Single-to-Balanced and Balanced-to-Balanced Dual-Channel Filters Using Multilayer Substrate Integrated Waveguide Cavities

This article presents a scheme for designing single-to-balanced and balanced-to-balanced dual-channel filters using multilayer substrate integrated waveguide (SIW) cavities. By sharing the common SIW cavities, two single-to-balanced or two balanced-to-balanced filters are flexibly integrated as one dual-channel circuit, resulting in very high integration. The input and output ports are properly arranged to the SIW cavities, where the two modes of the TM110 degenerate modes can be separately excited by the ports of the two filter channels. Moreover, the resonance modes of one channel have no coupling to those of the other channel. Thus, isolation between the two channels is achieved even though the two channels are designed sharing the same SIW cavities. The desired balanced ports are achieved based on the inherent out-of-phase electric field property of the SIW cavity at TM110 degenerate modes. For verification, a six-port single-to-balanced dual-channel filter is implemented, exhibiting excellent single-to-balanced filtering responses of each channel and high isolation between the two channels. By converting the single-ended ports to balanced ports, second-order and third-order balanced-to-balanced dual-channel filters are proposed. Moreover, the proposed designs can also realize different channel bandwidth or channel frequencies to meet different wireless applications.