We report on the architecture and performance of a highly sensitive 95 GHz Doppler radar instrument with 0.6Watt transmit power designed for low power consumption and small size. The radar's sensitivity is validated using a calibration target, and its remote sensing capabilities are demonstrated through the detection of clouds, rain, insects, and distant vehicles. The radar uses a frequency-modulated continuous-wave (FMCW) waveform, a single antenna with ultra-high-isolation quasioptical transmit/receive duplexing, an InP low-noise amplifier for receiving, and a GaN power amplifier for transmitting. A DC power consumption of 22 W for the RF and digital subsystems is achieved, in part, by a combination of a power-efficient waveform generation/detection and signal processing board and a CMOS-based system-on-chip W-band oscillator. Excluding power supplies and a computer interface, the radar system mass is under 6 kg, making it attractive for future deployment from platforms with constrained accommodation resources.