Polarisation effects investigations in quasi-optical metal grid filters

Many theories have been developed to describe metal grid filters that are commonly used for wavelength selection in far-infrared and millimetre wavelengths experiments. Application of these filters has shifted from simple photometric measurements to the more demanding requirements needed to accurately measure the polarisation. It has therefore become necessary to investigate residual polarisation effects inherent in these kinds of filter structures. In this work we present an alternative modelling approach, based on finite-element analysis software (HFSS) available commercially. To validate the model we have made Fourier transform spectrometer, FTS, measurements of a real capacitive grid component as a function of incidence angle and grid orientation for both s and p polarisations. The excellent agreement between model and data enable accurate predictions of performance of these structures when used in polarimetric experiments as well as determining the cause of parasitic effects.