Adaptive airborne MTI: comparison of sideways and forward looking radar

Clutter echoes received by a moving radar exhibit a motion induced Doppler bandwidth which degrades detection of slowly moving targets. This Doppler spread effect can be overcome by use of adaptive space-time clutter filters which implicitly compensate for the radar platform motion. To apply space-time processing a multi-channel antenna is required (spatial dimension of the space-time filter). In the existing literature on airborne MTI only the sidelooking case is considered. We focus on a forward looking antenna configuration. While sidelooking MTI is based on the DPCA property (physical motion compensation) this is not true for the forward looking antenna. Numerical calculations have shown that near-optimum clutter rejection can be achieved even for forward looking radar. Some basic considerations are made to explain the underlying principles of forward looking MTI. Optimum and suboptimum adaptive receiver structures are compared. An overall comparison of sidelooking and forward looking MTI is presented. It turns out that in general the forward looking configuration is more sensitive to interfering effects, such as system bandwidth, range ambiguities and jamming.