Search

The internet of things (IoT) paradigm aims to make the world smarter by reducing human intervention and promoting automated interactions. A radio frequency identification (RFID) reader is a necessary component for automated object identification and data transfer in an IoT network. Its performance is primarily determined by the characteristics of the integrated or externally connected antennas. This article provides a review of the state-of-the-art reader antenna designs, as well as research challenges. The RFID reader antennas are investigated based on their operating frequency bands, gain, and polarization. Generalized procedures for designing specific antenna configurations, which are useful and widely used by readers, are illustrated and explained. Several design challenges have been investigated and analyzed, including narrow bandwidth, bidirectional radiation pattern, low gain, linear polarization, and a larger footprint. Subsequent solutions have also been provided. Cross-dipole configurations are one method for achieving a compact footprint and circular polarization characteristics without using complicated feeding circuitry. Low antenna gain has a direct impact on the read range of the reader. Therefore, increasing the gain of the reader antennas is an essential requirement. One of the gain-enhancing techniques is to use an artificial magnetic conductor (AMC) surface beneath the antenna. This reduces backward radiation of the antenna-AMC integrated configuration, increasing the antenna peak gain. The AMC also helps in the achievement of unidirectional radiation.

This article presents a four-port multiple-input-multiple-output (MIMO) flexible antenna design for Ultrawideband (UWB) application using Polydimethylsiloxanes substrate. The single UWB antenna structure consists of modified circular radiator with elliptical slot and partial ground plane. To achieve high isolation among antenna element, a Defective Ground Structure (DGS) is adopted to decouple the low frequency band. DGS comprises a centrally placed square shape slotted structure connected by horizontal and vertical lines, achieving isolation below −20 dB. The proposed antenna has a dimension of 56×41×1.6mm3(0.41λ×0.3λ×0.0117λ), bandwidth of 3.4–11.8 GHz (110.5 %) and 4.3 dBi peak gain. Simulation and measurement findings show that the antenna performs well under bending situations with different curvature radius. At 4 GHz and 8.1 GHz, W/kg specific absorption rate (SAR) for 1/10 g tissue is examined. A low value of SAR is obtained at both the resonating frequencies. Additionally, an analysis is conducted on the diversity parameters, and the antenna demonstrates comparatively good results having mean effective gain (MEG) ratio 9.99 dB, implying that it's appropriate for wearable MIMO applications.

The rapid augmentation of wearable technology and IoT contributes to a substantial consideration in the design and development of flexible sensor antennas. These types of antennas could detect variations in the signal even when the antenna is deformed when placed over the body for wearable sensing applications. This paper proposes a highly flexible CPW-fed antenna for 5G wearable sensor applications. Holding an overall dimension of 40 × 30 × 0.1 mm3, the antenna covers a measured impedance bandwidth of 4.57–5.50 GHz with a peak gain of 3.8 dBi. The design optimization of the proposed antenna is investigated using the characteristic mode analysis (CMA) which provides a clear insight into the physical performance and radiation characteristics of the antenna. Bending analysis of the antenna is performed for various bending radius along x and y axis, and the antenna gives a satisfactory bending profile. The favourable SAR value as well as the on-body analysis of the antenna demonstrate the application possibilities of the proposed antenna for wireless wearable sensing applications.

A four-port dual-band notch ultrawideband (UWB) multiple input and multiple output (MIMO) antenna for automotive applications is presented. Initially, a circular patch monopole antenna is designed and optimized by embedding a rectangular stub onto the radiator and lowering the ground plane to realize the UWB frequency spectrum. The dual-band frequency notch, from 4.6 to 5.9 and 6.8–8.8 GHz, is achieved using a half wavelength slot onto the feedline and a pair of H-shaped stubs across the feedline, respectively, to cover WLAN and complete x-band satellite communication. Further, the designed dual-band notch UWB antenna is transformed to a four-port MIMO antenna with interelement spacing much smaller than λ/4 (λ at 3.1 GHz) and a size of 0.46 × 0.41 × 0.01 λ3. Isolation improvement is achieved by a hybrid decoupling technique comprising a distinctive neutralization line (NL) and defected ground structure (DGS). The average isolation of the proposed design is better than 22 dB. Characteristic mode analysis of the proposed antenna is performed to analyze the specific significant mode and their contribution to the antenna radiation. The antenna design's diversity and time-domain properties are analyzed and found suitable for automotive applications. The antenna's electromagnetic interaction with the electrically large structure is studied by mounting the antenna onto an open-source automobile model, and the gain is determined to be more than 6.1 dB at the antenna's resonant frequencies.

A linearly polarized, compact, dual-band, high gain antenna is proposed for aircraft collision avoidance system (ACAS) or aircraft surveillance applications. The ACAS is an airborne electronic equipment developed to prevent mid-air collisions between two civilian airplanes. A multi-element patch antenna is utilized to address the shortcomings of the conventional ACAS antenna (an array of four monopole antennas) concerning gain (3.6dB), bandwidth, and dimensions ( $\lt \mathrm {1.5}\lambda $ ) when operating at 1.06GHz central frequency. The antenna design consists of four symmetric radiator panels organized in a circular pattern with dimensions of $\mathrm {0.88\times 0.88\times 0.01}\mathrm {\lambda }^{3}\mathrm {(250\times 250\times 3.175}{\mathrm {mm}}^{3})$ . It is fed in sequence to provide complete 360° coverage in the azimuth plane, which is crucial for surveillance purposes. To achieve the dual resonance with the precise band coverage required for the ACAS, significant work on the ground structure has been done by integrating numerous approaches, including an array of metamaterial (MTM), defected ground structure (DGS), and meandering line (ML). Later, an MTM slab ( $6 \times 4$ MTM unit cells) is deployed vertically on all four sides of the antenna to improve overall antenna gain. The effective medium ratio (EMR) of the presented MTM cell is 12.86, which implies the overall size of the MTM cell is $\lt \mathrm {\lambda /12}$ , and it exhibits double negative behavior between 0.9−1.18GHz, making it an extremely compact double negative MTM structure. The proposed design is resonating at 1.03GHz and 1.09GHz with an impedance BW of 8.54% (0.98GHz−1.068GHz), 6.88% (1.07GHz−1.145GHz), and a gain of 9.2dB with a 3dB gain BW of 16.98% (0.96GHz−1.14GHz), respectively. Finally, the proposed MTM and antenna structures are fabricated and measured, and the findings affirm the simulations.

The aircraft collision avoidance system (ACAS) is a surveillance system required in all airplanes to ensure a safe flight. To locate the presence of any surrounding aircraft that may pose a threat, the ACAS sequentially scans the fixed sectors (0° to 90°, 90° to 180°, 180° to 270°, and 270° to 360°) for a specified duration. As a result, ACAS necessitates a highly directional multi-element antenna capable of spanning the whole 360° azimuth plane. Over the past decade, studies on the performance enhancement of ACAS antennas have become increasingly prevalent due to the numerous limitations of the typical ACAS antenna, which include poor gain ( $3.6dB$ ), larger size ( $>\lambda$ ), high side-lobe level ( $-7dB$ ), challenges with beam tuning, etc. The main focus of this study is to improve the gain and bandwidth (BW) of an ACAS antenna using the notion of MTM, hence a novel U and L-shaped compact negative index MTM structure is developed. Because the ACAS antenna broadcasts the signal in the entire azimuth region, the proposed MTM should be competent to endure its double negative behavior for all incident angles; thus, the MTM cell is evaluated for different incident angles ranging from 0° to 360° in the azimuth plane with a 60° offset, and for all incident angles, the proposed design exhibits DNG behavior in the required frequency spectrum. The effective medium ratio (EMR) of 12.86 at 1.06GHz demonstrates the efficacy and compactness of the proposed design. The proposed MTM cell is expanded as a $5\times 4$ array, and placed as a superstrate at a fixed distance from the proposed ACAS antenna, and the MTM-loaded antenna outperforms the conventional antenna in terms of overall gain by 2.09dB and BW by 27.2MHz. Further, for the experimental verification, the MTM cell and its array structures are fabricated, and in both designs, the fabricated results correspond well with the simulated results.

