The St. Andrews MM-Wave and Terahertz Technology Group have produced a variety of Quasi Optical filters. These can be used in free space as part of an optical system, or be encorporated into an oversized waveguide. A number of filters have been provided for applications such a MM-Wave/THz Plasma Diagnostics for Fusion Research. This page shows a pair of high-pass dichroic filters as examples, but specific filters have been produced to request.
2 THz Metal Mesh Filters
The small photograph to the right shows an example of some filters constructed with metal mesh. These filters were designed to pass frequencies around 2 THz but reject frequencies of a few hundred GHz or less. Click on the photograph if you wish to see a larger, more detailed, view.
The graph below shows the measured response of one of these filters. It can be seen that relative rejection ratios of over 40dB were obtained at 100GHz compared to efficient transmission at around 2 THz.
140GHz Drilled Plate Filters
The small photograph on the left shows a filter designed for insertion into an oversized rectangular waveguide. The filter is designed to have high-pass characteristic with a turn-over frequency of 140 GHz. Click on the photograph for a larger, more detailed, view.
The application required a high relative attenuation at 110 GHz, but good transmission for frequencies above 140 GHz. For this reason, a ‘drilled plate’ form of filter was chosen. The plate has a carefully machined uniform array of well over 1000 holes to achieve the required performance.
Each hole is just over 1mm in diameter, and they are placed as close together as possible. The above close-up view shows the close packing and uniformity of the array of holes that make up the filter.
The graph shows the response of this filter. It can be seen that the relative rejection at 110 GHz is around 60 dB compared to signals above 140 GHz. Note also that the response drops by around 30dB as the frequency is reduced by just 10 GHz (i.e. around 7%) from 145 GHz to 135 GHz. It can seen that the filter has both a very sharp cut-off and a high rejection ratio for low frequency signals.
The small photograph to the right shows an example of some filters constructed with metal mesh. These filters were designed to pass frequencies around 2 THz but reject frequencies of a few hundred GHz or less. Click on the photograph if you wish to see a larger, more detailed, view.
The small photograph on the left shows a filter designed for insertion into an oversized rectangular waveguide. The filter is designed to have high-pass characteristic with a turn-over frequency of 140 GHz. Click on the photograph for a larger, more detailed, view.
Content and pages maintained by: Jim Lesurf (jcgl@st-and.ac.uk)