Title of Paper: Low Power Silicon Germanium Electronics for
Microwave Radiometers
Principal Author: Mr. Terence Doiron
Abstract: Space-based radiometric observations of key
hydrological parameters (e.g., soil moisture) at the spatial and temporal
scales required in the post-2002 era face significant technological challenges.
These measurements are based on relatively low frequency thermal microwave
emission (at 1.4 GHz for soil moisture and salinity, 10 GHz and up for
precipitation, and 19 and 37 GHz for snow). The long wavelengths at these
frequencies coupled with the high spatial and radiometric resolutions required
by the various global hydrology communities necessitate the use of very large
apertures (e.g., >20 m at 1.4 GHz) and highly integrated stable RF
electronics on orbit. Radio-interferometric techniques such as Synthetic
Thinned Array Radiometry (STAR), using silicon germanium (SiGe) low power radio
frequency integrated circuits (RFIC), is the one of the most promising
technologies to enable very large non-rotating apertures in space. STAR
instruments are composed of arrays of small antenna/receiving elements that are
arranged so that the collecting area is smaller than an equivalent real
aperture system, allowing very high packing densities for launch. A 20-meter
aperture at L-band, for example, will require >1000 of these receiving
elements. SiGe RFIC's reduce power consumption enough to make an array like
this possible in the power-limited environment of space flight. An overview of
the state-of-the art will be given, and current work in the area of SiGe
radiometer development for soil moisture remote sensing will be discussed.