Design and development of a high-performance passive millimeter-wave imager for aeronautical applications

This paper describes a high performance opto-mechanically scanned mm-wave imager intended to monitor the ground movement of aircraft in adverse weather conditions. It employs two counter-rotating mirrors that are tilted about their axes of rotation. They simulate the linear scan of a single high speed, large aperture flapping mirror. When used with a linear receiver array they can produce a two-dimensional scan of the scene at TV rates. In the present application they were used with a single receiver and a large flapping mirror to produce a two-dimensional scan of the scene of ±10° vertically and 60deg; horizontally. One of the rotating mirrors had a concave surface and acted as the focusing element in the imager. The two mirrors were driven from a single servo motor using timing belts and toothed pulleys. The flapping mirror was slaved to the motion of the rotating discs using an electronic cam. The single channel 94GHz receiver consisted of an InP LNA followed by a down-converter and a detector. The video output passed to an A/D converter and was displayed on a conventional PC. This system has virtually 100% transmission and can be used at any waveband.