Windowing Functions for Improving the Frequency Response of Linear Matched Surface Acoustic Wave (SAW) Filters

Abstract

In signal processing, windowing is a technique used to shape the time portion of a certain function or data. Window function techniques can be applied to shape the IDT patterns, and thereby shape the filter bandpass frequency response, therefore, SAW filter designs with different types of standard window functions are used in the IDT geometry to enhance the desired frequency response. The performance of various window functions is evaluated with respect to shape factor and sidelobe level. In this work, several window functions are classified into four groups, where each group consists of several windows of similar shapes, and then a linear matched SAW filter design of an IDT geometry is made for every window function in each group to enhance the desired frequency response, improve the side-lob rejection, and the 3-dB bandwidth of the frequency response of linear matched SAW Filters. The input interdigital transducers (IDTs) of the linear SAW filters are uniformly apodized while the output IDTs has a windowing structure. Among the four groups that have been used and tested, we recommend of what we called a semi-Blackman group as the most appropriate one in the field of improving side-lob rejection, and 3-dB bandwidth of the frequency response of SAW filters. Semi-Blackman group has the best improvement in both the side-lob rejection and the 3-dB bandwidth, the increment ratios are around 466% and 174%, respectively.