A combination 95 GHz radar and 270/560 GHz spectrometer is being built as a space instrument prototype for probing plumes and jet phenomena in the solar system. Dubbed GAISR (Gas And Ice Spectrometer/Radar), the instrument's radar will make simultaneous range/Doppler measurements of 0.1-10 mm sized ice and dust particles out to a few km in range, while its tunable spectrometer will detect the abundance and velocities of gaseous water and other volatiles. Here we describe how the radar and spectrometer share a back-end architecture, and present some innovative elements of GAISR's frequency-modulated continuous-wave (FMCW) radar, including high-isolation and low-loss transmit/receive duplexing and a phase-noise-canceling RF architecture.