Mobilizing the Terahertz Beam: D-Band Analog-Beamforming Front-End Prototyping and Long-Range 6G Trials

This article presents a novel D-band (sub-THz) wireless transceiver developed in two consecutive phases: a waveguide-based discrete component phase, and a microstrip integrated structure phase. In fact, the wireless transceiver from the second development phase was recorded in 2022 as the world's first long-range and analog beam-forming-capable D-band transceiver, specifically operating from 150 GHz to 175 GHz. In technical terms, the transmitter reports an effective isotropic radiated power (EIRP) of 48 dBm in the boresight beam, and it supports eight RF beams based on a Rotman lens (RL) as a beamforming network solution. This is a significant improvement over a 31 dBm EIRP measured over the transmitter's boresight beam developed in the first phase (2021), which supported a waveguide-based RL with four beamforming configurations. A receiver prototype was also developed in phase two with eight beams and eight antenna uniform linear phased arrays similar to its transmitter counterpart. Monolithic microwave integrated circuit (MMIC) power amplifiers, low-noise amplifiers, and switches were designed and fabricated for the front-ends based on indium gallium arsenide (InGaAs) technology. This article also reports on 6G demonstration trials in indoor and outdoor scenarios. A transmission experiment over a 9-meter distance in an indoor environment was conducted using 5G-NR-compliant - orthogonal frequency division multiplexing (OFDM) - waveforms with 400 MHz bandwidth and 64 quadrature amplitude modulation (QAM) for the data symbols. In the same indoor setup, beam alignment and tracking, based on modified 5G NR synchronization blocks, were successfully tested. Furthermore, long-range outdoor trials based on the 5G NR waveform are reported for a distance of 320 meters, utilizing a 16QAM for the data symbols. Additionally, a generic OFDM waveform transmission trial was conducted outdoors for links up to 500 meters, 500 MHz bandwidth, and with various modulation schemes up to 64QAM constellations.