WITHDRAWAL WEIGHTING OF INTERDIGITAL TRANSDUCER

Previous design method for withdrawal weighing is only used in the design of narrow bandwidthtransducers and is directly given without detailed mathematical argumentations.In this paper themathematical expressions for withdrawal weighting are given.An improved method of withdrawalis presented,in which the corrections of end and neighbour effect are not necessary.It is noticedthat the initial weighting functions must satisfy certain conditions.Because of having consideredthese conditions and used computer-aided-design procedure,the performances of withdrawal weightedSAW filters can be improved greatly.The 3 dB relative bandwidth is increased up to 8% andthe initial weighting can have phase-reverse sidelobes.Some experimental withdrawal weighted SAWfilters have been developed.Experimental results agree well with the theory.