Application of modified P-matrix model to the simulation of radio frequency LSAW filters

In designing RF filters on the basis of leaky SAW, the main challenges are decreasing insertion loss and amplitude ripples in the pass band and increasing selectivity in the stop band. Ladder resonator (LDR) filters secure the minimum insertion loss as compared with other types of RF filters. However, the amplitude ripples in the pass band are strongly dependent on losses in the resonators of LDR filters and the presence of other excited modes. The selectivity in the LDR filter stop band is determined not only by SAW resonators but also by parasitic electric elements and couplings between them both in the chip and the filter package. In the present paper, we consider a modified P-matrix model that allows one to take comparatively simply into account resonator losses and describe LDR filters as electrical devices to make allowance for the influence of parasitic effects on their parameters. The model proposed have been used to design four RF filters for different communication systems, such as AMPS T-x 836 MHz and R-x 881 MHz; GPS R-x 1575 MHz; PCN R-x 1842 MHz.