A SAW-based Demodulator for Dehopped FDMA M-ary FSK Satellite Signals

A demodulator has been built and tested that is capable of performing the functions of an onboard-the-satellite processor for receiving M-ary noncoherent FSK signals with multiple users being separated by FDMA. It is based on spectral analysis of the received signal by a chirp transformer implemented with surface acoustic-wave devices. Demodulation of M=4-, 8-, and 16-ary FSK signals of 25 ps symbol duration was demonstrated with capability of handling up to 40/M users. The implementation loss was only 0.5 dB. Measurement of bit error rate performance in the presence of system noise, frequency errors, and partial-band-noise and multiple-tone jamming were made and found to agree well with theory. The effects were examined of three different time windows: rectangular, Kaiser Bessel ¿ = 1.6, and one intermediate between these two. The intermediate window is promising because of low window loss combined with good adjacent channel interference tolerance.