Radiation Pattern of Array Antenna with the Dual-Layer Butler Matrix

In order to fulfill the demands for the high data rates of the 5G mobile system at the millimeter wave (mm-wave) frequency, multi beam array antennas are needed at the base station. The multi beam array antenna includes the technology of the Butler Matrix which use the amplitude and the phase for beamforming. In addition, this technology is cost effective, and easily installed at the base station. Previously, dual-layer Butler Matrix was designed to achieve the crossover circuit. In this configuration, to connect between the upper and the lower layer lines, techniques such as slot coupled, substrate integrated waveguide and coplanar waveguide structure are proposed. However, most of the structures experienced the high insertion loss and the parasitic coupling. In this paper, to address the aforementioned limitation, a via-hole structure is proposed into the Butler Matrix design. By optimum design of the substrate thickness, through hole and the connection pin sizes, the low loss line is developed. The dual-layer Butler Matrix design is then combined with the patch antenna array with 0.5 λ spacing. The minimum transmission coefficient obtained is −6.05 dB with the low loss of ± 0.05 dB. Both reflection coefficients (Sii) and isolation (Sij) simulations are less than −15 dB while the transmission coefficient (Sji) value is 6 ±0.05 dB. Four beams are generated accordingly towards +10°, +32°, −36°, and −14° when the Port 1 till Port 4 is fed with the corresponding peak gains of 9.4 dB, 10.1 dB, 9.5 dB and 10.5 dB, respectively.