Circular double center stubs loaded microstrip bandpass filter

Based on the center stub loaded theory, a new microstrip bandpass filter using circular double center stubs loaded resonator is presented in this paper. By changing the shape of the center loaded stubs, the transmission zero shifts from left to right of the passband. One of the filters is designed, fabricated and measured. Both the experiment results and the simulation results agree with well. The proposed resonators have compact size and they are suitable for designing filters which require different selectivity in stopband.