Knowledge of the current distribution on a radome can be used to improve radome design, detect manufacturing errors, and to verify numerical simulations. In this paper, the transformation from near-field data to its equivalent current distribution on a surface of arbitrary material, i.e., the radome, is analyzed. The transformation is based on the scalar surface integral representation that relates the equivalent currents to the near-field data. The presence of axial symmetry enables usage of the fast Fourier transform (FFT) to reduce the computational complexity. Furthermore, the problem is regularized using the singular value decomposition (SVD). Both synthetic and measured data are used to verify the method. The quantity of data is large since the height of the radome corresponds to 29-43 wavelengths in the frequency interval 8.0-12.0 GHz. It is shown that the method gives an accurate description of the field radiated from an antenna, on a surface enclosing it. Moreover, disturbances introduced by copper plates attached to the radome surface, not localized in the measured near field, are focused and detectable in the equivalent currents.

Characteristics of a single-layer, dual-frequency microstrip patch antenna, which uses a T-strip loaded rectangular microstrip patch, are studied. This antenna is easy to achieve good impedance matching at both frequencies by tuning the feed position and other design parameters. Another advantageous aspect is that it has high polarization purity. A detailed parameter study is performed and the theoretical analysis is based on the finite-difference time-domain (FDTD) method. The FDTD programs are developed and validated by measurement results. The effects of various antenna parameters on two resonant frequencies, frequency ratio, and radiation pattern characteristics of the antenna are analyzed and discussed. It is shown that various frequency ratios (1.5-2.49) can be obtained by varying the design parameters of this antenna. Similar radiation patterns with same polarization are obtained at two resonant frequencies. Several design curves are presented.

This paper describes the performance of different loaded wire antennas (e.g., inverted L, T, I and C-shaped antennas) as electromagnetic interference (EMI) sensors. Loaded wire antennas in transmitting mode are widely used for low frequency communication. However, while using these antennas as EMI sensors, the extra loading is likely to introduce the reception of cross-polarized component of incident electric field and investigation on this has not yet been performed. This paper highlights the results of the initial investigation on the performance of these loaded antennas as EMI sensors in terms of the Antenna Factor for the desired and cross-polarized component of incident electric field. The Method of Moments with Pulse basis function and Point-matching technique has been used to evaluate the current distribution on the antenna surface and hence the Antenna Factor.

Abstract-In this paper, a two-dimensional inverse scattering problem dealing with microwave tomography is considered. To solve this non linear and ill-posed problem, an iterative scheme based on the Modified Gradient Method (MGM) is used. The object to be estimated is represented by a complex function, and some modifications of the MGM formulation have been considered. This algorithm leads to an efficient regularization scheme, based on edge preserving functions which act separately on the real and imaginary parts of the object. In order to show the interest of this regularized MGM, the algorithm is tested against laboratory-controlled microwave data.

The reconstruction capabilities of a microwave imaging algorithm can be enhanced by exploiting a multi-view measurement set-up. In the past, different researches have proved that collecting scattering data by probing the unknown scenario from different incidence angles, it allows to acquire more information on the scenario under test. This paper is aimed at verifying such an assumption in a real scenario when the Iterative Multi-Scaling Approach (IMSA) is used to fully exploit multi-view data. In fact, unlike synthetic data, in a real environment more measurements introduce larger systematic errors that could affect the physical constraints used in the inversion procedure and, consequently, the reconstruction process. Thus, the analysis is carried out by considering a set of experimental data concerning different scattering configurations involving single and multiple dielectric scatterers.

The scattering problem from the random interface with the Dirichlet boundary condition can be formulated as an integral equation x = K̂y with respect to surface sources y (here, K̂ is the integral operator). Starting with an approximate operator K̂₀, for which the inverse operator M̂=K̂^−1₀ is known, the series in powers of the operator Ẑ=M̂(K̂₀−K̂) is derived. As an approximate kernel, we consider the kernel depending only on the difference of arguments: K₀=K₀(r-r´), for which the kernel of the operator M̂ can be found in terms of generalized functions. The norm of the difference operator ||Ẑ|| is found; the conditions of convergency ||Ẑ||≤ 1 were obtained.

