The Notch Filter on Surface Acoustic Wave on Base of Single Phase Unidirectional Transducers

Abstract

High requirements on the electrical parameters of the filters are made in radio engineering systems. For bandpass filters, these requirements apply to the squareness coefficient of the amplitude frequency response and rejection. Therefore, the notch filter can be used as a complement to bandpass filters, since it serves to suppress signals in a certain frequency range. Notch filters on surface acoustic waves are not widely used, but they have a number of interesting features and advantages over types of filters that work on other principles. The purpose of the development is to produce a notch filter on surface acoustic waves at 40.05 MHz with 40 dB suppression, a bandstop at the level of -3 dB at least 135 kHz (relative value - 0.34 %), a bandstop at the level of -40 dB at least 35 kHz (relative value - 0.0875 %). Results: a brief classification of notch filters is given. Various variants of passive notch filters are considered. Based on the method of coupling of modes and the finite element method, key elements on surface acoustic waves were calculated and manufactured for a notch filter with the required parameters on a substrate of a 36°YX Quartz piezoelectric material. The key element is a unidirectional transducer of DART type. The scheme is based on a bridge scheme with additional passive tuning elements. It is shown that in order to implement this filter, it is necessary not only to select all the topology parameters of individual key elements included in the filter very precisely, but also to perform precise configuration and selection of passive LC-elements. These calculations are confirmed by the results of experiments.