Waveguide Flange Design and Characterization of Misalignment at Submillimeter Wavelengths

Recent technological developments are enabling components and instruments for realizing submillimeter (from 300 GHz to 3 THz) applications in a wide variety of fields, such as radio astronomy, communications, high resolution radars, imaging systems, and biomedical science. As interest in submillimeter applications have emerged, measurements of complex scattering parameters using vector network analyzers (VNAs) have become progressively extended into the terahertz frequency range. However, the measurement precision and accuracy of these instruments is limited by interconnection quality, repeatability, and the lack of traceable standards. In response to this need, the P1785 working group of the IEEE has been undertaking a study since 2008, aimed at providing recommendations for a new international standard waveguide interface for use above 110 GHz to at least 1 THz.
In this work, a new rectangular waveguide flange, the ring-centered flange, has been presented. The superior alignment, full backward compatibility, and simple design make it one of the most robust candidates being considered by IEEE P1785 group as a new international standard for waveguide interfaces for use above 110 GHz. In order to evaluate precision and accuracy of flanges at submillimeter-wave frequencies, several different techniques have been discussed and compared. Connection repeatability has been measured using VNA time-gating method and the load-separation method. The true reflection coefficient for a pair of flanges is characterized with a calibration technique insensitive to flange misalignment. Experimental results for various flange designs are examined and discussed in detail.