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.

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VIPR (vapor in-cloud profiling radar) is a tunable G-band radar designed for humidity and cloud remote sensing. VIPR uses all-solid-state components and operates in a frequency-modulated continuous-wave (FMCW) radar mode, offering a transmit power of 200–300 mW. Its typical chirp bandwidth of 10 MHz over a center-frequency tuning span of 167–174.8 GHz results in a nominal range resolution of 15 m. The radar’s measured noise figure over the transmit band is between 7.4 and 10.4 dB, depending on its frequency and hardware configuration, and its calculated antenna gain is 58 dB. These parameters mean that with typical 1 ms chirp times, single-pulse cloud reflectivities as low as −26 dBZ are detectable with unity signal-to-noise at 5 km. Experimentally, radar returns from ice clouds above 10 km in height have been observed from the ground. VIPR’s absolute sensitivity was validated using a spherical metal target in the radar antenna’s far-field, and a G-band switch has been implemented in an RF calibration loop for periodic recalibration. The radar achieves high sensitivity with thermal noise limited detection both by virtue of its low-noise RF architecture and by using a quasioptical duplexing method that preserves ultrahigh transmit/receive isolation despite operation in an FMCW mode with a single primary antenna shared by the transmitter and receiver.@en

A 95 GHz Doppler radar prototype has been developed with a design guided by requirements for potential space flight missions to comets or icy moons of the outer planets in order to probe ice- and dust-filled jets and plumes. The radar operates in a frequency-modulated continuous-wave (FMCW) mode with a bandwidth, pulse repetition interval, and coherent integration time chosen to achieve better than 10 m range resolution, 0.1 m/s velocity resolution, 5.1 km maximum unambiguous range, and 46 m/s maximum unambiguous velocity span. With an ultra-high transmit/receive isolation exceeding 85 dB, the radar operates with thermal-noise-limited sensitivity even with 1 Watt of continuous transmit power and a 540 K noise-temperature receiver sharing a single, 15 cm diameter monostatic aperture. Experimental testing has verified the radar's range-Doppler remote sensing capabilities using a developing rain shower as a dynamic and distributed target.

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Increasingly, terahertz systems are being used for multi-pixel receivers for different applications from mapping the star-forming regions of galaxies to stand-off radar imaging. Since microstrip patch antennas are too lossy and corrugated horn antenna arrays are difficult to machine at terahertz frequencies, suitable antenna array designs have been one of the key area of research for this field. Moreover, silicon micromachined waveguide housing for front-end integration is becoming very popular for multi-pixel terahertz instruments. This paper describes multi-pixel terahertz instruments with silicon-micromachined front-end and discusses design challenges for integrating terahertz antennas with such systems.

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