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An extremely low-profile/compact MIMO system is proposed by utilizing the dual antenna for 5G sub-6 GHz and mm-wave application. The antennas are integrated on a centrally located square-shaped slot-loaded octagon-shaped substrate board area of 3706.69 mm2. The identical dual antenna elements with the same orientation are orthogonally placed on an octagon-shaped substrate from the outer side, creating an 8-element MIMO antenna for sub-6 GHz application. From the inner side of the same substrate, a $1\mathbf {\times }4$ array-based antenna is orthogonally placed in front of the remaining side of the octagon, forming a 4-element MIMO antenna for mm-wave application. The edge-to-edge separation between element-1 and -9 is almost close to $\lambda _{0}$ /64 ($\lambda _{0}$ at 4.0 GHz). The stubs are connected to shared ground plane to reduce the coupling between closely placed antenna elements. The MIMO system provides dual −6 dB impedance bandwidth of ($S_{ij}{}_{\,\,} \mathbf {\mathrm {\in }}\,\,{i} = {j}$ , 1 to 8) 4.0–5.6 GHz and ($S_{ij}{}_{\,\,} \mathbf {\mathrm {\in }}\,\,{i} = {j}$ , 9 to 12) 24.25–29.5 GHz, can cover the 5G n79//n257/n258 bands. It has a minimum isolation ($S_{ij~}\mathbf {\mathrm {\in }}~{i} \mathbf {\mathrm {\ne }} {j}$) value of 12 dB and 22 dB, respectively. Also, the peak gain and total efficiency values for element-1 and -9 are 5.4 dBi and 8 dBi, and 56.5–77.4% and 70.3–96.2%, respectively. The measured and simulated results are found in close agreement those confirming that the proposed MIMO system may be a suitable candidate for 5G-smartphones. Due to 0.508 mm low-profile, antenna is integrated within the back cover of smartphones, thereby inside device volume will reduce. [ABSTRACT FROM AUTHOR]

In this brief, a low-profile wideband quad-element MIMO antenna with high isolation is designed, which is utilized to propose a 20-elements MIMO system. Each element of the MIMO antenna covers a wideband occupying a small area of $15\times 15$ mm2. The orthogonal symmetric arrangement of a single antenna forms an extremely compact quad-element MIMO antenna having shared ground, and its occupied volume is $0.84\lambda _{\mathrm{ g}} \times 0.84\lambda _{\mathrm{ g}} \times 0.019 \lambda _{\mathrm{ g}}$ ($\lambda _{\mathrm{ g}}$ at 3.95 GHz) with a minimum ($0.155 \lambda _{\mathrm{ g}}$) edge to edge distance between elements. The proposed antenna has a −10 dB ($S _{ij} \in i=j$) impedance bandwidth of 77.52% (3.95–8.95 GHz) and a minimum isolation ($S _{ij} \in i \ne j$) value of 17 dB. The measured and simulated results are found in good agreement that confirms the proposed antenna is appropriate for extending a higher-order MIMO system. Further, a low-profile quad-element MIMO antennas are arranged orthogonally at the four-corners and a quad-element MIMO antenna at the center of form a 20-elements planar MIMO antenna. It can be utilized as a localization system where different user’s devices are connected to the primary host. [ABSTRACT FROM AUTHOR]

A compact two‐element multiple‐input‐multiple‐output (MIMO) antenna system with improved impedance matching and isolation is presented for future sub‐6 GHz 5G applications. The two identical tapered microstrip line fed modified rhombus‐shaped radiating elements are placed in the same orientation at a compact substrate area of 0.24λ0 × 0.42λ0 (where, λ0 at 3.6 GHz) on a shared rectangular ground. A remodeled T‐shaped ground stub is placed between a pair of radiating element to achieve improved impedance bandwidth and isolation. Further, a split U‐shaped stub connected to center of each radiating element to achieve the desired resonant frequency of 3.6 GHz. The proposed antenna covers a −10 dB operating band of 3.34 to 3.87 GHz (530 MHz) with more than 20 dB isolation between a pair of elements. MIMO performances are also analyzed and experimentally validated. The measured performances of a prototype are found in good agreement with simulated performances. Further, the simulation study is carried out to see the effect of housing and extended ground plane on two‐element MIMO antenna for practical application. An idea of realization of 12‐element MIMO is also studied using the proposed two‐element MIMO antenna. [ABSTRACT FROM AUTHOR]

A single-layer, low-profile beam scanning reflectarray (RA) fed by a spoof surface plasmon polaritons (SSPPs) based endfire MIMO antenna is proposed in this manuscript. The RA is based on a variable elliptical-shaped unit cell designed at 10.4 GHz. The unit cell has a low insertion loss of 2.3 dB and a reflection phase of 315.2°in the working frequency band from 9.52–11.23 GHz. The SSPPs based endfire MIMO antenna is used to mitigate the aperture blockage, achieve high isolation between the feed elements, and accomplish the continuous one-dimensional (1-D) beam scanning of ± 8°from the broadside. The maximum realized gain of the proposed reflectarray in the broadside direction is 22.6 dBi with a 3-dB beamwidth of 5.7°. The minimal beam switching loss is in the other direction, and the realized gain is 22.4 dBi with a 3-dB beamwidth of 5.8°. The 3-dB gain bandwidth (GBW) of 9.7 % of the proposed RA benefits nano-satellite applications. The fabricated prototype measurements in an anechoic chamber environment verify the simulated results. [ABSTRACT FROM AUTHOR]

This work proposes a three-port, low-profile, coplanar endfire multiple-input-multiple-output (MIMO) antenna based on spoof surface plasmon polaritons (SSPPs). The proposed antenna comprises a coplanar waveguide (CPW)-fed SSPPs transmission line (TL). A transition to transform the CPW quasi-TEM mode to the SSPPs mode. The radiator section with asymmetric discontinuities converts the bounded SSPPs waves into radiating waves. The proposed MIMO antenna exploits the inherent feature of high isolation in the SSPPs TL due to its strong field confinement competency. Wider beamwidths for ample azimuth and elevation coverage with a stable pattern in the endfire direction are achieved in the 9.52–11.23 GHz operating band. In the operating band, the MIMO antenna has an average realized gain of 6 dBi. Mainly, it has high isolation below -35 dB (measured) in the operating range, a maximum envelope correlation coefficient (ECC) of 1.5 × 10−3, and a total active reflection coefficient (TARC) value below 0.3. The measured results are closely matched with the simulated ones in terms of S-parameters, radiation pattern, ECC, TARC, and CCL. [ABSTRACT FROM AUTHOR]