An On-Chip Sub-THz Scalable Beam Steering Antenna Array

We present a novel way of distributing signal to an antenna array without the use of power dividers. In our proposed method, we use the leaked fundamental from a non-linear harmonic generator circuit as an input to drive the next element in the chain. As a proof of concept, we show this distribution method at 240 GHz using 28nm bulk CMOS technology. A single transmitter (Tx) element consists of a 75-83 GHz driving stage, 75-83 GHz PA (power amplifier) followed by a frequency tripler to 225-240 GHz. The fundamental 75-83 GHz signal leaked from the frequency tripler is coupled using a balun and used to drive the next Tx element. The third harmonic current from the frequency tripler is coupled using the balun and delivered to the antenna element which is matched to third harmonic. 
For a single exciting antenna chip width and length of λ/2 and a height of λ/4 would lead to the highest gain irrespective of the exiting element. For a particular number of antennas and spacing, a die size exists which leads to maximum efficiency. To increase TRP/mm2 a denser antenna is required. As the number of elements increase, the number of surrounding driving circuit increases as well. Driving circuits and pads have a large footprint compared to the antenna. These sub-circuits and I/O pads increase chip size and lower the efficiency of the DRA. The EIRP and TRP density can be increased without loss in efficiency of the antenna by dicing the chip to appropriate size The narrow beam is only possible as the back dicing provides the radiation to combine in air rather than inside the die. 

1. 6G Communication 
The sub-THz frequency range is allocated for 6G applications. Higher available bandwidth allows higher data throughput. One of the major developments for 5G was the massive MIMO. At mm-Waves massive arrays can be developed owing to higher available power and lower transition loss. At sub-THz frequencies the available power is low in CMOS (effectively no PA) and the transition to PCB is high. Thus, designing massive MIMO arrays will require an efficient signal distribution and radiation system with phase control all integrated on a single die. Our methods seamlessly allow the use beam steering at sub-THz frequencies. 

2. Radar 
Current SoA radars at 77-80 GHz are widely available in the market for automotive and industrial use. These radars have enabled the use of self-driving cars to assist walking to differently abled individuals. The major hurdle these radars face is resolution in low range instances. The resolution of the radar depends upon the bandwidth and the frequency of operation. Our novel design can be a direct extension of the current radar systems improving the resolution by a factor of 3 whilst adding minimal product footprint. 

Patent Status:
Priority application filed in the UK, PCT application to be filed in Q1-2023

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