SAW synthesized resonator filters with two composite longitudinal mode 2-port resonators

Abstract

Since recent digital mobile communication demands higher transmission rates, the SAW IF filter bandwidth is required to be broader. This paper describes the new filter design technique, which can achieve broader bandwidth than conventional SAW resonator filters such as transversally coupled mode resonator filters. This new filter uses at least two multi-longitudinal mode resonators connecting in parallel electrically, and sets each resonator's different mode frequency to be at almost the same frequency position with in-phase. As a result, a synthesized resonator filter that has more resonant mode numbers than a single resonator filter can be realized. We also present expanded designs such as double synthesizing and asymmetric synthesizing for better performances, and show the performance of SAW IF filter for Japanese PHS. As a filter demonstration, we show the characteristics of IF filter for PHS with a bandwidth of 380 kHz, an insertion loss of 3.1 dB and center frequency of 248.45 MHz.