Enhancing isolation and bandwidth in planar monopole multiple antennas using thin inductive line resonator

Abstract

This paper presents efficient mutual coupling reduction and bandwidth enhancement method in planar monopole multiple antennas. High isolation and bandwidth extension are achieved by integrating a thin inductive line resonator as reflector and parasitic element between the antenna elements. A 36.9% bandwidth (4.69–6.5 GHz) is achieved at 4.9 GHz, which encompasses the sub-6 GHz (4.8–5.0 GHz) 5G and 5.15–5.85 GHz WLAN bands. The thin inductive line resonator provides an effective means of controlling the electromagnetic wave propagation. Approximately 45 dB isolation and 4.9 dB maximum gain can be achieved between two parallel monopole antennas with 0.36λ0 spacing. The physical meaning of electromagnetic propagation in MIMO antenna is studied by discussing the coupling mode between antennas and the working mechanism of thin inductive line as parasitic elements and reflectors. Furthermore, a four-element antenna with orthogonal polarization diversity is also proposed based on the thin inductive line. Correlation coefficients (CC) are well below 0.05 across the operating bandwidth.