Butler matrix-based beamforming with polarization reconfigurability for reducing electromagnetic interference

Abstract

In this paper, Circular-Polarization (CP) reconfigurability, switched beamforming, and Side Lobe Level (SLL) reduction necessary for electromagnetic interference suppression are achieved thanks to a novel modified single-layer 4×8 Butler Matrix (BM). The proposed feeding network is capable of exciting a linear array composed of four square patch antennas. Each antenna element is fed from its both adjacent edges with a ±90°phase difference, thus resulting in Left-Handed or Right-Handed Circular Polarizations (LHCP or RHCP). The suggested feeding network also reduces the SLL by engendering tapered amplitude distributions in its output ports. This feature has been introduced for the first time in a system providing simultaneous beam switching and polarization reconfigurability. It should be mentioned that beamforming is performed as the BM can generate progressive phase differences regarding the input port selected for the excitation. All the above-mentioned characteristics are well received by a straightforward and flexible modification in 4×8 BM. A sample of the structure operating at 2.4 GHz is designed, fabricated, and measured. Furthermore, the theta bandwidth in both RHCP and LHCP cases is evaluated, showing the full coverage of azimuth plane from –60 to 60 degree with an Axial Ratio (AR) below 3 dB.