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The problem of the scattering of an arbitrarily oriented and located Hertzian dipole from an impedance cavity with a circular aperture satisfying different impedance values at inner and outer spherical surfaces is solved with a method of auxiliary sources (MAS). The study of that canonical problem with Leontovich boundary conditions answers the effects of the location of the excitation, aperture size, and boundary conditions on the resonance and radiation characteristics of the semi-opened spherical cavity. The proposed approach employs the distribution of the two perpendicular Hertzian dipoles on auxiliary surfaces representing the scattered field inside and outside the spherical cavity with a circular aperture. As the numerical results, the total radar cross section and the near field distributions are provided for different cases including the aperture size, source location, and boundary conditions. The resonance characteristics are analyzed. The method is validated by other approaches for the limit cases. [ABSTRACT FROM AUTHOR]

Non-invasive concealed object detection, identification, and discrimination have been of interest to the research community for decades due to the needs to preserve infrastructures and artifacts, guarantee safe conditions for the detection and location of landmines, etc. A modern approach is based on the use of an unmanned aerial vehicle equipped with ground-penetrating radar, which has the advantage of not requiring direct contact with the ground. Moreover, high-resolution underground images are obtained by coherently combining measurements by using a synthetic aperture radar algorithm. Due to the complexity of the real scenario, numerical analyses have always been welcomed to provide almost real-time information to make the best use of the potential of such kinds of techniques. This paper proposes an analysis of the scattering from a zero-thickness perfectly electrically conducting disk buried in a lossy half-space surrounded by air and illuminated by a field generated by a Hertzian dipole located in the air. It is carried out by means of a generalized form of the analytically regularizing Helmholtz–Galerkin technique, introduced and successfully applied by the authors to analyze the plane-wave scattering from a disk and a holed plane in a homogeneous medium. As clearly shown in the numerical results, the proposed method is very effective and drastically outperforms the commercial software CST Microwave Studio 2023.

The accuracy of the first-order multiplicative (Ott–Clemmow) and additive (van der Waerden) modified saddle point integration methods for the Sommerfeld problem of a vertical Hertzian dipole over a lossy half-space is investigated using two theoretically equivalent formulations with either a positive or a negative image term extracted. It is demonstrated that whereas the additive method leads to the same asymptotic field representation irrespective of the sign of the image, the multiplicative variant yields distinct results in these two cases, both of which differ from the unique result of the additive method. It is further found that the positive-image Ott–Clemmow method yields the well-known Norton formula, but the negative-image variant is inaccurate and predicts a zero field in the on-surface transmitter–receiver configuration. It is also demonstrated that the first-order multiplicative method yields an incomplete representation of the first order in the inverse distance. [ABSTRACT FROM AUTHOR]

A key part of every space science mission, in the system-level approach, is the detailed study and modeling of the emissions from transmission lines. Harnesses usually emit electromagnetic fields due to the currents (of common and/or differential modes) that flow on their shields. These fields can be identified via conducted emissions measurements. Relying on the operating frequency, any cable can be considered as a dipole or a traveling-wave antenna. Limited work can be found in the literature regarding modeling methodologies for cable topologies, especially in the low frequency (ELF, SLF, VLF, LF) domain. This work intends to provide perceptions for the precise estimation of harness radiated emissions, consider a mission-specific measurement point (where the sensors are placed), and follow ESA's recent science mission studies for electromagnetic cleanliness applications. For the low frequencies considered herein, any linear cable path is considered as a point source (infinitesimal dipole) and we evaluate its effect on the calculated electric field extremely close to the source. For such distances, it is shown that the dipole representation is not accurate. To remedy this phenomenon, this article proposes a methodology, which can be easily expanded to complex cable geometry cases. [ABSTRACT FROM AUTHOR]

In this article, the coupling between the inner conductor and the shield of a coaxial cable is summarized with different coupling directions and shielding grounding conditions. An internal and external transmission line (IETL) transfer matrix is proposed to validate this coupling relationship. The induced voltage and current of the IETLs can be more intuitively represented by the IETL transfer matrix and the port voltage and current. By introducing the three-conductor system and the surface transfer impedance into the transmission line theory, the IETL transfer matrix representation of the transmission line equation with coupling components is obtained. Moreover, when analyzing the problems of coupling between field and transmission line, the coaxial cable can be equivalent to a bare wire by using IETL transfer matrix. According to this idea, an improved approximation method based on Hertzian dipole and a numerical method based on the finite element method algorithm are proposed to calculate the radiation of a coaxial cable and the crosstalk between a coaxial cable and a bare wire. Then, the results of the two methods are compared with the electromagnetic calculation software. [ABSTRACT FROM AUTHOR]

