This paper presents a novel stochastic microwave method for the detection, location and reconstruction of electric properties of breast cancer in a simplified breast phantom. The method is based on the inversion of time domain data. The problem is recast as an optimization one by defining a suitable cost function which is then minimized using an efficient evolutionary algorithm. Selected numerical simulations of a simplified three dimensional breast model and a realistic numerical phantom based on magnetic resonance images (MRIs) are carried out to assess the capabilities of the method. The results obtained show that the proposed method is able to reconstruct the properties of a tumor-like inclusion to a reasonable degree of accuracy.

A method of designing a cylindrical conformal array with shaped-beam and reconfigurable dual-beam using a modified particle swarm optimization algorithm is proposed in this paper. The proposed algorithm is easy to implement and efficient to be used in synthesizing conformal arrays with digital attenuators and digital phase shifters. Moreover, the proposed synthesis has taken the actual active element patterns into account, which can reduce the error between computation and realization. Good agreement can be obtained between the desired patterns and the synthesized patterns.

Space mapping (SM) is one of the most popular surrogate-based optimization techniques in microwave engineering. The most critical component in SM is the low-fidelity (or coarse) model --- a physically-based representation of the structure being optimized (high-fidelity or fine model), typically evaluated using CPU-intensive electromagnetic (EM) simulation. The coarse model should be fast and reasonably accurate. A popular choice for the coarse models are equivalent circuits, which are computationally cheap, but not always accurate, and in many cases even not available, limiting the practical range of applications of SM. Relatively accurate coarse models that are available for all structures can be obtained through coarsely-discretized EM simulations. Unfortunately, such models are typically computationally too expensive to be efficiently used in SM algorithms. Here, a study of SM algorithms with coarsely-discretized EM coarse models is presented. More specifically, novel and efficient parameter extraction and surrogate optimization schemes are proposed that make the use of coarsely-discretized EM models feasible for SM algorithms. Robustness of our approach is demonstrated through the design of three microstrip filters and one double annular ring antenna.

As studied by Jaulent in 1982, the inverse problem of lossy electric transmission lines is closely related to the inverse scattering of Zakharov-Shabat equations with two potential functions. Focusing on the numerical solution of this inverse scattering problem, we develop a fast one-shot algorithm based on the Gelfand-Levitan-Marchenko equations and on some differential equations derived from the Zakharov-Shabat equations. Compared to existing results, this new algorithm is computationally more efficient. It is then applied to the synthesis of non uniform lossy electric transmission lines.

The design and optimization of an annular ring dielectric resonator antenna (DRA) operating in the C frequency band is addressed. The DRA is intended to be used as the radiating element of a transmitting array of active integrated antennas, its input impedance must exhibit a proper resistive load at the fundamental resonance frequency, as well as a dominant reactive behavior, either inductive or capacitive, at higher harmonics. The configuration here proposed is a slot-coupled annular DRA where harmonic tuning is performed by resorting to a proper shape factor. The design procedure is performed by exploiting artificial neural networks, to find the resonator geometry starting form the desired resonance frequency, and a finite elements based numerical tool for the electromagnetic characterization of the antenna. Samples of simulation results are shown to demonstrate the capabilities of the proposed slot-based harmonic tuning technique for ring DRAs.

Evaluation of electromagnetic fields caused by the lightning channel is an appealing topic in order to consider the indirect effects of lightning on the power lines. A common assumption for the calculation of electromagnetic fields at the observation point is a vertical lightning channel, but the fact is that in reality the lightning channel is seldom vertical on the ground surface. In this study, the electromagnetic fields due to inclined lightning channel at various observation points with different angles and with respect to the image of lightning channel on the ground surface were explored. This study also proposes general equations that can estimate the electric fields due to inclined lightning channel through the 2nd FDTD method. The proposed method supports the notion of vertical lightning channel, while the channel angle, with respect to z-axis, is assumed to be zero. This method was validated through the data gathered from four fields: three at a close distance from inclined lightning channel and one at an intermediate distance from vertical lightning channel. Similarly, due to inclined lightning channel, the effects of geometrical and current parameters on the electromagnetic fields are considered. This study substantiates different coupling models with FDTD structure directly at the time domain without a need for extra converters.

This work presents a new type of CPW balun consisting of 3dB coupled-line sections, which are one eighth wavelength long, and a short redundant transmission line for the applications of the modern wireless communication systems. A set of design equations that can determine the values of the elements of balun is proposed. A new type of coupler constructed with a structure similar to the conventional step impedance resonator is developed to further reduce the size of the balun. An experimental prototype operated at 1.0 GHz was designed and fabricated to verify the proposed design method. The measurement results show quite good correspondences with the theoretical predictions and the EM simulations.

