1. The Doppler region where desired moving targets can be detected is called as _________
a) Doppler space
b) Doppler frequency
c) Doppler area
d) Doppler effect

Explanation: The Doppler region where desired moving targets can be detected is called Doppler space. A reduction in the available Doppler space causes loss in the detection of moving targets. Airborne radars suffer a widening of the clutter spectral width due to platform motion, further aggravating the reduction in the Doppler space available for the detection of targets.

2. Blind speeds become troublesome when the radar frequency is _________
a) decreased
b) increased
c) nullified
d) constant

Explanation: Blind speeds become troublesome when the radar frequency is increased. An increase in frequency, when the PRF remains constant, means a decrease in the first blind speed and more of them will appear within the desired Doppler space.

3. Which of the following factor increases the first blind speed and reduces the number of nulls found within the Doppler space?
a) Increasing target strength
b) Increasing clutter
c) Increasing PRF
d) Increasing time

Explanation: Increasing the PRF increases the first blind speed and reduces the number of nulls found within the Doppler space. A high PRF, however, can increase the problem of range ambiguities. Thus the trading of Doppler ambiguities for range ambiguities is something that has to be tolerated in order to obtain good detection of moving targets at the high microwave frequencies.

4. A radar with no blind speeds within the Doppler space is called as ________
a) no ambiguity pulse Doppler radar

Explanation: A radar with no blind speeds within the Doppler space is called high-PRF pulse Doppler radar. In some situations, however, it may be beneficial to operate at a slightly lower PRF and accept both range and Doppler ambiguities. Such radar is called a medium PRF pulse Doppler radar.

5. What is the significant difference between MTI and pulse Doppler radar (PDR)?
a) PDR receives more clutter than MTI
b) MTI uses high power whereas PDR uses low power amplifier
c) MTI receives more clutter than PDR
d) PDR uses filter bank while MTI used analog delay line canceller

Explanation: The significant difference between MTI and pulse Doppler radar is that PDR generally receives much more clutter than an MTI radar because of the fold over in a range of clutter echoes when ambiguous PRFs are employed, so that the pulse Doppler radar requires a much greater improvement factor than does an MTI radar of comparable performance.

6. Since there are many range ambiguous pulses simultaneously illuminating the clutter, the antenna sidelobe clutter in a high PRF pulse Doppler radar is ________
a) small
b) large
c) zero
d) constant

Explanation: The antenna sidelobe clutter is larger in a high PRF pulse Doppler radar since there are many range ambiguous pulses simultaneously illuminating the clutter. With a duty cycle of 50%, the antenna sidelobes are simultaneously illuminating half the total clutter within the radar’s coverage, much more than would be seen by a low PRF AMTI radar.

7. The PRF of an X band high PRF pulse Doppler radar designed for use with a military airborne fighter is from _________
a) 500 to 700 kHz
b) 300 to 700 kHz
c) 100 to 300 kHz
d) 200 to 600 kHz

Explanation: The PRF of an X band high PRF pulse Doppler radar is 100 to 300 kHz. With such a high PRF, there is not much room for long pulses. It is not unusual for the duty cycles of high PRF pulse Doppler radars to have values from 0.3 to 0.5. Such radars might operate with only one range gate.

8. If the center of the Doppler filter bank is always maintained at the frequency of the main beam clutter, the minimum PRF that can be used is _______
a) λ / 4vT
b) 4vT / λ
c) vT / 4λ
d) 4vT / λ

Explanation: If the center of the Doppler filter bank is always maintained at the frequency of the main beam clutter, the minimum PRF that can be used is 4vT / λ where vT is the maximum ground speed of the target. For this to occur, the main beam clutter frequency must be known and a tracking device used to keep the filter bank centered at the main beam clutter frequency.

9. The medium PRF results in less clutter being seen by the antenna sidelobes than the high PRF radar.
a) True
b) False

Explanation: The high PRF radar results in more clutter being seen by the antenna sidelobes compared to medium PRF because ambiguous range cells have fewer pulses. A better visualization of the target is provided due to the sidelobe’s region lower level clutter with low Doppler velocity.

10. The altitude line in the medium PRF pulse Doppler can be removed by range gating or by filtering.
a) True
b) False

Explanation: The altitude line in the medium PRF pulse Doppler can be removed by range gating or by filtering, not to mention the high PRF pulse Doppler can only be removed by filtering. Range gating permits the detection of low relative velocity targets near the radar transmitted frequency that might be rejected in a high PRF system where the altitude return is rejected by filtering.

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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