Fully-Connected Microwave Photonic Multi-Beamformer with Fast Beam-Steering for Broadband Wireless Communication

Abstract We report a fully-connected broadband microwave photonic beamforming architecture based on silicon-integrated optical true-time delay lines (OTTDLs), designed to meet the stringent demands of next-generation wireless communication systems. Unlike conventional partially-connected schemes, the fully-connected beamforming network enables each radio frequency(RF) beam to be synthesized by all antenna elements, significantly enhancing beamforming gain and multi-beam scalability. We design a silicon eight-channel integrated tunable OTTDL chip, with each OTTDL providing a maximum delay of 310.84 ps with a delay resolution of 4.93 ps. The switching time of the delay state is 60 ns, which is fast enough to satisfy the beam switching requirements of the 5G NR standards. By leveraging true-time delay rather than phase-shifting techniques, our system supports wideband, multi-frequency beamforming without beam squint. Experimental validation in a microwave anechoic chamber over the 12.4–13.6 GHz range confirms squint-free beam steering across 13 distinct directions, with beam deflections exceeding ±50.0°, closely matching theoretical predictions. System-level wireless communication tests using two identical OTTDL chips further demonstrate the advantage of the fully-connected approach. Compared to the partially-connected schemes, our architecture delivers stronger received signal magnitudes, achieving a 2.9 dB gain at 13.1 GHz under identical 8-element antenna array conditions. In particular, a 64-QAM downlink signal with 400 MHz bandwidth achieves an error vector magnitude (EVM) of 7.6%, confirming high communication quality under real-time multi-beam operation. This work establishes a scalable and high-speed solution for broadband, squint-free beamforming, advancing the practical deployment of microwave photonic technologies in future 5G and 6G networks.