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This paper describes the techniques and the measured radar return from "phantom targets" using 8.6 and 4.3- millimeter radars. The radar returns are compared to the measured back-scattering cross section of water drops, insects, steam and other materials at 8.6-mm wavelength as measured by a CW radar at this wavelength. Within the limits of the conditions used in the laboratory, it was impossible to produce returns from synthesized refractive index gradients of sufficient magnitude to account for those noted on the radar. It is concluded, therefore, that for the millimeter wavelengths and the short ranges considered, the observed phantom returns were due to solid or liquid particles in the atmosphere.