A 298–334-GHz Scalable Injection-Locked Phased-Array Radiator With Second-Subharmonic-Termination-Assisted Waveform Formulation for Power Enhancement

This article introduces an injection-locked $4\times 2$ phased-array radiator featuring scalability in both horizontal and vertical dimensions. The system architecture is constructed by sequentially cascading four identical phase-shifting and frequency-quadrupling (PSFQ) elements in a chain-like configuration and then cohering two such chains, thereby achieving global frequency synchronization. Particularly, phase shifting and sequential injection locking are carried out at a quarter of the output frequency, which enables high-resolution beamsteering and facilitates wideband operation. Within each PSFQ element, a second-subharmonic-termination-assisted waveform formulation (SSTA-WF) technique is proposed to substantially enhance the output power of the injection-locked frequency quadruplers (ILFQs). Prototyped in a 65-nm CMOS, the radiator array chip occupying a core area of 3 mm² measures an output frequency range from 298 to 334 GHz. After being assembled with a silicon lens, the system exhibits a maximum radiated power of 4.5mW and an equivalent isotropically radiated power (EIRP) of 20.3dBm at 310GHz, corresponding to a dc-to-THz conversion efficiency of 0.39%. Moreover, a 1-D digitally-controlled beamsteering range of 36° is demonstrated.