Substrate Integration of Widely Tunable Bandpass Filters

In the present work, a widely tunable, bandpass filter is integrated into a commercially available printed circuit board using standard PCB processing. The filter consists of two cylindrical evanescent-mode cavity resona-tors formed by metallized thru vias in a double sided circuit board with an additional copper layer laminated on top. The copper layer forms a thin, flexible membrane that allows variable frequency loading of each of the resonators. The membrane is displaced using two piezoelectric bending disc actuators for precise electrical tuning of the filter center frequency. The concept is demonstrated by creating a tunable filter in a 125 mil thick Rogers TMM® ther-moset microwave laminate. The filter can be continuously tuned from 1.5 to 3 GHz with a narrow 3 dB bandwidth of less than 25 MHz while having a low insertion loss of less than 3.1 dB. This type of filter can provide quality pre-select filtering for a reconfigurable front-end receiver while being embedded inside a multilayer circuit board which has the rest of the system components.