A 2.5-bit Polarization-rotating Ultra-wideband Transmit Array for 6G Communications

In this paper, a 2.5-bit polarization-rotating transmit array is proposed for ultra-wideband 6G terahertz communications. The transmit array utilizes a unit-cell structure combining a polarization rotator and a polarizer, enabling broadband phase tuning and impedance matching with 2.5-bit phase control. By applying single- and dual-bar topologies to the rotator, a low Q-factor matching controller was implemented, enabling low-transmission loss and wideband performance. Six types of unit cells were designed to realize 2.5-bit discrete phase states with a 260° tuning range. Arrangement of the unit cell was optimized based on the reference phase to minimize quantization loss, enabling optimal array configuration for high-efficiency beamforming. The fabricated 30 × 30 transmit array achieved a peak gain of 28.6 dBi, an aperture efficiency of 31.8%, and a 3 dB gain bandwidth of 46.5 GHz, 32.1%. Furthermore, the communication distance range was experimentally evaluated using error vector magnitude measurements with modulated signals, demonstrating increases of 3 times compared with that of a standalone horn antenna. Consequently, the proposed transmit array achieved a data rate of 1.44 Gbps at a distance of 100 cm, as confirmed by modulated signal throughput measurements.