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This communication presents a design of a dual-band circularly polarized antenna with structure reuse for 1U CubeSat applications. It is a challenging to design an antenna with the limited space of a CubeSat platform. To improve the space utilization, an antenna is designed inspired by the concept of structure reuse. A meshed-like-structure is designed, which works as the radiator of a microstrip antenna at UHF band. However, it works as a partial reflective sheet for a Fabry-Perot resonator cavity antenna at C band. Therefore, a microstrip patch antenna and a Fabry-Perot resonator cavity antenna share only single aperture. A shaped ground is used to decrease the resonance at the lower band. Then, the aperture of the antenna is only 0.3λ0 × 0.3λ0, which makes it easy to integrate with a 1U CubeSat. The measurement reveals that the antenna has a common bandwidth of (|S11| < -10 dB, AR < 3 dB) 1% and 1.4%, an isolation higher than 35 dB and 20 dB, a peak gain of 5.82 dBic and 13.75 dBic at UHF and C band, respectively. The frequency ratio of these two bands reaches 6.4. The above properties make the proposed antenna suitable for a CubeSat system.

Owing to the shorter wavelength in the millimeter-wave (mmWave) spectrum, miniaturized antennas can receive power with a higher efficiency than UHF bands, promising sustainable mmWave-powered Internet of Things (IoT) devices. Nevertheless, the performance of a mmWave power receiver has not been compared, numerically or experimentally, to its sub-6 GHz counterpart. In this paper, the performance of mmWave-powered receivers is evaluated based on a novel wearable textile-based higher-order mode microstrip antenna, showing the benefits of wireless power transmission (WPT). Firstly, a broadband antenna is proposed maintaining a stable wearable measured bandwidth from 24.9 to 31.1 GHz, over three-fold improvement compared to a conventional patch. The proposed antenna has a measured 8.2 dBi co-polarized gain with the highest thickness-normalized efficiency of a wearable antenna. When evaluated for compact power receivers, the measured path gain shows that WPT at 26 GHz outperforms 2.4 GHz by 11 dB. A rectenna array based on the proposed antenna is then evaluated analytically showing the potential for up to 6.3x higher power reception compared to a UHF patch, based on the proposed antenna's gain and an empirical path-loss model. Both use cases demonstrate that mmWave-powered rectennas are suitable for area-constrained and large-area wearable IoT applications.

A compact tag antenna, which has a geometrical dimension of 31.5 mm × 31.5 mm × 3.2 mm, is constructed using a stacked PILA for metal-mountable applications in the UHF 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.

Two compact UHF tag antennas, which consists of a square ring loaded with two distributed inductors, are proposed for on-metal applications. Miniaturization of the antenna footprint is realized through the incorporation of two distributed inductors. It will be shown that the required inductances are much dependent on their locations on the ring resonator due to the variation of the current intensity. Due to the high-inductive nature of the distributed inductor, the antenna resistance of the ring resonator can be significantly enhanced so that it can achieve a conjugate impedance match with the microchip. A detailed analysis has been performed to understand the resonance characteristics, and transmission line models have been constructed for designing the tag antennas. Due to the significant improvement in the impedance matching, the proposed miniature tag antennas can achieve a far read distance of greater than 9 m on metal when they are tested with an effective isotropic radiated power (EIRP) of 4 W. Important to mention is that the tag resonant frequencies of the proposed tag antennas are stable and they are not affected much by the backing metallic objects.

For the first time, the ionic polymer metal composite (IPMC) actuator is integrated with a RFID (Radio-Frequency Identification) tag antenna for achieving frequency reconfiguration in the UHF (Ultra-High-Frequency) band. Here, the IPMC movable flap serves as an actuator that can effectively tune the tag resonant frequency. By applying a 2-layer crenellated 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 2-layer crenellated 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.

