Loss mechanism analysis for SAW impedance element filters

The SAW Impedance Element Filters (IEFs) have some important advantages compared to Coupled Resonator Filters (CRFs). The losses in these filters can be made smaller because the effective propagation path of SAW is smaller and resistive losses are lower due to the greater number of short electrodes connected in parallel. The detailed analysis shows that the losses in IEFs due to SAW attenuation represent dominating contribution compared to resistive loss and mismatch loss if the filter is carefully designed. An equivalent network for a packaged filter was found including parasitic inductances of the bonding wires, mutual inductances, bridge capacitances and package pin's capacitances. Good agreement with measured data is obtained over-a wide frequency range up to 3 GHz. Using this approach, filters with less than 1 dB peak insertion loss were designed in the 1 GHz range. The estimations show that up to 10 GHz, the losses due to attenuation and resistivity of electrodes remain relatively low but the role of parasitics increases drastically. Existing packages and conventional assembly methods will fail at frequencies above 2 GHz, even if submicron photolithography is developed.