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.

A broadband stacked U-slot microstrip patch antenna is presented using circuit theory concept. The antenna shows two resonance frequencies that are very closely spaced to give broadband characteristics. The frequency band of 186MHz (36.4% impedance bandwidth) is achieved for the proposed antenna. The theoretical results are in good agreement with the simulated results.

Fractal structures have been widely used in many fields of science, such as biology, physics and chemistry. In this article, we analyze the basic properties of a fractal-like square lattice of air holes, with most of the holes having a lattice constant of Λ while others are repeated with a lattice constant of 2Λ. We change the radii of these holes and analyze their effects on the bandgap regions and transmission properties. The analysis conducted here is based upon band diagrams and 2D Finite difference time-domain (FDTD) solution of the full-wave Maxwell's equations. We show that this structure provides flexibility in tuning the bandgap of the photonic crystal structure and we show the appearance of mini-bandgap regions along certain directions.

In this paper, the Contiguous Partition Method (CPM) is applied to the optimization of the directivity of difference patterns in monopulse planar array antennas. Since the excitations providing maximum directivity of planar arrays can be analytically computed and because of the excitation matching nature of the CPM, the problem at hand is recast as the synthesis of the difference compromise solution close as much as possible to the reference pattern with maximum directivity. Selected results are shown to point out the potentialities of the CPM-based approach.

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.

With the recent advent on communication and satellite industry, there is a great need for efficient Reflector antennas systems, therefore more powerful techniques are requested for analysis and design of new reflector antennas in a quick and accurate manner. This work aim first to introduce wavelet-based moment method in 3D, as a recent and powerful numerical technique, which can be applied on a large reflector antennas, also the physical optics (PO) analysis technique is well known among the designers as an asymptotic method quick and powerful, ideally to predict far field and near field pattern, may be combined with the wavelet-based moment method therefore computing time and memory space can be saved, in this issue knowing the limit of use of this asymptotic technique is worth well.

A novel approach for the design of a compact multiband planar microstrip antenna is presented. This type of antenna is composed of composite metamaterial resonators (including conditional microstrip resonators and metamaterial resonators), and fed by signal feed. A sample antenna with composite closed-ring resonator and split-ring resonator (SRR) fed by 50Ω coplanar waveguide (CPW) developed on FR4_epoxy substrate for multi-band wireless communication applications is presented. Appropriate design of the composite structure resulted in three discontinuous resonant bands. The fundamental magnetic resonant and electric resonant frequency of SRR and the first electric resonant frequency of the closed-ring resonator were combined to form low, middle, and high resonant band. The properties of this antenna are investigated by theoretical analysis and finite element method (FEM) simulations. The numerical results show that the proposed antenna has good impedance bandwidth and radiation characteristics in the three operating bands which cover the required band widths of the 2.4/5.2/5.8 GHz wireless local-area networks (WLAN) and 3.5/5.5 GHz worldwide interoperability for microwave access (WiMax) with return loss of better than 10 dB. The antenna also has stably omni-directional H-plane radiation patterns within the three operating bands.

This paper suggests a pilot-less residual carrier frequency offset (CFO) estimator for ultra-wideband orthogonal frequency division multiplexing (UWB-OFDM) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols carry the identical information in the UWB-OFDM system, thus removing the need of pilot symbols. To demonstrate the efficiency of the proposed pilot-less CFO estimator, analytical expression of the mean square error (MSE) is reported and comparisons are made with the conventional pilot-aided CFO estimator in terms of MSE and throughput.

The aim of this workis to increase the instability of the marching-on-in-time (MOT) method that is used in the analysis of wide-band electromagnetic pulse scattering from structures made of thin wires. The stability problem has been identified with the advent of the MOT method in 1991, and although several improvements have been suggested to overcome this difficulty no exact solution has been found [1]. In this thesis two methods (the Newmark-Beta formulation and the analytic integration) to suppress the instabilities of the MOT algorithm for thin wire scatterers have been proposed and their effects on the stability have been inspected. The results are compared with the results obtained with time domain method of moments (MOM) [2] and it is observed that the results are both stable and accurate. It is shown how the stability is changed by a determined β parameter. Also, Newmark-Beta formulation results for selected different types of structures such as dipole antenna illuminated by a Gaussian pulse given in [3], three pole structure given in [4], loop antenna given in [3] has been shown.

Free standing planar frequency selective surfaces (FSSs) are studied when utilized as spatial filters for linearly polarized antennas. The antenna spatial filter investigated in the present work is constructed up as a finite planar array of conducting strip dipoles. The electric field integral equation (EFIE) technique with the Rao-Wilton-Glison (RWG) basis functions are used to get the current distribution on the conducting strips. The current distribution and backscattered electric field due to an incident plane wave are calculated and compared to some published work. The effect of polarization on the scattered field, and the frequency response of the spatial filter are studied. To test the operation of the proposed planar FSS, a bowtie antenna is used with the FSS employed as a spatial filter. The field transmitted by the antenna and passed over a wide frequency band through the FSS is calculated. It is shown that such a free standing planar FSS can operate as a band stop filter for linearly polarized antennas. It is also shown that even when the size of the array is reduced, the FSS maintains its frequency response with a very slight change in the center frequency of the stop band. The effect of element size, spacing between the elements, and interleaving the columns of the FSS on the frequency response of the FSS are studied. The effect of the spatial filter on the antenna input impedance is studied over a wide frequency band. The radiation pattern of the bowtie is calculated in the presence of the spatial filter. It is shown that the existence of the later causes considerable reduction in the radiation pattern within the stop band of the filter.

In this paper an efficient technique for the determination of the resonances of elliptic Substrate Integrated Waveguide (SIW) resonators is presented. The method is based on the implementation of Support Vector Regression Machines trained using a fast algorithm for the computation of the resonant frequencies of SIW structures. Results for resonators with a wide range of parameters will be presented. A comparison with results obtained with Multi Layer Perceptron Artificial Neural Network and with full wave simulations will show the effectiveness of the proposed approach.

This paper presents a method of antenna impedance measurement for RFID tag antenna based on a differential probe. The importance of accurate impedance measurement in optimal design of tag antenna, especially for the metal tags, is first addressed. Afterwards, an overview of the existing methods based on the singleended probe and the balun probe is presented. The proposed method using the differential probe is explained based the well-known two port network model. Experiments for both balanced and unbalanced tag antenna measurement demonstrate the differential probe can provided better agreement with simulated results.

We have investigated the scattering of the Magnetic Resonance Imaging (MRI) radiofrequency (RF) field by implants for Deep Brain Stimulation (DBS) and the resultant heating of the tissue surrounding the DBS electrodes. The finite element method has been used to perform full 3-D realistic simulations. The near field has been computed for varying distances of the connecting portion of the lead from the air-tissue interface. Dissipated powers and induced temperature rise distributions have been obtained in the region surrounding the electrodes. It is shown that the near proximity of the air-tissue interface results in a reduction in the induced temperature rise.

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.