Application of low loss SAW filters to RF and IF filtering in digital cellular radio systems

Digital cellular radio systems require high-performance low-loss filtering in both the front end and the IF (intermediate frequency) sections. Several surface acoustic wave (SAW) filters (one RF filter and two IF filters) specially developed for this application are presented. Various efficient low-loss technologies are used for optimum design of these filters in terms of performance to cost ratio. The RF filter has a moderate insertion loss (8 dB), a typical 1 dB bandwidth of 29 MHz centered at 902.5 MHz, and an equivalent four-pole Chebyshev-type response. It is used as a transmit preamplifier filter. The two IF filters are cascaded to perform a 14-dB loss equivalent four-pole Butterworth-type response filtering with a 180 kHz typical 3-dB bandwidth and 90-dB ultimate rejection. The high performance of these filters and their use in some common system architectures are discussed