The edge-based finite element method is used for the solution of scattering problems. The factorized sparse inverse preconditioner is considered for the conjugate gradient iterative solution of the large sparse linear systems generated from the finite element method. The efficiency of the proposed preconditioner is illustrated on a set of model problems in the final of the paper. The results suggest that the sparse inverse preconditioner is very efficient for the solution of large-scale electromagnetic scattering problems.

A simple half oval patch antenna is proposed for the active breast cancer imaging over a wide bandwidth. The antenna consists of a half oval and a trapezium, with a total length 15.1 mm and is fed by a coaxial cable. The antenna performance is simulated and measured as immersed in a dielectric matching medium. Measurement and simulation results show that it can obtain a return loss less than -10 dB from 2.7 to 5 GHz. The scattered field detection capability is also studied by simulations of two opposite placed antennas and a full antenna array on a cubic chamber.

In this paper, a wideband planar dipole antenna is proposed. Compared to conventional dipole antennas, this antenna has wideband impedance matching, simple structure and compact size. From EM simulations, dimensions of antennas are chosen for better performance. For verification, this newly proposed structure is fabricated and measured. It is shown that return loss of the antenna between 2.5 GHz and 8.0 GHz is better than -10 dB.

This paper presents the analysis and design of a two-probe excited circular ring antenna. The analysis is conducted by using induced emf method and transmission line model. The design process is to choose a suitable radius of the ring for a single probe antenna. Then, the suitable probe length and ring length are determined for the two-probe antenna. Finally, isolation between the two probes is enhanced by insertion of an inductor coil between the probes. The operational characteristics of the prototype antenna at the frequency of 5.2 GHz are measured and compared with calculation results. It is evident that these results are in good agreement. The antenna achieved isolation in excess of 20 dB and VSWR less than 2:1 over the desired bandwidth and a bidirectional radiation pattern with 4 dBi gain. This antenna is suitable for Multiple-Input Multiple-Output (MIMO) system covering a long and narrow environment.

We studied the practical limitations of a linearly transformed invisibility cloak due to the loss and discretization. We found that in order for the cloaking applications to be practically useful, for example, to reduce the scattering by two orders, the maximum loss tangent allowed in the cloak needs to be of or within the order of 0.01, which also limits the radius of a concealed object to be roughly within one wavelength. For a large cloak, if its size is increased by one order, the maximum allowed loss tangent needs to be reduced by one order accordingly. For discretization, we studied both lossless and lossy cases and found that a little loss will expedite the convergence of scattering with increase of the number of layers. Insufficient layers may increase the scattering and thus make the object more visible instead of invisible.

In this paper, a novel electromagnetic bandgap structure (EBGs) is proposed, which is similar to the mushroom-like EBG. By introducing double reverse split rings (RSR) into the square patch, the size of EBG cell is reduced by 30%, and the bandgap achieves bandwidth about 65%. A fractal microstrip antenna is implemented using the EBGs as a ground plane, and the measured results show that the reduction in the surface wave level is remarkable. Compared with the reference antenna at 5 GHz, an approximately 8 dB improvement of the return loss is achieved, and the back lobe is reduced by 10 dB in E plane and 8.73 dB in H plane at the resonant frequency, respectively. The front-back ratios of the antenna have significantly increased from 4.9 GHz to 5.2 GHz.

In this paper, a novel technique for electronic beam steering in time modulated linear array (TMLA) is proposed. The beam steering technique is realized at the first sideband by controlling the switch-on time sequences of each element in the TMLA without using phase shifters. The differential evolution (DE) algorithm is employed to improve the gain and suppress the sidelobe levels (SLLs) at both the center frequency and the first sideband, simultaneously. An S-band 8-element double-layered printed dipole linear array was used to verify the technique experimentally. Measured results are compared with numerical data, and good agreement is reported. Moreover, some simulation results on the binary phase shift keying (BPSK) modulated signals arriving from different directions received by the proposed approach are presented, which validates the application of the proposed beam steering technique.

Tracking a target is a fundamental and crucial problem in wireless sensor networks. It is well known that non-line-of-sight (NLOS) propagation will significantly degrade the tracking accuracy if its effects are ignored. In this paper, a line-of-sight (LOS) identification approach for range-based tracking systems is developed to discard the NLOS measurements. Based on Lp-norm LOS identification strategy, a novel target tracking method is devised with the use of cost-reference particle filter, which does not require the knowledge of the measurement noise distribution. Computer simulations are included to verify the effectiveness of the proposed approach under different noise distributions.

