A novel coplanar-waveguide bandpass filter using a dual-mode square-ring resonator

A novel coplanar-waveguide (CPW) bandpass filter using a dual-mode resonator is presented in this letter. In the filter, a square-ring is used as the resonator, and a microstrip line stub attached the inner corner of the square-ring is used as the perturbation element. The square-ring and the input/output CPW are constructed on the two sides of a dielectric substrate, respectively. The filter has been investigated numerically and experimentally. Measured result shows that the filter has a minimum insertion loss of 1.2dB in its passband and an out-of-band rejection level of -45dB