Advances in Mm-wave and THz Imaging

A survey of some of the recent advances in the field of microwave and millimeter-wave imaging is presented. This technology originally evolved from the approaches used in radar, and has been an active area of research since then, the primary attraction being the possibility of “seeing” objects hidden behind some opaque material such as wood, paper, concrete, fog etc. It is well-known that microwave/mm-wave signals ( usually defined as 0.3 – 300 GHz ) can penetrate such materials to greater or smaller depths depending on frequency , as opposed to visible light or infra-red whose penetration in most cases is negligible.

The applications are well-known today and many systems are in everyday use such as security screening , medical imaging , through the wall imaging for surveillance, non-destructive testing etc. Usually imaging systems operate in the “near field” in the sense that the distance to the target is of the same order as the size of the complete sensor set – most imagers use multiple antennas for receiving the microwave signal from the target and the sensors are physically spaced out in a region usually much larger than wavelength. In contrast there are a few imagers which operate in the radar mode where the object is located in the far-field of the antenna array.

In this talk we will describe some of the recent systems which have been developed by different researchers and which are likely to form the basis of future imagers used commercially , including for security applications.