Using a high-speed plasma as a conducting channel to enable a novel antenna approach

Abstract

A model for a proposed electrically short antenna using plasma with time-varying conductivity as the conducting medium was developed. The time-varying conductivity will eliminate tip reflections, allowing this conceptual antenna to radiate more efficiently at low frequencies than existing antennas. This technique offers greater efficiency and wider bandwidth than that of the currently employed frequency-domain matching techniques. First, we consider the pulse-amplitude-modulated (PAM) signals fed into the time-varying antenna. Their characteristics and limitations in generating radiation are examined. Next, we begin to develop a model for the time-varying antenna by examining nanosecond pulse propagation in two dimensions. The 2-D FDTD effort examines the morphology of nanosecond pulses as they travel on plasma antennas of varying electron density. The memory and time requirements to model low frequency signals became prohibitive in the 2-D model, so a 1-D model was developed. The 1-D model greatly reduces computational requirements, allowing for the simulation of PAM signals in the kHz frequency range. The error introduced by simplifications made in the 1-D model are mitigated using 2-D results for tuning. Finally, we consider feed methods for the time-varying antenna. Plasma antennas must be fed by indirect coupling due to sheath effects. The nanosecond feed pulses have wideband frequency content, so the wideband capabilities of existing coupling methods are examined. The work completed suggests that the proposed time-varying antenna can potentially be implemented and outperform existing electrically short antennas to a high degree if certain plasma density and switching requirements are met.