A Low-Cost 4x4 Butler Matrix-Fed Patch Antenna Array for Millimeter Wave Applications

A low-cost, low-profile, high-performance antenna array based on a 4×4 series-fed patch with elliptical slots is presented in this article for fifth-generation millimeter-wave communications (5G mmWave). The antenna array can be manufactured easily on a two-layer printed circuit board because of its simple design and lack of complex structures. It is designed for the Ka-band (n257 band) with an impedance bandwidth of 3.1 GHz, covering the range from 26.1 GHz to 29.2 GHz. There is a fractional bandwidth of about 11.2%, several times greater than the fractional bandwidth of a series-fed antenna. Within the impedance bandwidth, the radiation gain exceeds 11 dBi, with a maximum gain of 18.25 dBi. The radiation efficiency reaches an impressive 94% and the aperture efficiency reaches 44.6%. The isolation between the four excitation ports is less than −30 dB. Additionally, the 70% impedance bandwidth features right-hand elliptical polarization with a 3:1 axial ratio. It also has an excellent beam steering range (theta angle: ${\pm 45}^o$). The following section will provide a detailed description of the antenna array and an analysis of the resonance frequencies. Further, the array antenna is combined with the Butler matrix network to form a beamforming function. Finally, the measured results agree well with the simulation results. This low-cost, low-profile, high-performance antenna array will promote the popularization of 5G mmWave communications, which will be widely used worldwide.