Infinitesimal Dipole Research Articles

Deep neural network‐based infinitesimal dipole modeling using either near or far electric‐field

AbstractThis paper presents the deep neural network‐based infinitesimal dipole model using either near‐ or far‐field radiation patterns. Based on the radiating characteristic of an infinitesimal dipole, we generated a data set including near and far field radiation patterns corresponding to the phases of infinitesimal dipoles. We used the data set to train and validate the deep neural network (DNN) model. After checking the statistic of the fit function and the average error in expecting the phases of the infinite dipoles, we conclude that the proposed infinitesimal dipole modeling using DNN is sufficient to predict the characteristics of electromagnetic radiation.

Far-field pattern accuracy improvement in planar near-field measurement using infinitesimal dipole modeling

This paper discusses the challenges in accurately measuring the far-field performance of array antennas, which have become more complex and larger due to recent trends in increasing the number of elements and the antenna size. The far-field measurement method, which is a general method for measuring a radiation pattern in a far-field, is difficult to be utilized at a high frequency due to limitations in physical chamber size and difficulty in diagnosing an antenna. In order to improve these problems, a near-field measurement method is used as an alternative. Even though using a near-field measurement, the accuracy of the derived far-field pattern is reduced at low elevation angles due to zero-padding of data outside the measurement area. The integration of the near-field measurement with the source reconstruction is a promising approach to enhance the measurement limits of the far-field pattern analysis. This paper aims to extend the previous work to accurately predict the far-field radiation pattern, especially in the low elevation angles. The verification of the proposed method is performed for a standard gain horn and 4 by 4 patch array antennas, with and without beam steering.

Analysis of Near-Field EM Energy Densities for UCA-OAM Wave Based on Infinitesimal Dipoles

Analysis of Near-Field EM Energy Densities for UCA-OAM Wave Based on Infinitesimal Dipoles

Analysis of Scattering Characteristics of Large Array Structures Based on Infinitesimal Dipole Model

Analysis of Scattering Characteristics of Large Array Structures Based on Infinitesimal Dipole Model

Antenna Pattern Measurement for Mobile Terminals via Magnetic Infinitesimal Dipole Based Source Reconstruction

Antenna Pattern Measurement for Mobile Terminals via Magnetic Infinitesimal Dipole Based Source Reconstruction

Analysis and Compensation of Deformed Antenna Arrays Based on Infinitesimal Dipole Model

This paper presents a new method for analyzing the electrical performance of deformable antenna arrays based on the infinitesimal dipole model (IDM). The surface of the antenna array will inevitably deform during use. However, in practical engineering applications, it is time-consuming and expensive to use conventional methods to analyze the electrical performance of deformed antenna arrays. In this method, the deformation of the antenna is transformed into the translation and rotation of a group of infinitesimal dipoles by IDM equivalent. The mutual admittance of the deformed elements is calculated to consider the influence of the deformation and the mutual coupling effect between the radiating elements. Based on this, the influence of the deformation of the antenna structure can be quickly and effectively evaluated. Finally, the deformed antenna array is compensated based on the least squares error (LSE) method, and its correctness and feasibility are verified by a numerical example.

Near-field formation of the UCA-based OAM EM fields and short-range EM power flux profiles

Orbital angular momentum (OAM) multiplexing is a recently considered solution for enhancing wireless and free-space optical communications channel capacity, whether implemented separately or in combination with existing multiplexing techniques. The theoretically infinite number of paraxially propagating and mutually orthogonal OAM modes is expected to increase the channel capacity. However, the orthogonality for different OAM modes has been shown to decrease for far link range distances, and the paraxiality of the OAM beams is not very good for small radiating sources. Based on the current knowledge, OAM beams are most likely to be used for short-range communications. Many models of the electromagnetic (EM) fields carrying the OAM neglect the fact that the OAM beam sources could be electrically large or introduce other approximations that are appropriate for far-field analysis only. An in-depth analysis of the short-range properties of OAM EM fields is still lacking. To address this problem, we propose the use of the infinitesimal (Hertz) dipole method customized for the analysis of the OAM EM fields. This technique can model the positioning and basic radiation properties of separate antennas or antenna sub-arrays that are the building blocks of OAM arrays exactly and efficiently. Similar modeling can represent the OAM sources for free-space optical communications. We focus here on the uniform circular antenna arrays and provide an in-depth analysis of what can and cannot be expected, in the best case, in their utilization. We assume low losses, which is a common assumption for many methods, except for computationally much more demanding full-wave simulations. The obtained results indicate the need to simultaneously optimize the transmission of all planned OAM modes and allow estimates of the link distances that could provide adequate OAM wave reception in various cases.

