Dual-Layer Metamaterial Rectangular Antenna Arrays for In-Band Full-Duplex Massive MIMO

Abstract

This paper presents a prototype pair of dual-layer electromagnetic bandgap slotted circularly polarized patch $8\times 8$ Tx/ $8\times 8$ Rx orthogonally-polarized antenna arrays designed for in-band full-duplex massive MIMO. The design processes of the antenna array, beamforming feeding network, and beam steering algorithms are discussed. The proposed prototype operates in a bandwidth of 250 MHz (or 7.1% at 3.5 GHz) from 3.35 GHz to 3.6 GHz. Using orthogonal Tx/Rx polarization, an average mutual coupling between any two Tx and Rx antenna elements of −49.2 dB can be achieved. Further improvement in Tx-to-Rx isolation at the beam level can be achieved with the two proposed beamforming schemes. Illustrative results using Tx/Rx $1\times 4$ sub-arrays indicate the formed beams with an average mutual coupling of −65.6 dB between any two Tx and Rx beams (i.e., an improvement of 16.4 dB in Tx/Rx isolation). The sample Tx and Rx far-field beam patterns, radiation null depth and position, and corresponding Tx-to-Rx mutual coupling levels are investigated, which gives insight into the beamforming isolation improvement design. Within a steering range from −50 to 50 degrees, a directivity over 10.7 dB, a 3dB-beamwidth narrower than 33.0 degrees, and a normalized sidelobe level lower than −9.0 dB are achieved. Simulation and measurement results on the mutual coupling, beamforming directivity, beamwidth, and radiation patterns in various scenarios are investigated and found to be in good agreement.

Keywords

• Antenna isolation
• array beam
• beamforming
• full-duplex
• massive MIMO
• mutual coupling