Title: Progress Towards a 183 GHz Humidity Sounding Radar Transceiver
Presenting Author: Jose V. Siles
Organization: Jet Propulsion Laboratory
Co-Author(s): Ken Cooper, Matthew Lebsock, Raquel Monje

Abstract:
Conventional microwave methods for humidity sounding in the upper troposphere are based on passive radiometric sounding of the 183 GHz water absorption band, but the accuracy of these measurements is limited by the presence of clouds. The resulting measurement uncertainty of relative humidity in ice-phase clouds leads to uncertainty in ice crystal growth rates, crystal fall velocities, and ultimately to the water cycle and global climate models. To overcome the cloud-cover limitation of passive radiometric sounding, an active differential absorption radar near 183 GHz can be used. In this method, radar signals scatter off of ice crystals inside clouds, and by measuring how the received signal power depends on the transmitted frequency over the water absorption line, the range-resolved relative humidity inside the cloud can be inferred. In this talk, we will describe progress toward building a compact, highly tunable, continuous-wave 183 GHz radar transceiver for making such measurements. We will focus on the design details and characterization of the 183 GHz radar transmitter. By using state-of-the-art GaN high power amplifiers and Schottky diode based frequency multipliers based on a novel on-chip power combining technique, we have been able to produce more than 500 mW in the 180 GHz range with a single multiplier device. The device exhibits state-of-the-art efficiency and the output power level sets a world record in this frequency range, almost one order of magnitude higher than previously reported single-chip multipliers in the same frequency range. By combining two of these devices we expect to break the 1 W barrier in one year. Our models indicate that, from an airborne platform, this new radar transceiver will enable relative humidity measurements inside ice clouds with few-percent measurement error and 250 m range resolution. 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).