Compact and Wideband $4\times 4$ Butler Matrix for Millimeter-wave 5G Applications
Mehri Borhani Kakhki, Fayez Hyjazie, Ahmed Shehata Abdellatif, David Wessel
Abstract
In this paper, a compact and wideband (24 GHz-27.5 GHz) switched beam antenna array consists of a 4-dipole antennas fed by a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4\times 4$</tex> Butler matrix is presented. The Butler matrix is designed on a multilayer structure based on elliptically shaped <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{45^{\mathrm{o}}}$</tex> phase shifters and 3 dB hybrid couplers to improve the impedance bandwidth and eliminate crossover. A broadband printed-dipole antenna is designed and developed to an array of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1\times 4$</tex> with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{\lambda/2}$</tex> (at 26 GHz) inter-element spacing to fully utilize the beam-switching capability. Simulated radiation patterns of the integrated planar array with the proposed Butler matrix showed 4 output beams for different input port excitation with an average 8dBi radiation gain in the operating bandwidth.