[Show abstract][Hide abstract] ABSTRACT: Abstract—In this work, ohmic losses present in arbitrarily
shaped waveguide-based structures are rigorously considered.
For such purpose, a software tool based on the perturbation of
the boundary conditions on the metallic walls of the waveguides
combined with an Integral-Equation (IE) analysis technique is
proposed. In order to obtain the modal chart of waveguides
with arbitrary cross-section, the Boundary Integral - Resonant
Mode Expansion (BI-RME) method is also employed. To show
the advantages of the proposed technique a computer-aided
design software package based on this modal analysis tool has
been applied to predict the propagation loss effects in complex
X Iberian Meeting on Computational Electromagnetics, Baeza (Spain); 05/2015
[Show abstract][Hide abstract] ABSTRACT: Multipactor is a hazardous vacuum discharge produced by secondary electron emission within microwave devices of particle accelerators and telecommunication satellites. This work analyzes the dynamics of the multipactor discharge within a coaxial line for the mono-energetic electron emission model taking into account the space charge effects. The steady-state is predicted by the proposed model and an analytical expression for the maximum number of electrons released by the discharge presented. This could help to link simulations to experiments and define a multipactor onset criterion.
Physics of Plasmas 03/2015; 22(3):033512. DOI:10.1063/1.4915130 · 2.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work focuses on Green's functions (GFs) of planar multilayered structures that may include an arbitrary number of conductive sheets. The spectral-domain GFs are derived through an automatized strategy based on the propagator matrix technique, while the spatial-domain counterparts are evaluated using a novel, efficient, and error controlled numerical method. All of the procedures remain general in order to accommodate for the tensorial nature of the surface conductivity of the sheets. Numerical examples of GFs for the mixed potential integral equation method are provided, validating the proposed algorithms.
IEEE Transactions on Microwave Theory and Techniques 01/2015; 63(1):20-29. DOI:10.1109/TMTT.2014.2375829 · 2.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper proposes an efficient modeling technique for transient electromagnetic analysis of a rectangular metallic enclosure with multiple apertures, using the surface equivalent principle (SEP) and integral equations. The SEP is used to replace the apertures by perfect electric conductor surfaces while introducing appropriate magnetic current densities on both sides of the apertures. As a result, the problem is reduced to two independent regions. The first region is outside the enclosure for which the free-space Green's function with the aid of image theory can be used to obtain the total fields in it. The second region is the inside of the enclosure and a closed-form expression is then derived for its time-domain dyadic Green's function. Finally, the governing time-domain magnetic field integral equation (TD-MFIE) for the structure is derived by enforcing the continuity of the tangential magnetic field at the apertures. To eliminate the late time instabilities in solving the resultant TD-MFIE, an unconditionally stable marching-on-in degree scheme is used. A new accelerated algorithm is proposed for the internal problem that relies on the separation of time and space in the cavity Green's function. The validity of the proposed method is confirmed by comparing the simulation results of several case studies with those obtained using the frequency-domain methods and CST microwave studio.
[Show abstract][Hide abstract] ABSTRACT: The accurate consideration of propagation losses in arbitrarily shaped waveguide-based structures is studied in this paper. For such a purpose, a software tool based on the perturbation of the boundary conditions on the waveguide metallic walls and on the boundary integral - resonant mode expansion method has been developed. To show the advantages of the proposed technique with respect to the classic power-loss method, the complex propagation wavenumbers of a double ridge and an elliptical waveguide have been first computed and compared with results of a commercial software based on the finite element technique. Next a circular, a sectorial shaped and a triangular shaped waveguide have been considered. Then, a computer-aided design software package based on this modal analysis tool has been applied to predict the propagation loss effects in complex waveguide structures, such as an evanescent mode ridge waveguide filter, a traditional dual mode filter with circular cavities and a twist component for K-band applications.
