Influence of fabrication tolerances and circuit variations on the performance of SAW RF filters

By simulations based on the P-matrix model, we have studied the effects of fabrication tolerances on the performance of dual-track image impedance connected filters consisting of 6 and 22 transducers, respectively, a DMS filter, and an IIDT filter. All filters were fabricated on 36°rotY,X-LiTaO₃ and operated at about 900 MHz. We have also investigated the influence of matching element variations for all four of the above-mentioned device types. It was found, for instance, that the insertion loss of the device with the smallest passband ripple (the DMS filter) changed by 1 dB for variations of 10% in the values of the matching elements while the change in the IIDT-type filter was only 0.1 dB. Since, for example in the presence of an AGC circuit, the characteristic impedances of the transmission lines connected with the SAW filter may not be constant, the results of changes in these line impedances have also been studied