基于脉间中断调频连续波的高空慢速单基机载SAR成像

调频连续波用于高空慢速单基机载SAR成像时,收发隔离和远距离探测都是亟待解决的问题。结合高空慢速运动平台的特点,提出了一种脉间中断调频连续波(Inter-Pulses Interrupted Frequency-Modulated Continuous Wave, IPIFMCW)的信号模型,通过载频不同的门控信号调制多个发射信号,设置较大的脉间中断时间,将子脉冲回波差频信号在快时间域时移合成大带宽信号,实现高空慢速机载SAR成像。通过与脉间中断调频连续波(FMICW)的理论分析比较,说明该方法不仅解决了收发隔离难题,同时满足高空机载SAR远目标成像需求,避免出现距离模糊。最后结合频率变标算法(FSA)实现了基于IPIFMCW信号的高空慢速单基机载SAR成像。

A Study on Imaging of High-altitude Slow-speed Airborne SAR Based on Inter-pulses Interrupted FMCW

Remote-target detecting and isolation between transmitter and receiver are the problems that need to be solved when FMCW SAR is applied in high-altitude slow-speed airborne platform. A signal model of inter-pulses interrupted frequency-modulated continuous waveform (IPIFMCW) is proposed in consideration of the features of high-altitude slow-speed airborne platform. The imaging of high-altitude slow-speed airborne SAR is realized through the gating signal with different carrier frequency to modulate the transmit signal to obtain long inter-pulses interval and shifting the mixing echo of sub-pulse in fast time domain to get wide-band signal. Compared with the FMICW theory, the results show that IPFMICW not only overcomes the problem of isolation between transmitter and receiver, but also fulfills the need of remote-target imaging for high-altitude airborne SAR and avoids range ambiguity. Finally, the imaging of high-altitude slow-speed airborne SAR based on IPIFMCW signal is realized through frequency scaling algorithm (FSA).