Miniaturized Quarter-Mode SIW Filters Loaded by Dual-Mode Microstrip Resonator with High Selectivity and Flexible Response

A novel miniaturized multilayer quarter mode substrate integrated waveguide (QMSIW) filter with high selectivity and wide stopband is proposed. Firstly, a brand new multilayer dual-mode resonator is proposed to couple the QMSIW resonators located both at the upper and lower layers. The combination of the dual-mode resonator with the two QMSIW resonators leads to a fourth-order filtering response. As the even mode of the dual-mode resonator can provide a phase shift of 180˚. A transmission zero (TZ) is introduced at the right side of the passband. Moreover, an additional TZ is generated at the left side of the passband by cutting a coupling iris. Sharp skirt characteristic is obtained. Different responses are achieved by changing the position of the coupling iris, resulting in a wide stopband and flexible response. Two prototypes are fabricated and measured for demonstration. The measured results are in good agreement with the synthesized and simulated results.