This set of Radar Multiple Choice Questions & Answers (MCQs) focuses on “Radar Cross Section Fluctuations”.
1. Complex targets are made up of a number of individual scattering centers which are also called as __________
a) scatterers
b) point of contact
c) intersection
d) null point
View Answer
Explanation: Complex target is made up of a number of scatterers. The scatterers for an aircraft might be the engines, cockpit, nose, wings, tail and external stores. The echo from each scattering center has an amplitude and phase that usually is independent of the amplitude and phase of the echoes from other scattering centers.
2. The distance to the radar is assumed to be very small compared to the extent of the target.
a) True
b) False
View Answer
Explanation: The distance to the radar is assumed to be very large compared to the extent of the target because the R-4 variation of the echo signal power with range R need not be taken into account for the individual scatterers. Not to mention it is an adequate target representation for many purposes.
3. What happens during radar cross section fluctuation when the target aspect changes relative to the radar?
a) Constant fluctuation variation
b) Changes in the distance to the scattering centers
c) Overwhelming power dispersion
d) Fading of target echo
View Answer
Explanation: If the target aspect changes relative to the radar, there will be changes in the distances to the scattering centers and the times Ti. These can cause a change in the relative phases of the echo signals from the various scatterers that make up the target.
4. Selecting a small value of cross section that has a high probability of being exceeded almost all the time is one of the methods to find a fluctuating radar cross section.
a) True
b) False
View Answer
Explanation: It’s true that using this method fluctuating radar cross section in the radar range equation can be accounted since this procedure has the advantage of being simple. Though it is not precise, but neither are the analytical methods which require knowledge of the actual statistics of the target fluctuations.
5. The method often employed for finding the minimum detectable signal to noise ratio when the target cross section is not constant is based on ____________
a) doppler frequency shift
b) probability of detection
c) probability density function
d) pulse repetition frequency
View Answer
Explanation: The method is based on probability density function (Pdf) since it gives the probability of finding a particular value of the target cross section between the values of σ and σ + dσ, and in addition to the pdf the variation or correlation of the cross section with time, or pulse to pulse, must also be known.
6. Who gave the popular method for representing the fluctuations of targets by the four statistical models?
a) Albert Rowe
b) John Randall
c) Vladimir Kotelnikov
d) Peter Swerling
View Answer
Explanation: Peter Swerling gave the popular method for representing the fluctuations of targets by the four statistical models. For each of these he calculated the signal to noise ratio required as a function of the probability of detection, probability of false alarm and the number of pulses integrated.
7. The received echo pulses from a target on any one scan with constant amplitude throughout the entire scan but independent from scan to scan are called as ___________
a) halted fluctuations
b) slow fluctuations
c) fast fluctuations
d) intermediate fluctuations
View Answer
Explanation: It is called as slow fluctuations or scan to scan fluctuations. The probability density function for the cross section σ is represented by p (σ) = (1 / σav) exp (- σ / σav) where σ>=0. This Pdf is applied to a target consisting of many independent scatterers of comparable echo areas.
8. Who gave the relationship for the signal to noise ratio which compares favorably with an exact analysis of Kanter who provided curves for the signal to noise ratio when expressed in terms of the correlation coefficient?
a) Elizabeth Alexander
b) Wilhelm Runge
c) David Atlas
d) Barton
View Answer
Explanation: It was Barton who gave the empirical relationship. Barton states that the fluctuation loss when ne independent samples are integrated is approximately Lf(ne) = (Lf)1/ne where Lf is the fluctuation loss for detection with a single pulse.
9. If a target can be considered as a mixture of two major scatterers separated in the range coordinate by a distance D, what is the phase difference of the echo signals from the two?
a) 2π (f * c) D
b) 4π (f * c) D
c) 4π (f/c) D
d) 2π (f/c) D
View Answer
Explanation: The phase difference of the two echo signals is 4π (f/c) D. SA change in frequency ∆f produces a change in phase ∆φ = 4π (∆f/c) D. If the phase change is greater than 2π radians, the resultant signal is considered independent of the previous signal.
10. How many transmitters does most air traffic control radars usually employ in order to achieve the redundancy necessary for reliable air traffic control?
a) Two
b) Three
c) Four
d) Five
View Answer
Explanation: Most air traffic control radars have two transmitters. Rather than have each transmitter operate at the same frequency, they generally operate at two different frequencies in order to obtain two independent echo signals. If an echo is small in one, it will likely be larger on the other.
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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