A narrow transition bandwidth SAW filter using withdrawal weighting with decomposed weighting functions

Abstract

Thousands of taps with small weights are required for IDTs to achieve narrow transition bandwidths in SAW filters used for satellite applications. In this paper, withdrawal weighting for IDTs is employed to eliminate difiaction problems encountered in overlap weighting. To obtain a good approximation, an original weighting function is decomposed into two functions such that number of small weights decreases. In the decomposition procedure, the so called zero separation method is applied to the sampled original weighting function, because it is difficult to calculate zeros of thousands order polynomial. The decomposed functions are interpolated, and then approximated by withdrawal weighting. The resultant two weighting functions are applied to input and output IDTs respectively.