This thesis describes various analysis techniques used in the optical characterisation of millimetre wave radiation. The results presented relate to both computational simulation and experimental measurements carried out at NUI Maynooth. The majority of the analysis is centred around a frequency of 100 GHz, or a corresponding wavelength of 3 mm. Experimental measurements were performed on diffractive optical elements known as axicons, and the results were presented and compared with simulations. An introduction to KID devices was given, along with their potential uses and a potential analysis method using CST was outlined. These techniques using plane wave illumination in CST were compared and verifed with Gaussian Beam Mode Analysis. A method of analysing the form of standing waves present in a system involving metallic rings was described. A method previously used for the analysis of standing waves between feedhorns was adapted to examine the form of the modes present in the resonant Fabry-Perot cavity. Detailed analysis was performed using CST, a full electromagnetic modelling package on resonant metallic cavities related to describing a waveguide coupled bolometer for the SAFARI instrument on the proposed SPICA space telescope mission. A cavity geometry was optimsed manually for optimum cavity size and absorber size and location by performing a large number of simulations. SCATTER, an in-house mode matching software was used to verify the results from CST in a simple case. Various other cavity geometries were also investigated briefy. A simplifed cavity model which could potentially be manufactured to perform measurements at NUI maynooth was outlined, as well as a potential detector method known as a patch antenna. Patch antennas were designed for use at 100 GHz and briefy examined in operation within a cavity using CST.