Compact Sub-6 GHz and mmWave 5G Wideband 2 × 1 MIMO Antenna with High Isolation Using Parasitically Placed Double Negative (DNG) Isolator

In this paper a multiband modified ‘W’ shaped, Multiple input multiple output (MIMO) antenna with a metamaterial inspired isolator for enhanced isolation is proposed for 5G application. The two-element MIMO antenna comprises of a closely placed (edge to edge gap of 0.117λ_o, λ_o = highest operating wavelength) antenna elements that covers both sub-6 GHz (3.42–4.25 GHz) and millimeter wave (mmWave) range bands (24.8–26.5 GHz) of 5G with bandwidth of 821 MHz and 1630 MHz. The MIMO antenna also covers bands C (7.44–7.92 GHz), X (9.9–10.49 GHz), Ku (12.02–13.39 GHz & 15.92–17.492 GHz), K (19.49–22.42 GHz), partially. The isolation level in all resonating bands remain near to the acceptable value of (|S₁₂|>  −15 dB) however a very significant mutual coupling effect is observed in sub-6 GHz range (|S₁₂|=  −11.92 dB at 3.94 GHz). To improve the isolation in sub-6 GHz band, a metamaterial inspired isolator comprising of Double negative (DNG) unit cells is uniquely placed along the side of the closely positioned antenna elements. Simulated results indicate that isolation level improves to (|S₁₂|=  −16.1 dB at 3.94 GHz) after placing the DNG metamaterial based isolator. The antenna performance parameters such as gain, return loss, bandwidth, Envelope correlation coefficient (ECC), Diversity gain (DG) and radiation efficiency are not affected by placement of isolator. The metamaterial equipped MIMO antenna (Meta–MIMO antenna) has a compact structure of 70 × 40 × 0.8 mm³, with a high isolation in all bands (|S₁₂|> −16 dB), peak gain of 7.8dBi, low ECC (< 0.05), high diversity gain (9.98 dB) and efficiency (≈91.38%). Further the proposed Meta-MIMO antenna performance for practical applications is investigated by connecting to different sizes of ground plane, the results indicate that the isolation levels and efficiency do not deteriorate.