DSpace Community:
http://hdl.handle.net/2117/657
20140822T06:03:11Z

New graphical processing technique for fast shadowing computation in PO surface integral
http://hdl.handle.net/2117/23208
Title: New graphical processing technique for fast shadowing computation in PO surface integral
Authors: Rius Casals, Juan Manuel; Carbó Meseguer, Alexis; Bjerkemo, Jakob; Úbeda Farré, Eduard; Heldring, Alexander; Mallorquí Franquet, Jordi Joan; Broquetas Ibars, Antoni
Abstract: This paper presents a new graphical processing technique for fast computation of PO surface integral. In contrast with the original graphical processing approach introduced by the authors in 1993, the new one combines a novel shadowing computation algorithm together with the conventional facetbased Gordon's formula, instead of the pixelbased Asvestas' approximation. The resulting hybrid approach needs more CPU power for very complex radar targets, but is free from the pixel discretization noise inherent to graphical processing. It has the same accuracy as conventional Physical Optics computation, but shadowed facets detection is more than 10 times faster than with the most efficient alternative algorithms of O(N log N) computational cost. © 2014 IEEE.
20140612T13:33:08Z

Unit cell for frequencytunable beamscanning reflectarrays
http://hdl.handle.net/2117/23126
Title: Unit cell for frequencytunable beamscanning reflectarrays
Authors: Rodrigo López, Daniel; Jofre Roca, Lluís; Perruisseau Carrier, Julien
Abstract: A reflectarray cell able to dynamically control the reflection phase at a variable frequency is presented. This capability enables beamscanning reflectarrays with frequency reconfigurability, which is a novel capability with applications in frequencyhopping systems, cognitive radio and satellite communications. The proposed cell combines switching and variable impedance loading techniques to maximize the frequency range over which a large dynamic phase range can be obtained. Analytical and numerical approaches are used to design and optimize the reflecting cell, which uses two semiconductor RFswitches and one varactor. An analog phase range above 270 degrees is achieved over a 50% frequency range, from 1.88 GHz to 3.07 GHz, with flat losses of 0.8 dB. For an analog phase range of 180 degrees the cell achieves a 1: 2 frequency reconfiguration range. It is also verified that the cell preserves good performance, and in particular low crosspolarization, under oblique incidence as well. A fully operational cell was fabricated and measured, demonstrating good agreement with simulation results.
20140602T15:12:00Z

Reconfigurable pixellayer isolator for frequencytunable onfrequency repeaters
http://hdl.handle.net/2117/22788
Title: Reconfigurable pixellayer isolator for frequencytunable onfrequency repeaters
Authors: Rodrigo López, Daniel; Díaz Tapia, Edgar; Jofre Roca, Lluís
Abstract: The maximum gain in onfrequency repeaters is limited by the isolation level between their two antennas due to closeloop stability conditions. In this letter, a novel pixellayer isolator for tunable onfrequency repeaters is presented. The scattered field of the reconfigurable pixel layer is used to dynamically minimize the mutual coupling between the antennas. Insight is given on the linkage between coupling and reflection coefficients, and a useful design procedure is proposed. The optimized pixel repeater can tune the operating frequency over a 40% range, with tunable instantaneous bandwidth (1%3%) and achieving a reliable isolation of 50 dB. The repeater has a radiation efficiency of 93% and a constant radiation pattern for the different configurations. Good agreement is obtained between simulations and measurements.
20140430T12:30:33Z

Optical signal processor for millimeterwave interferometric radiometry
http://hdl.handle.net/2117/22617
Title: Optical signal processor for millimeterwave interferometric radiometry
Authors: Nova Lavado, Enrique; Romeu Robert, Jordi; Capdevila Cascante, Santiago; Torres Torres, Francisco; Jofre Roca, Lluís
Abstract: In interferometric radiometry, the correlations between all pairs of radiofrequency (RF) receivers must be performed in order to obtain the scene visibilities. This represents a cumbersome problem in passive imaging where large signal bandwidths are typically required to achieve fastacquisition times and improve the radiometric resolution of the image. In this case, the signal distribution and the correlation at intermediate frequencies require very fast signal acquisition and processing subsystems. This paper presents a technique to perform correlations of millimeterwave signals produced by thermal emission in the optical domain as a solution to the aforementioned problem. The proposed method is based on converting the RF signal to the optical domain by modulating a laser beam with the RF signal using a {\rm LiNbO}3 phase modulator. This conversion allows to perform the signal distribution in the optical domain to obtain the combination of the receiver pairs. The correlation is obtained by measuring the power of the photocurrent produced by photodetecting the combined signal. The results of an experimental validation consisting on the acquisition of passive images using a linear interferometric array are presented to support the feasibility of the method. In addition, performance considerations of the system have been developed and validated by calculating the standard deviation of a visibility measurement.
20140411T12:01:45Z