This article presents a flexible four-element MIMO antenna designed on a thin polyimide substrate to operate at 30.50 GHz for wearable applications. The antenna element structure is a combination of circular rings combined with T-shape stubs. The MIMO antenna isolation is enhanced through a novel decoupling structure consisting of a rectangular stub, four open-ended horizontal strip lines, and two vertical strip lines connecting the ground plane. It provides 22.5 dB isolation, even with conformal orientation. A metamaterial (MTM) reflective surface of $9\times9$ unit cells is designed and placed below the antenna to improve its radiation characteristics, bandwidth, gain, and specific absorption rate (SAR). The metamaterial unit cell provides a double negative property with a wide stop-band range of 26.27–36.49 GHz. With an MTM surface, the measured bandwidth is 25.2–33 GHz with a maximum broadside gain of 8.90 dBi. The resulting SAR is reduced from 1.71 W/kg to 0.86 W/kg by incorporating MTM reflective surface. The MIMO antenna with MTM improves the bandwidth by 56%, gain by 32.5%, and radiation from bidirectional to broadside, compared to the MIMO antenna without MTM. Also, the antenna is measured and validated for diversity parameters such as Envelope correlation coefficient (ECC), Diversity gain (DG), Channel coefficient loss (CCL), Total active reflection coefficient (TARC), and Mean effective gain (MEG). The reduced SAR and improved antenna performance suggest the proposed MIMO antenna with an MTM reflective surface is suitable for on-body wearable applications in IoT devices, smart watches, headwear, and footwear devices.

One of the most prevalent forms of malignant tumor affecting the digestive system is the Colorectal Cancer (CRC). Due to the recurrent nature of occurrence of CRC tumors the morbidity and mortality rate associated with CRC tumors is very high, making it the fourth leading cause of cancer worldwide. Although colonoscopy, is considered as pre-dominant screening mechanism for detection of CRC, over the recent years several researchers have attempted in developing AI diagnostic tools for segmenting colonic polyps. However, manual intervention and decreased accuracy rate is a major drawback witnessed by these approaches. In this study, we propose a novel automated colonic polyp segmentation mechanism using U-Net and chroma based deformable model termed as ContourNet. The proposed model eliminates the need for manual identification of region of interest irrespective of the high degree of variability between the lesion and non-lesion pixels. The model considers the chromaticity and statistical information from the identified region of interest to evolve the contour close to the affected area. The proposed algorithm was developed using Clinic CVC dataset for training, and a test accuracy of 94% was obtained. The generalization ability of the proposed design is validated on three different datasets, considering all the images as test set, a high degree of accuracy was obtained in identifying the affected regions. Thereby the results obtained prove the ability of the proposed method to be adopted in developing a CAD tool in detection of pathologies associated with gastroenterology in contrast to the state of art methods reported in literature.

Deep learning methods have shown promise for automated medical image analysis tasks. However, class imbalance is a common challenge that can negatively impact model performance, especially for tasks with minority classes that are clinically significant. This study aims to address this challenge through a novel hyperparameter optimization technique for training convolutional neural networks on imbalanced data. We developed a custom Convolutional Neural Network (CNN) architecture and introduced a Tangent Optimization Algorithm (TOA) based on the trigonometric properties of the tangent function. The TOA optimizes hyperparameters during training without requiring data preprocessing or augmentation steps. We applied our approach to classifying B-mode ultrasound carotid artery plaque images as symptomatic or asymptomatic using a dataset with significant class imbalance. On k-fold cross-validation, our method achieved an average accuracy of 98.82%, a sensitivity of 99.41%, and a specificity of 95.74%. The proposed optimization technique provides a computationally efficient and interpretable solution for training deep learning models on unbalanced medical image datasets.

A high gain antenna system with improved isolation for 5G applications is proposed and investigated. The radiating structure consists of a combination of multiple strips to make the proposed design resonate within the desired frequency band of 28 GHz being of major interest for 5G applications. The antenna element provides 684 MHz operating bandwidth and a peak gain of 5.85 dB with a radiation efficiency of 70.9%. Using four antenna elements in an antenna array, connected with a T-shaped feeding network, provides a 12.5 dB peak gain and radiation efficiency of 91.5%. The efficiency improvement of almost 20% is achieved by the reducing transmission co-efficient in feed network elements. This also leads to a low side lobe level (SLL) and an improvement in the bandwidth to 1.53 GHz. Furthermore, the four-port multiple-input-multiple-output (MIMO) configuration is obtained using the proposed array configuration which gives an optimum gain, uncorrelated fields, reasonable bandwidth, and isolation of more than 30 dB with a satisfactory MIMO performance metrics. Due to the abovementioned promising features of presented design, it can be very useful for important 5G services.

This article presents a compact six-element multiple-input multiple-output (MIMO) antenna for vehicle-to-vehicle (V2V) communications. The proposed structure is planar, having a dimension of $1.28\lambda _{0} \boldsymbol {\times } 2.04\lambda _{0}$ , where $\lambda _{0}$ is the wavelength at 25.5 GHz, resonating in n258 and n260 bands. The antenna is a modified rectangular patch designed to generate TM10 and TM02 modes, resulting in vertical and horizontal polarization at 25.5 GHz and 38 GHz. The measured bandwidth of the MIMO antenna is 800 MHz at the n258 band, i.e., 25.1-25.9 GHz, and 850 MHz at the n260 band, i.e., 37.75-38.6 GHz. The isolation between the elements is improved by incorporating a novel open-ended decoupling structure. It resulted in an isolation that surpass 20 dB at both bands. The antenna has a broadside radiation pattern with a maximum realized gain of 9 dBi and 7.2 dBi at 25.5 and 38 GHz, respectively. The antenna is validated for various diversity parameters such as envelope correlation coefficient, diversity gain, channel capacity loss, and mean effective gain. Also, the performance of the proposed antenna for V2V communication is analyzed for line-of-sight and non-line-of-sight conditions. The estimated channel capacity, path loss, and link budget for the above-said condition suggest that the antenna is suitable for V2V communications.

In this article, a slotted wideband eight-element multiple-input multiple-output (MIMO) antenna system is designed for the N77 (3.3-4.2 GHz) spectrum. The MIMO system is fabricated FR-4 substrate with standard smartphone dimensions, The orthogonal placement of two element pairs at each corner ensure pattern and polarization diversity characteristics useful for signal reception in downlink and uplink conditions from various directions. The wideband performance, spanning 3.25-4.49 GHz according to criteria VSWR 2:1, is achieved by incorporating series-modified U-slots. Each MIMO element exhibits radiation and total efficiency exceeding 70%. An inter-element isolation of 14.5 dB is attained via a slot introduced along the PCB width. The design achieves an envelope correlation coefficient (ECC) below 0.02 and a diversity gain (DG) above 9.95 dB. Additionally, the Mean Effective Gain (MEG), Channel Capacity Loss (CCL), and Total Active Reflection Coefficient (TARC) are found to be within well-accepted limits. The MIMO system’s performance is also evaluated in single and dual-hand modes. S-parameters remain stable within the frequency range of 3.25-4.49 GHz, indicating robust performance under user influence. The developed prototype’s measurements agree well with simulations, indicating that the proposed MIMO system is a potential candidate for future 5G handheld devices.

