Title: Schottky Diode Sources and Initial Testing of a 183 GHz FMCW Humidity-Sounding Cloud Radar Transceiver
Presenting Author: Ken Cooper
Organization: Jet Propulsion Laboratory, California Institute of Technology
Co-Author(s): Jose Siles, Raquel Monje, Robert Lin, Choonsup Lee, and Matt Lebsock

Abstract:
Under an ACT-13 effort, a frequency-modulated continuous-wave (FMCW) radar transceiver operating near the 183 GHz water absorption line is being developed for humidity sounding inside ice clouds, where passive radiometric remote sensing systems are relatively inaccurate. The radar transceiver’s source relies on Watt-level W-band GaN power amplifiers driving high-efficiency GaAs Schottky diode frequency-doublers, which as individual devices show conversion efficiencies as high as 30%. With power combining, hundreds of mW over 183-193 GHz are reached. A new geometry that stacks two diode doublers in a single waveguide cavity has recently been shown to be highly efficient and stable, achieving more than 200 mW at G-band without multi-waveguide power combining. Meanwhile, a 183 GHz radar test bench has been built to evaluate the performance of the high-isolation duplexing optics that would be needed for high-sensitivity measurements. To mitigate the propagation of noise from the transmitter directly to receiver in the monostatic FMCW radar, high-isolation feed optics and a phase-noise-cancellation RF architecture are employed. Measurements confirm that isolation levels of 90-100 dB are attainable, enabling the radar receiver to be thermal-noise limited. These results open a path for deploying a Watt-level FMCW radar at 183 GHz in an aircraft, enabling humidity sounding inside upper-tropospheric clouds with hundred-meter scale resolution from few-kilometer distances.