Simulation and Design of a Low Loss Leaky Surface Acoustic Wave (LSAW) Resonator

Abstract

The lters for the front end of modern wireless communication systems should have several desirable characteristics like low insertion loss (less than 3 dB), sharp cuto , minimum ripples in pass band, maximum rejection and very compact size. There are very few choices in lter technology which simultaneously satisfy all of the above requirements. Due to several favorable features of Leaky Surface Acoustic Waves based Impedance Element Filters (IEFs) like very compact size at high frequen- cies, low insertion loss, good rejection characteristics and moderate power handling capability they become the primary choice for RF lter designers for applications in wireless communication systems operating in the frequency range from 800 MHz to 2000 MHz. Surface Acoustic Wave (SAW) resonators are the basic building blocks of these RF lters. In the present thesis, SAW devices are thoroughly studied and various SAW res- onator modeling techniques have been investigated. The Coupling of Modes (COM) theory is described in detail and modeling of one port SAW resonator is carried out using COM technique. A MATLAB program is written to simulate the admittance response of one port Leaky SAW Resonator structures on 42 YX LiTaO3 substrate, incorporating COM equations. A Graphical User Interface based simulation tool is developed to study the e ects of geometry changes such as variation in metallization thickness and metallization ratio on the admittance characteristics of resonators fabri- cated on 42 YX LiTaO3 substrate. The e ects of geometry variations on admittance characteristics are simulated and analyzed. These results are compared with Finite Element Model (FEM) based simulation of LSAW resonators, from an earlier work.