Dual-Band SIW Differential Bandpass Filter With Improved Common-Mode Suppression

A dual-band differential bandpass filter with controllable differential-mode (DM) center frequencies, and high common-mode (CM) suppression as well as band-to-band isolation, is proposed in this letter. The presented filter is implemented based on the substrate integrated waveguide (SIW) technology. The first DM passband can be derived by the dominant modes, while the second DM passband response can be obtained by employing the higher order modes. The center frequencies of two DM passbands can be tuned by changing the dimension parameters. To improve the CM suppression, four slotlines with different locations are etched on the top metal plane. The measured and simulated results are in good agreement.