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This paper proposes a 10 × 10 MIMO multiband broadband planar antenna for tablets or laptops. The designed antennas cover a large number of the popular sub‐6‐GHz application bands, such as 0.617–0.96, 2.1–2.7, 3.5–4.5, and 6.1–7.2 GHz for public safety communications, radio systems, Bluetooth, Wi‐Fi, and satellite communications. The proposed antenna is designed with grounded branches, which can generate a wide bandwidth and cover most of the sub‐6‐GHz application band by coupling between branches of different lengths and antennas. MIMO antennas have been measured to have an envelope correlation coefficient of less than 0.7 and have met the standards set by international organizations for human radiation absorption simulations. The proposed antenna validates the unique 10 × 10 MIMO antenna structure and feasibility. Multiple operable frequency bands are realized, and the radiation effect of the antenna on the human body is analyzed if it complies with international market standards. The proposed antenna design is well suited for multiband and broadband requirements. [ABSTRACT FROM AUTHOR]

In this article, the authors present the design of a compact multiband monopole antenna measuring 30 × 10 × 1.6 mm3, which is aimed at optimizing performance across various communication bands, with a particular focus on Wi-Fi and sub-6G bands. These bands include the 2.4 GHz band, the 3.5 GHz band, and the 5–6 GHz band, ensuring versatility in practical applications. Another important point is that this paper demonstrates effective methods for reducing mutual coupling through two meander slits on the common ground, resembling a defected ground structure (DGS) between two antenna elements. This approach achieves mutual coupling suppression from −6.5 dB and −9 dB to −26 dB and −13 dB at 2.46 GHz and 3.47 GHz, respectively. Simulated and measured results are in good agreement, demonstrating significant improvements in isolation and overall multiple-input multiple-output (MIMO) antenna system performance. This research proposes a compact multiband monopole antenna and demonstrates a method to suppress coupling in multiband antennas, making them suitable for internet of things (IoT) sensor devices and Wi-Fi infrastructure systems. [ABSTRACT FROM AUTHOR]

In this proposed article authors present the design, analysis and development of the hybrid shaped multiband microstrip patch antenna for various wireless communication applications. Multiband characteristics of the proposed antenna is achieved by modifying the conventional circular radiating patch into “DUMBBELL” shaped hybrid patch geometry along with slotted reduced finite ground plane. A circular shaped reference patch is modified into dumbbell shaped patch by loading another circular shaped patch. Initial ground plane of same dimension as substrate is first decreased in width and four rectangular shaped slots are loaded in the appropriate locations to construct the final ground plane. Physical and electrical dimension of the proposed antenna are 24 mm × 40 mm × 16 mm and 0.18λ × 0.3λ × 0.12λ where λ represents wavelength corresponding to lowest operating frequency of 2.3 GHz. Proposed antenna is designed using FR-4 substrate (1.6 mm thick, loss tangent (tanδ) of 0.02, dielectric constant (εr) of 4.4) and simulated by CST Microwave Studio software. Antenna prototype is fabricated, measured and compared with the simulated results. The proposed hybrid shaped antenna exhibits measured multiband characteristics (2.3-2.5 GHz, 2.6-3 GHz, and 6.9-7.1 GHz) with centre frequency at 2.4, 2.7 and 7 GHz. Observed Reflection Coefficient, efficiency, peak gain and E plane and H plane radiation pattern of the antenna are very close to simulation result. Antenna can be suitably used for 2.4 GHz Wi-Fi and Bluetooth application, 5G mid band spectrum (3 GHz) and 7 GHz VSAT applications as well. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Benefiting from the discovery of novel organic semiconductor materials bearing tunable absorption characteristics, narrowband organic photodetectors (OPDs) with improved performance are reported. Alongside new photoactive materials synthesis, several device engineering strategies are introduced to achieve narrowband OPDs, allowing less dependence of the device performance on the synthetic variation control, such as batch‐to‐batch differences in molecular weight. However, fabrication of multiband OPDs remains a challenge. Current solutions are usually based on vertical multi‐stacking of photosensitive layers with different absorption spectra and voltage‐modulated charge collection/injection, which renders the device fabrication too complex, while their response speed and band selectivity is limited. In this work, the concept of optical cavity is adopted to demonstrate self‐powered and fast response speed single‐junction bidirectional organic photodetectors with dual narrowband detection in the ultraviolet (UV) and visible part of the spectrum. Application of these devices in encrypted UV communication is successfully demonstrated. A third band in the near infrared (NIR) is possible to be isolated, rendering these high‐performing and simple to manufacture multiband OPD devices attractive for high‐resolution imaging and optical wireless communication. [ABSTRACT FROM AUTHOR]

In this paper, a multiband microstrip antenna of compact size (0.2 × 0.25 ) is designed by loading multiple notches in the patch of antenna. The patch of antenna consist two L-shaped and two rectangular shaped notches. The modified patch of antenna provides triple resonating bands from 1.58 to 1.71 GHz, 1.89 to 2.06 GHz and 2.81 to 2.93 GHz under the − 10 dB scale resonating at frequency 1.63 GHz, 2 GHz and 2.87 GHz respectively. The bandwidth of triple band antenna is obtained 7.9% (130 MHz), 8.61% (170 MHz) and 4.18% (120 MHz) with − 16.6 dB, − 26.99 dB and − 31.88 dB reflection coefficient at resonating frequency. The lower and middle resonances are due to L-shape notches while higher resonance is due to rectangular shape notches. The presented antenna is fed by microstrip line feed of 50 Ω and the simulation is performed by IE3D software. It shows 2.6−3.1 dB, 2.9−3.5 dB and 4.2−5 dB simulated gain and 85−93%, 87−95% and 88−96% antenna efficiency in three resonating bands. The three resonating bands of proposed antenna can be used for the application of different wireless communications in L and S-bands. The proposed work is also compared with the previous published articles to find out the improvement. [ABSTRACT FROM AUTHOR]

