The Global Precipitation Mission (GPM) has an immediate need for a matched-beam Ku-band/Ka-band antenna system that can be used as a component of a ground validation radar. Retrieval techniques based on both polarization and differential absorption at the two wavelengths can be used to provide additional insight into precipitation type and particle size distribution over a 10- to 40-km spatial domain. These measurements can then be compared with long range radar, such as the WSR-88D, and in situ sensors to provide a comprehensive dataset for evaluating and improving satellite-based precipitation estimates.
The development of this single aperture antenna design was motivated to fill a number of needs within NASA for a high-performance antenna system for conducting satellite ground validation and improving cloud and precipitation retrieval algorithms. The antenna system has a number of unique characteristics, including high gain (approximately 1° half power beam width) and matched antenna beam shapes. The antenna will support multiple frequencies used for cloud and precipitation sensing. The basic design will provide Ku-band (13.56 GHz) and Ka-band (35.56 GHz) channels that can support a variety of polarization- and absorption-based rain retrieval algorithms. The antenna will have extremely high cross-polarization isolation.
Multi-wavelength, multi-polarization radar measurements of the atmosphere can provide unique information for estimating the drop size distribution of precipitation and clouds and their phase. This design features single dual-wavelength, dual-polarized feed and aperture; ultra-low integrated cross-polarization isolation (less than –30 dB); very low sidelobes (peak sidelobe less than –25 dB); matched beams to below –20 dB and shapes to less than 2.3% between wavelengths, and less than 1% between polarizations; and high gain (1° beam width).
Radars such as D3R can be adapted to work in conjunction with the antenna to provide a complete precipitation sensing system for GPM and other NASA and non-NASA research programs.
This work was done by James Carswell of Remote Sensing Solutions, Inc. and Do-Hoon Kwon of the University of Massachusetts for Goddard Space Flight Center. GSC-16552-1