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The characteristics of external electromagnetic fields (EEMFs) produced by underground cables in the lossy earth are further investigated and studied. This paper develops an excitation current in the cables with the bi-directional propagation for the calculations of the vectors of EEMFs. By adopting the newly proposed method in this paper, it allows the considerations of the terminating conditions and the lengths of the cable on the calculations of the vectors of EEMFs. Moreover, the vectors of EEMFs are calculated, compared and discussed using various load/source impedances. The effects of lengths of underground cables on the vectors of EEMFs are studied. Also, the frequency-dependent earth models are included into the investigations of the EEMFs. The results presented in this paper are compared and verified with the Numerical Electromagnetics Code.

A generalized formulation of electromagnetic fields generated from a multi-phase underground cable is proposed based on a complete solution of Maxwell equations. The lateral electromagnetic field components, the shielding effect of cables and the phase currents at high frequencies of a three phase underground cable are evaluated by the newly derived formulas. The accuracies of the recently developed extended transmission line approach of underground cables are investigated based on the performance of electromagnetic field components. It is also shown that Numerical Electromagnetics Code verifies the results calculated from the new formulas presented in this article.

A four-element moxon antenna array is proposed in this paper. Its directive properties are shown with simulations and compared with the classical dipole array. In order to synthesize the pattern of moxon array, a hybrid method that consists of differential evolution (DE) and numerical electromagnetics code version 2 (NEC2) is also introduced. Basically, the cost function used by DE is designed with the help of NEC2 simulations to achieve more realistic optimum antenna array designs. Patterns having one and double sidelobe suppression at predetermined angles are successfully synthesized by using this method whereas the gain value is maintained properly. Robustness of the proposed method is also examined. For this aim, multiple executions of the method implementation are performed under same conditions. The results show that the method introduced in this paper is very stable in terms of the radiation pattern and convergence curves.

This paper proposes a simple method to take into account non-vertical risers through an equivalent partial inductance. The proposed approach was validated considering several examples and taking as reference full-wave results obtained using a numerical electromagnetics code numerical electromagnetics code (NEC)-4 .

We present the design of a new inductive proximity sensor to detect metal targets and their direction of movement. The proposed sensor design includes a base board with the necessary microcontroller based circuitry for driving and reading the sensing LC tanks and several different solutions for the printed sensor coil. Different coil configurations are fabricated on separate printed circuit boards designed to plug-and-play into the base board. They are intended for different specific applications including for sensing metal targets approaching perpendicularly on the coil plane and for sensing and identifying the lateral direction of movement (i.e., left-to-right or right-to-left). The coil designs are studied via simulations using the freely available Numerical Electromagnetics Code (NEC). A complete hardware prototype is developed and demonstrated to detect different metal targets, including copper, brass, aluminum, and stainless steel. It is also shown that measurements obtained from hardware experiments are in good agreement with the simulations.

It is important to recognize that the Numerical Electromagnetics Code (NEC) is no magic tool—it does some things very well but it cannot do other things. In spite of this, it is a valuable tool that makes a significant contribution to easing the design and adjustment of medium-frequency (MF) broadcast directional antennas.

An alternative method to compute the free-space antenna factor using time-domain transformation and deconvolution filter for pulse compression is proposed. The deconvolution filter helps in compressing the time-domain pulse to distinguish the direct wave from the reflected wave and help evaluate the free-space antenna factor for site validation of fully anechoic rooms. The antenna pair of ETS-Lindgren Model 3110C and 3180C antennas, simulated with numerical electromagnetics code, is subjected to the proposed method with deconvolution filter and Wiener filter. Based on the simulation results, the proposed method is implemented over the measured results of the antenna pair and used for the site validation of a fully anechoic room. The free-space normalized site attenuation results of the fully anechoic room comply with the ±4 dB specification.

This paper shows the results of an investigation on the self-structuring antenna. This antenna consists of a combination of planar paths interconnected by controllable switches. A numerical electromagnetics code (NEC) environment and application with implemented genetic algorithms were used in this research. As a result of the investigation, an antenna template was built and measured.

