Two-element Multiple-input Multiple-output Antenna Research Articles

High isolation MIMO antenna array for multiband terahertz applications

The advancement of future technology seeks to create wireless systems capable of achieving faster data transfer rates. One solution to confront this challenge is by employing Multiple-Input Multiple-Output (MIMO) systems. Nonetheless, the primary obstacle in assessing MIMO performance revolves around the size and spacing of the antennas to maintain isolation among the ports. Consequently, it is essential to devise an approach to tackle these challenges, with the utilization of a DGS as a viable and promising approach. Hence, in this study, we developed a dual-frequency MIMO system featuring two linear array antennas with two elements each and configured to function at 128 GHz and 178 GHz. Initially, this design is conceived as a single-element structure before evolving into a two-element MIMO antenna array configuration. The antenna's physical dimensions are 2.7 × 3.65 × 0.15 mm3, and it consists of two linear array nodes positioned at a separation distance of 0.18 mm. Additionally, the antenna delivers peak gains of 5.16 dB and 6.24 dB at frequencies of 128 GHz and 178 GHz, respectively. The values of various MIMO performance indicators meet stringent standards with ECC values below 0.012 and a DG of approximately 10 dB. Furthermore, the TARC remains below 0 dB. The aim of this research is to create a novel design for a THz antenna that can achieve a wide bandwidth and a high gain while maintaining the standard compact antenna size necessary for THz applications.

SMALL-SCALE MIMO ANTENNA WITH HIGH ISOLATION FOR 5G COMMUNICATION

This manuscript describes two- and three-element small-scale multiple-input multiple-output (MIMO) antenna configurations for 5G communications ranging from 23.5 to 28.6 GHz. Modern device antennas have two essential features: isolation and a larger bandwidth. In this regard, firstly a single element antenna has been designed using quarter wavelength impedance transformer and semi-circular loaded patch along with defected ground structure. Furthermore, two single-element antennas are placed orthonormal to each other having quarter wavelength distance from the center of the single-element antenna. To increase the bandwidth and isolation, additionally a rectangular patch and strip isolate from ground. This structural change alters the current path, improving the impedance matching and isolation of the two-element MIMO antenna configuration. After that the three-element MIMO configuration was formed by placing two single-element antennas orthogonally at quarter wavelength from the center of the single-element antenna. The total size of two- and three-element MIMO antenna is 15 × 11 × 1.6 mm and 20 × 11 × 1.6 mm, respectively. The proposed MIMO antennas provide isolation of more than 21 dB and gain more than 25 dB throughout the working band. MIMO diversity features function reasonably well, with an envelope correlation coefficient of less than 0.002 and diversity gain of 10. Proposed antennas can be a good candidate for MIMO applications in the 5G communication frequency range 2 (FR2), 28 GHz bands.

Frequency reconfigurable two-element MIMO antenna for cognitive radio and 5G new radio sub-6 GHz applications

Abstract In this paper, a compact two-element reconfigurable multiple-input multiple-output (MIMO) antenna for 5G new radio sub-6 GHz is presented and discussed. The proposed MIMO antenna has four frequency operating modes: a wideband operating mode (2.41–6 GHz), a wideband operating mode with a notching band at 3.5 GHz (3.2–3.66 GHz), a low-pass filter mode that filters the higher frequencies with a wide operating band from 2.41 GHz to 4.7 GHz, and a dual-band mode with two operating narrow bands (2.41–3.16 GHz and 3.64–4.7 GHz). To improve the isolation over the entire operating band, a strip line connecting the two ground planes of the two antenna elements has been used. To validate the proposed approach, different prototypes have been fabricated and measured. The simulation results are in good agreement with the measurement results. The proposed antenna has good MIMO diversity performance with a maximum gain of 4.64 dBi. The minimum isolation is 18 dB for the four operating modes, while a measured envelope correlation coefficient of less than 0.008 is achieved. The diversity gain is near 10 dB for various operating modes. The antenna is suitable for cognitive radio and 5G sub-6 GHz applications.

