Interlaboratory mmWave and THz Quasi-Optical Characterization of Commercial Conventional and 3-D Printable Substrates

The growing interest in terahertz (THz) circuits and devices for next-generation communication and sensing technologies, combined with the increasing need for novel non-planar designs, necessitates accurate and broadband characterization of advanced dielectric substrates. This study comprehensively characterizes industrial-grade Radix™ dielectric resins alongside conventional substrates from 50 GHz to 2.5 THz, with measurements conducted at both the National Physical Laboratory and University of Birmingham using quasi-optical systems run by vector network analyzers (VNAs) and time-domain spectrometers (TDSs). Five different collimated beam measurement setups are used, each using in-house developed material extraction algorithms that incorporate the influence of surface roughness into the extraction process, extending proprietary VNA and TDS-based extraction algorithms. The comprehensive interlaboratory measurement campaign demonstrates strong consistency, validating the robustness and reliability of the methodologies. Detailed analysis confirms that the additional surface roughness introduced by 3D additive manufacturing of Radix™ resins has a negligible impact on electrical parameters.