In the present emerging trends of 5G communication, long-distance communication cannot be accomplished with a single antenna. To enhance the gain and efficiency, a multi-band double hook shaped micro strip array antenna with defected ground structure has been designed and analyzed in this work for 5G communication applications. A quarter-wave transformer with a good impedance matching network is employed to provide the antenna's radiating components, and the designed antenna is prototyped on a 0.2 mm thick polyimide substrate with a dielectric constant of 2.9. Antenna resonating in the quad band with 10 GHz bandwidth at first resonant band and 1 GHz bandwidth at other three resonant bands. Gain of 8.8 dB at 22 GHz, 11 dB at 28 GHz, 13 dB at 32 GHz and 14.2 dB at 38 GHz is attained from radiation characteristics. The antenna is flexible and conformal with respect to the host surface, providing excellent correlation in simulation and protype real time measurement. [ABSTRACT FROM AUTHOR]

Transformation optics (TO) provides a powerful tool to manipulate electromagnetic waves, enabling the design of invisibility cloaks, which can render objects invisible. Despite many years of research, however, invisibility cloaks experimentally realized thus far can only operate at a single frequency. The narrow bandwidth significantly restricts the practical applications of invisibility cloaks and other TO devices. Here, a general design strategy is proposed to realize a multiband anisotropic metamaterial characterized by two principal permittivity components, i.e., one infinite and the other spatially gradient. Through a proper transformation and combination of such metamaterials, an omnidirectional invisibility cloak is experimentally implemented, which is impedance‐matched to free space at multiple frequencies. Both far‐field numerical simulations and near‐field experimental mappings confirm that this cloak can successfully suppress scattering from multiple large‐scale objects simultaneously at 5 and 10 GHz. The design strategy and corresponding practical realization bring multiband transformation optical devices one step closer to reality. [ABSTRACT FROM AUTHOR]

Electromagnetic (EM) absorbers are specially designed structures that dissipate the absorbed EM energy into heat by minimizing the reflection as well as transmission. The absorbers operating in microwave and millimetre wave regimes have been found essential in applications such as radar, communication systems, EM interference prevention, and stealth technologies. Design concepts such as Salisbury, Jaunman screens, and impedance-matching layers are discussed. As a game-changing innovation in wave attribute manipulation, metamaterial behaviour provides an unprecedented command over how waves interact with matter. This review examines the significant hurdles and restrictions metamaterial absorbers must overcome, like fabrication, the tradeoff between absorption bandwidth and thickness, and material losses. Broadband absorption, tunability, and feasibility of producing thin, lightweight absorbers all contribute to their desirability for various applications. Different losses responsible for the absorption phenomena are detailed for both narrowband and broadband cases. This critical analysis highlights the enormous promise of metamaterial absorbers while emphasizing the ongoing research efforts needed to overcome the associated obstacles. Its goal is to advance state-of-the-art designs by critically assessing the existing status of the field, thereby guiding future research, development, making it easier to implement microwave and millimetre wave absorbers in a wide range of real-time applications. [ABSTRACT FROM AUTHOR]

An electrically small multiband planar antenna is presented by using rectangular split ring resonator (RSRR) metamaterial element for LTE, WiMAX and WLAN applications. The designed antenna possesses asymmetric coplanar strip (ACS)-fed Hilbert Curve Fractal Antenna (HCFA) loaded with RSRR metamaterial for multiband radiation at 1.44 GHz, 3.76 GHz and 5.27 GHz. ACS-fed HCFA is responsible for creating the first (at 1.44 GHz) and second (at 3.76 GHz) resonance frequencies owing to the coupling between ACS-fed HCFA and ground plane. Moreover, the RSRR yields upper resonance at 5.27 GHz owing to the metamaterial transmission line. The stop band and pass band nature of the RSRR and its negative permeability characteristics are described using an effective medium theory. An equivalent circuit model of the proposed antenna is investigated with the help of Agilent ADS to validate the operating frequencies. Also, the geometrical parameters have been optimized using the artificial neural network (ANN), which is performed by MATLAB. The proposed antenna has been fabricated on a 18 × 16.5 × 1.6 mm3 FR-4 dielectric having ε r = 4.4 and tan δ = 0.02. It provides multiband response at 1.4 GHz, 4.4 GHz and 5.3 GHz with a − 10 dB impedance bandwidth of 330 MHz, 570 MHz, and 340 MHz, respectively, which is usable for LTE, WiMAX and WLAN band applications. [ABSTRACT FROM AUTHOR]

The demand for multiband and high-gain THz antennas is escalating due to advancements in terahertz (THz) applications, particularly in biomedical conditions. An innovative fork microstrip antenna design has been introduced, operating at THz frequencies, providing multi-band capability, soft characteristics, and high-gain results. The recommended antenna utilizes a series-fed configuration with dual patch elements constructed on a polyethylene substrate, with a thickness of 0.0224 mm, a loss tangent of 0.001, and a permittivity of 2.25. The proposed antenna, with dimensions of 1 × 0.6 × 0.0224 mm³ in its maximum configuration and operating at 0.530 THz and 0.590 THz, exhibits a 10 dB return loss bandwidth of 13 GHz and 15 GHz, respectively. Notably, the realized antenna gain is simulated at 9.01 dBi and 9.53 dBi for their respective frequencies. To assess the antenna's flexibility, simulations are conducted with the antenna configured in bent positions, considering radii of 7 mm, 6 mm, and 5 mm. Furthermore, the study includes an examination of the specific absorption rate (SAR) to validate the suitability of this pliable antenna. The outcomes underscore the potential of the recommended antenna for flexible biomedical THz applications such as the detection of skin tumours and medical imaging.

