A dispersive antenna, formed by locating a
dielectric sheet waveguide in the near-field zone of a millimetric
scale diffraction grating, is described for the application of
passive millimeter-wave imaging in the W-band. Two
dimensional radiometric contrast images are formed by
frequency scanning in the radial direction of the image and
mechanically scanning in the azimuthal direction. Mechanical
scanning is by means of rotation of the antenna at a uniform
angular speed, while frequency scanning is achieved by careful
selection of antenna parameters to provide a near linear
dependence of beam angular position with frequency of ~ 1
degree per GHz. The imaging system operates over the frequency
range 84-100 GHz and utilizes a single millimeter-wave LNA
(Low Noise Amplifier) and mixer to produce a microwave
frequency intermediate frequency; further down conversion
stages result in 64 baseband channels. In this way, the 16 GHz
operational bandwidth is divided into 64 equal width frequency
channels, giving the system a field of view of ~ 16 degrees.