Design and Implementation of Digital Correlator for CAS Synthetic Aperture Radiometer

摘要

We present a new method of digital correlation,which uses the technology of direct intermediate frequency or radio frequency sampling and digital phase shift. Digital correlators down-sample IF or RF signals with 3-bit analog-to-digital converters and then delay one sampling interval for quadrature phase shift. Following the same procedure as analog correlation, the digitalized I/Q pairs are processed in a FPGA chip. Analysis and simulations show that sample delay introduces linear phase offset which is proportional to the deviated frequency from the center of digital IF. Derived equation proves that linear phase offset can be compensated simply by a SINC function. Flight tests conducted in April 2004 achieved image as we expected.