Spatial Spectrum Analysis:A metrology for accurate analysis of signal beam field aberration by planar optical components in quasi-optical feed systems

Many great scientific discoveries from medicine to astronomy have been the result of painstaking attention to detail and careful measurement. Classic examples of these have been the discovery of the double helix of DNA by Crick and Watson which critically dependended on the careful x-ray analysis of the DNA molecule by Wilkins and Franklin. But for the want of such high-quality measurements, the famous chemsit Linus Pauling would likely have achieved the correct solution earlier. Similarly, the discovery of Pluto was the result of careful attention to fine detail in the slight perturbations that were observed in the orbit of its neighbour, Neptune.This project is to do with such a concern for making measurements to a high accuracy, and thereby understand and control sources of error. The particular error of concern is the distortion that a cm or mm wavelength radio signal beam suffers when it travels through a box that can have many flat or focussing mirrors or other flat components that can condition a signal, by for example, either splitting the beam into different paths or, joining many signal beams of differing wavelength into one path. The mirror components in the box that focus or shape the beams have been well studied, and their distorting effects are well understood. The flat components that can perform a wide variety of signal conditioning functions, have not been so well studied. Their effects to distort a radio signal beam need careful measurement. The importance for measuring and controlling their effects to mis-shape a beam, stem from their wide and vital use in instruments that are used for remote sensing. These so-called quasi-optical wave guiding structures enable the electromagnetic wave to be guided with little loss, just as visible light can be with mirrors. Remote sensing has a vital role to play in gathering and supplying data that is being used now, for example, in monitoring global weather patterns. Specifically, a radiometer operating from 90-200 GHz can detect the natural emission from the upper atmosphere, process it into frequency bands with a quasi-optical system and, after processing, give information about the water vapour content. This is vital to accurate weather prediction. With higher quality data, achieved by having better-performing components in the measuring instrument, more reliable models can be made for instance in understanding and verifying global warming, or plotting the growth of the holes in Earth's ozone layer at its poles. Quasi-optical systems have many current and potential applications in areas ranging from medical diagnotics to security. This project therefore aims to build a facility that will enable accurate measurements of beam distortion caused by these lesser-studied, but indispensible, flat signal-conditoning components.