Ka-Band Systems and Processing Approaches for Simultaneous High-Resolution Wide-Swath SAR Imaging and Ground Moving Target Indication

Although high-resolution wide-swath (HRWS) SAR imaging and ground moving target indication (GMTI) systems from the system architecture point of view look quite similar (both system types employ multiple receiving (RX) channels arranged along azimuth direction), they generally need to be operated in different modes, in particular with significantly different PRFs. HRWS systems require a comparatively low PRF, reflecting the overall length of the full antenna. The low PRF enables wide-swath imaging, and the multiple RX channels are used for signal spectrum reconstruction. In contrast, GMTI systems require a high PRF, reflecting the short length of the individual RX channel. The multiple RX channels are then used for clutter suppression and moving target parameter estimation. The high PRF additionally shall ensure that aliasing of the Doppler shifted moving target signal energy is avoided. It is known that the Doppler shift is proportional to the target’s velocity and inversely proportional to the radar wavelength. Thus, especially at Ka-band with small wavelengths in the millimeter range, the Doppler shift and, hence, the required PRF for avoiding aliasing may be very high. In general the high PRF required for GMTI prevents wide-swath SAR imaging as well as wide-swath GMTI. The resolution of this conflict is the issue addressed in this contribution. In the frame of a contract extension of the ESA-funded TRP Activity “Study of Multi-Channel Ka-Band SARs for Moving Target Indication”, novel low PRF system operation modes and processing approaches which allow for simultaneous GMTI and HRWS SAR imaging have been developed and investigated in detail. In particular, a special matched reconstruction filter bank (MRFB), which is the heart of all proposed processing approaches, has been developed. With the MRFB low PRF target signals acquired with a conventional HRWS system can be reconstructed and refocused. The application of the MRFB also provides accurate estimates of the target’s velocity. Furthermore, potential extensions of conventional HRWS systems have been proposed for additionally enabling effective clutter suppression without the need of increasing the PRF. In the final paper the results of the contract extension of the TRP Activity will be presented. The MRFB principle, the proposed and investigated HRWS-GMTI system concepts and the corresponding processing approaches will be introduced and explained in detail. The HRWS performance and the GMTI performance obtained from Monte-Carlo simulations will be presented and discussed. Also potential drawbacks of the proposed HRWS-GMTI modes will be addressed