Low-loss GCPW-to-WG transition in multilayer resin substrate for millimeter-wave applications

A low-loss grounded coplanar waveguide (GCPW)-to-rectangular waveguide (WG) transition in a multilayer resin substrate for millimeter-wave applications is presented. The structure for the proposed transition is composed of a GCPW, a patch antenna and a quasi-dielectric waveguide (QDWG) in a multilayer resin substrate. The QDWG is formed by surrounding through holes, and the length of the QDWG is a quarter of the guide wavelength (λg). In this transition, a metallic WG is not used for a back short to simplify the structure. The dimensions and pattern layouts for the new GCPW-to-WG transition are designed with consideration of the estimated anisotropic permittivity of the resin substrate. Measurement results indicate a transition loss of 0.39 dB at a frequency of 77 GHz and a bandwidth of 5.6 GHz for a reflection coefficient below -20 dB, which corresponds to a fractional bandwidth of 7.3%. These results show the low transition loss of the planar-waveguide-to-WG transition which does not require an additional metallic WG for a back short. By applying the proposed GCPW-to-WG transition to a multilayer circuit board on which monolithic microwave integrated circuits (MMICs) are directly flip-chip-mounted, a high-performance, low-cost and compact transceiver module can be obtained.