Compact and wide-stopband bandpass filter based on quad-mode resonator

This paper presents the design and fabrication of 7-9.4GHz microstrip bandpass filter with stub-loaded quad-mode resonator. Simulated results indicate that the filter with a passband of 7.55-10.25GHz exhibits insertion loss of 0.7-1.52 dB and sharp attenuations of above 40 dB in stopbands. The input and output return losses are no more than -10dB, respectively. Due to fabrication error, the initial measured passband shows frequency shift. The measured results imply that the input and output return losses are lower than -10dB and the insertion loss with a passband ripple of 1dB varies between 1.5dB and 2.4 dB. Filter has a sharp skirt and out-of-band rejection level approaching to 40dB in all desired stopbands.