This paper presents a comprehensive review of machine learning and metasurface/metamaterial-assisted MIMO antennas for mmWave applications. Machine learning algorithms such as random forest, regression models, XGBoost regression, artificial neural networks (ANN), k-nearest neighbors (KNN), convolutional neural networks (CNN), and deep neural networks (DNN) are discussed for optimizing complex antenna parameters and reducing the simulation time of electromagnetic (EM) solvers. Moreover, the fundamentals of metasurfaces and metamaterials are reviewed, and their roles in improving antenna performance are discussed in detail. Subsequently, a metamaterial unit-cell structure ($\mathbf{3 6} \boldsymbol{\times} \mathbf{3 6} \mathbf{m m}^{\mathbf{2}}$) is carefully designed at the center of the MIMO antenna structure to provide electromagnetic shielding. Furthermore, a complete design procedure for a mmWave MIMO antenna intended for $5 \mathrm{G} / 6 \mathrm{G}$ applications is discussed and critically reviewed. This review demonstrates a comprehensive understanding of machine learning-based metasurface/metamaterial-assisted MIMO antenna design for next-generation applications.

This study presents the design and analysis of a small, high-gain, high-isolation 4-port multiple-input multiple-output (MIMO) array antenna engineered for 5G millimeter-wave (mmWave) applications at 28 GHz. The suggested antenna array, with dimensions of 30 & times; 30 & times; 0.8 mm(3), is optimized on a Rogers RT/Duroid 5880 substrate to provide an efficient and broadband response. Each element in the array is designed to resonate precisely at 28 GHz, achieving a remarkable return loss of -30 dB, indicating exceptional impedance matching and minimum reflection losses. The antenna has a broad impedance bandwidth of 2.2 GHz (about 7.85%), guaranteeing dependable performance throughout the designated 5G mmWave spectrum. The simulated and observed outcomes show a maximum gain of 13.50 dBi, guaranteeing robust link quality for high-data-rate transmission conditions. The antenna exhibits an isolation greater than 27 dB over the working band, underscoring its appropriateness for MIMO applications by efficiently mitigating mutual coupling effects. The key performance parameters, including the envelope correlation coefficient (ECC < 0.005) and diversity gain (nearing 10 dB), validate the antenna's efficacy for multi-antenna systems. This work introduces a novel MIMO antenna solution characterized by small dimensions, high gain, low mutual coupling, and extensive operating bandwidth, successfully fulfilling the rigorous requirements of next-generation 5G mmWave communication systems.

Abstract This article presents an ultra-compact (1.02λ × 1.02λ mm2) and highly isolated 8-port MIMO antenna designed for NR-n46 and n79 bands, as well as licensed assisted access (LAA). A systematic study was performed to choose an optimal antenna (Design-3) among all designs (Design-1, Design-2, and Design-3) after systematic study (parametric study and circuit theory analysis) of Ref. design-1, Ref. design-2, Ref. design-3 and Ref. design-4. An optimal and proposed antenna geometry consists of two orthogonal radiators on the top and a novel ground plane (rectangular ring, centered annular ring and plus shaped slot) at the bottom of each corner of the dielectric substrate to create a perfectly matched 8-port antenna. The proposed antenna demonstrates a wideband frequency operation of 700 MHz within the 4.75–5.45 GHz range, specifically in the sub-6 GHz 5G band. It resonates at 5.2 GHz, achieving an isolation of 33 dB, a gain of 4.7 dB, and a radiation efficiency of 92.5%. The MIMO characteristics, including ECC, DG, TARC, MEG, and CCL, were evaluated and found to be within acceptable parameters. The antenna was fabricated, tested in a laboratory setting, and its performance was validated against simulated results.