A hybrid equivalent source—particle swarm optimization model for accurate near-field to far-field conversion

This paper proposes an improved equivalent source (ES) model based on particle swarm optimization (PSO) to predict the radiated emissions of a 2.4 GHz ISM band patch antenna. The proposed model uses near-field data to extract an equivalent set of infinitesimal electric dipoles representation. Characterized by their positions, orientations, and currents, these dipoles can reproduce the same field distribution as the target device under test (DUT). To build an accurate equivalent dipole model, a numerical experiment is performed and presented in this paper, where many variable selections of observation points and dipole numbers and locations of the dipole plane are examined, with the aspiration of determining a suitable conversion problem. Based on the proper combination of the two methods (ES-PSO), the complete modeling procedure consists of the application of the pseudo-inverse method to find the minimum norm solution to the least-square problem. Then, the obtained solution is provided to the PSO algorithm to initialize the search for the best-fit dipole parameters. The PSO method can further enhance the stability of the obtained dipole solution and improve the accuracy of the far field prediction. Promising and encouraging results in terms of field prediction at higher planes above the DUT are obtained.

Infinitesimal Dipole Modeling From Sparse Far-Field Patterns for Predicting Electromagnetic Characteristics of Unknown Antennas

The identification of unknown antennas and analysis of electromagnetic wave vulnerability are important for effective attacks and/or protection in high-power electromagnetics (HPEM). Using electromagnetic clues, antenna modeling becomes possible, and its electromagnetic properties can be analyzed by predicting area-wide radiation patterns. To model an antenna, an infinitesimal dipole modeling (IDM) technique, utilizing clues from sparse far-field patterns, was used in the present study. The IDM approach obtained the equivalent infinitesimal dipole (ID) for the antenna configuration current using Green’s function. The sparse far-field pattern was determined for a movement trajectory, using air reconnaissance. Random far-field data acquisition paths were considered cumulatively in the 1–10 range in this case. The approach also used external exposure information about the antenna, such as the operating frequency and size. For simulations and measurements, a ridged-horn antenna operating at 2.4 GHz was used. The overall radiation pattern reconstructed using the IDM approach was correlated at 0.78 when one path was considered in the simulations. As the considered paths were accumulated, the correlation tended to increase, with the correlation for ten paths exceeding 0.98. The estimated radiation pattern characteristics of antennas can be utilized for communication reception characteristics and/or electromagnetic wave vulnerability analysis.

Improvement of Radiation Efficiency for Platform-Mounted Small Antenna by Evaluation of Characteristic Mode with Metal Casing Using Infinitesimal Dipole

Improvement of Radiation Efficiency for Platform-Mounted Small Antenna by Evaluation of Characteristic Mode with Metal Casing Using Infinitesimal Dipole

Compact expression of dyadic Green's function for homogeneous dielectric half‐space and its efficient double integral representation

The dyadic Green's function can be represented via spatial derivatives of two Sommerfeld integrals when an infinitesimal electric dipole and an observation point are located above an infinite planar dielectric interface. The two dielectric spaces are assumed to be homogeneous. Recently, new representations have been proposed for two Sommerfeld integrals and their complete uniform asymptotic expansions. The new formulation for the dyadic Green's function contains fourth-order spatial derivatives, so its explicit expression is lengthy and not compact. Thus, a compact form of the dyadic Green's function was formulated by converting the fourth-order spatial derivatives into second-order ones. Based on the new representation, a numerically efficient double integral expression of Green's function was obtained and numerically verified. In addition, five components among nine total electric field components were analytically evaluated in terms of the incomplete Hankel function when the source and observation point both are on the interface.

