The design and performance of a circularly polarized microstrip patch antenna, for the application in Wireless Local Area Network (WLAN), are reported here. The antenna is a proximity coupled microstrip patch antenna where the radiating patch is loaded by a V-slot. This miniaturized microstrip antenna has wide bandwidth in the frequency band of WLAN and exhibits circularly polarized far field with very good axial ratio bandwidth. The simulated results using IE3D software are verified by measurement.

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.

A compact printed ultra-wideband (UWB) antenna with band-notched characteristic is presented. The antenna is designed to cover the Federal Communications Commission (FCC) bandwidth for UWB applications (3.1--10.6 GHz) with band-notched at frequency band (5.15--5.825 GHz). The proposed antenna is fed by microstrip line, and it consists of square radiating patch on the top layer with a slotted-parasitic patch on the bottom layer of the antenna. The slotted-parasitic patch acts as a notch filtering element to reject the frequency band (5.15--5.825 GHz) which is used by IEEE 802.11a and HIPERLAN/2. Moreover, the pulse distortions of different input pulses are investigated based on S₂₁ parameters for two cases; face to face and side by side orientations. There is a small acceptable influence on the matching between the input and the output pulses and it is found that the pulse distortion is low. Therefore, the proposed antenna is a good candidate for UWB applications.

A tomography method is proposed to image magnetic anomaly sources buried below a non-flat ground surface, using the expression of the total power associated with a measured magnetic field. It is shown that the total power can be written as a sum of crosscorrelation products between the magnetic field data set and the theoretical expression of the magnetic field generated by a source element of unitary strength. Then, applying Schwarz's inequality, an occurrence probability function is derived for imaging any distribution of magnetic anomaly sources in the subsurface. The tomographic procedure consists in scanning the half-space below the survey area by the unitary source and in computing the occurrence probability function at the nodes of a regular grid within the half-space. The grid values are finally contoured in order to single out the zones with high probability of occurrence of buried magnetic anomaly sources. Synthetic and field examples are discussed to test the resolution power of the proposed tomography.

This paper presents an aperture coupled microstrip antenna with a rectangular patch which is located on top of two slots on the ground plane. The patch and slots are separated by an air gap and a material with low dielectric constant. There is a 50Ω feed line which is divided into two 100Ω feed lines by a two way microstrip power divider under the ground plane. Using a parametric study on the effect of the position and dimensions of the feed line the impedance bandwidth of the antenna (VSWR < 2) is increased to 7.9 GHz (86%) centered at 9.25 GHz and the gain of the structure is more than 7 dB from 5.4 GHz to 8.8 GHz (48%).

The problem of electromagnetic scattering by thin metal plates is formulated in terms of Electric Field Integral Equation and solved by an improved form of the Spectral Iteration Technique. The local solution at the edges of the plate is chosen as initial guess for the unknown surface current in order to guarantee and enhance the convergence of the iterative scheme. Numerical simulations on a square conducting plate are presented to validate the proposed approach.

The geometryof a broadband (0.7-2 GHz) monopole antenna intended to be inserted in a narrow borehole for ground penetrating crosshole application is proposed. The monopole antenna is supposed to be designed on a printed circuit board (PCB) using the low-cost microstrip technology. Based on the FDTD approach, the modeling of the antenna surrounded byits environment has been made, and the influence of several parameters on the radiated waveforms has been studied in details. The modeling of a transmission link has also been considered. Such a studyaims at the realization of a narrow broadband antenna.

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.

Integration of planar circuits to non-planar ones has been recently considered as a credible technique for low-cost mass production of microwave and millimeter-wave circuits andsystems. This paper regards these concepts that provide for a complete integration of planar circuits andw aveguide filters synthesizedon a single substrate by means of metalizedp ost (via-hole) arrays. A method of designing a waveguide filter derived from a synthesis technique using dual array of inductive posts is presented. An experimental five-pole Chebyshev filter which has 2.5 dB insertion loss and return loss better than 10 dB is demonstrated. Such a technique of integration of planar andnon-planar circuits on the same substrate shows a significant reduction in size, weight and cost.

A novel printed version of the classic volcano smoke antenna is presented and investigated in this article. The effects of some important parameters on the VSWRof the proposed antenna have been investigated in the design. The measured bandwidth of VSWR<2 is from 1.80 to 14.35 GHz, which covers all UWB (3.1- 10.6 GHz) and 2.4 GHz WLAN (2.4-2.4835 GHz) bands. Moreover, the antenna features near omnidirectional characteristics in the operation range and good radiation efficiency. A gain variation from 2.04 to 7.02 dBi (2-13 GHz) is obtained.

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.

An interference excision algorithm in direct-sequence spread spectrum (DS-SS) communication systems is introduced. The proposed excision algorithm is developed for linear frequency modulated (LFM) signals that have broadband frequency characteristics. It is based on the time-frequency analysis of received signals employing short-time Fourier transformation (STFT). To analyze the interference, STFT of the received signal block is evaluated and thresholded. The interference detection is followed by an inverse-STFT computation to estimate the high-power jamming signal. The estimated jammer is then mitigated before demodulation. Simulations present adequate interference estimation results with mean estimation errors less than 0.01%. Various scenarios with different jammer-to-signal ratios (JSRs) and signal-to-noise ratios (SNRs) vs. bit error rates (BERs) are presented for single and multi-component LFM signals. Interference excision algorithms improve the system performance more than an order of magnitude.

Analytical theory and numerical approaches to the simulation and optimal design of multilayer mirrors and optical Bragg waveguides are developed. Optimal refractive index profiles in planar and cylindrical geometry are found. Reduction of the full set of Maxwell's equations to a scalar boundary value problem in the lowcontrast approximation is discussed. An efficient finite-difference scheme is used to simulate realistic Bragg fibers.

Scattering of dipole field by a perfect electromagnetic conductor (PEMC) cylinder is studied theoretically. Electric dipole and magnetic dipole are considered separately as source of excitation. Plots are given for different values of admittance parameter of the PEMC cylinder.

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.

In this paper, a carrier frequency offset estimation scheme in orthogonal frequency division multiplexing is proposed. We focus on increasing the correlation of each PN sequence code repeated in one preamble. We aim at getting an efficiency like using many preambles. The proposed method can improve the performance of the system by estimating fine frequency offset. Also, the proposed method enhances reliability by maximizing the number of correlations compared with the established method in time domain.

Acompact planar microstrip ultra-wideband (UWB) bandpass filter is presented in this paper. The proposed UWB filter is realized by cascading a high pass filter (HPF) and a lowpass filter (LPF). HPF with short-circuited stubs is used to realize the lower stopband and a lowpass filter based on a defected ground array in the ground plane employed to attenuate the upper stopband. One such a bandpass filter is designed and simulated.