DMS filter with reduced resistive losses

Resistive losses in the metal fingers of an acoustic track are an essential loss mechanism, limiting the electrical performance of RF SAW filters. In this paper, we present two alternative models to account for finite finger resistance in IDT tracks. The more comprehensive one assumes an individual, continuous function of current and voltage for each finger. By dividing the track into infinitesimal transversal strips, we obtain a system of coupled differential equations which can be integrated analytically. Applying the proper boundary conditions at the upper and the lower finger ends, we obtain the nodal admittance matrix of the acoustic track. We also developed a second model, which uses an equivalent circuit for each finger and is a very good approximation for small and moderate values of finger resistance. The accuracy of both models are demonstrated and compared to experimental results for an exemplary DMS filter. Furthermore, we show how resistive losses can be minimised by using DMS tracks with five or more IDTs, which are essentially a parallel connection of conventional 3-IDT DMS tracks.