Abstract: A rotor tip synthetic aperture radar is described including a rotor operable to rotate, a radar receiver positioned in the rotor and for relaying received signals to a second position such as the cab of a helicopter. A radar transmitter and receiver located within the second location for transmitting radar signals towards a target and for receiving target reflected signals relayed from the rotor tip. The doppler frequency shift imposed on the relayed target reflected signals is cancelled by generating a pilot signal at a predetermined frequency and transmitting the pilot signal to the rotor tip which has a receiver for receiving the pilot signal and for relaying the pilot signal back to the second location and frequency multipliers and mixers for generating a first order doppler frequency shift signal appropriately scaled to cancel the doppler frequency shift signal of the target reflected signals when the two are subtracted in a mixer.

Abstract: In moving target indication or synthetic aperture systems, double pairs of measurements of returned energy are made from displaced spatial locations to enable computation of side and angular deviation from the flight path, without the requirement for inertial navigational measuring instruments.