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High PRF is limited to systems that require close-in performance, like proximity fuses and law enforcement radar. For example, if 30 samples are taken during the quiescent phase between transmit pulses using a 30 kHz PRF, then true range can be determined to a maximum of 150 km using 1 microsecond samples (30 x C / 30,000 km/s).
Ground targets further than this range cannot be detected, so the PRF can be quite high; a radar with a PRF of 7.5 kHz will return ambiguous echoes from targets at about 20 km, or over the horizon. If however, the PRF was doubled to 15 kHz, then the ambiguous range is reduced to 10 km and targets beyond this range would only appear on the ...
Pulse repetition frequency (PRF) is too low to sample Doppler frequency directly; PRF is too high to sample range directly; Pulse Doppler sonar uses similar principles to measure position and velocity involving liquids.
The signal processing enhancement of pulse-Doppler allows small high-speed objects to be detected in close proximity to large slow moving reflectors. To achieve this, the transmitter must be coherent and should produce low phase noise during the detection interval, and the receiver must have large instantaneous dynamic range.
The Nyquist frequency will also change when the PRF is changed. This is explained best using an example with 2 different PRF, although real systems use a different method. In the example, PRF A can detect true speed up to 600MPH and PRF B can detect true speed up to 500MPH.
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Velocity information for aircraft cannot be extracted directly from low-PRF radar because sampling restricts measurements to about 75 miles per hour. Specialized radars quickly were developed when digital techniques became lightweight and more affordable. Pulse-Doppler radars combine all the benefits of long range and high velocity capability ...