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Low Cost, Miniature, Programmable SAW Matched Filter for Tactical Spread Spectrum Systems

Programmable matched filters (PMF) are key processors in tactical spread spectrum systems. These filters provide the processing gain necessary for jam-resistant operation and the electronic programmability essential for a secure system. Small size, low cost, and operation in a military environment are additional requirements imposed by tactical systems. This paper describes the design and performance of a matched filter that meets these requirements by using a custom-designed LSI chip to provide the programmability for a surface acoustic wave (SAW) tapped line. This combination of bipolar-LSI and SAW technology results in a matched filter with near theoretical electrical performance, substantially reduced size and cost, and excellent reproducibility. Additionally, since the LSI circuits are designed for carrier frequency operation up to 300 MHZ, PN code rates of 100 Mb/s are possible. The PMF provides the correlated output (compressed pulse) for a 128-bit, PN coded, MSK input waveform having a carrier frequency of 80 MHz and a code rate of 12.8 Mb/s. Electrical performance is demonstrated by oscilloscope photographs of the impulse and matched filter response of the unit. The sidelobe level is within 1 dB of theoretical and the mismatch loss (processing gain implementation loss) is less than 0.5 dB. Additionally, satisfactory performance is demonstrated over the temperature range of -55 to +125°C.