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This work presents a methodology for the generation and classification of phase-resolved partial discharge (PRPD) patterns based on the use of a printed UHF monopole antenna and signal conditioning circuit to reduce hardware requirements. For this purpose, the envelope detection technique was applied. In addition, test objects such as a hydrogenerator bar, dielectric discs with internal cavities in an oil cell, a potential transformer and tip–tip electrodes immersed in oil were used to generate partial discharge (PD) signals. To detect and classify partial discharges, the standard IEC 60270 (2000) method was used as a reference. After the acquisition of conditioned UHF signals, a digital signal filtering threshold technique was used, and peaks of partial discharge envelope pulses were extracted. Feature selection techniques were used to classify the discharges and choose the best features to train machine learning algorithms, such as multilayer perceptron, support vector machine and decision tree algorithms. Accuracies greater than 84% were met, revealing the classification potential of the methodology proposed in this work. [ABSTRACT FROM AUTHOR]

Efforts to protect electric power systems from faults have commonly relied on the use of ultra-high frequency (UHF) antennas for detecting partial discharge (PD) as a common precursor to faults. However, the effectiveness of existing UHF antennas suffers from a number of challenges such as limited bandwidth, relatively large physical size, and low detection sensitivity. The present study addresses these issues by proposing a compact microstrip patch antenna with fixed dimensions of 100 mm × 100 mm × 1.6 mm. The results of computations yield an optimized antenna design consisting of 2nd-order Hilbert fractal units positioned within a four-layer serpentine arrangement with a fractal unit connection distance of 3.0 mm. Specifically, the optimized antenna design achieves a detection bandwidth for which the voltage standing wave ratio is less than 2 that is approximately 97.3% of the UHF frequency range (0.3-3 GHz). Finally, a prototype antenna is fabricated using standard printed circuit board technology, and the results of experiments demonstrate that the proposed antenna is capable of detecting PD signals at a distance of 8 m from the discharge source. [ABSTRACT FROM AUTHOR]

A Spaceborne broadband circularly polarized conformal antenna for ultra high frequency band is presented. The antenna mounted on the outer surface of the circular arc spherical cone satellite works in 390–450 MHz frequency band, and has the characteristics of broadband, light miniature. The measured results for the antenna demonstrate an impedance bandwidth of 32.5% from 360 to 500 MHz, an axial ratio bandwidth of 27.2% from 380 to 500 MHz, and a peak gain of 6.7 dBic. The antenna form can be applied to the field of broadband circularly polarized conformal antenna on satellite and missile, and has a wide application prospect. [ABSTRACT FROM AUTHOR]

A semi‐spherical combined transverse electromagnetic (TEM) horn and loop antenna is designed for directional ultra‐wideband operation from 0.42 to 6 GHz for 5G and beyond 5G applications across military and commercial sectors. The antenna structure fits within a sphere with 3‐cm radius, thus operating as electrically small over the lower part of the band (ka = 0.5 at 0.795 GHz and ka = 1 at 1.59 GHz). To spread the currents across the volume while maintaining the required relationship between the lowest order TE and TM modes, the loop section is modified to conform with the enclosing minimum sphere. The TEM horn, bowtie, and resistive loading are then tuned to achieve improvement over the conventional topology in the radiation efficiency by >7% when ka = 0.5 and >22% when ka = 1. [ABSTRACT FROM AUTHOR]

Parallel transmission (pTX) techniques are required to tackle a number of challenges, e.g., the inhomogeneous distribution of the transmit field and elevated specific absorption rate (SAR), in ultra-high field (UHF) MR imaging. Additionally, they offer multiple degrees of freedom to create temporally- and spatially-tailored transverse magnetization. Given the increasing availability of MRI systems at 7 T and above, it is anticipated that interest in pTX applications will grow accordingly. One of the key components in MR systems capable of pTX is the design of the transmit array, as this has a major impact on performance in terms of power requirements, SAR and RF pulse design. While several reviews on pTX pulse design and the clinical applicability of UHF exist, there is currently no systematic review of pTX transmit/transceiver coils and their associated performance. In this article, we analyze transmit array concepts to determine the strengths and weaknesses of different types of design. We systematically review the different types of individual antennas employed for UHF, their combination into pTX arrays, and methods to decouple the individual elements. We also reiterate figures-of-merit (FoMs) frequently employed to describe the performance of pTX arrays and summarize published array designs in terms of these FoMs. [ABSTRACT FROM AUTHOR]

Magneto-dielectric antennas (MDAs) provide small sizes, enhanced bandwidths, and frequency/polarization agility. We describe the fabrication and efficiency characterization at 0.4–0.8 GHz of five microstrip MDAs, whose gradually thicker substrates were 3D-printed using an off-the-shelf polylactic acid (PLA) filament doped with ferromagnetic particles. It was experimentally discovered that efficiency increases monotonically from 12% (−9.2 dB) to 37% (−4.3 dB) as substrate thickness goes from 1.6 to 4.3 mm; the rate is faster than expected for microstrip antennas. Numerical analysis indicated that the apparent magnetic loss tangent of the MD substrate experiences a threefold decrease as the 3D printer deposits more layers of iron-doped PLA. The MDAs exhibit radiation quality factors that are 3.7–7.2 times better than the dielectric counterparts. Moreover, a simple optimization of ground plane size could increase efficiency to 55% (−2.6 dB). The reduction in magnetic loss is attributed to a reduction in eddy current loss due to the separation of agglomerate iron particles. Therefore, despite the inherently lossy material used, the potential of 3D-printed MD substrates in providing acceptable antenna efficiencies is demonstrated together with unprecedented design freedom and fabrication flexibility. [ABSTRACT FROM AUTHOR]

