Abstract
A dual-functional antenna array operating in the long term evolution (LTE) band 42 (3.4-3.6 GHz) and 5.8-GHz wireless wide area network (WLAN) band (5.725-5.875 GHz) for multiple-input multiple-output (MIMO) applications in 5G smartphones is proposed. The proposed 8-antenna array is composed of two different antenna elements, namely, the folded L-shaped antenna and couple-fed U-shaped antenna. It can be applied in the 8 × 8 (by using 8 antenna elements) and 4 × 4 (by using 4 antenna elements) MIMO system across the LTE band 42 and 5.8-GHz WLAN band, respectively. The quasi-orthogonal polarization, balanced mode excitation and pattern diversity are properly used to achieve high isolation within the operation bands. A prototype of the proposed antenna array was fabricated and measured. The measured isolations in the LTE band 42 (6-dB impedance matching) and 5.8-GHz WLAN band (10-dB impedance matching) are better than 17.1 dB and 34.6 dB, respectively. The total efficiencies are 45%-62% and 52%-59% in the two operation bands, respectively. Besides, the measured envelope correlation coefficients (ECCs) are less than 0.045 and 0.0001, the calculated peak ergodic channel capacities are 37.9 bps/Hz and 19.3 bps/Hz in the 8 × 8 or 4 × 4 MIMO system across the operation bands. Furthermore, user's hand and head effects are investigated and desirable results are obtained. The above results show that this proposed antenna array is a good candidate for MIMO applications in smartphones.
Highlights
With the growing demands of higher data rates in the future 5G communication system, the multiple input multiple output (MIMO) technology has attracted increasing attention both in industry and academia [1]
As for the couple-fed U-shaped antenna (CUA) operating at long term evolution (LTE) band 42, it is composed of a rectangular feeding strip (8.2 mm × 1 mm) and a U-shaped metal strip (27.6 mm × 5.6 mm)
Under DM scenario, the proposed 8-antenna array is still good for 7 × 7 (Ants 2–8) and 3 × 3 (Ants 4 5 and 8) MIMO operation across the LTE band 42 and 5.8-GHz WLAN band, respectively
Summary
With the growing demands of higher data rates in the future 5G communication system, the multiple input multiple output (MIMO) technology has attracted increasing attention both in industry and academia [1]. Several high-isolation antenna arrays operating in the sub-6 GHz bands for smartphone application have been reported in [10]–[18]. These works only support single band operation. The design of high-isolation MIMO antenna array covering the LTE band 42 and WLAN band is rarely reported. As for the CUA operating at LTE band 42, it is composed of a rectangular feeding strip (8.2 mm × 1 mm) and a U-shaped metal strip (27.6 mm × 5.6 mm) They are printed at the front and back surface of FR4 dielectric frames, respectively. Due to the selfresonance characteristics of the dipole antenna, the intensity of induced ground current is very weak
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