Title: A 4 Meter 180 to 680 GHz antenna for the Scanning Microwave Limb Sounder
Presenting Author: Richard E Cofield
Organization: Jet Propulsion Laboratory
Co-Author(s): Samuel C. Bradford (1) Nathaniel J. Livesey (1) Paul C. Stek (1) Eldon P. Kasl (2) 1. Jet Propulsion Laboratory, California Institute of Technology. 2. Vanguard Space Technologies, Inc.

Abstract:
The Scanning Microwave Limb Sounder (SMLS) is a space-borne heterodyne radiometer which will measure pressure, temperature and atmospheric constituents from thermal emission between 180 and 680 GHz. SMLS, planned for the Global Atmospheric Composition Mission of the NRC Decadal Survey, uses a novel toric Cassegrain antenna to perform both elevation and azimuth scanning. These provide better horizontal and temporal resolution and coverage than were possible with elevation-only scanning at the orbit spacings of two previous MLS satellite instruments. We report final results of a 2010 Instrument Incubator Program (IIP) to develop the SMLS antenna. This program continues a 2006 Small Business Innovative Research (SBIR) program whose phase II culminated in the fabrication and thermal stability testing of a composite demonstration model of the SMLS primary reflector. That reflector had the full 4m height and 1/3 the width planned for flight. The current project, titled "A deployable 4 Meter 180 to 680 GHz antenna for the Scanning Microwave Limb Sounder", contains 5 tasks: 1) detailed mathematical modeling of antenna patterns from which we simulated geophysical parameter retrievals in order to establish FOV performance requirements; 2) Correlation of finite-element model predictions with measurements made on the SBIR reflector. We also measured this reflector's deformations under more flight-like thermal gradients, using higher precision metrology techniques available in a large-aperture test facility at JPL; 3) fabrication of a full-width breadboard primary reflector followed by measurements and model correlation of its deformations during similar thermal gradient testing; 4) integration of the primary with other reflectors, and with residual front ends from a 2007 IIP, in a breadboard antenna; and finally 5) RF testing of the breadboard on a Near Field Range at JPL. This paper describes results in all 5 areas of the recently completed IIP.