Wire Antenna Research Articles

Determination of Far Fields of Wire Antennas on a PEC Sphere Using Spherical Harmonic Expansion

Far-field patterns of wire antennas on a PEC sphere are calculated from quasi-static near fields using spherical harmonic expansion. Three cases of the wire antennas—F-antenna, dipole, and resonant loop on the PEC sphere—are considered. With the assumed sinusoidal current distribution on the antenna, the method of images is employed to obtain currents and charges on the antenna's image against the sphere. Only from the charge density and current distributions of the wire antenna and its image, ignoring the sphere, the quasi-static near fields are calculated using Coulomb's and Biot–Savart's laws. The fields in a source-free region are expressed in spherical harmonic expansion with the coefficients obtained from the radial components of the calculated quasi-static electric and magnetic near fields. The far fields thus obtained from the expansion match well with that of the simulated patterns. Deviations between simulation and theory are discussed and explained.

Uncertainty Quantification for the Transient Response of Human Equivalent Antenna Using the Stochastic Collocation Approach

The paper deals with the uncertainty quantification of the transient axial current induced along the human body exposed to electromagnetic pulse radiation. The body is modeled as a straight wire antenna whose length and radius exhibit random nature. The uncertainty is propagated to the output transient current by means of the stochastic collocation method. The stochastic approach is entirely nonintrusive and serves as a wrapper around the deterministic code. The numerical deterministic model is based on the time domain Hallen integral equation solved by means of the Galerkin-Bubnov indirect boundary element method (GB-IBEM). The stochastic moments, i.e., the mean and the variance of the transient current, are calculated. Confidence margins are obtained for the whole duration of the transient response as well as for the maximal current value. The presented approach enables the estimation of the probability for the induced current to exceed the basic restrictions prescribed by regulatory bodies. The sensitivity analysis of the input parameters indicates to which extent the variation of the input parameter set influences the output values which is particularly interesting for the design of the human equivalent antenna.

The Spatial Singularity Expansion Method for Electromagnetics

We develop a general singularity expansion method (SEM) focused on the spatial structure of electromagnetic fields and currents. In contrast to the traditional temporal SEM, where complex analytical continuation is performed on the forward Green’s function of free space, we propose applying the SEM to the reverse Green’s function of the electromagnetic device, the recently introduced antenna current Green’s function, leading to the discovery of new current and radiation modes. The new spatial SEM turns out to depend only on single-frequency field/current measurement besides completely avoiding the problem of separating early- and late-time responses that have been hindering the traditional approach. The theory is first developed at a very general level and then applied in detail to 1-D wire antennas. We manage to express the far field in terms of the spatial-SEM modes in a closed analytical form. The theory is confirmed by directly comparing with the full-wave method of moment solutions, and excellent agreement between theory and numerical analysis was obtained for generic wire array configurations. The resulting spatial-SEM is expected to stimulate researches into a new generation of frequency-domain RCS target identification technologies and electromagnetic sensing by developing special algorithms relying mainly on the spatial structure of the fields and currents fed by measurements at single frequency instead of the time-domain data usually required in traditional SEM.

Failure investigation of antenna wire of helicopter

Abstract Present report describes the failure investigation of high frequency (HF) antenna cable of the helicopter. The incidents of HF antenna cable being broken near finger insulator were reported by helicopter operating unit. The present work includes thorough failure investigation to find out the reason for this failure. The in-depth analysis includes visual observation, stereo microscopy, chemical analysis by energy dispersive spectroscopy, fractography, microstructural characterisation and hardness measurement. The experimental evidences suggest the main cause of the HF antenna cable failure is overload.

On the Radiation Characteristics of Full-Loop, Half-Loop, and Quasi-Half-Loop Bond Wire Antennas

The theory, modeling, measurement, and analysis of the radiation characteristics of bond wire antennas (BWAs) is presented in this paper. We commence with rigorous formulations and derivations of analytical models for calculating the vector potential, radiated electromagnetic fields, and directivity of full-loop BWAs (FL-BWAs), considering nonconstant current distribution along the BWAs. Based on the image theory, we derive an analytical model for calculating the directivity of half-loop BWAs (HL-BWAs) from that of FL-BWAs. Very good correlation is obtained between the directivities calculated analytically using the derived models, and numerically using commercial full-wave solvers, thus validating our analytical approach. We apply the verified models to thoroughly analyze the radiation characteristics of FL-BWAs and HL-BWAs. The radiation characteristics of an HL-BWA are based on the assumption that its reference plane is infinitely large and perfectly conducting. However, for the development of wireless systems, reference planes of finite sizes are required. Therefore, we investigate the impact of realistic planes sizes. Our results reveal that the radiation characteristics of BWAs referred to as “HL-BWAs” in published literature differ significantly from those of true HL-BWAs. Therefore, we introduce the term “quasi-half-loop BWA (QHL-BWA)” to describe BWAs with small reference planes. For experimental verification, QHL-BWAs which operate in the 60 GHz band were fabricated using the wedge–wedge bonding process. Both S-parameter and radiation pattern measurements were performed. Very good correlation was obtained between measurement and simulation results.

