Under studying the function of a multi-mode polarization Synthetic Aperture Radar ( SAR ), the operation parameter, mixing, filtering method for digital IF receiver is presented based on Field Programmable Gate Array ( FPGA ). Digital quadrature demodulation for three bandwidth signal is realized. 针对一种多模式极化合成孔径雷达(SAR),给出了中频数字接收机工作参数选择,混频滤波方法,实现了三种带宽信号的数字正交解调。