Capacitively-coupled resonators for terahertz planar-Goubau-line filters

TL;DR

This paper introduces a novel capacitively-loaded resonator filter design for planar Goubau lines at terahertz frequencies, enabling easy tuning and clear design procedures for arbitrary filter responses.

Contribution

It presents a new filter design method using periodically loaded capacitively coupled resonators on planar Goubau lines, with a validated fabrication and measurement at 0.9 THz.

Findings

Achieved a passband filter at 0.9 THz with 7 dB insertion loss

Demonstrated excellent agreement between measurements and simulations

Provided a simple, tunable filter design procedure

Abstract

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 {\lambda}/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-{\mu}m silicon-membrane substrate and compared measurement results between 0.5 THz and 1.1 THz to electromagnetic simulations, showing excellent agreement in both S11 and S21. 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.