The design of a real time 94GHz passive millimetre wave imager for helicopter operations

It is well known that millimetre wave systems can penetrate poor weather and battlefield obscurants far better than infrared or visible systems. Imaging in this band offers the opportunity for passive surveillance and navigation allowing military operations in poor weather. We have previously reported a novel prototype real time mechanically scanned passive millimetre wave imager operating at 94GHz. This 94GHz imager has diffraction limited performance over the central two thirds of the 30 x 60 degrees field of view with and a 25Hz frame update rate. This paper reports the redesign of the prototype to operate in a helicopter environment. The vibration resulting from the helicopter rotors can typically range up to 3g peak at specific frequencies and is the major challenge for imaging systems. The mechanical design of the new imager is based on a rigid space frame utilising expanded polystyrene as a structural element to support the receiver array. The optical design of the imager has also been toleranced so that the impact of vibration on image quality is minimised. The use of novel design techniques and materials support a development path to a low cost low mass production unit.