Multi-input Multi-output Antenna System Research Articles

Comprehensive review of isolation techniques in MIMO antennas for 5G mobile devices

Recently, due to the fast development in multimedia applications of wireless communication systems and the urgent demands of increasing the capacity and data rates to meet the requirements of 5G mobile communication systems, new transmission techniques are needed. One of the powerful enabling tools of the 5G communication systems is the Multi-Input Multi-Output (MIMO) antenna system employing multiple antennas and utilizing the multipath fading mobile environment to increase the channel capacity without any additional bandwidth and/or transmitted power. However, because of the limited space of the mobile devices, the distances between antennas are decreased. The mutual coupling between antennas severely affects the overall performance of the MIMO system. So, isolation improvement methods are applied to reduce these influences. In this review, the different isolation techniques and their features and drawbacks are presented, and the techniques for applying them in modern MIMO antenna systems are illustrated. Besides, the performance characteristics of these MIMO systems are compared. The review contains also the basic concepts of the MIMO antenna system and its performance metrics. Finally, the future directions and trends for the MIMO antenna system design are discussed briefly.

Multi-Input Multi-Output Antenna Array Design for 5G N78 Applications in Smartphones

This article presents a compact, high isolation Multi Input Multi Output (MIMO) Antenna system operating on (3408-3760) MHz for the fifth generation N78 Applications in mobile phone terminals. The suggested MIMO antenna system is built from four antenna elements. These antennas are placed over two slim side borders of a mobile device's frame to adhere to the current trend of slim and full-screen smartphone devices. The antenna element is composed of two parts: the front part and the back part. The front part consists of the second iteration of Moore curve fractal geometry and an I-shaped feeding line. The back part is of an L-shaped shorted to the system’s ground plane. The desirable antenna diminishment is accomplished based on Moore curve fractal geometry. Low mutual coupling among antennas is attained based on self-isolated and spatial diversity methods, which are less than -16.6 dB. The scattering parameters, antenna gains, antenna efficiencies, and radiation pattern characteristics have all been examined to gauge the performance of the suggested antenna element. In addition, the MEGs and ECCs are examined to understand the MIMO performance of the suggested system. The proposed four-element MIMO antenna system achieves the desired antenna and MIMO characteristics, making it a strong contender for the upcoming 5G mobile devices.

Dual-Band (28/38 GHz) Compact MIMO Antenna System for Millimeter-Wave Applications

The present work proposes a novel design of a dual-band-printed antenna for operation at the millimeter-wave frequencies 28 and 38 GHz that are utilized for the modern and future generations of mobile communications. The antenna is composed of two radiating elements. The first element is the main patch that is fed through a microstrip line with inset feed, and the second element is a parasitic element that is fed through capacitive coupling with the main patch. The design parameters of the proposed antenna are optimized through a complete parametric study to give excellent impedance matching at 28 GHz over the band 27.7–28.3 GHz and at 38 GHz over the band 37.7–38.3 GHz. The surface current distributions at the two operational frequencies are investigated. The designed antenna is used to construct a four-port efficient multi–input–multi–output (MIMO) system. The MIMO system performance is investigated regarding the envelope correlation coefficient (ECC), diversity gain (DG), and the channel capacity loss (CCL) showing very good performance. The single-element antenna and the MIMO are fabricated and experimentally evaluated showing excellent impedance matching over the lower and higher frequency bands, which come in agreement with the simulation results. It is shown that the antenna produces maximum gain of 7.4 and 8.1 dBi at 28 and 38 GHz, respectively. The average radiation efficiencies of the proposed antenna are 88% and 88.8% over the lower and higher frequency bands, respectively. In addition, the coupling coefficients between the MIMO antenna systems are measured experimentally showing very low coupling values resulting in an efficient MIMO system that is suitable for future millimeter-wave (mm-wave) applications.

