Concept of Near-Field Millimeter-Wave Imaging System with a Spatial Resolution beyond the Abbe Barrier

A near-field millimeter-wave (mm-wave) imaging system with a spatial resolution of less than 0.5 lambda has been designed in the millimeter wave range for on-line inspection of nonmetallic (dielectric) materials. The imaging system consists of a transceiver block coupled to an antenna that scans the material to be imaged; a reflector plate is placed behind the material. As an antenna a diffractive optics with focus F < lambda is used. Such an antenna allow to focusing of millimeter-wave radiation beyond the Abbe barrier. A quadrature IF mixer in the transceiver block enables measurement of in-phase and quadrature-phase components of reflected signals with respect to the transmitted signal. The initial results show the feasibility of the near-field mm-wave sensor for nondestructive inspection of materials with sub-Rayleigh resolution. Using future optically dense modified Fresnel lenses, a resolution of the order lambda/100 seems to become possible.