Wide-bandwidth inverted-F stub fed hybrid loop antenna for 5G sub-6 GHz massive MIMO enabled handsets

A ten-element multi-antenna terminal for massive multiple-input–multiple-output (MIMO) in the fifth-generation (5G) sub-6 GHz with wide impedance bandwidth (IBW) is proposed. A grounded coplanar waveguide is employed to feed an inverted-F stub coupled to a hybrid loop antenna element. Through tuning, the multiple resonant modes are combined so that a wide IBW is achieved. Antenna element sites are selected along the periphery of the typical smartphone back plane of size $120\,{\rm mm}\times 70\,{\rm mm}$120mm×70mm. To improve the diversity performance, two elements are placed along the horizontal edge orthogonal to the rest of elements placed along the vertical side. The prototype of the antenna is fabricated and measured exhibiting a wide IBW of ($|S_{ii}| \leq -6$|Sii|≤−6 dB) 63% centred around 4.68 GHz. The minimum measured isolation achieved is 18 dB. The maximum simulated envelope correlation coefficient is found to be $\sim $∼0.21 and while the minimum antenna efficiency is 78.4%. Each element has a form factor of $17.2\times 3.8\,{\rm mm}{^2} (0.018 \lambda _{\mathrm {g}}^2)$17.2×3.8mm2(0.018λg2) and printed on a 1.52 mm thick Rogers 4003 substrate with $\epsilon _r = 3.38$ϵr=3.38 and $\tan \,\delta =0.0027$tanδ=0.0027. The proposed multi-antenna terminal is suitable for 5G sub-6 GHz (3.2–6.1 GHz) communication including long-term evolution bands 42, 43 and 46.