Design of Tunable Balanced Dual-band filter Using SIR and EMSIW

This paper presents a compact balanced dual-band filter with the tunable first passband and the fixed second passband. The proposed filter is composed of three mental layers. Varactor diodes are loaded at the end of the stepped-impedance resonators (SIRs) to construct the tunable first passband. Two slotlines are embedded in the middle layer in order to couple signals to or from the resonators, meanwhile, the middle metal layer is also regarded as a common grounding. The eighth-mode substrate integrated waveguide (EMSIW) cavity placed in the bottom layer has been utilized to generate the fixed second passband