SAW two resonator filter using synchronous coupling interdigital transducers

Surface acoustic wave (SAW) two resonator filter with coupling interdigital transducers (IDT) placed inside reflectors, was designed, fabricated and tested. In the filter, electrodes of the coupling IDTs are in spatial synchronism with reflectors´ electrodes. Compared to the case when the coupling IDTs are between reflectors, resonators are shorter, the unwanted longitudinal modes are suppressed and better rejection should be obtained in the stopband. The filter, fabricated on ST-cut quartz, had the centre frequency of 302.6 MHz, insertion loss about -14 dB, and minimum rejection in a stopband higher then 40 dB