A 94 GHz spaceborne cloud profiling radar antenna system

The CloudSat spacecraft, scheduled to launch in 2003, will carry a 94 GHz cloud profiling radar. The electrical design of its antenna system has been completed and is presented here. It consists of a quasi-optical transmission line that performs signal relaying and duplexing (using a Faraday rotator), and a collimating antenna that provides the required gain and spatial resolution. A shaped open Cassegrain collimating antenna is used because of its clear aperture, which allows for accurate electrical modeling, good performance, and significant reduction in implementation time and cost. The complete antenna system (horns to free space) has a worst case predicted gain of 63.1 dBi (59% efficiency) and exceeds the sidelobe envelope requirement of 50 dB below the peak gain at angles from boresight greater than 7 degrees.