Isolation-enhanced dual band MIMO antenna with defective ground structure and stubs as a hybrid decoupling structure for next-generation sub-6 GHz uses

Abstract

This article presents a two-element and four-element isolation-enhanced dual-band MIMO antenna operating at 5.03 GHz and 6.02 GHz. With an ultra-compact inter-element spacing of only $0.03{\lambda }_0$, mutual coupling becomes a major challenge. To address this issue, a hybrid decoupling (DC) structure integrating a defective ground structure (DGS) and a T-like shaped stub is proposed. This technique efficiently alters the surface current distribution, thereby suppressing mutual coupling and improving isolation. The two-element MIMO antenna with the proposed DC structure achieves an isolation ($\left|S_{21}\right|$) of 31 dB at the lower band and 45 dB at the upper band, with a peak gain of 6 dBi over both frequencies. In the four-element configuration, a maximum isolation of 15 dB at 5.03 GHz and 20 dB at 6.02 GHz is obtained, with corresponding gains of 5.3 dBi and 6.5 dBi, respectively. ECC below 0.0037 and a diversity gain close to 10 dB indicate excellent diversity performance within the antenna’s 10-dB impedance bandwidths of 90 MHz (4.98–5.07 GHz) and 80 MHz (5.98–6.06 GHz).The novelty of this work lies in achieving ultra-compact element spacing combined with remarkably high isolation (up to 45 dB), very low ECC (0.0037), and high radiation efficiency (up to 90%). These benefits make the suggested antenna ideal for tiny sub-6 GHz 5G and WLAN applications that need strong isolation and diversity.