Adaptive interference rejection for wide-band systems

The authors describe the RAC (reflective array compressor) exciser, an adaptive band-reject or notch filter based on the multiply-convole chirp-Z transform algorithm. This system uses RAC, which are surface-acoustic-wave dispersive delay lines, in a preprocessor for rejection of overpowering interferers in wideband signal-processing systems. The exciser has been successful in adaptively removing unpredictable interference (e.g. push to talk), as well as tailoring stop/passband functions. The performance of this filtering process of Taylor-weighted input signals attenuates unwanted signals by greater than 40 dB (residual sidelobes) and allows for automatic excision of over 150 narrowband signals from a 30-MHz instantaneous bandwidth. For this filter design, similar downchirp RACs are used for chip generation, signal compression, and signal expansion, reducing time-frequency errors associated with designs using dissimilar devices. Temperature effects are reduced by placing these devices in a stabilized temperature environment.<
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