Design of a Modified MIMO Antenna Based on Tweaked Spherical Fractal Geometry for 5G New Radio (NR) Band N258 (24.25–27.25 GHz) Applications

This article describes a fractal-based MIMO antenna for 5G mm-wave mobile applications with micro-strip feeding. The proposed structure is a fractal-based spherical configuration that incorporates spherical slots of different iterations on the patch, as well as rectangular slots on the ground plane. These additions are meant to reduce patch isolation. The two-element MIMO antenna has closely spaced antenna elements that resonate at multiple frequencies, 9.5 GHz, 11.1 GHz, 13.4 GHz, 15.8 GHz, 21.1 GHz, and 26.6 GHz, in the frequency range of 8 to 28 GHz. The antenna’s broadest operational frequency range spans from 17.7 GHz to 28 GHz, encompassing a bandwidth of 10,300 MHz. Consequently, it is well-suited for utilization within the millimeter wave (mm wave) application, specifically for the 5G new radio frequency band n258, and partially covers some other bands X (8.9–9.9 GHz, 10.4–11.4 GHz), and Ku (13.1–13.7 GHz, 15.4–16.2 GHz). All the resonating bands have isolation levels below the acceptable range of (|S12| > −16 dB). The proposed antenna utilizes a FR4 material with dimension of 28.22 mm × 44 mm. An investigation is conducted to analyze the effectiveness of parameters of the antenna, including radiation pattern, surface current distributions and S parameters. Furthermore, an examination and assessment are conducted on the efficacy of the diversity system inside the multiple input multiple output (MIMO) framework. This evaluation encompasses the analysis of key performance metrics such as the envelope correlation coefficient (ECC), diversity gain (DG), and mean effective gain (MEG). All antenna characteristics are determined to be within a suitable range for this suggested MIMO arrangement. The antenna design underwent experimental validation and the simulated outcomes were subsequently verified.

Design and Fabrication of the Split Ring Resonator Shaped Two-Element MIMO Antenna with Multiple-Band Operation for WiMAX/5G/Zigbee/Wi-Fi Applications.

In this manuscript, we proposed the split ring resonator loaded multiple-input multiple-output (MIMO) antenna design for the frequency range of 1 and 25 GHz. The proposed antenna is numerically investigated and fabricated to analyze the different antenna parameters. We provided statistics on a wide range of antenna parameters for five different designs, including a simple circular patch antenna, a single-split-ring antenna, and a double-split-ring antenna. Reflectance, gain, directivity, efficiency, peak gain, and electric field distribution are all analyzed for all proposed antennas. The maximum achievable bandwidth is 5.28 GHz, and the double-split-ring resonator structure achieves this with a return loss of -20.84 dB. The radiation patterns of all the antenna with different port excitation conditions are presented to identify the behavior of the antenna radiation. We found the effect of the split-ring resonators to form radiation beams in different directions. We found the maximum and minimum half-power beam widths of 75° and 2°, respectively, among the different antenna designs. It was found that the split-ring resonator geometries in patch antenna convert wide-beam antenna radiation patterns to several narrow-beam radiation patterns. We found that each antenna's bandwidth, gain, and return loss performance significantly differs from the others. Overall, the proposed results of the antenna may apply to a wide range of communication applications, including those for Wi-Fi, WiMAX, and 5G.

Simple Structure E-Plane Decoupled Millimeter Wave Antenna Based on Current Cancellation Model

A simple structure E-plane decoupled millimeter wave (mmW) multiple-input multiple-output (MIMO) antenna based on current cancellation model is proposed in this communication. First, a coupling model of E-plane MIMO antenna is established by analyzing the coupling current. Then, a high-isolation two-element E-plane MIMO antenna loaded with decoupling branch Bar-L is designed by current cancellation method. Finally, a high-isolation four-element E-plane MIMO antenna is designed, fabricated, and measured to verify the applicability of the decoupling method in large arrays. The measured results show that the antenna achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{\mathbf {11}}\,\,\vert &lt; -10$ </tex-math></inline-formula> dB in band of 25.5–26.5 GHz, and the measured isolation of adjacent ports in this band is greater than 35 dB, which effectively improves the isolation without deteriorating other performance. The proposed antenna with a simple structure is suitable for mmW MIMO systems requiring high isolation.

Polarization Converter Surface Integrated MIMO Antenna for Simultaneous Reduction of RCS and Mutual Coupling

This letter provides an effective solution to deal with the radar cross section (RCS) and mutual coupling of the multiple-input–multiple-output (MIMO) antenna simultaneously. A wideband reflective type polarization converter (PC) is designed and its strategic placement in between the antenna elements of the two-element MIMO antenna has been conceived to mitigate these two issues concurrently. The antenna elements of the proposed MIMO antenna are placed at a proximal distance of 0.088 λ from each other. The proposed MIMO architecture ensures a maximum coupling reduction of 46 dB compared to the conventional MIMO across 4.4–8 GHz. The PC surface reduces the reflection of copolarized waves and enhances cross-polarized reflection. A supercell formed by a unit cell of PC and its 90° rotated counterpart causes phase cancellation of cross- polarized reflected waves, which contributes to wideband RCS reduction by a maximum value of 7 dB. The alignment of PC cells in a column between the adjacent antenna elements causes a reduction in the mutual coupling due to introduction of an extra coupling path and cross-polarization conversion. A good agreement between the simulated and measured results validates this concept of the proposed MIMO design with low RCS and mutual coupling.

