Group III-Nitride LNAs for Microwave Radiometry

This phase I proposal addresses the need for microwave and millimeter wave Low Noise Amplifiers (LNAs) for remote sensing applications of the earth's atmosphere. In this work, IIIAN proposes using group III-nitride materials, specifically AlGaN/GaN HEMT structures, to fabricate LNAs for microwave radiometers operating from 165 GHz up to 270 GHz. The group III-nitrides have excellent physical properties for high frequency transistors with the added benefit that the high breakdown voltage of the material renders them less susceptible to failure due to spurious strong signals, eliminating the need for protective circuitry between the antenna and the LNA. Passive microwave radiometers used in the PATH and GACM missions are used to quantify levels of trace species in the atmosphere such as O3, CO, N2O, HNO3, ClO and SO2, and also to estimate water content, both gas phase and as aerosols. The instruments used for these measurements rely on microwave emission from the relevant species. Key to such low signal level measurements are front-end LNAs used to amplify the weak microwave emission signal from the antenna prior to the RF detection diode.

High frequency AlGaN/GaN transistors are of great interest to the Department of Defense for communications, radar, and microwave surveillance imaging. Telecommunication industries will find applications both for base stations and satellite communications. This technology can lead to significant improvements in radar (phased array radar) that is applicable to commercial aircraft and shipping. Other related radar applications can be found in collision avoidance for automobiles.

In addition to the applications for microwave radiometry discussed in this proposal, nitride LNAs will also find application within NASA for space communications and navigation. In the 2010 NASA SBIR solicitation, Topic O1.03 calls for ," Ka-band RF Devices and Components: Investigate novel RF (especially Ka-band) communications technologies and innovative approaches for high bandwidth, Ka-band devices and components (transceivers, modulators, highly efficient amplifiers, etc.). Approaches to significantly reducing size, mass, and power requirements for these components are paramount as well." The group III-nitride devices are especially valuable for microwave communications. The high breakdown voltage of nitrides can eliminate the need for limiters between the antenna and the LNA which can result in a significant improvement in signal-to-noise. Nitride devices also have very good ~60% DC-to-RF conversion efficiencies which is valuable for reducing power consumption of satellites and spacecraft.

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