In this paper, a new evolutionary learning algorithm based on a hybrid of improved real-code genetic algorithm (IGA) and particle swarm optimization (PSO) called HIGAPSO is proposed. In order to overcome the drawbacks of standard genetic algorithm and particle swarm optimization, some improved mechanisms based on non-linear ranking selection, competition and selection among several crossover offspring and adaptive change of mutation scaling are adopted in the genetic algorithm, and dynamical parameters are adopted in PSO. The new population is produced through three approaches to improve the global optimization performance, which are elitist strategy, PSO strategy and improved genetic algorithm (IGA) strategy. The effectiveness of the proposed algorithm has been compared with GAs and PSO, synthesizing a circular array, a linear array and a base station array. Results show that the proposed algorithm is able to adapt itself to different electromagnetic optimization problems more effectively.

The problem of wide bandwidth management in ultra-high resolution SAR systems can be solved by adopting stepped chirps and applying synthetic bandwidth approach. However, high resolution SAR image formation is a non-separable 2-D impulse compression processing, so the synthetic bandwidth procedure should be modified correspondingly with the image formation algorithm adopted. This paper demonstrates the application of synthetic bandwidth approach in SAR Polar Format Algorithm (PFA) using the deramp technique. The problem of motion compensation between the sub-pulses within a burst is discussed, and the signalpro cessing flows are investigated in detail. The presented approach is validated by point target simulation.

In the military applications, electro-optics and electromagnetics features of the cloths made of special textile structures and certain fibers play an important role in producing textile characterized with high ability of camouflage. This means not allowing enemy to precisely determine the moving and mute targets using available radar or any other electro-optics sensors. The aim of this paper is to determine the effect of the composite fabrics structure parameters on the fabrication of a resistive sheet used in many radar applications. The objective sheet can be used as a lossy sheet in absorbing mechanism. The radar absorbing mechanism has been studied with emphasis on the single layer structure mechanism with a resistive sheet. Fabric structure of the resistive sheet was accurately chosen and coated with lossy material. For coating, several formulas of fabrics using carbon black were tested to determine the best chemical treatment in accordance with their functional performance. Lab measurements have been done to get optimum formulas and optimum fabrics structures for high radar absorption performance.

In this communication, we theoretically report the reflection properties of a photonic crystal with alternate layers of air and GaAs for specified values of the lattice parameters. By employing the transfer matrix approach, the reflection spectra of the layered media are obtained for chosen sets of number of unit cells and incident angles. It is observed that the photonic crystals with different number of unit cells completely reflect a wide band in the infrared region of radiation. Also, we find that the reflectivity decreases and the completely reflected bands are shifted towards lower wavelength side with increase in the incident angle. Further, the reflected broadbands in the reflection spectra correspond to the forbidden ranges of wavelength obtained by using the analogy of Kronig-Penney model. It indicates that the completely reflected ranges are forbidden bandgaps, which is considered as an important feature of the proposed photonic crystals.

In this paper an effective numerical method for determining the scattered electromagnetic fields from thin wires is presented and discussed. This problem is modeled by the integral equations of the first kind. The basic mathematical concept is the method of moments. The problem of determining these scattered fields is treated in detail, and illustrative computations are given for several cases.

The asymptotic strip boundary condition (ASBC) is applied to analyze the solution of the electromagnetic scattering from a conducting cylinder coated with a homogeneous linear material layer and loaded with conducting helical strips. Such homogeneous material layer can be implemented by a conventional dielectric material, a single negative (SNG) or double negative (DNG) meta-material layer. A study of different materials' constitutive parameters is presented with accordance to Drude and Lorentz material modeling. The boundary condition assumes that the strips are rounded around the coated cylinder in a helical form and both the strip's period and the spacing between the helix turns are very small and mathematically approaching the zero. Scattering due to normal and oblique incident plane waves (θ_i, φ_i) of arbitrary polarization using the series solution is also computed. A number of parametric studies were investigated to illustrate the advantages of using metamaterials compared with conventional coating materials in terms of strip's rounding pitch angle and coating layer electrical thickness variations. It is also shown that for SNG materials, modified Bessel functions are used to accept negative arguments. Coating with metamaterials proves to achieve higher forward scattering compared with conventional materials for the same electrical coating thickness.

This paper proposes a novel beamforming technique to form an arbitrary-shaped cell for the high altitude platforms (HAPs) mobile communications. The new technique is based on pattern summation of individual low-sidelobe narrow-beams which constitute the desired cell pattern weighted by an amplitude correcting function. The new cell pattern can be adapted to cover the main highways forming worm-shaped cells which may cover the highway for long distances up 100km and it will has an important role in reducing frequent handoffs and signaling traffic of location updating from moving users over the long highways.

The electronic structure of finite parabolic GaAs/Al_xGa_1-xAs superlattices is studied. A detailed analysis of the miniband formation is given and the importance of all system parameters is discussed. The dependence of the equidistant miniband separation on the superlattice size is revealed. A comparison with different theoretical methods and experimental data is presented. The calculations are conducted in the framework of the semi-empirical sp³s^* tight-binding model including spin applying the Green function formalism and the Surface Green Function Matching Method (SGFM) method.

This paper presents a proposal of taking the left-handed material as the structural defects of one-dimensional photonic crystals and uses the transfer matrix method to analyze the band-gap of that structure. The simulation result shows that the structure investigated can be considered as a narrow pass band optical filter. By tuning the refractive index of the left-handed material, the ideal transmission rate in the pass band is as higher as 99.99%, while in the band-gap is lower than 0.01%. In addition, we show that the bandwidth can be increased by reducing the cycle number of the photonic crystals.

