Terahertz Antenna Technology and Verification: Herschel and Planck - A Review

One of the aspects that the space and terrestrial terahertz imaging systems have in common is that they require state-of-the-art technology to achieve their ambitious goals. Although technology is advancing at a rapid pace in this frequency range, the requirements for these systems go well beyond what is currently available such that there are also no standards or calibration reference sources in this field. This paper describes the novel procedures that have been implemented to assess the "in-orbit" RF performance of two European Space Agency (ESA) satellites using on-ground verification procedures. These consisted of using several different measurement techniques at both ambient and cryo-temperatures and software model correlation to be able to predict the final performance. ESA's Herschel and Planck observatories are used as an example to highlight some of the hurdles that had to be overcome for the challenging task of flight-performance verification at (sub)millimeter-wave frequencies. Significant advances have been achieved despite the lack of internationally agreed procedures and practices pushing terahertz reflector and instrument technologies to new limits. This is a review paper and has been written on behalf of the large scientific, engineering, and management teams that were involved over many years in the development, production, testing, and operation of the two spacecraft