Adaptive array processing techniques for terrain scattered interference mitigation

The mitigation of terrain scattered interference (TSI) in airborne radar sensor arrays presents a unique adaptive array processing problem. TSI is produced by jammer multipath reflections that are incident on the radar from a large sector of the azimuth plane. Often, the interference is found throughout the mainbeam of the receiver array, precluding any spatial nulling methods. Instead, TSI mitigation techniques use temporal correlation found in the returns to achieve interference suppression. A beamspace canceler is proposed that uses TSI energy found in the spatial sidelobes of the mainbeam to estimate and remove the mainbeam TSI. The method is shown to have several important advantages over the currently used method, the single-reference beam canceler. Namely, the beamspace canceler is able to effectively mitigate TSI produced by airborne jammers without the use of Doppler compensation channels and is implemented with a drastic reduction in the blind interval. The proposed method is demonstrated on experimental TSI collected as part of the DARPA/Navy Mountaintop program. An extension of the beamspace canceler is also proposed for mainbeam jammer cancellation where the target and jammer are spatially co-located.; Another important aspect of this thesis is the investigation of issues essential for the implementation of the beamspace canceler in actual airborne radar systems. First, a number of rank reduction strategies are investigated for the TSI mitigation problem. Rank reduction is necessary due to computational restrictions and sample support limitations. Another important issue is the mitigation of combinations of TSI and monostatic clutter since actual airborne radars almost inevitably contain ground clutter returns. Using an extension of the beamspace TSI canceler, a factored mitigation approach is proposed that performs TSI mitigation in the entire beamspace domain to preserve the spatial dimension of the data. Then, the output of the TSI cancellation stage can make use of all the spatial degrees of freedom to perform space-time adaptive processing (STAP) for monostatic clutter suppression. Results with experimental data comparing the performance of the proposed method to single-beam TSI mitigation with moving target indicator (MTI) clutter nulling are presented.