This set of Radar Multiple Choice Questions & Answers (MCQs) focuses on “Low Angle Tracking”.
1. A radar that tracks at low elevation angles illuminates the target via two paths, one is the path that includes a reflection from the earth’s surface and the other one is the _______
a) direct path
b) indirect path
c) parabolic path
d) circular path
View Answer
Explanation: The two paths include the direct path and the path that includes a reflection from the earth’s surface. It is as though the radar were illuminating two targets, one above the surface and the other its image below the surface. This is an example of the classic two scatterer model.
2. At low grazing angles over a perfectly smooth reflecting surface, what is the reflection coefficient from the surface?
a) 0
b) -1
c) 0.5
d) 0.33
View Answer
Explanation: At low grazing angles over a perfectly smooth reflecting surface, the reflection coefficient from the surface is approximately -1. That is, its phase is in the vicinity of 180° and its magnitude is approximately unity so that the signal amplitude reflected from the surface is almost equal to the signal amplitude incident on the surface.
3. With a rough surface, the angle error due to multipath is _________
a) equated
b) nullified
c) reduced
d) increased
View Answer
Explanation: With a rough surface, the angle error due to multipath is reduced because the surface-reflected wave is of lower magnitude (the reflection coefficient is less). Not to mention the roughness of a surface depends on its physical variations in height relative to the radar wavelength.
4. In addition to causing errors in elevation-angle tracking, it is also possible for multipath to introduce errors in the ________
a) tracking angle tracking angle
b) phase angle tracking channel
c) elevation angle tracking channel
d) azimuth angle tracking channel
View Answer
Explanation: In addition to causing errors in elevation-angle tracking, it is also possible for multipath to introduce errors in the azimuth angle tracking channel. This can be caused by cross talk where a portion of the elevation angle channel signal enters in some manner the azimuth angle channel.
5. The method that has been successfully used operationally to obtain low angle tracking capability is to employ two radars, one at X band (9 GHz) and the other at _______
a) Ka
b) K
c) Ku
d) V
View Answer
Explanation: To obtain low angle tracking capability, the two radars are employed at X band (9 GHz) and the other at Ka band (35 GHz), using a single antenna system to provide operation at the two frequencies. The lower frequency radar generally has a longer range.
6. A conventional four-element feed in a monopulse tracker has how many degree of freedom in the vertical plane?
a) 0
b) 1
c) 2
d) 3
View Answer
Explanation: A conventional four-element feed in a monopulse tracker has one degree of freedom in the vertical plane. It is designed to track only a single target. When multipath occurs, there are two target signals present. A conventional monopulse radar cannot cope since it is designed on the assumption that there is only a single target present.
7. How is the range resolution ∆R which is required to separate the direct from the ground-reflected signal approximately given as?
a) ∆R = 2htR / ha
b) ∆R = 2haR / ht
c) ∆R = 2haht / R
d) ∆R = 2R / haht
View Answer
Explanation: The range resolution ∆R required to separate the direct from the ground-reflected signal is approximately ∆R = 2haht / R where ha = antenna height, ht = target height, R = range. For a radar antenna height of 20 m, target height of 30 m, and a range of 4 km, the range resolution ∆R must be 0.3 m.
8. Which of the following states that use of more than one frequency each sufficiently separated from one another could smooth the angle error due to glint?
a) Narrow beamwidth
b) Illogical target trajectory
c) High range resolution
d) Frequency agility
View Answer
Explanation: Frequency agility states that use of more than one frequency each sufficiently separated from one another could smooth the angle error due to glint and produce an average result that was less likely to have large errors. The frequencies had to be separated by the amount ∆f = 150/D in order to obtain independent values of the glint error.
9. A fence surrounding the radar can’t mask the echo from the image, especially when the near-in sidelobes are a factor in creating a multipath error.
a) True
b) False
View Answer
Explanation: A fence surrounding the radar can mask the echo from the image, especially when the near-in sidelobes are a factor in creating a multipath error. Fences can be expensive and are only of value when the radar is at a fixed site. Since the main beam illuminates the top edge of the fence, diffracted energy might illuminate the image.
10. The normal monopulse receiver uses only the in-phase (or the out-of-phase) component of the difference signal.
a) True
b) False
View Answer
Explanation: It is true since when a multipath signal is present along with the direct signal, the difference signal has a quadrature component. The in-phase and quadrature components of the error signal define a complex angle error signal. By measuring the complex angle, the target elevation can, in principle, be inferred.
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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