Recently, the relevance of multiple input multiple output (MIMO) technology has increased due to the growing user base and the surge in demand for high data rates. It provides an essential answer to the pressing requirement for high-capacity communication systems compliant with new standards. In this study, a four-element MIMO antenna with specific properties—a thickness of 0.0224 mm and a relative permittivity of 4.3 —is presented on a polyamide substrate. It is intended to operate in terahertz (THz) applications at 0.395 and 0.629 THz. The configuration of the antenna is based on a traditional fork antenna. At the resonant frequencies, this MIMO antenna can achieve bandwidths of 9.53 GHz and 24.19 GHz, with reflection coefficients of -16.19 dB and -24.27 dB, respectively. Moreover, a gain of 5.17 dB and 3.19 dB are obtained at the second and first resonant frequencies, respectively. In the effort to maintain the operational band and enhance gain, a significant challenge arises from the insufficient isolation between the four antenna elements within the limited space. A Defected Ground Structure (DGS) is constructed and the inter-element distance is carefully investigated in order to effectively address this issue. Mutual coupling effects are effectively reduced with this antenna, and an amazing MIMO diversity response is shown. Additionally, it achieves a mean effective gain of less than -3, envelope correlation coefficients below 0.0125, diversity gain of around 10 dB, and total active reflection coefficients below -4 dB. The suggested design was simulated using the ansys High-Frequency Structure Simulator program. These enhancements show that the recommended MIMO antenna is a suitable choice for terahertz applications like 5 G networks of the future and terahertz imaging systems used in medical settings for tissue imaging and cancer diagnosis.

This paper deals with the design, simulation, and practical modeling of metamaterial-based multiband conformal bandpass filter (BPF) for various wireless communication applications with improved quality factors. The novel metamaterial in the form of a split ring resonator is loaded on the ground plane face of the proposed BPF. The overall dimension of the designed BPF is only 2 8 × 2 8 mm 2 . The proposed BPF is tuned initially for quality factor enhancement based on the thickness of the substrate, physical parameters of the f transmission line, ground plane, externally loaded elements, and the gap in the metamaterial loading. The suggested filter operates at triple band covering the frequency bands from 1.4 to 2.2, 3.6 to 3.9, and 4.8 to 5.9 GHz, which are suitable for sub-6 GHz 5G and other wireless applications. The insertion loss is observed as 1 dB, which is suitable for the proposed BPF. The conformal behavior of the filter is judged through bending deformation analysis at various bending positions like (15 ∘ , 30 ∘ , 45 ∘ , 60 ∘ , and 90 ∘ ). The proposed BPF retains triple pass band characteristics at various bending deformations, which makes it suitable to be used in curved structures or flexible circuitry. The theory of equivalent circuits and quality factor (Q) of the designed BPF is discussed in this paper. The results are analyzed experimentally through ANRITSU-MS2037C combinational analyzer. The proposed BPF is suitable for sub-6 GHz 5G, WLAN, and Wi-Max applications. [ABSTRACT FROM AUTHOR]

Purpose: The characterization of tissue microstructure using diffusion MRI (dMRI) signals is rapidly evolving, with increasing sophistication of signal representations and microstructure models. However, this progress often requires signals to be acquired with very high b‐values (e.g., b > 30 ms/μm2), along many directions, and using multiple b‐values, leading to long scan times and extremely low SNR in dMRI images. The purpose of this work is to boost the SNR efficiency of dMRI by combining three particularly efficient spatial encoding techniques and utilizing a high‐performance gradient system (Gmax ≤ 300 mT/m) for efficient diffusion encoding. Methods: Spiral readouts, multiband imaging, and sampling on tilted hexagonal grids (T‐Hex) are combined and implemented on a 3T MRI system with ultra‐strong gradients. Image reconstruction is performed through an iterative cg‐SENSE algorithm incorporating static off‐resonance distributions and field dynamics as measured with an NMR field camera. Additionally, T‐Hex multiband is combined with a more conventional EPI‐readout and compared with state‐of‐the‐art blipped‐CAIPIRINHA sampling. The advantage of the proposed approach is furthermore investigated for clinically available gradient performance and diffusion kurtosis imaging. Results: High fidelity in vivo images with b‐values up to 40 ms/μm2 are obtained. The approach provides superior SNR efficiency over other state‐of‐the‐art multiband diffusion readout schemes. Conclusion: The demonstrated gains hold promise for the widespread dissemination of advanced microstructural scans, especially in clinical populations. [ABSTRACT FROM AUTHOR]

