Dispersion and attenuation characteristics of steady-state microwave plasma waveguide

Near the electrostatic plasma frequency, plasma exhibits a relative permittivity near zero, and this property has been used to make transient plasma waveguides at microwave and optical wavelengths by ionizing gases with pulsed electromagnetic fields and laser radiation. However, to our knowledge, no one has constructed a steady-state RF-excited plasma waveguide for the purpose of studying its microwave attenuation and dispersion characteristics. We report here the results of investigations at 2.8-3.7 GHz of a variable-length plasma waveguide up to 30 cm long in which the plasma's relative permittivity was as low as 0.2. De-embedded S-parameter power loss is as low as 4.6 dB and the dispersion is largely consistent with theory, although further work remains to be done.