A b s t r a c t: The well know hybrid electromagnetic model (HEM) is widely used for analysis of grounding systems. However, it has been proven that results obtained by HEM diverge from referent results in the high frequency (HF) domain. This paper presents implementation of complex image theory to take into account the earth-air interface instead of the quasi-static images used up-to-date with HEM. Parametric analysis of the achieved improvement in precision of the HEM method on high frequencies is visualized in multiple figures by comparison to referent results calculated by the renowned numerical electromagnetic code NEC-4. It may be concluded from the research presented in this paper that usage of complex images with HEM extends notably the applicability domain of the method. Key words: hybrid electromagnetic model; complex images References: [1]Visacro S., Soares A. and Schroeder M. A.: An interactive computational code for simulation of transient behavior of electric system components for lightning currents, Proc. 2002 Int. Conf. Lightning Protection, pp. 732–737, 2002. [2]Visacro S. and Soares A.: HEM: A model for simulation of lightning – Related engineering problems, IEEE Trans. Power Delivery, vol. 20, no. 2, pp. 1206–1208, (2005). [3]Guimaraes M., Araujo L., Castro R. V., Santos L. F. D., Murta Vale M. H. and Visacro S.: Impulse response of grounding grids: Experimental versus simulated results, Proc. 2012 Int. Conf. Lightning Protection, 2012. [4]Alipio R. S., Schroeder M. A. O., Afonso M. M. and Oliveira T. A. S.: Electromagnetic fields of buried conductors, Proc. Int. Conf. Grounding Earthing (GROUND 2008), pp. 399–402, 2008. [5]Alipio R. S., Schroeder M. A. O., Afonso M. M. and Oliveira T. A. S.: Electric fields of grounding electrodes: frequency and time domain analysis, Proc. X International Symposium on Lightning Protection 9th–13th November, Curitiba, Brazil, 2009. [6]Kuhar A., Ololoska-Gagoska L. and Grcev, L.: Numerical analysis of complex grounding systems using circuit based method, Proc. 12th Int. Conf. ETAI, Ohrid, Macedonia, Sep. 2015. [7]Jankoski R., Kuhar A. and Grcev L.: Frequency domain analysis of large grounding systems using hybrid circuit model, Proc. 8th Int. PhD Seminar on Computational and Electromagnetic Compatibility – CEMEC, Timisoara, Romania, Sep. 2014. [8]Kuhar A. and Grcev L.: Contribution to calculating the impedance of grounding electrodes using circuit equivalents, FACTA UNIVERSITATIS, Series: Electronics and Energetics, vol. 29, no. 4, pp. 721–732 (2016). [9]King R. W. P.: Antennas in material media near boundaries with application to communication and geophysical exploration, Part I: The baremetal dipole, IEEE Trans. Antennas Propag., vol. AP-34, no. 4, pp. 483–489, (1986). [10]Watt A. D., Personal communication, 1962. [11]Wait J. R., and Spies K. P.: On the image representation of the quasi-static fields of a line current source above the ground, Can. Journal of Physics, 47 (23), pp. 2731–2733, (1969). [12]Bannister P.: Applications of complex image theory, Radio Science, vol. 21, no.4, pp. 605–616 (1986). [13]Burke G. J.: Numerical Electromagnetics Code — NEC- 4, Method of Moments, Part II: Program Description—Theory, UCRL-MA-109338, Lawrence. [14]Livermore National Laboratory, Livermore, 1992. Arnautovski-Toseva V. and Grcev L.: On the image model of a buried horizontal wire, IEEE Trans. Electromagn. Compat., vol. 58, no. 1, pp. 278–286 (2016). [16]Otero A. F., Cidras J., Alemo J. L.: Frequency-dependent grounding system calculation by means of a conventional nodal analysis technique, IEEE Transactions on Power Delivery, Vol. 14, No. 3, pp. 873–878 (1999). [17]Park D.: Magnetic field of a horizontal current above a conducting earth, J Geophys. Res. 78 (16) pp. 3040–3043 (1973 [18] Chow Y. L., Yang, J. J. and Srivastava, K. D.: Complex images of a ground electrode in layered soils, Journal of Applied Physics (1992). [19] Arnautovski-Toseva V.: Approximate closed-form solution of the electric field due to HED within finitely conductive earth. In: Proc. 2011 International Conference on Electromagnetics in Advanced Applications, ICEAA’11, Torino, Italy, pp. 670–673, 2011. [20] Arnautovski-Toseva V, Grcev L. and Kacarska M.: Applicability of approximate Green’s functions in MPIE model of a horizontal wire conductor in lossy soil, 5 th International Symposium on Applied Electromagnetics – SAEM’2014, Skopje, Macedonia, 2014.