Minimally Coupled Two-Element MIMO Antenna with Dual Band (28/38 GHz) for 5G Wireless Communications

This paper presents a dual-band 28/38 GHz two elements multiple-input multiple-output (MIMO) antenna with high isolation for 5G applications. The suggested antenna is a monopole with rectangular and triangle stubs added to the patch and a partial ground plane to achieve the dual band’s behavior. Two elements of the suggested antenna are combined and placed orthogonally to achieve the high isolation features of the MIMO configuration at 28/38 GHz. The MIMO configuration has a size of 27.65 times 12 times 0.273 mm3. The suggested MIMO prototype is fabricated and tested. The tested results achieved dual frequency bands with S11 lower than − 10 dB within two frequency bands (26–30 GHz and 36–41.5 GHz) and S21 lower than − 20 dB through the two operated bands. The suggested antenna has semi-omnidirectional radiation patterns in both planes. As well, its measured peak gain is 5.2 dBi and 5.3 dBi at the two operated frequency bands, respectively. Also, the MIMO parameters are extracted to validate the simulated results. The simulated and tested results have a good matching within the two operating bands which suggests the proposed structure be utilized in 5G communications.

Field Decorrelation and Isolation Improvement in an MIMO Antenna Using an All-Dielectric Device Based on Transformation Electromagnetics.

This work presents a new technique for enhancing the performance of a multiple-input multiple-output (MIMO) antenna by improving its correlation coefficient ρ. A broadband dielectric structure is designed using the transformation electromagnetics (TE) concept to decorrelate the fields of closely placed radiating elements of an MIMO antenna, thereby decreasing ρ and mutual coupling. The desired properties of the broadband dielectric wave tilting structure (DWTS) are determined by using quasi-conformal transformation electromagnetics (QCTE). Next, the permittivity profile of the DWTS is realized by employing air-hole technology, which is based on the effective medium theory, and the DWTS is fabricated using the additive manufacturing (3D printing) technique. The effectiveness of the proposed technique is verified by designing two-element patch-based MIMO antenna prototypes operating at 3 GHz, 5 GHz, and 7 GHz, respectively. The proposed technique helped to reduce the correlation coefficient ρ in the range of 37% to 99% in the respective operating bandwidth of each MIMO antenna, thereby, in each case, improving the isolation between antenna elements by better than 3 dB, which is an excellent performance.

Circularly polarized MIMO antenna utilizing parasitic elements for simultaneous improvements in isolation, bandwidth and gain

A circularly polarized (CP) multiple-input multiple-output (MIMO) antenna with wideband operation and high isolation characteristics is presented. The proposed antenna is first designed with two diagonal slotted square patches and then, four parasitic elements are utilized to significantly improve the antenna performances. Notably, besides enhancing the operating bandwidth and the gain radiation, the parasitic elements also contribute to reduce the mutual coupling between the MIMO elements. The measurements demonstrate that the proposed two-element MIMO antenna with edge-to-edge spacing of 0.09λo and profile of 0.05λo at the center operating frequency has operating bandwidth of 12.8% (5.1–5.8 GHz) and high isolation of better than 22 dB. The antenna also achieves high gain of better than 7.5 dBic and good diversity performances. Compared to other CP MIMO antennas reported in literature, our design possesses several exclusive features including wideband operation, high gain, very small edge-to-edge element spacing as well as low-profile configuration.

Integrated LTE and Millimeter-Wave 5G MIMO Antenna System for 4G/5G Wireless Terminals.

This work demonstrates an integrated multiple-input multiple-output (MIMO) antenna solution for Long Term Evolution (LTE) and Millimeter-Wave (mm-wave) 5G wireless communication services. The proposed structure is comprised of a two-element LTE MIMO antenna, and a four-element 5G MIMO configuration with rectangular and circular defects in the ground plane. For experimental validation, the proposed structure is fabricated on a Rogers RO4350B substrate with 0.76 mm thickness. The overall substrate dimensions are 75 mm × 110 mm. The proposed structure is capable of operating at 5.29–6.12 GHz (LTE 46 and 47 bands) and 26–29.5 GHz (5G mm-wave) frequency bands. Additionally, the measured peak gain of 5.13 and 9.53 dB is attained respectively for the microwave and mm-wave antennas. Furthermore, the analysis of the MIMO performance metrics demonstrates good characteristics, and excellent field correlation performance across the operating bands. Furthermore, the analysis of the Specific Absorption Rate (SAR) and Power Density (PD) at the lower frequency band (5.9 GHz) and PD only at mm-Wave frequency band (28 GHz) verifies that the proposed antenna system satisfies the international human safety standards. Therefore, the proposed integrated MIMO antenna configuration ascertains to be a potential contender for the forthcoming communication applications.

