This set of Radar Multiple Choice Questions & Answers (MCQs) focuses on “Antenna Parameters”.

1. The radar antenna should have high directivity.
a) True
b) False

Explanation: It’s important for a radar antenna to be highly directive because of its relative narrow beam widths that direct the energy in a particular direction, hence this results in large gain due to which it can radiate a strong signal and receive a weak pulse during transmission and reception.

2. Antenna is the most important part of the radar.
a) True
b) False

Explanation: Antenna is an important part of radar as per the radar equation. It serves to place energy on target during transmission, collect the received echo energy reflected from the target, and determine the angular location of the target.

3. When practical considerations do not limit the physical size of an antenna, what size of antenna is generally desirable?
a) Size doesn’t matter
b) Medium
c) Small
d) Large

Explanation: Large antennas are generally desirable in most radar applications because there is always a trade between antenna size and transmitter size when long range performance is required. If one is small the other must be large to make up for it.

4. What is the difference between power gain and directive gain?
a) Power gain is more efficient
b) Directive gain is more efficient
c) Power gain accounts for losses within the antenna
d) Directive gain accounts for losses within the antenna

Explanation: The difference between the two is that the power gain accounts for losses within the antenna. Power gain is a function of direction. If it is greater than unity in some directions, it must be less than unity in other directions. The directive gain is the same except the denominator is the power radiated by the antenna by the antenna per 4π steradians.

5. Which out of the following equations correctly relate directive gain G and the effective area Ae?
a) G = 4πAe / λ2
b) G = 4ρaAe / λ2
c) G = 4πAe / π2
d) G = 2πAe / λ2

Explanation: The directive gain G and the effective area Ae can be related by the equation G = 4πAe / λ2 where λ = wavelength, G = directive gain, Ae = effective area or effective aperture. The equation can also be written as G = 4πρaA / λ2 where ρa is the antenna aperture efficiency.

6. When no specific information is available regarding the nature of the antenna, which of the following relation between beam width and antenna dimension D is used?
a) θB = 27 λ/D
b) θB = 85 λ/D
c) θB = 49 λ/D
d) θB = 65 λ/D

Explanation: The relationship used between beam width and antenna dimension is given by the equation θB = 65 λ/D where the wavelength λ has the same units as the aperture dimension D. When D is the horizontal dimension of the antenna, the beam width θB is the azimuth beam width.

7. The time that an antenna takes to return to view the same region of space is known as __________
a) redo time
b) revisit time
c) reclose time
d) reset time

Explanation: The revisit time is the time that an antenna takes to return to view the same region of space. It usually represents a compromise between the need to collect sufficient energy and the need to have a rapid re-measurement of the location of a moving target.

8. The beam width of the pencil beam in the horizontal plane and the beam width in the vertical plane is ___________
a) fairly distorted
b) not equal
c) almost equal
d) not present

Explanation: The beam width of the pencil beam in the horizontal plane and the beam width in the vertical plane is equal or almost equal. Its beam width is generally less than a few degrees, one degree might be typical, not to mention the pencil beam is popular for tracking radars.

9. Since a single pencil beam has difficulty searching out a large angular volume, which method is used to reinforce this issue?
a) Pulsated beam
b) Fan beam
c) Shaped beam
d) Stacked beam

Explanation: This problem can be solved by employing a number of scanning pencil beams, also called as a stacked beam coverage which is used in the vertical dimension of a 3D radar. This consists of a number of contiguous fixed pencil beams like six to sixteen contiguous beams.

10. A simple fan beam is not adequate for the detection of aircraft targets at high altitudes close to the radar because _______
a) it requires broad fan beam
b) requires undesirable high gain
c) high effective area
d) low beam angle

Explanation: A simple fan beam is not adequate for the detection of aircraft targets at high altitudes close to the radar because it requires a very broad fan beam and therefore an undesirable low gain. In addition, a fan beam radiates more energy at the higher elevation angles than needed.

Sanfoundry Global Education & Learning Series – Radar.

To practice all areas of Radar, here is complete set of Multiple Choice Questions and Answers.

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