In this work, we presented the design, analysis and optimization of the multiband slotted antennas based on SINC function for 5G applications. The proposed antennas are designed and modelled by CST Studio Suite software. A parametric study is performed to determine sinc function parameters that control the performance of the proposed antenna. The parametric study is implemented by varying the amplitude of the sinc function, the frequency, the location of the slot along Y-axis, the slot width and the slot window (number of cycles). The simulated results showed that the designed slotted antennas in this paper exhibits multiband operation and they offer the feasibility of controlling and adjusting the resonant frequency by changing the sinc function parameters. The proposed antennas have various resonant frequencies at around 1.5 GHz, 2.65 GHz, 5 GHz and 5.8 GHz covering the 5G sub-6 GHz band. Extensive simulation process were carried out to determine the optimum antenna performance and three antennas were selected based on the reflection characteristics and number of operation frequency bands. Finally, the three selected antennas were manufactured and their performance were measured in the lab for validation. Experimental results showed that an excellent agreement between the measured and simulated results was achieved. [ABSTRACT FROM AUTHOR]

This paper proposes a texture-enhanced network (TENet) for intertidal sediment and habitat classification using multiband multipolarization synthetic aperture radar (SAR) images. The architecture introduces the texture enhancement module (TEM) into the UNet framework to explicitly learn global texture information from SAR images. The study sites are chosen from the northern part of the intertidal zones in the German Wadden Sea. Results show that the presented TENet model is able to detail the intertidal surface types, including land, seagrass, bivalves, bright sands/beach, water, sediments, and thin coverage of vegetation or bivalves. To further assess its performance, we quantitatively compared our results from the TENet model with different instance segmentation models for the same areas of interest. The TENet model gives finer classification accuracies and shows great potential in providing more precise locations. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to design a Frequency Selective Surface (FSS) generating multi stop-band and having the property of a large scanning angle from a mixed polarization insensitivity structure for GPS, PCS, WiFi, IEEE S-band radar, 5G mobile phones, (802.11j) WLAN applications. To fulfill the objective, a hexa band-stop FSS has been developed using a novel symmetrical structure with a compact dimension of 0.095 λ 0 × 0.095 λ 0 , where λ 0 is the wavelength of free space at 1st resonant frequency. The proposed FSS covers a broad scanning angle of 60 0 for shielding electromagnetic wave radiation and smaller resonant frequency ratio ( f n + 1 / f n ) to improve compactness under TE and TM polarizations. The six achieved stop frequency bands are 1.36 GHz–1.56 GHz, 1.66 GHz–1.99 GHz, 2.34 GHz–2.46 GHz, 3.08 GHz–3.42 GHz, 3.6 GHz–4.12 GHz and 4.5 GHz–5 GHz for improving shielding performance. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, a novel design method for quad-band Wilkinson power dividers is proposed. The design method is based on using a quad-band microstrip line. In comparison with other design methods, the proposed method has the advantages of simplicity and low insertion loss. To validate the proposed method, an equal quad-band power divider operating at four bands of 0.7, 1.2, 1.78, and 2.28 GHz was simulated and measured. Good agreement between measured results and simulated ones is obtained. The measured results show that the developed quad-band power divider features low insertion loss of less than 0.75 dB, isolation greater than 20.92 dB, and return loss better than 18 dB at four operating bands. [ABSTRACT FROM AUTHOR]

A novel multiband metamaterial (MTM) unit cell antenna loaded with split ring resonator (SRR) slots that resonates at seven bands, which are (1.91 GHz), (3.6 GHz), (6.25 GHz), and (8.69 GHz, 9.69 GHz, 10.70 GHz), and 12.33 GHz of the spectrum, making it suitable for L-band, worldwide interoperability for microwave access (WiMax), C-band, X-band downlink, and Ku-band applications, respectively, is proposed and discussed in this work. The proposed antenna has a very compact size of 14×15×1.6 mm³ with an FR4 substrate. The simulation results show that the presented antenna attains a reflection coefficient of less than -10 dB (S11 -10 dB) and a radiation pattern across all operating bands. In addition, the suggested antenna provides good gains over the resonant frequency signals with an average of 6.75 db. The antenna simulations and parametric studies have been done using both computer simulation technology microwave studio (CST microwave studio) and high frequency structure simulator (HFSS) to confirm the obtained simulation results. [ABSTRACT FROM AUTHOR]

The manuscript represents a metamaterial-inspired superstrate patch antenna with a multiband response. The design consists of three superstrate layers over the patch antennaand SRRloaded over parasitic patches. The performance observation is carried out for 2–10 GHz. The simulation and fabrication are taken into consideration, and comparisonsbetween both of them are included. FR4 is used as a substrate material which helps reduce the structure's cost. The metamaterial approach is incorporated over superstrate regions for the improvement of results. The superstrate approach helps for enhancing the strength and Bandwidth of the design. Impedance response is analyzed for different resonating frequencies to check the metamaterial response. Two types of Parametric Analysis are considered to achieve the targeted goal, like changing feed position and the gap among superstrate layers. The presented work shows eight bands of reflectance response with a minimum value of − 44.83 dB with a Bandwidth of 3.139 GHz, peak directivity of 3.16 dB, a gain of 8.02 dB at 9.04 GHz, maximum E-field distribution of 1.160 × 105 v/m at 6.52 GHz. Presented work compared with other design structures to identify the improvement. Many wireless communication-related applications like military, WiMAX, and Maritime mobile services. [ABSTRACT FROM AUTHOR]

For future fifth-generation (5G) smartphones, a high-efficiency multiple-input/multiple-output (MIMO) antenna system capable of operating in Long Term Evolution (LTE) 42/43/46 is suggested. A pair of small microstrip-fed slot antenna and inverted F antenna is part of the single antenna design structure. They are positioned on the longer side of the FR-4 printed circuit board. In an effort to lessen the mutual coupling, two antenna elements have a U-shaped rectangular slot inserted between them. The detailed study of the suggested MIMO system includes measurement of the reflection parameter, analyzing the radiation performance, performing envelope correlation coefficient (ECC) and channel capacity calculations, and analyses of the effects of user's hand in the vicinity of the antenna array. Simulation and measurement results demonstrate the required performance of the proposed design, that is, greater than 80% of total efficiency, isolation >12 dB, and ECC <0.15. The suggested antenna has the benefits of multiband operation, high efficiency, good isolation, and a small footprint. [ABSTRACT FROM AUTHOR]

