Pulse Compression With Very Low Sidelobe For Spaceborne Weather Radar

Spaceborne weather radar is a powerful tool for global precipitation measurement. When measuring precipitation from space, the sea clutter will stain the radar signals. To detect the weak echoes of clouds occurring near the strong echoes of sea surface from spaceborne weather radar, sidelobe performance below -60db is needed in the pulse compression system. Pulse compression with very low sidelobes is one of challenges in the design of spaceborne weather radar.Based on the traditional way of pulse compression, double Kaiser Windows are applied here for sidelobe suppression and the peak sidelobe level (PSL) can reach -75db. To avoid the power and SNR loss, the time domain Kaiser Window added on the transmitter was replaced by the frequency domain window added on the receiver equally.Abundant multiple and convolution operations in down conversion and pulse compression are hard to implement in a real time processing system. So complex demodulation using series-parallel converting and distributed arithmetic are applied here as an alternative. In this way, the demodulation arithmetic and pulse compression of multi-channels can be packed into a single FPGA.To compensate the nonlinear effect of power amplifier (PA), a successive overrelaxation (SOR) iterative method of digital predistortion is applied here to ensure the low sidelobe performance, high output power and fast iterative speed. A test system based on RFPA, ESG and VSA is carried out to verify and optimize the predistortion arithmetic.Finally, parameters of airborne and spaceborne precipitation radar are discussed.