Transmission loss evaluation of 94GHz NRD guide toward THz-band dielectric integrated circuits

Tera-Hertz frequency bands have been attractive for novel application such as medical sensor, drugs detection, and so forth. The non-radiative dielectric waveguide (NRD guide) is a promise candidate for dielectric integrated circuits at THz frequencies due to its low transmission loss as well as high Q factor, however the transmission loss was not evaluated at higher frequency region more than 60 GHz. In this paper, the transmission loss of the NRD guide was firstly measured at 94GHz using a new evaluation method toward THz-band applications. Although the transmission loss is usually measured by compared with transmission losses of transmission lines with different lengths, it was difficult to use such manner because the characteristics of the transition between the W band NRD guide and the rectangular hollow metal waveguide or coaxial cable, connected into a network analyzer, was no so good due to fabrication accuracy. As another evaluation method of the transmission loss, the unloaded Q factor of the resonator made by related transmission line is usually measured because the transmission loss is inversely proportional to the waveguide Q factors. However we should pay attention to using this Q factor method because the waveguide Q factor is not usually identical with the unloaded Q factor. In this paper, this issue was clarified as an example of the coaxial cable resonator. Based on the consideration, new evaluation method of the transmission loss was proposed using a resonator with multimode resonance, and finally the low loss nature of the W band NRD guide was verified theoretically and experimentally.