High packet losses when uplinking commands to small satellites have been reported in the UHF amateur band (430-440 MHz) since late 2013. Measurements of the uplink radio environment have shown high levels of in-band interference in previous works, but public measurement results are limited. Average interference levels are usually measured over some time to build heat maps. In this paper, the analysis is focused on sustained interference over a 24 ms time window using a maximum-minimum method. New heat maps and interference power distributions over Europe, Africa, the Middle East and the Americas were obtained using this method on measurements from the SERPENS satellite . One of the missions of SERPENS was to test an in orbit store-and-forward communication system to exchange short messages with ground sensors for disaster monitoring. The satellite operators had difficulties commanding the satellite due to interference, causing bit errors in uplink packets. Interference power of up to -70 dBm was detected during in-orbit measurements over Europe and North America, while expected received power from the ground stations was not more than -80 dBm. High power space-object tracking radars on the ground operating in the 420-450 MHz band could be the cause, but further measurements are required to verify this. Characterizing this interference can help develop mitigation techniques for future satellite communication systems.

A Partial Discharge (PD) monitoring system for Air Insulated Substations (AIS) has been developed for monitoring of partial discharge activities of various insulators and insulating media that are distributed over an electrical substation. The proposed system utilizes four UHF sensors, which are to be placed around the area of interest so that any impulsive UHF signal originated from PD activity can be captured and subsequently processed for detection and localization of multiple PD sources. To improve the localization accuracy and to improve the detection specificity, i.e. to eliminate false impulsive UHF signals originated from other sources, a novel nearest-neighbour based approach is proposed, which utilizes the physical layout of the AIS to identify most probable PD source locations. The proposed algorithm can accurately find the PD source locations even in the presence of high time-delay-of-arrival (TDOA) estimation error by making necessary corrections in the PD source location estimation. The proposed algorithm has been field trialed in many small and medium-size distribution substations. A detailed comparative study with the other algorithms in different extreme situations has been performed with the help of simulation and laboratory-based testing. The obtained results are worthwhile for supporting widespread implementation of the proposed method.

In this communication, a dual orthogonal port stacked annular ring microstrip patch antenna for polarization diversity applications and full-duplex communications is presented. Vertical pins which extend from SMA connector inner pins have been employed to implement a port coupling cancellation mechanism and achieve high isolation between the two ports. Furthermore, the structure is completely symmetric and does not require any feed network bridge (differently from differential feeding structure), making it very suitable for simultaneously transmit and receive (STAR) applications which employ balance feeding structures and therefore require very similar port performance. An antenna prototype has been designed for the ultra-high frequency (UHF) radio frequency identification (RFID) bandwidth, and measurement has revealed excellent isolation performance, with a peak of 42 dB at the frequency 922 MHz.

This article presents the development of an electrical model of a doubly wound planar (DWP) circular spiral inductor. Closed-form models for substrate capacitance, adjacent metal capacitance, and inter-spiral mutual inductance of this structure are developed, which have, so far, not been addressed in the literature. The proposed developed model presented in this article is applicable to any dielectric substrate. As an example, this inductor is fabricated on a glass-epoxy FR4 dielectric substrate, where close agreement is observed between the analytical model and experimentally measured inductance, over a broad range of frequencies, up to the UHF band (900 MHz). The proposed model can extend known existing planar inductors into symmetric two-terminal structures and can be used for circuit applications for a broad range of frequencies.

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.

This article presents a novel miniaturized circularly polarized (CP) antenna based on periodically structured surfaces inspired by the vertical split-ring resonator (VSRR). The VSRR is considered as a magnetic dipole placed above the ground, which could excite strong boresight radiation with a reduced size. To enhance the aperture gain, multicapacitors and inductors (Multi-C&L) are loaded on the loop, which replace the single capacitive gap of the conventional split-ring resonator (SRR). Here an SRR-inspired periodic structure with a relatively uniform field distribution is achieved. The stepped impedance resonator (SIR) structure, as the unit cell of the SRR-inspired surface, is analyzed and investigated using the circuit models derived from the SRR. By cascading multiple high-value capacitors, a larger aperture with a uniform field distribution is obtained. Linearly polarized (LP) and CP antennas are studied. The proposed CP antenna is made of thin substrates and metallic screws, resulting in a negligible dielectric loss. It offers attractive features including a compact size, a low profile ( $0.191\lambda _{0} \times 0.191\lambda _{0} \times 0.032\lambda _{0}$ ), good radiation efficiency, novel working principle, flexible performance control, and a bandwidth well covering the 902–928 MHz UHF band, which is well situated for radio frequency identification (RFID) application.

