This work presents the derivation of high frequency electromagnetic field expressions for two dimensional Gregorian system embedded in a chiral medium. Two cases have been analyzed. Firstly, the chirality parameter is adjusted to support positive phase velocity (PPV) for both left circularly polarized (LCP) and right circularly polarized (RCP) modes traveling in the medium. Secondly, the chirality is adjusted in such a way that one mode travels with PPV and other with negative phase velocity (NPV). Method proposed by Maslov is used, for finding the field expressions, to overcome the problem of Geometrical Optics (GO) because GO fails at caustics. The results for both the cases are given in the paper.
A set of algorithms, specifically developed to facilitate an effective modeling of fractal-boundary microstrip antennas in the analysis of such structures through numerical electromagnetic (EM) solvers is presented in this paper. A fractal generator based on the implementation of an Iterated Function System (IFS) produces the geometry specified in accordance with the user-defined input parameters. The structure is created through a solver-specific interface and is thus applicable to a commercially available EM simulation suite. The generation of specific shapes through these algorithms provides a flexible method to study different geometries without the need to modify either the interface or the solver. Three structures based on the Minkowski fractal obtained through these techniques have been studied using two EM solvers for comparison. The frequency-domain results show good agreement between the two solvers, thus validating the algorithms implemented. Complex structures with higher iterations can be studied using these algorithms.
A new approach to design digitally tunable optical filter system for DWDM (Dense Wavelength Division Multiplexed) optical networks is presented. This digitally tunable optical filter system uses semiconductor optical amplifiers (SOAs) and DWDM thin film filter based wavelength selection elements. The design is very easy to configure, expand and reduce. This digitally tunable optical filter system is smaller in size, lesser in weight, cheaper in costt, consumes low power and has better timing performance as compared to digitally tunable optical filter suggested by researchers recently.
A novel interpolation scheme based on Adaptive Integral Method (AIM) is presented to solve electrically large radiation problem of conducting surface/surface configurations. For a complex structure that involves wires and surfaces, three basis functions must be assigned to surfaces, wires and wire/surface junctions. To simplify this, the thin strips with no thickness instead of wires are proposed, and the wire/surface junctions can be replaced by surface/surface junctions, thus it is only necessary to define a uniform basis function. The Electric Field Integral Equation (EFIE) is solved using the Method of Moments (MoM) to obtain the equivalent surface current on PEC surfaces. To facilitate the analysis of electrically large radiation problem, the interpolation scheme based on AIM is employed to accelerate the matrix-vector multiplications and reduce matrix storage. Numerical results are presented to demonstrate the accuracy and efficiency of the technique.
This paper describes the alternating-direction implicit finite-difference time-domain (ADI-FDTD) method for physical modeling of high-frequency semiconductor devices. The model contains the semiconductor equations in conjunction with the Maxwell's equations which describe the complete behavior of high-frequency active devices. Using ADI approach leads to a significant reduction of the full-wave simulation time. We can reach over 99% reduction in the simulation time by using this technique while still have a good degree of accuracy compared to the conventional approaches. As the first step in the performance investigation, we use the electrons flow equations in the absence of holes and recombination as semiconductor equations in this paper.
For an harmonic plane wave impinging on a perfectly reflecting smooth plane the total field, incident and reflected, satisfying on this plane a Dirichlet or Neumann boundaray condition, has an integral representation that we extend to the specular reflection from a perfectly reflecting rough plane. To make this generalization possible, some constraints must be imposed on the wavelength of the incident field and on the rough amplitude to make the diffuse field negligible so that only the coherent field is important and we may use the fact that the coherent power is identical to that of a smooth surface. This generalized integral representation supplies an approximation of the coherent field valid far from the rough plane. We limit the discussion to acoustic, TE, TM electromagnetic wave incident on 1D-perfectly reflecting rough planes with roughness described by zig-zag functions piecewise linear with opposite slop on adjacent intervalls.
Possibilities for the extension of the operational frequency band of slotted waveguide antennas are studied. It is shown that by using both conventional longitudinal slots and subarraying techniques it is possible to reach the relative bandwidth of about 15%. This result is illustrated by the development of a novel slotted waveguide antenna for high-resolution SAR applications. The antenna operates in the X-band and forms the beam of 4°×6° with the gain of about 30 dB.
