THz LO Sources for Heliophysics

This proposal is responsive to NASA SBIR Subtopic S14.02: In Situ Particles and Fields and Remote-Sensing-Enabling Technologies for Heliophysics Instruments; the bullet item “Technologies for precise radiometry at THz bands corresponding to upper atmosphere thermal emissions in the 1-5 THz range, particularly at 4.7 THz.” The primary goal of this SBIR effort is the development of local oscillator (LO) sources for NASA applications in the 1 – 5 THz frequency range. A prime example is the measurement of wind and temperature in the lower thermosphere and E-region ionosphere using terahertz limb sounding measurements of the OI thermal emissions at 2.06 THz or 4.75 THz. The primary Phase I goal is to demonstrate a compact and power efficient LO source that achieves the ~2.0 mW required to fully pump a subharmonic mixer operating at 2.06 THz*. This prototype system will use a power amplifier at 172 GHz, followed by a varactor doubler to 343 GHz, and a new varactor tripler to 1.03 THz. The PA will use four-way power combining, generating about 450 mW. The dissipated power is estimated to be 14W. The doubler will generate more than 100 mW. Thus, the new tripler must achieve an efficiency of about 2%. However, even higher efficiency is greatly desired, and efficiency as high as 4% is feasible. The Phase I effort will include the design of a more powerful and power efficient power amplifier MMIC. In Phase II the new amplifier MMIC will be fabricated and used to greatly improve the power efficiency of the 2.06 THz source. The source will also be integrated into a single waveguide housing, creating a very compact and power efficient module ideal for use on a SmallSat or CubeSat platform. The work will also be extended to other frequencies, and potentially to 4.7 THz. *D.L. Wu et al, “THz limb sounder for lower thermospheric wind, oxygen density, and temperature,” J. Geophysical Research: Space Physics, Vol. 121, Issue 7, June 2016.