The joint usage of sub-6 GHz and millimeter wave (mmWave) bands is believed to satisfy the high data rate, low latency, and ultrahigh reliability requirements of the vehicle-to-everything (V2X) communication; thus, its channel modeling has advanced to the state of the art. This paper offers a comprehensive review of existing multiband based V2X communication channel modeling techniques and their associated challenges. To provide an overview of V2X communication, the system layout describing the vehicle to vehicle/infrastructure/pedestrian (V2V/V2I/V2P) links and performance goals is presented. Then, trend of large-scale and small-scale propagation parameters acquisition using deterministic and stochastic channel modeling approaches is described. The received power for various scatterers size is also examined to simulate the real-world scenarios in which a group of scatterers surround a car and observed that size of blockers impacts the receiving power. The 3D non-stationarity issue and lack of a flexible algorithm that can transition between sub-6GHz, mmWave, or combined modes based on the links' traffic inquiry category are challenges that have not yet been overcome. On the other hand, developments in mobile edge computing, integrated signal processing, channel modeling tools, and measurement-driven findings are presented as opportunities to further advance V2X communication. The role of potent technologies in advancing vehicular communication goals by their synergistic relation with mmWave frequency is also illustrated. Specifically, developing flexible algorithm and loading into edge computing enabled roadside units aids to meet dynamic resource scheduling targets which in turn triggers the realistic intelligent transport system. The hybrid sub-6/mmWave mode selection pseudo code is provided as well in this study as an insight to algorithm developers. Therefore, this article serves as a valuable reference for academics who are interested in this field providing an in-depth review of the joint sub-6GHz/mmWave based V2X channel modeling techniques for autonomous driving. [ABSTRACT FROM AUTHOR]

This review article provides a detailed overview of current techniques in the field of Dielectric Resonator Antennas (DRA). The primary aim of study aims electrical size downsizing, retrofitting bandwidth to meet commercial needs, and radiation pattern stability by managing the modes in the DRA with the evolution starting from rectangular shape to contemporary investigations. Various research strategies for miniaturizing the physical and electrical size, mode excitation by various mechanisms such as a probe, microstrip, slot, and others, along with increasing bandwidth and radiation characteristics have been mentioned. In this review, the innovative geometries and fractal notions introduced to the DRAs are also discussed. [ABSTRACT FROM AUTHOR]

Abstract Transformation optics (TO) provides a powerful tool to manipulate electromagnetic waves, enabling the design of invisibility cloaks, which can render objects invisible. Despite many years of research, however, invisibility cloaks experimentally realized thus far can only operate at a single frequency. The narrow bandwidth significantly restricts the practical applications of invisibility cloaks and other TO devices. Here, a general design strategy is proposed to realize a multiband anisotropic metamaterial characterized by two principal permittivity components, i.e., one infinite and the other spatially gradient. Through a proper transformation and combination of such metamaterials, an omnidirectional invisibility cloak is experimentally implemented, which is impedance‐matched to free space at multiple frequencies. Both far‐field numerical simulations and near‐field experimental mappings confirm that this cloak can successfully suppress scattering from multiple large‐scale objects simultaneously at 5 and 10 GHz. The design strategy and corresponding practical realization bring multiband transformation optical devices one step closer to reality.

The primary concern addressed in this article is the inherent difficulty in creating antennas capable of effectively operating across a range of frequency bands within the terahertz (THz) spectrum. Conventional antenna designs often fall short in terms of delivering the required bandwidth and power for such applications. To mitigate this problem, we present a technique that uses photonic crystals integrated into the antenna design to generate photonic band gaps (PBG) with the graphene loaded in the THz band. So, the purpose was to find the optimal multiband antenna that can function across 1.13 and 0.65 THz. Simulations were conducted for rectangular patch antennas using different types of substrates, which included homogeneous, periodic, and aperiodic photonic crystal substrates, and by using a graphene load, simulations were carried out. Multiple sets of air holes (rectangular and cylindrical) were punched into the polyimide substrate of each modified photonic crystal substrate, and the load graphene was placed in the patch. The anticipated multiband antenna design has successfully achieved impressive performance metrics, including a minimal reflection coefficient of −36.8 dB and −41.812 dB, a substantial bandwidth of 25 GHz, and 110 GHz at 0.65 THz and 1.13 THz, respectively. Additionally, the design boasts a gain of 6.44 dBi, 9.45 dBi, and a remarkable radiation efficiency of 75.12 % and 80.03 %, respectively, with a VSWR

Terahertz antennas have garnered significant attention for use in the fields of telecommunications and medical applications. One of the major issues with THz antennas is the integration of flexibility with multiband characteristics. This article focuses on designing and constructing a new, compact, and flexible dual-band THz antenna using different slots for terahertz applications. The essence of the antenna design is rooted in a careful strategy for positioning slots, both on the ground plane and within the patch. The rising need for flexible electronics is the primary motivation behind the investigation of this flexible, multiband antenna. The examined antenna is supported by a flexible polyimide substrate with small dimensions of 1.5 × 1 × 0.15 mm3. Several adjustments are made to the radiating patch to enable multiband functionality, resulting in operation at 123 GHz and 180.4 GHz. The corresponding return losses are -35.03 dB and -38.71 dB, while the bandwidths for the two frequency bands are 3.3 % and 8.86 %, respectively. For all working bands, the VSWR of the given antenna is lower than 2, with a gain of 4.12 dB and 5.05 dB at the resonating frequency, as well as a radiation efficiency of 81.6 % and 89.3 % inside the resonating bands. Moreover, a parametric investigation was additionally carried out to ascertain the ideal dimensions of the suggested antenna. As the antenna is constructed using a flexible substrate, this article also delves into the analysis of antenna bending in both the x- and y-axes. The suggested antenna can be applied in modern handheld fifth-generation (5 G) and terahertz medical imaging applications, such as breast cancer detection.