Modern wireless communication systems have undergone a radical change with the introduction of multiple-input multiple-output (MIMO) antennas, which provide increased channel capacity, fast data rates, and secure connections. To achieve real-time requirements, such antenna technology needs to have good gains, wider bandwidths, satisfactory radiation characteristics, and high isolation. This article presents an eight-element CPW-fed antenna for the 5G mid-band. The proposed antenna consists of eight symmetrical, modified circular monopole antennas with a connected CPW-fed ground plane that offers 24 dB isolation over the operating range. The antenna is further investigated in terms of the scattering parameters, and radiation characteristics under both the x and y-axis bending scenarios. The antenna holds a volume of 83 × 129 × 0.1 mm3 and covers a measured impedance bandwidth of 4.5–5.5 GHz (20%) with an average gain of 4 dBi throughout the operating band. MIMO diversity performance of the antenna is performed, and the antenna exhibits good performance suitable for MIMO applications. Furthermore, the channel capacity (CC) is estimated, and the antenna gives a value of 41.8–42.6 bps/Hz within the operating bandwidth, which is very close to an ideal 8 × 8 MIMO system. The antenna shows an excellent match between the simulated and measured findings.

Lung cancer, the treacherous malignancy affecting the respiratory system of a human body, has a devastating impact on the health and well-being of an individual. Due to the lack of automated and noninvasive diagnostic tools, healthcare professionals look forward toward biopsy as a gold standard for diagnosis. However, biopsy could be traumatizing and expensive process. Additionally, the limited availability of dataset and inaccuracy in diagnosis is a major drawback experienced by researchers. The objective of the proposed research is to develop an automated diagnostic tool for screening of lung cancer using optimized hyperparameters such that convolutional neural network (CNN) model generalizes well for universally obtained computerized tomography (CT) slices of lung pathologies. The aforementioned objective is achieved in the following ways: (i) Initially, a preprocessing methodology specific to lung CT scans is formulated to avoid the loss of information due to random image smoothing, and (ii) a sine cosine algorithm optimization algorithm (SCA) is integrated in the CNN model, to optimally select the tuning parameters of CNN. The error rate is used as an objective function, and the SCA algorithm tries to minimize. The proposed method successfully achieved an average classification accuracy of 99% in classification of lung scans in normal, benign, and malignant classes. Further, the generalization ability of the proposed model is tested on unseen dataset, thereby achieving promising results. The quantitative results prove the efficacy of the system to be used by radiologists in a clinical scenario.

A compact wearable four-element dual-band antenna with good isolation is presented here. The antenna constitutes of a circular monopole with slits and slots incorporated into it to generate dual-band function, and a unique defected ground structure (DGS) with vertical stubs to neutralize coupling current and enhance isolation. The proposed antenna has a dimension of 62 × 52 × 0.25 mm3, bandwidth of 3.8–4.43 GHz (15.31%) and 5.25–6.3 GHz (18.18%), and 5.2 dBi peak gain. The specific absorption rate (SAR) analysis in W/kg for 1/10 g tissue exhibits values of 0.877/0.356 at 4.1 GHz and 0.309/0.105 at 5.3 GHz respectively. The antenna radiation characteristics are analysed using characteristic mode analysis. Furthermore, the diversity parameters are investigated, and the antenna exhibits relatively good results with envelope correlation coefficient (ECC) 9.99 dB, total active reflection coefficient (TARC)

This paper introduces a multiport monopole antenna featuring high isolation and a broad operating bandwidth, specifically designed for K-band and 5 G applications. The proposed antenna configuration comprises four antenna elements assembled to achieve a compact design. A 0.254 mm thick Rogers RT-5880 substrate is used, with an overall size of 24 × 22 mm. Each antenna element is supported by a truncated ground plane, and four symmetrical slots are introduced into the radiating structures. As a result, the proposed multiport antenna covers a frequency band of approximately 18–27 GHz, based on the −10 dB criterion, providing a wide bandwidth of nearly 9 GHz. The separation between the antenna elements is about 4.5 mm. Additionally, a decoupling structure is inserted between the radiating elements to enhance isolation within the desired band, also resulting in a minor improvement in the operating bandwidth. Several performance metrics, including total active reflection coefficient (TARC), diversity gain (DG), envelope correlation coefficient (ECC), and channel capacity loss (CCL), are evaluated and show satisfactory performance within the operating bandwidth. The proposed antenna achieves more than 75% radiation efficiency. The overall performance of the multiport antenna indicates its potential for K-band and 5 G applications.

Reduction of mutual coupling in the radiating elements of multiple input multiple output (MIMO) antenna is always an issue and a big challenge for antenna researchers. To address this issue of mutual coupling reduction, an effective method of decoupling has been proposed in this paper. Here, a bandstop filter based isolation technique has been introduced to limit the mutual coupling in each element of the MIMO antenna. A 2 port and a 4 port MIMO antenna have been designed with the proposed decoupling technique, and it is found that the decoupling technique successfully achieves isolation of more than 30 dB for both antennas. In addition to achieving high isolation, the designed MIMO antennas are also made circularly polarized to overcome poor mismatch, lower directive gain, and signal to noise problems in wireless communication. The antenna performance is observed in simulation and verified with measurements. Simulated and measured results show that the 2 port antenna exhibits a 10 dB impedance bandwidth of 5.26 % (2.78–2.93 GHz) and a 3 dB axial ratio bandwidth of 13.08 % (2.65–3.02 GHz), while those for the 4 port antenna are 2.46 % (2.41–2.47 GHz) and 13.10 % (2.36–2.69 GHz). The 2 port antenna supports a peak gain of 3.27 dBi with a maximum efficiency of 85.11 %, while the 4 port antenna successfully increases the gain to 6.49 dBi but decreases the maximum efficiency to 80.54 %. Both the MIMO antennas show excellent diversity performance in terms of envelope correlation coefficient (ECC), Directive Gain (DG), Total active reflection coefficient (TARC), channel capacity loss (CCL), and mean effective gain (MEG) ratio. Both the structures achieve ECC of less than 0.006, DG of more than 9.9 dB, TARC of less than −19.84071 dB, CCL of less than 0.00179 bits/s/Hz, and MEG of less than −0.00577 dB in measurements. The overall dimensions of 2 port and 4 port antennas are limited to 44×22×1.6mm3 and 44×52×1.6mm3, respectively. These characteristics of the proposed antennas make them suitable for use in wireless high-speed communications.

The wireless communication system is steered towards the millimeter wave spectrum to achieve low latency and high-speed data rate. The MIMO antennas aid in attaining a higher data rate. The prominent spectrum at millimeter wave is Ka-band, suitable for short-range communication. The $\vert \text{S}$ -parameter $\vert $ response and radiation pattern of the existing MIMO antenna at this band are relatively unstable. Hence it encouraged to design and develop a four-element MIMO antenna operating at Ka-band. The antenna is a circular ring shape with two concentric rings with a plus-shape stub overlayed on circular rings. The structure is developed in four-stage with the comprehension of characteristic mode theory (CMA). The proposed structure generated Mode 2 as an efficient mode, with minor Modes 3 and 5 contributing for resonance out of five modes. The overall antenna profile is $3.27\lambda _{0} \times 3.74\lambda _{0}$ (where $\lambda _{0}$ is the wavelength at a resonance frequency of 28 GHz). The novel decoupling structure has improved the isolation to 30 dB and increased the bandwidth. The antenna has an operating bandwidth of 24.1-30.9 GHz, with a maximum gain of 6.5 dBi. The $\vert \text{S}$ -parameter $\vert $ from all the ports has an exact and stable response. The proposed antenna has resulted in bidirectional radiation tilted at an angle of $334^{0}$ and $210^{0}$ in the XZ plane. In the YZ plane, it has a triple beam. The radiation pattern is also stable throughout the bandwidth. The proposed MIMO antenna has a symmetrical design, demonstrating the possibility of expansion to n-element MIMO through a six-element MIMO antenna design. The article also presents the channel capacity, path loss, and link margin calculation for designed antenna line-of-sight (LOS) communication. The antenna has been evaluated with diversity parameters such as ECC, DC, CCL, TARC, and MEG.

