MIMO Antenna Array Research Articles

Wideband MIMO Antenna Array Design for Future Mobile Devices Operating in the 5G NR Frequency Bands n77/n78/n79 and LTE Band 46

An eight-antenna array with wideband operation for future 5G New Radio mobile devices is studied. Each array element is composed of an inverted-F antenna with shorting branches and parasitic elements. The driving element (monopole structure) and the shorting element (inverted-L branch and inverted-C branch) enable the antenna to obtain multiple modes, whereas the parasitic element, open slit, and stub can improve the impedance matching. The 6 dB impedance bandwidth of the proposed eight-antenna array can completely cover the 5G Sub-6 GHz NR frequency Bands n77/n78/n79, which include the 5G band of U.S. (3.55–4.2 GHz), China, EU, and Japan (3.6–4.2 GHz and 4.4–4.9 GHz), as well as the LTE Band 46 (5.15–5.925 GHz). From the measured results, the isolation between adjacent array elements is lower than 10 dB and its corresponding envelope correlation coefficient is also lower than 0.1.

A Lumped-Element Decoupling and Matching Network for a Four-Element Mobile Handset MIMO Antenna

This paper presents the first realization of a lumped-element decoupling and matching network (DMN) for more than two-element mobile MIMO arrays. The realization of the DMN is based on an existing method, which is improved in terms of bandwidth and the number of network elements. The array is designed to operate in the 2.6–2.7 GHz LTE band. The DMN is applied to a four-element MIMO antenna array located on one side of the mobile phone chassis. The array initially has a strong coupling of −3 dB, which is improved to −7 dB with the DMN. In other words, this denotes a reduction of 30 percentage points in coupled power. The DMN also improves the total efficiency by 21 percentage points at best.

Quasi-optics-inspired low-profile endfire antenna element

In this paper, the design, operational principle and experimental validation of an endfire antenna element that is inspired by the energy-focusing characteristics of graded-index optical fibre are presented. The antenna operates with a bandwidth of 1.5 GHz centred around 14 GHz. It has a gain of around 5.5 dBi along the band of interest and a good pattern stability over the band. The antenna derives its unique nature from the arrangement of the arc-shaped parasitics, that couple onto the antenna´s driver dipole. An electromagnetic refractive index retrieval mechanism is used to guide the placement of the parasitics to enhance the gain. In addition to the design principle, a parametric study of the main parameters and their influence on the antenna behaviour is presented. The antenna is a potential candidate for use in multi-user massive MIMO antenna arrays for 5G communications where space is premium and in antenna array applications where a low-profile antenna element with a high gain is a necessity.

Mutual Coupling Suppression With Decoupling Ground for Massive MIMO Antenna Arrays

A concept of decoupling ground is introduced in this paper to enhance the isolation of massive MIMO antenna arrays. For an array, mutual coupling between array elements can be achieved by the free-space coupling and the coupling currents flowing on the ground plane shared by elements. The isolation in this paper is improved by adjusting the shape of the ground plane under each element to make the mutual coupling from the free space and the ground plane out of phase. In this way, low mutual coupling is realized. As the first example, a single-polarization linear array with eight elements is designed, simulated, and measured to verify the concept as well as the simulation accuracy. The measurements align very well with the simulations. Another two examples of dual-polarization 2×2 and 4×4 square arrays are also given and simulated to demonstrate the effectiveness of the proposed technique. In all of these examples, the isolation can efficiently be enhanced with the DG for all the co-polarization and cross-polarization coupling paths of the massive MIMO elements. Compared with the previous literature, the arrays with the DG method can achieve either much better isolation or a much lower profile while keeping the other performance comparable.

A Dual-Band MIMO Antenna With Enhanced Isolation for 5G Smartphone Applications

In this paper, a compact dual-band MIMO antenna array for 5G smartphone applications is proposed. The MIMO antenna consists of eight folded monopole antennas operating at 3.45-GHz band (3300~3600MHz). And the antenna elements with a size of $6.8\times 6.6\times4$ mm3 (about $0.078\lambda \times 0.075\lambda \times 0.046\lambda $ at 3.45 GHz), are disposed along each edge of the system circuit board. By introducing the decoupling structures, the isolation between inner antenna elements is improved from 10dB to 15.1dB in 3.45-GHz band (3300~3600MHz). Meanwhile the inner antenna units can generate an additional operating band covering 2400~2700MHz due to the coupling effect between the antenna elements and the proposed decoupling structures, which is promising for solving the problem of terminal space shortage. To verify the design principle of the proposed MIMO antenna array, the antenna is fabricated and measured. The measured results of efficiency and ECC are analyzed as well to demonstrate the performance of the proposed MIMO array. Channel capacity, user proximity and SAR analysis and are also given in this paper.

