A substrate-integrated-waveguide (SIW) quadrature hybrid-junction for low cost millimeter-wave planar antenna array

Couplers are critical elements in microwave and millimeter-wave frequency range systems and circuits [1]. Metallic rectangular waveguide couplers have been widely used in various millimeter-wave and microwave applications. However, metallic waveguide is not only a relatively high cost technology but also difficult to be integrated with planar circuits. The substrate integrated waveguide (SIW) is a planar technology that provides an attractive low- cost and low- loss alternative [2]. Planar circuits can be integrated into the same SIW substrate using planar transitions. In this paper, a SIW quadrature hybrid (−3 dB branch[3] line coupler) is presented and designed for millimeter- wave applications. Furthermore, a simple circuit model is proposed for fast design optimization of the presented junction. Simulated S-parameters results using both the proposed circuit model and HFSS package are provided for verification of the proposed model.