Mutual coupling reduction using near‐zero ε and μ metamaterial‐based superstrate for an MIMO application

Here, a near-zero permittivity (ε) and permeability (μ) metamaterial superstrate is presented as a decoupling structure for a multiple-input–multiple-output (MIMO) antenna. The proposed design offers peak isolation of 41 dB with reduced edge separation of 0.042λo at the resonating frequency. To verify the simulation results, the prototype of the proposed superstrate and antenna is fabricated and tested. The two-element MIMO antenna has −10 dB impedance band of 5.5–5.92 GHz with a peak measured gain of 7.41 dBi and efficiency above 78%. The measurement results ensure an isolation enhancement of 30 dB with a correlation coefficient of <0.26 within the operating band. The proposed method offers a good design technique for high gain and a closely packed MIMO antenna system for WLAN applications.

Highly isolated dual band stop two-element UWB MIMO antenna topology for wireless communication applications

A novel compact Ultra Wide Band (UWB) Multiple Input Multiple Output (MIMO) antenna with dual filtering property is proposed. Two monopole antennas with W-shaped and n-shaped slots on their radiating patch are arranged vertically to form the MIMO antenna topology. Each monopole is composed of a slotted radiating patch and a simple ground plane which yield band stop feature in Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Local-Area Network (WLAN) frequency band. In the sequel, to enhance the isolation, a parasitic structure has been wiely embedded between two monopole antennas. Applying the aforementioned decoupling structure improves the isolation level from -17dB to -22dB. The proposed two-element MIMO antenna with vertical arrangement, covers UWB frequency range from 3.1 to 10.6 GHz with notches at WiMAX (3.3–3.8 GHz) and WLAN (5–6 GHz) bands. The inter element isolation is less than -22 dB and in most cases even is less than -25 dB over the entire operating frequency band. The obtained simulated and measured results confirms suitable good matching acceptable Envelope Correlation Coefficient (ECC), efficiency, group delay, and radiation patterns. All these gurantrees a promising performance for the proposed MIMO antenna.

Isolation enhancement of MIMO antennas using shorting pins

ABSTRACTThis paper provides an effective technique to reduce the mutual coupling between two adjacent probe-fed microstrip antenna elements operating at 3.5 GHz in multiple input multiple output (MIMO) configurations. The required reduction in the mutual coupling is achieved via loading of six metallic pins near the adjacent edges of two square patch radiators to ground the radiating elements in order to alter the polarization of the antennas. The two radiating elements are closely spaced with an edge-to-edge separation of 0.012λo and a centre-to-centre separation of 0.027λo. The idea is to make the two antennas orthogonal in terms of polarization via loading of shorting pins at appropriate locations. In order to validate the proposed technique, a two-element MIMO antenna is designed, fabricated, and measured. A good agreement between measurement and simulation is observed. Simulated and measured results are used to analyse the performance of the proposed technique in terms of mutual coupling between the two ports, radiation pattern, and realized peak gain. The measurement results show that the isolation between the two elements is enhanced from 2.8 dB to 20 dB at around 3.5 GHz.

A miniaturized multi-wideband Quasi-Yagi MIMO antenna system

A multi-band directional multiple-input–multiple-output (MIMO) antenna system is presented based on a rectangular loop excited Quasi-Yagi configuration. A 64% reduction in size is obtained using a rectangular meandered element as well as a small ground plane. The proposed two-element MIMO antenna system covers the Telemetry L-band and several LTE/WLAN bands. It has a wide measured bandwidth of 689 MHz (1.897–2.586 GHz) in the desired band centered at 2 GHz, and a measured bandwidth of more than 168 MHz across rest of the bands. The MIMO antenna system has a total size of 45 × 120 × 0.76 mm3, with a single element size of 55 × 60 × 0.76 mm3. The non-desired back-lobe radiation which is obtained using a small ground plane, is significantly reduced by using a novel defected ground structure (DGS) as compared with the complex techniques present in literature. The proposed DGS provides a high measured front-to-back ratio of 14 dB at 2 GHz and 11 dB in other bands. A maximum measured realized gain of 5.8 dBi is obtained in the desired band using a single parasitic director element. The proposed MIMO antenna system has a minimum measured radiation efficiency of 70%, isolation of 12 dB, and envelope correlation coefficient of 0.098 within all bands which ensures very good MIMO performance.

