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A heterodyne radiometer, operating in the range 73-139 GHz, is used at JET to measure the cyclotron emission (ECE) spectrum from which the electron temperature profile is obtained. Radiation from the plasma is transmitted through a single long oversized (S band/WG 10) waveguide. The radiometer uses five waveguide beamsplitters to divide the incident power six ways between six broadband mixers, which provide simultaneous measurements over the wide RF bandwidth from the single waveguide input. Efficient demultiplexing in the millimetric and submillimetric bands can be achieved by employing arrays of self-resonant conducting elements which are supported on a dielectric substrate. This technology can also be applied to waveguide beamsplitters. Although the electromagnetic environment in the waveguide differs from that in free-space, the modelling technique is shown to give good agreement with measurements.

Additional information

Authors: CAHILL R, RF Systems and Technology Group, MMS Space Systems, Bristol (GB);BARTLETT D V, JET Joint Undertaking, Abingdon, Oxon. (GB);PORTE L, JET Joint Undertaking, Abingdon, Oxon. (GB);ROOKES A, Imperial College of Science, Technology and Medicine, Department of Physics, London (GB);STURLAND I M, British Aerospace Sowerby Research Centre, Materials Science Department, Bristol (GB)
Bibliographic Reference: Report: JET-P(94)60 EN (1994) 4 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199510220 / Last updated on: 1995-02-21
Original language: en
Available languages: en
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