The ability to detect abnormalities in infrastructure automatically and remotely with a small number of sensors would greatly contribute to efficient and timely infrastructure inspection. Here, we propose a passive sensor that can be installed by painting. The painted waveguide-based sensor detects abnormalities in infrastructure from abnormality-induced changes in the resonance frequency of electromagnetic waves resonating inside the sensor. In this paper, the principle of detecting loose bolts with the painted waveguide-based sensor is demonstrated by simulation and experiment. The sensor is designed and fabricated as a resonator with resonance frequencies from 100 kHz to 2.5 GHz, which includes the UHF radio-frequency identification band, and the measurement frequency was set within this range. The fabricated sensor is capable of detecting not only a single loose bolt but also two or more loose bolts on the waveguide of the sensor to monitor.

Radio technologies are appealing for unobtrusive and remote monitoring of human activities. Radar-based human activity recognition proves to be a success, for example, Project Soli developed by Google. However, it is expensive to scale up for multiuser environments. In this article, we propose a solution—the HoloTag system—which circumvents the multichannel-radar scaling problem through the use of a quasivirtual ultralow-cost UHF RFID array over which a holographic projection of its environment is measured and used to both localize and monitor the health of several targets. The method is first described in detail, before the image reconstruction process, employing known beamforming algorithms—Delay & Sum, and Capon—is shown and its scaling properties simulated. Then, the idiosyncrasies of the implementation of HoloTag using low-cost off-the-shelf hardware are explained, before its ability to simultaneously measure the breathing rates and positions of multiple real and synthetic targets with accuracies of better than 0.8 bpm and 20 cm is demonstrated.

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.

A novel ultrahigh frequency (UHF)/ultrawideband (UWB) hybrid radio frequency identification (RFID) tag is reported for object-specific remote vital-sign monitoring application. The tag achieves a record energy-harvesting sensitivity at the UHF band by codesigning a meander dipole antenna and a passive rectifier. The especially high quality-factor makes the frontend sensitive to near-field motions such as heartbeats and respiration in a wearable setting. The custom CMOS integrated circuit (IC) of approximately 1- $\mu \text{W}$ power consumption builds around a low-power UWB transmitter and converts the variations in the supply voltage to the impulse repetition rate. The tag consisting of the IC and UHF/UWB antennas requires no other discrete components and features a size of 4.2 cm $\times2.9$ cm and a weight of 0.93 g. A long-distance experiment verifies that the tag can be wirelessly powered up at 51 m from a 4-W effective-isotropic-radiation-power UHF transmitter. Remote vital-sign monitoring is validated on a human subject, in which the UHF power source is placed 2 m away from the subject with a power emission of less than 20 dBm. This work proposes a first-of-its-kind remote vital-sign monitoring solution based on a passively powered noncontact wearable tag. The design of the far-field energy-harvesting frontend with a record sensitivity serves as a reference for future works on battery-free remote sensors.

