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A compact VHF/UHF ultrawideband discone antenna with consistent patterns is proposed in this article. The proposed antenna consists of a disk, a modified cone, an inverted cone, four shorting probes, and two sleeves. To improve the radiation angular distortion at high frequencies, two sleeves are inserted into the discone antenna. Higher-order modes are suppressed, and ultrawideband consistent patterns are obtained without antenna size increasing. An inverted cone and four shorting probes are introduced to achieve broadband and profile reduction. An antenna prototype is fabricated and measured. The proposed antenna possesses consistent patterns in a 11.36:1 bandwidth. The pattern nulls is improved by 26.1 dB. The antenna occupies a cylindrical volume of 0.227 λ 0 (D) and 0.096 λ 0 (H). It is a competitive candidate for future in-vehicle communication systems. [ABSTRACT FROM AUTHOR]

Power transformers are crucial and require continuous monitoring to prevent failures. Partial discharge (PD), a significant phenomenon, emits electromagnetic waves, acoustic waves, and light, and causes chemical decomposition of insulation materials. Current technology allows a real-time PD monitoring using the Ultra-High Frequency (UHF) method. This contribution aims to design a small printed antenna for internal UHF sensing within the transformer tank, using low-cost Printed Circuit Board (PCB) materials. A printed antenna less than 4 cm x 4 cm was designed and optimized through parameter sweeps to achieve a proper return loss below 1 GHz. Impedance matching is important to achieve an appropriate return loss, and smaller antennas face high impedance mismatching challenges. Adding a resistive loading can solve the impedance mismatching. To study the impact of the transformer tank model as a cavity resonator on the impedance matching of the printed antenna, the antenna was inserted into the tank model through different valves, and the return loss measurement was conducted. Furthermore, a frequency analysis was performed using a spectrum analyzer to identify the optimal frequency range for PD detection, ensuring a high signal-to-noise ratio. Validation of the performance of printed the antenna in PD detection for different PD models was done through a comparison of the Phase-Resolved Partial Discharge (PRPD) patterns obtained through conventional electrical PD measurements according to IEC 60270 and acquired by the printed antenna using the UHF method. This study demonstrates the feasibility of using a small printed antenna for real-time PD monitoring in high-voltage transformers. [ABSTRACT FROM AUTHOR]

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]

In this study, a low-cost dual-chip RFID tag antenna is proposed for indoor localization. The antenna integrates two RFID chips, each generating opposing radiation patterns. Angle-of-arrival based localization is performed with a single reader by analyzing the Received Signal Strength Indicator (RSSI) and the RSSI ratio of both chips. The antenna incorporates a mechanically adjustable reflector at the back that allows simple beam elevation control to tune the antenna for different indoor environments. The proposed dual-chip tag was measured in an indoor environment with different beam configurations. The localization is performed using a simple sinusoidal regression model with three model parameters and a linear regression model with two model parameters to fit the RSSI ratio of both chips and the RSSI of each individual chip, respectively. The proposed technique yields an average angle-of-arrival error better than 6.6° within the tag’s horizontal detection range of 4.2 meters.

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]

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.

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]

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]

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]

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]

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]

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.

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.

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]

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]

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]

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]

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 work, a circularly-polarized ultra-high frequency (UHF) partial discharge (PD) antenna is proposed to detect the PD in 0.6 GHz - 1.7 GHz. The proposed PD antenna consists of an Archimedean spiral antenna, a balun, and a cavity. The Archimedean spiral antenna is embedded by FR-4 as substrate and superstrate for miniaturization. The microstrip-to-paired strips balun is designed to yield good performance in the return loss, insertion loss, and amplitude and phase imbalances which are of great necessity for low axial ratio. The cavity is employed to obtain unidirectional radiation patterns and prevent external signal interference. However, it is found that the originally-designed cavity-backed antenna does not work properly near 1.35 GHz due to resonance phenomena in the cavity. In this work, the cavity is modified to tackle this problem. The proposed UHF PD antenna is fabricated and measured and the results show that it provides good impedance matching, realized gain, radiation pattern, and circular polarization.

