A novel fractal tag antenna constructed with Hilbert-curve and self-complementary configuration is proposed for UHF RFID applications. The main aim of this paper is to merge the meander line and meandered-slot structure of the RFID tag antenna in order to obtain a good performance of compact, broadband, circular polarization and conjugate impedance matching. The tunable inductive and broadband (-10 dB BW = 115 MHz) characteristics of frequency responses and directivity (1.62 dBi) as well as circular polarization (-3dB AR BW = 315 MHz) of radiation patterns for 900 MHz are studied and presented.
This paper presents a Fisher information based Bayesian approach to analysis and design of the regularization and preconditioning parameters used with gradient based inverse scattering algorithms. In particular, a one-dimensional inverse problem is considered where the permittivity and conductivity profiles are unknown and the input data consist of the scattered field over a certain bandwidth. A priori parameter modeling is considered with linear, exponential and arctangential parameter scalings and robust preconditioners are obtained by choosing the related scaling parameters based on a Fisher information analysis of the known background. The Bayesian approach and a principal parameter (singular value) analysis of the stochastic Cramer-Rao bound provide a natural interpretation of the regularization that is necessary to achieve stable inversion, as well as an indicator to predict the feasibility of achieving successful reconstruction in a given problem set-up. In particular, the Tikhonov regularization scheme is put into a Bayesian estimation framework. A time-domain least-squares inversion algorithm is employed which is based on a quasi-Newton algorithm together with an FDTD-electromagnetic solver. Numerical examples are included to illustrate and verify the analysis.
This paper presents a design of Wide-Band Microstrip Yagi-Uda antenna with high gain and high front to back (F/B) ratio. Numerical and measured results of our design show more than 18dB front to back ratio at 5.5 GHz and no backward radiation at 5.2 GHz. An impedance bandwidth of 22.05% was achieved around 5.5 GHz. The antenna gain (10-12.4 dBi) can be varied to be suitable for various applications. Measured return loss and radiation pattern of this antenna is presented to validate the results of simulations by two methods. The first method based on finite element method (FEM) and the second one based on finite integral technique (FIT) were used to analyze antenna structure, and subsequently the Genetic Algorithm (GA) was applied by using HFSS simulator to obtain the optimized parameters. In order to find the best design method for this antenna, the effect of distance between the parasitic elements of proposed antenna was studied. Finally two microstrip Yagi-Uda array antennas were combined to increase the gain of antenna. To demonstrate the major benefits, a comparison of our initial and final designs of Yagi-Uda antenna is provided.
In this work, a design method of an Ultra-Wideband (UWB), low-noise amplifier (LNA) is proposed exerting the performance limitations of a single high-quality discrete transistor. For this purpose, the compatible (Noise F, Input VSWR V_{i}, Gain G_{T}) triplets and their (Z_{S}, Z_{L}) terminations of a microwave transistor are exploited for the feasible design target space with the minimum noise F_{min}(ƒ), maximum gain G_{Tmax}(ƒ) and a low input VSWR V_{i} over the available bandwidth B. This multi-objective design procedure is reduced into syntheses of the Darlington equivalences of the Z_{Sopt}(ƒ), Z_{Lmax}(ƒ) terminations with the Unit-elements and short-circuited stubs in the T-, L-, Π- configurations and Particle Swarm Intelligence is successfully implemented as a comparatively simple and efficient optimization tool into both verification of the design target space and the design process of the input and output matching circuits. A typical design example is given with its challenging performance in the simple Π- and Π-configurations realizable by the microstrip line technology. Furthermore the performances of the synthesized amplifiers are compared using an analysis programme in MATLAB code and a microwave system simulator and verified to agree with each other.
This paper presents a graphics processing based implementation of the Finite-Difference Frequency-Domain (FDFD) method, which uses a central finite differencing scheme for solving Maxwell's equations for electromagnetics. The radar cross section for different structures in 2D and 3D has been calculated using the FDFD method. The FDFD code has been implemented for the CPU calculations and the same code is implemented for the GPU calculations using the Brook+ developed by AMD. The solution obtained by using the GPU based-code showed more than 40 times speed over the CPU code.
This paper presents a comparison of cylindrical and plane air gap magnetic couplings in which the tile permanent magnet polarizations can be either radial or tangential or axial. The expressions of the torque transmitted between the two rotors of each coupling are determined by using the coulombian approach. All the calculations are performed without any simplifying assumptions. Consequently, the expressions obtained are accurate and enable a fast comparison between the structures presented in this paper.
The dispersion equation for free electromagnetic waves guided by an anisotropically conducting open tape helix is derived from the exact solution of a homogenous boundary value problem for Maxwell's equations without invoking any apriori assumption about the tape-current distribution. A numerical solution of the dispersion equation for a set of typical parameter values reveals that the tape-helix dispersion curve is virtually indistinguishable from the corresponding dominant-mode sheath helix dispersion curve except within the tape-helix forbidden regions.
