An amplitude and phase imbalance correction scheme for a switch ULA FMCW SAR system

A switch uniform linear array (ULA) frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) system transmits and receives FMCW waveform by firing elements of the ULA sequentially under the control of a switch network. Resolution in range is achieved by range compression and in ULA direction is achieved by digital beamforming. Compared with a conventional SAR system, a switch ULA FMCW SAR has a lot of advantages, such as high-speed data acquisition, forward-looking/downard-looking 3D imaging mode and simpler hardward. However, it inevitably suffers from multi-channel amplitude/phase imbalance and sweep rate non-linearity error, which lead to resolution degradation and image defocussed. In practical system, the two kinds of errors coupled together so that the existing correction method is no longer suitable. This paper presents correction scheme to solve this problem. First, seperate the two kinds of errors by two calibration signal differential. Next, correct the sweep rate non-linearity error by residual video phase (RVP) filter. Then, correct the multi-channel amplitud/phase error by S parameters measurement and estimation from point-like target echo. At last, repeat the above procedure for each channel to complete the entire correction process. We develop a real switch ULA FMCW SAR system and validate the the effectiveness of the presented calibration scheme by real data processing.