Awideband E-shaped microstrip patch antenna has been designed for high-speed wireless local area networks (IEEE 802.11a standard) and other wireless communication systems covering the 5.15-5.825 GHz frequency band. Two parallel slots are incorporated to perturb the surface current path, introducing local inductive effect that is responsible for the excitation of the second resonant mode. The length of the center arm can be trimmed to tune the frequency of the second resonant mode without affecting the fundamental resonant mode. Acomprehensiv e parametric study has been carried out to understand the effects of various dimensional parameters and to optimize the performance of the antenna. Asubstrate of low dielectric constant is selected to obtain a compact radiating structure that meets the demanding bandwidth specification. The reflection coefficient at the input of the optimized E-shaped microstrip patch antenna is below -10 dB over the entire frequency band. The measurement results are in excellent agreement with the HFSS simulation results.
Fractional curl operator is utilized to construct the solutions corresponding to fractional dual rectangular waveguides. Fractional dual rectangular waveguides may be considered as intermediate of two given waveguides, where both waveguides are related through principle of duality. Characteristic impedance of fractional waveguide is determined. Behavior of field lines in transverse plane is also investigated.
This paper presents a complete ray-tracing based model which takes into account scattering from rough surfaces in indoor environments. The proposed model relies on a combination between computer graphics and radar techniques. The paths between the transmitter and the receiver are found thanks to a Bi-Directional Path-Tracing algorithm, and the scattering field after each interaction between the electromagnetic wave and the environment is computed according to the Kirchhoff Approximation. This propagation model is implemented as a plug-in in an existing full 3-D ray-tracing software. Thus, we compare the results of classical ray-tracing with those of our model to study the influence of the scattering phenomenon on the wave propagation in typical indoor environments.
In this paper a novel intelligent method to identify an unknown medium (type of apodization and chirping) is developed. Our consideration is concentrated on complex fiber Bragg Gratings. For realization of the idea the Genetic Algorithms (GAs) is used. So, GAs is used to solve inverse scattering problem for reconstruction of nonuniform or complex fiber Brag gratings. In this method, the reflection coefficient measured in practice is inserted to a suitable algorithm. According to the proposed method, first medium discrimination is performed between predefined large classes of mediums and then the whole and necessary parameters for reconstruction of the medium are extracted. Full numerical method is used for compare of the results obtained from the presented algorithm. Our simulation shows good agreement between them. So, a novel method for identification and discrimination of optical mediums especially complex Bragg Gratings is presented. Finally the presented method can be used to identify optical mediums and complex Bragg Gratings systems.
In this paper, we propose an optimization method based on real-coded genetic algorithm (GA) with elitist strategy for thinning a large linear array of uniformly excited isotropic antennas to yield the maximum relative sidelobe level (SLL) equal to or below a fixed level. The percentage of thinning is always kept equal to or above a fixed value. Two examples have been proposed and solved with different objectives and with different value of percentage of thinning that will produce nearly the same sidelobe level. Directivities of the thinned arrays are found out and simulation results of different problems are also compared with published results to illustrate the effectiveness of the proposed method.
This paper investigates the scattering of electromagnetic plane wave from an impedance strip. Both E- and H-polarizations are considered. The method of analysis is Kobayashi potential, which uses the discontinuous properties of Weber-Schafheitlin's integrals. Imposition of boundary conditions result in dual integral equations. Using the projection, equations reduces to matrix equations. The elements are given in terms of infinite integrals that contains the poles for particular values of surface impedance and these integrals are computed numerically. Far diffracted fields in the upper half space for different angles of incident are computed. To check the validity of the results, we have derived the physical optics (PO) approximate solutions. Numerical results for both the methods are compared. The agreement is good. Current distribution on the strip is also presented.
It is well known that a left-handed-medium (LHM) slab with negative permittivity −ε0 and negative permeability −μ0 can be made as a perfect lens for its negative refraction. In this paper, we show that such two semi-infinite lossless LHM slabs can realize electromagnetic energy localization completely through an accurate analysis. If two current sources with the same amplitude and opposite direction are placed at the right edge of the left LHM slab and the perfect-imaging point of the right LHM slab separately, we have demonstrated that all electromagnetic waves are completely confined in a region between the two sources and there is no power radiating outwards the region.
A compact dual-band bandpass filter using equal-length split-ring resonators (SRRs) is proposed in this paper. The tworesonance frequency response of equal-length split-ring resonator is described in detail. A cross-coupled dual-band filter with four equallength split-ring resonators is designed. Several finite out-of-band attenuation poles are realized to improve the selectivity of the proposed filter. The measurement of the filter is in good agreement with the simulation.
Cognitive Ultra Wideband Radio is proposed to exploit the advantages of combining Cognitive Radio with Ultra Wideband technologies, so as to solve the problems of coexistence and compatibility between UWB and other existing narrowband wireless systems. A novel adaptive UWB pulse shaping algorithm with low complexity, instead of notch filter, is presented for producing the expected spectral notches right in the frequency band occupied by the nearby wireless devices. Simulation results show that the proposed UWB waveform has better single-link BER performances in AWGN channel and stronger anti-jamming ability than other conventional waveforms such as Scholtz's monocycle, etc. Besides, the power spectral density of UWB pulse does not need to be reduced over the whole frequency band. Therefore, it is possible to expand the communication range of UWB systems by increasing the transmitted power of UWB pulse.
