Miniaturized bandpass filter based on slot perturbation

In order to meet the demand of compact filter in wireless communication system, a miniaturized bandpass filter is proposed in this paper. The filter generates transmission zeros in the upper stopband through the electromagnetic coupling between half mode substrate integrated waveguide and quarter-wavelength resonant unit. The fundamental resonant frequency is reduced by the slot perturbation of the metal surface in the strong magnetic region, which forms the transmission zero in the lower stopband. The designed filter has the bandwidth ranges from 8.8 to 12 GHz with the fractional bandwidth 30.7%, and the in-band insertion loss is less than 0.5 dB and the return loss is better than 15 dB. The size is reduced by 10% compared with that of the non-slot structure under the circumstance of the same bandwidth. The extra resonant unit forms the transmission zero in the upper stopband, thus the bandwidth of the upper stopband with the suppression level of 20 dB reaches 4 GHz, and the measured results are well matched with the simulated ones. The filter has the characteristics of easy fabrication, small volume, low loss and easy integration, which provides a novel design idea for the miniaturization of filters.