Abstract This article presents a 16-port compact (26.2 $$\times$$ 79 $$\times$$ 0.508 mm $$^3$$ ) massive MIMO antenna for mmWave applications. The proposed antenna consists of five triangular-shaped parasitic elements, one triangular-shaped feed-line fed element, and impedance matching network on the radiating plane, whereas defected ground and stubs are used on the ground plane. A systematic study is performed to select an optimal single element antenna (design) among design-1, design-2, design-3 an design-4. Thereafter, a 16-port massive MIMO antenna is implemented using a replica of a single element with modified ground plane structure. The proposed antenna resonates at 40 GHz frequency in mmWave band (37.5–49 GHz) with a 40 dB peak return loss. According to 3GPP bands n259 (39.5–43.5 GHz), n260 (37–40 GHz) and n262 (47.2–48.2 GHz), the resonating band (37.5–49 GHz) of the proposed antenna is part of the upper band of the mmWave spectrum and contains some of the most crucial licensed 5G and beyond wireless communications bands such as 39 GHz, 41 GHz and 47 GHz. Moreover, the proposed antenna achieves a high antenna gain of 17.9 dB and 17.2 dB at 39 GHz and 41 GHz, respectively. In addition, the specific absorption rate analysis of the proposed antenna is conducted by placing the antenna on the right hand of a human male model and 0.045 W/kg of SAR value at 40 GHz is achieved for the proposed antenna. An equivalent circuit of the intended antenna is proposed and simulated using the ADS tool and validated with the results simulated using HFSS.

This article introduces an 8 × 8 petal shape MIMO antenna for 5G NR-n48, n77, n78 band applications. A petal shape geometry is used as a radiating element on the top plane whereas defected ground plane, central unit structure, parasitic elements and rectangular slits are used on the ground plane. The petal shape geometry consists of one central circular geometry and four semicircles wherein; semicircles are mounted on each orthogonal diameter endpoints of central circular patch. The curved, tapered edges of petal shape geometry reduce abrupt discontinuities in surface current distribution for transition from feed to radiating edges, which mitigates reflections and surface wave losses. The proposed antenna design is fabricated over FR4 substrate with dimensions of 112 × 112 × 1.6 mm³. The proposed antenna resonates at 3.7 GHz and achieves a bandwidth of 700 MHz with more than 20 dB isolation. The design exhibits a gain of 4.8 dB and 6 dB at 3.7 GHz and efficiency greater than 88

In this study, a compact (30 × 30 × 0.508 mm3) 8-port MIMO antenna for unmanned aerial vehicles (UAV), vehicle-to-everything (V2X) and 5G applications is designed, developed, tested and discussed. After a systematic study, an optimal single element of the proposed antenna is chosen from four steps (Step 1, Step 2, Step 3, Step 4). The geometry of the proposed antenna comprises eight circular radiating elements on the top plane of the substrate in which pentagon structure is etched out from each element to resonate it at 5.5 GHz. Stepped rectangular structure is removed from the ground plane underneath of each radiating elements. A dielectric substrate (RT/Duorid (5870 tm)) is used to fabricate the proposed antenna design with following specification: εr = 2.33, h = 0.508 mm, loss tangent (tan δ = 0.0012). A unique structure of the proposed antenna geometry exhibits −10 dB wideband bandwidth of 1.32 GHz (5–6.32 GHz) and high isolation (> 30 dB) in entire band. A peak gain of 6.5 dB and 92

This study details the design, modeling, and experimental validation of a high-gain four-element microstrip patch array antenna using a corporate-fed network for sub-6 GHz 5G N79 band applications. The suggested antenna array is constructed on a FR4 substrate, which has a thickness of 1.6 mm, a dielectric constant of 4.4, and a loss tangent of 0.002. The design incorporates a ring-slotted patch layout, a stepped impedance feeding mechanism, and a defective ground structure (DGS) to improve impedance matching and bandwidth. The single-element antenna, measuring 60 mm x 60 mm, attains a bandwidth of 4.4-4.8 GHz, a peak simulated gain of 2.7 dBi, and a radiation efficiency of 98.8%. To improve gain performance, a 1 x 4 linear array is constructed by combining four identical antenna components with an optimized corporate-fed network. The ultimate array arrangement is 180 mm x 130 mm and attains an impedance bandwidth ranging from 4.48 to 4.89 GHz, with a maximum recorded gain of 11.31 dBi. The modeling, simulation, and optimization of the proposed configuration have been carried out by Ansys HFSS is a 3D electromagnetic (EM) simulation software. The simulated and measured results demonstrate significant concordance, with slight discrepancies ascribed to manufacturing tolerances, material losses, and connection mismatches. A comparison examination with current sub-6 GHz array antennas demonstrates that the suggested design has enhanced gain, bandwidth, and radiation efficiency, positioning it as a formidable option for next-generation 5G wireless communication systems.

