Design of compact bandpass filter based on quarter-mode substrate integrated waveguide with mixed coupling

In this paper, a compact bandpass filter using quarter-mode substrate integrated waveguide (QMSIW) cavities with mixed coupling is presented. The mixed coupling is realized by etching a coplanar waveguide(CPW) at the magnetic coupled neighborhood section of two cascaded QMSIW resonators, which introduces two transmission zeros at the lower and higher rejection band. The filter enjoys merits of good selectivity, miniaturized size and wide stop band. In order to verify the design concept, a bandpass filter with center frequency of 8.625GHz is fabricated and measured. The measured results show good agreement with the simulated results.