The use of flexible, built-in, ultra-high-frequency (UHF) antenna sensors is an effective method to solve the weak high-frequency electromagnetic wave signal sensing of partial discharge (PD) inside gas-insulated switchgears (GISs), and the compatibility of flexible UHF antenna sensor substrate materials and SF6/N2 mixtures is the key to the realization of a flexible UHF antenna sensor inside a GIS. Based on this, this paper builds an experimental platform for the compatibility of a 30% SF6/70% N2 gas mixture and a PD flexible UHF antenna sensor substrate and conducts compatibility experiments between the 30% SF6/70% N2 gas mixture and PD flexible UHF antenna sensor substrate under different temperatures in combination with the actual operating temperature range of the GIS. In this article, a Fourier transform infrared spectrometer, scanning electron microscope and X-ray photoelectron spectrometer were used to test and analyze the gas composition, the surface morphology and the elemental change in the PD flexible UHF antenna sensor substrate, respectively. PET material will be slightly oxidized under the environment of a 30% SF6/70% N2 gas mixture at 110 °C, PI material will generate metal fluoride under the environment of a 30% SF6/70% N2 gas mixture and only PDMS material will remain stable under the environment of a 30% SF6/70% N2 gas mixture; therefore, it is appropriate to use PDMS substrate in the development of flexible UHF antenna sensors. [ABSTRACT FROM AUTHOR]

In this paper, a planar tag antenna for UHF band RFID composed of a spiral ending meandered line with meandered inductive loop is presented. The presented novel compact spiral ended meandered tag having double sided meandered inductive loop microstrip dipoles scales down the extent of tag antenna and provides an upgraded conjugate impedance matching between tag antenna and semiconductor ASIC. This tag antenna operates at 866 MHz. Here, a compact UHF tag having volume of 60×16×1:6mm3 (0:173λ×0:046λ×0:0046λ) is testified. This antenna produces impressive reflection coefficient and is able to access detection territory of 12.6 m. The proposed RFID antenna layout is simulated in favor of reader having 4W EIRP. [ABSTRACT FROM AUTHOR]

Spiral antenna sensors are commonly used in partial discharge (PD) ultra-high frequency (UHF) detection in gas-insulated switchgears (GISs). However, most of the existing UHF spiral antenna sensors are based on a rigid base and balun, such as FR-4. The safe built-in installation of antenna sensors requires the complex structural transformation of GISs. To solve this problem, a low-profile spiral antenna sensor is designed based on a polyimide (PI) flexible base, and its performance is optimized by improving the clearance ratio. The simulation and measurement results show that the profile height and diameter of the designed antenna sensor is 0.3 mm and 137 mm, which is 99.7% and 25.4% smaller than the traditional spiral antenna. Under a different bending radius, the antenna sensor can maintain VSWR ≤ 5 in 650 MHz~3 GHz, and its maximum gre is up to 6.1 dB. Finally, the PD detection performance of the antenna sensor is carried out on a real 220 kV GIS. The results show that, after being built in, the PD with a weak discharge magnitude of 4.5 pC can be effectively detected by the antenna sensor, and the antenna sensor has the ability to quantify the severity of PD. In addition, through the simulation, the antenna sensor has potential for the detection of micro water in GISs. [ABSTRACT FROM AUTHOR]

High-frequency (HF) and ultrahigh-frequency (UHF) dual-band radio frequency identification (RFID) tags with both near-field and far-field communication can meet different application scenarios. However, it is time-consuming to calculate the return loss of a UHF antenna in a dual-band tag antenna using electromagnetic (EM) simulators. To overcome this, the present work proposes a model of a multi-scale convolutional neural network stacked with long and short-term memory (MSCNN-LSTM) for predicting the return loss of UHF antennas instead of EM simulators. In the proposed MSCNN-LSTM, the MSCNN has three branches, which include three convolution layers with different kernel sizes and numbers. Therefore, MSCNN can extract fine-grain localized information of the antenna and overall features. The LSTM can effectively learn the EM characteristics of different structures of the antenna to improve the prediction accuracy of the model. Experimental results show that the mean absolute error (0.0073), mean square error (0.00032), and root mean square error (0.01814) of the MSCNN)LSTM are better than those of other prediction methods. In predicting the return loss of 100 UHF antennas, compared with the simulation time of 4800 s for High Frequency Structure Simulator (HFSS), MSCNN-LSTM takes only 0.927519 s under the premise of ensuring prediction accuracy, significantly reducing the calculation time, which provides a basis for the rapid design of HF-UHF RFID tag antenna. Then MSCNN-LSTM is used to determine the dimensions of the UHF antenna quickly. The return loss of the designed dual-band RFID tag antenna is −58.76 and −22.63 dB at 13.56 and 915 MHz, respectively, achieving the desired goal. [ABSTRACT FROM AUTHOR]

A novel miniaturized dipole antenna design incorporating triple sleeves and shorting load leading to enhanced bandwidth is proposed in the present work. The Triple Sleeve Dipole Antenna with Shorting Loads is designed from 500 to 3000 MHz with no tuning mechanism. The concept of triple sleeve and distributed shorting loads reduced the length of the antenna by 51.5% compared to a half wave dipole antenna at the lowest frequency. The equivalent circuit of the antenna in terms of lumped elements is determined by using a Genetic algorithm. The proposed antenna is simulated in CST Microwave Studio, fabricated, evaluated and the results are presented. The antenna can be used for trans-receive applications of wireless communications in military systems. [ABSTRACT FROM AUTHOR]

A simple method is proposed for the realisation of compact dual‐polarised antennas. The aperture area of a dual‐polarised dipole antenna can be reduced by half by surrounding the antenna with a square loop. Based on the method, a broadband compact dual‐polarised antenna is developed. The broadband dual‐polarised antenna consists of two ±45°‐polarised dipoles surrounded by a square loop and fed by two orthogonal broadband baluns. A resonance at a sfrequency (fLr = 0.7 GHz) is created by the square loop, leading to a compact size of about λLr/4 × λLr/4, where λLr is the wavelength in free space at fLr. Another resonance at a higher frequency (fHr = 1.5 GHz) is generated by etching open slots on the ±45°‐polarised dipoles. A combination of the lower‐frequency and the higher‐frequency resonances results in a broadband operation. Simulation and experimental results show that the compact dual‐polarised antenna achieves an impedance bandwidth of 75% (0.69–1.52 GHz) for return loss > 15 dB with stable radiation patterns, which is potential to be used for 5G new radio base‐station applications. [ABSTRACT FROM AUTHOR]

