Tunable, High-Q, Substrate-Integrated, Evanescent-Mode Cavity Bandpass-Bandstop Filter Cascade

A new single substrate-integrated bandpass-bandstop (BP-BS) filter cascade, implemented using high-Q, heavily-loaded, evanescent-mode cavity filters, is presented. The cascade has the capability of dynamically tuning its passband and stopband at any two independent frequencies within a frequency range. A modular design approach is used to design the cascade by directly cascading synthesized coupling matrices of bandpass and bandstop filters. To demonstrate the concept, a 4% second-order Butterworth bandpass filter is integrated with a second-order Butterworth bandstop filter, with 2% fractional bandwidth at 10-dB rejection, to form a cascade that can be tuned continuously from 3000 to 3600 MHz. Measurement shows that a filter cascade with insertion loss as low as 0.9 dB and isolation as high as 100 dB is feasible.