A 28-GHz Switched-Beam Antenna with Integrated Butler Matrix and Switch for 5G Applications

This work presents a 28-GHz Butler matrix based switched-beam antenna for fifth-generation (5G) wireless applications. It integrates a 1 x 4 microstrip antenna, a 4 x 4 Butler matrix, and a single-pole four-throw (SP4T) absorptive switch in a single planar printed circuit board and is housed in a metal enclosure. Co-integration of a packaged switch chip with the Butler matrix based switched-beam antenna greatly enhances the form factor and integration level of the entire system. A wideband two-section branch line coupler is employed to minimize the phase and magnitude errors and variations of the Butler matrix. The aluminum metal enclosure stabilizes the electrical performances, reduces the sidelobes, and improves the structural stability. The fabricated antenna with the metal enclosure assembled has a dimension of 37 x 50 x 6.2 mm(3). With an RF input signal fed to the antenna's input port through a single Ka-band connector, and the switching states chosen by 2-bit dc control voltages, the antenna successfully demonstrates four directional switched beams. The beam switching operations are verified through the over-the-air far-field measurements. The measured results show that the four beam steering directions are -43 degrees, -17 degrees, +10 degrees, +34 degrees with side lobe levels < -5.3 dB at 28 GHz. The antenna also shows reasonably wideband radiation patterns over 27-29 GHz band. The 10-dB impedance bandwidth is 25.4-27.6 GHz, while a slightly relaxed 8-dB bandwidth is 25.2-29.6 GHz. Compared to previous works, this four-directional switched-beam antenna successfully exhibits the advantages of high integration level and satisfactory performances for the 28-GHz 5G wireless applications.