Plasma Reflectors For Electronic Beam Steering In Radar

A phased array antenna for a radar has a significantly shorter response time than one that is mechanically steered. However for high frequency radars (X-Band and above), phased arrays are generally not used because of the difficulties with packing density as well as expense and availability of the phase shifting elements. We examine here, theoretically and experimentally, the use of plasma reflectors for electronically steered beams for higher frequency radar systems. The elements of such an electronically steered reflector include a means to designate the reflecting surface, a means to produce the main plasma, and a way to sweep away the discharge in time for the next radar pulse. Surface designation by magnetically guided glow discharges and laser/aromatic preionization have been studied. The main plasma can be produced by dc, rf or microwave ionization. The plasma can be swept away by the inclusion of an attaching species such as SF
₆
, whose attachment coefficient, being a strong function electron temperature, can be controlled by the power source. The powers to generate these plasma reflectors appear small enough that their use in a compact radar system is feasible. A plane plasma sheet designated by a magnetized glow discharge, followed by pulsed breakdown has been produced. Results of microwave transmission and reflection measurements will be presented. Implication for agile beam radars for military shipboard radars at X-Band, airborne radars at 94 GHz, and space based radars at 60 Ghz will be discussed.