A 2.5-Bit Polarization-Rotating Ultrawideband Transmit Array for 6G Communications

In this communication, a 2.5-bit polarization-rotating transmit array is proposed for ultrawideband sixth generation (6G) terahertz (THz) communications. The transmit array utilizes a unit-cell (UC) 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 UCs were designed to realize 2.5-bit discrete phase states with a 260° tuning range. The arrangement of the UC 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 (EVM) measurements with modulated signals, demonstrating increases of three times compared with that of a standalone horn antenna. Consequently, the proposed transmit array achieved a data rate of 1.44 Gb/s at a distance of 100 cm, as confirmed by modulated signal throughput measurements.