This study introduces a coplanar waveguide MIMO antenna design that offers both frequency and pattern reconfigurability. The antenna is intended for applications in WiMAX, WLAN, and X-Band. It is constructed using an FR4 substrate with dimensions of 1.6mm thickness and 0.025 loss tangent. Based on the proposed design, MIMO antennas can operate at 3.5 & 3.9GHz (WiMAX), 5.5 & 5.8GHz (WLAN) and 10.5 & 12.5GHz (X-Band). To accomplish this, two open-circuited 3mm x 3mm quatre wavelength transformers are linked to each radiator through PIN diodes. The performance enhancement of the reconfigurable MIMO antenna was fine-tuned utilizing microwave solvers in both CST and ADS. The system’s performance was validated through practical measurements. Furthermore, the analysis of diversity conducted on the suggested antenna reveals that the antenna has a low correlation coefficient (

A multiband microstrip-fed wideband (WB) antenna with filtering notches is described for $3 \mathrm {G} / 4 \mathrm {G} / 5 \mathrm {G}$ applications. The proposed antenna comprises three notch bands by etching a modified inverted U-slot, a square ring slot, and an interdigital inductor slot on the patch element and feedline. The antenna resonates at $1.9,2.3$ , and $3.5 \mathrm {~GHz}$ due to the resonant components’ mutual interaction, which eliminates interference at other frequencies. The antenna’s measured $S_{11}$ are $18.79 \mathrm {~dB}$ at $1.9 \mathrm {~GHz},-24.8 \mathrm {~dB}$ at $2.4 \mathrm {~GHz}$ , and $-40.6 \mathrm {~dB}$ at $3.5 \mathrm {~GHz}$ , showing a multiband function with a band-reject level of $0.4 \mathrm {~dB}$ . The VSWR is less than two at all resonant frequencies. The effects of altering the notch dimensions on the $S_{11}$ and VSWR were explored. The antenna was developed and tested using a Rogers RT/Duroid 5880 substrate. The agreement between measured and simulated results was satisfactory. The $S_{11}$ result was validated using the ADS schematic and machine learning techniques. The proposed triband-notched antenna offers encouraging results, with radiation patterns exhibiting omnidirectional characteristics and effective performance within the required frequencies. Current distribution analysis reveals how notches disrupt surface current and lower radiation at specific frequencies. The antenna’s gain and efficiency performed satisfactorily in the stated frequency ranges.

As communication technology advances, high-gain antennas are being investigated for a variety of long-distance applications. One such high gain antenna is reflectarray, it has combined advantageous characteristics of a reflector and phased array antennas. However, to design the reflectarray antenna its phase range, bandwidth, gain, cross polarization and the side lobe levels must be in optimal range to meet the requirements for distant applications. In this article, we have reviewed various research works of reflectarray antenna and highlighted the techniques to develop an efficient high gain reflectarry antenna. Recently, for high gain applications, as per end user requirement, there is a need to vary the frequency and radiation characteristics in a controlled manner. This can be achieved by using reconfigurable reflectarray antennas. In this article, reconfigurable mechanisms and active elements used for reconfiguration are reviewed in detail. In the end of this survey, some of the works on reflectarray antenna which were published by the research society are compared, summarizing the important parameters such as operating frequency, phase range, gain bandwidth, peak gain, cross polarization levels, and side lobes.

New multiband antenna array structure with high gain is proposed for 5G communication handheld systems (700MHz/3.5 GHz and 28/38 GHz). The designed structure is proposed using a combination of sub-6GHz and mm-Wave antenna arrays. The antenna is based on S-shaped strip etched on the top side to operate at 700 MHz. On the other hand, the 3.5GHz band is generated by coupling a meander line to an inverted-C strip on the bottom side. Finally, the mm-Wave antenna array is based on four quadrupole elements with a 1:4 microstrip power divider. This configuration ensures that all four quadrupole antennas receive in-phase feeding power. Obtained results confirm that the designed antenna array achieves gains of 4.6 dBi, 10.5 dBi, at sub-6 GHz and mm-Wave band, respectively. Owing to its simplicity and compactness, the proposed handset antenna is a good candidate for 5G multiband applications.

The Pythagoras Tree Fractal patch is considered on a SiO2 substrate thickness of 1.5 µm to radiate at four frequencies of 4.975THz, 5.38THz, 6.73THz, and 7.61THz with Voltage Standing Wave Ratio (VSWR) ≤ 2. This is a very creative fractal design of a multiband THz antenna, based on a very thin graphene layer, the study proved a value in terms of high radiation efficiency and high gain, at the level of current research we made a comparison study where the design has evidently huge potential regarding applicability for telecommunication technology in the terahertz regime. The demand for high-performance terahertz (THz) antennas has increased significantly in recent years due to their potential applications in various fields such as medical imaging, security screening, and wireless communications. In this paper, the authors present an analysis of a graphene Pythagoras Tree Fractal (GPTF) antenna with a thin SiO2 substrate for THz regime. The GPTF antenna is designed using a fractal geometry approach, which provides multiple resonant frequencies and enhances the overall radiation efficiency. The thin SiO2 substrate is used to reduce the substrate losses and improve the radiation performance of the antenna. The authors use the Finite-Difference Time-Domain (FDTD) software to simulate the performance of the proposed antenna. The results show that the proposed antenna exhibits high gain, low return loss, and wide bandwidth, making it a promising candidate for THz applications.