The Effects of Increasing Antenna Arrays for MIMO in Mine Tunnels

The aim of this paper is to prove theoretically by using waveguide and geometrical optical models that increasing MIMO array elements at the transmitter and receiver will have a limit on capacity where the equivalent spatial subchannels can be limited by the number of allowable modes.

The MIMO Antenna Array with Mutual Coupling Reduction and Cross-polarization Suppression by Defected Ground Structures

The MIMO Antenna Array with Mutual Coupling Reduction and Cross-polarization Suppression by Defected Ground Structures

Compact 3‐D eight elements UWB‐MIMO array

AbstractAn eight elements, compact, ultra‐wideband multiple‐input‐multiple‐output (MIMO) 3‐D antenna array is reported. The proposed antenna system consists of eight monopole radiators, four elements are designed in planar configuration and four elements are placed perpendicularly to the planar configuration. Four elements are provided with a U‐shaped slot to match the input impedance over the entire bandwidth. All the monopoles are placed strategically to exploit polarization diversity which is believed to improve isolation. Good impedance matching and isolation higher than 15 dB are observed over the 3‐11 GHz frequency range. The proposed MIMO antenna array has a total size of 50 50 25 mm3 and measurements of prototype printed on a 1.524 mm thick Rogers TMM4 laminate resulted in good agreement with full wave numerical simulations. The proposed design provides high degree of isolation without compromise on compactness and also operated over wideband.

A Meta-Surface Antenna Array Decoupling (MAAD) Method for Mutual Coupling Reduction in a MIMO Antenna System

In this paper, a method to reduce the inevitable mutual coupling between antennas in an extremely closely spaced two-element MIMO antenna array is proposed. A suspended meta-surface composed periodic square split ring resonators (SRRs) is placed above the antenna array for decoupling. The meta-surface is equivalent to a negative permeability medium, along which wave propagation is rejected. By properly designing the rejection frequency band of the SRR unit, the mutual coupling between the antenna elements in the MIMO antenna system can be significantly reduced. Two prototypes of microstrip antenna arrays at 5.8 GHz band with and without the metasurface have been fabricated and measured. The matching bandwidths of antennas with reflection coefficient smaller than −15 dB for the arrays without and with the metasurface are 360 MHz and 900 MHz respectively. Using the meta-surface, the isolation between elements is increased from around 8 dB to more than 27 dB within the band of interest. Meanwhile, the total efficiency and peak gain of each element, the envelope correlation coefficient (ECC) between the two elements are also improved by considerable amounts. All the results demonstrate that the proposed method is very efficient for enhancing the performance of MIMO antenna arrays.

A 5G MIMO Antenna for Broadcast and Traffic Communication Topologies Based on Pseudo Inverse Synthesis

This paper proposes a new design of a dual-polarized base station antenna for sub-6-GHz 5G communication covering the band from 3.3 to 3.8 GHz. The proposed antenna offers a good impedance matching across the desired frequency band with $\text {VSWR} \le 1.5$ , a stable radiation pattern with a half power beam width of 65° ± 5°, and a high isolation between the ports with a small size and a low profile. The antenna is converted to a planar MIMO antenna array with low envelop correlation coefficients between the array elements to perform in either a broadcast or traffic communication topology whenever required. In the broadcast communication topology, the proposed MIMO antenna array covers a sector of 65° in the horizontal plane with three different down-tilted beam directions at 0°, 10°, and 20° in the vertical plane as conventional base station antennas used for 2G, 3G, and 4G. In traffic topology, the proposed MIMO antenna array can direct multiple beams to concurrent multiple users in a point-to-multipoint communication based on a novel pseudoinverse synthesis (PIS). The novel PIS is proved to be better than the other approaches which use spatial or frequency diversity as it possesses the advantage of the spatial diversity (by using a single frequency for multi-user coverage) and the advantages of the frequency diversity (by offering good steering capability and high directivity for each user). It is capable of radiating dynamic multiple beams simultaneously with an excellent flexibility and steering capability in real-time processing and outperforming other multi-beam antenna array methods. Thus, this new design is an ideal candidate for the new 5G mobile base stations.

Finite Large Antenna Arrays for Massive MIMO: Characterization and System Impact

Massive MIMO is considered a key technology for 5G. Various studies analyze the impact of the number of antennas, relying on channel properties only and assuming uniform antenna gains in very large arrays. In this paper, we investigate the impact of mutual coupling and edge effects on the gain pattern variation in the array. Our analysis focuses on the comparison of patch antennas versus dipoles, representative for the antennas typically used in massive MIMO experiments today. Through simulations and measurements, we show that the finite patch array has a lower gain pattern variation compared with a dipole array. The impact of a large gain pattern variation on the massive MIMO system is that not all antennas contribute equally for all users, and the effective number of antennas seen for a single user is reduced. We show that the effect of this at system level is a decreased rate for all users for the zero-forcing MIMO detector, up to 20% for the patch array and 35% for the dipole array. The maximum ratio combining on the other hand, introduces user unfairness.