In this paper, a novel 3D planar inverted-L antenna (PILA) Ultrahigh Frequency (UHF) Radio Frequency Identification (RFID) tag mountable on metallic surfaces is proposed for the Internet of Things (IoT) indoor localization applications. The proposed tag antenna (45 mm × 82 mm × 4 mm or 0.137λ × 0.25λ × 0.012λ) is designed for mounting on metallic objects. The 3D PILA antenna is fabricated using a copper sheet of thickness 1 mm and air as the dielectric substrate in order to minimize costs for materials and realization. In the design, T-slot has been inserted in the radiating element for tuning of the tag’s resonance for achieving good matching with the chip. Also, a simple equivalent circuit model has been obtained to analyze the impedance of the 3D PILA. Based on the optimized design, the fabricated prototype has been measured in the anechoic chamber. The resonant frequency of the proposed tag is stable, and it is not affected much by the metallic object. The measurement results of the antenna prototype demonstrated a reasonable agreement with the simulation results, and a read range of 3.6 m was measured inside an anechoic chamber. Most importantly, in the building hallway, the proposed tag is able to achieve a maximum read distance of 18 m with a transmitted power of 31.5 dBm at 867 MHz when placed on metal. With the 3D PILA antenna structure, the proposed antimetal tag is a suitable solution that can be integrated into an indoor localization scenario.

Ultrahigh magnetic fields offer significantly higher signal-to-noise ratio, and several magnetic resonance applications additionally benefit from a higher contrast-to-noise ratio, with static magnetic field strengths of B0 ≥ 7 T currently being referred to as ultrahigh fields (UHFs). The advantages of UHF can be used to resolve structures more precisely or to visualize physiological/pathophysiological effects that would be difficult or even impossible to detect at lower field strengths. However, with these advantages also come challenges, such as inhomogeneities applying standard radiofrequency excitation techniques, higher energy deposition in the human body, and enhanced B0 field inhomogeneities. The advantages but also the challenges of UHF as well as promising advanced methodological developments and clinical applications that particularly benefit from UHF are discussed in this review article.

One of the major challenges faced by passive on-body wireless Internet of Things (IoT) sensors is the absorption of radiated power by tissues in the human body. We present a battery-less, wearable knitted Ultra High Frequency (UHF, 902-928 MHz) Radio Frequency Identification (RFID) compression sensor (Bellypatch) antenna and show its applicability as an on-body respiratory monitor. The antenna radiation efficiency is satisfactory in both free-space and on-body operations. We extract RF (Radio Frequency) sheet resistance values of three knitted silver-coated nylon fabric candidates at 913 MHz. The best type of fabric is selected based on the extracted RF sheet resistance. Simulated and measured performance of the antenna confirm suitability for on-body applications. The proposed Bellypatch antenna is used to measure the breathing activity of a programmable infant patient emulator mannequin (SimBaby) and a human subject. The antenna is highly sensitive to respiratory compression and relaxation. Fluctuations in the backscatter power level/Received Signal Strength Indicator (RSSI) in both cases range from 6 dB to 15 dB. The improved on-body read range of the proposed sensor antenna is 5.8 m, about 10 times higher than its predecessor wearable knitted strain sensing Bellyband antenna (0.6 m). The maximum simulated Specific Absorption Rate (SAR) on a human torso model is 0.25 W/kg, lower than the maximum allowable limit of 1.6 W/kg.

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.

This paper describes a effect of solar radiation and radio signal within ultra-high frequency (UHF), which statistically deduced using Spearman correlation method. The observation was done in several location including Balai Cerap KUSZA (BCK) during dry and wet season. Solar radiation one of meteoparameters that measured simultaneously using a weather station. This data was analysed and compared to power level (radio signal) in dBm during wet and dry seasons. Findings show that telecommunication services occupy the UHF band. Hence, it can be concluded that, there are still some frequencies available for radio astronomical sources including that below 400 MHz. This allocation is suitable for solar observation, Jupiter observation, continuum observation, solar wind observation, as well as pulsar and deuterium observation and VLBI application. Statistical analysis indicate that solar radiation was significantly prominent during peaks of 382.5 MHz, 1800.0 MHz and 2160.0 MHz. It is largely related with a correlation of 0.6252, 0.6769, 0.5965 during the wet season and only small and moderate correlation at all peaks during the dry season. This important information could be a significant contribution for radio astronomers when trying to identify the best allocation for observing radio astronomical sources in the future.

