Spherical radar reflectors with high-gain omnidirectional response

Two basic types of passive reflectors are described: one uses the spherical Luneberg lens with a circumferential reflecting ring, the other is essentially hollow and lighter, and hence applicable to balloon targets. Both types use parallel-wire grating (Helisphere) techniques to achieve omni-azimuth response with wide elevation coverage, and both have much larger RCS than equal-size metal spheres. Isotropic response can be approached with either type if the proper polarization is used to illuminate the reflector. Recent approaches by other workers are reviewed, including one which provides truly isotropic response with no polarization restrictions.