Architectures and Devices for Millimeter Wave Imaging

A research effort was conducted to explore the ways in which sub-wavelength gratings can be used to reduce the reflections from the optics of millimeter-wave imaging systems. A moth-eye lens is sometimes used at optical and infrared frequencies for this purpose, but it is too fragile to be applied directly to the plastic lenses used in the millimeter-wave. A modification of this structure, called the inverse moth-eye lens, was designed, fabricated, and tested. Within the report we present results at 35 GHz showing a 15-dB reduction of surface reflections in Rexolite. The technique was also applied to a material with a dielectric constant of 9. Transmission increased an average of about 30 dB between 30 and 40 GHz with the inverse motheye, anti-reflection (AR) surface. The implication of these results is that the weight and bulk of millimeter-wave imaging systems could be significantly reduced by using optical systems with high dielectric materials and etched, sub-wavelength AR surfaces.