Abstract
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.
Highlights
While microwave interactions with plasma have been studied for many years, the use of a plasma as a waveguiding structure has so far been limited to transient experiments involving pulsed plasmas1 or laser-beam-induced plasmas2 in which the confining plasma was present for well under 1 μs
Recent activity in the area of metamaterials with relative permittivity near or below zero3 shows that these materials can have interesting and possibly useful properties, but relatively little work has been done to characterize a microwave plasma waveguide existing in a steady-state condition
We perform a theoretical analysis of the power transfer efficiency expected between the plasma-waveguide mode and the TE11 metallic waveguide mode used to excite the plasma waveguide
Summary
While microwave interactions with plasma have been studied for many years, the use of a plasma as a waveguiding structure has so far been limited to transient experiments involving pulsed plasmas or laser-beam-induced plasmas in which the confining plasma was present for well under 1 μs. Recent activity in the area of metamaterials with relative permittivity near or below zero shows that these materials can have interesting and possibly useful properties, but relatively little work has been done to characterize a microwave plasma waveguide existing in a steady-state condition. Besides the applications in metamaterials, some theories of ball lightning propose that ball lightning is a “radiation bubble” of plasma encapsulating a standing microwave field. These are sufficient reasons to attempt evaluation of a plasma waveguide with respect to basic characteristics such as phase shift per meter (dispersion) and loss. We perform a theoretical analysis of the power transfer efficiency expected between the plasma-waveguide mode and the TE11 metallic waveguide mode used to excite the plasma waveguide
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