A well known property of large circular closed-loop arrays is that when the dimensions and the distance of the cylindrical dipoles are properly chosen, the arrays possess very narrow resonances. As far as single isolated loop arrays are concerned, the phenomenon has been predicted and analyzed in the past in the framework of ``two-term" theory. In the present paper the same methodology is, for the first time, applied to investigate the system of two coupled identical circular arrays. It is found that the spectral profile of this new array is characterized by the coupling-induced splitting of the resonances of the single loop array into symmetric and antisymmetric supermodes, in direct analogy with other types of coupled electromagnetic cavities. Due to the circular symmetry of the individual arrays, the phenomenon is strongly correlated to the optical counterpart of two coupled traveling-wave optical resonators, such as whispering gallery or microring resonators. By borrowing the resonance splitting model from optical resonators, this analogy connection is investigated and interesting conclusions are reached.

This paper presents a dispersive finite difference time domain (FDTD) method suitable for the analysis of electromagnetic field rotator (and cloaking) devices. The method employs a coordinate transformation which accurately accounts for the radial dependence of the permittivity and permeability tensors, with Drude material models applied to the respective diagonal elements. The key aspect of the present formulation is the inclusion of the radial dependence of the plasma frequency, which makes this formalism quite attractive for the modeling of a general class of cloaking and field rotator geometries. Firstly, the method is validated by comparing its results with a previously published simulation of a cloaking device. Then, it is applied for the first time to the analysis of dispersive effects on the performance of field rotators.

In this paper, a statistical approach to evaluate randomly rough surfaces (RRS) in an inverse scattering problem is presented. Whereas in these investigations the roughness criterions possess random variables, the use of deterministic techniques such as the target decomposition (TD) can not be useful by itself as a tool of analysis. In these conditions, a statistical approach is essentially required to evaluate the target parameters. The goal of this study is the estimation of the polarimetric signatures, such as the scattering mechanism α and the entropy H, via a novel approach including the combination of TD and a new statistical model. To validate our work, SAR data sets, provided by the European Space Agency (ESA), are analyzed and compared with the simulation results.

We describe an experimental set-up for exposure of small animals to radiofrequency standing waves that allows direct measurement of the power absorbed by the animal. Essentially, the set-up consists of a metallic box containing an antenna and experimental animal immobilized in a methacrylate holder; a signal generator feeding the antenna; and a power meter. In addition, the box can also contain a video camera to record the animal's behaviour, and a receiving antenna (connected externally to a power meter and a spectrum analyser) to detect alien radiation and harmonics. The absorbed power measurement trivially allows calculation of whole-body mean SAR from the animal's weight; and assuming local SARs to be proportional to whole-body mean SAR, the latter can be used to adjust organ-specific SAR predictions obtained by simulation using a commercial FDTD program with a numerical phantom. The use of the system is illustrated by application to rats given subconvulsive doses of picrotoxin to induce a seizure-prone state analogous to epilepsy: levels of the neuronal activity marker c-Fos in the frontal and piriform cortex of picrotoxin-treated rats exposed to 900 MHz GSM radiation were twice as high as those of unexposed animals.

In this paper, a high performance phased antenna array is designed. Compared with the traditional ones, this antenna array has a lower sidelobe characteristic of down to -16 dB. At different scanning angles, the comparison between calculated and measured results of S-parameters and E- and H-plane antenna patterns is made and a very good agreement is found. Moreover, the precorrected fast Fourier transform method is employed to accelerate the entire computational process to reduce significantly both the memory requirement and computational time, but to increase the design accuracy and optimization efficiency.

Multicarrier Phase-Coded signals have been recently introduced to achieve high range resolution in radar systems. As in single carrier phase coded radars, the conventional method for compression of these signals is based on using matched filter or direct computation of autocorrelation function. In this paper we propose a new method based on Discrete Fourier Transform (DFT) that has lower computational complexity compared to the conventional approach. It has been proved that the proposed method is mathematically equivalent to matched filtering, so there is no processing loss. Also the effect of sampling frequency on compression loss has been investigated and for the oversampled matched filter of MCPC signals, a computational efficient algorithm based on polyphase implementation has been proposed.

A novel transition structure based on Substrate Integrated Circular Cavity (SICC) is proposed in this paper. The design approach has been developed for transition designing in other operating frequency. Good performance of flexibility and S-parameters were observed for the new transition structure. Different design tools were used to validate the design method.

In this paper, a novel structure for Ka-band micro electromechanical switches with low actuation voltage is proposed. In this structure, the membrane of the switch is chosen to be a Koch fractal. We have analyzed these switches in order to extract their parameters such as insertion loss, return loss and deformation posture. The effect of the actuation voltage on the deformation of the bridge has been analyzed and the results are compared with simple rectangular bridges. It is shown that bias voltage of these kinds of switches is remarkably lower than that of its other counterparts. This switch may be used as a low loss and effective element for more complicated systems such as distributed phase shifters and phased arrays.

