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Emerging data processing techniques brought back into attention the HF range communication as an interesting alternative to third-party solutions for IoT applications, such as data transmission in distributed energy production facilities. The physical size of HF antennas, often comparable to the surrounding objects, require in situ radiation measurements resulting in site-customized antenna design and positioning, and consequently in a higher reliability of such HF grid communications. Drone-borne measuring systems are already known as a flexible solution, but are mostly restricted to higher frequency ranges where full-wave, wide-band probes are feasible. In this work, we propose to use an electrically small, folded dipole as a probe for drone-borne measurements on HF antennas. We also propose a calibration approach for the effects related to the near-field zone, and to the drone body proximity; corrections on these two effects are the key methodological steps. We show that despite a realized gain figure in the order of −20 dBi, such a probe can provide stable results for near-field measurements, even at input power levels as low as 1 mW. Compared to other similar approaches, our configuration provides a wider frequency band of operation, higher stability in terms of pattern diagram, and a lower cost. [ABSTRACT FROM AUTHOR]

A general theory on noise matching performance of receivers with electrically small antennas (ESAs) emphasizing HF (3MHz to 30MHz) and VHF (30MHz to 300MHz) applications is presented through theoretical analyses, discussions, and circuit simulations with practical device models from a state-of-the art semiconductor technology. The theory considers all the noise sources and their interplay. The impact on the noise performance from both the physical constraint of the ESA in terms of its radiation quality factor and the scaling of transistor technology and periphery such as gate resistance, gate cutoff frequency and transition frequency has been discussed. Two receiver examples, one with electrically small dipole and the other with electrically small loop are studied with full-wave simulations. The antenna equivalent models are then connected to low noise amplifiers designed with the state-of-the-art Gallium Nitride (GaN) transistor models to evaluate the noise performance of the systems and compared against the theory. It is demonstrated that both the noise figure and its bandwidth can be significantly improved over traditional matching strategy when optimized active direct matching is applied at the price of increased device periphery and power consumption. In particular, the bandwidth of such low noise matching can be orders of magnitude wider than the antenna’s conjugate impedance matching bandwidth that is defined by Harrington-Chu’s limit.

In this paper a study of a helical antenna resonating at high-frequency (HF) band with a very compact structure is reported. The designed antenna's S11 parameter magnitude change with frequency was calculated for different geometrical parameters. For each case, first, only a single parameter was changed. Then for a fair comparison, multiple parameters were changed simultaneously while the total wire length was set to be constant. Also, shifts in resonance frequencies and variations in -10 dB bandwidths were investigated. Our results show that resonance behaviour changes distinctively with the geometrical parameters and it allows shortening of the antenna wire length. For the designed antenna, the resonances shift to lower frequencies and -10 dB bandwidths around the resonances decrease as the winding wire thickness, number of turns, and turn radius increase. Whereas as the turn spacing increases the resonances shift to higher frequencies and -10 dB bandwidths widen, although the total wire length of the antenna increases. To verify the simulation results, the designed antenna was fabricated with an exclusive manufacturing process and characterized. The measurement results are in good agreement with the simulation results. It demonstrates the feasibility of the proposed manufacturing technique, which is new in the literature and enables accurate and rigid antenna fabrication with simple and low-cost steps. [ABSTRACT FROM AUTHOR]

In this article, we showcase an application of neural networks (NNs) to solve an inverse problem in electromagnetics (EMs). Wires are randomly distributed into an area of known dimensions. The wires are then illuminated with a monochromatic plane wave (PW) at a certain angle of incidence, and the EM field measured at a finite number of uniformly spaced points along the perimeter of the area is then fed into a convolutional neural network (CNN) designed to predict the number of wires. Counting the wires is posed as a supervised classification problem with a known upper limit to the number of wires, and accuracy of 96% has been achieved for the case where the number of the wires is known to be ten or less. A number of approaches have been taken to improve the network performance including frequency variation analysis and illuminating the wire distributions with additional PW angles of incidence. We conclude with an analysis of the network capability to resolve objects based on its performance on known wire distributions, which suggests the existence of a characteristic resolution limit corresponding to the CNN topology. [ABSTRACT FROM AUTHOR]

Abstract For vehicle tactical radio communications, positioning antennas along the structure is a complex task. In vessels, there are several radio systems installed operating from HF to SHF. Consequently, the antennas need to share the same restricted space while preserving electromagnetic compatibility. In this context, this work presents a parametric analysis of the positioning of HF monopole antennas on the upper bridge of a typical Navy frigate. A numerical antenna analysis tool was chosen to support the intended analysis. Six positioning scenarios were simulated, evaluating the performance change of figures of merit such as the reflection coefficient and gain, due to the mutual coupling between the antennas and the main metallic objects within their close range. Furthermore, from the analysis, it was possible to establish recommended distances of decorrelation between the antenna and the main nearby objects.