Antenna Diagnostics Based on Infinitesimal Dipole Modeling With Limited Measurement on Antenna Aperture

This letter presents an antennadiagnosis method using infinitesimal dipole modeling. For antenna diagnosis, it is important to estimate the current distribution of the antenna aperture. By using the measured near-field data of the antenna, the infinitesimal dipole current distribution that can generate the same near-field measurement result is extracted. This current distribution can be considered as a back-projection image on the antenna aperture. Using the infinitesimal dipole modeling, accurate antenna diagnosis is possible even by using only the measured near-field which is limited over the antenna aperture. We compared the results of the conventional antenna diagnosis method based on Fourier transform and the proposed method for the near-field measurement results of the standard gain horn antenna. Although the limited near-field measurement over the antenna aperture, the back-projection image for the antenna diagnosis of the proposed method has a very high resolution.

An Approach for Modelling Harnesses in the Extreme near Field for Low Frequencies

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.

극소 다이폴 모델링 및 최소자승법을이용한 능동 배열안테나의 근접전계 빔패턴 재구성 및 합성방법

In future-oriented communication, such as wireless power transmission or 6G, large array antennas are used to maximize energy and signal transmission efficiency in the near field. Therefore, the analysis of the near-field beam pattern of an array antenna is a very important research field. In this paper, we propose a method to accurately and efficiently reconstruct the near-field beam pattern, which is difficult to analyze, using the infinitesimal dipole modeling (IDM) of an array antenna. First, IDMs are extracted from the active element pattern (AEP) of the far-field acquired through measurement or simulation, and the mutual coupling effect of the array antenna is reflected in the IDM. Near-field active element patterns (NAEP) can be obtained by performing electromagnetic wave re-radiation for an observation area preset for each of the current distributions of IDMs. Subsequently, a method to easily and accurately analyze the desired near-field electric beam pattern through the combination of the corresponding NAEP and beam coefficient is proposed. Moreover, a method to efficiently extract the beam coefficients using the least squares method and a mask is proposed. Using the obtained beam coefficients, a near-field beam pattern can be synthesized into the desired shape. The proposed method is described in detail using a simulation of a 12-dipole linear array antenna as an example.ample.

Dyadic Green's function of partially filled graphene‐loaded rectangular waveguides

In this study, dyadic Green's functions (DGFs) for a partially filled rectangular waveguide in the presence of a graphene layer is derived in closed form using the Ohm-Rayleigh method and the method of scattering superposition. Having DGFs of a linear medium, the response of the structure to any arbitrary current distribution can be achieved. In this work, after a brief review on governing equations for graphene conductivity, the electric fields of the structure due to infinitesimal electric dipoles are obtained using the proposed DGFs in closed form. To show the efficiency and accuracy of the proposed method, the results are compared with the simulation results of commercial software, where excellent agreement is observed.

Finite Range Integral Representation of Sommerfeld Integral for Homogeneous Dielectric Half-Space and Complete Uniform Asymptotic Expansion

Since the existing integral representations of the Sommerfeld integral (SI) are of the (semi) infinite type, a numerical error is inevitable due to the truncation of the integral range. In this article, a new finite range integral representation of the SI is formulated based on the exact image theory. To derive the new representation, a finite range integral expression of the exact image current is first derived. The radiated field by the exact image current is expressed in terms of a double integral in the complex domain where the exact image current flows. One of the two integrals is a semiinfinite line integral along the current path. This integral is deformed into a more convenient form as the exact image representation for the impedance plane. To convert the line source in the complex domain into a line source in the real domain, the path-deformation technique is again applied. The final line source consists of three line segments along which the exact image current flows vertically from the image source point to ±∞. In addition to the line source, a lateral wave component is also obtained. The impedance exact image representation can be evaluated as a closed-form expression in terms of an incomplete cylindrical function. Thus, the SI can be represented as the finite range integral of the incomplete cylindrical function. To efficiently evaluate the proposed integral, a complete uniform asymptotic expansion is formulated. All the proposed formulations are numerically verified, including, in some cases, near-Earth propagation, and their behaviors are investigated. Also, the electric field is computed for a vertical and horizontal infinitesimal dipole and compared by the exact Sommerfeld and known approximate formulations.

