Design of generalized SPUDT filters

Single phase unidirectional transducer (SPUDTs) exhibit excellent frequency characteristics and are used in many surface acoustic wave (SAW) filters for IF filtering in mobile communication systems. They allow the design of narrow-band low-loss filters with smooth amplitude response. In the classical type of SPUDT filters the mechanical reflections are used to cancel the electrical regeneration. Thus the impulse response is close to the one calculated using the impulse model. In this limit has been overcome for the first time. Resonances in the transducers, or between the transducers, respectively, are used for improving the performance of a SPUDT filter for a given chip size. In this paper a general approach for the design of transducers including reflections will be outlined and the correlation to already well known SAW structures, e.g., inline resonator filters, will be figured out. A classification of the different types of generalized SPUDT based SAW filters will be given.