SIW Dual-Mode Dual-Band Balanced Filter With Good Common-Mode Suppression

A substrate integrated waveguide (SIW) dual-mode dual-band balanced filter (DBBF) with good common-mode (CM) suppression is proposed in this paper. The first differential-mode (DM) passband can be obtained by the TE201 mode in SIW rectangular cavities and the second can be achieved by utilizing the TE
₄₀₁
mode. The two bandwidths could be realized over a wide range of ratio by applying the design parameters ratio technique, the desired coupling coefficients of both passbands are achieved by properly setting positions and size of the coupling windows which are opened on the first and the second rectangular cavity with common post-wall. Besides, four slotlines are etched on the bottom layer of the substrate to improved CM suppression. A prototype operating at 10.25GHz and 14.60GHz with the fractional bandwidth ratio of 0.93 is designed. The simulated and measured results show good performance.