Wideband and Wide-Scan Gap Waveguide Antenna Array at W-band for 6G Applications

Licentiate thesis, 2023

The future wireless communication for 6G (or beyond 5G) holds the promise to reach Tbps level throughput at distances ≥ 1 km with flexible user mobility. The upper millimeter-wave bands (100+ GHz), especially W- and D-band, are being widely considered for these applications. In this context, high-gain mm-wave antenna systems with intelligent beam-forming are seen as the key technological enablers. However, high dissipation losses, components cost, and tight manufacturing tolerances at these frequencies severely restrict suitability of the traditional phased antenna array solutions.
This work attempts to fill in this knowledge gap by presenting a new array antenna type based on the open-ended ridge gap waveguide (RGW). Such an antenna is of a particular interest at 100+ GHz owing to its contactless waveguide sidewall design, which alleviates active beam-steering electronics integration. Its fractional bandwidth is broadened by a relatively simple wideband impedance matching network, consisting of an aperture stepped ridge segment and a single-pin RGW section. Furthermore, the E- and H-plane grooves are added that effectively suppress antenna elements mutual coupling effects when used in arrays of such elements. Results demonstrate a wideangle beam-steering range (≥ 50◦) over ≥ 20% bandwidth at W-band, with ≥ 89% radiation efficiency. This significantly outperforms existing solutions at these frequencies. An experimental prototype of a 1×19 W-band array validates the proposed design concept through the embedded element pattern measurements.
In the second part of this Licentiate thesis, we present a linear array architecture as a building block of 2D arrays that can enable efficient beamsteering and a simplified array design. It includes a low-loss gap waveguidebased quasi-optical (QO) feed to provide a desired antenna port excitation with 1- /2-bit phase shifters which are co-integrated with the array antenna elements. The array design goals, i.e. the maximum available gain and minimum sidelobe levels are achieved through the optimum quasi-randomization of phase errors through the QO feed. The relationships between the key design parameters of the QO feed are determined analytically. The system-level performance for above-mentioned goals is studied numerically based on cascading the simulated / measured results of each individual system component: the QO feed, the RGW-to-phase-shifter transitions, the on-chip phase-shifters, and the array antennas.