Wide Field of View Inversely Magnified Dual-Lens for Near-Field Submillimeter Wavelength Imagers

A wide field of view (FOV) inversely magnified dual-lens system for submillimeter wavelength imagers is presented in this paper. The antenna is designed for near-field focusing, at a range of 2.1 m from the primary aperture and to work in the frequency range from 200 to 600 GHz. The half-power beamwidth (HPBW) is 0.27° (1 cm in the image plane) at 500 GHz, corresponding to a focused antenna directivity of approximately 55 dBi. The FOV is as large as ±25.4° (±1 m at the nominal range), corresponding to a scan range of ±100 HPBWs. The shapes of the lens surfaces are optimized to minimize the phase aberration loss over the entire scanning range. Moreover, the lenses are designed to be as thin as possible to limit the dielectric absorption loss. The directivity reduction of the edge pattern with respect to broadside is approximately 1 dB with efficiency of 56%, making this lens an excellent candidate for imaging applications. The dual-lens system can be refocused by displacing the secondary lens and shows an essentially unchanged angular HPBW over a refocusing range of ±50% with respect to the nominal imaging distance. A demonstrator was fabricated and the experimental results at 500 GHz confirm the predicted performance.