The growing demand for high-speed communication has resulted in developing terahertz (THz) antennas that operate at high-frequency, high-speed, and high data rates. An ultra-broadband functioning four port THz multiple input and multiple output (MIMO) antenna with a defective ground plane as a decoupling structure is proposed in this study. A rectangular metallic patch was changed by integrating parasitic components onto the radiator with the lowered ground plane on a polyamide substrate to obtain the ultra wideband THz frequency operating antenna. The designed THz antenna has been transformed into a MIMO antenna by replicating horizontally and vertically with the separation of 0.08 λ and 0.01 λ, respectively (λ computed at 2 THz). The proposed THz MIMO antenna operates in the 2–10.7 THz frequency range and has an overall substrate dimension of 40 μm x 46 μm × 2 μm. The proposed antenna equivalent circuit is designed to validate the impedance bandwidth of the antenna. The designed THz MIMO antenna has isolation better than 20 dB across the impedance bandwidth. The isolation enhancement is achieved by creating alternate current channels through the defected ground structure of the antenna. The proposed THz MIMO antenna's MIMO diversity features are studied and determined to be ECC

This article presents a novel S/C/X band antenna specifically designed for 5G and beyond applications. The antenna's performance is thoroughly analyzed through comprehensive simulations using CST Microwave Studio on an FR-4 substrate, measuring 10λ × 14λ × 0.014λ (where λ is calculated at a lower resonance frequency). The proposed design displays remarkable characteristics, boasting an outstanding impedance bandwidth of 124% and an impressive return loss of −38 dBi. Its operational frequency ranges from 2.8 to 12 GHz, with a central frequency of 7.4 GHz. Throughout this range, the antenna maintains stable polar patterns, ensuring consistent and efficient performance with a wide gain of 3.98 dBi and an impressive efficiency of 84.2%. This antenna proves to be well-suited for diverse applications, including S-band: 3.1–4.2 GHz, C-band: 4.4–5.0 GHz, X-band: 8.0–12.0 GHz, and 5G and beyond communication. The innovative features of this S/C/X band antenna offer significant potential for advancing wireless communication technologies.

A double-stub matching technique is used to design a dual-band monopole antenna at 28 and 38 GHz. The transmission line stubs represent the matching elements. The first matching network comprises series capacitive and inductive stubs, causing impedance matching at the 28 GHz band with a wide bandwidth. On the other hand, the second matching network has two shunt inductive stubs, generating resonance at 38 GHz. A Smith chart is utilized to predict the stub lengths. While incorporating their dimensions physically, some of the stub lengths are fine-tuned. The proposed antenna is compact with a profile of 0.75λ1×0.66λ1 (where λ1 is the free-space wavelength at 28 GHz). The measured bandwidths are 27–28.75 GHz and 36.20–42.43 GHz. Although the physical series capacitance of the first matching network is a slot in the ground plane, the antenna is able to achieve a good gain of 7 dBi in both bands. The proposed antenna has a compact design, good bandwidth and gain, making it a candidate for 5G wireless applications.

This article presents a planar, non-angular, series-fed, dual-element dipole array MIMO antenna operating at 28 GHz with the metasurface-based isolation improvement technique. The initial design is a single-element antenna with a dual dipole array which is series-fed. These dipole elements are non-uniform in shape and distance. This dipole antenna results in end-fire radiation. The dipole antenna excites the J1 mode for its operation. Further, with the view to improve channel capacity, the dipole array expands the antenna to a three-element MIMO antenna. In the MIMO antenna structure, the sum of the J1, J2, and J3 modes is excited, causing resonance at 28 GHz. This article also proposes a metasurface structure with wide stopband characteristics at 28 GHz for isolation improvement. The metasurface is composed of rectangle-shaped structures. The defected ground and metasurface structure combination suppresses the surface wave coupling among the MIMO elements. The proposed antenna results in a bandwidth ranging from 26.7 to 29.6 GHz with isolation improvement greater than 21 dB and a gain of 6.3 dBi. The antenna is validated with the diversity parameters of envelope correlation coefficient, diversity gain, and channel capacity loss.

Broadband antennas with a low-profile generating circular polarization are always in demand for handheld/ portable devices as CP antennas counter multipath and misalignment issues. Therefore, a compact millimeter-wave antenna is proposed in this article. The proposed antenna structure comprises two circular rings and a circular patch at the center. This structure is further embedded with four equilateral triangles at a 90° orientation. The current entering the radiator is divided into left and right circular directions. The equilateral triangles provide the return path for current at the differential phase of ±90°, generating circular polarization. Structural development and analysis were initially performed through the characteristic mode theory. It showed that Modes 1 to 4 generated good impedance matching from 20 to 30 GHz and Modes 1 to 5, from 30 to 40 GHz. It also demonstrated the summation of orthogonal modes leading to circular polarization. The antenna-measured reflection coefficient |S11| > 10 dB was 19 GHz (23–42 GHz), and the axial ratio at −3 dB was 4.2 GHz (36–40.2 GHz). The antenna gain ranged from 4 to 6.2 dBi. The proposed antenna was tested for link margin estimation for IoT indoor conditions with line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. The communication reliability with co- and cross-polarization was also studied under these conditions, and the results proved to be satisfactory.

This article introduces a miniaturized antenna for 5G-II band millimeter-wave communication. The antenna’s performance is meticulously examined through comprehensive simulations carried out using CST Microwave Studio, employing an FR-4 substrate with dimensions measuring 12 × 14 × 1.6 mm3. The proposed design exhibits exceptional qualities, featuring an impressive impedance bandwidth of 70.4% and a remarkable return loss of −35 dBi. The operational frequency range of this antenna extends from 16.2 GHz to 33.8 GHz, featuring a central frequency of 25 GHz, positioning it effectively within the 5G-II Band. The antenna consistently maintains polar patterns throughout this spectrum, which guarantees dependable and efficient performance. It showcases a substantial gain of 3.85 dBi and an impressive efficiency rating of 82.9%. Renowned for its versatility, this antenna is well suited for a diverse range of applications, including but not limited to Ka band, Ku band, 5G-II bands, and various other purposes in microwaves.

In this work, a switchable bandstop filter is used as a decoupling structure for developing a miniaturized reconfigurable multiple input multiple output (MIMO) antenna. Initially, a dual band ((2.43-2.60 GHz and 3.51-3.79 GHz)) single monopole antenna structure is developed on FR4 substrate. Then the single monopole antenna and its replica are accommodated in a small space with an edge to edge separation distance of 11 mm to form a 2 port MIMO antenna. Now, a switchable bandstop filter is used as a decoupling network between two closely spaced monopole antenna elements to prevent mutual coupling and reconfigure the antenna characteristics. The dual pole switchable bandstop filter is configured in such a way that one of its poles lies at 2.5 GHz in one state (Mode 1) and at 3.68 GHz in another state (Mode 2) under the switching action of two PIN diodes. Controlling the ON/OFF states of the PIN diodes in the bandstop filter, high isolation is achieved alternately in lower (2.43-2.60 GHz) and upper (3.51-3.79 GHz) frequency bands of the MIMO antenna. Also, stub network is used to improve impedance matching in the upper frequency band. The proposed isolation technique helps the antenna to yield high isolation (>30 dB), fair gain (>2.97 dBi), reasonable radiation efficiency (>86.8 %), low envelope correlation coefficient (< 0.16), high diversity gain (DG >9.88 dB), low Mean effective gain ratio (MEG 1/MEG 2 < 0.05 dB) and low channel capacity loss (CCL < 0.06 bits/s/Hz) for both the operating frequency bands. The overall dimension of the antenna is restricted to 44mm $\times $ 22mm ( $0.36\lambda _{o}\,\,\times \,\,0.18\lambda _{o}$ ) for its easy integration in compact wireless devices. This type of reconfigurable MIMO antenna is best suited for cognitive radio communication, which promotes efficient spectrum utilization.

