A Millimeter-Wavelength Dual-Polarization Doppler Radar for Cloud and Precipitation Studies

Abstract

A pulse Doppler radar system operating at 35 GHz and having full polarization (linear and circular) diversity capability is described. Separate antennas are used for the transmitter and the receiver because this design approach allows better overall radar sensitivity. The transmitter operates in the double-pulse mode to optimize the unambiguous Doppler velocity measurable with the system. A polarizer capable of handling about 200 kW of peak power when pressurized with sulfur hexafluoride (SF6) at 25 psi was developed for the transmitter. The radar system has built-in test sequences for checking the gain and alignment of the transmitter and receiver antennas. The dual-polarization intermediate frequency (IF) receiver has a total of six analog channels. A very flexible data acquisition and processing system has been developed to allow both coherent and incoherent dual-polarization measurements to be performed; the system includes a microprocessor-controlled pulse-pair processor and a minicomputer with associated peripherals. The radar was operated successfully in Montana during the 1981 Cooperative Convective Precipitation Experiment (CCOPE). Preliminary results on the observed variation of the circular depolarization ratio (CDR) are shown and related to the storm and cloud structure.