InP HEMT low-noise amplifier-based millimeter-wave radiometers from 90 to 180 GHz with internal calibration for remote sensing of atmospheric wet-path delay

The recent introduction of 35-nm gate length InP MMIC low-noise amplifiers has enabled significant advances in Earth remote sensing. These low-noise amplifiers achieve 2-dB and 3-dB noise figure at 180 GHz and 90 GHz, respectively, at room temperature. For Earth remote sensing using ocean surface altimeters, the design of new millimeter-wave radiometers is motivated by the fact that these missions include nadir-viewing, co-located 18–37 GHz microwave radiometers to measure wet-tropospheric path delay. However, due to the substantial area of the surface instantaneous fields of view (IFOV) at these frequencies, the accuracy of wet path retrievals begins to degrade at approximately 50 km from the coasts. In addition, conventional microwave radiometers do not provide wet-path delay over land. For a maximum antenna aperture size on Earth observation satellites, the addition of higher-frequency millimeter-wave (90–170 GHz) radiometers to current Jason-class radiometers is expected to improve retrievals of wet-tropospheric delay in coastal areas and to increase the potential for over-land retrievals.