Simplifying mmWave transmission: a time modulated array at 73 GHz with beam steering and direct digital modulation of QPSK, 8PSK and 16QAM to 128QAM

We describe a beam steering 73 GHz Time Modulated Array (TMA) system that provides direct digital vector symbol modulation onto a carrier. This concept removes the need for conventional RF modulator hardware in a TX RF chain and requires only a local oscillator source. Simple digital logic control waveforms are used to both steer the beam and apply symbol modulation. Lab demonstration results using a custom 73 GHz hardware prototype with QPSK, 8PSK, 16, 32, 64 and 128QAM constellations are presented. The measured Error Vector Magnitude (EVM) contribution from the TMA modulation process is an average of 3.0%. With modulation applied, a beam can be steered to circa ±10 degrees on the first harmonic beam, and ±27 degrees on the second harmonic beam. Timing based symbol predistortion to compensate higher-order constellation distortion is also demonstrated as beneficial, and viable in the TMA. We believe this is the first demonstration of a TMA steerable phased array at 73 GHz with data symbol vector modulation applied digitally, directly, by the TMA – offering a significant simplification for potential future mmWave transmitter architectures.