Synthesis Considerations for Shunt-Starting Acoustic Wave Ladder Filters and Duplexers

This paper explores how acoustic wave (AW) filters whose first resonator is in shunt configuration require particular phase conditions to ensure network feasibility. The position of the transmission zeros (TZs) might lead to non-feasible solutions with negative values of the static capacitance Co of the first and last resonators and, therefore, the role of the first TZ in this behaviour is investigated. A lowpass synthesis view of these issues is presented providing different approaches for designers to achieve feasible networks.