This paper presents a compact dual-band slot antenna for 2.4/5 GHz WLAN applications. The radiating elements of the proposed antenna are composed of a square ring slot and a circular ring slot, operating at 2.4 GHz and 5 GHz bands respectively. The antenna size is very compact (40mm × 40mm × 1mm), and can be integrated easily with other RF front-end circuits. It is demonstrated that the proposed antenna can completely cover the required bandwidths of IEEE 802.11b/g (2.4-2.485 GHz) and IEEE 802.11a (5.15-5.825 GHz) with satisfactory radiation characteristics. Good agreement is achieved between the simulated and measured results.
In this paper,the propagation model considers the two half-spaces as a homogeneous isotropic medium and one-dimensionally anisotropic medium. From the exact formulas for the transient field with delta-function excitation,it is obtained readily the exact formulas for the transient field excited by a horizontal electric dipole with Gaussian excitation when both the dipole point and field point are located on the boundary between a homogeneous isotropic medium and one-dimensionally anisotropic medium. It is seen that the final exact formulas can be expressed in terms of several fundamental functions and finite integrals,which are evaluated easily.
The Development of numerical techniques enables us to analyze a large number of complex structures such as dielectric resonator (DR) filters and planar passive elements for coplanar monolithic microwave integrated circuits. As for DR filters, numerical analysis of these structure is highly intricate mostly because of their non-homogenous composition (dielectric constant of DR is greater than 80, dielectric constant of the maintainer is less than 2 and dielectric constant of the atmosphere is 1). Hence, numerical analysis of such a structure, either in time domain (TLM, FDTD and . . . ) or frequency domain (FE, moment, mode matching, boundary element, FD and . . . ) is both complex and time-consuming. From one hand, the non-homogenous structure and from the other hand, the high frequency of applications, demand high density meshing in order to achieve accurate response [1-3]. The explained method in this paper enables us to design a Chebyshev band passes filter by coaxially placing high-Q TM_{01δ} dielectric resonators in a cutoff circular waveguide. In the presented work, discussions are made regarding high-Q resonators and interresonator coupling. It can be used for TE and TM modes of dielectric resonators. The advantages of such a method are simplicity and accuracy. Furthermore, this method is very quick in calculating resonant frequencies of a single dielectric resonator and coupling factor between two dielectric resonators. Compared with HFSS software, the total required time in this method is less than 1 percent. Based on the presented method, a DR filter is designed, implemented and fabricated and the results are provided. The fabricated filter has an exclusive feature, i.e., it contains no screw for frequency tuning and it gives out the desired result without a need to modification.
In this paper, we apply the Shannon wavelet basis functions to the method of moments to evaluate the radar cross section (RCS) of the conducting and resistive surfaces. The problem is modeled by the integral equations of the first or second kind. An effective numerical method for solving these problems based on the moments method and using Shannon wavelet basis functions is proposed. The validity and accuracy of the method is checked on some examples, and the Shannon wavelets are compared with the well-known block-pulse functions (BPFs) from the viewpoint of computational efficiency. The problem of evaluating the RCS is treated in detail, and illustrative computations are given for some cases. This method can be generalized to apply to objects of arbitrary geometry and arbitrary material.
In the present work, a precise optimization method is proposed for tuning the parameters of ITU-R P.1546 recommendation to improve its accuracy in VHF and UHF propagation prediction. In this optimization method, the genetic algorithm is used to tune the model parameters. The predictions of the tuned model are compared with those of the ITU-R P.1546 recommendation and verified in comparison with some electric field strength measurements obtained by utilizing the IS-95 pilot signal in a commercial CDMA network in rural Australia.
In this paper, the region of interest consists of a perfect conductor, coated with the two layer dielectrics under the air. The completed analytical formulas have been derived for the electromagnetic field due to a vertical electric dipole in the four-layered region when both the source point and observation point are located in the upper dielectric layer. Similar to the three-layered case, the trapped surface wave, which is contributed by the sums of residues of the poles, can also be excited efficiently by a vertical electric dipole in the four-layered region. The lateral wave is determined by the integrations along the branch cuts.