This paper presents a theoretical model for the propagation of a hollow Gaussian electromagnetic beam [HGB], propagating in a plasma with dominant relativistic-ponderomotive nonlinearity. A paraxial like approach has been invoked to understand the nature of propagation; in this approach all the relevant parameters correspond to a narrow range around the irradiance maximum of the HGB. The critical curves for the propagation of various order HGBs have been discussed, and the dependence of the beam width parameter on distance of propagation has been evaluated for three typical cases of steady divergence, oscillatory divergence and self focusing of the HGB.
In this paper, a new design of a compact narrowband bandpass filter is proposed. This new narrowband bandpass filter is designed using an octagonal form of dual-mode closed-loop microstrip ring resonator based on a meander structure in order to achieve compactness. The designed filter has a 3 dB fractional bandwidth (FBW) of 5% at 2.3 GHz. The filter has been fabricated on Taconic CER-10 substrate having 0.64 mm thickness and a relative dielectric constant of 10. Experimental results show good agreement with simulated values. Apart from WiMax, this new model of filter is also useful for WLAN and mobile communication applications, since it is compact in size, low loss, and low cost with good performance of elliptic response with sharp rejection and adequate fractional bandwidth.
In this paper, the electromagnetic field of a horizontal electric dipole buried in a four-layered region is treated in detail. The region of interest consists of a perfect conductor, coated with the two-layered dielectrics under the air. Because of existing multi-reflections, the final representations of the six field components are much more complex. It is noted that the trapped surface wave and the lateral wave along the boundary between the air and the upper dielectric layer and those along the boundary between the two dielectric layers are included. Analysis and computations have some practical applications in microstrip antenna with super substrate.
The wide-angle bicone antenna terminated by a spherical cap is investigated. The antenna radiation patterns have been observed for various values of where represents the phase constant and represents the conical length. It is seen that for large values of the radiation pattern is limited within an angular sector bounded by the cones of the antenna. Next the antenna is optimized for ultra-wideband (UWB) operation through the use of loading techniques. The transient wideband radiated and received responses of the antenna have been observed and the relationship between the wave shapes of the transient field and the input pulse have been determined.
This paper addresses the design of fractal antennas placed onto dielectric object in the UHF RFID band and introduces a tag antenna configuration of simple geometry having impedance tuning capability. Through the paper, the dimensions of the fractal antenna are optimized to improve the impedance matching with the chip impedance. The tag performance changes are studied when it is placed on different objects (e.g., cardboard boxes with various content), or when other objects are present in the vicinity of the tagged object. It has been shown that a tag antenna can be designed or tuned for optimum performance on a particular object. Using the finite element method the open circuit voltage and the polarization mismatch factor against the operating frequency are calculated. The input impedance, reflection coefficient, power transmission coefficient and the read range as a function of frequency are illustrated. The performance of the tag antenna in the presence of the dielectric box and different object materials inside the box is illustrated. The effect of the objects that are placed in the center of the dielectric box didn't have a significant effect on the performance of the tag antenna; there is a small shift in the resonance frequency but still within the operating frequency band. Both the power transmission coefficient and the read range change with the object material. The backscattering properties of the tag antenna have been studied. The differential radar cross-section of the tag antenna is calculated for different antenna loads.
A completely analytical computation of the electromagnetic field produced by an optical fiber helix is presented for the first time. The analysis utilizes the transformation of radially traveling cylindrical waves between two skew cylindrical coordinates systems, that has been previously derived by the author, in order to express the waves radiated by each infinitesimal part of the helix in terms of cylindrical waves around the helix axis and be able to integrate the contributions analytically. Under certain realistic geometrical assumptions, an unperturbed propagation of a single fiber mode is assumed to account for the infinite fiber length, leading to elegant final series expressions in terms of mixed angular-axial Hartree space harmonics, which show clearly the effect of the helical geometry on the field distribution. Analytical formulas are obtained for the field inside and outside the helix cylinder and an interesting two-term decomposition of the outward radiated field is concluded.
This paper presents a rigorous approach for the propagation of electromagnetic (EM) fields along a helical waveguide with arbitrary profiles in the rectangular cross section. The main objective is to develop a mode model to provide a numerical tool for the calculation of the output fields, output power density, and output power transmission for an arbitrary step's angle and the radius of the cylinder of the helical waveguide. Another objective is to demonstrate the ability of the model to solve practical problems with inhomogeneous dielectric profiles. The method is based on Fourier coefficients of the transverse dielectric profile and those of the input wave profile. Laplace transform is necessary to obtain the comfortable and simple input-output connections of the fields. This model is useful for the analysis of dielectric waveguides in the microwave and the millimeter-wave regimes, for diffused optical waveguides in integrated optics. The output power transmission and the output power density are improved by increasing the step's angle or the radius of the cylinder of the helical waveguide, especially in the cases of space curved waveguides.