A number of recent works have shown that moment-method solutions of Hallen’s and Pocklington’s equations with the approximate kernel present undesirable and unphysical oscillations near the ends of the antenna and possibly (depending on the feed model) near the driving point. Such oscillations have been associated with the nonsolvability of the underlying integral equations. They necessarily occur when the number of basis functions is sufficiently large and cannot be blamed on finite computer word length or matrix ill-conditioning effects. In this communication, we show that similar phenomena occur when one uses the extended thin-wire kernel, originally proposed by Poggio and Adams in the 1970s and currently used by the Numerical Electromagnetics Code, which is an antenna modeling software suite that has many variants (e.g., GNEC, EZNEC Pro, SuperNeC, MiniNEC). We discuss the nature and properties of the oscillations. In particular, we show that they are milder and less rapid than those with the approximate kernel. Our main tools of study are: 1) numerical investigations that carefully distinguish from effects due to roundoff and 2) an analytical study for the case of the antenna of infinite length. We finally apply the so-called effective-current method as a remedy to the issues arising from the said oscillations.

This research presents novel isotropic antenna designed by applying machine learning algorithm. Fitness proportionate selection algorithm resulted a design that has a total gain variation of 0.35 dB. This is the best design isotropy for an antenna with non-zero impedance so far reported in the literature. The design was optimized over parameters of isotropy, impedance, structure complexity and standing wave ratio (SWR). After compensating the imaginary part (jX Q) of impedance, the resulting wire antenna showed an input resistance of 48.3 Q at an operating frequency of 107 MHz. SWR is 1.03 reference to 50 Q transmission line. For VSWR ≤ 2, the bandwidth is 1 MHz. Isotropic property of learned antenna resulted to be independent of frequency-dimension scaling as well as independent from compensation of jX Q. All the simulations were performed in Numerical Electromagnetics Code (NEC) for evaluations. The measured variation in total gain for the fabricated antenna was 1.37 dB with an input impedance of 61.7 Q. The minimum SWR of 2.84 was observed at a slightly shifted frequency.

In this study a near isotropic extended arc antenna has been designed and simulated in Numerical Electromagnetics code at a frequency of 1 GHz. Simulations show that antenna has a maximum total gain variation of 0.5 dB, an input impedance of 81.5 Ω and SWR of 1.08 with 75 Ω transmission line after compensating the imaginary part. The maximum gain of antenna is 0.2 dB with a bandwidth of 40 MHz for VSWR ≤ 2.

The paper deals with the comparison of three different models for the assessment of the electric field radiated by a base station antenna system, thus featuring the Free Space Model (FS), Perfect Ground Model (PG) and Fresnel Reflection Coefficient Model (RC). The results obtained with mentioned approaches are compared to the results computed via Numerical Electromagnetics Code (NEC). Several variables have been varied to examine the accuracy of each calculation model. The calculations have been undertaken for the far field only. As many European countries performs the field estimation using the FS model, the final goal of this work is to come up with the most convenient model for the field calculation.

This paper discusses the construction and measurement of Prismatic Polyhedron antenna or known merely as Pn. The antenna element in this research work is half of a wavelength at the design frequency. Several types of Pn are available, where n denotes the number of radiators on the antenna. In this work, the antenna consists of 2 radiators, which is regarded as P2. Also, a half-wave dipole antenna is also discussed because of the similar attributes with the P2 antenna. To determine the antenna’s characteristic, a network analyser, i.e. Agilent Technologies HP8714B RF is used as the measurement tool. The Numerical Electromagnetics Code 2 (NEC2) is employed to simulate the antenna’s ideal characteristics. Both simulation and empirical data are collected and quantified. Based on the measurement, the antenna has shown the results as expected. The antenna may be suitable for UHF-related application, e.g. Zigbee, sensor network, and amateur radio. Such design may be feasible for such applications, which require minimal, sporadic communication and data transfer. Indeed, radio waves at lower frequencies may propagate further and able to penetrate through standard construction wall. Nonetheless, longer wavelengths can lead to an increase in antenna size. At low operating frequency, the constructed antenna can operate at the range between 700-900MHz, and at a higher frequency, the range can be between 1700 - 2000 MHz.

An effective method based on the regularization technique to solve the problem of the high-frequency electromagnetic field coupling to an overhead transmission line is presented. The integral-differential equation describing the field-induced current into a line of finite length, is solved by expressing the unknown by means of the Fourier series. The Landweber iterative method is then used to determine the series coefficients. The proposed method is tested taking as reference numerical results obtained using the numerical electromagnetics code (NEC). The obtained results using the proposed approach are found to be in excellent agreement with those obtained using NEC.