The intra-channel collision of optical solitons, with power law nonlinearity, is studied in this paper with the aid of quasi-particle theory. The perturbation terms that are considered in this paper are of Hamiltonian type. The suppression of soliton-soliton interaction, in presence of these perturbation terms, is achieved. The numerical simulations support the quasi-particle theory.

In this paper a novel antenna is presented. This antenna, employing microstrip circular disc as radiator is seen to perform over a large impedance bandwidth (130 MHz to 876 MHz). The disk resonator is loaded with L-C-R circuit across a selective location in the disk via a thin shorting pin. The theoretical modeling predicts TM₀₁ mode of operation. Therefore the beam pattern shows a null in the broadside direction. The said antenna is proposed to be developed for end use in coal mine where the antenna can be flush mounted on coal strata. Thus it will be able to measure the angle of arrival of any reflective component due to presence of waterbed at a distance. The measured as well as simulated results regarding impedance bandwidth and beam pattern agrees well. The simulated efficiency using IE3D is 48% whereas measured efficiency is nearly 45%.

New possibilities to design artificial magnetic materials for microwave frequencies are considered. Such composites can be used in microwave engineering at frequencies where no natural low-loss magnetic materials are available. A new magnetic particle (metasolenoid) formed by a stack of many parallel and very closely spaced single broken loops is proposed and analyzed analytically, numerically, and experimentally. It is shown that the effective permeability can reach reasonably high values over a wide frequency range when using such inclusions.

A fast technique based on the Poggio, Miller, Chang, Harrington and Wu (PMCHW) formulation and the precorrected-FFT method is presented for accurate and efficient analysis of electromagnetic transmission through dielectric radomes of arbitrary shape (including airborne radomes). The method of moments is applied to solve the integral equations in which the surfaces of the radomes are modeled using surface triangular patches and the integral equations are converted into a linear system in terms of the equivalent electric and magnetic surface currents. Next, the precorrected-FFT method, a fast approach associated with O(N ^1.5 log N) or less complexity, is used to eliminate the requirement of generating and storing the square impedance matrix and to speed up the matrix-vector product in each iteration of the iterative solution. Numerical results are presented to validate the implementation and illustrate the accuracy of the method.

igh-frequency asymptotic expansions of electric and magnetic fields are obtained at a perfectly conducting smooth 2-D surface illuminated by a plane incident wave in two cases of TE and TM linear polarization. Diffraction corrections up to the second order of the inverse large parameter p = ak (where a is a curvature radius at the specularly reflected point, and k is a field wavenumber) to the geometrical optics fields, and specifically to their phases, backscattering cross-sections (HH and VV for TE and TM polarizations, correspondingly), as well as the polarization ratio HH/VV, are derived for the specular points of a general form. These general results are applied to backscattering from cylinders with conical section directrixes (circle, parabola, ellipse and hyperbola), and a number of new compact explicit equations are derived, especially for elliptic and hyperbolic cylinders illuminated at an arbitrary incidence angle relative to their axes of symmetry.

A square slot antenna fed by two orthogonal feedlines is designed for dual polarized applications. The presented antenna has not only dual operating band, but also very wide bandwidth. The bandwidth is 18% in the first band and 82% in the second one. It can sever most of wireless communication applications that operate at 0.9, 1.8, 1.9 and 2.4 GHz and require wide band characteristics. The antenna can also produce circular polarization with wideband characteristics. Arrays of this antenna are also designed and presented.

The T-matrix method is used to model semicircular channels filled with chiral materials in a conducting plane. The coupling of both TM and TE polarizations is represented explicitly. Addition theorems in half space are derived and used to take account of the multiple scattering of parallel channels. The boundary conditions are checked for chiral channels to verify the algorithm proposed. Co- and cross-polarization effects of chiral materials are investigated by varying several physical and geometrical parameters of the parallel channels.

