L.W. Li

Precorrected-FFT algorithm for solving combined field integral equations in electromagnetic scattering

The precorrected-FFT method is applied in this paper to solve the combined field integral equation (CFIE) for scattering by arbitrarily shaped three-dimensional conductors. The object is first discretized using triangular elements with the Rao-Wilton-Glisson (RWG) basis functions. The source singularities on the original triangular meshes are then projected onto uniform rectangular grids, which enables the calculation of the resultant matrix-vector product to be performed by using the fast Fourier transforms. The memory requirement and computational complexity of the resulting algorithm are of O(N1.5) and O(N1.5 log N), respectively, where N denotes the number of unknowns. In addition, the employment of CFIE eliminates the interior resonance problem suffered by both the electric field integral equation (EFIE) and the magnetic field integral equation (MFIE) and thus significantly improves the convergence of the iterative solution. A unique advantage of the present method is that the computational expense per iteration of CFIE is almost the same as that of EFIE. This fast algorithm renders problems associated with electromagnetic scattering by large complex objects be handled on a normal personal computer.

On the eigenfunction expansion of dyadic Green's function in planarly stratified media

Using the eigenfunction expansion, a terse expression of the scattering dyadic Greens function is presented for defining electromagnetic fields in a planarly stratified medium with a current source arbitrarily located in one of the layers. The scattering dyadic Greens function for each layer is constructed in terms of the cylindrical vector wave functions by applying the method of scattering superposition. The general but succinct expression of the coefficients of the scattering dyadic Greens function for each layer of the multilayers is derived directly from the boundary conditions of the dyadic Greens function. To demonstrate how to apply this method, the coefficients of the scattering Green dyads for a three-layered medium, as an example, are reduced from the general expression for the cases where the current source is located in the first, the intermediate, and the last layers. The complete agreement of such coefficients derived in this article and obtained in the previous published papers asserts...

LEFT-HANDED MATERIAL EFFECTS ON WAVES MODES AND RESONANT FREQUENCIES: FILLED WAVEGUIDE STRUCTURES AND SUBSTRATE-LOADED PATCH ANTENNAS

In this paper, we apply the Double Negative Material in some basic applications, including waveguide, rectangular patch antenna and disc patch antenna. By analyzing theoretically we find that the sizes of these equipments can be greatly reduced by using multi-block (which may include both double positive and double negative material) dielectric materials. In addition, the sizes of patch antennas are no longer proportional to the working frequency but roughly to the ratio of the thicknesses of dielectric slabs. Still some new modes in both waveguide and patch antennas are found, and by working at the new modes the bandwidth of the patch antenna can be dramatically increased.

On the eigenfunction expansion of electromagnetic dyadic Green's functions in rectangular cavities and waveguides

The electric dyadic Greens functions of both the first and the second kinds due to the presence of electric and equivalent magnetic sources in rectangular cavities are obtained. A method for directly reducing the dyadic Greens functions for a rectangular cavity to those for a semi-infinite and an infinite rectangular waveguides is presented. The Green dyads of the second kind for an infinite and a semi-infinite rectangular waveguides, and a rectangular cavity are obtained. >

An Efficient Hybrid Method for Analysis of Slot Arrays Enclosed by a Large Radome

A hybrid method that combines the integral equation (IE) method and Physical Optics (PO) is proposed for efficient analysis of slot arrays enclosed in an electrically large radome. The integral equations are applied over the aperture of the slot antenna and the tip region of the radome by enforcing continuity of the tangential magnetic or electric field. Equivalent PO currents are assumed on the relatively smooth region of the radome walls, induced by the radiated fields from the antenna. The radiated fields due to the PO currents on the radome are coupled back to the integral equations to account for interactions between the radome and the antenna, as well as the interactions between the tip and other parts of the radome. This method leads to considerable reduction in memory and computational time, since PO is applied to a large part of the electrically large radome, with unknown currents defined only on the aperture of the slot antenna and the small tip region of the radome. Better efficiency can be attained if the integral equation is applied only to the slot aperture and the entire radome wall taken as the PO region, with acceptable degradation in accuracy.

