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Radar Fundamentals
Answers to RF Cafe Quiz #7

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All RF Cafe quizzes would make perfect fodder for employment interviews for technicians or engineers - particularly those who are fresh out of school or are relatively new to the work world. Come to think of it, they would make equally excellent study material for the same persons who are going to be interviewed for a job.

Some of these books used in quizzes are available as prizes in the monthly RF Cafe Giveaway.

Note: Many answers contain passages quoted in whole or in part from the text.



1. What is a “radar mile?”

c) 12.36 µs

A radar mile is the time required for a signal leaving the antenna to go out and back one nautical mile (6076 feet).   2 * 6076 ft / [9.8356e8 ft/s] = 12.36 µs

 

 

 

2. Which best describes a bi-static radar?

a) Fixed transmitter and fixed receiver at
    different locations

Many bi-static systems use multiple receiving sites to be able to pick up weaker reflected signals and to correlate position information with more certainty.



3. What is a radar cross-section (RCS)?

b) A target’s reflecting capacity equivalent to a perfectly reflecting surface of the same area

For radar evasion (stealth), a low RCS is desirable. To guarantee being detected (general & commercial aviation, a high RCS is desirable. A B-52 bomber has an RCS of about 100 m2 (20 dBsm, whereas an F-117 Stealth Fighter has about a 0.003 m2 RCS (which at X-band puts it in the realm of birds).



4. What are common units of radar cross-section (RCS)?

a) dBsm

Decibels relative to a square meter.



5. Who is known as ”The Father of Radar?”
a) Robert Watson-Watt

Sir Robert Watson-Watt, with the help of his assistant Arnold Wilkins, drafted, in February 1935, a report titled "The Detection of Aircraft by Radio Methods." Walter Eugene O'Reilly was "Radar" from the television show M*A*S*H.



6. Which flying (movement) condition will always result in a Doppler speed of 0 m/s?

b) Perfect concentric circle around antenna at constant altitude

Doppler speed is manifested on the boresight radial line (main radiation lobe) so, neglecting “blind speeds,” the only way to be moving and have the Doppler speed at 0 m/s is to not have any motion relative to the boresight radial line.



7. What does “MTI” stand for?

c) Moving Target Indication

Moving Target Indication (MTI) uses a cancellation
system that blanks out stationary targets to permit only moving targets to be displayed on the display. Doing so greatly reduces the clutter and allows relatively weak moving targets to be seen in the midst of buildings, trees, etc.



8. Synthetic Aperture Radar (SAR) radar is mostly likely to be located on which platform?

c) Airplane

Synthetic Aperture Radar (SAR) relies on the motion of the platform to produce the “scan” that would otherwise be provided by a rotating or steerable antenna.



9. Which feature of a “stealth” aircraft is most responsible for its low observability?

b) Multi-faceted surfaces

The angle of a signal’s reflection form a surface is equal to the angle of its incidence on the surface. By minimizing the area presented perpendicular to any given direction (particularly those direction most likely to be illuminated, like from below and the side), a minimum amount of incident radar signal energy will be reflected back in the direction from which it originated (the radar).



10. What kind of radar did the webmaster of RF Cafe work on while in the U.S.A.F?

a) MPN-14

In the U.S. government system designation standard, the "M" stands for ground Mobile, the "P" stands for Radar, and the "N" stands for Navigational aides. The "-14" designates position in a series.
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