Large-area, tridimensional uniform microwave antenna for quantum sensing based on nitrogen-vacancy centers in diamond

For quantum sensing based on nitrogen-vacancy (NV) centers in diamond, microwave irradiation with uniform power density and large detection volume is necessary to achieve ultrahigh sensitivity. We demonstrate the fabrication of a double magnetic ring stereoscopic antenna used for the tridimensional uniform control of NV spin ensembles with a 4π mm2 × 2 mm large volume. Compared with those of traditional microwave antennas (copper wire and single-loop antenna), the sensitivity of the sensor can be improved 4.93 and 9.98 times, and the linearity of the lock-in signal can be increased by 2.04 and 1.11%, respectively. Moreover, the proposed antenna can suppress the thermal noise generated by itself and is amenable to three-dimensional (3D) integration.

Application of the Method of Moments for Calculating Electrodynamic Characteristics of a Quasistatic Antenna in an Anisotropic Medium

We develop the numerical method of moments for solving an integral equation that describes the distribution of the charge along a thin finite-length antenna wire in an anisotropic medium in the quasistatic approximation. It is shown that the method of moments can be used to calculate the electrodynamic characteristics of such an antenna under the conditions where the kernel of the integral equation has a singularity related to the resonance cone. The influence of the ratio between the elements of the dielectric permittivity tensor and the method of partitioning of the antenna surface on the calculation accuracy is analyzed. It is shown that the relative error of calculations of the antenna characteristics is a fairly small value of about 1% if the antenna wire is divided into ten segments.

Multi‐channel helical‐antenna inner‐volume RF coils for ultra‐high field MR scanners

AbstractRF coil design for human ultra‐high field (7 T and higher) magnetic resonance (MR) imaging is an area of intense development, to overcome difficult challenges such as RF excitation spatial heterogeneity and low RF transfer efficiency into the spin system. This article proposes a novel category of multi‐channel RF volume coil structures at both 7 T and 10.5 T based on a subject‐loaded multifilar helical‐antenna RF coil that aims at addressing these problems. In some prior applications of helix antennas as MR RF coils at 7 T, the imaged sample was positioned outside the helix. Here, we introduce a radically different approach, with the inner volume of a helix antenna being utilized to image a sample. The new coil uniquely combines traveling‐wave behavior through the overall antenna wire structure and near‐field RF interaction between the conducting elements and the imaged tissues. It thus benefits from the congruence of far‐ and near‐field regimes. Design and analysis of the novel inner‐volume coils are performed by numerical simulations using multiple computational electromagnetics techniques. The fabricated coil prototypes are tested, validated, and evaluated experimentally in 7‐T and 10.5‐T MR human wide bore (90‐cm) MR scanners. Phantom data at 7 T show good consistency between numerical simulations and experimental results. Simulated B1+ transmit efficiencies, in T/√W, are comparable to those of some of the conventional and state‐of‐the‐art RF coil designs at 7 T. Experimental results at 10.5 T show the scalability of the helix coil design.

Antenna design using dynamic multi‐objective evolutionary algorithm

To enhance the robustness and stability of the antenna design, a novel methodology is presented for modelling the antenna design problem as the constrained optimisation problem (COP). Then a framework is introduced for solving the COP. The framework converts a COP into an equivalent dynamic constrained multi-objective optimisation problem (DCMOP). A dynamic constrained multi-objective evolutionary algorithm is applied to address the transformed DCMOP, which means the COP as well as the antenna design problem can be solved. Then it is applied to design three classes of antennas: a wire antenna, a patch antenna and an antenna array. Obtained results of these three kinds of antenna suggest that the proposed methods can well satisfy the antenna design requirements.

The Spiral Solenoids and the Leaf Antenna in Phyllotaxis Differential Geometry

In this paper new classes of spiral thin filamentary wire magnetic coils and antennas are introduced theoretically. This study shows that the thin wire circular loop coil as well as the cylindrical solenoid are particular cases of these classes. If the small spiral filamentary wire leaf loop coil is driven by an alternating electrical current, it will radiate as an antenna, whose theoretical analysis is provided throughout the paper. The fundamental spiral coil named leaf coil is obtained by joining together the so called forward and backward spiral coils which define the new concept of the Phyllotaxis differential geometry. The other spiral coils are composed of symmetrically rotated leaf coils, combined together in such a way to eliminate the transverse magnetic components along the longitudinal z axis. The magnetic moments and the multi-pole expansions of the various types of spiral loop coils are obtained by using the Taylor series of the spiral vector magnetic potentials. According to the formulas and simulations, the magnetic flux density created by the long spiral solenoids is uniform and dovetails with the one created by the long cylindrical solenoid. The bifolium coil may be flattened along one axis to meet the requirements of specific geometrical needs in space technology. Furthermore the crown solenoids may be cooled down to low temperatures by exploiting the holes in between their coils. Applications of the spiral induction coils are countless and can be found in space technology measurements, spacecraft magnetic shielding, telemetry, telecommunication, electron optics, physics and engineer.