Quad-Element MIMO Antenna System Using Half-Cut Miniaturized UWB Antenna for IoT-Based Smart Home Digital Entertainment Network

This work presents a miniaturized quad-element multi-input multi-output (MIMO) antenna with low mutual coupling, inherent isolation, and easy upgradability for an Internet of Things (IoT) based high-speed smart digital entertainment network using ultra-wideband (UWB) technology. Ultra Wideband (UWB) technology is anticipated to play a significant role in the future IoT based smart systems due to its ability to provide high precision location information, low power consumption, high data rates and secure communication. An elliptical quadrant-shaped radiator with a C-shaped protuberant ground plane is conceptualized as a quasi-monopole UWB antenna following the half-cut miniaturization approach with very compact dimensions of 18W11 mm2. The elliptical quadrant radiator in combination with C-shaped ground plane introduces multi-resonance characteristic in addition to providing better impedance matching with miniaturization and inherent high isolation for MIMO configuration. The single element antenna is then organized in an orthogonal arrangement with an edge-to-edge distance of 5 mm to develop a quad-element MIMO antenna system. The MIMO antenna structure realizes a wide bandwidth of 3.14-11.23 GHz (center frequency at 7.19 GHz), peak gain of 7.2 dBi, and radiation efficiency of above 60% with good isolation (>-20 dB) between the adjacent elements without employing any dedicated decoupling structure. The diversity performances of the proposed MIMO antenna are relatively good, with a very low envelope correlation coefficient (ECC) of less than 0.35 and diversity gain (DG) nearly at 10. Further, the total active reflection coefficient (TARC) <-10 dB and channel capacity loss (CCL) <0.4 bit/s/Hz, parameters are witnessed to be within acceptable limits. The simulated and measured results agree well, testifying that the proposed four-element MIMO antenna is suitable for UWB applications.

Circularly polarized MIMO filtering dielectric resonator antenna for 5G sub-6 GHz applications

This research presents an innovative hexagonal dielectric resonator antenna (DRA) with circular polarization and multi-input multi-output (MIMO) characteristics. The DRA consists of two dielectric layers, providing a fractional bandwidth of 9% (4.05 to 4.38 GHz).The antenna ground plane features has an S-shape slot, when coupled with a 50Ω microstrip line, enables the generation of right-hand circular polarization. To enhance performance, the feed line includes a bandpass filter with a semi-elliptical form, resulting in outstanding selectivity. The proposed design demonstrates a gain of 9.2 dBi and encompasses a 3 dB axial ratio bandwidth of 9.29%. The proposed design is fabricated, and a comparison is made between the simulated and the measured results. Furthermore, the study introduces a MIMO antenna system by combining two filter arrays. The MIMO antenna demonstrates a reasonable port isolation of >25 dB across the operating band with acceptable MIMO parameters.

MIMO antenna array with the capability of dual polarization reconfiguration for 5G mm-wave communication

This communication presents a polarization reconfigurable antenna array (PRAA) with Multi-input Multi-output (MIMO) formation for 5th generation (5G) millimeter wave (mm-Wave) communications. At first a single corner curtailed diagonal slotted cylindrical patch is printed on Roger RT Duriod 5880 and the overall size of the single antenna is 12 × 12 × 0.787 mm3. The circular polarization (CP) is realized by adding the diagonal slot in the circular patch. The antenna design is extended into two elements antenna array which occupies 20 × 20 × 0.787 mm3 footprint. The collection is formed using a T-shaped power divider/combiner. Pin-diodes are integrated with the patches to switch the polarization state between LP (Linear polarization) and CP radiation. The edge-to-edge distance between antenna elements is 6 mm. The design covers the 25.2–29.4 GHz band, and the maximum peak gain is 11.5 dBi. Moreover, a two-port (2 × 2) MIMO design is formed to increase the channel capacity. To isolate the ports, a sin-like slot is engraved in the ground, defected ground structure (DGS) technique of mutual coupling reduction; it can easily be implemented and increases the design efficiency. The port isolation is well above 30 dB for the entire operating band. Moreover, the Mean Effective Gain (MEG), Diversity Gain (DG), and Envelope Correlation Coefficient (ECC) are investigated, which are key performance metrics of MIMO. A prototype of the realized MIMO antenna system is fabricated, and the simulated outcomes carried out by Computer Simulation Technology (CST) tools are validated by experimental findings.

A Compact Self-Isolated MIMO Antenna System for 5G Mobile Terminals

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.

Quad-Band MIMO Antenna System for 5G Mobile Handsets

An efficient Multi-Input Multi-Output (MIMO) antenna system with a spatial diversity configuration for the Fifth Generation (5G) mobile handsets is constructed from a compact-size quad-band (28/45/51/56GHz28/45/51/56⁢GHz) microstrip patch antennas. The antenna is constructed as primary and secondary patches which are capacitively coupled and designed to realize impedance matching and to produce appropriate radiation patterns in the four frequency bands. The novel quad-band patch antenna includes complicated radiation mechanisms required for multiple-band operation. Two-port and four-port MIMO antenna systems that employ the quad-band patch antenna are proposed in the present work for the 5G mobile handsets. Numerical and experimental investigations are achieved to assess the performance of both the single-element antenna and the proposed MIMO antenna systems including the return loss at each antenna port and the coupling coefficients between the different ports. It is shown that the simulation results agree with the experimental measurements and both show good performance. The bandwidths achieved around 2828, 4545, 5151, and 5656 GHzGHz are about 0.60.6, 2.02.0, 1.81.8, and 1.31.3 GHzGHz, respectively. The radiation patterns produced when each port is excited alone are shown to be suitable for spatial diversity scheme with high radiation efficiency. It is shown that the envelope correlation coefficient (ECC) and the diversity gain (DG) are perfect over the four frequency bands.