This letter is dedicated to develop an effective high-frequency method for the near-field (NF) scattering from an electrically large ship illuminated by a Hertzian dipole. First, for primary illumination, a local expansion technique based on the facets of the target is introduced to account the NF scattering, which has a singularity-free characteristic. Second, for secondary rays, the ray-generation technique on the sphere grid is proposed to reduce the number of ray tubes. And the ray-tracing strategy based on one central ray is proposed to accelerate the tracing process, which benefits to the parallelism by utilizing the graphics processing unit (GPU). Therefore, it is particularly attractive since the proposed method requires very little increase in computational cost and yields a good accuracy in the NF scattering computation of an electrically large ship problem. [ABSTRACT FROM AUTHOR]

A key part of every space science mission, in the system-level approach, is the detailed study and modeling of the emissions from transmission lines. Harnesses usually emit electromagnetic fields due to the currents (of common and/or differential modes) that flow on their shields. These fields can be identified via conducted emissions measurements. Relying on the operating frequency, any cable can be considered as a dipole or a traveling-wave antenna. Limited work can be found in the literature regarding modeling methodologies for cable topologies, especially in the low frequency (ELF, SLF, VLF, LF) domain. This work intends to provide perceptions for the precise estimation of harness radiated emissions, consider a mission-specific measurement point (where the sensors are placed), and follow ESA’s recent science mission studies for electromagnetic cleanliness applications. For the low frequencies considered herein, any linear cable path is considered as a point source (infinitesimal dipole) and we evaluate its effect on the calculated electric field extremely close to the source. For such distances, it is shown that the dipole representation is not accurate. To remedy this phenomenon, this article proposes a methodology, which can be easily expanded to complex cable geometry cases.

The classical Sommerfeld problem of a vertical electric dipole radiating over an imperfectly conducting half-space is revisited. Two variants of the modified saddle-point integration method are employed to derive new, closed-form, second-order approximations of the far-zone electromagnetic fields. The new formulas are applied to compute radiation patterns and surface fields for sample problems including both ordinary and plasmonic media, and their accuracy is assessed by comparison with the results of rigorous numerical evaluation of the Sommerfeld integrals. [ABSTRACT FROM PUBLISHER]

We address the non-uniqueness of the vector potential for the Sommerfeld half-space problem with a horizontal Hertzian dipole. In contrast to the classical solution, which utilizes horizontal and vertical components of the vector potential, the formulation presented here employs two horizontal components. In this approach, unlike in the traditional one, the scalar potentials of single-point charges associated with the vertical and horizontal Hertzian dipoles are identical. [ABSTRACT FROM AUTHOR]

In this work, a method is proposed for the calculation of the electromagnetic field radiated by a grounding system in a semi-infinite dissipative medium subjected to a current excitation generated by the lightning strike. The assessment of the induced current distribution on the grounding system due to a transient excitation is obtained by solving Pocklington’s equation using the method of moments. A new method for the calculation of the transient electromagnetic field following the injection of a lightning current or short circuit is also developed. This method is based on the concept of the hertzian dipoles and the asymptotic expansion of a single dipole. A MATLAB computer program has been developed for the determination of the induced currents. The program is validated by comparing its results with those obtained with the commercial software NEC 4.

In this work, a method is proposed for the calculation of the electromagnetic field radiated by a grounding system in a semi-infinite dissipative medium subjected to a current excitation generated by the lightning strike. The assessment of the induced current distribution on the grounding system due to a transient excitation is obtained by solving Pocklington’s equation using the method of moments. A new method for the calculation of the transient electromagnetic field following the injection of a lightning current or short circuit is also developed. This method is based on the concept of the hertzian dipoles and the asymptotic expansion of a single dipole. A MATLAB computer program has been developed for the determination of the induced currents. The program is validated by comparing its results with those obtained with the commercial software NEC 4. [ABSTRACT FROM AUTHOR]

