Active radome material

A material with a novel structure combines a material that is transmissive of radio waves, such as a widely used glass fiber-reinforced plastic (GFRP), with a radio wave shutter that can be controlled to reflect or transmit radio waves. When this new material is employed in a radome, the radome can be used as an active substitute for the reflector of a parabolic antenna. As a result, a parabolic antenna reflector is unnecessary; just a radome and a primary feed may operate as a parabolic antenna. This means radio waves can be emitted in any desired direction. Accordingly, structural components of a parabolic antenna, such as a main reflector and a supporting structure, can be omitted and the burden on a driving mechanism can be reduced. In the radio wave shutter, reverse voltages are applied to varactor diodes that are connected in series along equidistantly spaced parallel wires, switching the varactor reactances between short-circuit states and open-circuit states. In this manner, the radome is configured to be reflective in certain directions and to be transmissive in directions in which radio waves should be emitted. Because varactors are controlled by reverse biases, power consumption can be kept small. In addition, the bias directions of the varactors are alternated; consequently, the voltages of a whole set of varactors may be controlled with a voltage sufficient for control of a single varactor. Therefore, high voltage is not required even when a radio wave shutter with a large area is formed.