In this paper, a unique negative refractive index-metamaterial (NRI-MTM) structure is proposed for traffic alert and collision avoidance system (TCAS) for aircraft application. The NRI-MTM unit-cell structure is a combination of square and circular split ring structures. The proposed square and circular split ring metamaterial (SCM) is designed on the top of a 1.6 mm thick FR-4 substrate, with a single circular split ring on the bottom of the substrate. The total dimension of the SCM unit-cell is 23 $\times $ 23mm2 ( $0.08\lambda \,\,\times \,\,0.08 \lambda$ ), resonating at 1.06 GHz. This unit-cell is further used to create a 5 $\times $ 4 array structure with a dimension of 130 $\times $ 111mm2 ( $0.46\lambda \,\,\times \,\,0.4 \lambda$ ). A High-Frequency Structure Simulator (HFSS) is used to assess the electromagnetic properties of the proposed structures. Furthermore, in order to analyse the double negative (DNG) behaviour of the designed SCM structure, the unit-cell is rotated from 0 to 360 degrees with a step of 60 degrees along the azimuthal plane. On doing so, it is observed that, the proposed SCM structures, including unit-cell and array structures, exhibit DNG and NRI properties over the frequency band of 0.5 to 1.2 GHz, thus making it optimum for aircraft surveillance application. The SCM unit-cell and 5 $\times $ 4 SCM array structure were fabricated, and the measured results are in well agreement with the simulated results. Further, the array structure is used as a superstrate on the patch antenna to analyze the impact of the MTM on the antenna performance. In comparison to the antenna without the MTM structure, the $5\times $ 4 SCM array loaded antenna has a gain improvement of 2.8dB and a bandwidth enhancement of 31.5MHz.

A low-profile printed six-port ultrawideband (UWB) antenna with a novel decoupling structure for enhancing port-to-port isolation is analyzed in this paper. Six symmetrical pyramidal form UWB antennas with defective ground structures interspersed with parasitic components served as a unique decoupling structure in the proposed design. The grounded branches and modified rectangular stubs on the ground plane generate closed and open current distribution channels, causing the uniform current flow to be disrupted and the coupling effect to be neutralized. The projected six-port antenna has an electrical dimension of $0.68\times 0.89 \times 0.01\,\,\lambda ^{3}$ ( $\lambda $ is computed using a lower frequency of 2.9 GHz), having a below -10 dB impedance bandwidth of 116% from 2.9 to 11 GHz. Across the impedance bandwidth, the average port-to-port isolation is better than 20 dB. The antenna design has acceptable radiation properties with a peak gain of 8.3 dBi at a frequency of 7.5 GHz. Further, the projected design is also exposed to the time domain characteristics and diversity metrics. Among the different ports, the values of the group delay and fidelity factors are less than 1.5 ns and more than 0.92, correspondingly. The values of the diversity parameters such as ECC < 0.075, DG approximately 10 dB, MEG $ < -3$ dB, TARC $ < -10$ dB, CCL < 0.3 bps/Hz, and ME $ < -2$ dB ensure that the projected design is appropriate for the MIMO applications. The designed antenna is fabricated and measured, and the results are in line with the simulation.

The demand for wide bandwidth has driven us to focus on the higher spectrum, the millimeter wave (mmWave) spectrum. The mmWave offers several advantages, such as wide bandwidth, low latency, and higher data rate, but the signal at these frequencies significantly suffers high atmospheric attenuation and path loss. To overcome these issues, array antennas are used as it provides high gain, better directivity, and bandwidth. This paper presents a detailed review of array antennas based on feeding methods and discusses reconfigurable arrays. The series-fed array results in a narrow bandwidth, high return losses, and low gain that can be resolved with tapered structures, coplanar waveguide (CPW), and SIW technique. Similarly, transmission losses, coupling losses, and high side lobe-levels in parallel-fed arrays can be addressed with multilayer structures, coplanar strips with CPW, pill-box transmission, ridge gap waveguide (RGWG), graphene material, and magnetoelectric dipoles. The merits of series and parallel feed methods are availed with the hybrid feed method. These feeding methods with arrays are extended to reconfigurable array along with active RF switch with stubs, continuous or discrete phase shifter, butler matrix, and/or graphene nanoplates. The parameter performance metrics of these arrays are summarized and concluded with the future scope.

The increased traffic in e-commerce, cloud-based processing, social media, and online video streaming demands higher data rates. The current 4G has reached the bottleneck, due to which it may not be able to fulfill the high data demand, so the focus is drifting toward millimeter wave (mmWave). The mmWave spectrum ranging from 30 to 300 GHz offers wide bandwidth with low latency, which finds its application in various communication fields, including 5G cellular. Despite its atmospheric attenuation and non-line-of-sight (NLOS) propagation, most countries are currently adopting mmWave 5G at the 28/38 GHz band due to less atmospheric attenuation, low path loss exponent, and low signal spread at these bands. The single-element patch antenna is a compact solution for mmWave applications, but its performance is inferior in terms of bandwidth, gain, and radiation efficiency. The array antennas have overcome these demerits, as it has shown a significant increase in bandwidth, gain, and radiation efficiency. Still, it has a limitation on data rate support. As a result, Multiple-Input-Multiple-Output (MIMO) technology can increase the data rate to 1000 times through spatial diversity and multiplexing techniques. So, to refine the performance further, there is a need to comprehend the MIMO antenna structures designed so far at mmWave. This paper presents the planar MIMO antenna structures developed so far, categorized here as slot, coplanar waveguide, defected ground structures, tapered/Vivaldi, meta-surface/metamaterial, dielectric resonator, and flexible antennas. The performance of these designs is compared based on bandwidth, gain, isolation, efficiency, and radiation pattern. This article also discusses the effects of slots, partial ground, and decoupling structures on impedance matching, bandwidth, and isolation levels. Also, a thorough discussion of the design issues and future work to be undertaken is discussed in this here.

The development of electronic systems and wireless communication has led to a proportional increase in data traffic over time. One potential solution for alleviating data congestion is to augment the bandwidth capacity. This study presents a novel asymmetric circular slotted semi-circle-shaped monopole antenna design using a defective ground structure. The extended ultrawide bandwidth is achieved by implementing a design where the semi-circle radiator is etched in a specific asymmetric circular slot. This involves etching a circle with a radius of 1.25 mm at the center of the radiator, as well as a succession of circles with a radius of 0.75 mm along the edges of the radiator. In addition, the ground plane is situated at a lower elevation and features a U-shaped truncation that has been etched onto its surface. The expansion of the impedance bandwidth can be accomplished by making adjustments to the radiator and ground plane. The UWB antenna under consideration possesses a geometric configuration of 21.6 × 20.8 × 1.6 mm3 and the antenna is fabricated using an FR-4 glass epoxy substrate. The UWB antenna operates throughout the frequency range of 2.2–16.5 GHz, exhibiting a gain of at least 3.45 dBi across the entire impedance bandwidth and the maximum peak gain of 9.57 dBi achieved at the mid-resonance frequency of 10.5 GHz. The investigation of the antenna’s physical properties is conducted utilizing characteristic mode analysis. The investigation also includes an analysis of the time-domain characteristics, revealing that the group delay was found to be less than 1 ns across the operational frequency range. The predicted and measured findings demonstrate consistency and confirm that the suggested antenna is suitable for electronic systems and wireless applications.