This paper aims to enhance the gain of a microstrip patch antenna for ultra-high frequency (UHF) radio frequency identification (RFID) reader. The paper proposes a new antenna design that consists of a perfectconductor rectangular patch with a quasi H-shaped slot using a flame retardant substrate and an aluminum ground plane. In order to improve the gain while keeping a modest antenna size, an empirical parametric study is performed using the CST Studio Suite software. As a result, an enhanced slotted antenna design is obtained with a total size of 136 × 124 × 3 mm3 and a gain of 5.24 dBi at 922-MHz frequency. Such a gain magnitude is shown to be significantly higher than those obtained by analogous single patch antennas.

External partial discharge (PD) sensors for the ultra-high frequency (UHF) method are widely used to detect the PD signals in highvoltage power equipment for ease of installation and maintenance. However, conventional external PD sensors detect not only PD signals but also LTE signals; thus, a microwave filter is usually employed. In this work, a UHF filtering antenna (filtenna) is proposed as the external PD sensor to detect PD signals and simultaneously block LTE-band signals. The proposed UHF filtenna is the printed monopole antenna with a built-in interdigital bandpass geometry, which is selected for its compact size. Measurement results show that the proposed UHF-printed monopole filtenna operates adequately in the frequency range of 1 GHz to 1.6 GHz and simultaneously blocks LTE signals significantly. [ABSTRACT FROM AUTHOR]

One of the most common failures or breakdowns that can occur in high-voltage (HV) equipment is due to partial discharges (PDs). This occurs as a result of inadequate insulation, aging, harsh environmental effects, or manufacturing flaws. PD detection and recognition methods have gained growing attention and have seen great progress in the past decades. Radiometric methods are one of the most investigated detection approaches due to their immunity to electromagnetic interference (EMI) and their capabilities to detect and locate PD activities in different applications such as transformers, cables, etc. Several review articles have been published to classify and categorize these works. Nonetheless, some concepts are missing, and some improvement techniques, such as PD detection at high-frequency (HF) and very high-frequency (VHF), have been overlooked. We present in this paper an exhaustive review study of state-of-the-art PD detection based on radiometric methods at different usable radiofrequency bands (i.e., HF, VHF, and UHF). Accordingly, we propose a new generic categorization approach based on the detected electromagnetic wave component (magnetic or electric fields) and pick-up location, either from free space or ground cable. [ABSTRACT FROM AUTHOR]

In this article, we have performed a comprehensive investigation in the specialty of ultra-high frequency (UHF) printable antennas for partial discharge (PD) diagnostics. Due to the complex characteristics of PD signals in UHF range, selection of printable antenna becomes a major concern for PD diagnostics. The main contribution of this article is that we have provided a complete roadmap of selecting UHF printable antennas through relating antenna parameters with their practical significance on PD diagnostics in high-voltage equipment. We have highlighted 7 intrinsic parameters of UHF antennas and indicated their relationship with 7 extrinsic parameters of PD diagnostics performance. Following the extracted relationship, we have investigated on 8 different designing methods of UHF antennas. Based on the available results of recently reported works and their critical analyses, we have pointed out the existing challenges and indicated the future direction of UHF printable antennas for contactless partial discharge diagnostic systems. [ABSTRACT FROM AUTHOR]

Summary: The growth of small communication devices has pushed designers to design compact‐size antennas. These antennas must be low cost, lightweight, needed for mechanically robust construction, and ease of installation. In this paper, we use a novel genetic algorithm (GA) to produce an ensemble of compact self‐avoiding (SA) antennas such that the voltage standing wave ratio (VSWR) is less than 2 at the desired frequencies (as a measure of efficiency); an optimization criterion to get a desirable multiband antenna in the ultra high frequency (UHF) band. First, the electromagnetic properties of these antennas are simulated using the method of moments in MATLAB. SA antennas form a particular set of dipoles introduced here by applying a novel backtracking algorithm. We also use a Lindenmayer system that generates the geometries by a Turtle graphics render to reach our goal. Next, we simulate the VSWR for 150,000 SA antennas with lengths L from 0.1 to 0.4 m; 10 different frequencies are chosen randomly within the UHF band to obtain our results. All the VSWR ≤ 2 are clustered using density‐based spatial clustering of applications with noise algorithm (DBSCAN), so our method provides the frequency ranges where this condition is fulfilled. From this, we obtain the VSWR minimums used for the antenna design. Finally, as an instance, we use our results to select the appropriate size of a multiband antenna and, through genetic algorithms, modify the geometry to satisfy the design requirements. [ABSTRACT FROM AUTHOR]

This letter proposes a new ultrahigh frequency (UHF) flexible planar biconical antenna design method for partial discharge (PD) detection in gas-insulated switchgear. Continuous transverse branching increases the electrical length to expand the bandwidth and miniaturize the antenna. For comparison of the effects of the lateral branch structure model, the optimized dimensions of both designed antennas are 150×150 mm, and both use polydimethylsiloxane, flexible material with a thickness of 0.5 mm, as the substrate. The results show that the S11 of the antennas is less than −10 dB in the bands of 0.3–0.5, 0.64–1.25, and 1.4–3.0 GHz, and the planar biconical antennas still maintain good bandwidth and gain under different bending radii of 0, 150, 350, and 500 mm. The PD test platform was built to test the antenna. The experimental data show that the two flexible antennas designed in this letter can detect the PD-radiated electromagnetic wave signal with a discharge of 15 pc before and after the bending deformation and meet the UHF partial discharge detection requirements. [ABSTRACT FROM AUTHOR]