The partial discharge (PD) in inverter-fed motors generated from high frequency and short rise time impulsive voltage are more complex than traditional sinusoidal voltage operated motors due to the noise initiated from fast switching power electronics devices. Available PD sensors and related technology for DC and sinusoidal voltage cannot be used at repetitive impulsive voltage conditions. This work aims to report the design of antenna with optimized geometry and satisfied parameters to detect PD for impulsive voltage. The antenna is verified and the influence of both impulse voltage parameters and test configuration on PD features are discussed. The envelope detection technique after the filter in the frequency domain was proposed to reduce the complexity and cost of PD test hardware under impulsive voltages with fast rise times. The frequency domain energy of PD from motor insulation is mainly distributed in the range of 0.6-1.8 GHz. By increasing the amplitude and frequency of input impulsive voltage, the range of PD energy spectrum is enlarged to (1.5-1.8 GHz) and by decreasing input amplitude the PD signal strength decays abruptly. Moreover, the high-frequency distribution of PD energy attenuates more severely with the distance and the electromagnetic energy of PD decays nonlinearly with the increase of propagation distance. Therefore, under the premise of satisfying the safety test, selecting the test distance below 15 cm can ensure that the test results have a high signal-to-noise ratio and signal integrity. The experience reported in this study could provide suggestions for off-line PD measurements for inverter-fed motor insulation evaluations for manufacturers.

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.

In this communication, a planar inverted-F antenna (PIFA) structure is employed for the realization of a compact and low profile metal mountable tag device for ultrahigh-frequency (UHF) radio frequency identification (RFID). In order to compensate dielectric parameters and/or tag chip impedance variations, and the effects of manufacturing tolerances or other imperfections which can cause severe performance degradation at the target frequency, a tag structure with three lumped elements and a U-shape slot with adjustable length for post-manufacturing working frequency and impedance matching tuning is proposed. In order to simplify the post-manufacturing tuning process, both the PIFA and the tag chip matching network are designed to match an intermediate $50~\Omega $ real impedance, which makes it possible to easily verify the impedance matching performance. A $29.8\times 29.8\times0.813$ mm3 prototype is manufactured for the 920.5–924.5 MHz Chinese bandwidth, and it has been verified that the post-manufacturing tuning operation can effectively restore the design working frequency, with a read range of 3.6 m at 922.5 MHz when the tag is mounted on a $10\times10$ cm2 aluminum plate. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

HFCT method is a common detection technology for partial discharge (PD) in transformer. However, it suffers a lot from electromagnetic interference in field applications because conventional detection band of it is relatively low, usually in HF band. In this paper, a HFCT, which frequency response includes the whole of the VHF band and extends up to 500 MHz in the UHF band, is adopted to improve the anti-interference capacity of HFCT method. And we make a full investigation on the detection characteristics of HFCT method in UHF band based on an actual 220 kV transformer with complete internal structures. Four typical defects model is established as PD sources, additionally, conventional methods are also adopted in the experiment to make comparison with HFCT method in UHF band. The experiment results indicate that HFCT method can detect PD effectively in UHF band, and the detection sensitivity of it is no less than that of conventional methods. The results confirm the effectiveness of HFCT method in UHF band, therefore, the problem of low anti-interference capacity of conventional HFCT method that detects PD in HF band can be overcome. It offers a new effective and practical solution for transformer field monitoring of PD, especially for the transformers to which internal antenna UHF method can't be applied due to the lack of dielectric window. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

In this paper, a novel compact broadband antenna at UHF frequencies is presented with canonical shapes. Hemispherical, conical and cylindrical shapes have all been considered for antenna configuration. The designed antenna provides an instantaneous frequency range from 370 to 5,000 MHz with omnidirectional characteristics. The antenna was simulated in CST Microwave Studio, fabricated and evaluated; the results are presented. The simulated and measurement results are in good agreement. The antenna has voltage standing wave ratio (VSWR) ≤ 1.9:1 in 400-570 MHz, 2,530-3,740 MHz and 4,180-4,620 MHz; it has VSWR ≤ 3:1 over the operating frequency range 370-5,000 MHz and the measured gain varies from -0.6 to 4.5 dBi over the frequency band. The concept of canonical-shaped antenna elements and the incorporation of triple sleeves resulted in a reduction of the length of the antenna by 62% compared to the length of a half-wave dipole antenna designed at the lowest frequency. The antenna can be used for trans-receiving applications in wireless communication. [ABSTRACT FROM AUTHOR]

This research article presents a design and performance analysis of a metamaterial inspired ultra-high frequency (UHF) compact planar patch antenna for the CubeSat communication system that could be smoothly integrated with commercially available 2U Cube Satellite structure and onboard subsystem. The proposed antenna consists of two layers, one is two different width meander line antenna patch with partial ground plane and another layer is 3 × 2 near-zero-indexed metamaterial (NZIM) metamaterial array structure with ground plane. The NZIM array layer has been utilized to minimize the coupling effect with Cube Satellite structure and improve the frequency stability with enhanced antenna gain and efficiency. The fabricated antenna can operate within the lower UHF frequency band of 443.5–455 MHz. with an average peak gain of 2.5 dB. The designed antenna impedance stability characteristic has been explored after integration with the 2U Cube Satellite body layout. Besides, the antenna communication performance has been verified using 2U Cube Satellite free space path loss investigation. Small antenna volume with trade-off between the antenna size and performance are the key advantages of the proposed design, as the antenna occupies only 80 × 40 × 3.35 mm3 space of the 2U Cube Satellite body structure and the geometrical parameters can be designed to provide the best performance between 449 and 468.5 MHz. [ABSTRACT FROM AUTHOR]