The design of high‐power vehicle‐mounted log periodic dipole antenna for 8‐22 MHz use was discussed. It is shown that the antenna has a power endurance of 150 kW. With the application of the coefficients variation method, the total size of the proposal was shrunk to 12 × 18 m so that it can be mounted on a vehicle of 10 m long by an elevation tower. The voltage standing wave ratio over the entire frequency band is lower than 2.0 without utilizing any match network. [ABSTRACT FROM AUTHOR]

For vehicle tactical radio communications, positioning antennas along the structure is a complex task. In vessels, there are several radio systems installed operating from HF to SHF. Consequently, the antennas need to share the same restricted space while preserving electromagnetic compatibility. In this context, this work presents a parametric analysis of the positioning of HF monopole antennas on the upper bridge of a typical Navy frigate. A numerical antenna analysis tool was chosen to support the intended analysis. Six positioning scenarios were simulated, evaluating the performance change of figures of merit such as the reflection coefficient and gain, due to the mutual coupling between the antennas and the main metallic objects within their close range. Furthermore, from the analysis, it was possible to establish recommended distances of decorrelation between the antenna and the main nearby objects. [ABSTRACT FROM AUTHOR]

This paper examines the design of a 13.56 MHz Radio Frequency Identification (RFID) reader that is used in secure TV access applications. It also presents the performance analysis between different geometry and sizes of the reader's antennas in order to achieve the optimum operational excellence. Four different antenna geometries and sizes are designed and analyzed; square (4 loop and 6 loop), rectangular, and circular antennas. In order to find the best way for achieving the optimum performance, simulations, calculations, and measurements have been implemented by comparing the antennas in terms of gain, read distance, and cost performances with the availability of proximity of metals and smart cards, considering accuracy and reliability. The reader design for secure TV access is aimed to work with a passive tag. The rectangular antenna operated at the 13.56 MHz of frequency level with a return loss of -27 dB. The 6 loop square antenna and circular antenna operated with frequencies different than the optimum frequency of 13.56 MHz for the desired application, so the adjustments and other tests were not necessary for such antennas. It has been observed that for such TV applications, the best performance in terms of read range and gain, is achieved for a read distance up to 5 cm using the 4 loop square antenna operating at the 13.56 MHz of frequency level with a return loss of -30 dB. Some enhancement techniques to optimize system performance against the capacitive effects of close proximity to metals and smart cards are also discussed like detuning the capacitor values in the matching circuit. This paper aims to fill the gap in literature in observing RFID systems' performance with comparison of different size and geometry antennas by setting forth the best antenna geometry with metal and smart card effects. [ABSTRACT FROM AUTHOR]

Antennas operating in the high-frequency (HF) bands are generally relatively large in size, which severely limits the application of the antennas. Therefore, miniaturisation of the antenna is necessary. Here, a dual-folded structure Yagi antenna is designed for HF surface wave radar (SWR). Genetic algorithm is employed to optimise and balance the antenna size and performance. At the same operating frequency, the optimised antenna size is much smaller than the traditional Yagi antenna size and can meet the performance requirements of HF surface wave radar transmitting antenna.

Antennas operating in the high-frequency (HF) bands are generally relatively large in size, which severely limits the application of the antennas. Therefore, miniaturisation of the antenna is necessary. Here, a dual-folded structure Yagi antenna is designed for HF surface wave radar (SWR). Genetic algorithm is employed to optimise and balance the antenna size and performance. At the same operating frequency, the optimised antenna size is much smaller than the traditional Yagi antenna size and can meet the performance requirements of HF surface wave radar transmitting antenna. [ABSTRACT FROM AUTHOR]

A warship represents a very complicated platform with very different electronic systems operating on a variety of frequencies and working also with different output powers, some of which might reached the order of MW. The electromagnetic radiation coming from each of these systems (named as RADHAZ) may harm the personnel on board, so it turns out necessary to carry out measures in order to verify whether the intensity of the electromagnetic fields present on the ship fulfills the in force regulations (according to the maximum permitted exposure levels) or not. In this paper we will obtain the value of those electromagnetic fields for a HF communication system (the most common system in any kind of ship and also radiating high powers) by two different methods: results coming directly from measures conducted on the decks of a warship and results coming from the HEMCUVE simulation program. [ABSTRACT FROM PUBLISHER]