[Show abstract][Hide abstract] ABSTRACT: Prof. Julien Perruisseau-Carrier passed away on June 6, 2014, at the age of 34. Of Swiss and French nationalities, Julien was born in Lausanne, Switzerland, on October 30, 1979. In 1998, he started his university studies at the Ecole Polytechnique F¿¿d¿¿rale de Lausanne (EPFL), Switzerland, from where he got his Electrical Engineering MSc in 2003. The colleagues, mentors, and teachers who knew Julien during his undergraduate studies quickly recognized in him a very clever mind, combining outstanding human, scientific, and leadership qualities.
[Show abstract][Hide abstract] ABSTRACT: Cosmic microwave background (CMB) studies require observations in
several frequency bands simultaneously. For example, the detection of
clusters of remote galaxies can be performed by comparing CMB photon
fluxes at different frequencies, using the spectral deformation of the
Planck law, due to the Sunyaev-Zeldovich effect. We propose a
single pixel design to receive and detect simultaneously two frequency
bands of the (CMB), centered at 150 and 220 GHz. It is composed of a
bow-tie antenna, sensitive to the polarization of the incident
radiation, feeding a diplexer structure to separate the signal towards
two kinetic inductance resonators associated respectively with the
130-170 and 200-270 GHz frequency bands. The diplexer makes
use of 150 nm thick niobium-based superconducting transmission lines of
the coplanar strip-lines (CPS) type, for filtering and separation
purposes, deposited on a 30 μm thick quartz substrate. A new coplanar
matching structure, taking into account the kinetic inductance of the
superconducting films, is proposed and achieves a nearly perfect match
over more than 25% of each frequency band, along with a signal
separation ratio above 30 dB at both center frequencies. The size of a
single pixel is 0.9 mm × 1.2 mm.
[Show abstract][Hide abstract] ABSTRACT: This paper analyzes the microwave gas discharge within elliptical waveguides excited by the fundamental mode. The Rayleigh-Ritz method has been applied to solve the continuity equation. The eigenvalue problem defined by the breakdown condition has been solved and the effective diffusion length of the elliptical waveguide has been calculated, what is used to find the corona threshold. This paper extends the microwave breakdown model developed for circular waveguides and shows the better corona withstanding capabilities of elliptical waveguides. The corona breakdown electric field threshold obtained with the variational method has been compared with the one calculated with the Finite Elements Method, showing excellent agreement.
Physics of Plasmas 12/2013; 21(1). DOI:10.1063/1.4863458 · 2.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Starting from the separate codes BI-RME and ECLOUD or PyECLOUD, we are
developing a novel joint simulation tool, which models the combined effect of a
charged particle beam and of microwaves on an electron cloud. Possible
applications include the degradation of microwave transmission in
tele-communication satellites by electron clouds; the microwave-transmission
tecchniques being used in particle accelerators for the purpose of
electroncloud diagnostics; the microwave emission by the electron cloud itself
in the presence of a magnetic field; and the possible suppression of
electron-cloud formation in an accelerator by injecting microwaves of suitable
amplitude and frequency. A few early simulation results are presented.
[Show abstract][Hide abstract] ABSTRACT: The development of Green's Functions (GF) for structures including graphene layers is a keypoint for the design and analysis of future graphene-based antenna components. Their properties and computational challenges are presented and discussed within this contribution. Additionally, a novel computational technique that offers high evaluation speed and good accuracy for calculating such GFs is proposed and compared to reference methods.
2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
[Show abstract][Hide abstract] ABSTRACT: This paper describes a fast algorithm to calculate a
large number of roots of the cross-product of Bessel functions
and of their first derivatives. The method uses the Newton–Raphson
algorithm following a pyramidal scheme using the interlacing property
of the cross-product of Bessel functions. The algorithm shows
globally convergent behavior for a large range of values of the
argument and of the order of the Bessel functions. The roots
can be computed to any precision, limited only by the computer
implementation, and the convergence is attained in six iterations
per root in average, showing a much better performance than
previous works for the calculation of these roots.
IEEE Transactions on Antennas and Propagation 04/2013; 61(4):2180. DOI:10.1109/TAP.2012.2231929 · 2.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper demonstrates how an already developed finite element code for solving electromagnetic problems can be manipulated and simply extended so as to investigate complicated corona breakdowns. A safe criterion based on the eigenvalue analysis is used in order to predict the maximum electric field that a structure can withstand without suffering from a corona breakdown. Comparison with other semi-analytical techniques developed by researchers solely focusing on high power phenomena verifies the results of the developed algorithm.