The aim of this work is to develop a method for the synthesis of matching devices for broadband radio engineering systems with varying impedance in different operating conditions. To achieve this goal, a criterion (complex criterion) is proposed for minimizing the value of the modulus of the sensitivity invariant of the reflection coefficient function to a change in the load impedance with restrictions on the square of the deviation of the power transmission ratio from a given level. It is proposed to use a combination of methods of real frequencies together with the shown complex criterion, which made it possible to implement an effective approach to the synthesis of matching devices for broadband radio engineering systems with an unstable load impedance. To verify the approach, a matching device was synthesized, which made it possible to reduce the loss of the power transmission factor level transmitted to the UHF/VHF antenna of the AD-44 / CW-TA-30-512 range when it is located in various operating conditions by at least 50 % in relation to losses obtained with a standard matching device.

In this era, the role of telecommunications facilities is very important because of that we needed several components of good telecommunications support equipment. One of the most important components in telecommunications is the antenna to be used in the transmitter as well as receiver transmission system. The most widely used antenna is the Yagi antenna. In communication, especially satellite communication also uses Yagi antenna type Cross Yagi. This Cross Yagi Antenna uses different frequencies to distinguish the uplink and downlink processes. when the uplink uses the VHF frequency and the downlink uses the UHF frequency. This simulation is done to find out the changes that occur if there is a rounding of the size made during manufacture. Rounding on the antenna is done because at the time of manufacture it is not possible for someone to measure and cut the components precisely according to calculations. The test results indicate a change that occurs from the radiation pattern where the UHF antenna radiation pattern becomes leaner. In the Gain for UHF antennas it also changes where it becomes larger, while for beamwidth there is a calculation error wherein the simulation cannot designate 3 dB. Saat era ini peranan sarana telekomunikasi sangatlah penting sehingga diperlukan beberapa komponen alat pendukung telekomunikasi yang baik. Salah satu komponen yang sangat penting dalam telekomunikasi adalah antena yang digunakan pada sistem transmisi pemancar maupun transmisi penerima. Antena yang paling banyak digunakan adalah antena Yagi. Pada komunikasi khususnya komuniksi satelit juga menggunakan antena Yagi bertipe Cross Yagi. Antena Cross Yagi ini menggunakan frekuensi yang berbeda untuk membedakan proses uplink dan downlink . saat uplink menggunakan frekuensi VHF dan downlink menggunakan frekuensi UHF. Simulasi ini di lakukan untuk mencari tahu perubahan yang terjadi jika adanya pembulatan ukuran yang dilakukan saat pembuatan. Pembulatan pada antena dilakukan karena pada saat pembuatan tidak memungkinkan untuk seseorang mengukur dan memotong komponen dengan tepat sesuai perhitungan. Hasil pengujian menunjukkan adanya perubahan yang terjadi dari pola radiasi dimana pada antena UHF pola radiasi menjadi lebih ramping. Pada Gain untuk antena UHF juga berubah dimana menjadi lebih besar, sedangkan untuk beamwidth mengalami kesalahan perhitungan dimana pada simulasi tidak dapat menunjuk 3 dB.

This paper presents a new coplanar waveguide (CPW)-fed circularly polarized square slot antenna (CPSSA). The proposed antenna uses an inverted Z-shaped feedline protruded from the signal line of the feeding CPW. Circularly polarized (CP) radiation can be achieved by adequately inserting the arc-shaped grounded strip into the upper right corner of the square slot. The widened vertical tuning stub on the L-shaped grounded strip can improve impedance matching and axial ratio (AR) performance. The measured results indicate that the 10 dB impedance bandwidth is 620 MHz (652-1272 MHz), and the 3 dB axial ratio bandwidth is 320 MHz (840-1160 MHz), which has a broadband characteristic. In the range of the universal UHF RFID band, the measured peak gain is about 4.4 dBi. The proposed CPSSA uses low-cost FR4 material as the dielectric substrate. The overall size of the antenna is 119 × 119 × 0.5 mm3. The proposed antenna has a simple structure, easy processing, good performance, wide operating bandwidth, and dual circular polarization characteristic. It can be applied to the universal UHF RFID handheld reader environment.

