Design Guidelines for Acoustic Wave Ladder Filters Starting in Shunt Resonator

This work aims to provide design rules for shunt-starting acoustic wave (AW) ladder filters concerning the input reflection phase. Thanks to a general synthesis methodology, the paper proves that when the first resonator is shunt the AW ladder can only implement a Chebyshev filter function if the input reflection phase is set appropriately, depending on the position of transmission zeros. For phases out of the correct range, inductive static branches appear at the first and last resonators. Moreover, if the filter is designed as part of a duplexer, the reflection phase to avoid loading effects requires two input reactive elements unless the resonance frequency of the first resonator is placed below the central frequency of the duplexer's counter band.