IEEE Transactions on Antennas and Propagation

The feasibility and performance of an aperture-coupled cavity-fed microstrip patch antenna and an aperture-coupled cavity antenna are demonstrated using reciprocity and moment method analyses, followed by practical design guidelines and equivalent circuit models. Each antenna incorporates a thick ground plane that can be useful as a heat sink for active MMIC circuitry and as structural support for... View full abstract»

This paper deals with adaptive array beamforming based on eigenspace-based (ESB) techniques with robust capabilities. It has been shown that ESB adaptive beamformers demonstrate the advantages of fast convergence speed and less sensitivity to steering angle error over conventional beamformers. In conjunction with a signal subspace construction method, we present an efficient technique to achieve t... View full abstract»

The problem of plane wave scattering by a slightly rough boundary of an arbitrarily layered medium with general anisotropy of electric and magnetic properties is considered using boundary conditions transference method and a small perturbation approximation combined with the Green's functions technique. It is shown that in the Born approximation, the second statistical moments of the fluctuation f... View full abstract»

The mass and bulk of conventional absorbing materials make it difficult to use them to reduce the radar scattering from objects at low radar frequencies such as in the VHF and UHF bands. A more attractive alternative is the impedance line or string, which is a two-dimensional (2-D) version of the one-dimensional (1-D) Salisbury screen. Using a method-of-moments (MoM) computational scheme, we explo... View full abstract»

A method is presented for computing accurate solutions of Maxwell's equations in the presence of perfect electrical conductors (PECs) with sharp corners and highly curved surfaces using conventional nodal finite elements and a scalar/vector (S/V) potential formulation. This technique approximates the PEC with an impedance boundary condition (IBC) where the impedance is small. Critically, it couple... View full abstract»

This letter presents an algorithm for suppressing the cross polarization of single offset reflector antennas illuminated by a cluster of multimode horn feeds using a constrained minimization routine. The design variables are the mode ratios for the higher order modes excited in the feeds relative to the dominant TE11 mode. The goal is to systematically determine the optimum mode ratios ... View full abstract»

Expressions are presented for the computation of mutual admittance between rectangular apertures of different size, in a finite planar array. The equations allow any orientation for any of the apertures, with any number of transverse electric (TE) and transverse magnetic (TM) waveguide modes. Furthermore, the expressions also include the effect of dielectric covering of these apertures. A versatil... View full abstract»

The solution for the two-dimensional (2-D) Green's function for a wedge with impedance faces is presented. The important feature of this Green's function is that there are no restrictions on the locations for the source and observation points-they can be anywhere. Its development proceeds along two separate lines: one for when the source or observation point is far from the wedge vertex and anothe... View full abstract»

This paper presents a novel design of triangular microstrip antenna with dual-frequency operation. In this design the microstrip patch is short-circuited using a shorting pin and fed by a single probe feed. By varying the shorting pin position in the microstrip patch, such a design can provide a large tunable frequency ratio of about 2.5-4.9 for the two operating frequencies. Experimental results ... View full abstract»

A coordinate transformation is used to reduce the dimensionality of impedance integrals coupling linear filamentary monopoles printed on grounded dielectric substrates. Computer processing times for the remaining numerical integrations are significantly reduced while accuracy is maintained View full abstract»

The generalized network formulation is applied in combination with the method of moments to calculate the electromagnetic scattering from conducting objects containing near-resonant open-ended cavities. The presence of the cavity increases the iteration number in conjugate gradient iterations due to the near-resonant modes and the multiple wave bounces inside the cavity. The equivalence principle ... View full abstract»

Two-dimensional (2-D) TEM horns are modeled using the finite-difference time-domain (FDTD) method. The boundary walls are perfect electric conductors and one wall, which does not align with the Cartesian grid, is approximated using a staircased representation. By carefully comparing the FDTD results to those of the analytic solution, one can make conclusions about the coarseness with which a bound... View full abstract»

In recent years, there has been an increasing interest in dual linear polarization antennas for various purposes, e.g. polarimetric synthetic aperture radar (SAR) imaging. A key design goal for dual polarization antennas is to obtain a high cross-polarization suppression. When using standard techniques for improving the cross-polarization suppression in dual linear polarization antenna arrays unde... View full abstract»

We have measured (at 57.5 GHz) the reflection and transmission coefficients of typical walls, floor, ceiling, window, and partitions and have compared the measured reflection characteristics with the reflection characteristics estimated by multilayer dielectric models. Although the positional inhomogeneity of structures gives rise to some variation from one measured position to another, these posi... View full abstract»

A line integral representation of the Kirchhoff-type aperture integration is derived for an open-ended waveguide with arbitrary cross section, excited by an arbitrary mode. The problem is formulated by taking advantage of the equivalence between the radiation of the aperture and the radiation of the modal currents along the semi-infinite waveguide walls View full abstract»

A stochastic optimization algorithm is used to characterize the polarization states of a nonpolarimetric radar transmitter and receiver antennas for optimal target classification. Specifically, the optimized solution is sought when a multitude of targets are to be categorized. It is shown that the objective function of the optimization problem is highly nonlinear and discontinuous, hence, classica... View full abstract»

A frequency extrapolation algorithm for the fast multipole method (FMM)-based moment method code FISC (Fast Illinois Solver Code) is presented. Our approach is to parameterize the induced current on the target, which is available from the FISC solution based on a multipath excitation model. The ESPRIT super-resolution algorithm is applied to extract the time-of-arrival and amplitude parameters in ... View full abstract»

An array antenna composed of crank-line elements is investigated on the basis of the element current distributions determined by the method of moments. A technique of gradually increasing the antenna height above the ground plane is adopted to enhance the gain. It is found both numerically and experimentally that a gain of approximately 30 dB is obtained with an axial ratio of less than 3 dB over ... View full abstract»

This paper describes the behavior of a compact two-port integrated mixer active antenna element with low cross polarization, high two-port circuit isolation, and good mixer detection sensitivity. Using this element as an elemental building block, a self-tracking antenna array has been realized which uses an in-band carrier signal for self calibration. The array is relatively insensitive to absolut... View full abstract»

Corrections to the uniform geometrical theory of diffraction (UTD) that account for the caustics caused by the coalescence of the diffraction points on a curved edge are derived. This creates a new curvature dependent diffraction coefficient that has not been previously accounted for in the UTD. The far-zone radiation by a short monopole mounted on an elliptic disk is analyzed using this caustic c... View full abstract»

This paper presents an alternative vector analysis of the electromagnetic (EM) fields radiated from thin circular-loop antennas of arbitrary radius a. This method, which employs the dyadic Green's function in the derivation of the EM radiated fields, makes the analysis more general, compact, and straightforward than those two methods published recently by Werner (1996) and Overfelt (1996). Both ne... View full abstract»

An accurate method for the evaluation of the Cauchy principal value integrals arising in time-domain electromagnetic wave scattering is presented. This is applied to a boundary integral equation (BIE) method employing quadratic curvilinear surface elements where such singularities do not vanish (as they generally do when simpler but less accurate discretizations are employed). The technique involv... View full abstract»

A double line integral representation of the mutual coupling between open-ended waveguides of arbitrary cross section is presented, which is useful to speed up calculations inside the framework of a Galerkin method of moments View full abstract»

Small planar-type loop antennas used in pagers have fixed directivity patterns. As a result, the received signal strength depends on the orientation of the antenna. A new type of small planar loop antenna (PLA) is, therefore, proposed. The position of the conductor posts can be changed and MOSFETs are adopted for switching the conductor posts. If the positions of the posts can be switched at will,... View full abstract»