UHF RFID reader suffers from a strong transmitter (Tx) leakage signal coupled to a receiver (Rx), especially for an area-compact single-antenna implementation. Then, several Tx leakage cancellation schemes have been developed not to saturate the Rx and to minimize the performance degradation. This brief proposes a UHF RFID reader Rx with a low noise performance and a fast settling time by employing a digitally controlled leakage cancellation method in both passive and active realizations. A digitally-controlled passive vector reflector enhances the Tx to Rx isolation ratio by providing the optimum load impedance. An active anti-leakage feedback loop adaptively tracks the time-varying leakage and generate the phase-inverted leakage replica to suppress the leakage. The prototype chip is fabricated in a CMOS 55 nm process and the area of the chip is 2.1 mm $\times1.8$ mm. The passive leakage cancellation (PLC) with a vector reflector endures the 1 dBm leakage with a low Rx noise figure of 12.5 dB and 35.7 mW power consumption. The active leakage cancellation (ALC) with an anti-leakage feedback loop covers 6 dBm leakage with a fast settling time of $4.6~\mu \text{s}$ and 58 mW power consumption.

As an essential component of power transformers, the detection and diagnosis of incipient partial discharge (PD) activities of bushings are of great significance. A 35‐kV oil‐impregnated paper (OIP) bushing is investigated. The bushing is modelled by coaxial theory and electromagnetic (EM) simulation. As the paths of PD‐induced ultra‐high frequency (UHF) signal propagating in the bushing are OIPs and oil gap, small attenuation during signal propagation is seen. Since OIP is composed of heterogeneous media compared with pure oil, there will be relatively less UHF signal leakage from OIPs, whereas more leakage from the oil gap. This leakage provides the possibility of non‐contact detection outside the bushing by UHF method. PD measurements with UHF method are carried out on the bushing. Then, the minimum energy method is used to extract time‐difference‐of‐arrival (TDOA), and Chan algorithm is adopted to locate points of UHF signal radiation. High accuracy locating with a small error of 15 cm has been achieved. The contactless UHF method‐based tests have demonstrated the effectiveness of online monitoring and locating of bushing PD.

To overcome the problem of data transmission of the aeroengine health management system, a multilink communication system combining ultrahigh-frequency communication link, 4G cellular mobile communication link, and BeiDou satellite communication link was proposed. This system can realize the functions such as data receiving and sending, data encryption, and resuming transfer from the break point based on multiple links. When the flight altitude is not high, the communication distance is short, so the UHF digital transmission radio communication link is adopted, which is highly efficient and stable. When the communication distance is long, the 4G cellular mobile communication link can ensure both the communication distance and the communication rate. In the area where 4G signal cannot be covered in extreme terrain environment, BeiDou satellite communication link is used for data transmission. Besides, in order to ensure the communication rate of the link, a multilink adaptive switching technology was also developed. The test verified that the system can perform adaptive switching among multiple links, realize air-ground data communication in the whole airspace, and achieve a good communication rate, which has significative value of engineering application.

The proposed RFID reader antenna progressed with perfect electric conductor (PEC) as the radiating element and FR 4 as the substrate to achieve circular polarization, enhancement in bandwidth, and read range. The design presents a CPW feed RFID antenna for near-field reading applications, between the range of 903 MHz to 929 MHz. The operating frequency of the proposed design is 900 MHz, axial ratio of the model is less than 3 dB, impedance bandwidth is 256 MHz, and axial bandwidth is 36 MHz, proving to be adequate for near-field RFID reader applications such as item-level tagging and smart shelf. The proposed antenna model is realized with fractal structure to achieve miniaturization. The developed antenna is optimized using EM software for numerical analysis. The designed antenna is fabricated, and the prototype is characterized in terms of dielectric constant and loss tangent. The obtained results indicate high correlation with simulation results.

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.

