Modified structures of RSPUDT

In this paper, improved structures of RSPUDT is presented. Based on this structure, the modified filter has better performance in some aspects because the resonant cavities become simple and more flexible and are uniformly distributed in the whole transducer. Thus we can conveniently design RSPUDT based filters using this modified structure. Calculation and experimental results based on the improved RSPUDT structure indicate that it can obtain a better shape factor less than 2.5/sub (-40 dB)/:1/sub (-2 dB)/. In comparison, the original RSPUDT filter is about 3.3 /sub (-40 dB)/:1/sub (-2 dB)/. Moreover, a smaller ripple in passband is also gained with the modified structure.