Compact Design of Hybrid-Coupled Filter Module (HCFM) Using Inter-Resonator Couplings

The hybrid-coupled filter module (HCFM) multiplexers are widely used as RF combiners in wireless and satellite communication systems. A conventional HCFM consists of two complete 3dB hybrid couplers. In this paper, compact designs of HCFM are presented. The inter-resonator coupling between two filters is used to replace one of the branches in a 3dB hybrid coupler, resulting in significant size reduction. As demonstrated using design examples implemented in different technologies, including rectangular waveguide and substrate integrated waveguide (SIW), the proposed compact structure preserves the responses of a conventional design. EM simulations and/or measurements results are presented to validate the design concept. Moreover, using tuning elements, such as tuning screws or varactor diodes, tunable designs can be realized.