Adaptive pre-suppression of wideband noise jammers in conjunction with space-time adaptive processing

In theory, a Space-Time Adaptive Processor (STAP) based radar system can be used to simultaneously suppress clutter and wideband noise jammers (WNJ). Simultaneous suppression typically involves the estimation of a joint space-time covariance matrix which can be quite large even for moderately sized radar systems required to handle a number of WNJ. As a result of the large estimation problem, this approach may be suboptimal in terms of both performance and cost. Common methods for reducing the estimation problem size involve the application of dimension reducing transformations (i.e. beamformers) to the data prior to adaptive processing. In conjunction with dimension reduction, a different concept is investigated here which handles the WNJ and clutter separately. System architectures are explored which cascade an adaptive spatial pre-processor, for WNJ suppression, with a STAP for clutter suppression. Two key aspects to the successful application of this divide-and-conquer technique are (1) the construction of beamformers which allow jammers to be suppressed without sacrificing STAP clutter rejection, and (2) extraction of the WNJ data for adaptive-filter calculation. Three versions of Butler-based beamformers are developed to establish baseline system performance. A new approach to WNJ data extraction which utilizes a frequency sideband, next to but distinct from the radar\u27s signal bandwidth (i.e. mainband), to obtain jammer-only training data is investigated. This sideband approach offers greater flexibility and performance potential because the collection of training data is not Surface provides description only. Full text is available to ProQuest subscribers. Ask your Librarian for assistance. to specific clutter-free range gates or Doppler regions typically used in low and high PRF systems. Since the weights for jammer suppression are derived from data with a carrier frequency different from the radar signal, compensation techniques are required. Methods of sideband compensation are developed herein which can provide ample jammer suppression in the radar\u27s mainband. Effects of receiver errors are analyzed for the proposed sideband cancelation systems. A calibration method is developed providing nearly error-free performance if the main- and sideband errors do not drift. Finally, a beamformer design investigation is conducted in an attempt to improve upon the baseline designs. A new beamformer design approach is developed which has the potential to outperform previous design methods as well as offer some improvements over the Butler based designs. However, because of their implementation advantages, the Butler-based baseline system configurations are still considered the best choice for use in airborne radar systems