H. A. Ragheb

Scattering by N parallel conducting circular cylinders

The scattering pattern and back-scattering cross-section, due to an E-polarized plane wave incident on N circular parallel conducting cylinders in an arbitrary configuration, is computed by the boundary-value method. The results compare favourably for thin cylinders with an approximate solution based on an extension of the Karp–Russek technique for large separation between any two adjacent cylinders relative to the larger diameter. The results indicate that for broadside incidence and fixed radii and separation of an equi-spaced linear array of cylinders, the maximum back-scattering cross-section increases monotonically with an increasing number of cylinders. On the other hand, for normal incidence and fixed radii, the peak of the maximum back-scattering cross-section occurs at the same separation between the cylinders for any number of cylinders.

Plane wave scattering by a conducting elliptic cylinder coated by a nonconfocal dielectric

The scattering properties of a dielectric-coated nonconfocal conducting elliptic cylinder are investigated. The theoretical treatment of such a problem is based on the boundary value solution, which is an exact treatment of the problem. Only the transverse magnetic (TM) case is considered, although the transverse electric (TE) case can be treated in the same way. It is shown that this solution is much more general than all previous solutions because it can handle a variety of scattering geometries. Numerical results are presented in graphical form for the echo width pattern of various geometries. >

Inverse black body radiation at microwave frequencies

The inverse black body radiation, which is the problem of determining the area-temperature distribution of a black body from its measured radiated power spectrum, was recently solved by Bojarski. His solution employs the inverse Laplace transform to reconstruct the area-coldness distribution from an integral equation based on Plancks law. Our solution is similar but restricted to microwave frequencies and employs the Rayleigh-Jeans approximation to yield the corresponding portion of the area-coldness distribution using the inverse Laplace transform but avoiding the iterative procedure of Bojarski.

Electromagnetic scattering from a coaxial dielectric circular cylinder loading a semicircular gap in a ground plane

An exact dual series solution of a plane wave incident on a coaxial dielectric circular cylinder imbedded in a semicircular gap of a ground plane is presented. Both TM and TE cases are considered here. The scattered field is represented in terms of an infinite series of cylindrical waves with unknown coefficients. By applying the boundary conditions and employing the partial orthogonality of the trigonometric functions the scattering coefficients are obtained. The resulting infinite series is then truncated to a finite number of terms to produce numerical results. For the sake of comparison with the published data some special cases are introduced first. The comparisons showed excellent agreement in all cases. >

Simulation of a cylindrical reflector by conducting circular cylinders

A cylindrical reflector is simulated by N parallel circular conducting cylinders of arbitrary radius and distribution along the trajectory of the continuous reflector surface. The resulting radiation pattern of the transmitting reflector antenna is computed as the backscattering pattern of the circular cylinders due to a line source excitation. The results for large N are compared with published data for a cylindrical parabolic reflector by Kinzel and for a corner reflector by Tsai. It is shown that the beamwidth and first sidelobe level can be improved by using cylinders of unequal radii and spacing but that, contrary to expectation, further improvement by increasing the number of cylinders is not necessarily possible.

Analysis of a nonconfocal suspended strip in an elliptical cylindrical waveguide

The separation of variables method along with an addition theorem of Mathieu functions are employed in this paper to analyze the problem of a nonconfocal suspended strip in an elliptical waveguide. An infinite-dimensional determinant is obtained, which represents the characteristic equation of the proposed structure. To obtain the cutoff wavenumbers for both TE and TM cases of such a structure, the infinite determinant is truncated. Convergence when truncating was observed. Numerical results for the special case of a confocal structure is discussed first for comparison with published data. Results of other interesting cases are also presented.

Electromagnetic wave scattering by a two layered piecewise homogeneous confocal elliptic cylinder

The scattering properties of a homogeneous elliptic cylinder with a confocal dielectric or magnetic coating are investigated analytically. The method of separation of variables is used to determine, exactly, the field distributions in each region for both transverse electric and transverse magnetic excitations. The technique can be easily extended to handle any number of layers. The behavior of the scattered field in the far zone is illustrated with numerical results for different core and coating material types, axial ratios, and electrical sizes.

Rigorous solution of the scattering by two multilayered dielectric cylinders

In this paper the scattered field due to a plane wave incident on two parallel multilayered dielectric cylinders is derived using the boundary value approach. An asymptotic solution is also presented in which fictitious line sources located at the cylinder axes are used to account for the multiple interactions. For the sake of simplicity two layered-dielectric cylinders and two dielectridy coated conducting cylinders are investigated, however the solution can be easily extended to many layers as well as to many cylinders.

Analysis of arbitrary shape printed line microstrip antennas

A rigorous solution for arbitrary-shape printed line antennas is developed using the microstrip Greens functions. The current distribution of the line is determined by a moment method and the use of sinusoidal basis functions. Analytical expressions for the far zone fields are obtained using an asymptotic method for evaluating the Sommerfeld integrals. Examples illustrating the accuracy of the method and characteristics of selected printed antennas are presented. It is found that, for undulated printed line elements, the resonance length increases when the undulation height increases. Various examples of undulated printed line elements which are useful for array design are investigated. The effect of the undulation height on the radiation characteristics of the printed line is studied. >

An approximation of Planck's formula for the inverse black body radiation problem

A modification to the Hamid-Ragheb approximation leads to a new approximate formula for the Plancks radiation law valid at all frequencies. The modified regime is useful in solving the inverse black body radiation problem in closed form. The absolute percentage errors in constructing the area-coldness distribution due to the proposed and previous approximations are presented. The results suggest that our modified approximation to Plancks law is more suitable than all other approximations at all frequencies.