A new concept in SPUDT design: the RSPUDT (resonant SPUDT)

Presents new concepts in SPUDT design, leading to a new low loss transducer structure called Resonant SPUDT (RSPUDT). Resonant acoustic cavities are created inside the transducer while keeping a global unidirectionality required for low loss. As a result, some areas of the transducer are locally backward directional. SAW filters utilizing the RSPUDT exhibit improved filter characteristics (e.g. passband ripple, shape factor) and result in more compact filters. Two kinds of RSPUDT elementary cells were developed. The first one is the generalization of classical EWC cells to RSPUDT concept while the second improves the reflectivity per wavelength by 50% with the same critical dimensions. Measurements on both 200 MHz and 110 MHz lowloss filters on 38° Y rotated quartz are presented to illustrate the interest in these new SPUDT structures. The 200 MHz filter exhibits a 2 dB bandwidth of 0.30 MHz and a 40 dB bandwidth of 1.01 MHz while the 110 h MHz filter combines a 40 dB bandwidth 912.25 MHz and a 0.5 dB bandwidth of 0.9 MHz