EXTRACTION OF CONSTITUTIVE RELATION TENSOR PARAMETERS OF SRR STRUCTURES USING TRANSMISSION LINE THEORY

In this paper, the transmission line theory is utilized to characterize the metamaterials comprising of microscopic elements of a periodic array, specifically, the traditional split-ring resonators (SRRs), as an example. The bianisotropic property of the metamaterials is characterized in a new way different from the existing wave methods. As evident from both simulations and experiments, the SRR array structure is found to be quite lossy even though it is made of very good conductor or even perfect conductor as in simulation. With the present characterization, we are able to explain physically very well on how or why the energy gets lost in this structure. Finally, the theoretical result is compared with numerical simulation data obtained based on quasi-static Lorentz theory to further verify our analysis.

Electromagnetic dyadic green's functions in spectral domain for multilayered cylinders

Dyadic Greens function (DGF), as an electromagnetic response of dielectric medium or the field contributed due to a delta source, is quite useful to solve electromagnetic boundary-value problems. DGFs for multilayered structures are of particular interest to many engineers and scientists because of its better accuracy in modelling practical problems. Cylindrically multilayered medium is one of the most common structures used in practice, and the DGF for such a medium was recently published by Xiang and Lu [1]. However, it is found that there are some critical mistakes made and certain constraints assumed in the representation of the DGFs and their coefficients. The present paper serves as an amendment of [1] so as to avoid possible misleading of readers.

Analysis of Electromagnetic Wave Propation in Forest Environment Along Multiple Paths

The electromagnetic radiation of an electric dipole in a medium with four layers is examined using dyadic Greens functions in their vector wave eigenfunction expansion forms. In this four-layered model, two lossy dielectric layers are used to represent the canopy and trunks of vegetation that covers the ground plane. The dyadic Greens functions for a four-layered medium are first applied to derive the integral expression of the electric fields. Asymptotic evaluations of the integrals are then made using the steepest descent method, and the branch-cut integrations in complex planes; and correspondingly the direct wave, multi-reflected waves, and lateral waves along various interfaces have been obtained. The far-zone field for problems of this nature is, as found, primarily determined by the lateral wave. The transmission losses for tropical forest are calculated numerically for both vertical and horizontal dipoles, and a dipole with a 45 ° inclination. Also, a serious mistake made in the literature has been pointed out in this paper.

A dual-frequency compact microstrip patch antenna

In this paper, a new dual-frequency, compact antenna, which uses an H-shaped microstrip patch with a shorting pin, is described. Compared with the conventional rectangular patch antenna, this antenna can achieve both a significant reduction of antenna size and a dual-frequency operation with a single feed. More freedoms for tuning the resonant frequencies, the frequency ratio, and the input impedance are available because of more design parameters. A detailed parameter study is performed, and the theoretical analysis is based on the finite difference time domain (FDTD) method. The FDTD programs are developed and validated by measurement results. The effects of several antenna parameters on two resonant frequencies, frequency ratio, and radiation pattern characteristics of the antenna are analyzed and compared. It is shown that various frequency ratios (1.91–4.23) can be obtained by varying the design parameters of this antenna. Several design curves are presented.

Eigenfunctional expansion of dyadic green's functions in gyrotropic media using cylindrical vector wave functions: Abstract

This paper presents a novel eigenfunction expansion of the electric-type dyadic Greens function for an unbounded gyrotropic medium in terms of the cylindrical vector wave functions. The unbounded Green dyadics are formulated based on the Ohm-Rayleigh method, orthogonality of the vector wave functions, and the newly formulated curl and divergence of dyadic identities. The irrotational part of the Greens function is obtained from the residual theorem. Unlike some of the published work where some assumptions are made prior to the formulation, the irrotational dyadic Greens function in this paper is formulated rigorously based on the idea given by Tai.