Microwave Beamformer Based on Reconfigurable Matching Networks

This paper presents the design of a microwave beamformer that electronically controls the excitations of a phased array over a wide scanning range while maintaining active input impedance matching for all radiators. Closed-form equations are derived for the circuit design, and a synthesis strategy is proposed for its implementation. We introduce two beamforming topologies that control both amplitude and phase: the first requires variable gain components, while the second does not. The circuit eliminates the need for phase shifters, resulting in a low-loss, cost-effective solution based on transmission lines and varactor diodes. To validate the proposed approach, we performed electromagnetic/ circuit co-simulations and conducted experimental bench tests on a fabricated beamformer integrated with a 2.2 GHz linear array of six printed monopoles. The array exhibits significant mutual coupling, leading to a high-mismatch scenario where the active VSWR could exceed 10, corresponding to only about 33% of the incident power being transferred to the antenna at certain beam angles. This challenging condition provided an ideal testbed for the proposed methodology, which successfully achieved the required excitations and impedance matching, resulting in a VSWR better than 2 (over 90% power delivered to the load) across a wide range of beam directions. Finally, extensive tests in an anechoic chamber confirmed the beamformer performance under various operational scenarios.