In this paper, new fractal curves are designed, simulated, and implemented for passive UHF RFID application. 5-, 6-, 7-, and 8-sides polygon fractal loops are proposed and implemented in this work based on the 2nd iteration. It is shown that increasing the number of sides can improve the performance and minimize the size of the fractal antenna. The designed fractal loop antennas have been compared with other fractal loop antennas published previously, and the recent antennas show a better performance. The designed antennas are fabricated using PCB technology, and the antenna parameters are measured experimentally and compared to CST simulations. There is an acceptable agreement between the simulated and measured results. The effect of different materials on antenna performance is also studied. [ABSTRACT FROM AUTHOR]

A novel circularly polarized (CP) square slot antenna for covering the universal ultrahighfrequency (UHF) radio frequency identification (RFID) band is proposed. The antenna uses low-cost FR4 material as the dielectric substrate and coplanar waveguide (CPW) to feed. Circularly polarized radiation can be realized by embedding two symmetrical rectangular grounded planes with L-shaped slits in opposite corners of the square slot. The widened vertical tuning stub at the end of the signal line fed by CPW can improve the CP and impedance matching operation, and finally realizes broadband characteristic. The measured 10 dB impedance bandwidth and 3 dB axial ratio (AR) bandwidth are 1250 MHz (710-1960 MHz) and 180MHz (840-1020 MHz), respectively. The measured peak gain is about 3.4 dBi in the whole UHF RFID frequency band (0.84-0.96 GHz). The dimension of the CP square slot antenna is 116 × 116 × 1.6mm³. The proposed antenna has the advantage of simple structure, is easy to be processed, can exhibit dual CP radiation characteristic, and covers the broadband frequency range, which can be applied to the UHF RFID handheld reader environment. [ABSTRACT FROM AUTHOR]

A conformal circularly polarized UHF antenna integrated on the body of a CubeSat is presented. The antenna operates at 485MHz and provides at least 10MHz impedance bandwidth. Traditional UHF antennas for CubeSat have been wire or tape measures that require mechanical deployment, whereas the antenna reported in this paper does not need such treatment and therefore has a potential application in CubeSat mission by promising a more reliable communication link and reduced cost. The measurements showed good agreements with the design data, validating frequency response, bandwidth, and circular polarization level of the proposed antenna. [ABSTRACT FROM AUTHOR]

UHF RFID tags need to be attached or embedded into various objects. Unlike traditional free-standing antennas, UHF antenna shapes and form factors may vary significantly. There have been no systematic methods that facilitate the design practice of antenna with unconventional shapes. In this paper, using the geometries of 26 English letters (in capital) as examples, we explore the general methodology of shape-specific antenna design. More specifically, we show that 26 letter geometries can be categorized into 9 groups, and the antennas in each group can be divided and conquered into standard baseline geometries. Through prototypes and measurements, we demonstrate that each letter-shaped antenna, although exhibiting different gains and radiations, can achieve satisfactory performance, as compared to standard UHF dipole antennas. Specifically, letters "M" and "J" achieve the longest reading range of more than 20 meters with a good radiation pattern, which is comparable or even better than many commercial UHF RFID tags. [ABSTRACT FROM AUTHOR]

Multi-element transmit arrays with low peak 10 g specific absorption rate (SAR) and high SAR efficiency (defined as (B1+/√peak SAR10g) are essential for ultra-high field (UHF) magnetic resonance imaging (MRI) applications. Recently, the adaptation of dipole antennas used as MRI coil elements in multi-channel arrays has provided the community with a technological solution capable of producing uniform images and low SAR efficiency at these high field strengths. However, human head-sized arrays consisting of dipole elements have a practical limitation to the number of channels that can be used due to radiofrequency (RF) coupling between the antenna elements, as well as, the coaxial cables necessary to connect them. Here we suggest an asymmetric sleeve antenna as an alternative to the dipole antenna. When used in an array as MRI coil elements, the asymmetric sleeve antenna can generate reduced peak 10 g SAR and improved SAR efficiency. To demonstrate the advantages of an array consisting of our suggested design, we compared various performance metrics produced by 16-channel arrays of asymmetric sleeve antennas and dipole antennas with the same dimensions. Comparison data were produced on a phantom in electromagnetic (EM) simulations and verified with experiments at 10.5 Tesla (T). The results produced by the 16-channel asymmetric sleeve antenna array demonstrated 28 % lower peak 10 g SAR and 18.6 % higher SAR efficiency when compared to the 16-channel dipole antenna array. [ABSTRACT FROM AUTHOR]

