Low power silicon germanium electronics for microwave radiometers

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 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 20meter 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.

Integrated silicon-germanium electronics for CubeSat-based radiometers

“…Although multiple publications [8][9][10] have concluded that SiGe technologies are well-suited for use in radiometers, they have mainly been used in laboratory demonstrations to date. The general paradigm in the radiometry community is to design one-of-a-kind radiometers with maximum performance, so III-V MMICs are typically used.…”