A planar UHF RFID tag antenna with a hybrid nested slot and T-match network is presented. A novel T-match network in a nested slot is introduced to have superior conjugate impedance matching between tag antenna and the semiconductor microchip. Size curtailment is acquired by means of exploiting the T-match network branches and feeder strip line. Moreover, expanding the nested slot area and increasing the T-match branch length modify the electrical length and increase the antenna inductance. Thus by utilizing the arm of matching network and feeder, conjugate impedance is achieved in accordance with the semiconductor chip at 865 MHz. A surpassing UHF tag with volume 120 x 60 x 1:6mm³ (0:346λ x 0:173λ x 0:0046λ), with outstanding 10-dB return loss of 12 MHz, has been ourishingly demonstrated, and it is able to obtain a detection range of 13.9 m. This tag antenna composition is simulated with respect to 4W EIRP reader. [ABSTRACT FROM AUTHOR]

The simulation of a novel drone‐based near‐field (NF)/far‐field (FF) antenna measurement system enabling the reconstruction of Antenna Under Test (AUT) phase and the true location of the untethered drone using multiple land‐based reference antennas is described. The mathematical approach follows the principle used within Global Positioning System (GPS) position and time recovery. Conceptually, the satellites are replaced by ground‐based reference antennas of known location, the user location is now the drone location and the user clock offset is replaced by the unknown AUT phase radiated at the angle subtended between the AUT and drone location. This addresses the need for drone‐based NF/FF antenna measurement of large in situ VHF/UHF antenna arrays plus the need to measure the installed performance of microwave antennas on structures such as buildings, aircraft and ships. To assess the viability, a computer simulation of the measurement system is constructed and its performance is analysed in terms of the accuracy of reconstruction of the AUT phase and true drone location, as well as the NF/FF radiation pattern accuracy in terms of the equivalent multipath level (EMPL). An example measurement 'range', comprising AUT location and six fixed reference antennas, demonstrates a wide AUT operating bandwidth of (0.5–2) GHz, with EMPL < −50 dB over the forward hemisphere. [ABSTRACT FROM AUTHOR]

A design approach of triband conformal monopolar antenna combining cavity mode and equivalent circuit (Ec) is proposed. First, based on mode analysis, two lower and closer resonant frequencies in the VHF-band are generated by introducing two slot rings and two circles of short vias to a circular parallel-plate structure. Second, its Ec is extracted and modified. Then, the geometry structure is improved accordingly. An inverted truncate cone is introduced to modify the characteristic impedance of the monolithic radial transmission line to obtain an available band in the middle frequency (UHF). Finally, a high-frequency (L) antenna is embedded into the truncate cone and excited by a novel composite feeding structure. Furthermore, the conformal performance of the triband antenna is investigated. The conformal antenna prototype is fabricated and achieves a triband within 69.3–72.5 MHz, 317–348 MHz, and 1.38–1.71 GHz with a size of $0.42\lambda _{0}\times 0.42\lambda _{0}\times 0.014\lambda _{0}$ (maximum wavelength). The realized gain in triband is −7.6 to −5.9, 4.7–5.4, and 4.7–5.9 dBi, respectively. For a 6 cm-thick FR-4 substrate combined with shorted metal columns, the triband conformal antenna has the potential on serving as a vehicle roof to bear the load, and it is attractive in vehicle communication too. [ABSTRACT FROM AUTHOR]

This letter presents a loop antenna array for ultrahigh frequency near-field and far-field radio frequency identification (RFID) reader applications. The antenna array consists of several microstrip collinear loop antennas, and each loop antenna is composed of several periodic radiating units. By deploying microstrip collinear radiating units, a novel loop antenna with in-phase radiating currents is realized, which generates a strong and uniform magnetic field over a large interrogation area and a horizontally polarized omnidirectional radiation. By configuring the array antenna, the magnetic fields distribute on the entire antenna array and create an enlarged near-field reading area. The far-field coverage is enlarged by the superposition of omnidirectional radiation. The antenna array is simulated and validated with a four-element prototype made on FR-4 substrates. The antenna array is measured to have a −10 dB impedance bandwidth from 802 to 963 MHz with an enlarged near-field reading volume of 280 × 280 × 540 mm and a far-field gain of 6.66 dBi at the UK RFID band. [ABSTRACT FROM AUTHOR]

Two novel multisegment loops coupled ultrahigh-frequency (UHF) radio frequency identification near-field (NF) antenna with a uniform and strong magnetic field distribution over an electrically large interrogation zone are designed. Each proposed antenna is composed of eight loops, and the current distribution along the loop is kept in-phase using a segmented line. To further achieve a more uniform magnetic field, the last four loops of the two proposed antennas (ANT 1 and ANT 2) are loaded with parasitic structures. Here, a 100% detection rate is achieved by ANT 1 within an interrogation area of 370×560×105 mm3 for the bidirectional operation setup. As for ANT2, it is backed by an artificial magnetic conductor to enhance the magnetic field strength and reduce the profile with respect to a configuration with a PEC reflector plane, and it has yielded a 100% detection rate within the interrogation area of 370×560×185 mm3 for the unidirectional operation setup. The proposed ANT2 can cover the UHF band of China, the Federal Communications Commission band of North America, and European Telecommunication Standards Institute band of Europe. [ABSTRACT FROM AUTHOR]

Abstract Achieving a high‐gain omnidirectional patch antenna with low profile is a challenging task. On the basis of improving antennas by metamaterials, a broadband near‐zero‐index metamaterial (NZIM) is designed to enhance the horizontal gain of the omnidirectional patch antenna. The zero‐index metamaterial is loaded on the substrate of three antennas with different working bands (4.99–5.50 GHz). The results show that the horizontal gain of antennas is enhanced by more than 0.6 dB at various frequencies. The roundness of antennas is also optimised. Therefore, using NZIM can increase the horizontal gain with a low profile (λ/30) structure size. The low profile, high‐gain omnidirectional patch antenna has great potential in the conformal field.