Helical antennas finds major applications from VHF to microwaves which requires circular polarisation. Helical antennas can operate in two principal modes of operation: normal (broadside) mode or axial (end fire) mode. They have got high gain in axial direction which makes them suitable for satellite communications. This paper presents optimum design of axial mode helical antenna using non linear pitch profile modeled using Catmull Rom Spline and radius exponentially varied along the axis of the helix. The antenna is optimized for maximising directive gain subject to unity axial ratio. The optimization is done using Particle Swarm Optimization (PSO) and simulation is done usng Numerical Electromagnetics Code NEC2. Original NEC2 source code is suitably modified to incorporate spline modeling and PSO. Simulation result show that antenna designed usng proposed method has better gain characteristics compared to antenna with uniform radius and non linear pitch profile.

Recently, several standards related to measurements of unintentional radiated emissions of electrical and electronic devices have introduced the need to have a knowledge of the half-power beamwidths (HPBW) of the antennas used during the measurements. Since above 1 GHz most antennas are very directive, information on the pattern has become very important, especially when it comes to understanding how much area the main beam is covering. The standards are extending the need to understand the radiation parameters of the antennas to frequencies in the 30 MHz to 1 GHz range. The present paper is intended as a reference to give information to the EMC engineer and technician on the radiation patterns of the most common EMC antennas used for radiated immunity. The paper also looks at simple methods of measuring the patterns of these antennas. The goal is to propose a simple approach to measure the patterns that will provide results that will be adequate for the EMC community at a low cost. The antennas covered are biconical antennas, log-periodic dipole arrays, hybrid antennas, and dual-ridge horns. As a quick check of the validity of the measured data, computational results are presented for the antennas measured. The Numerical Electromagnetics Code (NEG) and CST Studio Suite™ were used to generate data to compare with the measured results. These experiments give the EMC engineer the information needed to understand the radiation patterns and the half-power beamwidths of the antennas used to perform EMC measurements.

We examine the Doppler features from wind turbine scattering through a series of model measurements. Both backscattered and forward-scattered data are collected in the laboratory at Ku-band from various wind turbine models undergoing rotation. The tested models include a 1:160 scale model turbine, a three-arm wire model, and a small wind turbine from Bergey Windpower with 2' blades. The findings from the wire turbine model are corroborated by simulations performed using the Numerical Electromagnetics Code (NEC). Detailed accounts of the physics behind the observed Doppler features due to multiple scattering, near-field effects, and blade-shape effects are reported.

In this paper, the hybrid electromagnetic model is applied to calculate lightning-induced voltages over a lossy ground. Results provided by this model are compared with experimental data obtained from a reduced-scale model and with results simulated by the numerical electromagnetics code. Good agreement is achieved in all cases.

A novel FDTD-based virtual radar cross section (RCS) prediction tool is introduced. Characteristic examples using simple three-dimensional structures, as well as more-realistic complex air and surface targets, are presented. The virtual tool automatically constructs a wire-grid model of the structure under investigation. It is therefore also possible to compare FDTD results against MoM-based NEC (Numerical Electromagnetics Code) data. It is shown that this virtual tool can be used for both educational and research purposes.

The derivation of a novel delta source based on a reduced Green's function (RGF) is presented for thin-wire scattering problems. The impressed electric field, typically represented by a delta source, is generated by a current defined at the source location. By using electrically small assumptions at the source location, the electric field integral equations (EFIEs) representing the impressed field created by the defined current can be evaluated analytically with an RGF. This impressed field is denoted here as the RGF delta source, or simply, the RGF source. The RGF source is in the range of the EFIE operator and does not contain the dipole that is present in the traditional delta source. The numerical results show the improved convergence of the new RGF source while maintaining accuracy comparable to that of existing delta source models used in other thin-wire models, such as the numerical electromagnetics code.

This paper presents a short tutorial and overview of optimization algorithms based on particle-swarm schemes, and their application to solving electromagnetic problems. As a practical example, a particle-swarm optimization (PSO) tool has been applied in conjunction with the Numerical Electromagnetics Code (NEC) to get the design curves of optimized log-periodic dipole arrays (LPDAs). The graphs show the performance of several radiation parameters (directive gain, front-to-back ratio, bandwidth, SWR, and half-power beamwidth in the E and H planes) as a function of typical design parameters of log-periodic dipole arrays (geometrical parameters and characteristics of the feed). Examples of optimized antennas are given, and their performance is compared to that of standard log-periodic dipole arrays.

