This proposal is responsive to NASA SBIR Subtopic S1.03: Technologies for Passive Microwave Remote Sensing; specifically, the item titled “Correlating radiometer front‐ends and low 1/f‐noise detectors for 100–700GHz.” The focus is on low DC power radiometers for Small/CubeSats and the use of correlating receivers to improve system stability without the requirement for Dicke switching or noise-injection. Both direct detection (DD) and heterodyne (Het) correlating radiometers are of interest to NASA. The Het systems are technically preferred because of the excellent frequency resolution. However, the DD systems, with appropriate filters, can often achieve the necessary resolution with even lower size, weight and power requirements. Thus, the choice between Het and DD systems is mission specific. Through the Phase II effort, VDI will develop and demonstrate both types of correlating radiometers at frequencies of highest interest to NASA for atmospheric research and weather monitoring, specifically 118 and 183 GHz. At the end of Phase II, VDI will have demonstrated a total of four radiometer systems. At 118GHz, VDI will demonstrate a single channel DD correlating radiometer and a deliverable Het correlating radiometer with broad available IF bandwidth. At 183GHz, VDI will demonstrate two DD radiometer systems, a single channel prototype and a four-channel deliverable system. All systems are expected to achieve excellent performance and the four-channel DD and heterodyne systems will be sufficiently compact for use on Small/CubeSat platforms. Throughout the effort, VDI will focus on the development of basic building blocks for radiometers, including 90-degree hybrids, 180-degree phase shifters, narrow band filters and low 1/f noise detector diodes. Each of the components will be demonstrated at 118 and 183 GHz, and the prospects for scaling to higher frequency will be evaluated, with an emphasis on determining how to extend operation throughout the 100–700GHz range.
NASA applications include weather monitoring, atmospheric studies and investigations of planetary atmospheres. Correlating radiometers are known to improve performance over the more standard radiometers used in the present generation of Small/CubeSats such as TROPICS, TEMPEST-D, MiRaTa. However, they have not yet been implemented primarily due to the added complexity, which increases size, weight and power requirements. However, with increased system integration and advanced component design, these challenges can be alleviated.
TEMPEST-D and TROPICS are technology demonstrators for future systems of many CubeSats offering global observations. The goal is to replace the billion-dollar satellites with a more versatile and affordable technology that can be cost-effectively updated on a routine basis. These CubeSats must be produced by industry, and the proposed research will foster that goal.