Compact Multi-Beamforming Networks Based on Generalized Joined Coupler Matrix With Flexible Beam Angles and Low Sidelobe Levels

The investigation of beamforming networks (BFNs) for multibeam antenna arrays has been ongoing for decades. However, enabling individually controllable multibeams employing a BFN has remained a recognizable challenge. The utilization of generalized joined coupler (GJC) matrices has demonstrated its efficacy as a viable solution for achieving multibeams with independent individual beam directions and minimal sidelobe levels. In this paper, for the first time, the design of the GJC matrix as a multibeam feeding network is reported using planar circuits and verified experimentally. The GJC matrix design is built based on a mixture of one-section and two-section branch-line couplers, which are able to realize a wide range of coupling coefficients. A thorough investigation from theoretical analysis to electromagnetic modeling is conducted on one-section and two-section branch-line couplers, and a general design guideline is given for choosing the appropriate type and dimensions for each coupler in a GJC matrix. Then, two types of BFN using microstrip line working at 5 GHz and stripline working at 12 GHz are designed, fabricated and measured, respectively. Different beam angles are realized to demonstrate the independent and simultaneous multibeam steering functionality, the experimental results agree well with the theoretical ones.