Permittivity and permeability parameters of dielectric composites made of ferrite particles coated in a barium titanate (BaTiO3) layer were analyzed and compared against composites of ferrite powders without a dielectric layer. A hydrothermal synthesis process combined barium hydroxide (Ba(OH)2) and titanium dioxide (TiO2) to form the coating of barium titanate around a ferrite core. These barium titanate ferrite composites particles are then combined with a unique binder to form a metamaterial. Discs of the metamaterial are characterized with an Agilent coaxial airline and dielectric measurement software to determine the permittivity and permeability responses within a frequency range of 200 MHz to 4 GHz. By comparing these results to previous work on ferrite composites, the merit of insulating the magnetic particles with a dielectric layer is examined. [ABSTRACT FROM PUBLISHER]

The objective pursued in this work is to highlight the convenience of using electromagnetic simulation software as an alternative to the traditional scale model measurement when dealing with the design of HF antennas on real complex platforms. The experience was developed during the building process of a real vessel. A low and a medium band antennas (fan-wire type) were designed ad-hoc for this project. The HF broadband antennas’ study covered from the preliminary design stages to the final verification measurements completed onboard the ship. The experiment has demonstrated that more accurate results can be obtained when using an adequate electromagnetic simulation code, which, besides, brings important advantages in flexibility and usability. These advantages, inherent to the use of virtual models, hinge on the ability of the simulation tools to properly handle any modification of the vessel’s structure that might arise during the platform construction. [ABSTRACT FROM AUTHOR]

Design of low-profile vehicular on-the-move (OTM) wideband high-frequency (HF) antennas with 24-kHz instantaneous bandwidth for near-vertical communications is discussed. It is shown that multiarming significantly reduces the minimum antenna height, whereas the two-arm configuration is a tradeoff between antenna complexity and performance. A procedure for determining the minimum antenna height when the tuner loss is considered as a design parameter is introduced. The design evolves from a state-of-the-art magnetic dipole to a wire two-arm half-loop antenna (HLA). The profile for the amphibious assault vehicle (AAV) mounted antenna is 0.65 m ($\lambda/230$ at 2 MHz) for the parabolic shape and 0.50 m ($\lambda/300$) for the rectangular shape two-arm half-loop. The length of antenna base is 4.8 m ($\lambda/31$) and the width is 3.3 m ($\lambda/45$). A simple two-element tuner is considered in the scope of the results validation, along with the impedance and directivity patterns measurements on scaled 1/500 models. [ABSTRACT FROM PUBLISHER]

A novel single‐radiator card‐type tag is proposed which is constructed using a series Hilbert‐curve loop and matched stub for high frequency (HF)/ultra high frequency (UHF) dual‐band radio frequency identification (RFID) positioning applications. This is achieved by merging the series Hilbert‐curve for implementing the HF coil antenna, and square loop structure for implementing the UHF antenna to form a single RFID tag radiator. The RFID tag has directivity of 1.75 dBi at 25 MHz, 2.65 dBi at 785 MHz, 2.82 MHz at 835 MHz and 2.75 dBi at 925 MHz. The tag exhibits circular polarisation with −3 dB axial‐ratio bandwidth of 14, 480, 605 and 455 MHz at 25, 785, 835 and 925 MHz, respectively. The radiation characteristics of the RFID tag is quasi‐omnidirectional in its two orthogonal planes. Impedance matching circuits for the HF/UHF dual‐band RFID tag are designed for optimal power transfer with the microchip. The resulting dual‐band tag is highly compact in size and possesses good overall performance which makes it suitable for diverse applications. [ABSTRACT FROM AUTHOR]

In Internet‐of‐things devices, to alleviate the performance degradation of the ground radiation antenna due to the large battery, two compact electromagnetic bandgap (EBG) unit cells are introduced between the ground radiation antenna and the battery. The ground radiation antenna is comprised a small loop‐type circuit that is designed within a 5‐mm × 5‐mm ground clearance for 2.4‐GHz WLAN applications. The compact EBG unit cell is a modified square split‐ring resonator that is designed by meandering‐line technology. The measurement results showed that the 3:1 VSWR impedance bandwidth of the ground radiation antenna increased from 30 to 90 MHz, and the average total efficiency increased from 19% to over 54% with and without the introduction of the EBG structure, respectively. [ABSTRACT FROM AUTHOR]

