A Novel Low-Loss Millimeter-Wave 3-dB 90° Ridge-Gap Coupler Using Large Aperture Progressive Phase Compensation

A novel millimeter-wave (mm-wave) 90° phase-compensated hybrid coupler using the ridge-gap waveguide (RGW) technology is studied and developed. The coupler is low-loss at mm-wave frequency bands, whereas using conventional transmission lines, such as microstrip or substrate integrated waveguides, yields relatively a high amount of insertion loss. The proposed coupler is designed using large coupling apertures, which with their phase variation over the apertures can compensate for the progressive phase of the coupler and achieve a low output-phase error. The ridge-gap 3-db 90° hybrid coupler is suitable for designing mm-wave beamforming networks, such as the Butler matrix beamformer, where the cross-over transmission lines present a difficulty in designing such networks. In this paper, the dispersion diagram of the RGW is extracted, and a multicoupling aperture technique is formulated for designing the coupler. The coupler is fabricated and measured. The simulated and measured results show a good agreement.