Highlights The hierarchical porous structure is regulated by various species of PVP to achieve impedance matching. Interfacial engineering boosts conductivity and constructs a multiband (C, X, Ku) tunable electromagnetic wave absorber. Hierarchical porous molybdenum selenide/epoxy coating exhibits marine anticorrosion capability.

In this article, the authors present the design of a compact multiband monopole antenna measuring 30 × 10 × 1.6 mm3, which is aimed at optimizing performance across various communication bands, with a particular focus on Wi-Fi and sub-6G bands. These bands include the 2.4 GHz band, the 3.5 GHz band, and the 5–6 GHz band, ensuring versatility in practical applications. Another important point is that this paper demonstrates effective methods for reducing mutual coupling through two meander slits on the common ground, resembling a defected ground structure (DGS) between two antenna elements. This approach achieves mutual coupling suppression from −6.5 dB and −9 dB to −26 dB and −13 dB at 2.46 GHz and 3.47 GHz, respectively. Simulated and measured results are in good agreement, demonstrating significant improvements in isolation and overall multiple-input multiple-output (MIMO) antenna system performance. This research proposes a compact multiband monopole antenna and demonstrates a method to suppress coupling in multiband antennas, making them suitable for internet of things (IoT) sensor devices and Wi-Fi infrastructure systems.

A kind of acoustic metasurface (AMS) with multiple response frequency bands based on the replace method was proposed, which composed of six units, each containing three split hollow cubics (SHCs) (denoted as the AAA type of AMS). The simulation results demonstrated that the presented AMS can achieve the flexible modulation of the reflected wave direction. The AAA type of AMS had one response band, the AAC type of AMS had two different response bands, and the ABC type of AMS had three different response bands. Furthermore, the response bandwidth of the ABC type of AMS declined the most in the middle-frequency band, followed in the low-frequency band, and the least in the high-frequency band, when compared to the corresponding AAA type of AMS with single bandwidth. In addition, it was worth noting that the ABC type of AMS not only enlarged the manipulation direction of reflected acoustic wave, but also improved the effects of the wavefront distribution at the same frequency. This multiple band AMS will be beneficial for the application of architectural acoustics, and acoustic absorption and noise reduction. [ABSTRACT FROM AUTHOR]

A multiband half‐mode substrate integrated waveguide (HMSIW) slotted antenna is developed for ISM/WiMAX/WLAN applications. HMSIW technique has been utilized to acquire antenna compactness. Two inverted L‐shaped slots of half wavelength are embedded onto a HMSIW rectangular cavity for attaining a hybrid mode (i.e., Half‐mode of TE110+ ${\mathrm{TE}}_{110}+\phantom{\rule{}{0ex}}$ Half‐mode of TE120 ${\mathrm{TE}}_{120}$), which induces a lower resonance at 2.4 GHz. An inverted L‐shaped slot is influenced to radiate hybrid mode at 2.4 GHz, while the innermost inverted L‐shaped slot radiates modified TE110 ${\mathrm{TE}}_{110}$ mode at 3.30 GHz. A multiband is obtained by amalgamation of hybrid mode (at 2.4 GHz), modified TE110 ${\text{TE}}_{110}$ mode (at 3.30 GHz) and modified TE120 ${\mathrm{TE}}_{120}$ mode (at 5.38 GHz). The radiating modes are elucidated by using mode theory methodology for ascertaining the resonance characteristics of the prototype antenna. The antenna parameters have been optimized by artificial neural network technique using MATLAB. The antenna geometry possesses a shrinkage size of 30 × 16 × 1.6 mm3, which has been designed on FR‐4 substrate. To vindicate the simulated consequence, the fabricated prototype has been tested. It contributes the fractional bandwidth of 6.4% (2.09−2.23 GHz) in the hybrid mode at 2.18 GHz, 9.03% (2.89−3.17 GHz) in the half cavity mode TE110 ${\mathrm{TE}}_{110}$ at 3.10 GHz and 9.96% (5.11−5.65 GHz) in the half cavity mode TE120 ${\mathrm{TE}}_{120}$ at 5.42 GHz, respectively, which is beneficial for ISM, WiMAX and WLAN band wireless applications. [ABSTRACT FROM AUTHOR]

Fractal antennas are mainly used in multiband applications. However, these types of arrays suffer from numerous disadvantages, such as high sidelobe levels, low directivity, poor taper efficiency, and high design computational complexity. In this paper, the conventional fractal procedures are redesigned and efficient clustered subarrays are deployed, such that their multiband properties are maintained while simultaneously achieving significant improvements in radiation characteristics. A genetic optimization algorithm is used to find the optimal clustered fractal shapes and their associated amplitude distributions, such that the sidelobe levels are minimized at the narrower beam width, i.e. maximum feasible directivity. Since the optimization process is carried out at the clustered level, it can be represented by merely a few variables, which solves the problem of time intensity. Simulation results confirm the superiority of the proposed clustered fractal array, where the sidelobe level has been reduced to more than -10 dB over a wide range of frequencies. Directivity and taper efficiency have been improved by more than 6 dB and 50%, respectively, in comparison to the parameters of conventional, original fractal arrays. Moreover, the proposed fractal array pattern offers an additional advantage, as it is capable of wide sidelobe nulling at some undesired directions. [ABSTRACT FROM AUTHOR]

