Comparison Of Real-Time Acousto-Optic SAR Processor Architectures

Abstract

A comparison of real-time acousto-optic processors for synthetic aperture radar (SAR) image formation has been performed. These processors take advantage of the high processing speed and large time bandwidth product of acousto-optic devices (AOD's) in combination with the multichannel correlation capability of charge coupled devices (CCD) to form the SAR image in real time. They offer significant size, weight and power consumption advantages compared to conventional optical or digital processors. The required two dimensional matched filtering operation is performed as a series of one dimensional operations. First, the matched filtering is performed in range using an AOD. Then the azimuth correlation is performed using a reference mask and a CCD operating as time delay and integrate correlator. The first operation is performed coherently on each radar pulse return while the second is an incoherent correlation performed over the several pulses required to form the synthetic aperture. Two features common to this type of architecture which might limit their applicability are the presence of unwanted signal-dependent bias terms and the inability to perform true complex processing. Architectures utilizing both spatial carriers and subtraction schemes for elimiminating the unwanted bias terms have been analyzed. Also, multichannel architectures for complex (quadrature) processing have been addressed. In addition to imaging performance, the impact of these approaches on system complexity, real-time processing speed and required component capabilities will also be discussed. Results from both our analysis and the experimental implementation of a selected group of these architectures will be presented.