This paper is concerned with a modeling technique of electromagnetic radiations of power electronics circuits during a switching operation of a power electronic component. The electromagnetic radiating loops are formed by PCB traces assumed to be perfect conductor. We complete our study by proposing a technique using passive loops to reduce the magnetic field emitted by the power electronic converter. To achieve this, we propose to solve Maxwell's equations by using the FDTD method where open boundaries, dielectric board and ground plane are taken into consideration. A validation of the model used in our work (solving Maxwell equations using FDTD) is realized by comparison with other theoretical concepts.

This paper presents results of a dosimetry study at an FM broadcasting frequency of 100 MHz. The work focused on SAR calculations with high resolution Magnetic Resonance Imaging (MRI)-based full-body models. FDTD computer modeling used a half-wave dipole as the exposure source. Extensive calculations give the variation of SAR with distance and show that whole-body average SAR exhibits a different distance dependency from the incident power density. Body size has a significant effect on SAR. Based on the numerical results, an empirical formula was developed to describe the relationship between antenna input power and distance for the limiting SAR value.

The magnetic field of an axially symmetric coil or magnetic material system can be computed by expansion of the central and remote zonal harmonics, using the Legendre polynomials. This method can be 100-1000 times faster than the more widely known elliptic integral method and is more general than the similar radial series expansion. We present the zonal harmonic method for field, scalar and vector potential calculation of circular current loops, of general axisymmetric coils and magnetic materials, and of special coils with rectangular cross section, with various source representations: currents, magnetic dipoles and equivalent magnetic charges. We discuss in detail the convergence properties of the zonal harmonic expansions, and we show the generalization of the method for special three-dimensional magnetic systems.

The electric potential and field of an axially symmetric electric system can be computed by expansion of the central and remote zonal harmonics, using the Legendre polynomials. Garrett showed the usefulness of the zonal harmonic expansion for magnetic field calculations, and the similar radial series expansion has been widely used in electron optics. In this paper, we summarize our experience of using the zonal harmonic expansion for practically interesting axisymmetric electric field computations. This method provides very accurate potential and field values, and it is much faster than calculations with elliptic integrals. We present formulas for the central and remote expansions and for the coefficients of the zonal harmonics (source constants) in the case of general axisymmetric electrodes and dielectrics. We also discuss the general convergence properties of the zonal harmonic series (proof, rate of convergence, and connection with complex series). Practical considerations about the computation method are given at the end. In our appendix, one can find many useful formulas about properties of the Legendre polynomials, various derivatives of the zonal harmonic functions, and a simple numerical integration algorithm.

The knowledge of electromagnetic properties of biological tissues is required to assess the radio frequency energy deposition in children exposed to electromagnetic fields. The issue whether children should be considered a dosimetric sensitive group in comparison to adults, to which the confirmation of age-dependence of human tissue electromagnetic properties potentially may contribute remains debatable at scientific forums. This paper derives the formula for calculation of electromagnetic properties (permittivity and conductivity) of children tissues, as a function of height, weight, and age, respectively. By using the proposed formula, we have calculated and presented electromagnetic properties of the muscle, brain (gray matter) and skin for 1-year-old to 10-year-old children for 900 MHz, 1800 MHz and 2.4 GHz, at which frequencies most of radio frequency devices used by children operate. The trend over the age of child electromagnetic properties has been presented, and electromagnetic properties at different frequencies for the same child age have also been compared. For certain tissues, comparison between the children at various age and adult electromagnetic parameters has been given. A database with electromagnetic properties for children, of all ages, tissues and frequencies may be built up with the proposed approach. It will further advance research on the assessment of children exposure to electromagnetic fields. Formula can also be used for the determination of electromagnetic parameters for children with specific height and weight.

A method to improve the gain of axial-mode helical antenna is proposed. This method involves a parasitical circular metal disk, which is installed on the front of general axial-mode helical antenna and is apart from the helical line. A circular current whose phase lags behind that of helical line current appears, which brings a more concentrated radiation field. Consequently, the antenna gain is improved. Based on the simulation results, an antenna array model fed independently is proposed. This model gives an excellent explanation of the radiation characteristic of helical antenna. Both the simulation and experiment results show that for obtaining the same gain, the antenna length in this new method is only 71% of that in traditional helical antenna. The reduction of antenna length favors the miniaturization of antenna. In addition, this method has little effect on the bandwidth of antenna, so it can be widely used in the design of helical antenna element and array.

