| 摘要 |
An antenna connected to a waveguide can be used for level measurements of a bulk material by measuring the reflection of microwave radiation radiated towards the surface of the bulk material. Condensate droplets forming on the antenna may produce higher modes and echoes in the microwave signal. The effect caused by droplets can be ameliorated by increasing the size of the antenna and the waveguide. To obtain a usable measurement signal, a compromise between reducing the interference from condensate droplets and optimizing the electrical characteristics has to be found. The invention is directed to a waveguide which is designed to propagate at a particular frequency only the fundamental mode, while the antenna itself is capable of supporting higher order modes. A taper which is a dimensioned so as to transmit only the fundamental mode of the microwave signal, is placed between the waveguide and the antenna. At the particular frequency, the taper causes the waveguide/antenna combination to operate in the fundamental mode in spite of the multimode characteristics of the antenna.
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