We study the influence of atmospheric turbulence on satellite communication by the theoretical analysis of propagation characteristics of electromagnetic waves through inhomogeneous random media. The analysis is done by using the moment of wave fields given on the basis of a multiple scattering method. We numerically analyze the degree of the spatial coherence (DOC) of electromagnetic waves on a receiving antenna and the bit error rate (BER) of the Geostationary Earth Orbit (GEO) satellite communication in Ka-band at low elevation angles on the assumption that the spatial coherence of received waves decreases and spot dancing only occurs. In this analysis, we consider the Gaussian and the Kolmogorov models for the correlation function of inhomogeneous random media. From the numerical analysis, we find that the increase in BER for the uplinkcomm unication is caused by the decrease in the average intensity due to spot dancing of received beam waves and that the increase in BER for the downlinkcomm unication is caused by the decrease in DOC of received beam waves. Furthermore, we find that the decrease in DOC of received waves and the increase in BER becomes much more in the Kolmogorov model than in the Gaussian model.
This paper presents a curvelet based approach for the fusion of magnetic resonance (MR) and computed tomography (CT) images. The objective of the fusion of an MR image and a CT image of the same organ is to obtain a single image containing as much information as possible about that organ for diagnosis. Some attempts have been proposed for the fusion of MR and CT images using the wavelet transform. Since medical images have several objects and curved shapes, it is expected that the curvelet transform would be better in their fusion. The simulation results show the superiority of the curvelet transform to the wavelet transform in the fusion of MR and CT images from both the visual quality and the peak signal to noise ratio (PSNR) points of view.
A thin rectangular dielectric strip is located along the horizontal diameter of a penetrable rod, while the whole structure is illuminated by a plane wave at an arbitrary angle. The unknown field on the slab-sided scatterer is determined by dividing it into a large number of square pixels and thus the problem is solved via analytical integration. A quantity expressing the effect of the strip in the far region is defined and graphically represented with respect to the problem parameters. The attached diagrams are examined and discussed.
In this paper, we present a novel technique to reduce the size of edge-fed microstrip patch antenna. By etching the patch as the Sierpinski carpet, the resonant frequency can be lowered to lower values, and this property can be employed to reduce the size of the conventional patch antenna. The measurement results show, the patch achieved a maximum 33.9% size reduction by the edge-fed Sierpinski Carpet microstrip patch antenna (SCMPA) of the second iteration order, and other performances, such as return loss bandwidth and radiation patterns, were virtually unchanged.
This paper is concerned with a new time-domain modeling topology for signals which is appliedto OFDM systems. This model is a more accurate based on Wiener approach. Also the memory effect will be shown using two-tone intermodulation distortion (IMD) measurement with different tone frequency spacing and power levels. Next adaptive predistorter to counterbalance the AM/AM andAM/PM nonlinear effects of the transmitter power amplifier is proposedb y Hammerstein approach. Finally we consider the effectiveness of proposedmetho don performance of OFDM signal as the wideband system by reduction of distortion. It is confirmed by computer simulation that proposedapproac h produces a faster convergence speed than the previous adaptive predistortion technique.
This paper shows the efficiency of neural networks (NN), coupled with the finite element method (FEM), to evaluate the broadband properties of dielectric materials. A characterization protocol is built to characterize dielectric materials and NN are used in order to provide the estimated permittivity. The FEM is used to create the data set required to train the NN. A method based on Bayesian regularization ensures a good generalization capability of the NN. It is shown that NN can determine the permittivity of materials with a high accuracy and that the Bayesian regularization greatly simplifies their implementation.
In this paper, the characteristics of an L probe fed planar rectangular patch antenna mounted on a cylindrical surface for circular polarization is investigated. To obtain a large bandwidth an L probe feed is used which is in the shape of a fork attached to a coaxial cable and is placed under a corner of the patch antenna. Simulation results, obtained via HFSS, on the return loss and radiation pattern of the antenna for circular polarization are presented. Results show an impedance bandwidth of 74.6%, an average gain of 7.5 dBi with stable radiation patterns across the entire passband and a bandwidth of 58% for AR< 3 dB.
We intend to study two kinds of sources known as Hard Source and Soft Source, which are the simplest kinds of sources used in FDTD. We introduce an exact method to control the direction of propagation of a plane wave which can be either a hard source or soft source. Also we show that a simple implementation of a soft source in the Yee algorithm causes an undesired propagation which can result in incorrect answers. To remove this error we suggest a method for different kinds of sources and modes.
We present a new scheme for all optical multi-wavelengths switching and filtering using photorefractive materials to route optical signals without converting to electronic state. For this purpose the photorefractive effect which is a nonlinear optical effect seen in certain crystals and other materials that respond to light by altering their refractive index is used. When a photorefractive material is illuminated by patterned command light of intensity I(x), a dynamic superimposed Bragg grating can be obtained which is used for optical multi-wavelength switching and filtering purposes.
In this article, a design for wideband dual-frequency folded dual monopole antenna is presented. By the proper choice of the dimensions of the Y-shape patch and the gap distance for the feeding structure, an additional resonant mode and wide impedance matching can be realized. Both simulated and experimental results, such as antenna impedance bandwidth, antenna radiation characteristic, and antenna gain have been presented and discussed. The lower impedance bandwidth covers from 8.78 GHz to 9.05 GHz, and the upper impedance bandwidth covers from 11.64 GHz to 12.01 GHz.
Optical and electrical properties of Er-doped Sinanocrystal (Si-NC) fiber amplifier are studied. Presence of Si-NC near Er3+ ions in silica matrix induces strong coupling mechanism and improves the efficiency of Er3+ excitation but in this process the size of Si-NC is important. We investigate effect of radius variation of Si-NC in the range of 2-6nm by studying the steady state and time resolved luminescence signals at 1.54 μm. We conclude that by limiting the range of Si-NC sizes the amplifier gain is improved. On the other hand Si-NCs may introduce optical loss mechanism, such as confined carrier absorption loss that affects the possibility of obtaining positive net gain. But this detrimental event can be affected by change in the radius of Si-NC as reported in this article.
Multiple diffraction propagation path loss due to the successively located different shaped building roofs are important for mobile communication. In the literature, building roofs are considered as wedge shaped structures. In this paper, building roof is modelled with a more realistic structure and the propagation path loss between the transmitting antenna and the receiving antenna is calculated.
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 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.
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.
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.