Warships use strategic and tactical communications to be connected with national command headquarters and other units around the world. Therefore vessels need a communication system to be able to provide line-of-sight and long-haul communications. High Frequency (HF) communications can meet this requirement. Thus the ship needs to know the behavior of HF communications systems, for example, if they have any null in the radiation pattern. This article describes the measurements of the radiation patterns of HF whips in different places and with different polarizations (2–30 MHz) on a large vessel. Theoretically, HF shipboard antennas are close to be omnidirectional, so that the transmission and reception do not depend on where the ship is heading. We need to know the patterns at different frequencies first, to evaluate if the place where the antennas have been placed is adequate and second, to detect the possible nulls in the radiation pattern. [ABSTRACT FROM AUTHOR]

In this paper, we propose a coaxial-fed dipole array antenna in a borehole with ferrite loading to achieve a thin directional borehole radar sonde (diameter of 54 mm). This radar works between about 20 and 150 MHz. When the dipole array, proposed previously, is used for the thin radar sonde, this antenna suffers from scattered waves from the centered conducting cylinder (CCC). This disturbs the estimation of the direction of arrival (DOA) below 100 MHz. To overcome the interference of the CCC, commercial ferrite cores were added to the CCC. A method-of-moment analysis showed that we may decrease the resonant frequency of the CCC to below 20 MHz, making use of the inductive characteristics of the ferrite cores. This widens the frequency bandwidth of the antenna. Field experiments in soil showed that the ferrite core-loaded CCC works reliably and confirmed that we can estimate the DOA between 20 and 150 MHz. Other measurements in rock which examined the power spectrum of a direct wave found that the ferrite cores widened the operating frequency bandwidth of the radar system. [ABSTRACT FROM PUBLISHER]

The large wavelength of decameter wave brings a lot of practical difficulties to the design of shipboard antennas in high-frequency (HF) band. How to design conformal or even platform-embedded HF antennas raises us a new challenging topic. This paper proposes an approach to address such challenging problem through the combination of the characteristic mode (CM) theory with the structural antenna concept. 1) The CMs are solved to understand the resonant behavior of the ship platform. 2) We synthesize the radiating currents for designated radiation pattern by making use of the CMs of the ship platform. It allows the dominant radiating currents to locally distribute on the superstructure of the ship. Consequently, the superstructure becomes the main radiator. The modal solutions in CM theory ensure the efficiency of the synthesis procedure. 3) Nonprotruding slits are proposed to excite the synthesized currents. As the resultant HF shipboard antenna has no protruding elements around the ship, this design can be considered as either platform-conformal or platform-embedded. As an example, HF antenna on a realistic ship with broadside radiation pattern is designed. Simulation and experimental results on a 1:400 scale model demonstrate the effectiveness of the proposed approach in HF shipboard antenna designs. [ABSTRACT FROM PUBLISHER]

The bottom side of a vehicle is assessed for mounting HF-VHF antenna systems in terms of omni-directionality, efficiency and propagation loss. Accurate and numerically efficient procedure for calculation of propagation loss associated with sources electrically close to real grounds is proposed and carefully validated. It is shown that even though bottom sources cannot compete with conventionally mounted antennas in terms of far field omni-directionality and efficiency, in the near field region propagation loss margins are comparable for distances shorter than 10 m and frequencies from 20 to 100 MHz. The result points to the frequency range where antennas can be concealed at the bottom side and still used for emerging short distance applications. [ABSTRACT FROM PUBLISHER]

A hybrid self‐interference (SI) cancellation scheme, composed of a two‐tap analogue canceller and a digital multi‐path SI canceller, is proposed for single‐antenna full‐duplex radios. The analogue canceller mitigates the two strongest components of the SI to prevent saturating the receiver. The digital canceller deploys an auxiliary receiver chain to capture the RF‐transmitted signal to mitigate the residual multi‐path SI signal. As the proposed scheme uses the RF‐transmitted signal as reference, the transceiver impairments such as power amplifier non‐linearities and phase noise are suppressed along with the SI. Experiments have validated the effectiveness of the proposed scheme on a 20 MHz long‐term evolution signal of +20 dBm power. [ABSTRACT FROM AUTHOR]