Asymptotic techniques have been successfully applied to compute electromagnetic wave radiation in various high-frequency engineering domains. Recent approaches based on Gaussian beams for tracking fields may overcome some problems inherent to the ray methods such as caustics. The efficiency of these methods is based on the ability to expand surface fields into a superposition of Gaussian beams. However, some difficulties may arise when the surface is curved. In this paper, we propose a new efficient way to expand fields on a curved surface into Gaussian beams. For this purpose, a new beam formulation called Conformal Gaussian Beam (CGB) is used. The CGBs have been developed to overcome the limitation of the expansion into paraxial Gaussian Beams. The analytical Plane-Wave Spectrum and far-field of a CGB are derived and compared with numerical calculations. A brief parameter analysis of the CGBs is realised.
A numerical method is presented for determining the static charge distribution and capacitance of a round disk capacitor. Based on equivalent surface charge distributions, an integral equation subject to the boundary conditions is transformed into an algebraic equation by using the method of moments. In the proposed scheme to eliminate the discretizing errors often encountered in other techniques, annular patch subdomains are introduced, not only to improve the accuracy of solutions, but also to reduce the matrix size of the resultant equation. By solving the transformed algebraic equation, the charges per unit area on the interfaces are numerically determined. With use of the free charge on plates obtained by using annular patches, the capacitance is more accurately calculated. The equipotential lines around a round disk capacitor are also calculated. In order to show the usefulness of this method, the employed scheme is applied to a single circular disk with an exact solution, and to the dielectric filled capacitor partially covered by plates. Those results are examined and discussions are also made to support the validity of the presented scheme.
According to Einstein's Principle of Equivalence Mass- Energy (E = mc^{2}) the mass of a single photon (P) corresponds to 10^{-48} g/s and moving the P weighs 10^{-27} g/s, that is more than an electron. A light beam weighs 10^{-12} g/s, that is 1000 billiard times more than a proton.
This paper presents a block based digital image watermarking algorithm that is dependent on the mathematical technique of singular value decomposition (SVD). Traditional SVD watermarking already exists for watermark embedding on the image as a whole. In the proposed approach, the original image is divided into blocks, and then the watermark is embedded in the singular values (SVs) of each block, separately. The watermark embedding on a blockby- block basis makes the watermark more robust to the attacks such as noise, compression, cropping and lowpass filtering as the results reveal. The watermark detection is implemented by extracting the watermark from the SVs of the watermarked blocks. Extracting the watermark from one block at least is enough to ensure the existence of the watermark.
The probability tomography approach developed for the scalar resistivity method is here extended to the 2D tensorial apparent resistivity acquisition mode. The rotational invariant derived from the trace of the apparent resistivity tensor is considered, since it gives on the datum plane anomalies confined above the buried objects. Firstly, a departure function is introduced as the difference between the tensorial invariant measured over the real structure and that computed for a reference uniform structure. Secondly, a resistivity anomaly occurrence probability (RAOP) function is defined as a normalised crosscorrelation involving the experimental departure function and a scanning function derived analytically using the Frechet derivative of the electric potential for the reference uniform structure. The RAOP function can be calculated in each cell of a 3D grid filling the investigated volume, and the resulting values can then be contoured in order to obtain the 3D tomographic image. Each non-vanishing value of the RAOP function is interpreted as the probability which a resistivity departure from the reference resistivity obtain in a cell as responsible of the observed tensorial apparent resistivity dataset on the datum plane. A synthetic case shows that the highest RAOP values correctly indicate the position of the buried objects and a very high spacial resolution can be obtained even for adjacent objects with opposite resistivity contrasts with respect to the resistivity of the hosting matrix. Finally, an experimental field case dedicated to an archaeological application of the resistivity tensor method is presented as a proof of the high resolution power of the probability tomography imaging, even when the data are collected in noisy open field conditions.
The connections between Maxwell's equations and symplectic matrix are studied. First, we analyze the continuous-time Maxwell's differential equations in free space and verify its time evolution matrix (TEMA) is symplectic-unitary matrix for complex space or symplectic-orthogonal matrix for real space. Second, the spatial differential operators are discretized by pseudo-spectral (PS) approach with collocated grid and by finite-difference (FD) method with staggered grid. For the PS approach, the TEMA conserves the symplectic-unitary property. For the FD method, the TEMA conserves the symplectic-orthogonal property. Finally, symplectic integration scheme is used in the time direction. In particular, we find the symplectiness of the TEMA also can be conserved. The mathematical proofs presented are helpful for further numerical study of symplectic schemes.