Advancement in smartwatch sensors and connectivity features demands low latency communication with a wide bandwidth. ISM bands below 6 GHz are reaching a threshold. The millimeter-wave (mmWave) spectrum is the solution for future smartwatch applications. Therefore, a compact dual-band antenna operating at 25.5 and 38 GHz is presented here. The characteristics mode theory (CMT) aids the antenna design process by exciting Mode 1 and 2 as well as Mode 1–3 at their respective bands. In addition, the antenna structure generates two traverse modes, TM10 and TM02, at the lower and higher frequency bands. The antenna measured a bandwidth (BW) of 1.5 (25–26.5 GHz) and 2.5 GHz (37–39.5 GHz) with a maximum gain of 7.4 and 7.3 dBi, respectively. The antenna performance within the watch case (stainless steel) showed a stable |S11| with a gain improvement of 9.9 and 10.9 dBi and a specific absorption rate (SAR) of 0.063 and 0.0206 W/kg, respectively, at the lower and higher bands. The link budget analysis for various rotation angles of the watch indicated that, for a link margin of 20 dB, the antenna can transmit/receive 1 Gbps of data. However, significant fading was noticed at certain angles due to the shadowing effect caused by the watch case itself. Nonetheless, the antenna has a workable bandwidth, a high gain, and a low SAR, making it suitable for smartwatch and IoT applications.

This article is aimed at designing an inventive compact-size quad-port antenna that can be operated within terahertz (THz) frequency spectra for a 6G high-speed wireless communication link. The single-element antenna comprises a lotus-petal-like radiating patch and a defected ground structure (DGS) on a 20 × 20 × 2 µm3 polyamide substrate and is designed to operate within the 8.96–13.5 THz frequency range. The THz antenna is deployed for a two-port MIMO configuration having a size of 46 × 20 × 2 µm3 with interelement separation of less than a quarter-wavelength of 0.18λ (λ at 9 THz). The two-port configuration operates in the 9–13.25 THz frequency range, with better than −25 dB isolation. Further, the two-port THz antenna is mirrored vertically with a separation of 0.5λ to form the four-port MIMO configuration. The proposed four-port THz antenna has dimensions of 46 × 46 × 2 µm3 and operates in the frequency range of 9–13 THz. Isolation improvement better than −25 dB is realized by incorporating parasitic elements onto the ground plane. Performance analysis of the proposed antenna in terms of MIMO diversity parameters, viz., envelope correlation coefficient (ECC) < 0.05, diversity gain (DG) ≈ 10, mean effective gain (MEG) < −3 dB, total active reflection coefficient (TARC) < −10 dB, channel capacity loss (CCL) < 0.3 bps/Hz, and multiplexing efficiency (ME) < 0 dB, is performed to justify the appropriateness of the proposed antenna for MIMO applications. The antenna has virtuous radiation properties with good gain, which is crucial for any wireless communication system, especially for the THz communication network.

Mid-air collisions (MACs) are commonly caused by temporary or permanent loss of flight control resulting in catastrophic damages and hence must be countered with suitable technology. The avionic industry has been using Traffic Alert and Collision Avoidance System (TCAS) for avoiding mid-air collisions since 1987. The TCAS either uses an Omni-directional antenna or a directional antenna for the surveillance of other nearby aircraft. The existing TCAS directional antennas, i.e., an array of monopole antennas are characterized by a maximum gain of 3.6 dB, which is regarded as low. As a result, many research has been carried out to find the alternative for the TCAS antenna and have found microstrip patch antenna (MPA) which yield some promising results such as feed flexibility, multiband, beam steering, etc. However, the MPA still suffers from disadvantages such as low gain and narrow bandwidth. Hence, lately, a tremendous amount of work has been carried out to enhance the gain of the MPA. In this paper, we first review the key methods that has been reported so far to improve the gain of the traditional TCAS antenna. We note that, in most of the reported work, conventional techniques such as parasitic patches, and shorting pins are used to improve the gain of MPA, and no substantial work was done using advanced techniques such as electromagnetic-band gap (EBG), metamaterials and metasurfaces. Hence, we further review the work that has been carried out to improve the gain of vertically polarized MPAs using advanced techniques for L- and S-band (up to 3 GHz). Many advanced structures that are easily adapted to enhance the gain of TCAS antenna are thoroughly discussed in this work.

The progress of technology in consumer electronics demand an antenna having a compact size, high gain and bandwidth, and multiple antennas at transmitter and receiver to enhance the channel capacity. Over the last decade, numerous techniques are proposed to improve the performance of the antenna. One such technique is the use of metamaterials (MTMs) in antenna design. MTMs are artificial structures to provide unique electromagnetic properties that are not available in natural materials. The unique properties of these materials allow the design of high-performance antennas, filters, and microwave devices which cannot be obtained using traditional antennas. Loading antenna with the one, two, and three-dimensional MTM structures comprised of a periodic subwavelength unit cell exhibits RLC resonant structures and allows to manipulate electromagnetic waves in the antenna system. These structures offer low resonant frequency compared to the antenna resonant frequency resulting in antenna miniaturization and manipulation of electromagnetic waves helps in enhancing the gain and bandwidth, and achieving circular polarization (CP) of an antenna system. Also, metamaterial loading enhances isolation between the antenna elements in the multiple-input-multiple output (MIMO) system by suppressing the surface waves. In this paper, the electromagnetics of MTM with analytical expressions and its application in antenna design are discussed in detail. The MTM-based antennas are classified into MTM loading, MTM inspired antenna, metasurface loading, and composite right/left hand (CRLH) based antennas. The recent development in MTM inspired antenna and its application in antenna miniaturization, enhancing gain and bandwidth, achieving CP and mutual coupling suppression in MIMO antenna systems are discussed to make it useful for further research.

In the last decade, a new dawn for research on microwave imaging (MI) has been observed in the medical domain specially in the breast cancer diagnosis, since it offers many advantages over current imaging systems like computed tomography (CT), X-ray radiography etc. Microwave imaging system (MIS) provides a suitable platform for in-depth inspection of breast tissues. It helps in identification and localisation of morphological changes in these tissues. The emerging Ultrawideband (UWB) MI gives better results due to its non-ionizing signals which operate over the frequency ranging from hundreds of Megahertz (MHz) to tens of Gigahertz (GHz). In these systems, antennas play a significant role in establishing a sensor network. Hence, its optimization is very crucial because the device is placed at close proximity to the human body. In this paper, a miniaturised monopole patch antenna which operates at UWB frequency range with a microstrip feed line is proposed. The design is composed of a small rectangular patch with dimensions 0.17λ×0.25λ×0.02λ (where λ is wavelength calculated at lower operating frequency 4.8 GHz). It has four corner cuts and a centrally located square slot with a truncated ground-plane for achieving UWB properties. The proposed antenna has the measured fractional bandwidth of 141%(3.22-11.92GHz) with linearly increasing gain ranging from (1.4 to 6.43 dBi). The detailed time domain analysis is done to prove the efficacy of antenna for signal propagation. The advantage of proposed antenna is that it has low profile, compact size, easy to design which can be employed in MI breast cancer detection.

