Title: Ka-Band Highly Constrained Deployable Antenna For RainCube
Presenting Author: Yahya Rahmat-Samii
Organization: UCLA
Co-Author(s): Joshua M. Kovitz, Vignesh Manohar, Eva Peral, Richard Hodges, Simone Tanelli, Jonathan Sauder, Gregg Freebury

Abstract:
Precipitation radars in Low-Earth-Orbit (LEO) provide vertically resolved profiles of rain and snow on a global scale. Nevertheless, observations available from LEO platforms are sparse in time, and cannot monitor the short time scale evolution of most atmospheric processes. CubeSats and SmallSats enable cost-effective deployments, where multiple copies of the same instrument achieve the goal for short time scale observations. As part of the RainCube (Radar in a CubeSat) initiative, we have demonstrated a Ka-band precipitation profiling radar instrument in a 2500 cm3 volume, excluding the antenna. As a next step, our goal is to design, fabricate and test a 1.0m deployable mesh reflector antenna with a gain greater than 45dB at 35.75GHz and a stowed volume less than 2.5-3.0U (10x10x25cm3). This provides a 5km radar footprint from 400km LEO orbit. A successful demonstration brings the complete radar instrument to TRL 5, paving the way for a flight demonstration of a future RainCube-follow-on science mission. We developed a novel offset mesh reflector system with a 1.0m aperture diameter to accomplish the RainCube science mission objectives. Developing this reflector involved a detailed characterization, design, prototyping and measurement of many important system components. Other detailed characterization of the overall antenna system has been performed including: mesh surface effects, realistic surface profile of the reflector antenna, interaction with the CubeSat bus, etc. A detailed efficiency table was generated to budget losses from all aspects of the reflector antenna system design. The reflector is a tensegrity design utilizing spiral wrapped ribs as the compression members and tensioned offset dual nets. The front net includes a reflective gold wire mesh. Cross ties from the back to front net provide the paraboloid shaping. The reflector achieves 100:1 compaction ratios and can be scaled to larger apertures. An engineering model has demonstrated packaging, deployment and surface repeatability through photogrammetry.