Title: Submillimeter-Wave Sounders with Cryogenic Amplifier Based Receiver Front-End
Presenting Author: Goutam Chattopadhyay
Organization:NASA-JPL/Caltech

Abstract:
Radiometric and high-resolution spectroscopic studies at submillimeter-wave frequencies play a very important role in the Earth science, astrophysics, and planetary exploration. Its importance is underscored by the key role of heterodyne spectrometers in the ESA cornerstone Herschel Space Observatory, NASA's Microwave Limb Sounder (MLS) instrument on Earth Observation System (EOS) Aura satellite, and NASA's Microwave Instrument on the Rosetta Orbiter (MIRO). Spectroscopic measurements of O3, CO, CH2O, SO2, and NO2 (all has spectroscopic signatures in the submillimeter-wave band) in our own atmosphere is a priority for atmospheric scientists because the intercontinental transport of air pollution is most efficient in the troposphere. On planet Earth, clouds play a crucial role for the climate. They are also a major source of uncertainty in climate predictions. Particularly large uncertainties are associated with those clouds that consist partly or entirely of ice particles. Urgently needed global data on ice clouds, particularly on the so far poorly characterized 'essential climate variable' ice water path and on the characteristic cloud ice particle size. Therefore, low-noise, low-mass, low-power, and compact heterodyne receivers for spectroscopy and radiometry are highly desirable at these frequencies. Traditionally, cryogenically cooled superconductor-insulator-superconductor (SIS) and hot electron bolometer (HEB) mixers and Schottky diode-based receivers have been used for these applications as there were no amplifiers available at the submillimeter wavelengths. However, the availability of indium phosphide (InP) high electron mobility transistor (HEMT) based amplifiers and mixers would change all that. Low noise amplifiers with substantial gain at the front-end may reduce the noise contribution from mixers and IF amplifiers, and power amplification could significantly improve LO efficiencies. Moreover, HEMT based technology provides a great opportunity of high level of integration of various front-end components on a single chip. This is very attractive to future submillimeter instruments where multi-pixel receivers are of high priority. HEMT amplifiers and mixers cooled to 20 K provide a significant improvement in their noise performance compared to receivers at room temperature. Since SIS and HEB mixers require 4 K cooling, operation at 20 K offers a major simplification of system design and a significant risk reduction for the submillimeter-wave instruments. It is also important to note that the sensitivity to physical temperature is much less for amplifiers than SIS and HEB mixers. The amplifier-based receivers would still work at higher temperatures, though at a bit higher system noise, unlike the SIS and HEB receivers. In this presentation we will discuss the science drivers and progress in the cryogenic HEMT amplifier based heterodyne receivers at submillimeter wavelengths and their potential for future spectroscopic and radiometric instruments. This work has been carried out at the Jet Propulsion Laboratory, California Institute of Technology under a contract with National Aeronautics and Space Administration (NASA).