The time difference of arrival (TDOA) localization method has been widely applied in partial discharge (PD) localization in substations based on an ultra-high-frequency (UHF) antenna array. However, TDOA errors obtained from different UHF antennas can result in poor localization accuracy. In this paper, a novel nonlinear transform localization algorithm based on regularization for PD in substations is proposed. First, to avoid the problem of difficult solutions and heavy calculations caused by solving nonlinear localization equations, the equations are transformed from nonlinear to linear by eliminating the second-order terms. Then, for the ill-conditioned problem of the localization equations caused by the antenna array positions and time difference errors, the equations are optimized by centralization and row balance to reduce their ill-conditioned degree. Finally, the Tikhonov regularization method is used to solve the localization equations with an ill-conditioned problem, and then, the PD position is determined. The experimental results show that the proposed localization algorithm can improve the accuracy of PD localization in substations and that the localization errors are within 2.23 m. [ABSTRACT FROM AUTHOR]

A novel dual-band ultrahigh-frequency (UHF) radio frequency identification (RFID) sensor tag, designed to operate on metallic surfaces, is proposed. This particular UHF RFID sensor tag is capable of operating in both the main RFID frequency bands of the European Telecommunications Standards Institute (ETSI) and the Federal Communication Commission (FCC). The dual-band operation of the UHF RFID sensor tag is based on a very simple concept; by flipping the UHF RFID sensor tag on a metallic surface, it can operate either in the ETSI or FCC RFID frequency bands. The impedance and radiation characteristics of the UHF RFID sensor tag are presented with an extensive analysis of the effects of the metallic surface on the UHF RFID sensor tag. In addition, an equivalent model of the UHF RFID sensor tag, which includes the effects of the metallic surface on the sensor tag, is proposed. The UHF RFID sensor tag has a small form factor and presents a satisfying read range of around 3 m for both the operating frequency bands in a metallic environment as well as a read range of 1.4 m when operating in free space. [ABSTRACT FROM AUTHOR]

Phased antenna arrays of dipoles are widely used in ultrahigh field (UHF) magnetic resonance imaging for creating the controllable radio frequency (RF) magnetic field distributions in a human body. Due to safety and imaging quality reasons each individual channel of the array should be decoupled—electromagnetically isolated from the others. The required number of channels is large and in some techniques the dipole antennas should be located in the close proximity of the human body. Their ultimately dense arrangement leads to a strong mutual coupling and makes the conventional decoupling structures inefficient. This coupling needs to be suppressed without a significant distortion of RF fields in the imaged area. In this work, we propose and study a novel decoupling technique for two UHF transceiver on-body dipole antennas. The decoupling is performed by a periodic structure of five parallel resonant wires referred to as a metasurface (MS). In contrast to conventional decoupling with a single resonant wire, the MS decoupled by means of excitation of a higher order coupled mode of the wires, which field is highly confined. The main advantage is a low distortion of the RF-field in the central region of the body. [ABSTRACT FROM AUTHOR]

A deployable log periodic dipole antenna (DLPDA) is proposed. The antenna consists of pairs of collapsible steel tape springs (as the dipoles), a novel stretchable zigzag double-sided parallel stripline (ZDPS) (as the boom), and a coplanar waveguide on one side of the parallel striplines to guide the electromagnetic wave from the backend to the frontend. As a result, the proposed antenna becomes foldable and can be stored in a small volume prior to deployment. A design guideline for the DLPDA is given based on the simplified circuit model. Furthermore, the ZDPS, which is found as a slow wave structure, has been studied. The empirical equations are derived to obtain its characteristic impedance and propagation constant, which are the key parameters for the design guideline. One prototype of the DLPDA has been fabricated and tested. The deployment mechanism of the prototype has been successfully demonstrated using compressed air in a lab. The prototype has a stowed volume of < 2000 cm3, which is only 2% of the volume in fully deployed state. [ABSTRACT FROM AUTHOR]

In this article, a meander line dipole antenna for radio frequency identification (RFID) tag is presented. The loaded meander antenna has a simple meander line structure with a spiral inductor at the end for size miniaturization, a T-match structure, and an inductively coupled parasitic element for impedance matching with the tag IC. The antenna is designed to operate in North American UHF RFID frequency band of 915MHz. The size of the proposed tag antenna is 50mm x 12mm and has good impedance matching with Alien Higgs IC chip of 13.5 -- j111Ω at the desired frequency band. The proposed tag antenna provides omnidirectional radiation pattern with a maximum read range of 3.5m at an effective isotropic radiated power of 4 W. Simulation results are in good agreement with measurement results. [ABSTRACT FROM AUTHOR]