  This paper reports on 3D-printed dielectric image lines for low-loss subTHz
applications between 140 and 220 GHz. In contrast to conventional dielectric
waveguides, a conductive copper substrate is used to achieve robust routing and
increased mechanical stability. For easy integration and characterization of
the dielectric image line within a waveguide measurement setup, a low-loss
mode-converter for flexible mounting is further designed. The characterized
overall system exhibits a broadband match of at least 20 dB over the entire
frequency band, with minimal losses of below 0.35 dB/cm. Furthermore,
multi-line characterization is performed for de-embedding the propagation
parameters {\alpha} and \b{eta} of both the dielectric transmission line and
the mode-converter, and finally, the influence of discontinuities such as
bending radii on the transmission behavior is evaluated. Due to the simplicity
of the underlying 3D-printing technology, the proposed concept features
extremely low cost and complexity, yet offers high flexibility and outperforms
the losses of conventional transmission lines.
