Abstract: Detection of slowly moving and stationary targets that are normally obscured by ground clutter is accomplished by an AMTI synthetic aperture radar system that utilizes multiple receiving antennas mounted along the flight velocity vector of the radar bearing aircraft. Each antenna is separated by a distance d from each other. Synthetic arrays are formed by processing the radar returns from each antenna terminal. The radar PRF is controlled so that the aircraft flies a distance d during the interpulse period. The synthetic array outputs of adjacent pairs of antennas are subtracted to provide clutter cancellation. The resulting outputs from adjacent terminals can be used in a monopulse mode for angular discrimination.

Abstract: A radar system is operated in a manner that provides determination of the coincidence of radar signal polarization with the major axis of a target of unknown aspect angle. This information so obtained can be utilized to enhance radar signals or to improve target identification capabilities. One approach comprehends transmitting circularly polarized radar signals and receiving return signals on a linearly polarized receive antenna. By varying the polarization of the receive antenna over a 180.degree. range signal maxima and minima are detected that correspond to alignment of the target's major axis with the radar signal E and H field vectors. The method can also be practiced by transmitting linearly polarized radar signals, the polarization of which is also varied over a 180.degree. range.

Abstract: In an AMTI radar having digital doppler processing, adaptive clutter and interference rejection is achieved by automatically adjusting antenna phase and amplitude weights to trim for uncalibrated errors and to put nulls in the antenna receive patterns in the direction of the source of interference or jamming signals. Antenna weights are initially chosen to achieve an optimum signal to clutter ratio. The radar receive signals are averaged over many range cells, filtered and summed by adaptive processor circuits. Feedback loops adjust the antenna weights to minimize the summed output. The circuits effect this by mechanizing the steepest descent algorithm.

Abstract: Clutter cancellation between adjacent channels of a multichannel synthetic aperture AMTI radar is accomplished by delaying signals from the forward channel to coincide with signals from the aft channel and subtracting the outputs. Adverse effects from unknown, uncalibrated and time varying parameters are compensated for by adjusting the phase and amplitude of the aft channel coherent receiver output in response to the complex multiplier signal .omega.. The synthetic aperture processing circuit outputs of each channel are averaged over many range cells and summed to determine clutter magnitude. The complex multiplier signal .omega. is made to minimize the clutter magnitude by means of a steepest descent algorithm. A mathematical expression relating the complex multiplier signal .omega. to clutter magnitude for optimum clutter cancellation is developed and a circuit is provided for mechanizing the process.