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FOURTH ANNUAL
ASAP '96 WORKSHOP

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Simultaneous Mitigation of
Multipath Jamming and
Ground Clutter

Daniel F. Marshall and Robert A. Gabel
MIT Lincoln Laboratory
244 Wood Street
Lexington, MA 02173-9108
tel: (617) 981-0807
email: dmars@ll.mit.edu

Abstract Studies of the multipath jamming phenomenon have determined that it may potentially degrade the performance of state-of-the-art radar systems. The development of techniques that address this problem is a nascent field, and most work in this area to date has focused on mitigating multipath jamming in isolation. However, airborne surveillance radars will experience multipath jamming and ground clutter interference in combination. Space-Time Adaptive Processing (STAP) has been shown to be effective in nulling both ground clutter interference and clutter in combination with sidelobe jamming. But these algorithms do not effectively accommodate the presence of jamming in the main beam, thus widely scattered multipath jamming may degrade STAP performance over a large area. In the work documented in this paper, a preliminary effort has been made to address the challenge of mitigating the interference environment, where both ground clutter and multipath jamming are present. Our approach has been to combine existing STAP and multipath jamming mitigation techniques. One multipath jamming mitigation architecture produces a beamformed output corresponding to a desired look direction; this processing can be repeated for a number of look directions to form a suitable input to a beam-space STAP architecture. Alternatively, multipath jamming mitigation may be applied to each receive array element individually, providing a front end to any of the several STAP algorithms. The performance of these different approaches is evaluated and compared. Interactions between the jamming and clutter returns and nulling processes are discussed. In particular, the challenges raised by the task of training for jammer mitigation in the presence of clutter are addressed, for both ground-based and airborne jammer sources. The presentation concludes with a discussion of the effectiveness of our mitigation efforts to date, unresolved difficulties, and areas for future work.

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