A Fully Reconfigurable 1 <inline-formula> <tex-math notation="LaTeX">$\times $</tex-math> </inline-formula> 4 Filtering Beamforming Network With Continuous Phase and Amplitude Control

In this article, a reconfigurable 1 <inline-formula> <tex-math notation="LaTeX">$\times $</tex-math> </inline-formula> 4 filtering beamforming network (FBFN), which is capable of generating reconfigurable progressive phase difference and amplitude distribution, is presented for the first time. It simply consists of one standard Wilkinson power divider and two identical reconfigurable filtering power dividers (FPDs), where the FPD is constructed by four mutually coupled resonators and three nonresonating nodes. By controlling the nonresonating nodes, the coupling coefficients and the resonant frequencies of resonators, arbitrary progressive phase difference, and reconfigurable amplitude distribution can be easily obtained, demonstrating highly flexible reconfigurability. Meanwhile, since the proposed FBFN does not require any individual phase shifter or crossover, it also exhibits a more compact size compared to the conventional beamforming networks based on the Butler matrix. The detailed theoretical analysis of the FBFN is presented and design equations for determining its circuit parameters are deduced. To experimentally demonstrate the proposed concept, a 1 <inline-formula> <tex-math notation="LaTeX">$\times $</tex-math> </inline-formula> 4 FBFN prototype is fabricated and measured. Experimental results show that, within a center frequency tuning range from 1.01 to 1.1 GHz, the designed FBFN successfully achieves full reconfigurability, including: 1) continuously tunable progressive phase difference in full 360<inline-formula> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula>; 2) reconfigurable amplitude distribution; and 3) reconfigurable numbers of output ports. Furthermore, a four-element linear antenna array is designed to validate the performance of the FBFN for beam steering. It is shown that, when applied in a phased array, the proposed FBFN is able to perform continuous beam scanning and effective sidelobe level control while maintaining a reasonable filtering performance.