Multilayer mesh filters for quasi-optical beamsplitting applications in meteorological and science space instrumentation

Two computer models have been used to study the performance of a high-Q quasi-optical filter design where the dielectric material has been removed to reduce the insertion loss. It has been observed that agreement between the models improves when the number of screens increases, and for the triple screen FSS design the centre resonant frequency predictions are within 2.2%. Two micromachining processes are described which provide the required dimensional accuracy and repeatability for 300 GHz device fabrication. However comparisons between the FEM computer model and preliminary swept measurements, suggest that it is necessary to increase the conductivity of the metal and reduce the surface roughness in order to achieve an insertion loss <0.4 dB. A suitable metal deposition technique is currently being developed together with a test system which will lower the noise floor and so enable accurate determination of the filter rejection. This type of low loss quasi-optical filter will be employed in the next generation of space borne radiometers where it will contribute to the performance enhancement necessary to ensure the success of future Earth observation science space programmes.