In this paper, a quadri-folded substrate integrated waveguide (QFSIW) resonant cavity is proposed and investigated for the first time, which is able to reduce the circuit size by 89% compared with the conventional substrate integrated waveguide (SIW) resonant cavity. It has a two-layer configuration and a C-type coupling slot etched on the middle conductor layer. As an example, such a miniaturized resonant cavity is employed in the design of a four-order S-band SIW bandpass filter with the Chebyshev response. Negative couplings are used between two adjacent SIW resonant cavities, which don't influence the whole transmission characteristic of the filter. Experimental results are in good agreement with those from simulations.

The goal of this paper is to use defected ground structure (DGS) in microstrip antennas for dual band operation at microwave frequencies. The soft nature of the DGS facilitates improvement in the performance of microstrip antennas. A design study on microstrip patch antenna with specific DGS slot has been presented in the proposed work. In this paper, a stacked microstrip patch antenna (SMPA) has been designed for broadband behavior, and then skew-F shaped DGS has been integrated with a detailed study of possible DGS slots in a small area for dual band operation. The design and optimization of both the SMPA and DGS structures along with the parametric study were carried out using CST Microwave Studio V.9. Further, the dual band antenna, i.e., the SMPA with skew-F shaped DGS, has been fabricated, and the experimental results have shown a good agreement with the simulation ones.

In this paper, the transverse equivalent network (TEN) model based on the transmission line theory is employed to analyze and calculate the far-field radiation properties of the Fabry-Perot Resonator (FPR) antenna with perfect magnetic conductor (PMC) ground plane in detail, then the comparative study of the radiation property of FPR antenna with PMC and PEC ground plane is presented. The closed-form expressions for the radiated fields, field peak values, pattern beamwidths and pattern bandwidth of this type of antenna in the E- and H-planes are derived, respectively. The results demonstrate that in theory the radiation property of FPR antenna with two kinds of ground plane is not the same unexpectedly. An interesting characteristic of this type of antenna is that when the PMC acts as the antenna ground plane, the beamwidth and bandwidth of the antenna is increased by a factor of two in general cases, while its peak value of far field is the same as that of the conventional antennas of this class having PEC ground plane. Some results are validated through full-wave simulations of an actual antenna. The original results obtained here lead to a design method for getting the maximum directivity and keeping the bandwidth of this kind of resonant antenna, which is of great significance for antenna designing.

This paper mainly deals with the problem of target localization with unknown wall parameters for through-the-wall radar imaging (TWRI) applications. A novel approach is presented to correct the shift in target position due to the ambiguities of the wall parameters. This approach is based on imaging by using at least two assumed wall relative permittivities. For each assumed relative permittivity, a sequence of target images are obtained using different assumed wall thicknesses, and a linear trajectory is formed via Radon transform. The intersection of these linear trajectories corresponding to different assumed relative permittivities is the estimated target position. Besides, the estimated wall parameters are acquired to form the high-quality image. Simulation and experiment results show that the estimated target positions with the proposed approach are well consistent with the true target locations, and the high-quality images are generated with the estimated wall parameters.

We present new implementations in Method of Moments of two types of second kind integral equations: (i) the recently proposed Electric-Magnetic Field Integral Equation (EMFIE), for perfectly conducting objects, and (ii) the Müller formulation, for homogeneous or piecewise homogeneous dielectric objects. We adopt the Taylor-orthogonal basis functions, a recently presented set of facet-oriented basis functions, which, as we show in this paper, arise from the Taylor's expansion of the current at the centroid of the discretization triangles. We show that the Taylor-orthogonal discretization of the EMFIE mitigates the discrepancy in the computed Radar Cross Section observed in conventional divergence-conforming implementations for moderately small, perfectly conducting, sharp-edged objects. Furthermore, we show that the Taylor-discretization of the Müller-formulation represents a valid option for the analysis of sharp-edged homogenous dielectrics, especially with low dielectric contrasts, when compared with other RWG-discretized implementations for dielectrics. Since the divergence-Taylor Orthogonal basis functions are facet-oriented, they appear better suited than other, edge-oriented, discretization schemes for the analysis of piecewise homogenous objects since they simplify notably the discretization at the junctions arising from the intersection of several dielectric regions.

