A surfaguide fed plasma antenna

The plasma antenna considered in this paper is a standard glass °uorescent tube; the gas inside the dielectric cylinder is ionized by application of a strong electric field at microwave frequency at one termination of the tube. The main task of this section is the description of the characteristics for a surfaguide device; this structure is able to excite a surface wave that propagated along the tube axis and provides the power required to ignite the plasma. This is not the only way that can be used to energize the plasma, but it was chosen because of some advantages that can be favourably considered in designing plasma antennas. The ¯rst advantage is related to the exciting frequency adopted as pump signal, fp = 2450 MHz. This frequency does not interfere with telecommunication systems, and at this frequency high power is available at low cost. Therefore the surfaguide is the most suitable device to propagate a power signal at this frequency, con¯ning its electromagnetic ¯eld in a closed structure. Moreover the surfaguide is simple to realize, and matching stubs can be easily inserted in the design. The surfaguide consists of two trunks of a standard waveguide WR340, two transitions , and a waveguide with a reduced height to increase the electric ¯eld strength. The guide is terminated by a moving short, whose length can be varied for matching. Along the central axis of the reduced height guide two holes allow to insert the glass tube. A commercial software was used to optimize the structure for plasma ignition, in the sense that all geometrical parameters were determined for the maximum ¯eld strength along the axis of the glass tube. The experimental results are very satisfactory and will be presented at the Conference