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Planetary radar astronomy's greatest handicap is the extremely feeble power content of an echo. This echo is always masked by relatively strong background noise so that special signal processing is required. The basic task is the detection and measurement of the echo power. However, when the signal strength is greater than the requirements of simple detection, it is desirable to measure the power distribution in time or in frequency. When the signal is still stronger, it is possible to divide the power into the two dimensions of time delay and frequency shift simultaneously, and thus produce a radar "map" of the target. Some of the special techniques and devices which are required to make these measurements, as well as some of the results of applying these techniques to Venus, Mars, Mercury, and Jupiter, are described. There are several groups working in this field and the author has stressed the work at the Jet Propulsion Laboratory merely because of his familiarity with it.