The modern electronic device antenna poses challenges regarding broader bandwidth and isolation due to its multiple features and seamless user experience. A compact vase-shaped two-port ultrawideband (UWB) antenna is presented in this work. A circular monopole antenna is modified by embedding the multiple curved segments onto the radiator and rectangular slotted ground plane to develop impedance matching in the broader bandwidth from 4 to 12.1 GHz. The UWB monopole antenna is recreated horizontally with a separation of less than a quarter wavelength of 0.13 λ (λ computed at 4 GHz) to create a UWB multiple input and multiple output (MIMO) antenna with a geometry of 20 × 29 × 1.6 mm3. The isolation in the UWB MIMO antenna is enhanced by inserting an inverted pendulum-shaped parasitic element on the ground plane. This modified ground plane acts as a decoupling structure and provides isolation below 21 dB across the 5–13.5 GHz operating frequency. The proposed UWB MIMO antenna’s significant modes and their contribution to antenna radiation are analyzed by characteristic mode analysis. Further, the proposed antenna is investigated for MIMO diversity features, and its values are found to be ECC < 0.002, DG ≈ 10 dB, TARC < −10 dB, CCL < 0.3 bps/Hz, and MEG < −3 dB. The proposed antenna’s time domain characteristics in different antenna orientations show a group delay of less than 1 ns and a fidelity factor larger than 0.9.

A compact circular structured monopole antenna for ultrawideband (UWB) and UWB dual-band notch applications is designed and fabricated on an FR4 substrate. The UWB antenna has a hybrid configuration of the circle and three ellipses as the radiating plane and less than a quarter-lowered ground plane. The overall dimensions of the projected antennas are 16 × 11 × 1.6 mm3, having a −10 dB impedance bandwidth of 113% (3.7–13.3 GHz). Further, two frequency band notches were created using two inverted U-shaped slots on the radiator. These slots notch the frequency band from 5–5.6 GHz and 7.3–8.3 GHz, covering IEEE 802.11, Wi-Fi, WLAN, and the entire X-band satellite communication. A comprehensive frequency and time domain analysis is performed to validate the projected antenna design’s effectiveness. In addition, a circuit model of the projected antenna design is built, and its performance is evaluated. Furthermore, unlike the traditional technique, which uses the simulated surface current distribution to verify functioning, characteristic mode analysis (CMA) is used to provide deeper insight into distinct modes on the antenna.

A novel quadruple-notch UWB (ultrawideband) antenna for wireless applications is presented. The antenna consists of a decagonal-shaped radiating part with Sierpinski square fractal slots up to iteration 3. The ground part is truncated and loaded with stubs and slots. Each individual stub at the ground plane creates/controls a particular notch band. Initially, a UWB antenna is designed with the help of truncation at the ground plane. Miniaturization in this design is achieved with the help of Sierpinski square fractal slots. Additionally, these slots help improve the UWB impedance bandwidth. This design is then extended to achieve a quadruple notch by loading the ground with various rectangular-shaped stubs. The final antenna shows the UWB range from 4.21 to 13.92 GHz and notch frequencies at 5.02 GHz (C-band), 7.8 GHz (satellite band), 9.03, and 10.86 GHz (X-band). The simulated and measured results are nearly identical, which shows the efficacy of the proposed design.

Antenna design involves continuously optimizing antenna parameters to meet the desired requirements. Since the process is manual, laborious, and time-consuming, a surrogate model based on machine learning provides an effective solution. The conventional approach for selecting antenna parameters is mapped to a regression problem to predict the antenna performance in terms of S parameters. In this regard, a heuristic approach is employed using an optimized random forest model. The design parameters are obtained from an ultrawideband (UWB) antenna simulated using the high-frequency structure simulator (HFSS). The designed antenna is an embedded structure consisting of a circular monopole with a rectangle. The ground plane of the proposed antenna is reduced to realize the wider impedance bandwidth. The lowered ground plane will create a new current channel that affects the uniform current distribution and helps in achieving the wider impedance bandwidth. Initially, data were preprocessed, and feature extraction was performed using additive regression. Further, ten different regression models with optimized parameters are used to determine the best values for antenna design. The proposed method was evaluated by splitting the dataset into train and test data in the ratio of 60:40 and by employing a ten-fold cross-validation scheme. A correlation coefficient of 0.99 was obtained using the optimized random forest model.

This paper discusses an elliptical ultrawideband (UWB) antenna and a dual-band UWB notch antenna. To achieve a UWB bandwidth, two corner cuts are etched into the rectangular slot on the partial ground plane. An inverted-U-shaped and conductor-shaped resonator are utilized to achieve dual-band notch characteristics on a partial ground plane. The suggested antenna has an overall dimension of 24×32 mm2. The suggested UWB antenna has a gain of 4.9 dB, a bandwidth of 2.5–11 GHz, a linear phase response, a group delay of less than 1 ns, and a steady radiation pattern. The suggested UWB notch rejects WLAN and ITU bands from 5.2–5.7 GHz and 7.2–8.5 GHz, respectively, with an impedance bandwidth of 2.5–11 GHz. The UWB notch antenna features a linear phase, a group delay of less than 1 ns, and a stable radiation pattern.

The cognitive radio paradigm for developing next-century wireless communication systems is rapidly entering the mainstream, and various aspects of it are currently being applied in 5G technology, aeronautical engineering, military communications, emergency, and public safety applications, satellite communication, and healthcare. Cognitive radio focuses on the existence of software defined radio architectures that allow dynamic reconfiguration. Many researchers have taken initiatives in the last decade to achieve the reconfiguration ability in cognitive radio systems to support the concept of dynamic spectrum access. As cognitive radio adapts dynamic spectrum allocation for its users, the physical implementation requires reconfigurable filters that can alter the carrier frequencies and bandwidth. Although there are many ways to reconfigure filter operation, diode based reconfiguration has received utmost attention among researchers because of its shorter response delay and easy implementation. In the last decade, researchers have reported several diode-based reconfigurable filters, including their characteristics such as filter function, filter combination, tuning range, variation in bandwidth, isolation, and resonance. However, to examine the potential of these filters in the application of cognitive radio, a comprehensive review needs to be pursued. In this review article, the descriptions of several diode based reconfigurable filters are illustrated with their exhibiting characteristics. The detailed information provided in this article has disclosed that primarily three different types diode based reconfigurable filters have been reported by researchers: Tunable, Switchable, and Hybrid (Both Tunable and Switchable). It is also found that each type of reconfiguration can further be segregated in terms of filter function, centre frequency variation, and bandwidth variation. The detailed categorization of the reconfiguration presented in this paper provides a systematic approach to select the correct reconfigurable filter for the desired frequency reconfiguration in cognitive radio.

A compact Sierpinski Carpet square fractal multiband antenna operating at 3.9 (WiMAX) /6.6 (Satellite TV) /8.1/10.7/11.8 GHz (X-band) is presented. The proposed Microstrip Patch Antenna (MSPA) consists of a Sierpinski Carpet square fractal radiator in which square slots are etched out and a tapered microstrip feed line. The Sierpinski Carpet square fractal patch modifies the current resonant path thereby making the antenna to operate at five useful bands. Impedance matching at these bands are solely achieved by using Sierpinski square slot and tapered feedline, thus eliminating the need of any external matching circuit. The dimensions of the compact antenna is 32 x 32 x 1,6 mm3 and exhibits S11

A compact planar multiband antenna operating at 3.1 (S-band) /4.7/6.4/7.6 (C-band) /8.9/10.4/11.8 GHz (X-band) is presented. The proposed Microstrip Patch Antenna (MSPA) consists of a rectangular radiator in which an E-shaped slot is etched out and a microstrip feed line. The E-shaped slot modifies the total current path thereby making the antenna to operate at seven useful bands. No external impedance matching circuit is used and the impedance matching at these bands are solely achieved by using a rectangular microstrip feed line of length 10mm (L6) and width 2mm (W10). The antenna has a compact dimension of ���� × ���� × ��. �� ������ and exhibits S11

In recent years, there has been a surge of interest in the field of wireless communication for designing a monitoring system to observe the activity of the human body remotely. With the use of wireless body area networks (WBAN), chronic health and physical activity may be tracked without interfering with routine lifestyle. This crucial real-time data transmission requires low power, high speed, and broader bandwidth communication. Ultrawideband (UWB) technology has been explored for short-range and high-speed applications to cater to these demands over the last decades. The antenna is a crucial component of the WBAN system, which lowers the overall system’s performance. The human body’s morphology necessitates a flexible antenna. In this article, we comprehensively survey the relevant flexible materials and their qualities utilized to develop the flexible antenna. Further, we retrospectively investigate the design issues and the strategies employed in designing the flexible UWB antenna, such as incorporating the modified ground layer, including the parasitic elements, coplanar waveguide, metamaterial loading, etc. To improve isolation and channel capacity in WBAN applications, the most recent decoupling structures proven in UWB MIMO technology are presented.