The purpose of this paper is to introduce the concept of fractals and its use in antenna arrays for obtaining multiband property. One type of fractals namely, Cantor set is investigated. Cantor set is used in linear array antenna design. Therefore, this array know fractal Cantor linear array antenna. A comparison with conventional non-fractal linear array antenna is made regarding the beamwidth, directivity, and side lobe level. MATLAB programming language version 7.2 (R2006a) is used to simulate the fractal and conventional non-fractal linear array antenna and their radiation pattern.

The transverse electric (TE) field patterns and characteristics are considered for a cylinder with N infinite axialsl ots of arbitrary opening size and position. The cylinder is a thin circular conductor and covered by an eccentric material. Radiations are determined by applying the boundary conditions to the cylindrical wave functions of the fields. The addition theorem of Bessel functions is employed to find an infinite-series solution in Fourier-Bessel series form. Results are achieved by reducing the produced infinite series to a finite number of terms and judged against other published data. Numerical and graphical results for different values are also presented and discussed for small eccentricities.

Kelvin-Helmoholtz instability by parallel flow velocity shear in presence of inhomogeneous d.c. electric field and perpendicular density temperature magnetic field gradient has been studied by using method of characteristic solution and kinetic approach. Effect of in homogeneity of d.c. electric field and gradient have been discussed in result. The growth rates have been calculated for different effects and showing in stabilizing and destabilizing of instability.

An analysis of the modal propagation characteristics of a Bragg fiber having asymmetric loop boundary is made, using a simple matrix method. The boundary condition is replaced by matrix equation andthe modal eigen value equation is obtained under weak guidance condition. The computed results are shown in the form of dispersion curves and cutoff frequencies andare compared with the dispersion curves of a standard Bragg fiber having circular core cross section. It is seen that the proposed Bragg fiber with a small number of claddings (two of four) shows comparable or even better performance than the standard Bragg fiber with respect to a few mode-guidance properties.

Our method that uses current generator operator assumes the current on the entire surface of conducting scatterers. While, Physical Optics (PO) method assumes that the surface current generates only on the illumination region. The effect of the shadow region on the scattering waves is, therefore, proved by comparing our exact method with PO method. In this regard, radar cross-section (RCS) is calculated for smooth concave-convex contour. We work on numerical calculation of the RCS and analyze its characteristics with different target configurations including complexity and size. Concave illumination region is postulated with considering targets are taking large sizes of about five wavelengths. Here, we assume waves propagation and scattering from targets in free space and horizontal polarization (E-wave incidence).

This work is concerned with generating the digital elevation models (DEMs) from the SAR images of the region of interest using multiple sensor arrays that are fixed on the distributed satellites. We present an exact estimate of the unwrapped phase and the relationship between the unwrapped phase and the terrain height. The optimum scheme that jointly processes the signals from all sensors is based on the model of the multibaseline joint block vector. The method can simultaneously coregister the SAR images, phase unwrapping and DEM generation in the presence of the large coregistration errors. The performance of our approach is verified by a series of simulation experiments based on the distributed sensor arrays.

This paper describes a fast pattern synthesis method for a broadband array antenna using the particle swarm optimization (PSO) and cubic spline interpolation (CSI). Being an indispensable part of a high speed space-division communication system, the array antenna operates in a wide frequency band (200-400 MHz) and has stable patterns with 60-degree half power beam width (HPBW) in the whole frequency band. Firstly, by establishing a versatile objective function, the complex excitations of the circular array at the selected seven frequency points are determined via the PSO algorithm. Then, the complex excitations of the circular array at arbitrary frequency points in the whole working frequency band are calculated effectively using the CSI method. A uniform circular array with six broadband dipole elements is examined. The broadband patterns with 60-degree HPBW and the accuracy of the interpolation method are demonstrated.

A novel radiation pattern and frequency reconfigurable microstrip antenna is introduced in this paper. This antenna is designed on a thin substrate for the application of conformal phased antenna future. The proposed antenna make the operating frequency range 6 times larger than that of a simple rectangular microstrip antenna, and make the beam covering from -70^。∼70^。 compared with the traditional rectangular microstrip antenna beam which only covers -50^。∼50^。. It is potential on the application of wide-band and wideangle.

An axicon, which images a point source into a line along the optic axis, is used widely to generate an approximation to a Bessel beam. More recently many novel axicons, such as Fresnel axicons, Fractal axicons and fractal conical lenses (FCLs), have been proposed. Understanding the properties of Bessel beams generated by these axicons is very helpful to research their applications. However, in optical region, all of them are calculated approximately by the scalar theory. To accurately analyze FCLs when illuminated by a plane wave at millimeter wavelengths, the rigorous electromagnetic analysis method, which combines a two-dimension finite-difference time-domain (2-D FDTD) method and Stratton-Chu formulas, is adopted in our paper. By using this method, the properties of approximate Bessel beams generated by FCLs are analyzed and the conclusions are given.

This paper deals with the possibilities of cancellation of unwanted signals by steering nulls of the pattern in the direction of arrival of signal while keeping the main beam to the desired direction. New iterative adaptive digital beam forming technique is presented here to enhance the conventional effectiveness of beam forming in common commercial application. Simulation and measurement results confirm that this algorithm can achieve effective Co-Channel Interference (CCI) suppression, while increasing the strength of the desired signal.