By inserting a dielectric layer, covered by a grounded metal plane, into a hollow rectangular waveguide (HRWG), a planar rectangular waveguide (PRWG) is structured. It is a new candidate solution for both MMIC and hybrid planar RF circuit applications. An intensive numerical analysis of the PRWG is conducted by a 2-D FDTD method. The propagation characteristics of the PRWG with different physical dimensions and electrical parameters are presented. This analysis shows that the PRWG can give an alterable single mode working bandwidth for dominant mode compared with the HRWG, and the size of the transverse section of the PRWG is smaller than the HRWG under the same cutoff frequency of dominant mode.
We have proposed a new architecture for an array in which the elements are placed on a spiral curve in order to obtain an ultra wideband (UWB) radiation pattern. In addition, array factor and bandwidth of the proposed spiral array are calculated. Simulated results obtained by SuperNEC and CST software have shown good agreement with the analytic calculations. Although the proposed antenna array is wideband in nature, it lacks desirable efficiency, due to poor front to back ratio (FBR) and sidelobe level (SLL). In this paper, we have chosen three different approaches in order to improve the e±ciency of proposed array. First, the effect of length and thickness tapering of elements has been studied. Second, we have used Genetic Algorithm (GA) to optimized pattern shape. Finally, the influence of metamaterial cover on array performance has been investigated. Although the first and second methods improve the radiation pattern, the array bandwidth is reduced. It is shown that the third method improves array directivity and FBR by 5-7 dB and 15-17 dB respectively within the frequency band of operation.
Relationships between the properties of surface waves in radar absorbing materials (RAM) layers and mono-static radar cross section reduction (RCSR) performances of a coated slab are studied. In this paper, two kinds of RAM were employed for double-layer coating. By changing the thickness of each layer and the order of RAMs, mono-static RCSR performances of the coated slab are studied. Simultaneously mono-static RCSR performances of a slab coated with equivalent medium of the considered RAMs in situ are calculated and compared with the previous ones in regard to the properties of surface waves. It is found that surface waves in between layers for various coated projects can be evaluated. Our results suggest that the optimal coated order for RAMs exists, and the method may be efficient for coating strategy with various kinds of RAMs. Electromagnetic scatterings of the equivalent medium exclude the effect of surface waves in between layers. Therefore, the equivalent medium theory is not appropriated for the research of electromagnetic scattering on lossy mediums.
A Dual band Microstrip Antenna Arrays (DbMSAA) incorporated with Mushroom Electromagnetic band Gap (MEBG) and modified Minkowski Electromagnetic Band Gap structures to further improve its radiation characteristics is reported in this work. The two different types of EBG structures work like a Band Rejecter (BR), separating the branch of feed line feeding two different groups of patch antenna arrays operating at 2.4 GHz and 5.8 GHz, thus making them operate individually at their particular frequencies, simultaneously. Initially, the possibilities of having a uniform and controlled radiation patterns are quite complicated to achieve due to the single port feeding technique used and developments of grating lobes at the higher band frequency, but, through the incorporation of the EBG structures, the problems could be solved immediately. The antenna's performance is improved where the grating lobes at 5.8 GHz are diminished, and the radiation patterns of the dual band antenna at both frequencies become more symmetrical with increased gain.
The backscattering experiments of water surface by Ultra-High Frequency (UHF, 300 ~ 3000 MHz) Radar are presented in this paper. In order to study UHF radio propagation and backscatter mechanisms from fresh and salty water surfaces at a very low grazing angle, two experiments are carried out on Yangtze River bridge and cliff which face open sea with the same radar system. The physical parameters of different water surfaces are introduced as well as the signature of backscattered echoes.
The finite-difference frequency-domain (FDFD) method with the adaptive basis functions/diagonal moment matrix (ABF/DMM) technique is proposed in this paper for finite periodic linear arrays of inhomogeneous dielectric cylinders, in which the versatility of the FDFD method and the high efficiency of the ABF/DMM technique are combined. The method in this paper and the classical full-domain FDFD method are compared in the given numerical examples. The results obtained by the two methods respectively are in good agreement, but the computational times are largely reduced in the method in this paper.