We report on the use of a genetic algorithm (GA) in the design optimization of electrically small wire antennas, taking into account of bandwidth, efficiency and antenna size. For the antenna configuration, we employ a multisegment wire structure. The Numerical Electromagnetics Code (NEC) is used to predict the performance of each wire structure. To efficiently map out this multiobjective problem, we implement a Pareto GA with the concept of divided range optimization. In our GA implementation, each wire shape is encoded into a binary chromosome. A two-point crossover scheme involving three chromosomes and a geometrical filter are implemented to achieve efficient optimization. An optimal set of designs, trading off bandwidth, efficiency, and antenna size, is generated. Several GA designs are built, measured and compared to the simulation. Physical interpretations of the GA-optimized structures are provided and the results are compared against the well-known fundamental limit for small antennas. Further improvements using other geometrical design freedoms are discussed.

This paper deals with the wire-grid representation of metallic surfaces in numerical electromagnetic modeling. We discuss in particular the adequacy of the well known and widely used equal area rule (EAR) to calculate the radii of wire-grid models. We show that the EAR is accurate as long as the wire grid consists of a simple rectangular mesh. For more complex body-fitted meshes, using other polygons such as triangles, the EAR appears to be less accurate in reproducing the electromagnetic field scattered by metallic bodies. The conclusions of the paper are supported by numerical simulations performed using a parallel version of the numerical electromagnetics code and experimental data obtained on a vehicle illuminated by an electromagnetic pulse simulator

Lightning current distribution in a directly hit building is studied by using a simple equivalent circuit and an electromagnetic model. The Numerical Electromagnetics Code (NEC-4) is employed for numerical electromagnetic analysis. The error in the shunt ratio of lightning current entering wiring, which is calculated using the electromagnetic model, is estimated to be less than 4%. The shunt ratios for lightning current entering the wiring on the top floor and the first floor are largest. Although they are larger for a higher building, they are almost constant if the building struck has more than five floors. They are smaller when there are more vertical conductors, or the length of the wiring is longer. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(1): 9–16, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20449

In the present paper, transient-induced voltages on a distribution line over finitely conducting ground, which are associated with lightning to a 200-m high stack, have been analyzed by Numerical Electromagnetics Code (NEC-2). An electromagnetic model (EM) of a lightning channel, which contains additional distributed inductance to simulate the reduced propagation velocity of lightning current, has been employed. Validity of the employed model which incorporates a tall structure and a lightning channel has been discussed by comparing calculation with measurements.

Unit step response characteristics of impulse voltage measuring systems are studied with the help of numerical electromagnetics code (NEC-2). Prior to this analysis, the accuracy of a transient analysis by this method is investigated for a simple structure. An impulse voltage measuring system, under application of step voltage, behaves like an antenna until a traveling wave makes several roundtrips in its lead wire. NEC-2 code can analyze such dynamic electromagnetic field around a three-dimensional (3-D) conductor system. In the present paper, the role of a shield ring of a divider for lightning impulse voltage is intensively investigated and discussed.

Numerical Electromagnetics Code (NEC-2), which is a computer code to analyze the three-dimensional electromagnetic (EM) field around thin wires in the frequency domain, has been successfully used in lightning-related studies such as lightning surge analyses or lightning EM pulse calculations over a perfectly conducting ground. NEC-2 is still more useful in investigating lightning-induced effects over ground of finite conductivity. This application of NEC-2 is investigated by comparing calculated results with an experiment over lossy ground. The advantages of the analysis using NEC-2 are that it can accurately compute the current distribution along a wire structure with small amount of postulation. It automatically incorporates coupling between a lightning channel and transmission lines, and it can also take account of finitely conducting ground in transient condition. In addition, it can also model conductors in any arbitrary angles, and it is available in the public domain.

