Analysis of Plasma Antenna Options for Explosively-Driven Microwave Generators and Outline of Plasma Antenna Design

The development of portable microwave sources based upon explosively-driven generators requires the selection and design of an antenna that is well-suited to radiate the RF energy while meeting the very specific demands of the application. The magnetocumulative generator (MCG), which is often also called a flux-compression generator (FCG), the ferroelectric generator (FEG), and the ferromagnetic generator (FMG) convert the chemical energy of explosive materials into high-power electrical energy. Through power conditioning, the electrical energy converted from the explosive discharge can be radiated as microwaves. However, the extreme operating conditions for this application restrict the use of many conventional antennas and favor the use of some more unconventional plasma antenna systems. This paper provides an analysis of the viable plasma antenna options in which the plasma is actively radiating, as opposed to other designs in which plasma is used only to direct radiation from a metallic antenna. The four plasma antenna systems considered are based on laser-initiated ionization of atmosphere, confined plasma columns, silicon-based plasma, and an explosively-generated plasma jet. Each plasma antenna is analyzed on the device's operating principles, past experimental performances, and practical considerations when employed in an explosively-driven system. The explosively-generated plasma antenna is selected as the optimal plasma antenna for an explosively-driven mobile system. The explosively-generated plasma antenna has the favorable characteristics of having a common energy source with the explosive generators, being simple and durable in design to withstand the shock and thermal stresses of generator operation, relatively low mass and volume requirements, and high power capability. The significant radiating mechanisms of the explosively-generated plasma antenna and important plasma characteristics are outlined. The important considerations for the selection of explosive are detailed. Based upon the total plasma jet lifetime and the velocity of the combustion products in the jet, the minimal required mass of explosives is derived, completing the fundamental design parameters.