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How Radar Works
    Radar stands for radio detection and ranging. Radar was used first used on ships to detect icebergs and other obstacles. The most common radar transmits a train of narrow, rectangular-shape pulses modulating a sinewave carrier. The echo signal is returned and evaluated on a cathode ray tube, CRT. Distance is measured by the time it takes the pulse to travel to and from the target.

    A continuous waveform, CW, radar can also be used. This radar shows the doppler frequency shift to measure the velocity of a target.

    Most radars operate at frequencies from about 220 MHz to 35 GHz. However, some radars have operated as high as 5 MHz and others at 94 GHz. Knowing the frequency the wave length  is determined by dividing the frequency in MHz into 300 to give the wave length in meters. Usually the higher the frequency, the sharper the return signal and the more accuracy can be obtained in determining distance and location.

Standard Radar Frequencies and Wave Length
Band designation Wave length Frequency range Application
HF (high frequency) Decametric 100 - 10 m 3-30 MHz Radio, broadcast
VHF (very high frequency) Metric 10 - 1 m 30-300 MHz Radio, TV
UHF (ultra high frequency) Decimeter 1m - 30 cm 300-1000 MHz RADAR, TV
L, microwave region

30 - 15 cm

1000-2000 MHz RADAR, TV
S, microwave 15 - 7.5 cm 2000-4000 MHz RADAR
C, microwave 7.5 - 3.8 cm 4000-8000 MHz RADAR
X, microwave 3.8 - 2.5 cm 8000-12,000 MHz RADAR
Ku, microwave 2.5 - 1.7 cm 12-18 GHz RADAR
K, microwave 1.7 - 1.1 cm 18-27 GHz RADAR
Ka, extremely high frequency 11 - 7.5 mm 27-40 GHz RADAR
mm, extremely high frequency 7.5 - 1 mm 40-300 GHz  
Computer Classes and Books:
    Two Computer Courses are available on CD-ROM disks that are intended to provide a basic understanding of the subjects of radar and microwave tubes. Many explanations of various items are presented with animations to best describe the subject material. Test questions are available with scoring to assist in learning the subject matter. Available from CDtechware. One is How to Speak Radar and the other is Fundamentals of Microwave Tubes. Both are published by Arnold Acker who worked for over 30 years at Varian Brothers. Mr. Acker has taught many classes on radar so he has a good feeling and understanding of how to explain this most interesting topic. Mr. Acker at CDtechware can be reached at 209-847-2304 or e-mail address: arnacker@jps.net.
    A good book on radar is "Introduction to Radar Systems" by Merrill I. Skolnik. This book, in its second edition, is published by Mc GrawHill and can be purchased from Borders.

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© Copyright 2007 Martin Hollmann