About RF Cafe Copyright: 1996 - 2024Webmaster:    Kirt Blattenberger,     BSEE - KB3UON RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived... All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged. My Hobby Website: AirplanesAndRockets.com

All RF Cafe Quizzes make great 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. Bonne chance, Viel Glück, がんばろう, buena suerte, удачи, in bocca al lupo, 행운을 빕니다, ádh mór, בהצלחה, lykke til, 祝你好運. Well, you know what I mean: Good luck!

Note: Some material based on books have quoted passages.

This quiz is based on the information presented in Stimson's Introduction to Airborne Radar, Third Edition, by Hugh D. Griffiths, Christopher Baker, and David Adamy.

Note: Some of these books are available as prizes in the monthly RF Cafe Giveaway; however, this one will likely remain in my possession for a long time.

1.  What is another, more common name for a coherent radar system?

Both amplitude and phase are measured, thus enabling calculation of speed.

(see page 15)

2.  Match the following common radar frequency bands with their central frequencies.

a)  C - 3 GHz
b)  Ka - 38 GHz
c)  Ku - 15 GHz
d)  S - 6 GHz
e)  X - 10 GHz

(see page 99)

3.  In which direction(s) does(do) an antenna's sidelobe(s) exist?

d)  All directions

Sidelobes are due to non-ideal physical limitations of an antenna and its environment (ground integrity, antenna support, nearby structures, etc.).

(see page 115)

4.  What causes a grating lobe in an electronically scanned antenna?

a)  Spacing radiating elements at too great of a distance

Spacing the radiating elements is determined by the equation d < (1 + sin θ), which yields the distance of the grating lobe from the main lobe.

(see page 135)

a)  Pulsed radar avoids transmitter leakage issues

Pulsed radars emit a signal and then turn off the transmitter while listening for returns. Doing so eliminates having to contend with strong inband signals that will raise the noise floor and lower the minimum detectable signal.

(see page 149)

6.  What is radar cross-section (RCS)?

d)  Effective area of the signal reflecting surface relative to a perfectly reflecting sphere of the same projected area

Radar cross-section is a form of quality parameter that represents how large of an effective target a body appears relative to a perfectly reflective sphere. Something like an unpainted Cessna Citation bizjet will have a large RCS since there are so many large, reflective surfaces whereas an F-117 Stealth Fighter with its multifaceted surfaces with non-reflective paint will have a small RCS. Keep in mind, BTW, that the Cessna wants to be painted strongly by radar for air safety reasons.

(see page 166)

7.  What is "chirping?"

b)  Linear frequency modulation over the transmit time

Chirping gets its name from the sound hear when a linearly swept audio frequencies is broadcast through a speaker - it sounds like a bird's chirp.

(see page 233)

8.  Coherence in radar refers to which of the following?

d)  Phase of the signal from one pulse to the next

Phase coherence is relative to a reference oscillator that is used to measure time between the transmitted pulse and the return signal.

(see page 269)

9.  What defines bins in a Doppler filter bank?

a)  Frequency bands

Return signal information (phase, amplitude, angle of arrival, etc.) is sorted according to a prescribed range of frequencies that indicate what the Doppler shift - positive or negative - is relative to the transmitted signal.

(see page 297)

10.  What is the name for unwanted returns from the ground?

b)  Clutter

Clutter is an undesirable return signal that obscures the desired target. Moving target indication (MTI) can cancel stationary targets to reveal moving targets that would otherwise be undetectable.

(see page 329)

11.  Match each picture with what it represents.

A - High accuracy, low precision
B - Low accuracy, high precision
C - High accuracy, high precision
D - Low accuracy, low precision

Accuracy is keeping all the hits centered around the intended target. Precision is clustering all of the hits in the same area even if not centered on the target.

(see page 433)

12.  Which type of pulse repetition frequency (PRF) results in unambiguous range?

c)  Low

A low PRF assures that the echo from the farthest distance target arrives prior to the transmitting of the next pulse, thus eliminating 'second-time-around' responses.

(see page 383)