Substrate-Integrated Coaxial Line (SICL) Rotman Lens Beamformer for 5G/B5G Applications

High-band allocations in the millimeter-wave (mm-Wave) frequency spectrum offer high-capacity wireless information transmission as required by fifth generation (5G) communication standards. Among different beamforming structures, the Rotman lens (RL) is an attractive passive-microwave-lens-based beamforming network due to its low fabrication cost, reliability, design simplicity and wide-angle scanning capabilities. Conventionally, the RL is implemented using microstrip line (MSL) technology for which there are inherent radiation losses that become severe when operating in mm-Wave 5G frequency bands. In this context, a novel substrate-integrated coaxial line (SICL)-based RL is designed, fabricated and tested, for accurate beamforming with extremely low feed line insertion loss. This article presents a complete design, development and performance analysis of an SICL-based RL beamformer. By using an SICL, isolation of up to 15 dB is achieved between the input beam ports of the RL, while the mutual coupling is kept at less than 20 dB. The SICL design shows a -10 dB insertion loss between the array and beam ports when compared to the same RL developed using MSL technology having an insertion loss of -15 dB. Due to the use of low-loss SICL technology, a realized gain of up to 14.2 dBi is achieved with an excellent scanning capability of -30 to 30 degrees, verifying for the first time the beamforming capabilities associated with SICL technology. The operational frequency band is 20-45 GHz, while the center operating frequency is 26 GHz making it appropriate for above 6-GHz 5G New Radio (NR) operating bands n257 (26.5 GHz to 29.5 GHz), n258 (24.25 GHz to 27.5 GHz), n261 (27.5 GHz to 28.35 GHz) and n260 (37 GHz to 40 GHz). Owing to the low-loss and stable beamforming performance, the SICL RL is suitable for mm-Wave 5G and is extendable to B5G applications.