This paper presents a novel antenna architecture to achieve an extremely small form factor for HF band applications. The approach is based on manipulating the topology of a short monopole antenna without utilizing a high index material. A new architecture incorporating two radiating elements is configured, which allows significant gain enhancement. It is shown that such architecture can render a miniaturized HF antenna on air substrate having lateral and height dimensions as small as 0.0115\lambda0 \times 0.0115\lambda0 \times 0.0038\lambda0 (150 mm\,\times\,150 mm\,\times\,50 mm for operation at 22.9 MHz). It is found that the measured gain of such architecture can be as high as -18.1 dBi, which is 16.7 dB higher than a reference inverted-F antenna realized on a high index material (\varepsilonR =10.2) having exactly the same dimensions. The proposed antenna architecture is composed of two in-phase radiating vertical elements connected to two inductors between which a capacitive top load is connected to achieve the desired resonant condition. The two vertical elements act effectively as a monopole having increased height. It is also shown that the gain of the antenna can be increased monotonically by increasing the quality factor (Q) of the phase shifter. High Q air-core inductors that can be accommodated in electrically small monopole antenna are designed and incorporated in the phase shifter to achieve a gain value of -17.9 dBi. Details about the proposed design approach, simulation, and measurement results are discussed. [ABSTRACT FROM PUBLISHER]

Strategies and results for calibrating electric field sensors (antennas), as used in radio astronomy, onboard the spacecraft “Resonance” are presented. Calibration is performed for four boom antennas and four cylindrical sensors at the boom tips. These antennas are devised for the measurement of electric fields and plasma parameters. It is shown that the electrical representations of the antennas, the effective length vectors, differ from their mechanical originals and are shortened and tilted by several degrees of angle. The knowledge of the acquired parameters is of great benefit to the Resonance mission. In particular, goniopolarimetry techniques like polarization analysis and direction finding depend crucially on the effective axes. For the first time, this kind of analysis is performed for a space-borne antenna system consisting of boom monopoles and cylindrical tip antennas. [ABSTRACT FROM PUBLISHER]

In this paper, a metal-backed loop antenna (MBLA) at high frequency (HF) is characterized and applied to a radio-frequency identification (RFID) smart-shelf system. The antenna is investigated in terms of impedance matching, resonant frequency, magnetic-field intensity/field distribution, quality factor, and detection range. The study shows that the magnetic-field distribution of the metal-backed loop antenna can be effectively controlled by changing the size as well as the separation of the backing metal plate. As a result, the detection range of an RFID system using such an antenna can be controlled. Such a feature offers great promise for the metal-backed loop antenna in applications for RFID smart-shelf systems. For such systems, controlling the coupling zone of the antennas is vital for constraining the interference between the antennas in adjacent tiers of the shelves, in order to achieve high system-detection accuracy. In addition, using a metal-backed loop antenna provides more flexibility for RFID smart-shelf-system design and implementation, so that the system is more cost effective. [ABSTRACT FROM AUTHOR]

We describe the design, fabrication and measurement of reduced-size prototypes of the naval structural antenna, recently proposed as a compact and multifunction solution to broadband naval communications. The original broadband HF sub-radiator, loaded by lumped impedances, is scaled down to the VHF/UHF ranges and re-designed in planar technology in order to simplify and to automate the fabrication process. Measurement on single-port and 4-port antennas, in which the central structure resembles a naval funnel and a big mast, have shown a good agreement with the simulations. [ABSTRACT FROM PUBLISHER]

Frequency-swept input-impedance measurements to determine Q factors and field strengths for an electrically small tuned transmitting loop antenna in its operating environment have recently been made. These observational results are compared with numerical modeling by the computational electromagnetic code NEC-4D, since the validity of this code to simulate the performance of electrically small loops - and, in fact, even the fundamental characteristics of small loop antennas - has been questioned. [ABSTRACT FROM AUTHOR]

A real-coded genetic algorithm was successfully applied to the matching network problem. Our approach reduces the search across different network topologies by the means of a generalized network description, in which the algorithm "decides" whether a reactive element is inductive or capacitive. Compared to previous analytical and semianalytical techniques that do not require a priori information about the network topology, this method is considerably simpler and its application is straightforward, regardless of the network complexity. Our approach accounts for constrained lossy elements, tolerances, and network on-site tuning. The results for a canonical load show the effectiveness of this method in comparison with other known methods. Finally, for HF broadband antennas, which involve network complexity limits and component value restrictions, it will be shown that the use of lossy networks may help to fulfil system requirements, with only a moderate impact on system efficiency [ABSTRACT FROM PUBLISHER]

