This set of Radar Multiple Choice Questions & Answers (MCQs) focuses on “Limitations to MTI Performance”.

1. Which out of the following is not a limitation to MTI performance?

a) Resistance

b) Limiting

c) Antenna scanning modulation

d) Internal fluctuation clutter

View Answer

Explanation: Resistance is not a limitation to MTI performance. The limitation of MTI performance causes the clutter spectrum to widen. More clutter energy is then passed by the Doppler filter, which lowers the improvement factor.

2. What is the correct way to represent if the clutter power spectral density could be expressed as a Gaussian function with a standard deviation?

a) W (f) = W_{0} exp (f^{2} / 2σ_{c})

b) W (f) = W_{0} exp (-f^{2} / 2σ^{2}_{c})

c) W (f) = W_{0} exp (f^{2} / 2σ^{2}_{c})

d) W (f) = W_{0} exp (-f^{2} / 2σ_{c})

View Answer

Explanation: If the clutter power spectral density could be expressed as a Gaussian function with a standard deviation σ

_{c}in Hz, it can be represented as W (f) = W

_{0}exp (-f

^{2}/ 2σ

^{2}

_{c}) where W

_{0}is the peak value of the clutter power spectral density at f = 0. The clutter standard deviation is sometimes written In terms of the radial velocity, in units of meters/second, and denoted σ

_{v}.

3. Which out of the following is the correct way to represent the duration of the echo signal received from a target or a clutter scatterer as the antenna of a pulse radar scans past?

a) n_{B} / f_{p} = θ_{B} / θ_{s}

b) n_{B} / θ_{s} = θ_{B} / f_{p}

c) n_{B} / f_{p} = θ_{s} / θ_{B}

d) θ_{s} / n_{B} = θ_{B} / f_{p}

View Answer

Explanation: The duration of the echo signal received from a target or a clutter scatterer as the antenna of a pulse radar scans past is given by n

_{B}/ f

_{p}= θ

_{B}/ θ

_{s}where n

_{B}= number of pulses received, f

_{p}= pulse repetition frequency, θ

_{B}= antenna beam width in degrees and θ

_{s}= antenna scanning rate.

4. In antenna scanning modulation, the frequency spectrum has a bandwidth inversely proportional to the _____________

a) resistance

b) power

c) time duration

d) antenna scanning

View Answer

Explanation: The frequency spectrum has a bandwidth inversely proportional to the time duration t

_{0}. Consequently, even if the clutter scatterers were perfectly stationary and there were no instabilities in the radar equipment, there would still be a finite spectral spread due to the finite duration of the echo signal.

5. If the two way voltage is equal to the one-way antenna power pattern then, which is the correct way to represent the approximated Gaussian function?

a) G (θ) = G_{0} exp (-2.776 θ^{2} / θ_{B}^{2})

b) G (θ) = G_{0} exp (-2.347 θ^{2} / θ_{B})

c) G (θ) = G_{0} exp (2.154 θ^{2} / θ_{B})

d) G (θ) = G_{0} exp (2.590 θ^{2} / θ_{B}^{2})

View Answer

Explanation: The two way voltage is equal to the one-way antenna power pattern, which can often be approximated by a Gaussian function such as G (θ) = G

_{0}exp (-2.776 θ

^{2}/ θ

_{B}

^{2}) where G

_{0}= maximum antenna gain, θ = angle coordinate, and θ

_{B}= beam width. The scanning antenna beam modulates the amplitude of the received pulse-train.

6. The clutter model of clutter spectrum suggested in World War II was based on which of the following spectrum?

a) Absorption spectrum

b) Band spectrum

c) Lorentzian spectrum

d) Gaussian spectrum

View Answer

Explanation: The clutter model of clutter spectrum suggested in World War II was based on Gaussian spectrum. A Gaussian spectrum was and still is popular since it fit the early experimental clutter measurements and it is relatively easier to manipulate mathematically.

7. The standard deviation of windblown clutter echo fluctuations when measured in meters/second is independent of ________

a) noise

b) resistance

c) time

d) frequency

View Answer

Explanation: The standard deviation of windblown clutter echo fluctuations when measured in meters/second is independent of frequency. Here the standard deviation in meters/second is denoted σ

_{v}, and the standard deviation in hertz is denoted σ

_{c}. If the standard deviation is substituted in If ≈ 2n (f

_{p}/ 2πσ

_{c})

^{2n}/ n! gives the limitation on the MTI improvement factor due to windblown clutter.

8. The normalized power-law spectrum is given by _______

a) P (f) = 1 / (1 + (f/f_{c})^{n})

b) P (f) = 1 / (1 – (f/f_{c})^{n})

c) P (f) = 1 / (1 + (f_{c}/f)^{n})

d) P (f) = 1 / (1 – (f_{c}/f)^{n})

View Answer

Explanation: The normalized power-law spectrum is given by P (f) = 1 / (1 + (f/f

_{c})

^{n}). This was first suggested by Fishbein et al. as being a better description of measured clutter spectra than the Gaussian. At X band, they found the value of the exponent n to be equal to 3.

9. In phase noise, noise due to phase fluctuation associated with the stalo and coho oscillators can be a major limitation to the improvement factor of high performance MTI radars.

a) True

b) False

View Answer

Explanation: It is true because generally phase noise has a much larger effect than noise caused by amplifier instabilities. The phase noise from oscillators in the exciter of a power amplifier affects the transmitted signal as well as the signal in the receiver.

10. Saturation of the receiver by clutter echoes results in the spreading of the clutter spectrum that increases the improvement factor.

a) True

b) False

View Answer

Explanation: Saturation of the receiver by clutter echoes results in the spreading of the clutter spectrum that reduces the improvement factor. If the receiver is of large enough dynamic range, and there are sufficient bits in the A/D converter, and if the improvement factor is large enough to make the uncalled clutter residue smaller than receiver noise, there will be no problem since there will be no limiting.

**Sanfoundry Global Education & Learning Series – Radar.**

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