Compact planar 2 × 2 and 4 × 4 UWB mimo antenna arrays for portable wireless devices

AbstractA very compact 2 × 2 and 4 × 4 ultra wide band (UWB) multiple input multiple output (MIMO) antenna array with high isolation and polarization/pattern diversity are proposed in this letter. The compact size of antenna with orthogonally polarized elements help in achieving high isolation between elements of the arrays without using any decoupling circuit while maintaining its overall size very compact. The monopole UWB antenna prototype has compact size of 14 × 14 mm2 and enlarged to 2 × 2 array having size of 14 × 31 mm2 and 4 × 4 array having overall size of 31 × 31 mm2. The proposed designs have been fabricated and tested. Measured isolations |S21| are ≤ −25 dB and ≤ −20 dB for 2 × 2 and 4 × 4 arrays, respectively. However, impedance bandwidth |S11| is ≤ −10 dB for both arrays in the range from 3.6 to 10.6 GHz. The simulated, measured and calculated result shows good agreement for its impedance matching, isolation and dual polarization characteristics. Dual polarization improves its diversity performance and compact size improves its spatial multiplexing.

Ultra-wideband radio tomographic imaging with resolution near the diffraction limit

The experimental ultra-wideband radio tomographic imagings inside and behind dielectric barriers with resolution near the diffraction limit are described. The problem is solved by the method of radio wave tomosynthesis using the theory of spatial spectra of the received signals. The ultra-wideband pulse sensing of the air—building structure medium, developed in Tomsk State University, are described. It has been shown that for the case of sensing with ultra-wideband pulses of 0.2 ns duration, the resolution is about 2 cm. The paper also shows the possibility of accelerating scanning of the investigated space through the use of the MIMO (timed or switched) antenna array technology. As in the timed mode the distance between the receiving and transmitting antennas varies from time step to time step, the algorithm of processing the data obtained from the array is to be modified. The modification itself is a nonlinear stretching of the received UWB signal in time. The signal transformation allows preparation of data for the above algorithm to receive three-dimensional images of the tested space. The paper presents the results of the processed experimental data which confirm the efficiency of the proposed method for MIMO arrays. The resulting image resolution is about 2 cm.

Target parameter estimation for spatial and temporal formulations in MIMO radars using compressive sensing

Conventional algorithms used for parameter estimation in colocated multiple-input-multiple-output (MIMO) radars require the inversion of the covariance matrix of the received spatial samples. In these algorithms, the number of received snapshots should be at least equal to the size of the covariance matrix. For large size MIMO antenna arrays, the inversion of the covariance matrix becomes computationally very expensive. Compressive sensing (CS) algorithms which do not require the inversion of the complete covariance matrix can be used for parameter estimation with fewer number of received snapshots. In this work, it is shown that the spatial formulation is best suitable for large MIMO arrays when CS algorithms are used. A temporal formulation is proposed which fits the CS algorithms framework, especially for small size MIMO arrays. A recently proposed low-complexity CS algorithm named support agnostic Bayesian matching pursuit (SABMP) is used to estimate target parameters for both spatial and temporal formulations for the unknown number of targets. The simulation results show the advantage of SABMP algorithm utilizing low number of snapshots and better parameter estimation for both small and large number of antenna elements. Moreover, it is shown by simulations that SABMP is more effective than other existing algorithms at high signal-to-noise ratio.

Mutual Coupling Reduction in Millimeter-Wave MIMO Antenna Array Using a Metamaterial Polarization-Rotator Wall

An effective technique for reducing the mutual coupling between millimeter-wave dielectric resonator antennas (DRAs) using a novel metamaterial polarization-rotator (MPR) wall is investigated and presented. The mutual coupling is reduced by embedding an MPR wall between two DRAs, which are placed in the H-plane. Using this MPR wall, the TE modes of the antennas become orthogonal, which reduces the mutual coupling between the two DRAs. The proposed MPR wall is composed of 1 × 7 unit cells along the E-plane. The mutual coupling is reduced by more than 16 dB on average (8 dB at 57 GHz, 22 dB at 60 GHz, 14 dB at 62 GHz) when the MPR wall is placed between the antennas. The proposed MPR wall nearly has no effect on the antenna characteristics in terms of input impedance and radiation pattern. The radiation pattern is almost unchanged compared to a DRA multiple-input-multiple-output (MIMO) antenna array without MPR wall. The MIMO antenna array with MPR wall is fabricated and measured. The results give a low correlation coefficient (<;0.1e-6). This is due to the fact that the MPR wall makes the two antennas orthogonal in terms of mutual coupling. The measured and simulated results show a good agreement.

