| 摘要 |
Metal surfaces reflect microwave radiation. For a long time attempts have been made to coat reflective surfaces with various types of absorbent layer, with varying degrees of success. Particularly when it is a question of reflector antennas, the problem is complicated by the reflector having to reflect radiation at the frequency intended for the antenna. However, this invention solves this problem as it concerns a coating for metal surfaces which is selectively reflective for microwave radiation. It is built up of four layers, designated I to IV, viewed from the metal surface M, with a resistive foil r between the layers II and III. The layers III and IV are quarter-wave transformers, which adapt the surface resistance of the resistive foil r to the wave impedance of free space while the resistive foil r together with the layers I and II acts as a connection device which gives very great reflection around a predetermined reflection frequency but very low reflection at either side. The latter takes place by the resistive foil being short-circuited at the reflection frequency when the layer I acts as a resonator with resonance at this frequency and layer II has an electrical thickness of a quarter of the wavelength at this frequency. <IMAGE> |