A frequency reconfigurable cell for beamscanning reflectarrays
http://hdl.handle.net/2117/22467
Title: A frequency reconfigurable cell for beamscanning reflectarrays
Authors: Rodrigo López, Daniel; Jofre Roca, Lluís; Perruisseau Carrier, Julien
Abstract: Reflectarray antennas are excellent candidates for beamscanning applications thanks to their low loss, light and quasiplanar structure and ease of electronic control. However, reflectarray antennas suffer from narrower bandwidths than phased arrays and reflector solutions. In this context we present a frequencyreconfigurable cell for beamscanning reflectarrays, as a solution for applications that operate over a large frequency range but that require a narrower instantaneous bandwidth. The presented cell requires only two switches and one varactor to provide a reflection coefficient with continuously tunable phase over a 270° range which can be shifted over a 40% frequency range.
20140401T12:44:12Z

Enhancing RFID sensing capabilities: multiload backscattering
http://hdl.handle.net/2117/22268
Title: Enhancing RFID sensing capabilities: multiload backscattering
Authors: Capdevila Cascante, Santiago; Jofre Roca, Lluís; Romeu Robert, Jordi; Bolomey, Jean Charles
Abstract: This conference paper presents some experimental results using the concept of an multiloaded enhanced RFID tag capable of switching between different loads to fully determine the input impedance of the RFID tag antenna which can then be used for sensing applications.
20140318T16:36:19Z

Fast computation of an infinite, longitudinallyvarying and harmonic strip load acting on a viscoelastic halfspace
http://hdl.handle.net/2117/22264
Title: Fast computation of an infinite, longitudinallyvarying and harmonic strip load acting on a viscoelastic halfspace
Authors: Arcos Villamarín, Robert; Clot Razquin, Arnau; Romeu Garbí, Jordi; Martín Román, SaraRegina
Abstract: In the context of the developing of a numerically efficient model of railway induced ground vibrations, the problem of an infinite, longitudinallyvarying and harmonic strip load acting on the surface of a viscoelastic halfspace is reformulated in order to improve its numerical evaluation. On one hand, the static integrands of this specific problem are modified and introduced into the original integrands to reduce their spectral content at high wavenumbers, saving computational time needed for the numerical integration. On the other hand, a change of variable is applied on the displacements integral solutions resulting on frequency independent integrands. These formulae allow to obtain the displacement solution in the complete xyω field easier and, mostly, faster
20140318T16:01:01Z

LinkBudget: la missió Interestel·lar Voyager
http://hdl.handle.net/2117/21953
Title: LinkBudget: la missió Interestel·lar Voyager
Authors: Fabregas Canovas, Francisco Javier; Torres Torres, Francisco; Romeu Robert, Jordi
20140307T17:42:22Z

La gran lluita contra el mar (història del cable trasatlàntic)
http://hdl.handle.net/2117/21952
Title: La gran lluita contra el mar (història del cable trasatlàntic)
Authors: Fabregas Canovas, Francisco Javier; Torres Torres, Francisco; Romeu Robert, Jordi
20140307T17:35:46Z

Radiometric and spatial resolution constraints in millimetermave closerange passive screener systems
http://hdl.handle.net/2117/21939
Title: Radiometric and spatial resolution constraints in millimetermave closerange passive screener systems
Authors: Nova, Enrique; Romeu Robert, Jordi; Torres Torres, Francisco; Pablos Hernández, Miriam; Riera, Jose Manuel; Broquetas Ibars, Antoni; Jofre Roca, Lluís
Abstract: This paper presents a comparative study of the radiometric sensitivity and spatial resolution of three nearfield (NF) passive screener systems: real aperture, 1D synthetic aperture (SA), and 2D SA radiometers are compared. The analytical expressions for the radiometric resolution, the number of required antennas, and the number of pixels in the image are derived taking into account the distortion produced by the NF geometry at nonboresight directions where the distortion is dominant. Based on the theoretical results, a performance comparison among the studied systems is carried out to show the advantages and drawbacks when using the radiometers in a closerange screening application. Moreover, the screener performance in a closerange environment is discussed from the results obtained in the aforementioned comparison.
20140307T15:04:06Z

