Design of low loss surface acoustic wave filter with three interdigital transducers

A structure of low loss surface acoustic wave filter with Single-Phase Unidirectional Transducers (SPUDTS) is described in this paper. In this structure, two single-phase unidirectional transducers are placed at both sides of one apodized transducer. The loss has caused by bidirectional acoustic wave can be canceled by unidirectional characteristic of SPUDTS. Moreover the frequency response of the filter can be designed by changing weighting function of the apodized transducer. The simulation of this filter is based on Coupled-of-Mode, which can exactly calculate inner reflection of transducers. The transducers should be divided into so-called building blocks, and then calculate their P-matrixes, finally the response can be achieved by cascading P-matrixes. The center frequency of 110 MHz SAW filter is fabricated on YX-128deg LiNbO₃. Its 3 dB bandwidth is 1.7 MHz, and insertion loss is -5.6 dB.