Nonequidistant uniform-beam-profile IDTs in broadband SAW filters

An optimization algorithm has been developed for the design of nonequidistant SAW transducers with uniform electrode length. Equidistant transducers weighted by assignment of polarities of individual electrodes are used as initial ones for this procedure. A set of SAW filters with bandwidth of 2-7%, shape factor of 1.2-1.5 has been designed using the suggested algorithm. The improvement of out-of-band rejection for filters with nonequidistant transducers is 3-6 dB in wide stopbands or 5-10 dB in most important narrow frequency regions as compared with equidistant analogs. In addition, the proposed algorithm can synthesize specified nonsymmetric frequency responses.