Analysis of the metal-strip delay structure for microwave lenses

Abstract

The metal-strip delay medium is shown to be analogous to a transmission-line low pass filter. A filter analysis gives the image phase constant and image admittance of the equivalent filter section. The index of refraction of the medium is obtained from the former and the reflection coefficient from the latter. It is shown that the physical parameters may be chosen so that the strip medium is perfectly matched to space at a particular frequency. Formulas are given which hold for normal incidence even when the strips are close together. The same method may be applied to delay media consisting of thin metal obstacles of any shape arranged uniformly in parallel planes. Examples are circular disks, ellipses, and rectangles. Certain general conclusions are drawn for this class of media.