In view of parasitic passband in the filtering networks composed of distributed elements

a novel circuit of microstrip bandpass filters is presented in this paper.The filtering porperties of the filter are analyzed.The configurations of the filter and related equations are also presented.The circuit is composed of the parallel coupled microstrip lines and the specific combined transmission lines by cascaded connection

and the sturcture is simple.Theoretical results and experimental results indicate that the novel circuits of microstrip bandpass filters has good performance in harmonic suppression.Using this new structure as output filters in the microwave oscillators or amplifiers

the performance of the system in harmonic suppression will be improved.