Title: A Three-Frequency Spaceborne Radar for Precipitation and Cloud Measurement
Presenting Author: Gregory Sadowy
Organization: Jet Propulsion Laboratory

Abstract:
The National Resource Councils Earth Science Decadal Survey has identified the Aerosol/Climate/Ecosystems (ACE) Mission as a priority mission for NASA Earth science. The NRC recommended the inclusion of a cross-track scanning cloud radar with channels at 94 GHz and possibly 34 GHz for measurement of cloud droplet size, glaciation height, and cloud height. Several radar concepts have been proposed that meet some of the requirements of the proposed ACE mission but none have provided scanning capability at both 34 and 94 GHz due to the challenge of constructing scanning antennas at 94 GHz. Furthermore, there is great interest in adding Ku-band (13.4 GHz) to provide comprehensive measurements of clouds and precipitation over a very wide range of drop sizes. In this paper, we will describe a radar design that leverages new developments in microwave monolithic integrated circuits (MMICs) and microfabrication to enable an electronically-scanned radar with Ku-band (13.4 GHz), Ka-band (35 GHz) and W band (94-GHz) channels. This system uses a three-frequency linear active electronically-steered array (AESA) combined with a parabolic cylindrical reflector. This configuration provides a large aperture (3m x 5m) with electronic-steering but is much simpler than a two-dimensional AESA of similar size. Still, the W-band frequency requires element spacing of approximately 2.5 mm, presenting significant challenges for signal routing and incorporation of MMICs. By combining (Gallium Nitride) GaN MMIC technology with microfabricated radiators and interconnects and silicon-germanium (SiGe) beamforming MMICs, we are able to meet all the performance and packaging requirements of the linear array feed and enable simultaneous scanning of Ka-band and W-band radars over swath of up to 100 km. Acknowledgement: This work was performed at the Jet Propulsion Laboratory / California Institute of Technology under contract with the National Aeronautics and Space Administration.