Compact Multibeam Antenna Fed by Dual-Layer Substrate Integrated Waveguide Butler Matrix for 5G Millimeter-Wave Application

A
$1\times 4$
multibeam array antenna centered at 26 GHz fed by a compact
$4 \times 4$
Butler matrix is designed and manufactured in dual-layer substrate integrated waveguide (SIW) technology. This proposed configuration avoids two crossovers and two phase shifters in conventional designs, and therefore significantly reduces the overall size. In addition, wideband phase shifters are designed to enable a flat phase characteristic. The experimental results show a 15.4% impedance bandwidth from 24 to 28 GHz. The measured maximum gain achieves 10.4 dBi, and the 3-dB beam width covers
$\pm 63^{\circ}$
. Its good performance indicates the potential for 5G millimeter wave applications.