Compact Dual-Band and Tri-Band Tunable Bandpass Filters Based on Semicircular Substrate Integrated Waveguide

In this paper, compact dual- and tri-band bandpass filters with tunable center frequencies based on semicircular substrate integrated waveguide (SCSIW) are proposed. The dual-band bandpass filter is achieved by the fundamental mode and the first higher order mode of the SCSIW cavity. Two passbands are independently adjustable through the perturbation of posts and a pair of complementary split-ring resonators (CSRRs), respectively. The metal posts are loaded at the SCSIW cavities to adjust the center frequency of the first passband while the CSRRs are etched on the surface of the SCSIW in order to control the second passband center frequency. And similarly, the tri-band bandpass filter is achieved by the fundamental mode, the first higher order mode and second higher order mode of the S CSIW cavity, and two pairs of CSRRs can be employed to disturb the second and third passbands of the tri-band filter. The simulation results indicate that each passband has good independent adjustability without mutual interference. And the out-of-band rejection is also good overall.