Abstract In the study, a miniaturised printed quadrifilar helix antenna (PQHA) with isoflux coverage and wide‐angle circular polarisation is presented. It is composed of a three‐stage stepped impedance spiral arm and open stubs. Each of the three‐stage spiral arms has different pitches and number of turns. For the last‐stage spiral arm, meander lines are used. The proposed PQHA features the characteristics of wide bandwidth, isoflux radiation, small size, and wide‐angle circular polarisation. Moreover, in order to feed the proposed PQHA, a miniaturised quad‐feed network is designed to provide equal amplitude signals with sequential orthogonal phases. For demonstration, a prototype is designed, fabricated, and measured. The overall size of the proposed antenna is 88 × 88 × 132 mm (0.44 λ0 × 0.44 λ0 × 0.66 λ0). The results show that isoflux radiation with a coverage of about ±60° is realised from 1.40 to 1.62 GHz (14.6%) while maintaining more than 10 dB return loss and larger than 200° 3‐dB axial ratio beamwidth.

A novel broadband ultra‐high frequency radio frequency identification (RFID) tag antenna attached to the metallic surface is proposed in this paper. A rectangular wide slot combined with a U‐shaped thin slot outside is adopted in the proposed antenna, and the size of the patch can be reduced by adjusting the length of the U‐shaped slot. Furthermore, a pair of symmetric resonator structures inside the rectangular slot are connected to both ends of the chip, which can excite a new resonant mode to broaden the frequency band. All the structures above are realized by etching rectangular slits on the same surface. The antenna has the advantages of wideband, simple processing, and good reading distance, and the 10 dB bandwidth of the antenna is 30 MHz (from 895 to 925 MHz), with a maximum directional gain of −3.5 dB. The reading distance can reach more than 5.4 m on a metallic surface. [ABSTRACT FROM AUTHOR]

In this letter, we evaluate antenna designs for ultra-high frequency and field (UHF) human brain magnetic resonance imaging (MRI) at 10.5 tesla (T). Although MRI at such UHF is expected to provide major signal-to-noise gains, the frequency of interest, 447 MHz, presents us with challenges regarding improved B1+ efficiency, image homogeneity, specific absorption rate (SAR), and antenna element decoupling for array configurations. To address these challenges, we propose the use of both monopole and dipole antennas in a novel hybrid configuration, which we refer to as a mono-dipole hybrid antenna (MDH) array. Compared to an 8-channel dipole antenna array of the same dimensions, the 8-channel MDH array showed an improvement in decoupling between adjacent array channels, as well as ∼18% higher B1+ and SAR efficiency near the central region of the phantom based on simulation and experiment. However, the performances of the MDH and dipole antenna arrays were overall similar when evaluating a human model in terms of peak B1+ efficiency, 10 g SAR, and SAR efficiency. Finally, the concept of an MDH array showed an advantage in improved decoupling, SAR, and B1+ near the superior region of the brain for human brain imaging. [ABSTRACT FROM AUTHOR]

Radio Frequency Identification (RFID) technology is one of the simplest forms of wireless communication systems. It is a unique concept that aims at connecting and identifying tagged assets or objects to RFID readers to collect information. This paper presents the design and implementation of a compact dual-band monopole antenna for RFID applications. The proposed design is a microstrip antenna structure composed of two coupled armed meander-lines having 90° between them to achieve circular polarization. The proposed design is mounted on a 1.6mm thick FR4-epoxy substrate backed by a partial ground plane with the total area of (58 x 80mm²) to ensure compact size of the design. The designed antenna is fed through a 50-ohm transmission line of length 28.5 mm. The antenna is considered dual bands that resonate at 850MHz and 1.5 GHz and radiates circularly polarized waves with an axial ratio of 1.4. The simulation results using HFSS software showed promising performance with a bandwidth of 141MHz at centre frequency 850MHz and 287MHz at centre frequency 1.5 GHz, respectively. The S11 parameter shows return loss of -21 dB at 850MHz band while at the higher frequency band the return loss is much better which was -39 dB. The design provides a perfectly omnidirectional radiation pattern and high radiation efficiency of 93%. Fabrication of the proposed design is done with practical results having a similar trend to the simulated ones to convey good performance of the designed antenna. [ABSTRACT FROM AUTHOR]

In this article, a novel ultra-high frequency radio frequency identification (UHF RFID) reader antenna is proposed and experimentally investigated. The proposed RFID antenna design consists of three layers; the first layer has a ring shape with a feeding line at the center, the second layer has a small periodic structure that affects the radiation performance of the antenna, and the third layer has a bent metal structure. The final design, with the dimensions of 129.2 mm × 129.2 mm × 26 mm, yields a 10-dB impedance bandwidth of 34 MHz (854–889 MHz) and a 3-dB axial-ratio bandwidth of 118 MHz (857–975 MHz). The antenna is fabricated and tested for its RF parameters and RFID metrics. In performance tests, ISO 18000–63 and Gen2v2 compatible RFID reader and tags are used. RFID tag reading tests have been successfully performed under specified communication protocols without any operational failure while providing RF communication. The measured results prove the technical potential of the proposed antenna to possess good RF performance in RFID based wireless networks. [ABSTRACT FROM AUTHOR]

