In this paper six novel Dielectric Resonator Antennas (DRAs) providing Circular Polarization (CP) using single probe feeds are proposed. By splitting the fundamental mode of conventional rectangular or cylindrical DRAin to two near-degenerate orthogonal resonant modes, CP is obtained. The proposed antennas are numerically investigated using Finite Element Method (FEM). Parametric study on all antennas is carried out. The results show that the impedance bandwidth (S₁₁ < -10 dB) of all reported antennas is in the range of 112-140 MHz. Also, the Axial Ratio bandwidth (AR < 3 dB) range of presented antennas is 28-33 MHz. The investigation shows radiation patterns of all proposed antennas are remaining broadside throughout the bandwidth.

With the recent growth in the use of satellites for an increasing range of devices, services, applications and users, there is a need to optimize the signal received for availability, reliability and tolerance to interference. A lot of prediction models have been used in recent times to estimate intersystem interference due to hydrometeor scattering on vertically polarized microwave signals into the receiver of earth-space communications systems operating at the same frequency. The horizontal polarization is usually not investigated because coupling between the transmitting and receiving systems is much less than in vertical polarization. Much as this is true in the temperate regions, the nature and characteristics of tropical rainfall which are quite distinct from the temperate rainfall, means that the horizontal polarization when transmitted should be investigated for hydrometeor induced interference in tropical regions. This present work computes transmission loss on horizontally polarized signals based on two models (Awaka and Capsoni). The results obtained are compared and it is observed that there is only a difference of 1 dB in the transmission loss between the models. However, at higher frequency (>20 GHz), the Capsoni model does not produce values for the transmission loss L, while Awaka model predict a low interference at various antenna gain for percentages of time >0.1%.

In this letter,an application of energy balance method is applied to solve the nonlinear oscillators with uⁿ force. Comparison is made between the modification of harmonic balance method and energy balance method. The results reveal that the energy balance method is very effective and simple. Energy balance method is very effective and convenient and quite accurate to both linear and nonlinear physics and engineering problems.

In this paper, we design the zero-dispersion wavelength shifted fiber based on the WII-type triple clad single mode optical fiber and consider the transmission parameters fluctuations owing to environmental conditions such as temperature variations on dispersion behavior of fiber. In order to estimate the thermal coefficients, the model introduced by Ghosh [1] is applied. Our calculation show that the thermal coefficient extracted for the chromatic dispersion, its slope, and the zero dispersion wavelength swing are -1.21×10^-3 ps/km/nm/^oC, +2.96×10^-3 ps/km/nm²/^oC, and +3.33× 10^-2 nm/^oC at 1.55 μm respectively. It is shown that in optical fiber design especially for dense wavelength division multiplexing (DWDM) systems, effect of temperature on channel displacement is critical and should be considered carefully.

In this paper we introduce a rigorous numerical analysis to investigate the characteristics of double carrier multiplication homojunction avalanche photodiodes (APDs) considering the nonlocal nature of the ionization process in the wide range of multiplication region width. Also in our calculations the effects of dead space has been considered. Our analyses based on the history dependent multiplication theory (HDMT) and width independent ionization coefficient.

Features of spatial power spectrum (SPS) of scattered radiation in a randomly inhomogeneous medium with strongly prolated anisotropic inhomogeneities of dielectric permittivity are investigated. In single scattering approximation, it has been shown that a pronounced gap along a direction of prolate inhomogeneities appears in SPS. Features of SPS of multiple scattered waves at oblique illumination of a boundary of randomly-inhomogeneous medium with prolate irregularities have been analytically studied using smooth perturbation method taking into account diffraction effects. Numerical calculations have shown that with an increase of a distance passing by the wave in random media, SPS has a double-peaked shape and a gap substantially increases. Its maximum is slightly changed and the width is broadening. The results have been obtained analytically for the first time and could find extensive practical application in optics and be useful in development of principles of remote sensing of random media.

Numerical analysis of a generalized form of the recently developed electric and magnetic current combined field integral equation (JM-CFIE) for electromagnetic scattering by homogeneous dielectric and composite objects is presented. This new formulation contains a similar coupling parameter α as CFIE contains in the case of perfectly conducting objects. Two alternative JM-CFIE(α) formulations are introduced and their numerical properties (solution accuracy and convergence of iterative Krylov subspace methods) are investigated. The properties of these formulations are found to be very sensitive to the choice of α and to the permittivity of the object. By using normalized fields and currents the optimal value of α minimizing the number of iterations becomes only weakly dependent on the permittivity object. Using linear-linear basis functions instead of the more conventional constant-linear (RWG) basis functions the solution accuracy can be made less dependent on the choice of α.

A method based on adaptive neuro-fuzzy inference system (ANFIS) for computing the effective permittivity and the characteristic impedance of the micro-coplanar strip (MCS) line is presented. The ANFIS is a class of adaptive networks which are functionally equivalent to fuzzy inference systems (FISs). A hybrid learning algorithm, which combines the least square method and the backpropagation algorithm, is used to identify the parameters of ANFIS. The effective permittivity and the characteristic impedance results obtained by using ANFIS are in good agreement with the theoretical and experimental results reported elsewhere.

In this paper, planar multilayered antireflection coatings composed of isotropic and dispersive common materials and metamaterials (DPS, DNG, ENG, and MNG) are designed and optimized at Ku band under circularly polarized oblique plane wave incidence by a full-wave method and combination of the method of least squares (MLS), genetic algorithm (GA) and conjugate gradients (CG). The body on which the coating is applied may be selected as PEC, plexiglas, or any other material. As a result a new class of radar absorbing materials (RAM) are obtained, which may be effectively used for antireflection coatings. Furthermore, guidelines are presented for the selection of correct signs for the real and imaginary parts of propagation constant k and intrinsic impedance η.