Compact 4G MIMO antenna integrated with a 5G array for current and future mobile handsets

A novel integrated antenna solution for wireless handheld devices is proposed for the existing 4G standards and upcoming 5G systems for broadband, high data rate communications. The complete antenna system is a unique combination of a multiple-input-multiple-output (MIMO) antenna system at microwave frequencies and a millimetre (mm)-wave antenna array. The MIMO antenna system consists of two reactive loaded monopoles while the mm-wave array consists of a planar 2 by four slot antennas. The integrated antenna system covers the frequency bands from 1870 to 2530 MHz for 4G standards along with the upcoming 5G mm-wave band at 28 GHz. In addition, the integrated antenna system is planar and is designed for typical smart phone devices with a standard 60 mm by 100 mm by 0.965 mm back plane. Excellent field correlation values were obtained across the 4G band while realised peak gain values of 4 and 8 dBi were, respectively, measured for the MIMO and mm-wave antenna arrays. The proposed antenna design may also be useful for other compact implementations that support 4G and 5G communications.

Easily Extendable Compact Planar UWB MIMO Antenna Array

This letter presents a highly isolated compact four-element planar ultrawideband (UWB) multiple-input-multiple-output (MIMO) antenna array configuration. The main advantages of the proposed array configuration are that it requires no isolation/decoupling circuit and the configuration is easily extendable to larger size array. The array consists of novel miniaturized slotted annular ring monopole antenna and each element in the array is placed orthogonal to its adjacent elements. The fabricated structure provides good impedance bandwidth matching and high isolation between elements over the range from 3 to 15 GHz. The absence of decoupling circuit results in overall compact size of the proposed design. The prototypes are fabricated and tested. The simulated and measured results are in good agreement. Moreover, the envelope correlation coefficient and channel capacity loss of the array are calculated, which shows good MIMO performance. The proposed monopole antenna structure supports multielement UWB MIMO antenna array design with easy extension of elements and without any decoupling circuit. An example of eight-element array is also investigated.

Left-handed compact MIMO antenna array based on wire spiral resonator for 5-GHz wireless applications

A compact coplanar waveguide-fed multiple-input multiple-output antenna array based on the left-handed wire loaded spiral resonators (SR) is presented. The proposed antenna consists of a 2 × 2 wire SR with two symmetrical microstrip feed lines, each line exciting a 1 × 2 wire SR. Left-handed metamaterial unit cells are placed on its reverse side and arranged in a 2 × 3 array. A reflection coefficient of less than −16 dB and mutual coupling of less than −28 dB are achieved at 5.15 GHz WLAN band.

Quad‐element multi‐band antenna array in the smart mobile phone for LTE MIMO operations

ABSTRACTIn this paper, a quad‐element MIMO antenna array in the smart phone has been developed for multi‐wideband operations covering 750–960 MHz and 1700–3600 MHz. The proposed antenna element consists of two parts: one is a dielectric resonator that operates in a TE11δ mode and generates the antenna's upper band, and the other is a radiating patch with a meander line connected to the ground plane, which achieves composite right‐ and left‐handed (CRLH) metamaterial transmission lines structure and contributes the antenna's lower band. Each of four antenna elements fitting in a small region of 25 × 16 × 4 mm3 are located on a circuit board of 125 × 75 × 0.8 mm3. The slots are etched on the metallic ground plane to guarantee good isolation between four antenna elements. The MIMO antenna array is fabricated, and the simulated and measured results show good performance in terms of S parameters, radiation pattern, total efficiency, and envelope correlation coefficient (ECC). © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2619–2626, 2016

Compact 4 × 4 UWB‐MIMO antenna with WLAN band rejected operation

A compact planar UWB-MIMO antenna array with WLAN band rejection is presented. The array consists of four monopole radiators and a common ground plane. These monopoles are placed in such a way that the polarisation diversity of nearly placed radiators is exploited, resulting in high isolation. The proposed MIMO antenna array is electrically small (50 × 39.8 mm2), printed on a low loss 1.524 mm thick Rogers TMM4 laminate with a dielectric constant of 4.5 and a loss tangent of 0.002. A band-stop design was inserted on the ground plane to behave similar to a LC band-stop filter and reject the WLAN band. Simulation and measurement results satisfy the return loss requirement of better than 10 dB and isolation better than 17 dB over the entire 2.7–5.1 and 5.9–12 GHz bandwidths.