This work investigates the unique numerical dispersion behavior of the Compact-FDTD method for waveguide analysis, especially when the waveguide dimensions are much larger than the operating wavelength as in high-frequency EMC analysis or radio-wave propagation in tunnels. The divergence of this dispersion behavior from the standard FDTD algorithm is quantified and a major source of dispersion error is isolated and effectively eliminated. Optimized modeling parameters in terms of appropriate spatial and temporal resolutions are generated for computationally efficient and error-free numerical simulations of electrically large waveguiding structures.
Apractical problem in the reflection method for dielectric constant measurement is the difficulty to ensure the sample is placed exactly at the waveguide flange. Asmall position offset of the dielectric sample will give rise to some errors in calculating the dielectric constant, especially when a thin sample is used. To circumvent this problem, a method to determine the dielectric constant by measuring the transmission coefficient of the thin slab placed in a waveguide has been developed. Slab position offset from the measurement reference plane has no effect on the measurement accuracy. An explicit expression for the dielectric constant is obtained in terms of the transmission coefficient by simplifying the exact solution for transmission through a thin dielectric slab. The method is verified with measurement on Teflon of 0.5-mm thickness. The measured dielectric constant of Teflon shows excellent agreement of both ε' and ε'' with published data. Subsequently, the dielectric constant of a vegetation leaf was measured.
In this paper, we present a new scheme for the realization of a wide-band chaotic RADAR system. The remarkable characteristics of such scheme are: (1) Wide-band chaotic signal generated from microwave chaotic Colpitts oscillator is directly used as the RADAR signal; (2) Chaos synchronization is used to recover the chaotic signal from the back-scattered signal by targets; (3) The intrinsic sensitivities of the chaotic signal to the parameters of the chaotic circuit and to the initial conditions are used to realize the "multi-user" property. System simulations show that such RADAR can still work in an environment when the signal-to-noise ratio (SNR) is lower than −20dB.
In this paper, an analytical method for management of optimum group velocity dispersion (GVD) for compensation of chromatic dispersion in optical fibers is proposed. The proposed method mathematically is based on the Volterra series as alternative method for solution of the nonlinear Schrödinger equation (NLS). Based on analytical solution of the nonlinear equation in pulse propagation, we propose a differential equation including optimum GVD for complete dispersion compensation for given dispersion coefficient and fiber length. The obtained integro-differential equation is solved for special cases and it is shown that the obtained results are so better than traditional dispersion compensation cases. Also, the proposed technique can be applied to fiber design to introduce an especial GVD profile for dispersion less transmission.
We propose an inter-disciplinary approach to particle swarm optimization (PSO) by establishing a molecular dynamics (MD) formulation of the algorithm, leading to a physical theory for the swarm environment. The physical theory provides new insights on the operational mechanism of the PSO method. In particular, a thermodynamic analysis, which is based on the MD formulation, is introduced to provide deeper understanding of the convergence behavior of the basic classical PSO algorithm. The thermodynamic theory is used to propose a new acceleration technique for the PSO. This technique is applied to the problem of synthesis of linear array antennas and very good improvement in the convergence performance is observed. A macroscopic study of the PSO is conducted by formulating a diffusion model for the swarm environment. The Einstein's diffusion equation is solved for the corresponding probability density function (pdf) of the particles trajectory. The diffusion model for the classical PSO is used, in conjunction with Schr¨odinger's equation for the quantum PSO, to propose a generalized version of the PSO algorithm based on the theory of Markov chains. This unifies the two versions of the PSO, classical and quantum, by eliminating the velocity and introducing position-only update equations based on the probability law of the method.
A designed model based on the ultra-small silicon waveguide(WG) is demonstrated to generate high repetition rate picosecond pulse train. Research result shows that 50 GHz repetition rate pulse can be obtained inside a 2-mm-long ultra-small silicon WG using signal wave at 1550nm with a cw power of 0.2mW and different delay modulation Gaussian pulses at 1670nm with peak of 0.6mW before the WG. the signal pulse train obtained has duration time as short as around 6 ps full width of half maximum(FWHM) and extinction ratio as large as up to 30 dB. Additionally,eac h pulse of signal pulse train obtained holds equal intensity and close Gaussian waveform.
In this paper, novel structures using split ring resonators (SRRs) and coupled lines are proposed and analyzed. SRRs are etched on three different planes and their propagation characteristics are compared. Two compact narrow band band-pass filters based on these structures are designed and their performances are demonstrated by simulated and measured results, which are in good agreement.
One of the methods developed for accelerating the convergence speed of infinite series is theWatson transformation. It is a technique with an interesting theoretical background which is applied in a restricted number of cases due to its complexity. Most of the papers using this method do not extensively analyze every step of implementation. In this work we apply Watson transformation in a simple case and we focus on each aspect of the procedure.