In microwaves, ferrites are characterized by a tensorial permeability which represents their anisotropy under a constant magnetic field. We present, in this article, a rigorous study of the formulation of the transverse operator method (TOM) with an extension to the case of the guides of rectangular waves partially charged with longitudinally magnetized ferrite. We show the existence of the complex modes in these types of structures with ferrite. A good agreement of the constant of propagation with the literature is obtained.
Local Area Augmentation System (LAAS) based on multi-constellation GNSS can provide improved accuracy, availability and integrity needed to support all weather category II and III precision approach landing of aircraft. In order to receive satellite signals of GNSS, an antenna working over wide frequency band and high phase center stability is preferred. Commonly used antennas like crossed dipoles, patch etc. are inherently narrow band. This paper describes the design and development of half-cardioid shaped dual arm, wide band printed circuit antenna. The antenna has low VSWR of < 3:1, a stable phase center and good right hand circularly polarized radiation patterns covering full L-band frequencies. The simulated and measured results compare well. This compact antenna can also be used on ground, ship and airborne platforms to receive signals from multiple GNSS satellites above the horizon.
We propose a kind of novel photonic crystal fibers (PCFs) based on a super-lattice structure. Uniform air holes are used to form the basic cell structure. Using the uniform air holes in the PCF has the advantage of minimizing the structural distortion during fabrication while forming a complex-structure cross section. We propose an effective-circular-hole PCF with similar properties of the conventional circular-hole PCF to address the concept of the super-lattice structure PCF. An effective-elliptical-hole PCF based on a super-lattice structure is proposed and investigated, which has the similar birefringent and confinement loss characteristics as the previously reported elliptical-hole PCF. Other PCFs based on super-lattice structures such as the effective-triangular-hole PCF and effective-rectangular-hole PCF can also be achieved by using the design method proposed in this paper.
In this study, annular-ring microstrip patch on uniaxial medium is analysed in Hankel Transform Domain. Equivalent models of the structure are obtained depending on the TE and TM mode decomposition in this domain. For the simplification of the tensor form formulations, equivalent matrix operators are defined in cylindrical coordinates instead of the differential ones. Then, resonant characteristics of the structure is determined via the application of the moment method and compared with the isotropic case for different anisotropy ratio values and structural parameters. Equivalent circuit models for the case of multilayered substrates and superstrates are given in order to be used in the following studies on annular-ring microstrip patch.
This paper presents a novel optimization technique biogeography based optimization (BBO) for antenna array synthesis. BBO is a relatively new evolutionary global optimization technique based on the science of biogeography. It is capable of solving linear and non-linear problems. In this paper, BBO algorithm is used to determine an optimum set of amplitudes of antenna elements that provide a radiation pattern with maximum side lobe level reduction and/or null placement in the specified directions. The results obtained show the effectiveness of the BBO algorithm, and they are better than previous published results.
With the aim to improve the performance of Bulk Acoustic Wave resonators, the thickened edge load can be included on the top electrode. Using this solution, the energy trapping concept is forced, and lateral unwanted resonances are not present in the electrical behavior of the resonator. The way to design such a thickened edge load entails, on one hand, the presence of a resonant mode given by the thickened edge load; on the other hand, the degradation of the electromechanical coupling coefficient of the main thickness mode. In order to study the previous phenomena, the electric equivalent circuit has been developed. The obtained results have been validated with the three-dimensional simulations and compared with manufactured resonators.
A polarized 3D-electromagnetic wave propagating from an aperture source into a lossy medium can be modeled by an astigmatic Gaussian beam model (GBM) of complex source coefficients that characterize a radiating antenna uniquely. The source coefficients are determined numerically from phantom experiments, and then used in simulations of specific absorption rates (SAR), in both homogeneous and layered biological media, resulting in good agreement with experimental data. This paper shows that for an x-polarized E-field the GBM simulations of SAR enhancement or focus in the axial, z-directed, paraxial region are accurate, but approximate in the transverse, y-directed, non-paraxial regions due to a focal shift.
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