The Effects of Water on the Noise-Temperature Contribution of Deep Space Network Microwave Feed Components

Large increases in the system operating noise temperature,Top, occur when water collects on Deep Space Network (DSN) antenna and microwave feed-system components. This article describes measurements made at 8.4 GHz (X-band) to assess the efiects of water on the critical antenna components. It also describes the measurement results of improvements in performance achieved by the use of techniques or procedures developed to reduce the efiects of water on critical components. I. Introduction Large increases in the system operating noise temperature, Top, occur when water collects on Deep Space Network (DSN) antenna and microwave feed-system components. Components that add the most noise when wet, or moist, include the feed-horn cover, the dichroic plate, and the perforated antenna panels used on the outer portion of the main re∞ector. The noise temperature increase caused by water on these components is often higher than the contribution of the rain in the atmosphere. The increase continues to afiect the system after the rain at the site has stopped. It can take hours for the water to evaporate. A series of measurements was performed at 8.4 GHz (X-band) to study this problem and to flnd techniques to reduce the degradation.