A NOVEL COUPLING METHOD TO DESIGN A MICROSTRIP BANDPASS FILER WITH A WIDE REJECTION BAND

In this paper, we present a novel method to design a microstrip bandpass fllter (BPF) with high selectivity and upper rejection band. The proposed coupling structure mainly composes of half-wavelength input/output (I/O) microstrip lines and open-loop ring resonators. By properly selecting the coupling position between the I/O lines and resonators, the spurious response of the BPF can be well suppressed. A fllter example centered at 2.4GHz achieves a high band selectivity and a wide upper-stopband rejection greater than 20dB from 2.7 to 6GHz. Experimental results show a good agreement with the simulated ones.