A compact meander-line resonator is proposed in this paper, which could provide negative permittivity with a small unit-towavelength ratio. The meander-line structure is simple to be designed and is convenient to be controlled. Negative index materials (NIM) are realized using units composed of meander lines and split-ring resonators (SRRs), which have simultaneously negative permittivity and permeability in a specified pass band with relatively low loss. Simulation results show the identified properties of the meander-line resonator and NIM.
In this paper, effects of the different apodization and chirp functions in one-dimensional nonlinear Bragg grating on switching characteristics are studied. It is shown that with increasing the Gaussian width in the case of Gaussian apodization, slope of transfer function is increased. The situation is same in the case of raised cosine apodization function too. Also, in the case of quadratic apodization with decreasing the apodization parameter the slope of the transfer function is improved. Using the chirp different functions the switching threshold can be controlled. So, the presented structure as optical switch can be designed for optimum slope and threshold of switching using desired apodization and chirp functions. So, the presented material in this paper shows that there are possibilities for management of all-optical switching using suitable apodization and chirp functions.
Computation of the broadband matching potential of a microstrip antenna requires the wideband lumped equivalent circuit of the antenna. The general topology of the equivalent circuit of rectangular microstrip patch antennas has been used to model the feedpoint impedance of microstrip antennas over a wide frequency band and equivalent circuit parameters are determined using optimization techniques. The proposed procedure overcomes the problems of physical realizability of the equivalent circuit and estimation of the starting values of the optimization. Applying this technique, wideband lumped equivalent circuits of a rectangular and E-shaped microstrip antenna have been computed which are in good agreement with measurement data from 0.1 to 6 GHz.
A new and effective direct method to determine the numerical solution of specific nonlinear Volterra-Fredholm integral and integro-differential equations is proposed. The method is based on vector forms of block-pulse functions (BPFs). By using BPFs and its operational matrix of integration, an integral or integro-differential equation can be transformed to a nonlinear system of algebraic equations. Some numerical examples are provided to illustrate accuracy and computational efficiency of the method. Finally, the error evaluation of this method is presented. The benefits of this method are low cost of setting up the equations without applying any projection method such as Galerkin, collocation, . . . . Also, the nonlinear system of algebraic equations is sparse.
Electromagnetic coupling to cables has been a major source of EMC and EMI problems. In this paper, the methods of predicting the EM coupling and propagation in multiconductor transmission lines are presented. Crosstalk is an important aspect of the design of an electromagnetically compatible product. This essentially refers to the unintended electromagnetic coupling between wires and PCB lands that are in close proximity. Crosstalk is distinguished from antenna coupling in that it is a near field coupling problem. Crosstalk between wires in cables or between lands on PCBs concerns the intra-system interference performance of the product, that is, the source of the electromagnetic emission and the receptor of this emission are within the same system. With clock speeds and data transfer rates in digital computers steadily increasing, crosstalk between lands on PCBs is becoming a significant mechanism for interference in modern digital systems. To predict the crosstalk we designed a simple model of three conducting wires and took measurements for both nearend and farend crosstalk. Also the same model is being simulated by CST Microwave Studio (3D Electromagnetic Solver).
We propose a numerical methodto solve the problem of coupling through finite, but otherwise arbitrary apertures in perfectly conducting and vanishingly thin parallel planes. The problem is given a generic formulation using the Method of Moments and the Green's function in the region between the two planes is evaluated using Ewald's method. Numerical applications using Glisson's basis functions to solve the problem are demonstrated and compared with previously published results and the output of FDTD software.
Spatiotemporally localized luminal null electromagnetic fields are transverse with respect to the local flow of energy,whic h is equipartioned between the electric and magnetic fields,and the modulus of their local energy transport velocity equals the speed of light in vacuo. They have vortex structures on planes transverse to the direction of propagation,and,in general,are relatively simple so that explicit calculations can be made of the total energy and the total angular momentum they carry. A class of luminal null electromagnetic waves due originally to Robinson and Troutman is motivated by means of spherical Cunningham and Bateman transformations and their relationships to well-known scalar luminal localized waves are examined. This allows for the introduction of finite-energy localized null luminal electromagnetic waves with spatiotemporal spectra appropriate for applications in diverse physical areas.