In this paper, we describe a vehicular wire antenna, designed using a genetic algorithm that may be used for both the GPS and Iridium systems. It has right-hand circular polarization, near hemispherical coverage, and operates over the frequency band from 1225 to 1625 MHz. This antenna was simulated using the numerical electromagnetics code (NEC) and then fabricated and tested. The antenna consists of five copper tubing segments connected in series, has an unusually odd shape, and is very inexpensive. It fits in a volume approximately 10 cm/spl times/10 cm/spl times/15 cm, The input voltage standing wave ratio (VSWR) and circular polarization radiation patterns were computed and measured. The VSWR was under 2.2 at the design frequencies of 1225, 1575, and 1625 MHz. The gain varied by less than 12 dB for a 170/spl deg/ sector; it generally fell off near the horizon so the variation was less for 150/spl deg/ and 160/spl deg/ sectors. This new design process, which uses a genetic algorithm in conjunction with an electromagnetics code, produces configurations that are unique and seem to outperform more conventional designs.

An omnidirectional antenna with controllable nulls is desirable in some communication systems. It can suppress noise caused by stationary or mobile jammers and still maintain an otherwise omnidirectional coverage. A synthesis procedure for omnidirectional radiation patterns with multiple nulls for circular arrays of omnidirectional elements is presented. The depths of the nulls can be controlled individually, and the gain ripple in the omnidirectional pattern can be reduced by the use of a window function in the synthesis procedure. The pattern design is performed by the approximation of an ideal pattern, and results for two different approximation algorithms and two different window functions are presented. It is shown that the element excitations can be corrected for mutual coupling, and the results are verified using the numerical electromagnetics code (NEC).

In this paper the Genetic Algorithm (GA) is used to design and optimize a dual-band antenna system covering the UHF and VHF bands. The system contains two stacked vertical wire dipoles, one for each of the bands, above a perfectly-conducting ground plane. Unlike the case of the GA design of a single-band antenna [1, 2], the mutual coupling between the two dipoles introduces some complications in the design of dual-band antennas. Specifically, in the process of broad-banding one dipole by optimizing its loading and matching network for its own frequency band, it becomes necessary to take into account the influence of the second dipole operating in a different frequency band. It is, therefore, essential to carry out the analysis and the synthesis of the entire coupled system concurrently. This paper proposes a design procedure for the dual-band antenna system that makes initial choices for the antenna configuration on the basis of a systematic screening of the potential candidates, and then goes on to apply the GA in conjunction with the Numerical Electromagnetics Code (NEC4) [3] to meet the specifications for the two operating in a simultaneous manner.

An experimental method is described to trace scalar S/sub 21/-measurements with a precision network analyzer to the basic quantities frequency and power. The achieved measurement uncertainty is 0.11 dB for two standard deviations (95.5% confidence level) at a dynamic range up to 70 dB. Precision reference dipoles have been constructed for use as electric field-strength standards in the frequency range of 30-1000 MHz. The transmission loss between such pairs was calculated by using the numerical electromagnetics code and measured both on an open-area test site and in a fully anechoic chamber. Deviations between computations and measurement of the transmission loss were less than 0.3 dB for any measurement and less than 0.25 dB for the mean values. The expanded uncertainty in the antenna factor of one precision dipole is 0.15 dB for two standard deviations.

Orthogonal design method (ODM) is widely used in real world application while it is not used for antenna design yet. It is employed to optimize roughly designed antenna in this paper. The geometrical factors of the antenna are relaxed within specific region and each factor is divided into some levels, and the performance of the antenna is constructed as objective. Then the ODM samples small number of antennas over the relaxed space and finds a prospective antenna. In an experiment of designing ST5 satellite miniantenna, we first get a roughly evolved antenna. The reason why we evolve roughly is because the evolving is time consuming even if numerical electromagnetics code 2 (NEC2) is employed (NEC2 source code is openly available and is fast in wire antenna simulation but not much feasible). Then the ODM method is employed to locally optimize the antenna with HFSS (HFSS is a commercial and feasible electromagnetics simulation software). The result shows the ODM optimizes successfully the roughly evolved antenna.

A genetic algorithm is used to design a monopole loaded with a modified folded dipole so that it radiates uniform power over the hemisphere. Each of the wires that make up the antenna are given a range of possible lengths. The genetic algorithm randomly selects a sample population of possible antenna configurations from the total population of all configurations. The radiation pattern of each sample configuration is computed using the numerical electromagnetics code (NEC). The solutions are compared with the desired pattern and ranked in terms of performance. The best solutions are retained and mated with one another and the process is repeated until an optimal solution is obtained. The genetic algorithm quickly produced an antenna that has a nearly uniform power over the hemisphere. Although the antenna was designed to operate at a frequency of 1.6 GHz, it performed satisfactorily over the frequency range from 1.4 to 1.8 GHz. The antenna was fabricated and the computational results were verified experimentally. We have shown that the genetic algorithm is a very powerful tool for designing wire antennas; it is expected that this process can be used to design any antenna that can be analyzed using an electromagnetic code.