A unequal Wilkinson power divider based on asymmetrical coupled line section is presented in this paper. The proposed unequal Wilkinson power divider topology uses asymmetrical coupled-line section and two transmission-line transformers. For simplification, a section asymmetrical coupled line is applied to obtain front compact matching structure. For generalization, three ports terminated impedances are defined as arbitrary values. In particular, the output ports impedances are arbitrary complex values. Design parameters and analysis equations for scattering parameters are also provided. In addition, the theoretical external performances of several examples are illustrated. Finally, the EM simulated results are validated with the characterization of two microstrip unequal power dividers at 2 GHz.

The present work introduces a new optimization technique suitable for adaptive beamforming of linear antenna arrays. The proposed technique is a new PSO variant called Adaptive Mutated Boolean PSO (AMBPSO) where the update formulae are implemented exclusively in Boolean form by using an efficiently adaptive mutation process. The AMBPSO aims at estimating the excitation weights applied on the array elements considering that a desired signal and several interference signals are received by the array at respective directions of arrival. In order to exhibit the robustness of the technique, the optimization process does not take into account the interference correlation matrix. A certain power level of additive Gaussian noise is also considered by the technique. The AMBPSO has been applied in several cases of uniform linear antenna arrays with different spacing between adjacent elements and different noise power level and therefore seems to be quite promising in the smart antenna technology.

This paper investigates the use of the guard traces to improve the Time-Domain Transmission (TDT) waveform and eye diagram for a flat spiral delay line. Two types of guard trace are adopted to implement and analysis in microstrip line and stripline structures. One is Two Grounded Vias type Guard Trace (TGVGT) and the other is Open-Stub type Guard Trace (OSGT). The time-domain analysis results by HSPICE and the associated simple circuit modeling is presented. According to the simulation results, the original TDT crosstalk noises can be reduced by about 80% when using TGVGTs or OSGTs in a stripline structure and by about 60% when using TGVGTs in a microstrip line structure. Additionally, the eye diagrams also can obtain improvement. The crosstalk noise cancelation mechanisms of the flat spiral routing scheme on TGVGTs and OSGTs are investigated by graphic method. In addition, how the degradation for the OSGT inserted into the flat spiral delay line in microstrip structure is clearly investigated. A flat spiral delay line inserted into TGVGTs and OSGTs both can obtain good improvements of the TDT waveform and eye diagram in a stripline structure. Moreover, adding OSGTs to the flat spiral routing scheme is easily accomplished due to the open end of OSGTs. Finally, HSPICE simulation and time-domain measurements of crosstalk noises of TDT waveforms, and eye diagrams are use to validate the proposed structure and analysis.

This paper presents a novel time-harmonic electromagnetic model for determining the current distribution on conductor grids in horizontally stratified multilayer medium. This model could be seen as a basis of the wider electromagnetic model for the frequency-domain transient analysis of conductor grids in multilayer medium. The total number of layers and the total number of conductors are completely arbitrary. The model is based on applying the finite element technique to an integral equation formulation. Each conductor is subdivided into segments with satisfying the thin-wire approximation. Complete electromagnetic coupling between segments is taken into account. The computation of Sommerfeld integrals is avoided through an effective approximation of the attenuation and propagation effects. Computation procedure for the horizontally stratified multilayer medium is based on the successful application of numerical approximations of two kernel functions of the integral expression for the potential distribution within a single layer, which is caused by a point source of harmonic current. Extension from the point source to a segment of the earthing grid conductors is accomplished through integrating the potential contribution due to the line of harmonic current source along the segments axis.

This work examines reflection of a light from a semi-infinite medium which is modified with an ordered monolayer of spherical nanoparticles placed on or under its surface. We derive analytical expressions for the electric fields within and outside such structures and verify them with help of strict numerical simulations. We show that nanoparticles layer acts as an imaginary zero-thickness surface having complicated non-Fresnel reflection coefficients with wavelength dependent phase shift. It is shown that such monolayers may reduce reflection relative to reflection from a pure substrate surface. We derive and analyse a zero-reflection condition in the simple intuitive form. It is shown that a single layer of nanocavities near the medium-vacuum interface may increase the transparency of a dielectric medium to values close to 100% in a wide wavelength range.

This paper applies a meshless method based on radial basis function (RBF) collocation to solve three-dimensional scalar Helmholtz equation in rectangular coordinates and analyze the eigenvalues of spherical resonant cavity. The boundary conditions of spherical cavity are deduced. The RBF interpolation method and the collocation procedure are applied to the Helmholtz and boundary condition equations, and their discretization matrix formulations are obtained. The eigenvalues of spherical resonant cavity with natural conformal node distribution are computed by the proposed method. Their results are agreement with the analytic solution.