The capacitance of the circular parallel plate capacitor is calculated by expanding the solution to the Love integral equation into a Fourier cosine series. Previously, this kind of expansion has been carried out numerically, resulting in accuracy problems at small plate separations. We show that this bottleneck can be alleviated, by calculating all expansion integrals analytically in terms of the Sine and Cosine integrals. Hence, we can, in the approximation of the kernel, use considerably larger matrices, resulting in improved numerical accuracy for the capacitance. In order to improve the accuracy at the smallest separations, we develop a heuristic extrapolation scheme that takes into account the convergence properties of the algorithm. Our results are compared with other numerical results from the literature and with the Kirchhoff result. Error estimates are presented, from which we conclude that our results is a substantial improvement compared with earlier numerical results.

This paper presents a substrate independent empirical formulation for the bridge inductance of inductively tuned RF MEMS shunt switches, allowing a systematic design approach to tune their isolation bands. Inductive tuning of RF MEMS switches is achieved by inserting recesses in the ground plane and meanders to the bridges, allowing the tuning of the isolation band of the switch from the X-band to the mm-wave band. The bridge inductance is first extracted from parametric EM simulations of the RF MEMS shunt switches and then fitted to the proposed formulations using empirical coefficients. The accuracy of the formulations is verified with the measurements on the switches that are fabricated using an in-house surface micromachining RF MEMS process on a 500-µm thick glass substrate. Measurement results verify that the bridge inductances can be determined by the provided empirical formulation.

In this paper, the authors present an optimization method based on modified Particle Swarm Optimization (PSO) algorithm for thinning large multiple concentric circular ring arrays of uniformly excited isotropic antennas that will generate a pencil beam in the vertical plane with minimum relative side lobe level (SLL). Two different cases have been studied, one with fixed uniform inter-element spacing and another with optimum uniform inter-element spacing. In both the cases, the number of switched off elements is made equal to 220 or more. The half-power beam width of the synthesized pattern is attempted to make equal to that of a fully populated array with uniform spacing of 0.5 λ. Simulation results of the proposed thinned arrays are compared with a fully populated array to illustrate the effectiveness of our proposed method.

In this paper, we propose an iterative numerical approach based on the stochastic second degree (SSD) algorithm in combination with a new splitting of the impedance matrix to analyze electromagnetic scattering from 1-D dielectric rough surfaces. The embedded matrix-vector product is computed using the banded matrix iterative approach/canonical grid (BMIA/CAG) and the spectral acceleration (SA) technique. For Gaussian surface with Gaussian spectrum, through extensive numerical simulation, it is observed that for HH polarization, the proposed method is slightly less computationally efficient in terms of run time and number of iterations than its counterpart without the SSD algorithm. However, the proposed method obviously improves the convergence properties over its counterpart by changing cases from divergent to convergent when the rms height and rms slope are large. For VV polarization, the relative performance in terms of number of iterations of the proposed method shows appreciable improvement and becomes better starting from the rms slope of 0.55 uniformly across all rms heights. As far as the convergence properties are considered, the proposed method obviously improves over its counterpart for certain large rms slopes. In short, the proposed method demonstrates its superiority when dealing with truly rough surfaces.

The minimization of elements in a non-uniform antenna array is critical in some practical engineering applications such as satellite and mobile communications. However, due to the complexity in the synthesis of an antenna array, the available techniques are not equally successful for reducing the element number of a non-uniform antenna array with as few elements as possible with respect to both solution quality and solution efficiency. In this point of view, a combined strategy based on the matrix pencil method and tabu search algorithm is proposed with the goal of integrating the advantages of the high solution efficiency of the matrix pencil method and the strong global searching ability of the tabu search algorithm when solving an antenna array design problem. In the proposed strategies, the desired radiation pattern is firstly sampled to form a discrete pattern data set. The matrix pencil method is then employed to optimize the excitations and location distributions of the antenna array elements to reduce the element number. Finally, the excitation and location distributions of antenna array elements are (repeatedly) re-optimized by using a tabu search algorithm by starting from the solution of the matrix pencil method to efficiently find the global solution of the design problem. To make the tabu search algorithm suitable for solving antenna array designs, some innovative approaches such as the elimination of the tabu list, systematic diversification as well as intensification processes for neighborhood creations are made. Numerical examples have shown the effectiveness and advantages of the proposed combined strategies.