Antennas and Propagation (EuCAP), 2013 7th European Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: This paper studies the effect of digitally modulated signals on the evolution of the multi-paction phenomenon. Multipactor is numerically analyzed in a parallel plates waveguide for a variety of common digital modulation techniques. Breakdown power thresholds and the temporal evolution of the particle population are computed. Results demonstrate that the phenomenon may be remarkably affected depending on the applied modulation scheme.
Antennas and Propagation (EuCAP), 2013 7th European Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: The accurate consideration of propagation losses effects in arbitrarily shaped waveguide based structures is studied in this paper. For such purpose, a software tool based on the perturbation of the boundary conditions on the metallic walls of the waveguides, combined with an Integral-Equation (IE) analysis technique, is proposed. In order to obtain the modal chart of waveguides with arbitrary cross-section, the Boundary Integral -Resonant Mode Expansion (BI-RME) method is also employed. To validate this theory, first we have successfully compared our results with numerical data of a lossy hollow elliptical waveguide. Next, the software package based on this novel modal analysis tool has been used to predict the propagation losses effects in a complex dual-mode filter, and in a twist component for K-band application.
XXVII Simposium Nacional Unión Científica Internacional de Radio, Elche (Spain); 09/2012
[Show abstract][Hide abstract] ABSTRACT: The accurate consideration of propagation losses effects in arbitrarily shaped waveg-uide based structures is studied in this paper. For such purpose, a software tool based on the perturbation of the boundary conditions on the metallic walls of the waveguides combined with an Integral-Equation (IE) analysis technique is proposed [1–3]. In order to obtain the modal chart of waveguides with arbitrary cross-section, the Boundary Integral-Resonant Mode Expansion (BI-RME) method is also employed . Following the proposed technique all the drawbacks of the classical power-loss method , such as the meaningless results at the cut-off frequency or the losses associated with the evanescent modes, are overcome and at each analysis frequency both attenuation α and phase constant β are computed taking positive real values (e −γz = e −αz e −jβz). Furthermore, from Figure 1 it can be clearly noticed that, due to the finite conductivity of the metallic walls, the change in the phase constant results in a small deviation of the filter response with respect to the ideal case. This shift, which can be critical for narrow-band applications, cannot be considered either by the classical power-loss method. Figure 1: Scattering parameters of a four-pole dual-mode filter with elliptical waveguide resonators in stan-dard WR-75 rectangular waveguides computed considering losses (σ = 0.3 * 10 7 S/m, red lines) and perfect conductor (black lines). The filter was originally proposed and designed in . ACKNOWLEDGMENT
PIERS 2012 Moscow, Progress In Electromagnetics Research Symposium; 08/2012
[Show abstract][Hide abstract] ABSTRACT: The saturation stage of a multipactor discharge is considered of interest, since it can guide towards a criterion to assess the multipactor onset. The electron cloud under multipactor regime within a parallel-plate waveguide is modeled by a thin continuous distribution of charge and the equations of motion are calculated taking into account the space charge effects. The saturation is identified by the interaction of the electron cloud with its image charge. The stability of the electron population growth is analyzed and two mechanisms of saturation to explain the steady-state multipactor for voltages near above the threshold onset are identified. The impact energy in the collision against the metal plates decreases during the electron population growth due to the attraction of the electron sheet on the image through the initial plate. When this growth remains stable till the impact energy reaches the first cross-over point, the electron surface density tends to a constant value. When the stability is broken before reaching the first cross-over point the surface charge density oscillates chaotically bounded within a certain range. In this case, an expression to calculate the maximum electron surface charge density is found whose predictions agree with the simulations when the voltage is not too high.
Physics of Plasmas 07/2012; 19(7):072304. DOI:10.1063/1.4736852 · 2.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
IEEE Transactions on Microwave Theory and Techniques 07/2012; 60(7):2093-2105. DOI:10.1109/TMTT.2012.2197021 · 2.94 Impact Factor