TITLE: Multipaction Effect and its Verification: Innovative Experiments and Techniques for Space Testing Activities
AUTHOR: Martín García-Patrón Mendiburu, Head of the RF Power Laboratory at INTA-Spain
SUPERVISORS: Isabel Montero Herrero (ICMM-CSIC) y Jorge Ruiz Cruz (UPM)
WHERE: Salón de Grados de Escuela Politécnica Superior de la Universidad Autónoma de Madrid.
WHEN: November, 14th – 10.00h.
ABSTRACT: Space-borne radio-frequency (RF) systems must cope with strict qualification procedures, including the evaluation of high-power handling capability of equipment for space applications. Whatever the electrical parameter being measured, the general rule of thumb throughout a verification process is to check whether the system can operate up to certain thresholds, which are defined to ensure total reliability for the mission throughout its operational lifetime. The RF breakdown or multipaction effect is a physical phenomenon affecting RF equipment on board spacecraft, which may result in the failure of the spatial mission. Thus, its qualification is mandatory for space systems.
Therefore, assessing and reducing the uncertainty linked to their measurement is an essential issue as it directly affects the accuracy of the qualification process, and hence the safety of the entire space mission. In this doctoral thesis, it is presented a novel comprehensive study of all variables affecting measurement uncertainty for high RF power test activities. The study is focused on space applications, and, in particular, multipactor testing, because they involve the largest number of variables. This is not a restrictive case; in fact, the outcome of this work is applicable to both for space and ground RF applications. As a conclusion, a complete uncertainty for RF high-power testing is obtained, and, where possible, mitigation actions have also been defined.
This doctoral thesis also introduces an advanced methodology for detecting multipactor, utilizing a novel testbed with loaded transmission lines. This method has the potential to significantly improve power efficiency in testing facilities, allowing for higher power levels in launch experiments. The results have shown an average gain of approximately 4.5 dB, in both in continuous wave and pulsed operation. Compared to other traditional power enhancing setups, the novel testbed is both much less expensive and simpler to manufacture and operate, with the ability to work in large bandwidths and, also, under variable environmental conditions. This thesis includes the design of the testbed, as well as the 3D modelling of the device under test with its rigorous experimental characterization. The simulated results of multipaction or multipactor, based on the experimental secondary electron emission yield of the microwave device, demonstrate good agreement with the multipactor threshold. XIX
Additionally, several enhancements related to the detection methods are proposed in this thesis order to improve the operation and outcome of the multipactor testing, supported by experimental results obtained for the L-band of GNSS. These tests have been performed with different coaxial and radiating devices at L-band, with over 1 kW of pulsed power and at temperatures ranging from -60 ºC to 90 ºC. An effective combination of various methods is presented. Furthermore, a novel complementary classification is proposed for the detection methods: primary and secondary, which will help underscore their distinct detection capabilities, while fully respecting existing regulations.
