Moseley, P; (2015) Novel RF quasi-optical components for THZ astronomy. Doctoral thesis , UCL (University College London).

Text Paul Moseley thesis.pdf Available under License : See the attached licence file. Download (16MB)

Abstract

There have been many successful THz instruments used in ground and space based telescopes that operate over a range of frequencies from 10s of GHz up to 10s of THz. For some instruments, their operation depends on precise ltering of the received radiation, which can be achieved by using metal mesh lters. These lters can also be referred to as frequency selective surface, which are part of a broad category of metamaterials. By controlling the geometry of these surfaces and combining multiple layers, it is possible to steer the radiation or control the polarisation. This thesis expands on using existing knowledge and fabrication techniques of metal mesh structures to build new quasi-optical devices, which could be a lightweight replacement for existing components, such as lenses, or new devices with properties that are not possible using traditional materials. Initially an analysis of suitable modelling methods to predict the behaviour of the individual gird structures is performed. It is then shown that multiple girds can be combined to create an arti cial dielectric. By using the developed modelling tools a parameter space is found which sets a practical limit on devices that can be built. This theory is also applied to rectangular grids, which have the same properties, but are polarisation dependent. With this framework in place, a series of devices are designed and characterised. This includes a broadband gradient index at lens, which was characterised using a VNA from 90 to 220GHz. This design was modi ed to produce a lens that is capable of separating out two orthogonal linear polarisations and focusing them separated on the same focal plane. Finally an analysis of di erent of arti cial waveplates is performed, to determine which metamaterial structures are best suited for replacing traditional sapphire waveplates.

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