Tunable Center Frequency Negative Group Delay Filter Using Coupling Matrix Approach

In this letter, a negative group delay filter (NGDF) with tunable center frequencies is presented. The proposed filter is designed using finite unloaded-Q
_u
resonators based on the coupling matrix approach. The proposed NGDF does not require a lumped resistor to generate a negative group delay and has source-load and inter-resonator couplings. The center frequency of the filter is tuned by varying the bias voltage of the varactor diodes. The design theory for the proposed filter is validated experimentally through fabrication of a second-order NGDF at a center frequency of 2.14 GHz.