Adaptive Beam-Steering and Jammer-Nulling Photorefractive Phased-Array Radar Processor

Abstract

We are developing a class of optical phased-array-radar processors which use the large number of degrees-of-freedom (DOF) available in three-dimensional photorefractive volume holograms to time integrate the adaptive weights in order to perform beam-steering and jammer-cancellation signal-processing tasks for very large phased-array antennas[1,2]. For a large broadband phased-array antenna containing 1000s of array elements, beam steering and jammer cancellation in a dynamic signal environment represents an extremely demanding signal processing task well beyond the capabilities of microelectronic digital signal processing because of the large number of DOF required for adaptation. The three-dimensional nature of the signal environment (2 angle-of-arrival and frequency) represents a signal processing problem which maps well into a highly parallel optical processing architecture utilizing photorefractive volume holograms. The beam-steering and jammer-nulling processor we present uses relatively simple components; two photorefractive crystals, two single-channel high-speed detectors, and two single channel acousto-optic Bragg cells. The bandwidth capabilities of these components approach a GHz allowing the processing of wide-band signals. The required number of processor components used for implementing the adaptive algorithm is independent of the number of elements in the phased-array in contrast to traditional electronic or acousto-optic approaches[4,5], in which the hardware complexity of the processor scales in proportion to array size. We describe the two main subsystems of the processor, the beam-forming and the jammer-nulling subsystems, and present results demonstrating simultaneous main beam formation and jammer suppression in the combined processor.