Spurious Mode Suppression in Coupled Resonator Filters

The Coupled Resonator Filter (CRF) is a new type of Bulk-Acoustic-Wave (BAW) device in which two piezoresonators are stacked on top of each other in a way that a certain degree of acoustic interaction occurs. For a proper frequency response, a method for suppression of spurious resonances is of utmost importance. This will be discussed theoretically and the measured results in resonator and filter response will be shown. Moreover, internmetric measurements of the surface displacement of a 1.8 GHz CRF device are investigated with respect to dispersion relation and its effects on spurious mode suppression.