An Accurate Near-Field Focusing of Array Antenna Based on Near-Field Active Element Pattern and Infinitesimal Dipole Modeling

There are mainly three issues for Near-Field Focusing (NFF) using an antenna array. First, it is required to know the distribution of the near electric field in 3D space for each antenna element. In general, a huge amount of data is required to express the near-field for each antenna element in a 3D space with high resolution. Second, in the trade-off relationship between efficiency and accuracy for NFF, we require to solve the optimization problem in which energy can be concentrated to the focal point. Solving optimization problems with near-field represented by huge amounts of data is very inefficient. Third, accurate NFF must be performed by reflecting the mutual coupling phenomenon between antennas. In this paper, there are three key ideas to overcome the issues in the NFF by improving both accuracy and efficiency. The first is the extraction of the infinitesimal dipole model (IDM) using the active element pattern. This makes it possible to obtain a mathematical model of the antenna that perfectly reflects the mutual coupling effect. The second is the acquisition of near-field data to an adaptive resolution grid with appropriate resolution using the extracted IDM. This re-radiated near-field data has both accuracy and efficiency by maintaining high resolution only for a focal point. The third is an efficient optimization method for a desired focal area with an arbitrary elliptical shape using convex optimization. Through simulations for the verification, 4 types of grids with various resolutions are used to the same NFF problem. The computational time of the proposed method in optimization for the NFF could be reduced to 8% with a similar focal shift compared to a type of the finest resolution. In addition, the accuracy of the electromagnetic analysis of the proposed method was verified through comparative verification with the MoM results.

Dyadic Green’s Function for Electric Dipole Excitation of a Perfect Electromagnetic Conductor Sphere

In this article, we investigate the dyadic Green's function (DGF) of a perfect electromagnetic conductor sphere (PEMCS) due to electric dipoles, theoretically by employing the scattering superposition principle (SSP) and the Ohm-Rayleigh method. Then, the derived DGF is used to calculate the scattered field of a PEMCS due to an arbitrarily oriented infinitesimal electric dipole and also plane wave illumination. Numerical results are compared with those obtained by the FEKO commercial software to demonstrate the efficiency and accuracy of the proposed method. The results are in excellent agreement.

Localisation and permittivity extraction of an embedded cylinder using decomposition of the time reversal operator

In this study, first, the problem of time reversal imaging of an embedded dielectric or metallic cylinder inside another dielectric cylinder is studied. The direct problem is carried out numerically using the finite-element method. The background dyadic Green function (DGF) is computed analytically by computing radiated fields of an infinitesimal electric dipole near an infinitely long dielectric cylinder. The time reversal technique is then applied using this background DGF to image the embedded cylinder. Results demonstrate that while using a free-space DGF for imaging yields erroneous results, by employing a proper background DGF, the scatterer inside the cylinder is correctly localised. Next, the authors extract permittivities in two different scenarios with two different techniques. In the first case, the permittivity of a background cylinder that contains a metallic cylinder inside it is extracted by calculating the image entropy. In the second case, the permittivity of an embedded cylinder inside a priori known background dielectric cylinder is estimated by a new method based on an optimisation and evaluation of the largest eigenvalues of the multistatic data matrices. The proposed techniques are then verified using simulated and measured data. For measurements, a newly developed combined tapered sectorial antenna is designed, fabricated, and characterised.

Three-Dimensional Scattering From Uniaxial Objects With a Smooth Boundary Using a Multiple Infinitesimal Dipole Method

The formulations for three-dimensional (3D) scattering from uniaxial objects with a smooth boundary using a multiple infinitesimal dipole method (MIDM) are introduced. The proposed technique uses two sets of infinitesimal dipole triplets (IDTs), including three co-located orthogonally polarized electric infinitesimal dipoles, distributed inside and outside of a scatterer to construct simulated fields. The dyadic Green’s functions of uniaxial materials are deployed in the MIDM so as to obtain the simulated fields. The singularity issues in using the uniaxial dyadic Green’s functions, which cannot be solved analytically so far for a general uniaxial medium, can be easily eliminated by using the proposed MIDM. In comparison to the traditional single-layered distribution scheme of IDTs, the proposed multiple-layered distribution scheme can handle the scattering from uniaxial objects accurately and efficiently. Several numerical examples are presented to study bistatic radar cross section (RCS) responses under different scenarios. Excellent agreement is achieved by comparing numerical results with those obtained from commercial software packages, while the simulation performance including CPU time and required memory is drastically improved by using the MIDM when computing a general uniaxial material or a relatively larger object. The proposed technique has its merits on simplicity, conciseness and fast computation in comparison to existing numerical methods.