This article introduces a compact (32 x 64 x 0.8 mm(3)) four port MIMO antenna for K-band for satellite and for band 5G NR- n257, n258 & n261 for mmWave applications. The proposed antenna is designed at 24 GHz and selected an optimal design (Stage 3) after successive analysis of different stages (Stage 1, Stage 2 & Stage 3) performance. The radiating plane consists of an inverted L-shaped geometry, whereas the ground plane has a rectangular annular ring geometry. The proposed antenna offers an extremely large bandwidth of 20.02-30.8 GHz (simulated) & 20.2-30.3 GHz (measured) and an excellent isolation of greater than 25 dB in entire band. The suggested four-port MIMO antenna system obtained a significant peak gain of 9.5 dB at 24 GHz frequency. MIMO performance metrics in terms of ECC (envelope correlation coefficient), DG (diversity gain), TARC (channel capacity loss), CCL (channel capacity loss) and MEG (mean effective gain) of the proposed antenna is also studied and found in acceptable limits; ECC (0.00003), DG (9.87 dB), TARC (< -10 dB) CCL (< 0.4 bps Hz(-1) s(-1)) and MEG ((-12 dB < MEG < -3 dB). Simulated results of the proposed antenna are validated with experimental results and found in close proximity. The performance of the proposed antenna makes it suitable for satellite and 5G and 5G advanced applications.

The current study demonstrates a dual and wideband mmWave 4 × 4 port MIMO antenna for 5G and beyond applications. The proposed antenna is derived from a traditional inset-fed rectangular geometry, modified with multiple curved edges on the top plane to produce a large effective aperture and enable significant surface current distribution. Partial ground planes are connected using 45° tilted conducting strips to form a common ground, which enhances surface current distribution and balances power through each port. The antenna exhibits wide bandwidths of 2.3-6.5 GHz at resonant frequencies of 28-38 GHz, respectively. Moreover, the suggested antenna yields more than 21 dB isolation, 8.3 dB peak gain, 92% radiation efficiency, 89% multiplexing efficiency, an ECC of 0.00007, and a channel capacity of 21 bit/s/Hz. To validate the antenna design, the prototype was fabricated on a Rogers RT/Duroid 5880™ substrate, tested, and compared with simulated results, showing good agreement.

In this research, a dual-band Quasi-Yagi-Uda antenna array (1x2) for wireless applications is presented. The proposed antenna consists of two Quasi-Yagi-Uda elements and a perfectly matched corporate feed network. The proposed antenna exhibits resonance at 2.5 GHz and 3.3 GHz, yielding a dual- band nature in the 2.480-2.605 GHz (125 MHz) and 3.227-3.666 GHz (439 MHz) frequency bands. The driven and director elements of the array antenna enhance the antenna gain by up to 9 dB, compared to 5 dB for a single-element antenna. The proposed antenna exhibits directional radiation patterns with gains of 6.6 dB and 9 dB at 2.5 GHz and 3.3 GHz, respectively. Radiation efficiencies of 84% and 93% have been obtained at 2.5 GHz and 3.3 GHz, respectively, for the proposed antenna. The antenna geometry is designed and simulated using the EM tool High-Frequency Structure Simulator (HFSS). Moreover, the simulated results of the proposed antenna are compared with those of recently published works. A sufficient frequency ratio (1.32) between the lower and higher resonating bands makes the antenna suitable for multiband applications.

This paper presents the design and analysis of a dual-port wideband multiple-input multiple-output (MIMO) antenna featuring pattern diversity and high isolation for millimeter-wave (mm-wave) 5G applications. The single antenna element of the proposed MIMO antenna module consists of a T-shape feed printed on one side of the RT duroid low-loss substrate and two rectangular slots loaded ground plane on the other side. The MIMO antenna designs have been realized using the anti-parallel arrangement of two antenna units relative to one another. The proposed MIMO has a small design of 12.5 x 6.25 x 0.8 mm(3). The antiparallel arrangement is generating pattern diversity. The achieved impedance bandwidth ranges from 25.8 GHz to 32.8 GHz, including a total span of 7 GHz, which includes the critical band N257 (26.5-29.5 GHz) for 5G millimeter-wave communications. Wideband impedance matching is achieved by optimized feed geometry, guaranteeing steady performance over the designated mm-wave frequency range. High port isolation is achieved without intricate decoupling mechanisms, hence minimizing design complexity and preserving a small footprint. The simulation was conducted using the Ansys HFSS electromagnetic solver. The suggested MIMO antenna demonstrates a minimal envelope correlation coefficient (ECC) and substantial diversity gain (DG), and consistent gain patterns, making it an appropriate choice for next-generation high-speed wireless communication systems.

