Silica Glass Spheres as Omnidirectional Microwave Retroreflectors

Abstract

A retroreflector is a device that reflects an incoming radar wave back to the source. Microwave retroreflectors (radar reflectors) are widely used in microwave applications, for example, for calibrating antennas, marking vessels, buoys, airfield runways and power lines as well as for modifying radar cross section of military vehicles. Typical retroreflectors are metal spheres and plates, dihedral and trihedral (corner) reflectors as well as Luneburg lenses. A common problem of the mentioned devices is however that except for metal spheres their operation is limited in orientation (elevation and azimuth) range. Metal spheres are perfectly omnidirectional but rather weak reflectors. Homogeneous dielectric spheres are typically weak reflectors too, and a metallization of a portion of their surface is necessary to improve their performance, similarly to the cat’s eye optical reflectors. A spectacular exception is a sphere from silica glass. The paper will describe microwave properties of silica glasses, the theory of electromagnetic scattering from low-loss dielectric spheres and the results of experimental studies of the silica glass spherical retroreflectors.