Plasma antennas – a gentle introduction

Abstract – In this paper, we describe the theory, practical construction, and experiments of a plasma antenna to radiate a VHF signal. The primary goal is to provide an introduction to plasma antennas to undergraduate electrical engineering students and eliminate some of the mystery surrounding this antenna type. In our experiment, we implement a half-wave dipole whereby the conductor is a ionized gas or plasma that radiates a 120 MHz signal and is created using a 20 kHz source and mercury vapor gas contained in a florescent tube. We characterized the antenna's voltage standing wave ratio (VSWR), input impedance, radiation characteristics, bandwidth and then compare these to a similar half-wave metallic dipole antenna. Our learning objectives of this project are how to practically implement a plasma antenna using easily obtainable, low-cost components, and experience how ionized gas, acts like any other metallic antenna element, and thus can be an effective RF radiator. Furthermore, by doing the experiments, undergraduates will better understand dielectric breakdown, how dielectric breakdown in a gas forms a conductor, quantum mechanics associated with how color or spectrum of the discharge is a function of the elements in a gas. We consider the practical advantages and disadvantages of plasma antennas as compared to their metal counterparts which include how a plasma antenna when de-energized, is stealthy, how multiple plasma antennas can be configured for spatial multiplexing and how other plasma structures can be added to form reflectors, directors, etc.