A unified and succinct transmission line formulation is presented for the computation of the plane-wave impressed fields and far-zone radiation fields due to arbitrary electric and magnetic current source distributions embedded in planar layered media. The equivalence principle and the spectral-domain transmission-line network analogue of the multilayer medium are used to express the fields in terms of the voltage and current transmission-line Green functions. The new formulation is applied to sample problems involving both dielectric and plasmonic multilayer media. [ABSTRACT FROM AUTHOR]

The surface electromagnetic fields radiated by a vertical electric dipole over a lossy conducting half-space are investigated. A simple derivation is presented of the second-order asymptotic groundwave expression, using a modified saddle-point method based on integration around vertical branch cuts. The method takes into account the influence of the Sommerfeld pole, which in the plasmonic case contributes a surface plasmon polariton. The proposed groundwave formulation is shown to be superior to the state-of-the-art Norton–Bannister theory for noble metals at optical wavelengths. [ABSTRACT FROM PUBLISHER]

The approximate solutions of King and Norton—the latter as extended by Bannister—for the problem of a vertical Hertzian dipole radiating over a lossy ground are compared and their equivalence is established. [ABSTRACT FROM PUBLISHER]

The classical Sommerfeld half-space problem is revisited, with generalizations to multilayer and plasmonic media and focus on the surface field computation. A newab initiosolution is presented for an arbitrarily oriented Hertzian dipole radiating in the presence of a material half-space with arbitrary horizontal stratification. The solution method combines the vector potential approach and the spectral domain transmission line analog of the medium, which results in the most compact formulation and facilitates the inclusion of any number of layers in the analysis. Following Sommerfeld, the solution is first expressed in terms of the Fourier–Bessel transforms, also known as Sommerfeld integrals. Analytical properties of the integrands in the complex plane are then investigated, including the location of the Sommerfeld pole, which gives rise to the Zenneck wave (ZW) or surface plasmon polariton (SPP), and alternative field representations are developed by a deformation of the integration path and analytic continuation of the integrand functions, using hyperbolic and vertical branch cuts. Closed-form expressions for the asymptotic surface fields are also derived and the rôle of the ZW and SPP is elucidated. Numerical examples are included to illustrate the theory, from radio frequencies to visible light. [ABSTRACT FROM PUBLISHER]

Numerical analysis for the radiation of an elementary dipole is presented when it is located over a half-space gyroelectric medium, a grounded gyroelectric slab, and inside the slab. It is revealed that the direction of the maximum radiated field for a dipole over a half-space gyroelectric medium corresponds to the critical angles where total internal reflection occurs. Usually 6-dB enhancement can be obtained by placing a dipole above the anisotropic region, either over a half-space or grounded anisotropic slab. The effects of the frequency and the biasing magnetic field are studied for the radiation of a dipole over a grounded gyroelectric slab. In addition, it is discovered that more than 6-dB enhanced radiation along the broadside direction, compared with the radiation of the dipole in free space, is achievable if the vertically oriented dipole is placed inside the grounded gyrolectric slab with the proper adjustment of the thickness of the slab and the magnitude of the biasing magnetic field. This thickness is significantly less than the optimum thickness required to achieve the directive emission along the broadside direction using the horizontal dipole inside the grounded isotropic plasma slab without the biasing magnetic field. [ABSTRACT FROM PUBLISHER]

The electromagnetic interference generated by a switched-mode power supply on a victim circuit is analysed representing their electromagnetic field coupling by two-port networks. The essential electromagnetic interference sources of the switched-mode power supplies are individuated and their mutual impedances with the victim circuit are calculated by the induced EMF method. The two-port representation of the field coupling allows the noise voltage on a victim circuit to be predicted. As a victim circuit a circular loop representing a magnetic field probe used in near field measurements is considered. The approach is applied to a flyback converter and validated through experimental measurements. [ABSTRACT FROM AUTHOR]

