Title: Using a High-Speed Plasma as a Conducting Channel to Enable a Novel Antenna Approach
Dr. Cohen, Advisor
Dr. Durgin, Chair
The objective of the proposed research is to test and improve the wideband capabilities of capacitive surface wave launchers for plasma antennas, and to model the propagation of nanosecond voltage pulses on a time-varying conductivity plasma column. Generation of VLF and LF waves is limited due to the fact that their wavelengths are kilometers long, and antennas built for their generation can only be a small fraction of a wavelength in size. These electrically short antennas are inefficient due to poor charge distribution caused by reflections at the antenna tip. A recently proposed concept involves an antenna fed with nanosecond pulses. The antenna will have time-varying conductivity to suppress the tip reflections. This time-domain matching technique offers greater efficiency and wider bandwidth than that of the currently employed frequency-domain matching techniques. This concept can be realized with semiconductors, but these cannot handle high power. A plasma is a conducting medium with electrical properties that can be varied rapidly while handling high current flow. Plasma antennas have been designed and tested in the past, but not with rapidly time-varying conductivity in mind. These are fed via capacitive coupling at a narrow range of frequencies. The pulses fed into this antenna will be nanosecond Gaussian pulses, which have a wide range of frequency content. Electromagnetic techniques will be employed to design a coupler, and its wideband capabilities will be determined experimentally. FDTDs have been made to study the effect of spatial conductivity variation on antenna pattern, often operating at a single frequency. A new FDTD will be developed to model pulse propagation on a plasma column with temporally and spatially varying conductivity, accounting for the dispersive nature of plasma. To our knowledge, an FDTD of this type has not yet been implemented.