We present a multiline Thru-Reflect-Line (TRL) calibration standard for Planar Goubau Line (PGL) which allows setting the calibration plane along the PGL and thus removing the effect of the embedding structure. This opens the possibility of characterizing PGL-circuits. The presented structures were used for calibrating S-parameters measurements between 0.75 THz and 1.1 THz to characterize a 1 mm long and 10 µm wide PGL. The line shows negligible dispersion with an effective relative permittivity of 2.0 and an attenuation constant lower than 0.35 Np/mm (0.65 dB/λ).

In many cases, metallic planar waveguides are required in the design of integrated circuits. However, at terahertz frequencies, metallic planar waveguides present high losses, which make necessary the use more efficient waveguides to avoid power limitations. In this work, the attenuation constant of two popular planar waveguides for terahertz frequencies, Coplanar Waveguide (CPW) and Planar Goubau Line (PGL), are compared between 0.75 THz and 1.1 THz. To measure the PGL, its transition is deembeded using a multiline Thru-Reflect-Line calibration standard. Measurement results show a lower attenuation constant across the band for a PGL (0.13 mm -1 < α < 0.39 mm -1 ) than for a CPW (0.68 mm -1 < α < 0.99 mm -1 ) when an ultra-thin substrate is used suspended in air, which greatly reduces the substrate mode coupling from the PGL. These results put the PGL as a less lossy metallic planar waveguide for terahertz applications.

Terahertz spectroscopy is a promising tool for analyzing the picosecond dynamics of biomolecules, which is influenced by surrounding water molecules. However, water causes extreme losses to terahertz signals, preventing sensitive measurements at this frequency range. Here, we present sensitive on-chip terahertz spectroscopy of highly lossy aqueous solutions using a vector network analyzer, contact probes, and a coplanar waveguide with a 0.1 mm wide microfluidic channel. The complex permittivities of various deionized water/isopropyl alcohol concentration are extracted from a known reference measurement across the frequency range 750-1100 GHz and agrees well with literature data. The results prove the presented method as a highsensitive approach for on-chip terahertz spectroscopy of high-loss liquids, capable of resolving the permittivity of water.

Low-loss planar Goubau lines show promising potential for terahertz applications. However, a single-wire waveguide exhibits less design freedom than standard multi-conductor lines, which is a significant constraint for realizing standard components. Existing filters for planar Goubau line lack clear design procedures preventing the synthesis of an arbitrary filter response. In this work, we present a design for a bandpass/bandstop filter for planar Goubau line by periodically loading the line with capacitively coupled ∕2 resonators, which can be easily tuned by changing their electrical length. The filter's working principle is explained by a proposed transmission-line model. We designed and fabricated a passband filter centered at 0.9 THz on a 10-m silicon-membrane substrate and compared measurement results between 0.5 THz and 1.1 THz to electromagnetic simulations, showing excellent agreement in both 11 and 21 . The measured passband has an insertion loss of 7 dB and a 3-dB bandwidth of 31%. Overall, the proposed filter design has good performance while having a simple design procedure.

Low-loss planar Goubau lines show promising potential for terahertz applications. However, a single-wire waveguide exhibits less design freedom than standard multi-conductor lines, which is a significant constraint for realizing standard components. Existing filters for planar Goubau line lack clear design procedures preventing the synthesis of an arbitrary filter response. In this work, we present a design for a bandpass/bandstop filter for planar Goubau line by periodically loading the line with capacitively-coupled 𝜆∕2 resonators, which can be easily tuned by changing their electrical length. The filter's working principle is explained by a proposed transmission-line model. We designed and fabricated a passband filter centered at 0.9 THz on a 10-𝜇m silicon-membrane substrate and compared measurement results between 0.5 THz and 1.1 THz to electromagnetic simulations, showing excellent agreement in both 𝑆 11 and 𝑆 21 . The measured passband has an insertion loss of 7 dB and a 3-dB bandwidth of 31%. Overall, the proposed filter design has good performance while having a simple design procedure.