Avoidance of Spurious Spikes Arisen by the Cascading of Filters through Controlling Filters Input Phases

The combination of different type of filters is an engineering practice when aiming to improve the performance of a particular filtering device. The cascading of an acoustic wave (AW) bandpass filter with a bandstop device is a typical approach when the achievable out-of-band (OoB) rejection far from the passband, of the bandpass device, is limited. However, the cascading of different cells triggers the appearance of spurious resonances in the OoB region that are undesired. This work describes analytically how to avoid or mitigate the appearance of these spurious spikes from the beginning of the design process without resorting in the usage of intermediate networks between filters.