Novel Coupling Matrix Synthesis for Single-Layer Substrate-Integrated Evanescent-Mode Cavity Tunable Bandstop Filter Design

A new technique for designing tunable bandstop filters is presented. A novel coupling matrix synthesis method for this type of bandstop filter is shown. Phase cancellation, through combining two bandpass filters, is used to derive the coupling matrix. Therefore, classical coupling mechanisms utilized to implement bandpass filters can be used to design and realize bandstop filters. Using this method, bandstop filters can be designed without source-to-load coupling. This eliminates the need for a second substrate when compared to previously reported bandstop filters implemented using substrate-integrated evanescent-mode cavity technology, though the method itself is quite general. Finally, examples of tunable bandstop filters in the range from 3.0 to 3.6 GHz are demonstrated to verify the proposed method.