Abstract: A millimeter wave imaging system includes a plurality of millimeter wave radiometer elements disposed in a sparse antenna array integrated into a lower surface of an airborne vehicle. The antenna elements preferably form a cross or T-shaped sparse array. Images are formed using interferometric techniques. Each radiometer element includes a receive antenna coupled to an electronic mirror which provides beam steering. To compensate for deflection of the airborne vehicle, a mechanical deflection measurement system is provided. Additional radiometer elements having transmitter antenna elements may be integrated into the sparse array to provide active illumination to enhance image formation and to operate as target designators.