Hydrometeors (rain, fog and ice crystals) affect the transmission of electromagnetic signals. Previous research showed that alterations in the signal (amplitude and phase) are affected by the composition of the atmosphere, e.g. the presence of hydrometeors. The majority of hydrometeorological detecting methods are based on the attenuation of electromagnetic signals as they penetrate the atmosphere. Novel methods based on monitoring of parameters of the signal appeared in recent time. This article presents the first results from our investigation of how hydrometeors affect the phase differences in signals transmitted by BTS stations. Cell phone operators transmit electromagnetic signals in the 1 GHz frequency band. This paper describes a novel concept of how phase differences between two signals arriving at two different antennas can be used to detect hydrometeors. Although the described concept is assumed to be independent from the signal strength, the analysed signal must be detectable. The primary advantage of the proposed passive method is that the signal is almost ubiquitous and does not require demodulation. In densely populated areas, the network of BTS stations reaches a spatial density of 1 station per 1 km2 which gives excellent opportunity to use the signal for detection purposes.

A novel compact printed broadband circularly polarized slot antenna is proposed in this paper. The antenna consists of an inverted L-shaped coplanar waveguide feed structure and a square ground plate loaded with three rectangular slots. The antenna achieves good impedance matching and circular polarization characteristics by adjusting the size of the L-shaped band and the rectangular slot. The simulation results show that the antenna has a 10-dB impedance bandwidth of 1360 MHz (690-2050 MHz) and a 3 dB axial ratio (AR) bandwidth of 490 MHz (770-1260 MHz). Additionally, the maximum gain reached 4.02 dBi. The antenna proposed in this paper can be applied to UHF RFID and GPS frequency bands.

This article presents a fully differential high-dynamic-range direct-conversion receiver for sub-1-GHz band applications in a 180-nm CMOS technology. The integrated self-adaptive multipart automatic gain control (AGC) loops are designed to cope with large input signal. In the radio frequency (RF) domain, a gain-adjustable noise-canceling balun low-noise amplifier (LNA) and a high-linearity RF variable gain amplifier (VGA) are co-designed to keep a steady differential output power for the mixer stage. In baseband (BB), a novel gain distribution method is proposed to protect BB circuits from saturation. To prove the concept, one of the most typical and strict application scenarios in the sub-1-GHz band, digital television (DTV) standard, is analyzed and chosen as the design target. The receiver achieves a noise figure (NF) of 3.6–4.6 dB in the ultrahigh-frequency (UHF) band. A wide gain tuning range of 128.8 dB is realized in this work, featuring fully integrated AGC loops. The programmable bandwidth of the low-pass filter (LPF) can be adjusted from 1 to 4 MHz, supporting 2-/6-/7-/8-MHz signal channels. The maximum in-band third-order input-referred intercept point (IIP3) is 10 dBm under the conversion gain of 0 dB. The receiver consumes 49.56 mA from a 1.8-V voltage supply and occupies an area of 3.56 mm2.

The increasing need for electrical energy encourages the birth of methods to utilize various forms of energy available in nature called energy harvestin. One of them is from electromagnetic waves that are massif used daily by the community. In this study, a rectifier antenna (rectenna) was created using a 5-stage voltage doubler method with the aim of generating DC electrical energy from the input of electromagnetic waves that propagate freely in the air. Electromagnetic waves are captured using two types of antennas with the aim of capturing different frequencies, namely UHF TV antennas with a working frequency of 470-806 MHz and WiFi antennas with a working frequency of 2400 MHz commonly used by the public. Because testing is conducted in open spaces, where environmental change conditions greatly affect the captured electromagnetic geombang encroachment, DC electrical power tends to change during testing. The largest DC electricity generated by WiFi antenna input is 1,420V and the average voltage is 231.7mV/min with a distance of 90cm from the largest frequency source and UHF TV antenna is 648mV and the average voltage is 478.16mV/min with a distance of 0 cm from the largest frequency source

