David Raboso

Experimental Analysis of Passive Intermodulation at Waveguide Flange Bolted Connections

In this paper, the generation of passive intermodulation at rectangular waveguide flange bolted connections is investigated. An exhaustive series of tests has been performed in order to provide understanding on the physics lying behind such a phenomenon. In particular, the intermodulation response of the system has been studied as a function of the applied torque to the flange screws. It has been found that, in some situations, the intermodulation response differs from its expected behavior. An interpretation of such discrepancies is given, and practical guidelines for the design of waveguide flanges free of passive intermodulation are provided as well

Prediction of Multipactor Breakdown Thresholds in Coaxial Transmission Lines for Traveling, Standing, and Mixed Waves

In this paper, we present a numerical model for predicting the multipactor breakdown effect in coaxial transmission lines. To validate this method, we have first compared our results with numerical data from other theoretical studies and with experimental measurements. Then, we have investigated the multipactor phenomena in coaxial lines considering three kinds of RF signals: traveling, standing, and mixed waves. From this paper, we conclude that different breakdown thresholds are obtained for any of the considered RF excitations under high values of frequency times gap product. This effect is attributed to the existence of regions with zero (or very low levels) electric field amplitude in the propagation direction, where electrons are absorbed before the discharge occurs.

Prediction of Multipactor Breakdown for Multicarrier Applications: The Quasi-Stationary Method

A new prediction algorithm for multipactor breakdown determination in multicarrier signals is presented. This new algorithm assumes a quasi-stationary (QS) model based on the nonstationary theory for single-carrier signals. It determines the worst case, i.e., the combination of signal phases that yields the lowest breakdown level per carrier, using multipactor electron growth models. It considers the secondary emission yield properties of the material and the time-varying value of the multicarrier signal envelope.

High-Power Low-Pass Harmonic Filters With Higher-Order

In this paper, a method to design high-power low-pass harmonic filters in rectangular waveguide technology is proposed. The new filters consist of a collection of smooth E-plane bandstop elements along the propagation direction and a smooth variation of the filter width. This yields to a broad rejected band for the fundamental TE10 mode, together with higher-order ( TEn0 and non- TEn0) mode suppression. Two different examples with stringent requirements of the space industry are provided to demonstrate the capabilities of the new methodology. By means of high-power simulations and an extensive measurement campaign, it will be shown that the smoothness of the filter profile guarantees high-power operation even with small minimum mechanical gaps. Moreover, unlike classical techniques, our method is not restricted to filters with small gaps. Hence, filters with larger gaps (always fulfilling the demanding frequency specifications) are fabricated for even higher power-handling performance.

{\rm TE}_{{\rm n}0}

The main goal of this letter is the analysis of the multipactor effect within a coaxial waveguide structure when an external axial dc magnetic field is applied. We have designed and manufactured a coaxial waveguide sample that has been immersed within a long solenoid. Numerical and experimental results confirm a significant change in the RF breakdown behavior with regard to the case without the axial dc magnetic field, as well as the existence of single- and double-surface multipactor regimes. Good agreement between theory and experimental data has been found.

and Non-

Recently developed high-power radio-frequency discharges prediction tools have suggested that wedge-shaped waveguides are more resistent to multipactor effects than the equivalent rectangular waveguides. As a result of several research activities performed in cooperation with the European Space Research and Technology Centre of the European Space Agency, a filter structure based on wedge-shaped cavities is designed and manufactured, thus proving the previous theoretical results with a passive device widely used in the output (high-power) stage of satellite payloads. Experimental results are presented that confirm the developed prediction models. Finally, a discussion of advantages and potential limitations of this new filter topology is included, and further improvements for this waveguide topology are also suggested.

{\rm TE}_{{\rm n}0}

In this paper, the RF breakdown power threshold in arbitrary complex components based on rectangular waveguide technology is investigated. In particular, multipactor (in vacuum) and corona discharge (close to the Paschen curve minimum) are analyzed. The objective has been to predict the RF breakdown threshold for space applications. The simulation results have been validated with many experimental tests also performed within the frame of this work. The good agreement achieved shows the validity of the approach followed

Mode Suppression: Design Method and Multipactor Characterization

The main aim of this paper is the analysis of the multipactor effect within a coaxial waveguide structure excited by a phase-shift keying single-carrier digital modulated signal. To reach this aim, we developed in-house a software code which is able to predict the RF multipactor input voltage threshold. This code is based on the single effective electron model, and considers the space charge effect. Numerical simulations are performed for binary phase-shift keying and quadrature phase-shift keying modulated signals. In addition, an experiment is carried out to validate the proposed theoretical model. We have demonstrated that the digital modulation of the single-carrier signal may modify the RF voltage threshold in comparison to the nonmodulated scenario. Good agreement between theory and experimental data is found.

Multipactor in a Coaxial Line Under the Presence of an Axial DC Magnetic Field

Multipactor effect is a resonant avalanche of secondary electrons induced by an RF electromagnetic field, which endangers high-power payloads on satellites and particle accelerator structures. The main goal of this letter is to present a multimodal network characterization of a multipactor discharge occurring in a bounded waveguide region. This will allow to perform a rigorous analysis of a complete passive component considering the presence of a discharge. In order to verify the present formulation, we have measured the power spectrum generated by a multipactor event excited in a simple microwave circuit based on rectangular waveguides, which has been compared with the theoretical results, obtaining good agreement.

Study of the Multipactor Effect in Bandpass Wedge-Shaped Waveguide Filters

This work addresses the multipactor problem for multi-carrier operation inside rectangular waveguide-based devices, by means of numerical simulations of the electron trajectories and multiplication inside the structure. Accurate field calculation and considering space charge effects are mandatory. For this, a PIC-FDTD method has been employed. As a result, novel software has been implemented offering the possibility of predicting multipactor in multi-carrier systems for a wide variety of situations. Simulation results show that multipactor can occur even for short pulse durations if an inter-period charge accumulation is present.