Active Noise Sources

Microwave radiometry is a well-known and extremely useful method to study the chemistry and dynamics of the Earth's atmosphere. For accurate long term measurements, the calibration and stability of the radiometer is of primary importance. Thus, the noise-injection radiometer (NIR), which greatly reduces drifts due to gain and noise figure variation in the receiver system, is highly preferred. The NIR architecture requires an electronic noise injection system consisting of a noise diode, a switch and a coupler to inject the noise into the signal waveguide. NIRs are now commonly used at lower frequency, but above about 100 GHz the noise diodes become much more difficult to achieve. Recently, VDI has measured significant ENR above 100 GHz from GaAs Schottky barrier diodes. This preliminary measurement with a non-optimized diode design, coupled with the fact that the VDI diodes have been used as mixers and multipliers to well over 1 THz, offers some promise that GaAs diodes can be used to achieve useful noise power levels to well above 100 GHz. Thus, the focus of this Phase 1 proposal is the investigation of noise diodes and noise sources based on GaAs Schottky diode technology for noise-injection radiometer systems above 100 GHz.