This paper proposes an improved time domain finite element-boundary integral scheme for 3-D scattering from arbitraryshaped objects. The proposed scheme, which uses only one auxiliary boundary, is more efficient than the one reported in the literature that uses two auxiliary boundaries. While preserving the sparseness and symmetry of the finite element matrices, the proposed scheme reduces the computational domain for the finite elements. A major difficulty, here, is the treatment of the singularity of Green's function arising from this scheme. To overcome this problem, the contribution of singular point is computed analytically, and equivalent transformation technique is also included to reduce the integrals' singularity. And, a remedy is presented for the numerical error encountered in the course of the equivalent transformation, which essentially may be attributed to the inherent routine with the time domain finite element-boundary integral method. The validity and accuracy of the hybrid scheme are verified by numerical tests.
The magnetization of a ferro- or ferri-magnetic material has been modeled with the Landau-Lifshitz-Gilbert (LLG) equation. In this model demagnetization effects are included. By applying a linearized small signal model of the LLG equation, it was found that the material can be described by an effective permeability and with the aid of a static external biasing field, the material can be switched between a Lorentz-like material and a material that exhibits a magnetic conductivity. Furthermore, the reflection coefficient for normally impinging waves on a PEC covered with a ferro/ferrimagnetic material, biased in the normal direction, is calculated. When the material is switched into the resonance mode, two distinct resonance frequencies in the reflection coefficient were found, one associated with the precession frequency of the magnetization and the other associated with the thickness of the layer. The former of these resonance frequencies can be controlled by the bias field and for a bias field strength close to the saturation magnetization, where the material starts to exhibit a magnetic conductivity, lowreflection (around −20 dB) for a quite large bandwidth (more than two decades) can be achieved.
Abstract-In this paper, spectral properties of the Fibonacci-class one-dimensional quasi-periodic structures, FCJ(n), as an important optical structure are investigated. Analytical relations for description of the spectral properties of FCJ(n) are used. Fast Fourier Transform (FFT) for investigation of the spectral properties of these structures is proposed. FFT spectrum of the Fibonacci-class one-dimensional quasi-periodic structures contains peaks that are equivalent to photonic bandgaps or multiband reflection filter. Based on the proposed relations and FFT simulation results, the optical bandgap and other properties of these structures are studied. In this paper, the effects of the optical and geometrical parameters on optical properties of the Fibonacci quasi-periodic structures are considered. Our proposed relations show that the spectral contents of the Fibonacci-class onedimensional quasi-periodic structures have two main terms including the low and high frequency parts. Our results illustrate that the high frequency term depends up on the class order, n, and the width of the layer B, db, while the low frequency term depends on the width of the layer A, da. According to the proposed method, the spectral contents of FCJ(n) includes multi narrowband peaks multiplied by a quasi periodic envelope function. The number of multi narrow bands within a periods of the envelope function can be controlled by varying db and n and also the number of period of envelope function can be manipulated by da. Results obtained from our proposed analytical relations and FFT based simulation results are close together.
A new reconfigurable microstrip patch antenna allowing switching between two circular polarizations is proposed. It consists of a square radiating patch and a 3 dB hybrid coupler. Using only a single-polar-double-throw (SPDT) switch,the polarization switching can be achieved. This design of the dc-bias network is extremely simple. From experimental results,the proposed antenna avoids the frequency offset phenomena which often happened to antennas with switchable polarization.
In this article a new type of circularly cored highly birefringent (Hi-Bi) waveguide having elliptical cladding is proposed and analyzed for the first time in our knowledge. By choosing appropriate orthogonal co-ordinates and using the boundary conditions of the considered waveguide, the eigen value equation in terms of modified Mathieu functions is derived under the weak guidance condition and is presented in this paper. Using this equation the modal dispersion curves for even and odd guided modes are obtained and plotted for different cladding ellipticity e. It is seen that the proposed (Hi-Bi) fiber supports less guided modes than standard circular fiber. Finally, the modal birefringence in the said fiber is also estimated.
It is well known that the performance of a wireless multiple-input and multiple-output (MIMO) system depends on the propagation channel. The propagation channel models can generally be divided into two different groups, the statistical models based on information theory and the site-specific models based on measurement or ray tracing. In this paper, a general procedure for predicting the MIMO channel model has been presented. Analytical expressions for the channel matrix elements in a general scattering environment have been derived from the statistical theory for a narrow-band electromagnetic field, and have been verified by numerical simulation and experiments. The limitations of information capacity of the MIMO wireless communication system imposed by the antennas have also been discussed, and analytical upper bounds on the information capacity in terms of the antenna parameters for multiple antenna system in free space have been obtained. Once the capacity of a MIMO system is specified, these upper bounds can serve as a criterion for estimating how many antennas are needed or how big the antenna must be to achieve the capacity.
The input reactance and radiation resistance of a giant very low frequency (VLF) ‘T type' antenna with ground screen is computed by Method of Moment (MoM). The loss resistance of a complex grounding system is calculated by numeric integral of near field from MoM solution of the antenna on the ground surface. The numeric calculation results agree well with the measured data.