  Emerging high-frequency accelerator technology in the terahertz regime is
promising for the development of compact high-brightness accelerators and high
resolution-power beam diagnostics. One resounding challenge when scaling to
higher frequencies and to smaller structures is the proportional scaling of
tolerances which can hinder the overall performance of the structure.
Consequently, characterizing these structures is essential for nominal
operation. Here, we present a novel and simple self-calibration technique to
characterize the dispersion relation of integrated hollow THz-waveguides. The
developed model is verified in simulation by extracting dispersion
characteristics of a standard waveguide a priori known by theory. The extracted
phase velocity does not deviate from the true value by more than $ 9 \times
10^{-5} ~\%$. In experiments the method demonstrates its ability to measure
dispersion characteristics of non-standard waveguides embedded with their
couplers with an accuracy below $ \approx 0.5~\% $ and precision of $ \approx
0.05~\% $. Equipped with dielectric lining the metallic waveguides act as slow
wave structures, and the dispersion curves are compared without and with
dielectric. A phase synchronous mode, suitable for transverse deflection, is
found at $ 275~\text{GHz} $.
