Design of Three-Pole Bulk Acoustic Wave Coupled Resonator Filters

The control of longitudinal coupling in bulk acoustic wave (BAW) resonators makes it possible to design multilayer coupled resonator filters (CRF) with a desired response. This paper presents the methodology to face this kind of designs with a set of closed-form expressions that allow to control the coupling between resonators, and to determine the structure geometry of a three-pole CRF. A network transformation from the Mason model to an equivalent electric circuit makes it possible to apply the insertion loss filter design method. An UMTS RF filter has been designed using the proposed methodology.