A series of comparisons are drawn between the measured impedances of skeletal wire conical (SWC) antennas and theoretical impedances obtained using the method of moments computer simulation software code (numerical electromagnetics code) NEC2 formed the basis for this study. The validity of the numerical model was established on the basis of a favorable comparison between these results; this model forms the basis for the comprehensive computational investigation of SWC antennas presented. First, a definition of impedance convergency is provided; it serves to classify SWC antennas into two groups: sparse or convergent, and convergency curves are presented. Thereafter, the geometric mean-input resistance, voltage standing wave ratio (VSWR) performance and radiation patterns of these SWC antennas are examined. Finally, four graphs are considered. Used in conjunction, these graphs provide an initial approximation of the performance/parameter characteristics of SWC antennas.

Accurate numerical simulations are needed for analyzing and developing better electrical interconnects and electromagnetic compatibility (EMC) measurement systems. Numerical simulations enable one to predict the field behavior and compute the voltages, currents, impedances and other parameters of interest for a given structure such as cable shielding. A numerical simulation is used to analyze measured data from a cable radiation study. The finite difference time domain (FDTD) and the method of moments based Numerical Electromagnetics Code (NEC) are used to compute the total radiated power from the cable, and the results are shown to be in agreement with measured data. A numerical study is carried out to demonstrate the usefulness of the method at aiding the design of a measurement system without much additional experimental work.

To verify that the electromagnetic analysis system NEC2 is effective for the development and design of the second generation digital cordless telephone investigated for use in the frequency band of 1.9 GHz. Two types of personal handy phone models with metal housing and plastic housing were fabricated and measurement and analysis by NEC2 were carried out for radiation patterns. The analysis results were found to agree with the measured results in regard to the absolute gain and shape. For the metal housing model, examples of the procedures were presented for modeling the housing by wire grids or surface patch elements. It was shown that the analysis results agree well with the measured results. It was also found that the radiation pattern of the plastic housing model is only slightly affected by the housing material. By realizing the installed circuit as an analytical model, estimations and evaluations of the radiation pattern are possible by means of NEC2. As a result, NEC2 is effective for the analysis of the radiation pattern of personal handy phone systems at 1.9 GHz.

A traveling-wave current distribution can be produced on a monopole over a ground plane by inserting a resistance of suitable magnitude one-quarter wave length from its end. It has been shown that the resistor can be replaced with a modified folded dipole which has a radiation resistance approximately equal to that of the resistor. Furthermore, it was found that when the folded element was about 0.1/spl lambda/ above the ground plane, near hemispherical coverage was obtained in the plane of the element. In this paper, the resistor is replaced with orthogonal folded elements. The main objective is to obtain an antenna which is circularly polarized and which has near hemispherical coverage. The input impedance, current distribution, and radiation patterns of this antenna were computed using the numerical electromagnetics code (NEC); the radiation patterns and input impedance were also measured. To produce a circularly polarized wave it is necessary to tilt the folded elements. After experimenting with a number of different configurations an antenna design having directional and polarization properties approaching those that were desired was obtained. All computations and measurements were conducted near 1.6 GHz, a frequency close to that of the proposed IRIDIUM communications system and the L1 band of the Global Positioning System (GPS). The double-folded monopole may prove to be a very low cost option as a ground antenna for these systems.

The use of the numerical electromagnetics code for modeling wires and wire grids (EFIE) has been reviewed recently. This work is an extension of the work of C.A. Balanis that utilizes a patch model, and computes input impedance (as VSWR) using NEC. The work presented here is a simulation and measurement study for the proposed NASA waves in space plasma (WISP) experiment. Some modeling guidelines for patch models are discussed. >

The radar cross sections (RCS) and frequency spectra of a wind turbine consisting of three conducting blades of 42 m radius, with a vertical mast of 65 m over a perfect ground plane, was estimated using the Numerical Electromagnetics Code (NEC). The NEC input deck generation, parsing the NEC output to select the RCS numbers, plotting the time series, and calculating and plotting the frequency spectra were all done by bash shell scripts. The shell scripts generally set up several environment variables and then called Ruby, Octave or Gnuplot programs to perform the text manipulations, data calculations and plot generation. Calibrated plots of time series and frequency spectra for several cases are included. The effect of a dielectric blade is briefly considered.