The paper describes a theoretical investigation into a limited bandwidth operation of a microstrip reflectarray. Two main factors limiting the bandwidth are considered. One is related to the requirement of phase compensation to convert a spherical wavefront launched by a feed into a planar wavefront. The other one is linked to the limited phasing range of microstrip antenna elements. The two factors contribute to the reflectarray phasing errors that in turn reduce its gain as a function of frequency. Simple formulas for an upper bound of gain bandwidth are derived, assuming the phase compensation by the elements is independent of frequency changes and verified against the results produced by other researchers. It is shown that the phase errors incurred in the path equalization to obtain conversion from spherical to planar wavefronts have a more profound effect on the reduction of operational bandwidth of the reflectarray than the phase truncation implemented on the required phase from each element.

In this paper the problem of electromagnetic scattering from the resistive surfaces is carefully surveyed. We model this problem by the integral equations of the second kind. A new set of orthogonal basis functions is used to solve these integral equations via collocation method. Numerical solutions of these equations are given for some cases of resistance distributions. Presented method in this paper can be easily generalized to apply to other cases.

This paper presents a comprehensive study on the hybrid mode analysis of a periodic structure in a Suspended Microstrip and Broadside-coupled Suspended Stripline. The analysis has been use of Floquet's theorem in special harmonics to express the field equations in various sub regions of the periodic loaded suspended substrate. Their characteristic equation is derived, using the Galerkin's procedure. The unknown electric field distribution in the substrate region, corresponding to one unit cell of the periodic structure is specified in terms of suitable basis functions. The characteristic of slow wave properties, resonance behavior and the passband-stopband characteristics are at the millimeter wave frequencies as a various structural parameters are presented.

Obtaining scattering field for an ellipsoid irradiated by electromagnetic wave with arbitrary polarizing and propagating direction is a hard topic that has caused large attention in the world. Literatures relative to it are seldom found. In this paper, the scattering field for an ellipsoid is presented by utilizing the scales transformation of electromagnetic field and coordinate system rotation, as the incident wave irradiating the target with arbitrary polarizing and propagating direction. The result obtained is in good agreement with that in the reference when all the scale factors changes into 1. We take a conductor ellipsoid as an example, simulations both for ellipsoid and plant leaf are presented respectively by way of choosing the different scale factor. Results show that the scattering field is sensitively affected by polarization of the incident wave and varies not too greatly with the incident wave and changes with the observing point. At some points the scattering energy arrives to its maximum.

The techniques of ground-cut slots and miniaturization are applied in the design of microstrip antenna which reduces the resonance frequency and size of antenna and achieves the Radar Cross Section (RCS) reduction. Compared with the rectangular patch antenna working at the same frequency, the designed antenna realizes the RCS reduction in the whole frequency band of 2-8 GHz. And the RCS can be reduced 2-4 dB at its working frequency. The RCSp eaks are efficiently controlled to get a smooth curve while the gain loss is only approximately 0.9 dB, which assures the radiation performance. The measured results of radiation performance accord with the simulation results and it implies that this method is feasible.

The paper presents the electromagnetic (EM) wave propagation in cylindrical optical fibers with helical windings under slow- and fast-wave considerations. Field components are deduced for both the cases, and also, the dispersion relations are obtained by applying the boundary conditions, as modified by the presence of conducting helical windings. Two special cases are considered corresponding to the values of the helical pitch angle as 0^◦ and 90^◦. A comparison of the dispersion relations is presented.

To improve the parallel efficiency in the case of the finegrained FDTD computing on PC cluster, the concept of "two level parallelization on PC cluster" is presented, and a high performance MPI-OpenMP hybrid FDTD algorithmis developed. In the hybrid algorithm, MPI is used in conjunction with OpenMP multithreading to achieve two level parallelismof the data and tasks at the basis of the domain decomposition FDTD method. Besides, to enhance the flexibility of the parallel FDTD, the interpolation between subspaces is also discussed. The simulation example of a printed antenna for automobile is given. Computations are performed for different numbers of PCs and contrasted with two conventional parallel FDTD algorithms on PC cluster. The results show that with the decrease of the computational granularity on each computer, the novel algorithm is more efficient, and moreover, it can also lessen the influence of the sub-domains virtual topology on the parallel FDTD performance.

A compact dual-mode filter is proposed by using rectangle structure. The filter has the characteristics of compact structure,lo w insertion loss and so on. Several attenuation poles in the stopband are realized to improve the selectivity of the proposed bandpass filter. The experimented results were in good agreement with simulated results.

In this paper, the extension of the Contiguous Partition Method (CPM) from linear to planar arrays is described and assessed. By exploiting some properties of the solution space, the generation of compromise sum-difference patterns is obtained through an optimal excitation matching procedure based on a combinatorial method. The searching of the solution is carried out thanks to an efficient path-searching algorithm aimed at exploring the solution space represented in terms of a graph. A set of representative results are reported for the assessment as well as for comparison purposes.

A new FDTD modeling approach for active devices characterized by measured S-parameters is presented. This approach applies vector fitting technique and piecewise linear recursive convolution (PLRC) technique to complete modeling process, and does not need to know the equivalent circuits of active devices. It preserves the explicit nature of the traditional FDTD method, and a general updated formula is derived. Furthermore, the main data-processing procedure is directly handled over the frequency band of interest, which avoids the time-domain non-causal error in traditional techniques.

Shelkunoff circle synthesis techniques are only effective for equispaced antenna arrays. These techniques are based on reorganizing the zeros on the Shelkunoff circle. We propose a technique based on locating complex-direction zeros to synthesize arbitrary on-board antenna arrays. It is based on the analytical continuation of Green's functions and on a new representation of the complex plane (analogous to the Shelkunoff circle).