Frequency Selective Surfaces provides efficient beam splitting of energy in the millimetre/submillimetre wave bands. It can be used for the front-end channel demultiplexing and single band filtering in radiometers. The wire grid polarisers are extensively used as polarisation sensitive elements for separating different polarising signals at the same channel.
Dichroic Plate Filters (DCP)
The Millimetre Wave Technology (MMT) Group is able to manufacture and supply dichroic (high-pass) filters offering excellent frequency discrimination to 2 THz. In order to maximise the operating bandwidth, the hole spacing on the conductive metal sheet must be minimised, which is possible using a high precision machining and novel fabrication techniques. We can produce custom DCP filters designed and manufactured to meet your specification.
Frequency Selective Surfaces (FSS)
Airborne and spaceborne atmospheric sounding instruments generally use a quasi-optical antenna feed arrangement to reduce the system losses to acceptable levels. Multichannel operation is obtained in these instruments using FSS filters. Operation of the FSS at 45° incidence minimises the overall size of the system, and simplifies design and construction. We can produce and/or electromagnetically test FSS on low loss dielectric substrates such as quartz, Duroid board etc.
Wire Grid Polarisers (WGP)
Free standing wire grids are used at millimetre and sub-millimetre wavelengths in a variety of applications including interferometers, beam dividers, polarising elements etc. We can provide a complete grid fabrication service, including the manufacture of precision grid frames to customer specifications. Our grid fabrication facility allows grids to be made using either tungsten or gold-on-tungsten wire. While a typical application might require 20 μm diameter wire on a pitch of 80 μm, wire diameters of 10 μm on a pitch less than 40 μm can be accommodated.
Radio Frequency characterisation
The MMT Group can perform vector network anal yser based free space characterisation of FSS filters and polarisers in different configurations (i.e. transmission or reflection), incidence angles and polarisations over the frequency range from 15 GHz to 1 THz.
Quasi-optical test benches configured for characterising frequency selective surfaces for transmission measurements (left image) and reflection measurements (right image).
FSSs are utilised in millimetre and sub-millimetre wave remote sensing instruments with multiple sounding bands and in radar and communication systems to provide spatial filtering of the channels and to achieve band isolation respectively. WGPs are ideal for applications involving variable att enuators, reflectors, high efficiency polarisers and beam splitters.
