the aperture angle of a parabolic reflector antenna increases, then the aperture efficiency of the antenna will:

Increase

decrease

remain almost constant

First increase then decrease

Ans: d

Common data for Questions 4 to 6: A parabolic reflector antenna is designed with a diameter of 1.8 m at 5.8 GHz. Due to the manufacturing problem, the antenna efficiency is reduced to 40%.

4. What will be the approximate gain (in dBi) of the antenna?

48.4

42.4

36.8

30.6

Ans:  c

5. If the antenna efficiency is improved to 70%, the approximate gain of the modified antenna will be:

48.2 dBi

39.2 dBi

32.4 dBi

30.6 dBi

Ans: b

6. If f/d ratio of a parabolic reflector antenna is 0.65, then the value of in degrees will be:

24.4

36.2

42.0

50.4

Ans: c

7. Cassegrain feed is generally used instead of prime focus feed with parabolic reflector to affect which of the following factors?

Impedance

Bandwidth

Gain

To place the feed at convenient place for high power transmitter

Ans: d

8. To accurately measure the gain and radiation pattern of a test antenna, the minimum distance (in terms of λ i.e. free space wavelength) required between test antenna and reference antenna is given by (D is maximum dimension of the antenna.):

2D2/λ$2D^2/\lambda$

D2/λ$D^2/\lambda$

2D/λ2$2D/{\lambda }^2$

2D2∗λ$2D^2\ast \lambda$

Ans: a

9. To measure the gain and radiation pattern of a test antenna, the reference antenna and the test antenna must have

Same gain

Similar radiation pattern

Common resonance frequency of operation

Same polarization

Ans: c

10. A spectrum analyzer cannot be used to do the measurement of

Harmonic distortion

Third order intercept point

Phase noise

S-parameter

Ans: d