This paper presents a computational approach to the two-dimensional time domain inverse scattering problem of a dielectric cylinder based on the finite difference time domain (FDTD) method and the particle swarm optimization (PSO) to determine the shape, location and permittivity of a dielectric cylinder. A pulse is incident upon a homogeneous dielectric cylinder with unknown shape and dielectric constant in free space andthe scattered fieldis recorded outside. By using the scattered field, the shape and permittivity of the dielectric cylinder are reconstructed. The subgridding technique is implemented in the FDTD code for modeling the shape of the cylinder more closely. In order to describe an unknown cylinder with arbitrary shape more effectively, the shape function is expandedb y closedcubicspline function insteadof frequently used trigonometric series. The inverse problem is resolved by an optimization approach, and the global searching scheme PSO is then employedto search the parameter space. Numerical results demonstrate that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In addition, the effects of Gaussian noise on the reconstruction results are investigated. Numerical results show that even the measured scattered E fields are contaminated with some Gaussian noise, PSO can still yield good reconstructed quality.

This paper focuses on a tutorial overview of defected ground structure (DGS). The basic conceptions and transmission characteristics of DGS are introduced and the equivalent circuit models of varieties of DGS units are also presented. Finally, the main applications of DGS in microwave technology field are summarized and the evolution trend of DGS is given.

A set of scalar differential equations for treating scattering by rotationally symmetric radially inhomogeneous anisotropic sphere is presented. These equations may easily be treated by applying the integral equation method that has been developed. Besides a possible different expansion in a Neumann series is also discussed.

The sum and difference multiple channels were usually applied to the monopulse system only in a receiver. But this paper presents a technique of multiple beam modulation transmitted by the sum and difference multiple channels. The modulated field is designed as three chip signal vectors whose sum and whose differences are controlled by the gains of antennas,and the angle between the sum vector and the differential vector depends on the phase error between the channels so that the different microwave signals can be transmitted in the different directions. A receiver with single-antenna can extract azimuth and elevation with respect to the transmitter. Simulation results show that the proposed modulation system has been successfully designed to integrate digital communication with direction-finding in the way of the reverse monopulse.

A theoretical analysis of the lateral shift for an electromagnetic beam reflected from an uniaxial anisotropic slab coated with perfect conductor is presented. The analytic expression for the lateral shift is derived by using the stationary-phase approach, and the conditions for negative and positive lateral shifts are discussed. It is shown that the lateral shift depends not only on the slabthic kness and the incident angle, but also on the constitutive parameters of the uniaxial medium. Enhancement and suppression of lateral shift are observed and are attributed to the interference between the reflected waves from the two interfaces of the slab. By tuning the thickness of the slaband material parameters, large negative and positive shifts can be attained. In particular, when total reflection occurs at the upper interface, the lateral shift will saturate with increasing slabthic kness.

A new full-wave Parabolic --- Integral Equation Method (PE-IEM) for the simulation of wave propagation in realistic, highly complex indoor communication environments is proposed, together with an extensive validation via measurements. The method is based on a wide-angle parabolic equation, further enhanced by an integral equation correction and is capable of providing good approximations of the electromagnetic fields and the received power, incorp orating all fundamental propagation mechanisms in a single simulation. For a rigorous validation, it has been applied in a complex twelve-room office space and compared with measurements at the two different frequencies of 1 GHz and 2.5 GHz. The accuracy of the approximation is within reasonably expected margins, while the method retains all the advantages of full wave methods and it also has moderate requirements of computational resources.

In this paper an improved particle swarm optimization algorithm (IPSO) for electromagnetic applications is proposed. In order to overcome the drawbacks of standard PSO, some improved mechanisms for velocity updating, the exceeding boundary control, global best perturbation and the simplified quadratic interpolation (SQI) operator are adopted. To show the effectiveness of the proposed algorithm, a selected set of numerical examples, concerned with linear as well as planar array, is presented. Simulation results show that the refined pinpointing search ability and the global search ability of the proposed algorithm are significantly improved when compared to the particle swarm optimization (PSO) and Genetic Algorithm (GA).

The societal and technological priorities of the world have been continuously changing because of complex computer and technology-driven developments in everywhere like communications, health, defense, economy, etc. Electromagnetic (EM) systems have become more and more complex however the explosive growth of computer capabilities has revolutionized the design and analysis of such complex systems. This has made interdisciplinary exposure necessary in modern EM engineering, also has brought up discussions of educational challenges and novel teaching approaches that confront wave-oriented EM engineering in the 21st century. This paper reviews EM computer simulation strategies and summarizes novel virtual tools that may be used in connection with classical EM lectures as well as with a newly proposed EM Engineering Program.

Excitation of the electromagnetic fields by a wide-band current surge, which has a beginning in time, is studied in a cavity bounded by a closed perfectly conducting surface. The cavity is filled with Debye or Lorentz dispersive medium. The fields are presented as the modal expansion in terms of the solenoidal and irrotational cavity modes with the time-dependent modal amplitudes, which should be found. Completeness of this form of solution has been proved earlier. The systems of ordinary differential equations with time derivative for the modal amplitudes are derived and solved explicitly under the initial conditions and in compliance with the causality principle. The solutions are obtained in the form of simple convolution (with respect to time variable) integrals. Numerical examples are exhibited as well.

A novel compact Archimedean spiral antenna with gaploading is investigated in this paper. A circular frame sharing the same centre with the spiral elements introduces a capacitive gap. By adjusting the width of the gap and the width of the circular frame, the initial resonant frequency of the proposed antenna is shifted from 2.79 to 1.93 GHz. Compared with the traditional Archimedean spiral antenna with the same lowest operation frequency, the area of the proposed antenna can be reduced by more than 30simulated radiation pattern results.