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Frequency is relative to the size of the object you want to detect and the size of the wave. Higher frequencies detect smaller things and can discern between them. Go too far and you detect bugs. Too low and you only see barn doors.

Spinning blades are a dead giveaway for radars. Certain things reduce radar signature but the interesting part now is electronic countermeasures.

A radar can produce a fuzzball graphic to the viewer of the data, speed, distance, direction of movement, etc.