Low-cost multibeam millimeter-wave array antennas for 5 G mobile applications

This paper presents a low-cost, compact, multibeam planar antenna system with a wide beam coverage angle at 28 GHz for 5 G applications. The proposed microstrip based design includes two branch-line couplers and a Butler matrix with and series-fed array antennas. Unlike the conventional Butler matrix and branch-line coupler, which generally can generate 4 and 2 beams, respectively, the designed configuration employs a novel feeding technique which allows the system to generate 7 beams for butler matrix and 3 beams for the branch-line coupler. This system covers a wider spatial range, due to its unique placement of the branch-line couplers and the antennas, perpendicular to the sides of the main beamforming and the array antenna architecture. The measured gain, for the 13 beams, varied between 11.2 and 14.1 dBi at 28 GHz. A wide impedance bandwidth for the entire 26.5 to 29.5 GHz band was achieved, while more than a 10% fractional radiation bandwidth was obtained with a gain value over 10 dBi. The beamforming networks and rectangular series-fed microstrip array system was fabricated using low-cost PCB prototyping on Rogers 4003 C with dimensions of