The 5th generation (5G) network was planned to provide a fast, stable, and future-proof mobile communication network to existing society. This research presents a highly compact arc shape structure antenna resonating at 28 GHz for prospective millimeter-wave purposes in the 5G frequency spectrum. The circular monopole antenna is designed with a radius of 1.3 mm. An elliptical slot on the radiating plane aids in achieving an enhanced bandwidth resonating at the frequency of 28 GHz. Including an elliptical slot creates new resonance and helps improve the bandwidth. The antenna has an ultra-compact dimension of 5 × 3 × 1.6 mm3, which corresponds to an electrical length of 0.46λ × 0.28λ × 0.14λ, where λ is free space wavelength at the resonant frequency. The projected antenna has an impedance bandwidth of 15.73 % (25.83–30.24 GHz). The antenna has a good radiation efficiency of 89%, and the average gain is almost 4 dB over the entire impedance bandwidth. The simulated and experimental S11 findings are in good agreement.

The ever-increasing demand and need for high-speed communication have generated intensive research in the field of fifth-generation (5G) technology. Sub-6 GHz 5G mid-band spectrum is the focus of the researchers due to its meritorious ease of deployment in the current scenario with the already existing infrastructure of the 4G-LTE system. The 5G technology finds applications in enormous fields that require high data rates, low latency, and stable radiation patterns. One of the major sectors that benefit from the outbreak of 5G is the field of flexible electronics. Devices that are compact need an antenna to be flexible, lightweight, conformal, and still have excellent performance characteristics. Flexible antennas used in wireless body area networks (WBANs) need to be highly conformal to be bent according to the different curvatures of the human body at different body parts. The specific absorption rate (SAR) must be at a permissible level for such an antenna to be suited for WBAN applications. This paper gives a comprehensive review of the current state of the art flexible antennas in a sub-6 GHz 5G band. Furthermore, this paper gives a key insight into the materials for a flexible antenna, the parameters considered for the design of a flexible antenna for 5G, the challenges for the design, and the implementation of a flexible antenna for 5G.

A compact reconfigurable MIMO antenna was developed for cognitive radio applications in this research work. A bandstop filter-based decoupling network was employed in this MIMO antenna to keep mutual coupling at a minimum. A single PIN diode was connected in the filter configuration for the purpose of reconfiguration. Controlling the ON/OFF conditions of the PIN diode, it became possible to achieve a MIMO operating frequency of 4.75 GHz in mode 1 and 1.77 GHz in mode 2, respectively. At 4.75 GHz, isolation was 42.68 dB, while at 1.77 GHz, isolation was 26.52 dB. The proposed reconfigurable MIMO antenna achieved a peak gain and radiation efficiency of 6.63 dBi and 92.04 percent in mode 1 and 4.41 dBi and 89.64 percent in mode 2. MIMO characteristics such as an envelope correlation coefficient (ECC) less than 0.253, diversity gain (DG) greater than 9.675 dB, a mean effective gain (MEG) measurement ratio of less than 0.00388 dB, and channel capacity loss (CCL) of less than 0.06528 bits/s/Hz were measured for both operational frequency bands. To make it simple to integrate into small wireless devices, the overall size of the antenna is limited to 48 mm×24 mm 0.28 λ0×0.12 λ0.

The advancement of electronic gadgets makes it possible for a device to be multipurpose, which calls for attributes such as compactness and larger bandwidth, with improved data transfer rate. This paper introduces the compact, closely placed two-port dual band-notched UWB antenna using a neutralization line as a decoupling structure. The projected antenna design comprised a circle and rectangle embedded monopole radiator with the defected ground structure to attain the UWB spectrum. Further dual notches are attained by carving the U-shape and inverted U-shape slots on the feedline and radiator. The dual band-notched UWB antennas are placed with the separation of 3.8 mm (0.04 λ; λ is computed using 3.4 GHz frequency). The coupling effect between the close proximity elements is decoupled using the neutralization line. The presented antenna has overall dimensions of 21.5 × 28 × 1.6 mm3 (0.24 × 0.31 × 0.01 λ3) and exhibits S11 below −10 dB from 3.4–11.9 GHz, with isolation better than 16 dB throughout the impedance bandwidth. The antenna also provides frequency band rejection of 4.5–5.3 GHz and 7.2–9 GHz covering the WLAN and entire X-band satellite communication. The projected antenna is explored through characteristic mode analysis, time-domain characteristics, and MIMO diversity features to analyze the effectiveness and usefulness of the antenna. The group delay is less than 1 ns except for the frequency rejection band and fidelity factor greater than 0.96. The projected antenna exhibits MIMO diversity metrics ECC < 0.3, DG > 9.6 dB, MEG < −3 dB, TARC < −10 dB, CCL < 0.3 bps/Hz, and ME < −2 dB across the operational frequency, except for the notched bands. The designed two-port antenna is validated by printing on an FR4 substrate. The simulated and measured findings are in line with and appropriate for MIMO wireless applications.

Cognitive radio (CR), which is a common form of wireless communication, consists of a transceiver that is intelligently capable of detecting which communication channels are available to use and which are not. After this detection process, the transceiver avoids the occupied channels while simultaneously moving into the empty ones. Hence, spectrum shortage and underutilization are key problems that the CR can be proposed to address. In order to obtain a good idea of the spectrum usage in the area where the CRs are located, cooperative spectrum sensing (CSS) can be used. Hence, the primary objective of this research work is to increase the realizable throughput via the cluster-based cooperative spectrum sensing (CBCSS) algorithm. The proposed scheme is anticipated to acquire advanced achievable throughput for 5G and beyond-5G Internet of Things (IoT) applications. Performance parameters, such as achievable throughput, the average number of clusters and energy, have been analyzed for the proposed CBCSS and compared with optimal algorithms.

With the recent advancement and phenomenal progress in the field of wireless communication technology, there is an ever increasing demand for high data rates and improved quality of service for the end users. In recent times various designs of super wideband antennas (SWB) fulfilling diverse objectives have been proposed for modern wireless networks. Design of compact and wideband antenna for high speed, high capacity, and secure wireless communications presents a challenging task for designers of fixed and mobile wireless communication systems. In this paper, a comprehensive review concerning antenna structures and the technologies adopted for design and analysis of SWB antennas for wireless application is reported. Comparative parameters in terms of electrical dimension, bandwidth, Fractional bandwidth (FB) and Bandwidth Dimension Ratio (BDR) are presented which introduces the researchers to the technical challenges in the design of a compact wideband antenna. This paper contributes to present existing novel approaches along with its adequacy in the design techniques. This review exercise will assist the researchers with valuable support for further research and to achieve better impedance matching, wide bandwidth, high gain and good efficiency along with well directive radiation characteristics.