The vehicle localization, which aims to identify a vehicle and then position the vehicle with a high precision, can be used to facilitate various applications and services in vehicular networks. Unfortunately, conventional localization systems, e.g., global positioning system (GPS), hardly meet the accuracy requirements especially in certain specific scenarios, such as tunnels. At the same time, Ultrahigh frequency (UHF) radio frequency identification (RFID) has become an efficient booster for internet of things (IoT) due to the desirable advantages, such as low cost, battery-free, and unique identification. In this paper, based on the UHF-RFID, we propose a novel real-time vehicle localization scheme in GPS-Less Environments. Considering the practical implementation of multiple RFID reader antennas on a vehicle is constrained, we adopt single antenna multi-frequency ranging scheme, in which the integer ambiguity problem is solved by the maximum-likelihood estimation (MLE)-based robust Chinese remainder theorem (CRT). With the reconstructed distances between the tags and the reader, the coordinates of the vehicle then can be calculated with the Levenberg-Marquardt (LM) algorithm. Furthermore, the computational complexities of the algorithms and the time consumption of the proposed scheme are analyzed. The experimental results demonstrate that the proposed scheme can track vehicle’s location with error lower than 27 cm at the probability of 90%. [ABSTRACT FROM AUTHOR]

This paper presents ultrawide band (UWB) Cage Dipole Antenna, designed and developed for ultra high frequency band ground penetrating radar (GPR) system. The presented cage antenna consists of two thick diverging cages composed of 10 cylindrical metallic rods. It operates at 500 MHz center frequency and provides 105% impedance bandwidth for |S11| <−10 dB. Antenna has donut‐shaped radiation pattern and provides 2.6‐dBi gain at center frequency. Impedance variation of designed Cage dipole antenna has been matched using wideband lumped component‐based balanced to unbalanced (Balun) network. Integrated analysis of cage dipole antenna and Balun network has been carried out in 3D electromagnetic simulator and analyzed results are presented. Moreover, metallic mount with Teflon bush has been designed to support the cage dipole antenna during far‐field characterization and its effect has also been taken into account during the analysis. Time‐domain analysis of proposed Cage dipole has been carried out and its results are presented in detail. Presented cage dipole antenna provides suppressed late ringing, making it best suitable for GPR applications. [ABSTRACT FROM AUTHOR]

Simultaneous MR-PET/-SPECT is an emerging technology that capitalises on the invaluable advantages of both modalities, allowing access to numerous sensitive tracers and superior soft-tissue contrast alongside versatile functional imaging capabilities. However, to optimise these capabilities, concurrent acquisitions require the MRI antenna located inside the PET/SPECT field-of-view to be operated without compromising any aspects of system performance or image quality compared to the stand-alone instrumentation. Here, we report a novel gamma-radiation-transparent antenna concept. The end-fed J-shape antenna is particularly adept for hybrid ultra-high field MR-PET/-SPECT applications as it enables all highly attenuating materials to be placed outside the imaging field-of-view. Furthermore, this unique configuration also provides advantages in stand-alone MR applications by reducing the amount of coupling between the cables and the antenna elements, and by lowering the potential specific absorption rate burden. The use of this new design was experimentally verified according to the important features for both ultra-high field MRI and the 511 keV transmission scan. The reconstructed attenuation maps evidently showed much lower attenuation ($\sim 15$ %) for the proposed array when compared to the conventional dipole antenna array since there were no high-density components. In MR, it was observed that the signal-to-noise ratio from the whole volume obtained using the proposed array was comparable to that acquired by the conventional array which was also in agreement with the simulation results. The unique feature, J-shape array, would enable simultaneous MR-PET/-SPECT experiments to be conducted without unduly compromising any aspects of system performance and image quality compared to the stand-alone instrumentation. [ABSTRACT FROM AUTHOR]

An m-shapedspoof surface plasmon polaritons (SSPPs) structure as well as its application into end fire antenna with vertical polarization, low profile and compact size are proposed to be conformal with vehicle shell. Beside the primary odd SSPPs mode in the center, extra even mode at the top horizontal arms and odd mode at the end of the arms are introduced through folded arms. Consequently, the end-fire pattern can be adjusted by varying the aperture size. The multiple modes of SSPPs structure enable the antenna to operate in dual bands. The 1st mode operates from 447 to 515 MHz while the 2nd mode works from 0.97 GHz to 1.81 GHz simultaneously in simulation. The profile of the manufactured prototype antenna is merely 0.1 ${{\rm{\lambda }}_0}$ (@ 487 MHz). It achieves a measured gain peak of 8.4 dBi with HPBW 111.9 $^\circ $ in the 1st mode around 500 MHz and gain peak of 9.2 dBi at 1.6 GHz in the 2nd mode. It can be a very promising candidate for conformal antenna being embedded into the thin shell to high load bearing application on the high-speed vehicles for mobile communication. [ABSTRACT FROM AUTHOR]

Abstract One of the main tools for monitoring the condition of high voltage equipment is the measurement of partial discharges (PD). The electromagnetic (EM) radiation originated from this degradation phenomenon can be captured by various types of ultra‐high frequency (UHF) antennas carefully designed and optimised for specific frequency bands. However, the presence of environmental noise may limit the use of this technique. Different types of monopole antennas normally used in UHF PD measurement have been evaluated in order to validate the performance of a novel separation technique of EM sources. Accordingly, a new separation technique based on the energy ratio of the captured signals was developed, considering noise interferences. The results revealed that the new technique allows an adequate separation, even when three sources act simultaneously.

Abstract This article reports a new class of quadrature feeding network which integrates an asymmetrical phase shifter to obtain the compact size and wideband property simultaneously. By adjusting the impedance of two loading stubs, this asymmetrical phase shifter can realize 90° phase shift, impedance transformation, and phase slope alignment at the same time. Operation principle and design procedure for this introduced quadrature feeding network are provided with synthesis equations and design curves. By using the shape of Archimedes gradual‐change lines, the area of this circuit layout is fully utilized, and the overall size of the proposed feeding network is only 0.050λg2. Compared with a traditional compact design, this technique can effectively enhance the amplitude balance bandwidth by 1.7 times (from 58% to 101%) and phase balance bandwidth by 5.9 times (from 14% to 83%) as well as keep the circuit size nearly unchanged under the same conditions. To verify the design concept, two prototypes of the quadrature feeding networks are designed, fabricated, and tested. Good agreement between the measured and simulated results is achieved and they well reveal the attractive wideband equal amplitudes and 90° phase balance performance for this proposed new compact quadrature feeding network.

