Photonic-Assisted Frequency-independent Beam Steering for Wideband Terahertz Wireless Applications

While photonic phased array antennas (PAAs) show promise in addressing terahertz (THz) path loss challenges, their inherent frequency dependence limits wideband THz wireless communications and sensing (e.g., frequency-modulated continuous wave (FMCW) for THz radar systems and frequency-hopping spread spectrum (FHSS) for THz secure communications) by causing beam distortion during frequency changes. To overcome this, we propose and demonstrate a novel photonic beam steering technique that achieves frequency-independent operation using a pre-calibrated, feed-forward compensation scheme. The system independently adjusts array element phases using an OPA and photomixers to maintain stable beam direction during both frequency hopping and sweeping operations. Experimental results demonstrate significant improvements in beam intensity stability compared to conventional systems across different operating modes. During carrier frequency hopping between 290 GHz and 305 GHz, the system achieves a 1.29 dB enhancement in beam intensity stability and a 1.62 dB increase in minimum received signal strength compared to systems without phase control. During continuous frequency sweeping operations, our approach reduces beam pointing directivity variation by 76.51% and beam width variation by 67.65% across the entire bandwidth. Additionally, our technology enables synchronized beam-direction switching with frequency changes, allowing for custom beam direction settings based on frequency. This approach paves the way for next-generation THz systems in high-security communications, high-resolution radar, advanced sensing, and other emerging fields that demand frequency changing within PAAs.