Diffraction of waveguide waves by a finite system of strips in a layered dielectric

Abstract

Microwave engineering uses leaky-wave antennas, which are planar dielectric waveguides with metal strips deposited on their surface. The analysis of such antennas in the literature known to us [i, 2] is made in the approximation of an infinite periodic grating without variation of the field along the strips; this can result in a large error in the calculation of real antennas with a limited number of strips and strip sizes. Nonperiodic gratings, which are the basis for the fabrication of antennas with enhanced characteristics, cannot be studied in this approximation [3]. In our study we obtained the solution of the boundary problem for the diffraction of waveguide waves by a finite number of metal ribbons without any limitation on their size. The solution also makes it possible to study the properties of higher leaky waves of microstrip lines and to make an exact calculation of waveguide filters formed by metal strips deposited on a dielectric substrate in the E plane of a rectangular waveguide. Such filters have found application in the millimeter range [4, 5]. In contrast to those studies, we take the effect of the dielectric substrate into account. Let us consider a two-dimensional layered structure (the boundaries of the layers are parallel to the xz plane), in which N infinitesimally thin ideal conducting strips lie on one boundary (Fig. I). Boundary conditions of the "electric wall" or "magnetic wall" type are satisfied on the horizontal screens. One or both screens may be absent, in which even the conditions for emission are assumed to be satisfied.