One of the most common failures or breakdowns that can occur in high-voltage (HV) equipment is due to partial discharges (PDs). This occurs as a result of inadequate insulation, aging, harsh environmental effects, or manufacturing flaws. PD detection and recognition methods have gained growing attention and have seen great progress in the past decades. Radiometric methods are one of the most investigated detection approaches due to their immunity to electromagnetic interference (EMI) and their capabilities to detect and locate PD activities in different applications such as transformers, cables, etc. Several review articles have been published to classify and categorize these works. Nonetheless, some concepts are missing, and some improvement techniques, such as PD detection at high-frequency (HF) and very high-frequency (VHF), have been overlooked. We present in this paper an exhaustive review study of state-of-the-art PD detection based on radiometric methods at different usable radiofrequency bands (i.e., HF, VHF, and UHF). Accordingly, we propose a new generic categorization approach based on the detected electromagnetic wave component (magnetic or electric fields) and pick-up location, either from free space or ground cable.

A compact tag antenna, which has a geometrical dimension of 31.5 mm $\times31.5$ mm $\times3.2$ mm, is constructed using a stacked planar inverted-L antenna (PILA) for metal-mountable applications in the UHF radio frequency identification (RFID) passband. The new antenna is formed by inserting a shorted patch into a PILA structure to create a double-layered inverted antenna, which can be viewed as a cascade of two parallel resonant tanks. An increase in electric field intensity in the antenna structure has brought in sufficient capacitance for reducing the tag resonant frequency effectively to the useful UHF RFID passband. Due to the increase in the antenna reactance, conjugate impedance matching can be easily achieved between the antenna and the microchip. Fine-tuning schemes such as stubs and slits are also incorporated with the proposed tag antenna for adjusting the operating frequency to an exact precision. Measurements show that the proposed tag antenna can achieve a read distance of 7.25 m at an EIRP power of 4 W. The resonance of the proposed tag antenna is found to be very stable and it is insensitive to changes in the backing metal platform. [ABSTRACT FROM AUTHOR]

For the first time, the concept of inductive channel is introduced for tuning the resonant frequency of a bowtie dipolar tag antenna, which has a compact physical size of 50 mm $\times50$ mm $\times3.38$ mm (0.1447 $\lambda \,\,\times0.1447\,\,\lambda \,\,\times 0.0098\,\,\lambda$), for applying on metal surfaces. The narrow inductive channel, which is embedded with an external lumped inductor, is loaded on top of the dipolar antenna for achieving arbitrary tuning capability in a broad range. It has been found that the top-loading patch can enhance the fields of the dipole, and the inductive channel can regulate the current flows on the top-loading patch. By adjusting the channel width and the external inductance, the resonant frequency can be effectively adjusted without affecting the read performances of the tag much. Here, an equivalent circuit has also been constructed for analyzing the impedance characteristics of the proposed tag antenna. The proposed tag antenna can achieve a measured maximum reading distance of nearly 19 m at an effective isotropic radiated power of 3.28 W. It can be arbitrarily tuned to operate at any frequency in the UHF band by simply adjusting the lumped inductor’s value, without changing the antenna structure. The proposed antenna is found to be insensitive to the variation in the backing metal plate, and its operating frequency does not fluctuate with the plate size. [ABSTRACT FROM AUTHOR]

The use of LoRa (Long Range) wireless communication as an Internet-of-Things (IoT) protocol has great potential. This technology works in the unlicensed ISM band and covers all the globe with different frequencies, which can improve the wide and rapid spread of information. To obtain global IoT coverage using LoRa, the use of satellite networks is mandatory. The development of nanosatellites, mostly in the CubeSat form factor, for communication applications in general and LoRa communication in particular, is currently increasing. To date, these satellites usually use linear wire deployable antennas for communication. However, deployable mechanical systems present the risk of failure during the mission. In fact, one-unit CubeSat geometry allows a very small space (10 cm * 10 cm * 0.06 cm) for the antenna. Since the size of the antenna is proportional to wavelengths, the antenna size is a large problem for low frequencies, especially in the UHF band. For this reason, planar antennas are an attractive solution for CubeSat communications. This work presents the design of a miniaturized printed monopole meander line antenna working at a frequency of 920 MHz. The novelty of the design is obtained by placing the meander line and the ground plane onto similar sides of the antenna. The meander line allows reduction of the antenna size by a factor of λ/5 for the selected operating frequency. The structure of this proposed antenna has a low profile, and a small size of 50 * 80 * 1.635 mm3 or about 0.153λ 0 * 0.245 λ 0. It has an S11 magnitude of –33.53 dB obtained by simulation and S11 magnitude of −19 dB obtained through experimental measurements. The simulation results also show that the proposed meander line antenna will produce an omnidirectional radiation pattern and a maximum gain of 1.8 dB. [ABSTRACT FROM AUTHOR]

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For the first time, the ionic polymer metal composite (IPMC) actuator is integrated with a radio frequency identification (RFID) tag antenna for achieving frequency reconfiguration in the ultrahigh-frequency (UHF) band. Here, the IPMC movable flap serves as an actuator that can effectively tune the tag resonant frequency. By applying a two-layer-crenelated structure and employing a surface patterned electrode for restraining back relaxation, the deflection of the IPMC actuator can be significantly improved. The IPMC actuator can move in two directions, enabling two-degree frequency tuning. Numerical and experimental data confirm that the tip displacement of the IPMC actuator can be enhanced up to 266% with the use of the two-layer-crenelated structure. The IPMC actuator allows the resonant frequency of the tag antenna to be tuned back by as much as 35 MHz, after deviating due to placing on an unintended object. UHF RFID application is also performed using a portable commercial RFID reader. Good frequency reconfiguration and broad tuning range, along with far read distances, have been achieved with our tunable UHF RFID tag antenna. [ABSTRACT FROM AUTHOR]

