Abstract-This paper is aimed at studying the electromagnetic radiation pattern of a multipactor discharge occurring in a parallel-plate waveguide. The proposed method is based on the Fourier expansion of the multipactor current in terms of timeharmonic currents radiating in the parallel-plate region. Classical radiation theory combined with the frequency domain Green's function of the problem allows the calculation of both the electric and the magnetic radiated fields. A novel analytical formula for the total radiated power of each multipactor harmonic has been derived. This formula is suitable for predicting multipactor with the third-harmonic technique. The proposed formulation has been successfully tested with a particle-in-cell code.Index Terms-Microwave discharges, multipactor effect, parallel-plate waveguide, radiated power, third-harmonic detection technique.
Multipactoring is a non-linear phenomenon that appears in high-power microwave equipment operating under vacuum conditions and causes several undesirable effects. In this paper, a theoretical and experimental study of the RF spectrum radiated by a multipactor discharge, occurring within a realistic microwave component based on rectangular waveguides, is reported. The electromagnetic coupling of a multipactor current to the fundamental propagative mode of a uniform waveguide has been analysed in the context of the microwave network theory. The discharge produced under a single-carrier RF voltage regime has been approached as a shunt current source exciting such a mode in a transmission-line gap region. By means of a simple equivalent circuit, this model allows prediction of the harmonics generated by the discharge occurring in a realistic passive waveguide component. Power spectrum radiated by a third-order multipactor discharge has been measured in an E-plane silver-plated waveguide transformer, thus validating qualitatively the presented theory to simulate the noise generated by a single-carrier multipactor discharge.
A technique for the accurate computation of the electromagnetic fields radiated by a charged particle moving within a parallel-plate waveguide is presented. Based on a transformation of the time-varying current density of the particle into a time-harmonic current density, this technique allows the evaluation of the radiated electromagnetic fields both in the frequency and time domains, as well as in the near- and far-field regions. For this purpose, several accelerated versions of the parallel-plate Green's function in the frequency domain have been considered. The theory has been successfully applied to the multipactor discharge occurring within a two metal-plates region. The proposed formulation has been tested with a particle-in-cell code based on the finite-difference time-domain method, obtaining good agreement.
The objective of this paper is to study multipactor breakdown in coaxial to microstrip transitions. This kind of transitions generally exhibit a gap just below the central pin of the coaxial connector. This gap can create a region where the electric fields are relatively strong so that an electron path may be created that could potentially lead to a multipactor breakdown. In this paper, we study the multipactor modes which may be induced as a function of structural parameters, such as the substrate thickness and the gap length. In particular, it is found that two kinds of electron trajectory can be created leading to critical power levels that are even lower than those obtained with the parallel-plate model, generally used as a conservative model. In this context, we demonstrate that multipactor breakdown can happen for input power levels lower than 500 W. This, in turn, may become a critical issue for the use of classic coaxial to microstrip transitions in new high power satellites whenever payloads are manufactured using planar technology.Index Terms-coaxial to microstrip transition, high power applications, multipactor, power breakdown threshold.
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