The Method of Moments (MoM) is a numerical technique used to approximately solve linear operator equations, such as differential equations or integral equations. The unknown function is approximated by a finite series of known expansion functions with unknown expansion coefficients. The approximate function is substituted into the original operator equation, and the resulting approximate equation is tested so that the weighted residual is zero. This results in a number of simultaneous algebraic equations for the unknown coefficients. These equations are then solved using matrix calculus. MoM has been used to solve a vast number of electromagnetic problems during the last five decades. In addition to the basic theory of MoM, some simple examples are given. To demonstrate the concept of minimizing weighted error, the Fourier series is also reviewed. IEEE Antennas and Propagation Society

The propagation of current on a thin, straight wire in an infinite chiral medium is examined by solution of the integral equation for an infinite wire and also from the moment-method solution for a long wire of finite length. The current on the infinite wire is shown to consist of three components: a discrete mode that decays exponentially and two continuous-spectrum components from branch cuts from the two chiral wavenumbers. The integral equation for a finite wire in the chiral medium is solved by the method of moments using a modified version of the numerical electromagnetics code (NEC). The moment-method solution is shown to be in close agreement with the modal solution for the infinite wire, providing validation for the numerical treatment. >

IEC TR61400-24 [1] suggests interconnection of the grounding system of wind turbines to achieve low steady-state resistance, however, the transient behavior during a lightning strike to the interconnected wind turbine grounding system remains to be discussed. This paper investigates the influence of interconnection on the lightning surge response of wind turbine grounding system. Two different numerical methods, Numerical Electromagnetics Code (NEC-4) based on Method of Moments (MoM), and Virtual Surge Test Lab (VSTL) based on Finite Difference Time Domain (FDTD) method are used for electromagnetic analysis of lightning surge response of wind turbine grounding system. Comparison of results using NEC-4 and VSTL are made to clarify the usefulness of these methods for transient analysis of a large grounding system. The influences of resistivity of soil and front time of lightning impulse current, on the response of interconnected wind turbine grounding system are analyzed.

The Super Dual Auroral Radar Network (SuperDARN) is an international collaboration of researchers interested in near-Earth space plasma. This group uses high frequency (HF) radars to measure backscatter from magnetic field-aligned plasma irregularities to study space weather manifested in the Earth's magnetosphere and ionosphere. This paper describes a new antenna design, the twin terminated folded dipole (TTFD), used by the latest generation of SuperDARN radars. The TTFD design provides a less expensive alternative to the log-periodic antenna design previously used by SuperDARN radars. The radiation characteristics of the new antenna are analyzed with modeling results from a version of the Numerical Electromagnetics Code version 2 (NEC2). The TTFD antenna modeling results are then compared to a log-periodic antenna design used for a SuperDARN radar. It is concluded that the less expensive TTFD antenna design is an adequate replacement for the log-periodic antenna based on modeled performance characteristics. The TTFD antenna design demonstrates the ability to generate HF backscatter suitable for scientific analysis.

This paper presents a novel method for design of circularly polarized axial mode helical antenna with maximum directive gain. In this work helical antenna is compactly modeled by the following parameters - helix radius (a), number of turns (N) and nonlinear pitch profile represented by a Catmull-Rom spline curve. This spline curve consists of six pitch angles α 1 , α 2 , α 3 , α 4 , α 5 and α 6 at six equidistant points along the axial length of the helix. For a given number of turns, optimum values of radius and pitch profile are determined for maximizing the gain subject to unity axial ratio. The gain and axial ratio are determined using NEC2 (Numerical Electromagnetics Code) simulation and optimization is performed using Particle Swarm Optimization (PSO). The original NEC2 source code has been modified to incorporate Catmull-Rom spline modeling and PSO to suite the requirement of this work. Simulated and experimental results show that there is significant improvement in gain characteristics compared to design based on Kraus method which uses constant pitch profile.

Computer-modeling exercises performed indicate that it is possible to add a group of four elevated radials to a pre-existing conventional AM-broadcast vertical monopole antenna system in order to restore performance to its original level (or better) in situations where the buried-radial ground system has been damaged. A wide variety of different configurations for the elevated radials are examined, including variations in orientation, length, and height above ground. It is stressed that extensive outdoor testing should be performed in order to verify these computer predictions. The computer software used is the Numerical Electromagnetics Code. >