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.
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.
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  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.
A novel coupled T-matrix and microwave network approach is proposed for the multiple scattering from parallel semicircular channels. First, an equivalent network is set up to derive the T-matrix of a single channel, in which the S-parameters are derived for the semicircular boundary and the T-matrix of the inclusive cylinders is served as loading matrix of s-parameters. In addition, the T-matrix of the inclusive cylinders is obtained from the T-matrix of each cylinder in its local coordinates using the addition theorem of cylindrical harmonics. Thus, the T-matrix description of semicircular channels could be obtained steadily by the equivalent microwave network theory. Second, the addition theorems in half space are derived and utilized to take account of multiple scattering from several parallel channels. Comparing with previous dual-series eigenfunction solutions, the coupled method simplifies the analysis and could handle much more complex structures step by step. The method is verified by comparison with previous publications and both TM and TE wave illumination are considered.
This paper describes exactly a new formulation of the T-matrix method with R-matrix expression for the electromagnetic wave diffraction efficiency from dielectric coated metallic Fourier grating. We found that the parameters of numerical calculation are widely applied by using R-matrix expression in dielectric coating media whose thickness or depth groove on the Fourier grating is large. The absorption phenomena of diffraction efficiency in particular incident angle are observed in the two cases. One of the factor is a guided mode in the dielectric coated layer. Other factor is resonance absorption that occurs by plasmon anomalies on the substrate for the TM polarization.
Electromagnetic penetration through an aperture into a cavity is considered. The structure of interest comprises a slotted infinite conducting plane backed by a semielliptical channel. Three independent integral equations are used to study the structure of interest, for which analytical expressions are derived in another paper and involve summations of Mathieu functions. Numerical results from the analytical expressions for the electromagnetic fields are compared with those from integral equation methods for various cases of excitation and isorefractive materials. The agreement is excellent in all cases.
The intra-channel collision of optical solitons, with Kerr law nonlinearity, is studied in this paper by the aid of quasi-particle theory. The perturbation terms that are considered in this paper are the nonlinear gain and saturable amplifiers along with filters. The suppression of soliton-soliton interaction, in presence of these perturbation terms, is achieved. The numerical simulations support the quasi-particle theory.
The propagation of waves in a random medium is a very complex phenomena which presents numerous difficulties in its experimental approach, and in its theoretical analysis. In this work, the case of a laser beam direction during its random propagation through a hot free jet of air, is considered using geometrical optics. Some experiments are done in the jet and from the hypothesis of the Markovian process, the main stochastic characteristics of the laser beam direction are studied. In addition, the sensitivity of the probability density of the beam random direction with respect to the jet turbulent diffusion is determined.
In this paper, a new coplanar waveguide (CPW) feed structure is proposed to improve impedance matching of low-permittivity dielectric resonator antennas (LPDRAs). The structure is studied experimentally for a two element-rectangular LPDRA array. In the proposed structure, a horizontal strip is centrally connected at the center strip of the CPW and symmetrically added to a coplanar rectangular coupled slot. The dielectric radiators are fed by the CPW through the slot. Based on the above design concept, several antenna prototypes have been successfully designed, fabricated and tested. The measured results show that the proposed antenna exhibits unique and attractive features in terms of impedance matching, gain and the realization of an array.
In a recent solution of this problem there is a subtle error that shows up in the coefficient of reflection off the lower surface of the half plane for oblique incidence and that is attributable to an unacceptable normalization of the spectra to produce the incident field. The correction of this error requires a substantial modification to the original analysis, but this has been carried out and new data are presented.