Theory of plasma antenna windowing

Summary form only given. This paper sets forth a detailed numerical analysis of the performance of a reconfigurable antenna comprised of a linear omni-directional antenna surrounded by a cylindrical shell of conducting plasma. The plasma shield consists of a series of tubes containing a gas, which upon electrification, forms a plasma (in practice fluorescent light bulbs are used). The plasma is highly conducting and acts as a reflector for radiation for frequencies below the plasma frequency. Thus when all of the tubes surrounding the antenna are electrified, the radiation is trapped inside. By leaving one or more of the tubes in a non-electrified state, apertures are formed in the plasma shield which allow radiation to escape. This is the essence of the plasma window based reconfigurable antenna. The apertures can be closed or opened rapidly (on micro-second time scales) simply by applying voltages. The goal of the theoretical analysis is the prediction of the far-field radiation pattern of the plasma window antenna (PWA) for a given configuration. In order to simplify the analysis we make the approximation that the length of the antenna and surrounding plasma tubes are irrelevant to the analysis. Physically we assume that the tubes are sufficiently long so that end effects and be ignored. In so doing, the problem becomes two-dimensional and as such allows for an exact solution. The problem is therefore posed as follows:(1) assume a wire (the antenna) is located at the origin and carries a sinusoidal current of some specified frequency and amplitude.(2) Next assume that the wire is surrounded by a collection of cylindrical conductors each of the same radius and distance from the origin.(3) Solve for the field distribution everywhere in space and thus obtain the radiation pattern.