Compact mode-matched excitation structures for radar distance measurements in overmoded circular waveguides

Gunnar Armbrecht, Eckhard Denicke, Ilona Rolfes, Nils Pohl, Thomas Musch, Burkhard Schiek

Advances in Radio Science, DOI:10.5194/ars-6-9-2008, Vol. 6, pp. 9-17, 2008


Abstract

This contribution deals with guided radar level measurements of liquid materials in large metal tubes, so-called stilling wells, bypass or still pipes. In the RF domain these tubes function as overmoded circular waveguides and mode-matched excitation structures like waveguide tapers are needed to avoid higher order waveguide modes. Especially for high-precision radar measurements the multimode propagation effects need to be minimized to achieve submillimeter accuracy. Therefore, a still pipe simulator is introduced with the purpose to fundamentally analyze the modal effects. Furthermore, a generalized design criterion is derived for the spurious mode suppression of compact circular waveguide transitions under the constraint of specified accuracy levels. According to the obtained results, a promising waveguide taper concept will finally be presented.

[Adv. Radio Science]

Tags: radar measurements, stilling wells