It is well-known that low-frequency electromagnetic (EM) signals are heavily attenuated in a medium with dense electron population. All signals below the plasma frequency of the medium get cut off. If we create in this medium, a small population of relatively hot electrons the composite medium then supports low-frequency electrostatic oscillations known as electron acoustic waves (EAW) [e.g., Gary and Tokar, Phys. Fluids 28, 2439]. The dispersion relation of this composite medium shows that it supports EAW in the frequency band where EM signals are cut off. Thus, it is possible, in principle, to employ EAW to transmit signals across an overdense plasma medium. Our primary interest in this paper is to study the radiation characteristics of a source current distribution embedded in a half-space of our composite medium. To enable this, we derive the Green's functions for our problem and, hence, study the radiation characteristics of antennas. When the source signal frequency is below the plasma frequency, only EAW exist in the composite medium, while only EM waves can exist in the free space above. We find that the far-zone radiation fields of any current distribution consist only of \theta-polarized waves. Explicit expressions for the radiated fields are obtained for horizontally- and vertically-polarized Hertzian dipoles embedded in our composite medium. We, hence, find that in both cases the radiation patterns are skewed towards the horizon. In particular, we find that the radiation pattern of a horizontal dipole has two lobes as opposed to one in the underdense case. [ABSTRACT FROM PUBLISHER]

It has been found that a set of Hertzian dipoles can be optimized to model the radiation characteristics of an antenna. However, the existing models are normally for narrowband antennas and invalid for a wideband antenna. In addition, it is difficult to combine several such models at different frequencies into a wideband model because the interpolation of dipole parameters is not applicable. This paper presents a procedure to optimize a Hertzian dipole model for a wideband antenna, where each dipole parameter is a polynomial in the phase constant. The tangential electric field on a surface enclosing the antenna is first obtained by full wave analysis at multiple frequencies. An optimization method is then applied to determine the polynomial coefficients for each dipole parameter, by minimizing the error between the exact field and the field due to the dipoles. As an example, a wideband stacked dielectric resonator antenna (DRA) is modeled by four electric and three magnetic Hertzian dipoles. The dipole model is used to efficiently study the radiation characteristics of the DRA mounted on a circular ground plane. Moreover, it is pointed out that the dipole model is resistant to Gaussian noise added to the near-field data, and is frequency scalable. [ABSTRACT FROM PUBLISHER]

A transmission line method is proposed to compute the far-field radiation patterns of arbitrarily directed Hertzian dipoles that are embedded in a multilayer dielectric structure. The evaluation of the field in the far-zone region is transformed into the evaluation of the field inside the multilayer structure by applying the reciprocity theorem. The horizontal field component inside the structure is derived by analyzing a transmission line circuit, and the vertical component is obtained from the horizontal component by separating the forward and backward waves. This method is implemented and verified by IE3D for the case of a three-layer structure excited by either electric Hertzian dipoles, magnetic Hertzian dipoles, or their combination. The radiation patterns of any antenna embedded in a multilayer dielectric structure can be computed with this method after replacing the physical antenna with a set of Hertzian dipoles. As examples, a quarter wavelength thin wire monopole antenna and a dielectric resonator antenna, both embedded in a multilayer structure, are investigated. Furthermore, the arrangement of the structure is optimized to maximize the antenna directivity. The results are also verified by the simulation of the entire structure with IE3D. [ABSTRACT FROM AUTHOR]

Far field radiation from an arbitrarily oriented Hertzian dipole for two-layered uniaxially anisotropic medium with a tilted optic axis is treated analytically by using the dyadic Green's function of the problem when the dipole is placed over or embedded in a two-layered uniaxially anisotropic medium. The radiation fields are evaluated using the steepest descent method. Parameter studies including anistoropy, layer thickness and dipole location are performed to investigate the effects of changing different variables on the radiation fields. Results of this work can be applied in microstrip circuits and antennas. [ABSTRACT FROM AUTHOR]

A recently developed high-frequency asymptotic solution for the famous "Sommerfeld radiation problem" is revisited. The solution is based on an analysis performed in the spectral domain, through which a compact asymptotic formula describes the behavior of the EM field, which emanates from a vertical Hertzian radiating dipole, located above flat, lossy ground. The paper is divided into two parts. We first demonstrate an efficient technique for the accurate numerical calculation of the well-known Sommerfeld integrals. The results are compared against alternative calculation approaches and validated with the corresponding Norton figures for the surface wave. In the second part, we introduce the asymptotic solution and investigate its performance; we compare the solution with the accurate numerical evaluation for the received EM field and with a more basic asymptotic solution to the given problem, obtained via the application of the Stationary Phase Method. Simulations for various frequencies, distances, altitudes, and ground characteristics are illustrated and inferences for the applicability of the solution are made. Finally, special cases leading to analytical field expressions close as well as far from the interface are examined. [ABSTRACT FROM AUTHOR]