This manuscript focuses on the design and performance evaluation of a novel compact 2-port MIMO antenna that is designed for 5G frequency applications in the n260 band, starting from 37 to 40 GHz. In the new antenna design, an effective and compact radiating structure is proposed, which has been optimized for reduced size, wide bandwidth, and good radiation performance. To enhance the isolation between the ports, the antenna exploits the spatial diversity technique that reduces the ECC and enhances the DG. In this way, the optimum functioning of MIMO is guaranteed. The antenna element comprises a circular radiating patch that is excited with uneven power by a coplanar feed. The antenna exhibits a wide bandwidth that covers the n260 band, while showing adequate gain and high radiation efficiency, rendering it suitable for 5G frequency communications at very high data rates. Simulation results have shown a compact structure featuring a high level of isolation and exhibiting very good performance for a wide range of signals, and thus it is a potential candidate for next-generation mm-wave MIMO applications.

This study presents a novel and compact (1.25 lambda r x 1 lambda r x 0.02 lambda r mm3) 6-port MIMO antenna which comprises three elements (two rectangular concave patches and one elliptical patch) in the radiating plane and an effective isolator made up of an annular ring and rectangular strips in the ground plane. The proposed work has been meticulously investigated in six distinct steps (STEPS (1-6)), ensuring optimal performance across various parameters, and an optimal design STEP-6 is chosen among all six different designs. This work exhibits a fractional bandwidth of 17% (simulated) and 16. 7% (measured) at a resonating frequency of 2.4 GHz in the first frequency band (2.1-2.6 GHz) and 38. 4% (simulated) and 36. 1% (measured) at the center frequency of 2.8 GHz in the second frequency band (2.2-3.3 GHz). A maximum isolation of 40 dB, a peak realized gain of 3.1 dB and a total efficiency of 92%-95% have been obtained. The SAR value of the proposed antenna is also investigated with human body interaction, and SAR values of 0.8, 1.3, and 1.5 W kg-1 have been achieved at 2.4, 2.6, and 3 GHz, respectively. In addition, the MIMO characteristics in terms of ECC and CCL have also been studied, and values of less than 0.04 and 0.5 of ECC and CCL have been obtained. The proposed antenna is suitable for Sub-6 GHz band such as WiFi, Bluetooth, WLAN, RFID, ISM band and wireless applications. The simulated results based on a finite element method are experimentally verified and found in close proximity.

This paper presents a cavity model analysis of a novel penta-band MIMO antenna that is compact in size (measuring 76x33 mm2) and utilizes three PIN diodes for reconfigurability. This antenna resonates at 2.1, 3, 3.5, 4, and 4.2 GHz in different states (state-000, state-011, state-111, state-100, and state-000, respectively) and offers a fractional bandwidth of 4.95% (simulated), 5.5% (measured) and 4.92% (theoretical) in state-000, 3.09% (measured), 2.8% (simulated) and 2.3% (theoretical) at lower frequency (2.1 GHz), and 2.12% (simulated), 2% (measured) and 2.4% (theoretical) at higher frequency (4.2 GHz) in state-100, 12.5% (simulated), 12% (measured) and 11.6% (theoretical) in state-011 and 4.6% (simulated), 4.7% (measured) and 4.4% (theoretical) in state-111. Furthermore, the antenna exhibits impressive performance with a peak gain and isolation of 3.6 and 32.2 dB at 4 GHz and 3.5 GHz, respectively. The proposed design also maintains low specific absorption rate (SAR) and envelope correlation coefficient (ECC) values, with SAR and ECC values less than 1 W/kg and 0.01, respectively. Moreover, a lumped element RLC equivalent circuit for the intended antenna is proposed using cavity model circuit theory. The proposed circuit produces theoretical reflection coefficients of the proposed antenna and has been validated by comparison with simulated and measured results.