A Dual Band Additively Manufactured 3-D Antenna on Package With Near-Isotropic Radiation Pattern

Internet of Things (IoT) applications need wireless connectivity on devices with very small footprints, and in RF obscure environments. The antenna for such applications must work on multiple global system for mobile communication (GSM) bands (preferred choice for network connectivity), provide near isotropic radiation pattern to maintain orientation insensitive communication, be small in size so that it can be integrated with futuristic miniaturized IoT devices, and be low in cost to be implemented on billions of devices. This paper presents a novel 3-D dual-band near-isotropic wideband GSM antenna to fulfill these requirements. The antenna has been realized on the package of electronics through additive manufacturing to ensure efficient utilization of available space and lower cost. The proposed antenna consists of a meander line antenna that is folded on the faces of a 3-D package with two variations, $0.375\lambda $ length for the narrowband version and $0.67\lambda $ length for the wideband version. Theoretical conditions to achieve near-isotropic radiation pattern with bent wire antennas on a 3-D surface have been derived. The antenna has been optimized to operate with embedded electronics and a large metallic battery. The antenna provides 8.9% and 34.4% bandwidths, at 900 and 1800 MHz, respectively, with a decent near-isotropic radiation behavior.

Near-field microwave radiation function on spin assembly of nitrogen vacancy centers in diamond with copper wire and ring microstrip antennas

The spin manipulation of nitrogen-vacancy (NV) centers in diamond with high efficiency is associated with the optimized performance of a microwave antenna. We theoretically and experimentally compared two kinds of custom-built microwave antennas, namely, copper wire and ring microstrip antennas, in terms of frequency and impedance matching, near-field radiation distribution, spin excitation performance through energy distribution, Smith chart, and electron spin resonance. We observed that the microstrip antenna showed decreased impedance deviation errors by more than one half, as determined from the Smith chart and microwave echo loss, and its transmission efficiency was much lower than that of the copper wire antenna as determined by scattering parameter comparison. In addition, we found that the normalized contrast of the optical detection magnetic resonance (ODMR) spectra of the microstrip antenna is 5 times greater than that of the copper wire antenna as determined using our custom-built confocal microscopy system under the same conditions.

A New Modal Approach for Evaluating <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math> </inline-formula>-Factors of Antennas

This paper proposes a new modal approach for evaluating $Q$ -factors of antennas based on newly introduced XeR/XmR modes rather than characteristic modes (CMs). In our new approach, $Q$ -factors could be represented as direct linear superpositions of eigenvalues of XeR and XmR modes. We validate the accuracy of the new formula for $Q$ -factors by studying two canonical wire antennas. Moreover, the relations between XeR/XmR, TE/TM, and Xe/Xm modes are presented, which show interesting properties. It is found that eigenvalues of XeR/XmR modes reveal useful information about minimum $Q$ -factors. Compared with the CMs, some disadvantages of the proposed modes are also discussed.

Giant nonlinear interaction between two optical beams via a quantum dot embedded in a photonic wire

Optical non-linearities usually appear for large intensities, but discrete transitions allow for giant non-linearities operating at the single photon level. This has been demonstrated in the last decade for a single optical mode with cold atomic gases, or single two-level systems coupled to light via a tailored photonic environment. Here we demonstrate a two-modes giant non-linearity by using a three-level structure in a single semiconductor quantum dot (QD) embedded in a photonic wire antenna. The large coupling efficiency and the broad operation bandwidth of the photonic wire enable us to have two different laser beams interacting with the QD in order to control the reflectivity of a laser beam with the other one using as few as 10 photons per QD lifetime. We discuss the possibilities offered by this easily integrable system for ultra-low power logical gates and optical quantum gates.