Iterative method of moments solution of problems involving electrically large and concave geometries
http://hdl.handle.net/2117/21799
Title: Iterative method of moments solution of problems involving electrically large and concave geometries
Authors: Heldring, Alexander; Rius Casals, Juan Manuel; Úbeda Farré, Eduard
Abstract: This paper presents a study of the scaling with frequency (computational complexity) of preconditioned iterative solution, using the Multilevel Fast Multipole Method, of a class of radiation and scattering problems that exhibits particularly slow convergence: problems involving electrically large, open and concave geometries. A comparison is presented between a wellknown state of the art preconditioner (ILU) and a recently introduced preconditioning method, the Multiscale Compressed Block Decomposition.
20140227T18:46:20Z

Silicon micromachined lens antenna for THz integrated heterodyne arrays
http://hdl.handle.net/2117/21678
Title: Silicon micromachined lens antenna for THz integrated heterodyne arrays
Authors: Llombart Juan, Nuria; Lee, Choonsup; Alonso del Pino, María; Chattopadhyay, Goutam; Jung Kubiak, Cecile; Jofre Roca, Lluís; Mehdi, Imran
Abstract: In this paper, we present the design, fabrication, and measurements of a lens THz antenna that can be fabricated using conventional photolithography and deep reactive etching processes. The antenna is composed of an extended hemispherical silicon lens and a leaky wave waveguide feed. Both elements are fabricated using silicon micromachining techniques, enabling the fabrication of future large antenna arrays with a parallel process. To show the concept, a first antenna prototype has been fabricated using this fabrication process. Measurements obtained at 550 GHz are presented.
20140220T16:40:37Z

Volumetric testing for a nonconforming discretization in method of moments of the electricfield surface integral equation
http://hdl.handle.net/2117/21179
Title: Volumetric testing for a nonconforming discretization in method of moments of the electricfield surface integral equation
Authors: Úbeda Farré, Eduard; Rius Casals, Juan Manuel; Heldring, Alexander
Abstract: Implementations in Method of Moments of the ElectricField Integral Equation (EFIE) are traditionally carried out with divergenceconforming sets, with normal continuity of the current across edges. This gives rise to awkward implementations around junctions in composite dielectric objects. Also, RWGimplementations of the CombinedField Integral Equation for sharpedged objects suffer from some loss of accuracy. In this paper, we present a new nonconforming discretization of the EFIE, with no continuity requirements across edges. In the generation of the impedance elements, we employ a volumetric testing over a set of tetrahedral elements attached to the meshed surface to let the hypersingular Kernel contributions numerically manageable. We show that the decomposition of the current into normallycontinuous and discontinuous contributions leads to enhanced accuracy in the computed RCS.
20140108T17:33:44Z

Antenna input impedance measurement using multiload MST
http://hdl.handle.net/2117/20324
Title: Antenna input impedance measurement using multiload MST
Authors: Romeu Robert, Jordi; Capdevila Cascante, Santiago; Bolomey, Jean Charles; Jofre Roca, Lluís
Abstract: This paper presents the practical use of modulated scatterer technique (MST) for the measurement of the antenna input impedance using a multiload automatic switching device, and it also includes the analysis of the measurement error as a function of the selected loads in the MST circuitry.
20131007T16:16:38Z

Preconditioning the Electric Field Integral Equation with the MSCBD method
http://hdl.handle.net/2117/20137
Title: Preconditioning the Electric Field Integral Equation with the MSCBD method
Authors: Heldring, Alexander; Úbeda Farré, Eduard; Rius Casals, Juan Manuel
Abstract: A novel preconditioning scheme for Method of Moment computations is proposed. It consists of an adapted version of an accelerated direct solution method, the Multiscale Compressed Block Decomposition. It is of particular interest for accelerating the convergence of the iterative solution of open problems that are electrically large and exhibit strong concavity.
For such problems, when solved with the Multilevel Fast Multipole Algorithm, the convergence is the main efficiency
bottleneck. The novel scheme is compared with the de facto
standard preconditioner ILU for a representative problem and shown to be considerably more efficient
20130913T14:36:51Z