Implementation of a Broadside Switched-Beam Antenna Array Using a Butler Matrix Feed Network

Abstract

This paper presents a compact beamforming network designed to achieve broadside radiation when integrated with a microstrip antenna array. The steering mechanism employs a planar Butler Matrix (BM), which is composed of compact 90° 3 dB microstrip couplers. Antenna elements are spaced at 0.3Ȝ, allowing intentional overlap that shifts the main beam away from broadside, thereby producing a prominent grating lobe in the broadside direction. Both full-wave electromagnetic simulations and experimental measurements confirm that the design delivers broadside coverage, high gain, and a compact form factor.
The prototype exhibits good agreement between simulated and measured S-parameters, validating effective impedance matching and beam steering performance.