Design of two-phase unidirectional transducers for a predetermined triple transit signal suppression

In the design of broadband low-loss surface acoustic wave (SAW) filters, the reflection at the acoustical port of a transducer is a central problem. It determines the triple transit signal (TTS) and thus the unwanted passband-ripple which limits the achievable maximum bandwidth (BW) and minimum insertion loss (IL). The acoustical reflection of a two-phase unidirectional transducer (TPUDT) with respect to the phasing network, the matching network, and the electrode pattern of the TPUDT systematically is investigated. Furthermore, tradeoffs between IL, BW, and TTS are investigated. It is found that the amplitude ratio is a crucial design parameter. In general there exist two solutions of the amplitude ratio which lead to two possible phasing and matching networks. With a series arrangement, both solutions are applicable, but with a parallel arrangement, only one can be used, in order to suppress the acoustical reflection