Electronic THz Pencil Beam Forming and 2D Steering for High Angular-Resolution Operation: A 98 $\times$ 98-Unit 265GHz CMOS Reflectarray with In-Unit Digital Beam Shaping and Squint Correction

Abstract

Ultra-sharp beam forming and high-angular-resolution steering in both azimuth and elevation directions are required in high-performance imaging sensors, spatial-multiplexed wireless links and other applications. This poses great challenges due to the fundamental relationship between the beamwidth and the dimension of the antenna aperture. As shown in Fig. 4.5.1, the aperture size required to achieve 1 ° of 3dB beamwidth is $0.6\times 0.6\mathrm{m}^{2}$ and $0.2\times 0.2\mathrm{m}^{2}$ at 24GHz and 77GHz, respectively. In current radars, sparse MIMO antenna schemes are adopted to synthesize virtual arrays with the above size in one dimension. However, they require intensive signal processing of many channels. The complex signal routing and placement of active electronics also leads to challenges in the 2D scaling required for pencil beam forming. By increasing the wave frequency to 265GHz, the work in this paper significantly reduces the aperture area, allowing it to be fully realized by digitally controlled, reflective antennas in CMOS microelectronic chips (Fig. 4.5.1). Similar to a concave mirror, a reflectarray, when illuminated by a single radar source, applies incident-angle-dependent phase shifts (e.g. $\varphi_{1}$ and $\varphi_{2}$ in Fig. 4.5.1) to the wave and re-focuses it towards a desired direction. This quasi-optical spatial feed eliminates the high-frequency signal routing and complex processing inherent to MIMO arrays. Employing $98\times 98$ antenna elements, we experimentally demonstrate the forming and electronic steering of a THz pencil beam with- 1 ° beamwidth in two dimensions. With under-antenna integration of dense memory cells, sidelobe reduction and squint correction are also achieved.