Optimized Ridge Air-Filled Substrate-Integrated Waveguides for Beyond-5G Antenna Array Systems

A design strategy is proposed to optimize the ridge air-filled substrate-integrated-waveguide (RAFSIW), reconciling the conflicting low-loss and miniaturization requirements arising for antenna array feeding structures operating in the new sixth-generation (6G) frequency spectrum. Through comprehensive parameter analyses, the effect of the ridge dimensions on the waveguide's width miniaturization and efficiency is delineated, leading to general guidelines for identifying pareto-optimal RAFSIW cross-sections. To demonstrate the procedure, such a pareto-optimal RAFSIW is designed for operation in the fifth-generation (5G) n257 band (26.5-29.5 GHz), including a transition to grounded co-planar waveguide (GCPW). The waveguide design is prototyped and characterized, showcasing an insertion loss of 1.42dB for a length of 15mm and a fractional −10dB-impedance bandwidth exceeding 30%. A width miniaturization of 63% compared to the conventional air-filled substrate-integrated-waveguide (AFSIW) is obtained, facilitating a grating-lobe-free scanning angle (GLFSA) of 90° over the entire n257 band, when applying this waveguide in an antenna array feeding network. Hence, the proposed RAFSIW paves the way for miniaturized low-loss millimeter-wave (mmWave) components to realize highly efficient, beyond-5G antenna array systems.