Compact closed‐slot eight‐antenna system for 5G laptops with a metal back cover

SummaryThis paper presents the design of a compact closed‐slot sub‐6‐GHz dual‐band eight‐antenna system on a 5G laptop with a metal back cover. The antenna system is installed in a 277 × 2 mm2 clearance area that is 3 mm below the upper edge of the metal back cover of the laptop. Each single closed‐slot antenna element measures 32 × 2 mm2 and features an inverted‐C feeding section and a crossover path consisting of a meandered section and a series chip capacitor. The crossover path can help generate a resonance mode at high frequencies while adjusting the frequency location of the low‐frequency mode, allowing the closed‐slot antenna to support the 3300‐ to 3600‐ and 4800‐ to 5000‐MHz dual‐band operation required for sub‐6‐GHz 5G. The eight closed‐slot antenna elements are oriented in the same direction and aligned in the same axis with a 3‐mm separation between any two adjacent antenna elements. Without the help of any isolation elements, the resultant eight‐element multi‐input multi‐output (MIMO) antenna system possesses measured isolations of larger than 10 dB. The envelope correlation coefficients (ECCs) calculated from the measured complex radiation patterns are all less than 0.105, and the measured antenna efficiencies are over 40%. These results indicate that the proposed MIMO antenna system is ideal for use in laptop devices with a metal back cover and a large screen‐to‐body ratio.

Five-port MIMO antenna for n79-5G band with improved isolation by diversity and decoupling techniques

A compact five-port multi-input multi-output (MIMO) antenna for n79 (4.4–5 GHz) 5G band exhibiting pattern and polarization diversity with good isolation is proposed in this paper. This MIMO antenna system comprises of four linearly polarized (LP) endfire monopole antenna elements and one broadside L-shaped slot circularly polarized (CP) antenna element, which provides both pattern and polarization diversity. A T-shaped slot as a decoupling structure is further used to improve the interport isolation by 4 dB. The return loss bandwidth for all antenna elements is in the desired frequency range, and antenna elements provide isolation better than 23 dB. The pattern and polarization diversity provide a low envelope correlation coefficient and good isolation between any two-port of the MIMO antenna. For experimental verification, the proposed 5-port MIMO antenna system is fabricated and measured, which provides decent agreement with the simulated performance.

A 2 × 1 array‐based wideband mm‐wave antenna integrated with a 2‐element multiple‐input‐multiple‐output antenna for 5G mobile terminals

A novel wideband millimeter (mm)-wave antenna integrated with a multi-input multi-output (MIMO) antenna is presented for fifth-generation (5G) applications. The proposed model consists of a 2 × 1 array-based single-element wideband antenna for mm-wave applications, and a 2-element strip-based MIMO antenna system for sub-6-GHz band applications. In the ground plane, two clearance regions were etched to improve the impedance matching of MIMO elements while an open-circuit rectangular tuning stub is attached to the mm-wave antenna feed line to broaden its impedance bandwidth. The dimensions of the used panel are 100 × 60 × 0.8 mm3, which are among the typical dimensions used in mobile terminals. The mm wave antenna covers the frequency ranges from 25.08 to 28.08 GHz, while the frequencies from 2.88 to 4.58 GHz and from 5.15 to 6.15 GHz are covered by the MIMO antenna. Depending on the experimental results achieved, the suggested design might be considered a successful candidate for 5G applications, with wideband characteristics, excellent field correlation, and high gain functionality.

