High Performance 3dB Coupler (Hybrid) with Broadband Flat Amplitude Characteristics

Abstract

A new broadband 3dB waveguide coupler (hybrid) design is introduced, providing high performance, with extreme low amplitude variations of the semi signal portions. The basic principle relies on a dual-polarized waveguide section with propagating linear and circular polarized modes. The ends of the section are connected to the common ports of an OrthoMode Transducer (OMT) and a polarizer, respectively. Signals fed to one of the OMT ports pass the central waveguide section with the related linear polarization, while signals supplied to the polarizer ports exhibit circular polarization. Thus, the linear polarized signals are spilt by the polarizer into 3dB portions occurring at the respective ports; the OMT couples 3dB portions of the circular polarized signals to its ports. This solution is validated by a hybrid design at 11.7GHz, which comprise a compact OMT and a septum polarizer. The obtained results demonstrate high performance with flat amplitude responses over 18% bandwidth, while allowing the basic realization of the complete design with state-of-the-art manufacturing methods. Based on this novel hybrid a $4\mathrm{x}4$ Butler matrix is introduced to demonstrate the feasibility of power distribution with flat amplitude characteristics.