The high frequency scattering of a scalar plane wave from an impenetrable sphere with a diameter of several thousand wavelengths is treated by the Sommerfeld-Watson transformation, the saddle-point technique (SPT), and the numerical steepest descent method (NSDM). Both the near and far fields for the sphere are computed within the observation angle range of 0 to 180 degree. First, with the aid of the Watson transformation, the fast-convergent residue series replacing the slow-convergent Mie series is derived. Second, a new algorithm for finding the zeros of the Hankel functions is developed. Third, a novel NSDM, which is adaptive to frequency and is hence frequency independent, is proposed to overcome the breakdown of the traditional SPT in the transition region. Numerical results show that when the observation angle is very small, the Mie series solution of the near-field will not be accurate due to error accumulation. Furthermore, using the proposed methods, the CPU times for both the near-field and far-field calculations are frequency independent with controllable error. This work can be used to benchmark future works for high-frequency scattering.

An electromagnetic inversion method is proposed for the reconstruction of lossy dielectric slabs. The inversion is done using particle swarm optimization hybridized with Quasi-Newton algorithm. The inversion process is applied to reconstruct dielectric slabs with discrete or continuous profiles. Accurate reconstruction of lossy dielectric slabs is obtained from inversion of reflection coefficient data of normally incident plane waves in the specified frequency range. The proposed algorithm is also tested using noisy data and showed satisfactory performance.

The phase of the reflection coefficient of a TE₁₀ rectangular waveguide mode at the cut-off point in a gentle downtaper is investigated through both experiment and computer simulation. The result shows a very good agreement with the theoretical prediction based on the work by Katsenelenbaum et al., that is, a +90° phase shift occurs at the cut-off point for TE modes if the cut-off point is not too close to the end of the downtaper. An application for the determination of the resonant frequencies for the spurious trapped TE₃₀ mode in an uptaper-downtaper oversized resonant structure is presented.

This paper presents the design of a compact rectangular dielectric resonator antenna (RDRA) for wireless applications. A metal plate has been attached to top surface of the RDRA to achieve significant reduction in the resonant frequency of the antenna. A simple microstrip feeding mechanism has been used to excite this compact rectangular DRA. Performance parameters such as resonant frequency, impedance bandwidth, and volume of this compact RDRA are compared with those of the conventional RDRA. Measured characteristics of these RDRAs are in good agreement with the simulated results. The size of the compact RDRA using a low dielectric constant (ε_r = 10.3) material resonant at 2.4 GHz is 30 mm × 10 mm × 6.3 mm with a ground plane size of 200 mm × 200 mm.

A new method for evaluating the performance of the shield and coupling through holes on braided shields is introduced. The method is based on conducted immunity test. A comparison is made between two kinds of shields, based on introduced technique. One is braided shields and the other is adhesive foil that does not contain any holes. The value of coupling through holes in braided shields is determined via a new technique.

An easy and fast Probability-based Electrical Resistivity Tomography Inversion (PERTI) algorithm is proposed. The simplest theory follows from the principles of the probability tomography imaging, previously developed for the ERT method of geophysical prospecting. The new inversion procedure is based on a formula which provides the resistivity at any point of the surveyed volume as a weighted average of the apparent resistivity data. The weights are obtained as the Frechet derivatives of the apparent resistivity function of a homogeneous half-space, where a resistivity perturbation is produced in an arbitrary small cell of the discretised surveyed volume. Some 2D and 3D synthetic examples are presented, for which the results of the PERTI method are compared with the inverted models derived from the application of the commercial inversion softwares ERTLAB by Multi-Phase Technologies and Geostudi Astier, and RES2DINV and RES3DINV by Geotomo Software. The comparison shows that the new approach is generally as efficacious as the previous methods in detecting, distinguishing and shaping the sources of the apparent resistivity anomalies. Less certain appears, however, its ability to approach the true resistivity of the source bodies. Main peculiarities of the new method are: (i) unnecessity of a priori information and hence full and unconstrained data-adaptability; (ii) decrease of computing time, even two orders of magnitude shorter than that required by commercial softwares in complex 3D cases using the same PC; (iii) real-time inversion directly in the field in complex 3D cases using the same PC; (iii) real-timein complex 3D cases using the same PC; (iii) real-timein complex 3D cases using the same PC; (iii) real-time; (iv) total independence from data acquisition techniques and spatial regularity, (v) possibility to be used as an optimum starting model in standard iterative inversion processes in order to speed up convergence.

In this paper, we present a modified semi-elliptical monopole antenna with a two-branch feed line and dual band-notched filter structure for UWB applications. By adjusting the parameters of the proposed antenna an UWB impedance bandwidth with a very good impedance matching can be achieved. The designed antenna has a small size of 20 mm × 20 mm and operates over the frequency band between 2.7 to 11 GHz, rejecting the undesired frequency bands from 3.3 to 3.8 GHz and 5.1 to 5.85 GHz.