The system of Maxwell equations with an initial condition in a vacuum is solved in a cylindrical coordinate system. It derives the cylindrical transverse electromagnetic wave mode in which the electric field and magnetic field are not in phase. Such electromagnetic wave can generate and exist in actual application, and there is no violation of the law of conservation of energy during the electromagnetic field interchanges.

In this paper, dispersion characteristics of the partial H-plane waveguides are theoretically investigated by applying Galerkin's method in Fourier domain. By extracting the dyadic Green's functions of the structure and satisfying the boundary conditions along the longitudinal slit, propagation constant and consequently, the fields in the structure are obtained. It is seen than propagation constant not only depends on the waveguide dimensions, but also on the location and dimension of the slit. A significant feature of the structure is that its first and second propagation modes can be separately controlled which is very useful in designing single-mode and multi-mode filters. Two examples are given which in the first one, the parameters of the structure are assigned in such a way the first and second cut off frequencies are at f=3.1 GHz and f=6.2 GHz respectively, but in the second example, first and second modes are degenerate. The validity of the method is confirmed by comparing our results with ones from others.

It is highly desirable to use advanced sensor networks to continuously monitor the structural health of an aircraft. It would be advantageous if the network was wireless to avoid the need for additional wire bundles and associated interconnects but the reliability of a suitable wireless channel in low loss enclosed structures needs to be understood. This paper reports on work undertaken testing the 2.4 GHz ZigBee wireless protocol in a mode stirred and mode tuned reverberation chamber. The results show that even for very low loss enclosures wireless communications is possible but only under very specific conditions. A higher loss chamber has more reliable communication channels, but even with loading there are large variations in packet error rates even between adjacent ZigBee channels.

In this paper, a recursive computation method is developed to derive the multiple reflections of nonuniform transmission lines. The true impedance profiles of the nonuniform transmission lines are then reconstructed with the help of this method. This method is more efficient than other algorithm. To validate this method, two nonuniform microstrip lines are designed and measured using Agilent vector network analyzer E8363B from 10 MHz to 20 GHz with 10 MHz interval. The reflection coefficients of these nonuniform microstrip lines in time domain are attained from the scattering parameters using inverse Chirp-Z transform. The reconstructed characteristic impedance profiles of the nonuniform lines are compared with those reconstructed by Izydorczyk's algorithm. The agreements of the results illustrate the validity of the recursive multiple reflection computation method in this paper.

Although the automatic and robust cluster identification is crucial for ultra-wideband propagation modeling, the existing schemes may either require interactions with analyst, or fail to produce reasonable clustering results in more universal propagation environments. In this article, we suggest a novel cluster identification algorithm. Rather than assuming the limited exponential power decay characteristics on UWB channels, from a novel perspective cluster identification is formulated as the local discontinuity detection based on wavelet analysis. Firstly, in order to comprehensively reflect the prevailing amplitude changes induced by new clusters, the moving averaging ratio is extracted from the measured UWB channel impulse responses. Subsequently, the appealing local-transient analysis ability of wavelet transform is properly exploited, and a computationally efficient cluster extraction method is developed. Distinguished from the subjective visual inspection and excluding any analyst interaction, the presented scheme can automatically discover multiple clusters. Our algorithm is premised on the general amplitude discontinuity, and hence is applicable to various complicated operation environments. Moreover, the produced clustering results, essentially depicting realistic physical propagations, are also independent of parameter configurations. Experiments on both simulated channels and the measured data in typical vehicle cabin further validate the proposed method.

The reconfigurable design problem is to find the element that will result in a sector pattern main beam with side lobes. The same excitation amplitudes apply to the array with zero-phase that should be in a high directivity, low side lobe pencil shaped main beam. Multi-beam antenna arrays have important applications in communications and radar. This paper presents a new method of designing a reconfigurable antenna array with quantized phase excitations using a new evolutionary algorithm called differential evolution (DE). In order to reduce the effect of mutual coupling among the antenna-array elements, the dynamic range ratio is minimized. Additionally, compared with the continuous realization and subsequent quantization, experimental results indicate better performance of the discrete realization of the phase-excitation value of the proposed algorithm.

Electronically steerable passive array radiator (ESPAR) antennas are expected to gain prominence in the field of wireless communication, because they can be steered toward a desired signal and they can eliminate interference; in addition, they have a very simple architecture that has significantly low power consumption and are inexpensive to manufacture. In this paper, we proposed an ESPAR antenna that has fastest convergence time. The downhill simplex method is used to maximize the correlation coefficient between the received signal and the reference signal. The simulation results indicate that this antenna can be steered toward the desired signal if one signal is used; in addition, it can eliminate interference if two signals, namely, the desired signal and the delayed signal are used by automatically varying the reactance values.