The concept of Scale-Changing Network is reported for the electromagnetic modeling of complex planar structures composed of a collection of metallic patterns printed on a dielectric surface and whose size covers a large range of scale. Examples of such multi-scale structures are provided by multi-band frequency-selective surfaces, finitesize arrays of non-identical cells and fractal planar objects. Scale-Changing Networks model the electromagnetic coupling between various scale levels in the studied structure and are computed separately. The cascade of Scale-Changing Networks bridges the gap between the smallest and the highest scale levels and allows forming a monolithic (unique) electromagnetic formulation for the global electromagnetic simulation of complex planar structures. Derivation of these networks is presented and key advantages of the electromagnetic approach are reported.
The scattering of an arbitrary electromagnetic wave by a thin disk located in free space is formulated rigorously in terms of coupled dual integral equations (CDIEs) for the unknown images of the jumps and average values of the normal to the disk scattered-field components. Considered are three cases of the disk: (1) zero-thickness perfectly electrically conducting (PEC) disk, (2) thin electrically resistive (ER) disk and (3) dielectric disk. Disk thickness is assumed much smaller than the disk radius and the free space wavelength, in ER and dielectric disk cases, and also much smaller than the skin-layer depth, in the ER disk case. The set of CDIEs are "decoupled" by introduction of the coupling constants. Each set of DIEs are reduced to a Fredholm second kind integral equation by using the semi-inversion of DIE integral operators. The set of "coupling" equations for finding the coupling constants is obtained additionally from the edge behavior condition. Thus, each problem is reduced to a set of coupled Fredholm second kind integral equations. It is shown that each set can be reduced to a block-type three-diagonal matrix equation, which can be effectively solved numerically by iterative inversions of the two diagonal blocks and 2×2 matrix.
The efficiency of different ways for controlled changes of spectral characteristics of open electrodynamic resonant structures are studied and evaluated in the paper.
In this work, source equivalence and computation of the reflected (induced) electromagnetic field in geophysical situations are studied. It is shown that the application of Huygens' principle allows for full generalization of Fukushima's equivalence theorem that applies only for magnetic field. The source equivalence is revisited for a vertical line current element, and it is shown that the equivalent charge required to replace the original source by a planar equivalent source together with the surface charge associated with the reflected field generates a purely vertical total electric field on the ground. Consequently, if the magnetic field and horizontal components of the total electric field on the ground are of interest, only equivalent currents need to be considered. The classical Complex Image Method (CIM) is derived from exact image theory for planar impedance surfaces. The classical CIM is extended by considering a divergence-free source current that may have components also perpendicular to the ground plane. The extension is seen to generate a complex image charge not present in the classical CIM. Further, a generalized application of the extended CIM to geophysical situations having divergence-free volume source currents is introduced. The application involves decomposition of the source into line current elements and rotations, translations and reflections of the electromagnetic field expressions associated with each element. The validity of the new approach is verified for an example of external current system and ground model setup by means of comparisons to results obtained from exact formulation by~[18].
Solutions of the homogeneous 2D scalar wave equation of a type reminiscent of the "splash pulse" waveform are investigated in some detail. In particular, it is shown that the "higher-order" solutions relative to a given "fundamental" one, from which they are obtained through a definite "generation scheme", come to involve the relativistic Hermite polynomials. This parallels the results of a previous work, where solutions of the 3D wave equation involving the relativistic Laguerre polynomials have been suggested. Then, exploiting a well known rule, the obtained wave functions are used to construct further solutions of the 3D wave equation. The link of the resulting wave functions with those analyzed in the previous work is clarified, the pertinent generation scheme being indeed inferred. Finally, solutions of the Klein-Gordon equation which relate to such Lorentzian-like solutions of the scalar wave equation are deduced.
In this paper, a study is made of the electrostatic potential and field of an electric dipole located in the interface between two dielectric regions. When the dipole is oriented perpendicular to the interface, the detailed position of the charges of the dipole relative to the location of the interface has a significant effect on the value of the field produced away from the dipole, unlike the case of a dipole parallel to the interface. It is shown that it is the total dipole moment (due to both free and bound charges), rather than simply the impressed (free) dipole moment that is important in determining the field in this case. Based on these results, the question of defining and determining the electric polarizability of a perfectly conducting object partially embedded in a dielectric interface is examined. The example of a conducting sphere embedded halfway in the interface is studied as a demonstration of our general formulation. The results of this paper are important for the proper modeling of arrays of scatterers embedded in an interface, such as frequency-selective surfaces (FSSs) and metafilms.