Jordi Gil

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.

Enhanced prediction of multipaction breakdown in passive waveguide components including space charge effects

An enhanced prediction software tool of multipaction breakdown effect in passive waveguide components is proposed in this work. For such purpose, the space charge field effects are included employing a particle-in-cell code and finite differences in time domain integration techniques. As a result, the novel prediction tool models all the physical effects derived from multipactor such as reflected power, noise and/or harmonics, thus improving the accuracy of the threshold predictions and providing very valuable additional information of the phenomena. Such tool has been integrated within a full-wave modal analysis software for complex waveguide geometries (FEST3D), and the multipactor effect has been accurately predicted for two practical waveguide filter structures. The results provided by our tool have been successfully compared with data from standard multipactor susceptibility curves and experimental measurements.

Multipactor Analysis in Circular Waveguides

This paper mainly focuses on demonstrating that a multipactor discharge can occur within a circular waveguide operating under the fundamental TE 11 circular mode. Circular waveguides are widely used in the fabrication of many passive components, in order to implement resonant cavities as well as irises to connect adjacent guides for both application domains, particle accelerators and satellite subsystems applications. Thus, we present the first study of the multipactor effect in a circular waveguide, demonstrating its existence and providing a susceptibility chart for such a structure, which will be of great interest for the better understanding of multipactor physical phenomena.

An Analytical Model to Evaluate the Radiated Power Spectrum of a Multipactor Discharge in a Parallel-Plate Region

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 time-harmonic currents radiating in the parallel-plate region. Classical radiation theory combined with the frequency domain Greens 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.

A Systematic Design Procedure of Classical Dual-Mode Circular Waveguide Filters Using an Equivalent Distributed Model

In this paper, we propose a systematic procedure for the accurate design of classical dual-mode filters in circular waveguide technology. The design procedure is based on the previous synthesis of an intermediate distributed model, which links the standard lumped (or coupling matrix) elements circuit with the practical waveguide realization. We then show how the equivalent distributed model can be directly used to obtain the physical dimensions of these filter components (typically rectangular and cross-shaped irises, as well as tuning and coupling screws). The value of this paper lies in the fact that the proposed design strategy provides the final dimensions of these complex structures with unprecedented levels of accuracy and numerical efficiency, as it is shown through two dual-mode filter designs for narrowband applications, and measurements of a manufactured prototype.

Accurate Synthesis and Design of Wideband and Inhomogeneous Inductive Waveguide Filters

In this paper, a new synthesis and design methodology is presented and applied for the fast and accurate design of inductive rectangular waveguide filters. By using this technique, the dimensions of both homogeneous and inhomogeneous filters can be successfully synthesized for almost any practical filter bandwidth, return loss, or filter order. This novel technique is based on a prototype with additional degrees of freedom, able to match the response of the different filter components in a wideband frequency range, and an elaborated design procedure that fully exploits this flexibility. During the design procedure, the prototype and the real structure are continuously aligned in order to have the same electromagnetic behavior and jointly evolve to obtain an equiripple response. Once the final prototype has been synthesized, excellent filter dimensions can be extracted that, in most cases, do not require further optimization. Examples will show the outstanding performance of the proposed design technique in terms of versatility, accuracy, and CPU time.

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}

In this paper, a novel computer-aided design (CAD) tool of complex passive microwave devices in waveguide technology is proposed. Such a tool is based on a very efficient integral-equation analysis technique that provides a full-wave characterization of discontinuities between arbitrarily shaped waveguides defined by linear, circular, and/or elliptical arcs. For solving the modal analysis of such arbitrary waveguides, a modified version of the well-known boundary integral-resonant-mode expansion (BI-RME) method using the Nystro/spl uml/m approach, instead of the traditional Galerkin version of the method of moments, is proposed, thus providing significant savings on computational costs and implementation complexity. The novel theoretical aspects of this Nystro/spl uml/m approach, as well as their impact on the original BI-RME formulation, are fully described. Comparative benchmarks between this new technique and the classical BI-RME formulation using Galerkin are successfully presented for the full-wave analysis of frequently used irises (i.e., rectangular cross-shaped and circular multiridged) and for the CAD of complex waveguide components (such as rectangular waveguide filters considering mechanization effects and dual-mode circular waveguide filters with elliptical irises).

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The design of manifold-coupled multiplexers for wideband applications is considered in this paper. A systematic procedure, based on the sequential connection of filters to the manifold and subsequent adjustment of the interconnection elements, is presented. The filters are attached to the manifold without using stubs in order to minimize the effect of spurious resonances. The interconnection elements, the manifold, and the remaining filters are considered as the first inverter of each new filter that is attached. This technique has been applied to several practical examples. The obtained results validate the proposed design methodology.