As the market for internet of things (IoT) is growing and due to Ofcom's decision to reassign parts of the very high frequency (VHF) spectrum in the UK for IoT use, a propagation study has been conducted using the newly released VHF spectrum and the currently commercially operated ultra‐high frequency (UHF) spectrum, in order to compare and contrast the suitability of the VHF spectrum for IoT use. The authors conducted their study in a number of different environments (rural, suburban, urban and dense urban), with measurement equipment deployed in a manner suitable for a portable IoT use case. Results are presented in comparison to other propagation studies available in the literature and widely used propagation models such as the Hata model. Shadowing and noise are also measured and examined. It is found that current propagation models do not provide adequate predictions within the considered use case, but found it is possible to calculate log‐distance based models that provide good predictions. Path‐loss is found to be constantly lower at VHF than UHF, but radio frequency noise is consistently higher. The newly released spectrum is found to be suitable for IoT deployments in all the examined environments.

The article presents the structure of the method for the synthesis of microwave bandpass filters (BPF) on non-uniform lines, which makes it possible to select the structure and parameters of the BPF that provide the maximum length of the stop band to meet the requirements of electromagnetic compatibility (EMC) with given restrictions on the attenuation characteristics in the passband and barrier bands. and the established design and technological limitations on the drop in wave resistance and manufacturing tolerances. The results of experimental studies of the characteristics of ultrahigh-frequency bandpass filters with an increased protective band in order to ensure EMC are presented

In an ultrahigh frequency (UHF) radio frequency identification (RFID) system, the throughput can be greatly improved by collision resolution on a physical layer when tags collide, and high-performance coding technology can improve the bit error rate (BER) performance of the physical-layer separation. Most of the traditional physical collision resolutions focus on the code with a single subcarrier. This paper pays more attention to Miller code with multiple subcarriers and proposes a novel physical-layer separation method based on the Miller code. In this method, the separated collision signals are multiplied by clock signals with the same frequency as the subcarrier to complete the frequency shift. And then, a coherent demodulation and a low-pass filter are used to remove high-frequency separation noise. In the simulation, the Miller code with more subcarriers has lower BER than FM0 code with a single carrier. Especially when Miller 8 is selected, the separation efficiency and BER performance of the proposed method are 4 dB higher than those of the traditional XOR method at lower SNR.

This paper as an author contribution introduces the implementation of the new aspects in the modernization of the ships Radio Direction Finders (RDF) and their modern principles and applications for shipborne and coastal navigation surveillance systems. The origin RDF receivers with the antenna installed onboard ships or aircraft were designed to identify radio sources that provide bearing the Direction Finding (DF) signals. The radio DF system or sometimes simply known as the DF technique is de facto a basic principle of measuring the direction of signals for determination of the ship's position. The position of a particular ship in coastal navigation can be obtained by two or more measurements of certain radio sources received from different unspecified locations of transmitters on the coast. In the past, the RDF devices were widely used as a radio navigation system for aircraft, vehicles, and ships in particular. However, the newly developed RDF devices can be used today as an alternative to the Radio – Automatic Identification System (R-AIS), Satellite – Automatic Identification System (S-AIS), Long Range Identification and Tracking (LRIT), radars, GNSS receivers, and another current tracking and positioning systems of ships. The development of a modern shipborne RDF for new positioning and surveillance applications, such as Search and Rescue (SAR), Man over board (MOB), ships navigation and collision avoidance, offshore applications, detection of research buoys and for costal vessels traffic control and management is described in this paper.

Papers for the thermal transfer printing of UHF RFID antennas were prepared by coating and calendering. Real and imaginary components of the impedance of the UHF RFID antennas depended on their design, coating composition and conditions of paper calendering. Passive UHF RFID tags were constructed from antennas and chips whose real and imaginary components of impedance in the 860–960 MHz frequency band were at approximately the same level. The communication quality of passive UHF RFID tags was evaluated by measuring the reading range using the designed UHF RFID reading unit. The reading range of experimental UHF RFID tags with printed antennas on paper and commercial UHF RFID tags with chemically etched antennas on a PET film were identical in the 860 MHz frequency.