Focal Plane Arrays for Millimeter-Wave Beam-Steering Wireless Backhaul Antenna Systems

Licentiatavhandling, 2025

The rapid expansion of communication infrastructure and development of 5G/6G communication networks aim to reach the terabit-per-second (Tbps) data rates by utilizing the millimeter-wave (mmWave) frequency bands, particularly, E-, W-, and D-bands. One of the key applications for these systems is wireless backhaul, which offers flexible and cost-effective network deployment by connecting base stations to core networks using point-to-point communication links. This is accompanied by severe challenges at mmWaves, such as high free space path loss and limited power generation capabilities of semiconductor-based electronics. Hence, to overcome these challenges, antenna systems must achieve high Effective Isotropic Radiated Power (EIRP), which requires high-gain (>50 dBi) antenna systems with transmitters incorporating power-combining functionalities to increase SNR and, thereby, achievable data rate.

The high-gain antennas come with narrow beams of 0.5˚ half-power beamwidth (HPBW) which causes the problems of mast swaying leading to signal fading. To resolve this issue, the antenna system needs to incorporate beam-steering functionality.

This work explores potential solutions addressing the aforementioned challenges with a focus on electronic beam-steering. The presented comparison of the existing solutions outlines the strategies for antenna system implementation and integration with the transmitter front-end. Based on the findings of this analysis, the reflector antenna system fed by waveguide-based (WG) focal plane array (FPA) is proposed. The baseline design considerations explore the reflector and FPA designs, identifying suitable reflector type and FPA architecture. As a result, two focal plane array designs are proposed and implemented using decoupling, and beam shaping techniques at the element and array levels for performance enhancement. The proposed FPAs demonstrate 52–68% aperture efficiency, < –25 dB mutual coupling, and >1˚ 2D beam-steering range with gain loss <6 dB.

The proposed designs will be used in the active reflector antenna system demonstrator, including integration with the active transmitter front-end.