Design of Two-Track Surface Acoustic Wave Filters with Width-Controlled Reflectors

Abstract

In this study, the frequency response of two-track surface acoustic wave (SAW) filters with width-controlled reflectors is investigated. The SAW filter consists of two tracks of input and output interdigital transducers (IDTs) and grating reflectors. With proper tailoring, the frequency response of the two-track SAW filter will only be dominated by the reflection characteristics of the reflectors. To achieve optimum performance, the Chebyshev polynomial is employed to calculate the line width distribution of the metal strips of the reflector. The period of the reflector is then adjusted to retain a symmetric response. Different stepwise weighting schemes are applied to recalculate the line width distribution for the realization of the modulated reflector. A novel transmission matrix method is proposed in this study for calculating the frequency responses of these devices. Simulation results show that a filter with high sidelobe suppression, low insertion loss, good shape factor and significantly small ripples in the passband region can be designed by properly tailoring the two-track SAW filter. The results obtained in this study can be employed to design IF filters applicable to the code division multiple access (CDMA) system.