Frequency-Hopping Filters and Programmable Matched Filters for Spread-Spectrum Systems

The feasibility of using a surface acoustic wave device with switchable, closely spaced taps as a frequency hopping filter has been demonstrated. The test devices operate at 200-300 MHz for a Texas Instruments lithium niobate wire-bonded filter, (ref. 1) and 125-135 MHz for a United Technologies Research Center monolithic gallium arsenide (GaAs) device. (ref. 2) Future work is planned to develop GaAs monolithic versions at 0.5 and 1.0 GHz. These are, in fact, programmable transversal filters. They perform a variety of time domain functions such as matched filtering (asynchronous correlation), and they operate as variable frequency domain devices as well. In the latter mode, variable width passbands and notch rejection, as well as tunable bandpass, are achievable. Thus, adaptive operation in an electronic warfare scenario is a possible application. A planned use is in the Air Force's Integrated Communications, Navigation, Identification Avionics (ICNIA) program.