Matching of single-phase unidirectional SAW transducers and a demonstration using a low-loss EWC/SPUDT filter

Abstract

The authors present the theoretical criterion for calculating the electrical port load required for matching a SPUDT (single-phase unidirectional transducer) and an efficient procedure for tuning a SPUDT filter. The theoretical development identifies a potentially useful class of SPUDTs that requires no matching network to achieve a high degree of triple transit cancellation. The sensitivity of the SPUDT filter's insertion loss to parasitic resistance is explained. It is found that the insertion loss of a SPUDT can increase as the thickness of the metallic overlay is increased (contrary to conventional surface acoustic wave technologies). The process of matching a SPUDT filter is demonstrated using a 196 MHz filter packaged in an 18-pin DIP package and matched with miniature internal coils. A triple transit suppression of 55 dB was obtained for an insertion loss of 8.6 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>