Compact Sub-6-GHz Four-Element MIMO Slot Antenna System for 5G Tablet Devices

A sub-6-GHz four-element multi-input multi-output (MIMO) slot antenna system was proposed in this study for fifth-generation (5G) tablet computers, where each antenna element was constructed using a slot structure. To effectively use the available space in a tablet and maximize the screen, we have deployed the MIMO antenna system on the left side-edge frame of the tablet. The MIMO antenna system measuring $37.2\times7$ mm2 consists of two identical $13.6\times7$ mm2 dual-slot-antenna units that are separated by 10 mm. The two closely spaced slot antennas in the same dual-slot-antenna unit are arranged asymmetrically mirrored of each other with respect to the system ground plane. Although the dual-slot-antenna unit is very compact, the isolation between the two slot antennas in the same unit can be enhanced by using an ungrounded full-wavelength strip resonator. With the two ungrounded resonators in the MIMO slot antenna system, the simulated intra-unit isolations at the mid-band frequency can be enhanced by about 3.5 dB to meet the design requirement. As a byproduct, the two ungrounded resonators in the MIMO antenna system can also enhance the simulated mid-band antenna efficiency by about 4.5% and lower the worst simulated ECC by 0.195, from 0.518 to 0.323. This MIMO antenna system can support the frequency band of 3400–3600 MHz for 5G. In the operating band, the measured isolation is larger than 11 dB, and the measured antenna efficiency is larger than 40%. The envelope correlation coefficients (ECCs) calculated from the measured complex E-field radiation patterns are all smaller than 0.23, making the proposed design suitable for 5G mobile communications that require fast transmission.

Compact Eight-Element Antenna Array for Triple-Band MIMO Operation in 5G Mobile Terminals

In this paper, we have introduced a compact eight-element antenna array for triple-band MIMO (multi-input multi-output) operation in 5G (fifth generation) mobile terminals, which consists of two symmetric four-element sub-arrays disposed, respectively, along two long side-edges of the system ground plane of the mobile terminal. This antenna element can operate at two dual-wideband of 3250-3820 MHz and 4790-6200 MHz with three resonance frequencies which can fully cover 5G NR (New Radio) BandN78 (3300-3800 MHz), China 5G-Band of 4800-5000 MHz and LTE Band-46 (5150-5925 MHz). The main parameters that characterize the performance of the proposed MIMO antenna system, such as bandwidth, reflection coefficient, isolation (more than 10.5 dB), total radiation efficiency (more than 43%), ECC (envelope correlation coefficient, less than 0.12) and CC (channel capacity, 34.9-37.6 bps/Hz), are analyzed and presented in this paper. Besides, the effects of single-hand and dual-hand on performance of the MIMO antenna system are also discussed. The structure of antenna element is only 15 mm × 3 mm (0.175 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.035 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at the frequency of 3.5 GHz) with a very small ground clearance of 13 mm × 2 mm on the main board of the proposed mobile terminal. The antenna system has the possibility to be used in 5G mobile terminals with triple-band operation, narrow frame and large display. The corresponding antennas prototype is fabricated and measured; and a quite good agreement between simulation and measurement is obtained.

3.5-GHz four-element MIMO antenna system for 5G laptops with a large screen-to-body ratio

ABSTRACT This paper proposes a 3.5-GHz four-element multi-input multi-output (MIMO) antenna system for fifth-generation (5G) laptops. The four antennas are configured into two dual-antenna units, measuring 26 × 3 × 2 mm3 each and separated by a distance of 6 mm, the latter of which accounts for the isolation between the two units. The two antennas in each unit are located on the two sides of the same substrate and are both three-dimensional inverted-F antennas (IFAs) of the same size, but are deployed to be skew-symmetric with respect to the top edge of the display ground. With a decoupling neutralization line connecting the two antennas in the same unit, the simulated isolation between them is enhanced by up to 8 dB. Within the operating frequency band, its measured isolation exceeds 12 dB, the simulated electric field ECC (envelope correlation coefficient) is smaller than 0.15, and the measured realized radiation efficiency is more than 40%.

POLARIZED DIVERSITY COMPACT PLANAR MIMO ANTENNA FOR WIRELESS ACCESS POINT APPLICATIONS

In this paper, a wideband polarization diversity multi-input multioutput (MIMO) antenna system is proposed. The structure of the proposed antenna consists of four wideband coplanar waveguide (CPW)-fed monopole antennas with a common ground plane and radiated element. The simulated and measured -10 dB impedance bandwidth is 20% (2.25-2.75 GHz), which covers WiFi (2.4 GHz) and LTE (2.6GHz) frequency bands. The MIMO antenna system is applied to both an indoor and outdoor wireless access point (WAP) at the covered frequency bands. Due to the common structure of elements in the proposed MIMO antenna, an acceptable mutual coupling between the antennas ports is critical. Hence, a new parasitic element structure is presented to improve mutual coupling between the antenna ports. Acceptable values for the coupling coefficient (< -14 dB) are achieved by adding the parasitic element. The presented antenna system provides a nearly omnidirectional radiation pattern with an orthogonal mode of linear polarization. The results show a polarization diversity gain of 10 dB and an envelope correlation coefficient of less than 0.2. Moreover, each antenna port possesses peak gains of 5.33-6.97 dBi and efficiencies of 51.5-57%. A comparison between the simulation results and experimental measurements reveals good agreement between the two, confirming the validity of the proposed design.