The Pythagoras Tree Fractal patch is considered on a SiO2 substrate thickness of 1.5 µm to radiate at four frequencies of 4.975THz, 5.38THz, 6.73THz, and 7.61THz with Voltage Standing Wave Ratio (VSWR) ≤ 2. This is a very creative fractal design of a multiband THz antenna, based on a very thin graphene layer, the study proved a value in terms of high radiation efficiency and high gain, at the level of current research we made a comparison study where the design has evidently huge potential regarding applicability for telecommunication technology in the terahertz regime. The demand for high-performance terahertz (THz) antennas has increased significantly in recent years due to their potential applications in various fields such as medical imaging, security screening, and wireless communications. In this paper, the authors present an analysis of a graphene Pythagoras Tree Fractal (GPTF) antenna with a thin SiO2 substrate for THz regime. The GPTF antenna is designed using a fractal geometry approach, which provides multiple resonant frequencies and enhances the overall radiation efficiency. The thin SiO2 substrate is used to reduce the substrate losses and improve the radiation performance of the antenna. The authors use the Finite-Difference Time-Domain (FDTD) software to simulate the performance of the proposed antenna. The results show that the proposed antenna exhibits high gain, low return loss, and wide bandwidth, making it a promising candidate for THz applications. [ABSTRACT FROM AUTHOR]

In this paper, a truncated patch antenna based on the electromagnetic band gap (EBG) structure has been proposed. The fabricated antenna has five operating frequencies at 10.4, 15.68, 19.68, 27.2, and 35.04 GHz. The fabricated prototype of the antenna constitutes a truncated rectangular patch etched with the shape of a symmetrical slot (on top) and an EBG loaded on the ground plane of the dielectric substrate. The optimized volume of the antenna is 20 × 15 × 1.57 mm3. The proposed antenna gives a good radiation pattern for the E-H field in all covered bandwidth and also achieved better performances related to the reference papers. A multiband antenna also covered the 5 G bandwidth, which resonates at 27.2 GHz from 24.2 GHz to 27.84 GHz bandwidth and at 35.04 GHz from 33.84 GHz to 36.2 GHz bandwidth, which can be used in the Internet of Medical Things. On the other hand, X/Ku/K frequency bands have been committed for wireless communication where the multiband antenna can be used to help in monitoring, especially in the case of data transmission from radio frequency sensors to health-care system in real-time applications. [ABSTRACT FROM AUTHOR]

Highlights: The hierarchical porous structure is regulated by various species of PVP to achieve impedance matching. Interfacial engineering boosts conductivity and constructs a multiband (C, X, Ku) tunable electromagnetic wave absorber. Hierarchical porous molybdenum selenide/epoxy coating exhibits marine anticorrosion capability. Electromagnetic wave (EMW) absorbing materials have an irreplaceable position in the field of military stealth as well as in the field of electromagnetic pollution control. And in order to cope with the complex electromagnetic environment, the design of multifunctional and multiband high efficiency EMW absorbers remains a tremendous challenge. In this work, we designed a three-dimensional porous structure via the salt melt synthesis strategy to optimize the impedance matching of the absorber. Also, through interfacial engineering, a molybdenum carbide transition layer was introduced between the molybdenum selenide nanoparticles and the three-dimensional porous carbon matrix to improve the absorption behavior of the absorber. The analysis indicates that the number and components of the heterogeneous interfaces have a significant impact on the EMW absorption performance of the absorber due to mechanisms such as interfacial polarization and conduction loss introduced by interfacial engineering. Wherein, the prepared MoSe2/MoC/PNC composites showed excellent EMW absorption performance in C, X, and Ku bands, especially exhibiting a reflection loss of − 59.09 dB and an effective absorption bandwidth of 6.96 GHz at 1.9 mm. The coordination between structure and components endows the absorber with strong absorption, broad bandwidth, thin thickness, and multi-frequency absorption characteristics. Remarkably, it can effectively reinforce the marine anticorrosion property of the epoxy resin coating on Q235 steel substrate. This study contributes to a deeper understanding of the relationship between interfacial engineering and the performance of EMW absorbers, and provides a reference for the design of multifunctional, multiband EMW absorption materials. [ABSTRACT FROM AUTHOR]

This paper presents a highly isolated pattern diversity multiband MIMO antenna using two ring-shaped radiating elements with a rectangular stub placed inside it. The proposed multiband MIMO antenna is resonating at three frequencies centred at 2.45 GHz, 3.5 GHz, and 5.4 GHz. A high-quality factor U-shaped bandstop filter is designed and placed between the two antenna elements to achieve simultaneous high isolation and pattern diversity. The isolation between the antenna elements at 2.45 GHz, 3.5 GHz, and 5.4 GHz is −25 dB, −20 dB and −35 dB, respectively. The diversity gain is 10 dB, while the ECC is less than 0.05. The antenna is fabricated on a low-cost substrate, FR4, and its dimensions are 31 mm × 31 mm × 0.8 mm. Measured results verify the multiband behaviour of the proposed MIMO antenna. The proposed MIMO antenna is useful for WLAN, WiMAX and 5 G sub-6 GHz-based applications. [ABSTRACT FROM AUTHOR]