A compact self-isolated Multi Input Multi Output (MIMO) antenna array is presented for 5G mobile phone devices. The proposed antenna system is operating at the 3.5 GHz band (3400–3600 MHz) and consists of eight antenna elements placed along two side edges of a mobile device, which meets the current trend requirements of full-screen smartphone devices. Each antenna element is divided into two parts, a front part and back part. The front part consists of an I-shaped feeding line and a modified Hilbert fractal monopole antenna, whereas the back part is an L-shaped element shorted to the system ground by a 0.5 mm short stub. A desirable compactness can be obtained by utilizing the Hilbert space-filling property where the antenna element’s overall planar size printed on the side-edge frame is just (9.57 mm × 5.99 mm). The proposed MIMO antenna system has been simulated, analyzed, fabricated and tested. Based on the self-isolated property, good isolation (better than 15 dB) is attained without employing additional decoupling elements and/or isolation techniques, which increases system complexity and reduces the antenna efficiency. The scattering parameters, antenna efficiencies, antenna gains, and antenna radiation characteristics are investigated to assess the proposed antenna performance. For evaluating the proposed antenna array system performance, the Envelope Correlation Coefficients (ECCs), Mean Effective Gains (MEGs) and channel capacity are calculated. Desirable antenna and MIMO performances are evaluated to confirm the suitability of the proposed MIMO antenna system for 5G mobile terminals.
With increasing growth of wireless communication technologies, high data rates and intelligent services are being continuously demanded. Because of the advantages of large channel capacity, massive connection density and high spectral efficiency, the 5G wireless communication systems have attracted increasing attention in both academic and industrial fields [
In this paper, a compact self-isolated eight-element antenna system that operates in the (3400–3600 MHz) band is presented for future 5G MIMO mobile handsets. The main feature of this work is that it can effectively solve the isolation problem with keeping high antenna efficiency. Based on the self-isolated property, good isolation is obtained without utilizing decoupling elements and/or isolation techniques. In addition to that, a compact antenna size and simple structure is presented in the proposed system where the antenna element’s overall planar size printed on the side-edge frame is just (9.57 mm × 5.99 mm). Furthermore, a high diversity performance with very low envelope correlation coefficients (ECCs) is attained, where a very good independence antenna’s far-field radiation characteristics can be shown. Besides, good antenna and MIMO performances are achieved. The proposed antenna system was simulated and analyzed using the CST Microwave Studio software (version 2019). A prototype model of the proposed system was fabricated and its performance was measured. Reasonable agreement between the measured and simulated results has been obtained.
The proposed eight-element MIMO antenna system for 5G mobile phones is presented in
To further demonstrate the working principle of the proposed compact self-isolated antenna element, the effects of
The simulated results of the S-parameters for the proposed eight-element MIMO antenna system are sketched in
In addition to that, two cases have been studied to explain the effects of different array configurations. Due to the similarity, only the necessary S-parameters of a single side-edge are plotted in
In this subsection, important parameters are evaluated and discussed to assess the potential MIMO performance of the proposed antenna array. The correlation coefficient (ρ) indicates how much the multipath communication channels are correlated or isolated (
where Ω defines the solid angle,
In this formula, N is the number of antennas and the antenna elements are expressed as
The Mean Effective Gain (MEG) is considered as one of the effective performance metrics for MIMO antenna systems. It can be well-defined as the ratio between the mean received power of the antenna to the total mean incident power when the antenna is moved over a random mobile environment route. MEG can be obtained from
where the cross-polarization power ratio is denoted as XPR, and
Another significant parameter used to evaluate the multiplexing performance of the proposed MIMO antenna system is the channel capacity (CC), indicating the maximum data rate that can be achieved. It can be computed by
CC is the channel capacity of the MIMO system in bits/s/Hz,
where
The proposed 8-element MIMO smartphone antenna was fabricated and experimentally tested. The assembled prototype model is depicted in
Ref. | Bandwidth (GHz) | Total Efficiency (%) | Isolation |
ECC | Overall System Size (mm2) | Antenna |
MIMO Order | Isolation |
---|---|---|---|---|---|---|---|---|
[ |
(3.3–3.6) (–6 dB) | (44–53) | >15 | <0.15 | (40 × 100) | (14 × 44.7) | 8 × 8 | Pattern diversity |
[ |
(3.3–3.6) (–6 dB) | (45–60) | >15 | <0.15 | (40 × 124) | (12.5 × 4.9) | 8 × 8 | Ground slot etching and Neutralization line |
[ |
(3.4–3.6) (–10) | >40 | >10 | <0.1 | (75 × 150) | (7 × 10) | 8 × 8 | Self-isolated |
[ |
(3.3–5) (–10 dB) | >46 | >14.5 | <0.1 | (75 × 150) | (22 × 6) | 8 × 8 | Self-isolated |
[ |
(2.55–2.65) (–10 dB) | (48–58) | >13 | <0.2 | (68 × 136) | (18.6 × 18.6) | 8 × 8 | Polarization diversity |
[ |
(3.3–3.6) (–6 dB) | (42–75) | >13 | <0.15 | (75 × 155) | (28.8 × 1) | 8 × 8 | Balanced mode excitation |
[ |
2.55–2.65 (–10 dB) | (48–63) | >12.5 | <0.15 | (68 × 136) | (31.2 × 5) | 8 × 8 | Polarization diversity and Pattern diversity |
[ |
(3.4–3.6), (4.8–5.1) |
(41–72) LB, |
>11.5 | <0.08 LB |
(75 × 150) | (15 × 7) | 8 × 8 | Neutralization line |
[ |
(3.4–3.8) (5.15–5.93) (–6) | >42 | >11 | <0.15 | (80 × 150) | (16.2 × 3) | 10 × 10 | Polarization diversity and Space diversity |
This work | (3.4–3.6) (–10) | (56–66) | >15 | <0.02 | (75 × 150) | (9.57 × 5.99) | 8 × 8 | Self-isolated |
In this study, an eight-port MIMO antenna array is introduced and examined for 5G massive MIMO smartphone devices. Very good antenna miniaturization is achieved by utilizing the Hilbert fractal space-filling property. Due to the self-isolated property of the proposed antenna structure, good isolation is achieved (better than 15 dB) without using decoupling elements and/or isolation techniques. The main trait of the self-isolated property is that a single antenna can operate as a radiated and an isolated element simultaneously so that the antenna efficiencies do not decrease. The simulated and measured results of the antenna and MIMO performances obtained, as well as the structure simplicity, compactness, self-isolated property and position independency, show that the proposed eight element MIMO antenna system is a convincing candidate for the future 5G mobile phone devices.