Compact Bandpass Filter with Flexible Locations of Transmission zeros Based on Combining Patch and Microstrip Resonators

This letter reports a fourth-order box-section bandpass filter (BPF) based on three isosceles right triangle patch resonators with short-circuit right-angle corners and one straight stepped-impedance microstrip-line resonator (SIMLR). Based on the proposed structure, flexible response with almost arbitrary locations of two finite-transmission zeros (FTZs) can be realized. The two controllable FTZs with physical structure are analyzed. Four typical responses were designed and presented. Moreover, a compact size can be also achieved due to the new arrangement of stepped-impedance resonators. For the demonstration, a filter with one lower and one upper FTZs was fabricated and measured. The measured results agree well with simulated ones.