Improving the convergence rate of the conjugate gradient FFT methodusing subdomain basis functions

A technique to improve the convergence rate of the conjugate gradient-fast Fourier transform (CG-FFT) method is presented. The procedure involves the incorporation of subdomain basis functions associated with the current representation of linear and planar radiating elements. It is shown that significant improvements are achieved in the convergence of the CG-FFT when using sinusoidal basis functions. Numerical results are presented for thin cylindrical dipoles, conducting strips, and material plates of various sizes. In all cases, an increase in the rate of convergence by a factor of two or better was observed     

Eigenvalues and eigenvectors of general gyroelectric media

Explicit and relatively simple expressions for eigenvalues and guided (propagating) eigenvectors of a general gyroelectric medium, where the preferred guided wave direction, zˆ, is parallel to the gyrotropic axis and anisotropy is confined to a plane transverse to z, are given. Some special cases of interest, namely, Hermitian, symmetric (biaxial), and uniaxial permittivity tensors, are also considered. The natural, or optic, coordinate basis is used to derive the source-free eigenvectors and to explicitly reveal the polarization states of those eigenvectors. Also under this basis, the evolution of eigenvalues and eigenvectors as off-diagonal terms of the permittivity tensor uniformly vanish, a transition from the biaxial to the uniaxial case, is discussed     

Scattering from loaded grooves

Electromagnetic scattering from a two-dimensional groove recessed in an arbitrarily thick conducting screen is studied. The groove may be empty or loaded with a lossy material which may or may not completely fill the cavity. For the partially loaded groove, the filling material is assumed electrically dense so that the standard impedance boundary condition is applicable at the top surface of the material. Employing a full-wave analysis, integral equations are derived for the tangential components of the electric field over the aperture. It is shown that the equations are identical for both partially loaded and completely loaded (or empty) cases provided that the aperture admittance of the groove is treated as the equivalent admittance of the internal medium looking into the aperture, thus simplifying the integral equations. When the groove is completely filled by a dense material, the formulation reduces to that corresponding to a direct application of the impedance boundary condition over the aperture.     

On the location of proper and improper surface wave poles for thegrounded dielectric slab [microstrip antennas]

A recently obtained closed-form asymptotic representation due to S. Barkeshli (1988) of the microstrip surface Green's function is known to provide an efficient moment method analysis of microstrip problems. However, in order to make this closed-form expression accurate even for very small separation of source and field points (to within a few tenths of a wavelength), both the proper and improper surface wave transition effects must be included in the solution. This requires finding the location of the corresponding proper and improper poles. A good initial estimate that allows the poles to be located rapidly by using an iterative procedure is presented. The number of proper and improper surface wave poles that have to be considered and their values are tabulated     

Scattering from narrow rectangular filled grooves

The solution of the integral equation for a small width rectangular groove is considered. It is shown that by retaining the dominant mode supported by the rectangular groove, the resulting quasi-static integral equations are comparable to those associated with the perfectly conducting narrow strip. They are, therefore, amenable to analytic solution yielding the exact field distribution or equivalent currents across the groove's aperture. The derived currents exhibit the same edge behavior as that associated with the currents of a perfectly conducting half-plane. The corresponding current behavior based on a (numerical) impedance simulation of the groove is quite different. However the resulting echowidths are comparable. Both transverse electric (TE) and transverse magnetic (TM) polarizations are treated     

An asymptotic closed-form microstrip surface Green's function forthe efficient moment method analysis of mutual coupling in microstripantennas

A relatively simple closed-form asymptotic representation for the single-layer microstrip dyadic surface Green's function is developed. The large parameter in this asymptotic development is proportional to the lateral separation between the source and field points along the air-dielectric interface. This asymptotic solution remains surprisingly accurate even for very small (a few tenths of a free-space wavelength) lateral separation of the source and field points. Thus, using the present asymptotic approximation of the Green's function can lead to a very efficient moment method (MM) solution for the currents on an array of microstrip antenna patches and feed lines. Numerical results based on the efficient MM analysis using the present closed-form asymptotic approximation to the microstrip surface Green's function are given for the mutual coupling between a pair of printed dipoles on a single-layer grounded dielectric slab. The accuracy of the latter calculation is confirmed by comparison with numerical results based on a MM analysis which employs an exact integral representation for the microstrip Green's function     

On the electromagnetic dyadic Green's functions for planar multi-layered anistropic uniaxial material media

A complete, plane-wave spectral, vector-wave function expansion of the electromagnetic, electric, and magnetic, dyadic Green's function for electric, as well as magnetic, point currents for a planar, anisotropic uniaxial multi-layered medium is presented. It is given in terms ofz-propagating, source-free vector-wave functions, where ? is normal to the interfaces, and it is developed via a utilization of the Lorentz reciprocity theorem. The electromagnetic dyadic Green's function for periodic electric as well as magnetic point current sources is also presented. Some salient features of the Green's dyadics, along with a physical interpretation are also described.     

A novel implicit time-domain boundary-integral/finite-elementalgorithm for computing transient electromagnetic field coupling to ametallic enclosure

A time-domain boundary-integral/finite-element algorithm for transient electromagnetic field coupling into an enclosure (cavity) is developed. The model is based on a finite-element technique, which is coupled to the exterior region through the H-field integral equation directly in the time domain. The global electric field, throughout the interior region is driven by the tangential magnetic field over the outer surface of the enclosure. The tangential magnetic field, in turn, is related to the time-dependent incident pulsed field, and the tangential electric field over the surface of the enclosure. Hence, the electric and magnetic fields are coupled at the surface of the enclosure; the coupled equations are solved by a leap-frogging technique. Numerical based on the time-dependent finite-element/boundary-integral implicit scheme are compared with measurements. Some novel features of the newly developed algorithm are also presented     

On the dyadic Green's function for a planar multilayereddielectric/magnetic media

A complete plane wave spectral eigenfunction expansion of the electric dyadic Green's function for a planar multilayered dielectric/magnetic media is given in terms of a pair of the (zˆ)-propagating solenoidal eigenfunctions, where (z ˆ) is normal to the interface, and it is developed via a utilization of the Lorentz reciprocity theorem. This expansion also contains an explicit dyadic delta function term which is required for completeness at the source point. Some useful concepts such as the effective plane wave reflection and transmission coefficients are employed in the present spectral domain eigenfunction expansion. The salient features of this Green's function are also described along with a physical interpretation     

W-shaped enhanced-bandwidth patch antenna for wireless communication

In this paper a novel form of the familiar E-shaped patch antenna is presented. In the presented approach, by using the genetic algorithm (GA) based on fuzzy decision-making, some modifications have been implemented to the incorporated slots which lead to even more enhancement in the antenna bandwidth. The MOM (Method of Moment) is employed for analysis at the frequency band of 1.8GHz–2.6GHz by the optimization parameters of supply locations and slot dimensions. In the implemented fuzzy system, inputs are parameters like population, and outputs are parameters like recombination to produce the next generation. Fuzzy inference system (FIS) is used for the control of GA parameters. The design is also optimized by successive iterations of a computer-aided analysis package and experimental modifications. Prototype antenna, resonating at wireless communication frequencies of 1.88 and 2.37 GHz, has been constructed and experimental results are in relatively good agreement with the analysis. Dimensions of the modified slots for bandwidth enhancement, while maintaining good radiation characteristics, have been determined and the obtained antenna bandwidth of 36.7% is larger than that of a corresponding unslotted rectangular microstrip antenna or a conventional E-Shaped patch antenna. Details of the antenna design approach and experimental results are presented and discussed.