This paper describes the design of a highly efficient and linear GaN HEMT power amplifier which may be used in WiMAX application. To improve linearity of highly efficient power amplifiers, a technique using diodes in the gate DC path was applied to TL and 2HT amplifier. This solution using diodes offers a good manner to improve linearity near saturation zone compared to the approach using only a DC gate resistor for TL (tuned load) case as well as for 2HT (second harmonic tuning approach). A 2.5 GHz 2HT power amplifier circuit was built, and measured data confirm the linearity improvement, particularly near saturation zone, as predicted by simulation, maintaining higher power performances. An output power of 36.8 dBm has been measured with an associated power added efficiency of 46.5% and carrier to third order intermodulation (C/I3) of 53.4 dBc. A 2HT PA also exhibits good performances across the full (2.3-2.7) GHz band. An output power ranging from (35-36.9) dBm with an associated gain of $12.9±0.9 and a power added efficiency ranging from (40-46)% are measured across the full (2.3-2.7) GHz band.

In this paper, the electromagnetic properties of two different High Impedance Surfaces (HIS) with or without Electromagnetic Band Gap (EBG) in different configurations are investigated for mutual coupling reduction in small antenna arrays. The resonant mechanisms of these structures are studied using transmission calculations in a parallel plate waveguide. An optimum configuration is then proposed. It is shown that a good isolation performance can be achieved without the need of metallic vias when the structure is embedded in a metallic cavity, which limits significantly the number of HIS cells needed to perform a good isolation and the cost of manufacture.

In this paper, optically transparent ultra-wideband (UWB) monopole antennas in S-band and C-band are presented, compared and discussed. Three transparent UWB antennas elaborated from the AgGL (Silver Grid Layer) material with various levels of transparency (54.5%, 73.4% and 80.3%) and of sheet resistances 0.018 Ω/sq, 0.022 Ω/sq and 0.052 Ω/sq, respectively are tested. The radiofrequency measurements show performances very close to those of a light reflecting reference antenna made of a continuous silver/titanium bilayer (0.0026 Ω/sq sheet resistance). Conversely, the fourth transparent antenna, made of usual transparent conducting oxide/metal multilayer presents significant ohmic losses and weak radiofrequency performances. The gains of the UWB AgGL antennas are similar to that of the reference antenna (~6 dBi max.). Whereas the gain of the transparent multilayer antenna always stays ~2 dB lower than that of the reference. This work demonstrates the relevance of AgGL coating in the fabrication of transparent UWB antennas with high radiation efficiency.

Fresnel lenses are low-cost opcitical elements used for focusing sunlight to solar panels to ensure operation under high-flux density. However, the conventional Fresnel lens has a relatively high material usage and hence contributes to additional efficiency degradation. Moreover, traditional design of Fresnel lenses introduces additional prismatic facets, due to deviations in manufacturing, which reflect the light toward the back focal spot, leading to additional losses. In this paper, Fresnel lenses based on finite arrays of Nano Shell-Silver Coated Silica (NSSCS) are proposed to overcome the aforementioned drawbacks from infrared regime through the visible band to the ultraviolet region. To identify reflection losses, material losses of the NSSCS array and rejection bands due to the NSSCS array arrangement, three unique electromagnetic (EM) approaches are invoked: Frequency Selective Surfaces (FSS) to determine reflection bands, Metamaterial (MTM) to specify material losses and Electromagnetic Band Gap (EBG) to locate the rejection band. The EM characteristics of the NSSCS array are evaluated for wavelengths ranging from 0.3 μm to 300 μm, using CST MicroWave Studio (CST MWS), which is based on the Finite Integration Technique (FIT). It is found that the NSSCS array exhibits excellent transmittance within two bands, one from 545 nm to 857 nm and the other from 444.5 nm to 480 nm, for angles ranging from 0^o to 180^o along the azimuth and elevation. The effective refractive index (n_eff spectra showed that the NSSCS array does not provide a negative for its real (n_eff part over the considered wavelength band. The imaginary part of (n_eff value is found to be almost insignificant, between 0.857 μm to 1.714 μm and 316 nm to 414 nm and lossy elsewhere. In general, the NSSCS array shows no specific stop band over the considered frequency region. Fresnel lenses based on a 9×9 NSSCS array configuration with planar, concave and convex profiles are presented in this paper. The beam width and power density of the emerged beams are evaluated at different wavelengths for different lens sizes. In general, it is found that the power density spectrum is largely dependent on the imagery part of n_eff. Nevertheless, the beam width decreases by increasing the lens size, while it decays for wavelengths longer than 500 nm. The concave and convex profiles are introduced to further enhance beam width. The effects of increasing the lens size from 9×9 to 11×11 on the beam width are reported for the concave and convex profiles. It is found that the concave design provides almost a constant beam width at 666.7 nm, 461.5 nm and 316 nm with changing array size, while the convex design does not. Characteristics of the emerged EM beams, in terms of beam waist, depth of focus and phase retardation, are evaluated based on Gaussian optic formalisms for the 9×9 NSSCS array. It is found that the beam waist and the depth of focus for the flat profile vary from 334.03 nm to 387.90 nm and 105.16 nm to 285.65 nm, respectively. The beam waist changes from 365.12 nm to 381.41 nm, while the depth of focus changes from 125.65 nm to 289.45 nm for the convex profile. Finally, the beam waist changes from 313.36 nm to 318.19 nm, and the depth of focus changes from 925.49 nm to 201.45 nm for the concave profile.