This work is focused on how to efficiently shrink a patch antenna operating in the UHF band. Five typical independent methods are first introduced that were solely used to realize a small patch antenna. A potential combination method is further discussed utilizing two or more of these five methods. One miniature patch antenna is experimentally demonstrated operating at 735 MHz using the combination method, in which both of shorting wall and complementary split ring resonators are applied in a reconciling way. A two-step optimization procedure is given to show how the antenna sizes can be significantly reduced with this combination method. The antenna is fabricated on a simple dielectric with a low εr of 2.2. The patch size is only 0.127λ x 0.123λ. The antenna efficiency is considerably high as 77% in measurement. [ABSTRACT FROM AUTHOR]

The security aspects of aeronautical ad-hoc networks (AANET) relying on reflective intelligent surface (RIS) are considered. A projection-based deep neural network (DNN) is designed for maximizing the secrecy rate of the proposed RIS-aided AANET. While the multiple-layer architecture of the DNN enables learning the functional relationship between the target variables of the optimization problem and the ground-air channels, the projection method guarantees that the constraint of the optimization problem is not violated. Our design outperforms the state-of-the-art projected gradient descent algorithms and that the RIS is capable of enhancing the security. [ABSTRACT FROM AUTHOR]

In this letter,a circularly-polarized (CP) metal-tolerant tag antenna with a long reading distance (RD) is proposed for the ultra-high frequency (UHF) radio-frequency identification (RFID) systems. In order to realize CP radiation and high gain, a cross slot is etched on top patch to provide two orthogonal polarizations, whereas the meandered strip on the central copper layer is used to obtain a 90° phase difference between adjacent ports. An equivalent circuit model is established to better understand the operating mechanism and impedance characteristic. A prototype mounted on a 200 mm × 200 mm metal plate has been manufactured and measured to verify the design and shows an impedance bandwidth of 8 MHz (918–926 MHz) and axial ratio bandwidth of 1.3 MHz (921.6–922.9 MHz). Also, a maximum gain of 2 dBi at 922 MHz and a maximum RD of about 22.4 m have been demonstrated. [ABSTRACT FROM AUTHOR]

One of the main challenges in ultra-high field whole body MRI relates to the uniformity and efficiency of the radiofrequency field. Although recent advances in the design of RF coils have demonstrated that dipole antennas have a current distribution ideally suited to 7T MRI, they are limited by low isolation and poor robustness to loading changes. Multi-layered and self-decoupled loop coils have demonstrated improved RF performance in these areas at lower field MRI but have not been adapted to dipole designs. In this work, we introduce a novel type of RF antenna consisting of integrated multi-modal antenna with coupled radiating structures (I-MARS), which use layered conductors and dielectric substrates to allow dipole and transmission line modes to co-exist on the same compact dipole-shaped structure. The proposed antenna was optimally designed for 7T MRI and compared with existing dipole antennas using numerical simulations, which showed that I-MARS had similar B1 over specific absorption rate efficiency and superior isolation and stability. Subsequently, a prototype pTx coil array was built and tested in vivo on healthy volunteers at 7T. The articulated, modular construction of the I-MARS coil array allowed it to be readily conformed across multiple body regions (hip, knee, shoulder, lumbar spine and prostate), without requiring modification of the tuning and matching of the antennas. Using RF shimming, uniform and efficient excitation was successfully achieved in the acquisition of high-resolution MR images. [ABSTRACT FROM AUTHOR]

The incoming 5G and beyond 5G wireless communications provide unprecedented ultra-high-speed transmission data rates. This is enabled by driving the carrier frequency up to millimeter-wave (mmWave) and terahertz (THz) bands and developing advanced multiplexing technology to increase spectrum bandwidth and spectral efficiency. In this article, we present novel discrete lens antenna designs to solve the two leading open challenges of orbital angular momentum (OAM) applications in mmWave and THz bands: OAM multiplexing and the diffractive problem of OAM waves. For discrete lens antennas operating at THz frequencies, the emerging 3D printing technology and its superior geometric flexibility are utilized to design and implement OAM antennas. The successful demonstration of the mmWave and THz OAM discrete lens antennas can open avenues for future several-hundred-gigabits-per-second wireless communications. [ABSTRACT FROM AUTHOR]

In this paper, we present a new antenna for radio frequency identification (RFID) tag operating in the Moroccan ultra high frequency (UHF) band around 868 MHz, this antenna is designed on a flexible plastic substrate of relative permittivity 3 and low tangential losses which is 0.002. The proposed tag is designed to identify clothing in supermarkets. The tag antenna has a miniature size of 38 mm in length and 26 mm in width. This miniature size was obtained by using two rectangular split ring resonator (RSRR). The impedance matching of the RFID chip with the antenna was carried out by a double T-matching structure. The antenna is designed, simulated and optimized using computer simulation technology (CST) microwave studio software and good results have been obtained in terms of impedance matching, gain and read range. [ABSTRACT FROM AUTHOR]

In this paper, a backfire suppressed aperture coupled circularly polarized (CP) stacked patch antenna for universal ultra-high frequency (UHF) radio frequency identification applications is presented. Cross-polarized backfire radiation patterns were successfully suppressed by a planar high impedance surface (HIS) reflector. The size of the fabricated antenna is 250 × 250 × 26.9 mm3 (0.71λ0 × 0.71λ0 × 0.076λ0) and its peak gain value of 7.1 dBi is measured. The distance between the antenna and the HIS reflector is only 4.8 mm (0.014 λ0). The HIS reflector suppressed cross-pol backfire radiations by about 10 dB. Detailed antenna and HIS reflector design are discussed thoroughly in this paper. The presented backfire suppression technique using the HIS reflector is scalable to other applications and frequency bands. This paper demonstrates the feasibility of the HIS structure at UHF band. [ABSTRACT FROM AUTHOR]