Abstract: A novel coplanar waveguide(CPW) bandpass filter using a dual-mode square patch resonator is presented in this paper.In the filter,a conventional square patch is used as the resonator,and two small identical square patches cuts at its symmetrical corners are used as perturbation elements to split its degenerate modes and to introduce a coupling between them.The square-patch and the input/output CPW are constructed on the opposite sides of a dielectric substrate,respectively.The configuration and the performance of the filter obtained in both simulation and experiment are presented.Results show that the pass-band of the filter may be adjusted over the bandwidth range from 4.9% to 7.4%,and it has a minimum insertion loss of 1.85 dB in its passband.