Mutual Coupling Reduction in a Switched Beamforming Multilayer Antenna Array System

In this paper, we present a millimeter-wave beamforming antenna array for the fifth generation (5G) of mobile networks and beyond. One of our priority objectives was to minimize the antenna array's total physical size, by paying attention to avoid radiation performance degradation, such as bandwidth and efficiency. Another priority objective was to avoid mutual coupling (MC) between radiation elements and enhance the gain of the antenna to meet the requirements and challenges of the 5G. In these prospects, we have designed a 4x3 Chebyshev modified rectangular antenna array, engraved on the dielectric substrate of the top layer. The antenna array is powered across a 4x4 Butler matrix, engraved on the dielectric substrate of the bottom layer. The prototype overall size is 35.76x45.56x1.589 mm3. Hence, four switched main lobes pointed according to the angles -14 degrees, +26 degrees, -23 degrees and +12 degrees. The corresponded maximum gains at 28 GHz are 11.1, 10.5, 11, and 11.5 dB, respectively. Moreover, a reduction of the MC is ensured by using a CSRR metamaterial carved into the ground plane (GP) of the upper dielectric substrate layer. Experimental and simulation results concord well and show a multiband behavior at 26 GHz and in Ka-band. The impedance bandwidths are 1.5%, 2.7%, and 2.43% at 26, 28, and 40 GHz, respectively. A low MC, between the antenna array's elements, is also achieved, and the levels of the transmission coefficients vary between -11 dB and -68 dB.