A method for analysis of bulk mode effects on SPUDT based filters

Author

Dufilie, Pierre ; Roux, Frederic

Volume

1

fYear

1994

fDate

Oct. 31 1994-Nov. 3 1994

Firstpage

13

Abstract

Single Phase Unidirectional Transducer (SPUDT) based SAW filters are realized by withdrawal weighting of the sources to eliminate apodization losses. The withdrawal weighting creates unwanted bulk mode responses which degrade the filter rejection. For the rotated YX quartz substrate, the most commonly used substrate for this type of filter, the fast shear (FS) and longitudinal (L) modes contribute most of the degradation. This paper presents a method of analysis of SPUDT filters using a COM analysis with 2N acoustic ports to account for N propagating modes. This analysis with N=3 (SAW+FS+L) is used to predict the degradation in the rejection for a 188 MHz filter for PCN applications. An approximation is made that both the FS and L modes are surface propagating modes. Comparison of analysis and measurement is given, showing very good agreement

Keywords

VHF filters; quartz; radiofrequency filters; surface acoustic wave resonator filters; COM analysis; SAW filters; SPUDT based filters; SiO₂; analysis method; apodization losses; bulk mode effects; bulk mode responses; fast shear mode; filter rejection degradation; longitudinal mode; rotated YX quartz substrate; single phase unidirectional transducer; surface propagating modes; withdrawal weighting; Quartz materials/devices; Surface acoustic wave resonator filters; VHF resonator filters;

fLanguage

English

Publisher

ieee

Conference_Titel

Ultrasonics Symposium, 1994. Proceedings., 1994 IEEE

Conference_Location

Cannes, France

Print_ISBN

0-7803-2012-3

Type

conf

DOI

10.1109/ULTSYM.1994.401544

Filename

401544