Obstacle Based Concept for Compact Mode-Preserving Waveguide Transitions for High-Precision Radar Level Measurements

This contribution deals with a concept for the realization of compact mode-preserving waveguide transitions. For radar distance measurements, the cross-section of a single-moded waveguide is enlarged to an overmoded circular waveguide. In order to obtain a mostly monomode signal propagation within the waveguide, a parabolic waveguide transition in combination with a centrically mounted metallic obstacle is investigated. In comparison to the same transition without obstacle, a significant improvement in terms of the fundamental H₁₁ mode preservation can be achieved over a wide frequency range from 8.5 to 10.5 GHz. Radar measurements are presented that prove the capability of such a concept providing submillimeter distance accuracy without any need of modifying the applied conventional free-space signal processing algorithms.