Microwave imaging of buried ob jects has been widely used in sensing and remote-sensing applications. It can be formulated and solved as inverse scattering problems. In this paper, we propose a hybrid numerical technique based on the parallel genetic algorithm (GA) and the finite-difference time-domain (FDTD) method for determining the location and dimensions of two-dimensional inhomogeneous objects buried in a lossy earth. The GA, a robust stochastic optimization procedure, is employed to recast the inverse scattering problem to a global optimization problem for its solution. To reduce its heavy computation burden, the GA-based inverse computation is parallelized and run on a multiprocessor cluster system. The FDTD method is selected for the forward calculation of the scattered field by the buried inhomogeneous object because it can effectively model an inhomogeneous object of arbitrary shape. Sample numerical results are presented and analyzed. The analysis of the numerical results shows that the proposed hybrid numerical technique is able to determine the location and dimension of a 2D buried inhomogeneous object, and the parallel computation can effectively reduce the required computation time.

In this paper, simulated annealing algorithms are applied to the analyses of nonlinearly loaded antenna arrays. The analysis is first transformed into an optimization problem and then be solved by simulated annealing algorithms. Numerical examples show that the results calculated by the proposed method are consistent with those of other published papers. Nearly global optimum solutions can be obtained since the simulated annealing algorithm is inherently a direct searching method. It should be noted that the array mutual coupling effects are included in the analyses of this paper.

An FDTD methodology is provided herein that allows for TEM excitation and detection of signals associated with N-port network analysis. The scheme is based upon the numerical solution of Laplace's equation in the context of the standard Yee grid. The invocation of both equivalence and orthogonality of modes principles assures that the TEM mode of interest is both exclusively excited and detected. Electric and magnetic surface currents are employed to render zero backward radiation from the source plane. Orthogonality is utilized at the terminal plane to extract the TEM mode from a multi-mode signal, provided that the spectrum of the guiding structure is discrete. The advantage of this approach is found in the placement of both the terminal and source planes — both can be placed as close to each other and to the network as necessary, thus alleviating the computational and memory burdens of the simulation. Examples pertaining to this methodology include stripline structures and the monopole strip antenna. The microstrip patch antenna is also considered to demonstrate the difficulties associated with the excitation and detection of quasi-TEM signals in the midst of radiation terms.

In this report one-dimensional simulation of Electromag- netic pulses reflected from moving and/or vibrating perfectly conducting surfaces is presented. The computational results are obtained through the application of the method of characteristics with the aid of the characteristic variable and the relativistic boundary conditions. The reflecting perfect surface is set to constantly travel at relatively high speed and/or sinusoidally vibrate with very high frequency in order to easily observe the relativistic effects on the reflected pulses. To validate the numerical method, the reflected electric fields and the corresponding spectra are demonstrated side-by-side for comparisons with the theoretical Doppler shift values. It is found that the computational results and the theoretical values are in good agreement.

This paper presents a coplanar waveguide fed rectangular slot antenna tuned by a patch stub. The presented antenna has 98% impedance bandwidth, and 6 dB average gain. The antenna can be used in phased array applications with more than 61% usable bandwidth.

Buried ob ject detection by means of microwave-based sensing techniques is faced in biomedical imaging, mine detection, and many other practical tasks. Whereas conventional methods used for such a problem consist in solving nonlinear integral equations, this article considers a recently proposed learning by examples approach [1] based on Support Vector Machines, the techniques that proved to be theoretically justified and effective in real world domains. The article considers the approach performance for two different kernel functions: Gaussian and polynomial. The obtained results demonstrate that using polynomial kernels along with slightly sophisticated model selection criterion allow to outperform the Gaussian kernels. Simulations have been carried out for synthetic data generated by Finite Element code and a PML technique; noisy environments are considered as well. The results obtained by means of polynomial and Gaussian kernels are presented and discussed.

A study is made of the characteristics of a perfectly conducting cylindrical antenna insulated from the surrounding cold collisionless magnetoplasma by an isotropic coaxial cylindrical sheath for the case where the antenna is aligned with an external magnetic field and is excited by means of a delta-function voltage generator. A rigorous representation is obtained for the current distribution on an infinitely long antenna. It is shown that in the whistler frequency range, the current distribution of a sufficiently thin antenna is determined mainly by the eigenmode whose guided propagation is found to be supported along the antenna. Based on the results obtained for an infinitely long antenna, a generalized transmission-line theory is developed for determining the current distribution and the input impedance of an insulated antenna of finite length located in a resonant magnetoplasma. The influence of the sheath parameters on the antenna characteristics is analyzed.