  One terahertz (THz) waveguide based on 3D printed metallic photonic crystals
is experimentally and numerically demonstrated in 0.1-0.6 THz, which consists
of periodic metal rod arrays (MRAs). Results demonstrated that such waveguide
supports two waveguide modes such as fundamental and high-order TM-modes. The
high-order TM-mode shows high field confinement, and it is sensitive to the
geometry changes. By tuning the metal rod interspace, the spectral positions,
bandwidths, and transmittances of the high-frequency band can be optimized. The
investigation shows that a mode conversion between high-order modes occurs when
the MRAs symmetry is broken via change the air interspace.
