The AFGL 10-cm Doppler weather radar was modified to enable the measurement of the differential reflectivity between horizontal and vertical polarizations in addition to the absolute reflectivity and the Doppler mean velocity and spectrum variance. Polarization switching is achieved by means of a diplexer, which separates at the antenna the transmitted signals of two frequencies, 2710 and 2760 MHz, and permits nearly simultaneous transmission of signals of orthogonal polarizations. Signals of these frequencies can be transmitted either with horizontal and vertical polarization, respectively, or with left and right circular, polarization, respectively. We describe the design and performance of the diplexer and the performance of the real-time data processor, present examples of meteorological measurements, and discuss future developments of the radar system. Keywords: Polarization diversity weather radar, Dual polarization radar, and Polarization switching.

Observations of severe convective storms in June 1987 by an 11-cm polarization diversity Doppler radar are described. Specific features include heavy rain, large hail, melting ice particles, lightning, and signal propagation effects. Of particular interest are the first measurements of the polarization differential reflectivity of lightning channels, which reveal the predominant orientations of the channels. Successive radar pulses were transmitted with alternating horizontal and vertical polarization by means of a high-power microwave switch to permit derivation of the differential reflectivity with a small standard error of estimate.

Design concepts and test results are summarized for a Doppler weather radar system suitable for precipitation measurements over a wide span of radial velocities and slant ranges, even in the presence of ground clutter. The radar transmits two uniform pulse trains at 2.710 and 2.760 GHz. Uniformly spaced pulses permit ground clutter cancellation of up to 50 dB to be achieved with a three-pole elliptic filter. Pulse spacing at one frequency is consistent with long-range coverage in reflectivity, while spacing of the second is consistent with a wide unambiguous velocity measurement span.

A radar receiver design is presented that yields logarithmic and coherent signals of two orthogonal polarizations derived from each of two S-band transmitted frequencies. The radar is to be used for measuring Doppler velocity and polarization parameters of meteorological backscatter. The receiver design goals include phase and amplitude balance of 5 degrees and 0.5 dB between signals of opposite polarization. The logarithmic amplifiers are specified to have linearity of + or - 0.5 dB over a dynamic range of 90 dB. High-power ferrite switching devices are to be used to alternate the polarization of transmitted signals between orthogonal states on a pulse-to-pulse basis and to permit reception of co-polarized and cross-polarized signal components. Keywords include: Doppler weather radar; Dual frequency radar; Dual polarization radar; Multi-channel radar receiver, and Polarization diversity radar.