IEEE Transactions on Antennas and Propagation

A method-of-moments (MoM) analysis is applied to the problem of determining late-time resonances of dielectric bodies of revolution buried in a lossy layered medium, with application to plastic-land-mine identification. To make such an analysis tractable, we have employed the method of complex images to evaluate the layered-medium Green's function. The application of this method to resonant struct... View full abstract»

The formulas of the on-surface measured equation of invariance (OSMEI) for wire antennas are derived. The unknowns of each node on the antenna surface are expressed by the vector potential function and surface current density. The unknowns in the vicinity of each node are coupled in a linear equation and the coefficients of the linear equation are determined by the measured equation of invariance ... View full abstract»

The results of analytical and numerical study of the modes propagating on an impedance-surface circular cylinder are communicated. Besides the well-known axially symmetric Sommerfeld's mode, another hybrid mode, having a single azimuthal variation, can propagate at any frequency. For a realistic cylindrical conformal antenna, the both wavenumbers are quite comparable. This may cause additional cou... View full abstract»

The problem of providing robustness to the conventional narrow-band uniform linear array configuration so as to handle wide-band and moving jammers is addressed. This robustness is achieved via the use of derivative constraints in jammer directions. However, since the jammer directions are not known a priori, these constraints are incorporated with a maximum likelihood characterization of the so-c... View full abstract»

We develop a set of scalar integral equations that govern the electromagnetic scattering from a two-dimensional (2-D) trough in an infinite perfectly conducting ground plane. We obtain accurate and efficient numerical solution to these equations via the method of moments (MoM). Our numerical implementation compares favorably to popular methods such as the finite element/boundary integral (FE/BI) m... View full abstract»

Iterative techniques developed for solving general systems of linear equations have been applied to systems resulting from electromagnetic rough-surface scattering problems. Previously used iterative procedures that model the multiple scattering of the electromagnetic energy are shown to be mathematically equivalent to the application of stationary iterative procedures to the system of equations r... View full abstract»

Several new artificial nonlinear composite materials are introduced in this paper. They consist of electric molecules constructed with nonlinearly loaded electrically small dipole antennas. Their behaviors are studied with an augmented finite-difference time-domain (FDTD) simulator. The loads are based upon the use of multiple diodes and ideal operational amplifiers. The resulting composite materi... View full abstract»

The radiation fields of a line source enclosed in a circular dielectric radome with grating consisting of an array of thin lossy metal strips are analyzed. The variations of the directivity of the source beam with respect to the beam direction are studied. The possibility of damping these variations by an appropriate design of the radome is demonstrated View full abstract»

In this paper, we present a new and very fast ray-tracing method using a ray tube tree, which is based on uniform geometrical theory of diffraction (UTD) and can solve some of the problems that other ray-tracing methods have. It is developed for quasi three-dimensional (3-D) environments and can be applied to any complex propagation environment composed of arbitrary-shaped buildings and streets. I... View full abstract»

This paper focuses on a boundless homogeneous medium with general anisotropy of electromagnetic properties. The explicit exact form of the four spectral Green's dyads Gˆνξ(k) is obtained and a coordinate-free representation of the four spatial Green's functions Gˆνξ(x-x') in terms of one scalar potential W(x-x') is developed. On this basis, asymptotic ex... View full abstract»

A finite-element method (FEM) is developed for the analysis of complex axisymmetric radiating structures. The method is based on the electric field formulation with the transverse field expanded in terms of edge-based vector basis functions and the azimuth component expanded using nodal-based scalar basis functions. This mixed representation of the electric field eliminates spurious solutions and ... View full abstract»

This paper presents a new method for the reduction of quantization lobes produced by beam scan in an array of subarrays. These quantization lobes occur at the grating lobe angles and are decreased by the subarray pattern. It is shown that they can be further reduced by adding a random phase component to each subarray. For two element subarrays the quantization lobes (QL) suppression is roughly 10-... View full abstract»

A novel two-beam scanning active leaky-wave antenna (LWA) has been developed. This LWA with a two-terminal feeding microstrip line structure is integrated with a varactor-tuned X-band high-electron mobility transistor (HEMT) voltage-controlled oscillator (VCO). The signal of the VCO is injected via a T-divider into the radiating element. To excite the first higher order mode, the designed antenna ... View full abstract»

This paper presents 30-GHz linear-tapered slot antennas (LTSA) and 94-GHz constant-width slot antennas (CSWA) on synthesized low dielectric constant substrates (εr=2.2). The performance of tapered-slot antennas (TSA) is sensitive to the effective thickness of the substrate. We have reduced the effective thickness by selectively machining holes in the dielectric substrate. The machi... View full abstract»

The time-domain image reconstruction problem can be formulated as a sinogram recovery problem. The sinogram recovery problem is to find a complete sinogram based on the measured incomplete sinogram. In this paper, we solve the sinogram recovery problem by using linear prediction techniques. Since the scattered field of a target can be written as a superposition of distinct specular reflections ari... View full abstract»

Circular polarization (CP) operation of an annular-ring microstrip antenna with a pair of inserted slits at its fundamental TM11 mode is proposed and experimentally investigated. Two examples of the proposed antenna fed using a microstrip line at the inner and outer patch boundaries are studied. Results show that the proposed antenna can have good CP performance and, moreover, the requi... View full abstract»

The electromagnetic scattering from a multilayered sphere modal solution of Wait (1963) is modified to allow the inclusion of infinitesimally thin impedance films at layer boundaries. The modified solution is implemented in a computer algorithm and the scattering from an aluminum sphere coated with a dielectric DelrinTM layer containing an embedded impedance film is computed. This targe... View full abstract»

The electromagnetic radiation and scattering properties of thin knotted wires are considered in this paper. A special class of knots, called torus knots, are introduced for the purpose of this investigation. The parameterizations available for torus knots are used in conjunction with Maxwell's equations to formulate useful mathematical representations for the fields radiated by these knots. These ... View full abstract»

Hierarchical mixed-order tangential vector finite elements (TVFEs) for tetrahedral elements are attractive for accurate and efficient finite-element method simulation of complicated electromagnetic problems. They provide versatility in the geometric modeling of physical structures, guarantee solutions free of spurious modes, and allow local increase of resolution by selective expansion of the unkn... View full abstract»

New vector finite elements are proposed for electromagnetics. The new elements are triangular or tetrahedral edge elements (tangential vector elements) of arbitrary polynomial order. They are hierarchal, so that different orders can be used together in the same mesh and p-adaption is possible. They provide separate representation of the gradient and rotational parts of the vector field. Explicit f... View full abstract»

The effects of the variation in canting angle of falling raindrops and the distribution of raindrop sizes in different types of rain on cross polarization discrimination (XPD) on line-of-sight propagation paths in a tropical location in the frequency range 1-50 GHz are investigated. The dropsize distribution (DSD) model of Adimula and Ajayi (see Ann. Telecomm., vol.51, no.1/2, p.87-93, 1996) has b... View full abstract»