This set of Radar Multiple Choice Questions & Answers (MCQs) focuses on “Delay Line Cancelers”.

1. In frequency response of the single delay-line canceler, the signal from a target at range R0 at the output of the phase detector can be written as ___________
a) V1 = k sin (2πfdt – Φ0)
b) V1 = sin (2πfdθ – Φ0)
c) V1 = k sin (2πfdθ– Φ0)
d) V1 = sin (2πfdt – Φ0)

Explanation: response of the single Delay-Line Canceler, the signal from a target at range R0 at the output of the phase detector can be written as V1 = k sin (2πfdt – Φ0) where fd = Doppler frequency shift, Φ0 = a constant phase equal to 4πR0/λ, R0 = range at time equal to zero, λ = wavelength, and k = amplitude of the signal.

2. The output from the delay-line canceler is seen to consist of a cosine wave with different frequency fd from the input, and with an amplitude 2k sin (πfdTp).
a) True
b) False

Explanation: The output from the delay-line canceler is seen to consist of a cosine wave with the same frequency fd as the input, but with an amplitude 2k sin (πfdTp). Due to which the amplitude of the canceled video output depends on the Doppler frequency shift and the pulse repetition period.

3. The process in which the target is not detected whenever an uncalled clutter residue is generated that can interfere with the detection of moving targets is called as ________
a) delay line canceler
b) blind speed
c) clutter attenuation
d) time-domain filter

Explanation: Blind speed is when the target is not detected and there is an uncalled clutter residue that could interfere with the detection of moving targets. The response of the single delay-line canceler will be zero whenever the magnitude of sin (πfdTp) is zero, which occurs when πfdTp = 0, ±π, ±2π, ±3π, …..

4. There will always be zero response of the delay-line canceler whenever the Doppler frequency fd = 2vr / λ is a multiple of the _________
a) maximum power transmission
b) pulse repetition frequency
c) ambiguous region
d) doppler frequency shift

Explanation: It is true that there will always be zero response of the delay-line canceler whenever the Doppler frequency fd is a multiple of the pulse repetition frequency fp since the Doppler shift can be negative or positive depending on whether the target is receding or approaching.

5. Which out of the following four methods is not used for reducing the detrimental effects of blind speed in an MTI radar?
a) Operate with more than one pulse repetition frequency
b) Operate the radar at short wavelength
c) Operate with a high pulse repetition frequency
d) Operate with more than one RF frequency

Explanation: In order to reduce the detrimental effects of blind speed in an MTI radar, the radar is at long wavelength (low frequencies). Blind speed can be a serious limitation in radar MTI radar since they cause some desired moving targets to be canceled along with the undesired clutter at zero frequency.

6. Which out of the following is not a possible reason as to why VHF is not usually considered a desirable frequency choice for a long range air-surveillance radar?
a) Resolution in range and angle are poor
b) Low altitude coverage generally is poor
c) Portion of EM has other radar services
d) Multiple time around clutter echoes are not cancelled

Explanation: VHF is not usually considered a desirable frequency for a long range air-surveillance radar because resolution in range and angle are poor due to narrow and large bandwidth, portion of EM has other radar services such as FM and TV, and low altitude coverage generally is poor.

7. Which of the following is a limitation of a single delay line canceler?
a) Finite width of the clutter spectrum
b) High frequency transmission
c) Low sampling ratio
d) Insufficient value of Doppler frequency shift

Explanation: Insufficient attenuation of clutter that results from the finite width of the clutter spectrum is one of the limitation of the delay line canceler. The consequences of a finite width clutter spectrum are that the frequency response of the single delay line canceler encompasses a portion of the clutter spectrum.

8. How can we make the clutter attenuation infinite?
a) Turning off the radar transmitter
b) Increase bandwidth
c) Increase input power

Explanation: The clutter attenuation can be made infinite by turning off the radar receiver. This of course would not be done knowingly since it also eliminates the desired moving target echo signals. In order to avoid increasing of clutter attenuation, a measure of performance is used which is known as improvement factor.

9. Which out of the following canceler allows the designer N zeroes for synthesizing the frequency response using the classical z-plane procedure for filter design?
a) N-pulse nonrecursive canceler
b) Three pulse canceler
c) N-pulse recursive canceler
d) Five pulse delay line canceler

Explanation: N-pulse nonrecursive canceler allows the designer N zeroes for synthesizing the frequency response. Each feed forward line and its weight wi correspond to a zero in classical filter design on the z-plane. Filter design using only zeroes does not have the flexibility of filter design based on poles as well as zeros.

10. Recursive filters are usually avoided in military radars because of poor transient response.
a) True
b) False

Explanation: Because of the poor transient response of recursive filter (infinite impulse response), they are usually avoided in military radars that might be subject to deliberate electronic countermeasure. They have been widely used, however, to eliminate clutter in civilian Doppler weather radars.

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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