Relationship Between the Electromagnetic Wave Energy Coupled by Overhead Lines and the Radiation Source Current Explored in the Laboratory

AbstractIn order to solve the damage and interference problems to the electronic devices, which are induced by overvoltage excited by the coupling process between lightning electromagnetic wave and overhead lines, the lightning channel is set to be equivalent to a radiant wire antenna. Based on the integration model of lightning return stroke channel, transmission line, and ground, we take advantage of the derived formula gotten from the transmission line model. By combing the theoretical and experimental methods, we conduct a comparative analysis on the coupling process between natural/simulated lightning and overhead line. Besides, we also calculate the amplitude and energy of overvoltage, which is caused by the coupling process between lightning electromagnetic wave and overhead lines. Upon these experimental results, we can draw several conclusions as follows: when the amplitude of the lightning current in the channel is between 5 kA and 41 kA, it takes on an excellent linear relation between the amplitude of overvoltage and the magnitude of the lightning current, the relation between coupling energy and magnitude of the lightning current takes on an exponential trend. When lightning wave transmits on the transmission lines, the high‐order mode will be excited. Through analysis on the high‐order mode's characteristics, we find that the theoretical analysis is consistent with the experimental results, which has a certain reference value to the protection on overhead lines.

Time domain generalized telegrapher’s equations for the electromagnetic field coupling to finite-length wires buried in a lossy half-space

The paper deals with a derivation of a time domain variant of the generalized telegrapher’s equations for transient electromagnetic field coupling to buried wires. The formulation is based on the thin wire antenna theory in the time domain. The influence of a lossy half-space is taken into account by means of the time dependent reflection coefficient approximation arising from the modified image theory (MIT), while the per-unit-length surface impedance accounts for the conductor losses. The obtained space-time integral expressions are handled analytically. The concept of the scattered voltage is naturally included in the full model formulation. Computational examples are given for the induced currents along the buried wire and compared to the results obtained by using the transmission line (TL) approximation.

Transparent and miniature FM antenna in printed technology

AbstractAn optically transparent and electrically small frequency modulation (FM) radio receiving antenna has been designed and fabricated from a mesh silver layer printed onto a glass substrate. The studied FM antenna consists of a transparent meandering monopole associated with a micrometric size MEtal Semiconductor Field Effect transistor. An optical transparency of 87% and a sheet resistance lower than 0.22 Ω/sq are obtained. The received signal strength indicator and the signal-to-noise ratio are both measured and compared with those of a commercial monopole antenna (a quarter-wave wire antenna). The transparent FM antenna exhibits similar radiofrequency performance with, in addition, a low visual impact.

Multiobjective Optimization Design for Electrically Large Coverage: Fragment-Type Near-Field\/Far-Field UHF RFID Reader Antenna Design

The design of an ultrahigh-frequency (UHF) radio-frequency identification (RFID) reader antenna covering an electrically large near-field area is challenging for near-field UHF RFID applications. In such a design, magnetic field distribution on a large coverage area is required to be as uniform as possible. For some specific UHF near-field RFID applications, given radiation pattern characteristics are expected. A fragment-type wire structure is quite suitable for these demands because uniform magnetic field distribution and given patterns could be generated through optimizing the fragmented wires in a designated electrically large area to obtain corresponding current distribution. In this article, the concept of a fragment-type structure as well as some design guidelines are reviewed and summarized. Then, two omnidirectional fragment-type wire antennas with different cell size and two directional fragment-type wire antennas are designed. Both simulation and experiment results show that there is no reading null within an electrically large near-field zone having a perimeter of four operating wavelengths at 915 MHz (i.e., 320 mm x 320 mm). The omnidirectional designs are promising in the applications of UHF near-field RFID tag detection in self-confined volumes, and the directional designs are potential in the systems of UHF near-field/far-field RFID.

A Compact, Low-Profile Wire Antenna Applied to Wide-angle Scanning Phased Array

A linearly polarized wire antenna has been proposed. This antenna has wide-beam radiation patterns. The half-power beamwidth (HPBW) is 150° in the E-plane and 130° in the H-plane. The proposed antenna has a simple structure with compact size of 0.5 λg × 0.1 λg and low profile of 0.05 λg (λg is the waveguide wavelength at the operating frequency). The compact structure makes it easy to be integrated with RF circuits. A nine-element E-plane linear-phased array is constructed to demonstrate its potential application in wide-angle scanning phased array. The array can scan its main beam from –75° to 75° with a low gain fluctuation and has been experimentally verified. Measured results show a good agreement with the simulation.

Integral Equation Formulations and Related Numerical Solution Methods in Some Biomedical Applications of Electromagnetic Fields

The paper reviews certain integral equation approaches and related numerical methods used in studies of biomedical applications of electromagnetic fields pertaining to transcranial magnetic stimulation (TMS) and nerve fiber stimulation. TMS is analyzed by solving the set of coupled surface integral equations (SIEs), while the numerical solution of governing equations is carried out via Method of Moments (MoM) scheme. A myelinated nerve fiber, stimulated by a current source, is represented by a straight thin wire antenna. The model is based on the corresponding homogeneous Pocklington integro-differential equation solved by means of the Galerkin Bubnov Indirect Boundary Element Method (GB-IBEM). Some illustrative numerical results for the TMS induced fields and intracellular current distribution along the myelinated nerve fiber (active and passive), respectively, are presented in the paper.