In this article an 8-port annular ring-shaped MIMO antenna for 5G and 5G advanced applications is presented. An annular ring on the radiating plane and novel isolator structure on the ground plane are etched over a Rogers RT/Duorid (5870 tm) substrate to achieve high performance antenna for mm wave applications. A systematic study is performed, and an optimized single port antenna (Design-4) is selected among Designs (1-4). The intended 8-port MIMO antenna resonates at 36.4 GHz and exhibits 6.1 GHz (34.2-40.3 GHz) wide bandwidth |S-11|<-10dB and 40 dB high isolation level. The proposed antenna covers a complete band of 5G NR-n260 which supports time division duplexing (TDD) mode. Moreover, a unique design of suggested antenna attains a high-level gain of 8.3 dB at 39 GHz and more than 85.2 % radiation efficiency. MIMO characteristics such as ECC, TARC, MEG and CCL are studied and found them in acceptable limit. Additionally, an approach toward massive antenna with 16-port for mmWave applications is also demonstrated. The proposed 16-port massive antenna with more than 22 dB isolation exhibits two bands: first band in 30-33 GHz for ports P9-P16 and second band in 33.5-40.9 GHz for ports P1-P8. A prototype of suggested 8-port antenna is fabricated, tested and validated and found it in close agreement of simulated results.

A compact (17 × 10 mm2) microstrip patch antenna with dual-band notch characteristics is presented in this article. The designed antenna consists of a semicircular radiating patch and defected ground structure to cover the bandwidths for C/X/Ku/K-band applications. The Defected ground is created by the introduction of slot, slit and copper connecting strip on the ground plane. The measured dual-band notches (6.96–11.12 GHz and 12.97–16.28 GHz) and measured resonating impedance bandwidth 35.53

With innovative technologies developing at a rapid pace, machine learning has become essential to improve interdisciplinary applications such as wireless communications systems. In order to optimize, design and develop a compact (0.6 λ× 0.6λ× 0.03λ mm^3) four-elements MIMO antenna at 2.4 GHz resonating frequency, this study uses a machine learning technique. A single element antenna is selected among several steps (1–4) and thereafter, an antenna (A3) turns out to be the best option out of the antennas that were taken into consideration (A1–A3). The optimal antenna (A3) dimensions were carefully ascertained by means of a thorough investigation of 245,700 distinct iterations. The proposed antenna consists of a petal-shaped structure on the center of the radiating plane and rectangular ring with defected semicircles on the ground plane. The antenna exhibits 72.3

In this article, an F-shaped four-port multiple-input multiple-output (MIMO) antenna is designed and analyzed. In the designed antenna for achieving high isolation, we introduced a novel isolation technique that appears like plus-shaped wall placed in between the antenna elements. The antenna is designed on a low-cost FR-4 epoxy substrate with total dimensions of 0.61 lambda(0) x 0.61 lambda(0) x 0.03 lambda (0) x 0.61 lambda(0) x 0.03 lambda(0) (31 mm x 31 mm x 1.58 mm) where lambda(0) is the free space wavelength at 5.8 GHz and experimentally verified. This MIMO antenna design covers operating the range of frequencies 5.47-6.20 GHz (|S-11| < - 10 dB) which provides a bandwidth of 730 MHz. In terms of performance, the proposed antenna achieves high isolation of < -45.52 dB with an improved reflection coefficient of -30.44 dB, a peak gain of 3.77 dBi and a radiation efficiency more than 82% across the entire operating band. Moreover, the achieved MIMO diversity parameters of the proposed antenna are envelope correlation coefficient < 0.005, diversity gain < 9.99 dB, mean effective gain < -3 dB and total active reflection coefficient <-10 dB in the operating band of frequency. The simulated and measured results show a good agreement between them. Finally, after analyzing the performance of the proposed MIMO configuration, we can say that this antenna is suitable for C-band, WiMAX, Wireless-Fidelity (Wi-Fi), Wireless Local-Area Network (WLAN), Bluetooth and Industrial, Scientific, & Medical (ISM) bands applications.