Fast and efficient spectrum sensing is vital for multi-radio multi-channel cognitive radio (CR) networks where unlicensed secondary users (SUs) have to sense and opportunistically transmit on multiple spectrum bands without causing any harmful interference to the licensed primary users (PUs) of those spectrum bands. Accordingly, this paper presents a smart, practical and efficient wideband spectrum sensing scheme based on an optimal sensing stop policy that aims to optimize SU throughput while adhering to the PU interference constraints. Unlike existing work, this scheme is smart because in determining the best time for the multi-transmitter SU to stop sensing and start data transmission based on the channels that have been sensed idle, this scheme explicitly takes into consideration the number of transmitters on the SU; so-called N-transmitters constrained SU. Further, we formulate and solve the optimal sensing stopping problem. The numerical and simulation results presented verify the efficiency of the proposed sensing scheme.

This paper presents a novel synthetic aperture radar (SAR) image simulation approach to target recognition, which consists of two frameworks, referred to as the satellite SAR images simulation and the target recognition and identification. The images simulation makes use of the sensor and target geo-location relative to the Earth, movement of SAR sensor, SAR system parameters, radiometric and geometric characteristics of the target, and target radar cross section (RCS), orbital parameters estimation, SAR echo signal generation and image focusing to build SAR image database. A hybrid algorithm that combines the physical optics, physical diffraction theory, and shooting and bouncing rays was used to compute the RCS of complex radar targets. Such database is vital for aided target recognition and identification system Followed by reformulating the projection kernel in an optimization equation form, the target's reflectivity field can be accurately estimated. Accordingly, the target's features can be effectively enhanced and extracted, and the dominant scattering centers are well separated. Experimental results demonstrate that the simulated database developed in this paper is well suited for target recognition. Performance is extensively tested and evaluated from real images by Radarsat-2 and TerraSAR-X. Effectiveness and efficiency of the proposed method are further confirmed.

A novel compact quadruplexer based on defected stepped impedance resonator (DSIR) with high isolation is presented in this paper. The proposed quadruplexer consists of a common input feeding line, four kinds of folded DSIRs and four individual output feeding lines. Considering the loading effect among channel filters, the input DSIRs must be properly located with respect to the common feeding line in order to realize all external quality factors at the same time, so that the loading effect becomes very small. Furthermore, since the compact DSIRs resonate at multiple fundamental frequencies, a high-isolation quadruplexer with size reduction can be obtained. A fabricated prototype of the proposed quadruplexer is developed. The channel performance obtained by measurement and EM simulation are in good agreement.

We investigate a new mean of decreasing leakage and material loss from coaxial cables using different metallic shield and central conducting part geometries. The suggested model is composed of a central conductor surrounded by 40 metallic wires circularly disposed. The proposed cable is also a hybrid one allowing simultaneous transmission of optical as well as radio frequency (RF) signals. The fabrication techniques for the proposed cable are similar to the one applied in the realization of optical fibers. Besides the fact that the attenuation along the proposed cable is reduced, the most important result of this study is that the interference generated by this source on external cables is also lowered.

This paper presents the unified efficient fundamental alternating-direction-implicit finite-difference time-domain (ADI-FDTD) schemes for lossy media. The schemes presented include averaging, forward-forward, forward-backward and novel exponential time differencing schemes. Unifications of these schemes in both conventional and efficient fundamental forms of source-incorporated ADI-FDTD are provided. In the latter, they are formulated in the simplest, most concise, most efficient, and most fundamental form of ADI-FDTD. The unified update equations and implementation of the efficient fundamental ADI-FDTD schemes are provided. Such efficient fundamental schemes have substantially less right-hand-side update coefficients and field variables compared to the conventional ADI-FDTD schemes. Thus, they feature higher efficiency with reduced memory indexing and arithmetic operations. Other aspects such as field and parameter memory arrays, perfect electric conductor and perfect magnetic conductor implementations are also discussed. Numerical results in the realm of CPU time saving, asymmetry and numerical errors as well as specific absorption rate (SAR) of human skin are presented.