Ground Plane Alterations for Design of High-Isolation Compact Wideband MIMO Antenna

In this paper, a simple technique for improving element isolation in wideband multiple-input multiple-output (MIMO) antenna is investigated. We consider n-section rectangular slits below the feed line and analyze the effects of the number of sections on achievable isolation. The effect of the slits is indirect by improving the impedance matching, which creates a room for isolation enhancement through rigorous optimization of all antenna parameters. The results obtained for an exemplary antenna structure indicate the advantages of increasing the slit complexity as well as a saturation effect beyond <inline-formula> <tex-math notation="LaTeX">$n= 3$ </tex-math></inline-formula>. Using these considerations, a compact MIMO antenna is developed and optimized to operate in the ultrawideband (UWB) (3.1–10.6 GHz) frequency range. The final design features <inline-formula> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert \le -10$ </tex-math></inline-formula> dB and isolation <inline-formula> <tex-math notation="LaTeX">$\vert \text{S}_{21}\vert \le -20$ </tex-math></inline-formula> dB in the entire UWB range, as well as small dimensions of only <inline-formula> <tex-math notation="LaTeX">$25\times32$ </tex-math></inline-formula> mm². Excellent performance figures, including envelop coefficient correlation (< 0.005), diversity gain (> 9.99 dB), and total efficiency (>80% by average), demonstrate that the considered structure is suitable for practical applications and competitive to the state-of-the-art antennas reported in the literature. Experimental validation of the design is also provided.