A System-on-Chip millimeter-wave radiometer for the space-based observation of solar flares

Millimeter-wave observations of the Sun have never been carried out from a space-based platform. This work presents a feasibility study for a full-disk 90 GHz radiometer designed to detect the radio emission of solar flares. Such a feasibility study has been carried-out in the frame of the ADAHELI (ADvanced Astronomy for HELIophysics) mission, whose phase A has been funded by the Italian Space Agency (ASI) and successfully completed in December 2008. First flare radiation mechanisms are introduced, showing that millimeter-waves are very sensitive probe of the highest energy electrons accelerated in solar flares. The science requirements and the system design are presented. The instrument architecture is based on a 25 cm dish antenna with f/D = 0.6 and a 45 deg offset of the feed. The receiver uses a direct amplification configuration with 8 dB noise figure, 50 dB gain and 100 ppm gain stability. The target of 3 sfu radiometric resolution for a 1 s integration time is achieved with a 2 GHz pre-detection bandwidth. In order to reduce size, mass and power consumption part of the millimeter-wave receiver can be implemented in a single silicon (Si) chip, i.e. exploiting the Sysyem-on-Chip (SoC) approach. As an example the 250 nm SiGe BiCMOS process from IHP has been adopted. A three-stages 90 GHz amplifier featuring 13 dB gain and 9.4 dB noise figure is proposed. This circuit can be used in the last stages of the amplification chain.