Characterization and effects of the weld inductance in mechanical filters with longitudinal coupling

It is shown by finite-element analysis that a secondary coupling wire phenomenon, namely longitudinal shear, is capable of producing significant distortion in the response of a mechanical filter, without any contribution from other sources (such as resonator spurious modes). The simplest model for the presence of this longitudinal shear is the weld inductance, placed in series with the resonator model in the electrical equivalent circuit. The weld inductance can be determined by the comparison of the responses of three-pole mechanical filters with continuous versus bisected coupling wires. Underneath a bridging wire, the weld inductance causes an error in the bridging coupling that can be compensated for the predistortion