Dynamically scanned plasma reflector a rray for beam forming

Beam forming is vital to radar and mobile communication, particularly in WIMAX where the total power allowed is low (~1 W), the beam width requirement is less stringent compare d to radar, and the number of antennas needed is large. Traditionally beam forming is achieved by phase array, which requires expensive phase shifters. Previously we developed DC biased plasma antenna by coupling signal to a discharge tube filled with low pressure gas through capacitive coupling, and achieved positive gain at frequencies above the plasma characteristic frequency. Now we perform beam forming by positioning multiple discharge tubes in a circle to form a plasma reflector array. A monopole antenna is placed a t the circle center. By dynamically turning on and off part of the discharge tubes, we can reflect microwave signal emitted from the monopole antenna located at the center to a desired direction. For frequencies lower than the characteristic plasma frequency, the plasma screen behave like a metal reflector. Plasma reflector array can be turned on with in tens of mus to create a partially directed beam, thus rapid beam forming is possible. Radiation patterns of semicircular reflector are reported.