Recently, it was shown how to make a multipurpose broadband HF antenna system out of existing naval super-structures such as the funnel or a big mast. The idea was discussed by means of canonical structures, e.g., a cylindrical body of circular or square cross-section, placed onto an infinite ground plane. This paper investigates the critical aspects concerning the extension of naval structural antenna concept to real ship platforms with the aim to define a general design methodology for impedance matching and radiation pattern control. The method is described with reference to a realistic frigate model, whose big mast is transformed into a broadband HF antenna system able to perform communications by both sea-wave and sky-wave links. It is demonstrated that, even in a real environment, the multiport strategy permits to increase the system efficiency and to moderately shape the radiation pattern in order to overcome the shadowing effect due to other large objects. [ABSTRACT FROM AUTHOR]

A tunable, electrically small, wire antenna is developed for HF/VHF ground wave transmission. A variable capacitor is serially connected to tune the resonant frequency of the antenna. The optimal position for the placement of the capacitor is evaluated by numerical simulation. The tuning range and sensitivity are also investigated. A prototype antenna is built and tested, and the measured tuning performance is compared to the simulation results. Transmission loss tests are carried out in several nonline-of-sight environments. The measured transmission loss of the tunable small antenna is found to be within 1 to 2 dB of that of a commercial whip across the tested frequency range. [ABSTRACT FROM PUBLISHER]

The performance of a typical small loop antenna of I m diameter is presented at frequencies in the range 3.6-10.1 MHz. It is argued that the antenna may reasonably described as electrically small in this frequency range. Measurements of the antenna's bandwidth and, hence, Q factor are presented, along with direct measurements of the radiated field at various distances with a carefully measured RF input power. The radiation efficiency of the loop is derived from the measurements, and is compared with theoretical predictions of the efficiency based on classical electromagnetics. Close agreement is demonstrated between measurements and predictions. Consistency with the Chu bandwidth limit is also demonstrated for this antenna. [ABSTRACT FROM AUTHOR]

A concise review of the theoretical and experimental findings resulting from a study of small-height HF vertically polarized ground-wave jamming antennas in the form of conventional whip, helical whip, condenser (parallel plate, parabolic plate, and conical) and inverted L is given. These findings show that, for a given power input, the inverted-L and the conical condenser antennas can produce about the same ground-wave-field strength as whip antennas of twice and four times their height, respecively. [ABSTRACT FROM AUTHOR]

A planar loop antenna producing uniform magnetic fields horizontal to its plane is presented. The antenna consists of a pair of two‐turn spiral coils that are sequentially excited. To prevent undesirable magnetic coupling between the coils, a novel coil‐switching circuit is proposed, which is automatically operated using the interrogating signal from the reader. The antenna is suitable for a high‐frequency radio frequency identification reader antenna installed under a chip tray to monitor gaming chips in a casino. [ABSTRACT FROM AUTHOR]

A low‐profile inverted‐L antenna with one folding at 20−90 MHz bands for aircraft applications is presented. The designed antenna is installed on the top of the vertical stabiliser of an aircraft to increase the gain at 20 MHz using the ground edge current and to reduce air drag. The gain of the designed antenna is increased by 3 dB at 20 MHz, and the antenna length is reduced by 41% compared with the reference antenna, which is a folded monopole antenna coupled with a parasitic element. The measured 3 dB return loss bandwidth is 342.9 MHz (51.5%) and the peak gain at 200 MHz is −11.5 dBi for the 1/10 scaled sub‐model. In addition, the omnidirectional radiation pattern was observed in the operating frequency. [ABSTRACT FROM AUTHOR]

The feasibility of energy harvesting using the human body, which is used instead of a general antenna as an antenna in a low‐frequency band to harvest energy included in an ambient electromagnetic wave, is investigated. Using the presented method, it is possible to harvest much more power in comparison with that possible with the previous method, in which a general antenna is used to harvest power in the high‐frequency band. Also, this method can be easily applied to mobile devices because no antenna is required. [ABSTRACT FROM AUTHOR]

The design of a high‐frequency radiating element plus a broadband shifting circuit for reflectarray device cells is provided. The cell design is based on modified broadband 3 dB/90° reflecting circuit interlacing polarisation, along with a multilayered planar radiating element. The basics of the structure are to capture the signal at each cell of the reflectarray, to introduce the proper phase shift by means of the modified 3 dB/90° shifter and to re‐radiate the signal again towards the radiating direction. This device reduces the complexity of the reflectarray cells in terms of design and manufacturing, enabling it to deal with circular polarisation in an easily affordable manner. The complete design of the unitary cell is provided. [ABSTRACT FROM AUTHOR]