On Reusing Pilots Among Interfering Cells in Massive MIMO

Pilot contamination, caused by the reuse of pilots among interfering cells, remains a significant obstacle that limits the performance of massive multi-input multi-output antenna systems. To handle this problem, less aggressive reuse of pilots involving allocation of additional pilots for interfering users is closely examined in this paper. Hierarchical pilot reuse methods are proposed, which effectively mitigate pilot contamination and increase the net throughput of the system. Among the suggested hierarchical pilot reuse schemes, the optimal way of assigning pilots to different users is obtained in a closed-form solution, which maximizes the net sum-rate in a given coherence time. Simulation results confirm that when the ratio of the channel coherence time to the number of users in each cell is sufficiently large, less aggressive reuse of pilots yields significant performance advantage relative to the case, where all cells reuse the same pilot set.

M-ary OSTBC MIMO 시스템의 성능 연구

Performance of the Alamouti algorithm based M-ary OSTBC(Orthogonal Space Time Block Coded) MIMO(Multi Input Multi Output) system has been simulated varying two main parameters - the number of constellation(M), and the number of receiving antennas(N). Computer simulation has also been carried out using Matlab software for performance comparison between MIMO and MRC(Maximal Ratio Combining) diversity antenna system to evaluate the degree of enhancement achieved through the use of Alamouti MIMO. Under 10 dB EbNo QPSK scenario, MIMO brought 4.2 dB BER improvement over single antenna system and MIMO resulted in 7.4 dB BER improvement over MRC.

Wideband MIMO antenna system with dual polarization for WiFi and LTE applications

In this paper a wideband multi-input multi-output (MIMO) antenna system for WiFi-LTE wireless access point (WAP) application is proposed. The MIMO antenna system consists of two common element microstrip-fed monopole antennas with dual polarization. Physically closed integration of MIMO antenna elements requires a special technique to increase the isolation between the antennas. A novel structure of parasitic element is introduced to improve the isolation between the antennas. The proposed MIMO antenna system is simulated and optimized using CST Microwave Studio. The designed antenna system is fabricated and measured to verify the simulation results. Reflection coefficient of less than −10 dB and isolation more than 15 dB are achieved in the operating frequency range of 2.3–2.9 GHz which covers WiFi 2.4 GHz and LTE 2.6 GHz bands. The proposed system also provides dual polarization with 10 dB polarization diversity gain and envelope correlation coefficient less than 0.15. Each individual antenna has a gain of 5.1 dB and 68% efficiency.

Review of Space-time Coded Orthogonal Frequency Division Multiplexing Systems for Wireless Communication

Deployment of multi-input multi-output antenna systems with orthogonal frequency division multiplexing (OFDM) over wireless channels has been identified as one of the most promising techniques to support high-performance and high data rate communication for future wireless broadband services. This paper first highlights common space-time coding (STC) schemes used in wireless communication systems. The paper further reviews the deployments of these STC schemes over frequency selective fading channels with OFDM signalling through which there is coding over the space, time, and frequency domains.

Antenna Array Optimization Using Dipole Models for MIMO Applications

A very fast and efficient method for designing compact antenna arrays preserving the maximum channel capacity of multi input multi output (MIMO) systems using infinitesimal dipole model (IDM) theory is presented. Using this method each antenna element is replaced by a set of infinitesimal dipoles producing the same electric fields of the antenna. The recently introduced Invasive weed optimization (IWO) algorithm is employed to find the infinitesimal dipole models. The algorithm is applied to a planar inverted F-antenna designed as an element of a compact array for MIMO applications. Using the obtained IDMs, self and mutual admittances between the antennas are predicted. Therefore, correlation coefficients of the MIMO array system are achieved using S-parameters. Having the correlation of the system, the location and orientation of each antenna are optimized to find the minimum correlation value for the MIMO antenna system. Using the optimization technique, very low cross correlation coefficient is obtained for very close antennas over a finite ground plane.