Investigation on two modelling approaches for millimetre wave imaging system

Imaging is a historical topic in optics, however, in the region of millimetre or sub-millimetre wave, due to the difficulty in fabrication and technology, active imaging system is still in its childhood compared to the relatively mature passive imaging system in the same frequency band. System modelling is important during the design phase, which could help the designers to understand the image formation process and consequently to work towards a better system. Considering the huge electrical size of the practical system, it is extremely hard to do a full-wave calculation. Physical optics (PO) explores the possibility to fulfil this task. In this paper, two models based on PO will be explained with comparisons between frequency domain calculation and spatial domain calculation. The goal is to draw some attention on the application of Fourier optics when we design a millimetre wave imaging system, and moreover, to propose a more physical model for the coherent imaging system.