A new heuristic UTD diffraction coefficient for non-perfectly conducting wedges is proposed. The coefficient is an extension of the heuristic one given by Luebbers (1984) and as simple as that to compute. In the case of forward-scattering and neglecting the surface wave effects, the new coefficient gives a result close to Maliuzhinets's (1958) solution, also deep in the shadow region where the previous one fails. Moreover, it makes the special care used by Luebbers to deal with grazing incidence unnecessary.

A new heuristic UTD diffraction coefficient for nonperfectly conducting wedges

An asymptotic expansion of a multiple integral for knife-edge diffraction is derived. The expansion expresses the field in terms of single-edge diffraction. By considering this expression, a similar expansion for higher order UTD diffracted fields is proposed. By means of a set of transition functions, the result removes some of the shortcomings of the original set out of the UTD when the incident field is not a ray-optical field.

UTD-diffraction coefficients for higher order wedge diffracted fields

In this paper, we present a method of moments (MoM) program to analyze different configurations of arrays of cylindrical-rectangular patches. The patches can be located inside or on the surface of a multilayer circular-cylindrical structure and can be arbitrarily rotated. The antenna structure is rigorously taken into account by using proper Green's functions, and the array is analyzed by using an element-by-element approach. The elements of the MoM matrix are calculated in the spectral domain, and special attention is given to their numerical treatment when analyzing cylindrical antennas with large radii. A laboratory model is built to test different configurations of patches and to validate calculated results. The agreement between measurements and calculations is very good.

Analysis and measurements of conformal patch array antennas on multilayer circular cylinder

Radiation patterns of rectangular microstrip patches arranged circumferentially on a circular cylinder have been computed. Both the axial patches and circumferential patches have been used. It has been found that the number of circumferential patches required for a given ripple in gain pattern is considerably less, thus simplifying the feed network. Comparison with experimental measurements shows good agreement.

A conformal cylindrical microstrip array for producing omnidirectional radiation pattern

This letter presents a new solution to the diffracted field for dielectric wedges within the context of the uniform theory of diffraction (UTD). The relationship between the diffraction coefficient and the four characterization factors in its formulation is studied by using the high-frequency solution for impedance-surface wedge diffraction at normal incidence in a UTD-like form in a previous paper. A polynomial curve-fitting procedure is employed through the least square criterion to obtain simplified expressions of the four factors. The result is compared with rigorous and heuristic formulations. Both parallel and perpendicular field polarizations are tested. The new parametric formulation agrees the rigorous solution reasonably well and exhibits significant improvement in accuracy over heuristic methods. This approach enables faster and more accurate evaluation of diffracted field in propagation prediction models for urban and indoor environments for potential use in real-time propagation computations.

A parametric formulation of the UTD diffraction coefficient for real-time propagation prediction modeling

A geometrical theory of diffraction (GTD) interpretation of a uniform solution for the wedge given by Mohsen is given. The diffraction coefficients are equal to those given by Kouyoumjian and Pathak except that the Fresnel argument in the two solutions are different. This uniform geometrical theory of diffraction (UTD) result is compared with exact series expansions for a plane wave incident on a 90\deg wedge.

An alternative diffraction coefficient for the wedge

The radiation patterns for a quadratic microstrip antenna mounted on two-dimensional objects, the circular cylinder and the strip, have been calculated using both the transmission-line model and the resonator model. Analytical expressions for the far field are presented, and calculations are compared with measurements. All measurements clearly indicate that the resonator model is better than the transmission-line model in radiation pattern calculations outside the principal planes of the antenna.

The radiation from rectangular microstrip antennas mounted on two-dimensional objects

A simple power series has been developed for the radiation resistance of center-fed dipoles. This series has both a better accuracy and a wider range in which it is valid than other recently reported approximations expressed by elementary functions.

K. Jakobsen

Papers

An alternative diffraction coefficient for the wedge

The radiation from rectangular microstrip antennas mounted on two-dimensional objects

A simple power series for the radiation resistance of center-fed dipoles