Fully-connected microwave photonic multi-beamformer with fast beam-steering for broadband wireless communication

Beamforming technology featuring broad bandwidth, fast beam switching speed and multi-user access capability plays a pivotal role in the next-generation wireless communication systems. Here, we report a fully-connected broadband microwave photonic multi-beamforming architecture based on silicon optical true-time delay lines (OTTDLs). Unlike conventional partially-connected schemes, the fully-connected network allows each radio frequency beam to be synthesized by all antenna elements, enhancing beamforming gain and multi-beam scalability. Experimental measurements demonstrate squint-free beam steering across 13 directions with deflection angles exceeding ±50.0° and a fast beam reconfiguration speed of 60 ns. Compared with partially-connected schemes, our architecture achieves stronger received signals, delivering a 2.9 dB gain at 13.1 GHz for an identical 8-element antenna array. A 64-QAM downlink signal with 400 MHz bandwidth achieves an error vector magnitude (EVM) of 7.6% over 20-m outdoor wireless transmission. These results provide a scalable solution for broadband microwave photonic multi-beamforming and support future 5 G and 6 G wireless networks.