New dual-mode bandpass filters based on dual-plane structure

New dual-plane bandpass filters based on the coplanar-waveguide (CPW) square-ring resonators are proposed. In this study, the elevated metal air-bridges are used to suppress the parasitic coupled slotline mode and also to provide the shunt- capacitance perturbation. Moreover, the microstrip-to-CPW T- shaped transition is utilized as the feeding structure so that a large coupling may be achieved without using the surface-mount ceramic capacitors. By taking advantages of dual-plane layout capability, a wide bandwidth filter may be realized. Specifically, two filters with 3-dB fractional bandwidth of 20.85% and 31% are implemented and measured. Agreement between the measured and simulated results is also observed.