Low-Cost Multibeam Millimeter-Wave Array Antennas for 5G Mobile Applications

This paper presents a low-cost, compact, multibeam planar antenna system with a wide ±138∘ beam coverage angle at 28 GHz for 5G applications. The proposed microstrip based design includes two branch-line couplers and a Butler matrix with 2×10 and 4×10 series-fed array antennas. Unlike the conventional 4×4 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 2×10 antennas, perpendicular to the sides of the main beamforming and the 4×10 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 90×45×11 mm3 .