Passive imaging for security and other applications has reached an important level of development. Ka and W band imaging systems are now commercial products, thanks to cheap and stable amplifiers. While deployment numbers are still modest, improvements to these systems will come from engineering and algorithm development, and not fundamental research. What research should focus on are system volume reduction and resolution improvements.
Fundamental research has several potential paths to solve these problems. Silicon Germanium CMOS can build acceptable millimeter wave amplifiers, and while SiGe noise figure is higher than GaAs, the ability to integrate RF and back end processing will push us closer to a CCD-like sensor. Antimony Arsenide features higher mobility than GaAs, with very low flicker noise and operation above 200 GHz which will reduce aperture size for equivalent resolution. More focus is needed in material characterization, particularly for clothing and common commercial materials.
Finally, Sparse Array technology may build flat, conformal structures with high resolution and relatively low detector count. This paper will briefly discuss the time line of past innovations, and explore the advantages and challenges of the new technologies that will drive this field forward.