Bandpass filter with wide stopband

Abstract

Microstrip bandpass filter with wide stop bandare proposed using the theories of Centrolled Loaded Resonators(CLRs) and Discriminating Coupling. While the second and the third harmonic of the BPF has to be suppressed under -20dB in order to avoid interference with other nebor signal frequencies. The use of resistive load connecting to CLRs cause the value reduction at Q value of even order frequencies, so the even order harmonics can be eliminated. Besides, the Discriminating Coupling is used to obtain zero coupling coefficient at the third harmonic. With reference to the equation of Coupling Coefficient, tuning the resonators to suitable positions can get the zero Coupling Coefficient, in this way, the third harmonic can be rejected. The proposed filter could obtain at least 20dB rejection in the stopband from1.2f0 to 4.5 f0. The simulation result match the requirement of the filter.