Quasi-optical measurement of complex dielectric constant at 300 GHz |
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Authors: | Bernd Stö ckel |
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Affiliation: | (1) Lehrstuhl für Hochfrequenztechnik, Universität Erlangen-Nürnberg, Cauerstr. 9, D-91058 Erlangen, Germany |
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Abstract: | A two beam interferometer in the Martin-Puplett configuration is used to determine the complex dielectric constant at 300 GHz of teflon, TPX-plastics, SPECTRALON and paraffin waxes with melting temperatures of 48° C and 72° C, respectively. The design of the quasi-optical system leads to a constant beam diameter at the power detector independent of path delay and frequency. The power detector signal is recorded not only along one period but over about 50 periods. A spectrum estimation routine allows to determine more exactly amplitude and phase angle of the signal. A basic problem is noticed: imperfect detector and source match cause harmonic distortion of the power detector signal. The effects on processing the loss tangent and the invalidation are shown. Finally loss tangent and dielectric constant are determined indirectly by optimizing an equivalent microwave circuit using a commercial available microwave design system to take multiple reflections and losses in consideration. |
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Keywords: | Quasi-optics interferometer dielectric constant loss tangent TPX teflon SPECTRALON paraffin harmonic distortion complex overlap integral |
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