An Integrated Dual MIMO Antenna System With Dual-Function GND-Plane Frequency-Agile Antenna

In this letter, an integrated multiple-input–multiple-output (MIMO) antenna system is presented. The proposed design consists of a two-element printed inverted F-shape (IFA) MIMO antenna integrated with a two-element frequency-agile annular slot-based MIMO antenna system. The IFA operates at the WLAN band, while the annular slots act as an isolation enhancement structure between the two IFA elements. Furthermore, the annular slots are tuned over the bands from 1.73 to 2.28 GHz with a minimum bandwidth of 60 MHz. The slots are made reconfigurable using varactor diodes. The integrated MIMO antenna system is designed on commercially available FR-4 substrate with dimensions $\text{50} \times \text{110} \times \text{1.56}\,\text{mm}^{3}$ . All the antenna elements are of small size, low profile, and planar in structure and hence can easily be accommodated in wireless devices for second-generation cognitive radio applications.

A Two Concentric Slot Loop Based Connected Array MIMO Antenna System for 4G/5G Terminals

In this paper, an integrated design with a multiple-input multiple-output (MIMO) antenna system for fourth generation (4G) and fifth generation (5G) applications is presented. The proposed design contains a two-element slot-based MIMO antenna system for 4G and a connected antenna array (CAA)-based two-element MIMO antenna system for a potential 5G band. Two rectangular loops are etched on the periphery of the ground plane. The top and bottom portions of the thin loops act as the two 4G MIMO antennas, while parts of their sides are acting as 5G arrays. The antenna system is fabricated on a commercially available Roger 4350 substrate with $\epsilon _{r}$ equal to 3.5, while the dimensions of the board are $100\times 60 \times 0.76$ mm3 representing a typical smart phone back plane size. The integrated antenna system covers multibands at 4G with a combined bandwidth of 1.565 GHz (−6 dB BW) in addition to the band between 16.50 and 17.80 GHz for 5G. The design is planar, low profile, simple, and compact in structure making suitable for wireless handheld devices and mobile terminals. The measured gain at 3.46 GHz was at least 2.22 dBi and at 17 GHz was 8 dBi for the 4G and 5G MIMO antenna systems, respectively. The envelope correlation coefficient was also calculated from the measured 3-D patterns and showed good MIMO performance. This is the first integrated 4G/5G MIMO antenna system with below 6 GHz and above 10-GHz covered bands using CAA.

Compact and closely spaced tunable printed F‐slot multiple‐input–multiple‐output antenna system for portable wireless applications with efficient diversity

In this work, miniaturised tunable two-antenna multiple-input–multiple-output (MIMO) systems composed of printed F-slot shaped are developed to operate in the global positioning system (GPS), personal communication system (PCS), distributed control system and Universal Mobile Telecommunications System bands. The two-element MIMO antenna occupies a volume of 50 × 37.5 × 1.6 mm3, and is printed on an FR4 substrate. Initially, the frequency tunability of the MIMO antennas was verified by lumped capacitors with values between 0.75 to 2.75 pF to achieve a tuning range from 1.55 to 2.07 GHz while the low mutual coupling between the radiators was accomplished by adding an I-shaped branch to a cut-away ground plane. The two antennas are then loaded with varactors to simultaneously achieve miniaturisation and tunability. Simulation and measurement results demonstrate the successful implementation of a tunable MIMO with coupling reduction mechanism for a portable handheld wireless transceiver. The channel capacity of the proposed antenna is investigated and found to be close to that of a un-correlated system with efficient diversity in which the mutual coupling across the full bandwidth was better than −13 dB. Owing to the compact size and ease of manufacture, the proposed antennas can be a promising solution for adaptive MIMO systems in handheld devices.

DESIGN OF A COMPACT TWO ELEMENT MIMO ANTENNA SYSTEM WITH IMPROVED ISOLATION

A novel compact two-element MIMO (Multiple Input Multiple Output) antenna system operating from 6.1-7.8 GHz is proposed for wireless applications. The developed antenna system resonates at 6.8 GHz frequency, giving an impedance bandwidth of 25% (based on S11 < �10 dB). An efficient technique is proposed to reduce the mutual coupling developed in the antenna system by employing a simple microstrip patch element in between the antennas. Using the proposed method, the mutual coupling is reduced to around �33 dB at the resonant frequency and maintaining the overall mutual coupling less than �20 dB in the operating band. The experimental models are developed for both the MIMO systems, i.e., without and with patch element between the antennas and the results are compared with simulated results. Also, Envelope Correlation Coefficient (ECC) between the two antennas is calculated and compared.