DSpace Collection:
http://hdl.handle.net/2117/658
20140728T18:53:18Z

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

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 Robert, 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

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

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

Stable discretization of the electricmagnetic field integral equation with the taylororthogonal basis functions
http://hdl.handle.net/2117/20089
Title: Stable discretization of the electricmagnetic field integral equation with the taylororthogonal basis functions
Authors: Úbeda Farré, Eduard; Tamayo Palau, José María; Rius Casals, Juan Manuel; Heldring, Alexander
Abstract: We present two new facetoriented discretizations in method of
moments (MoM) of the electricmagnetic
field integral equation (EMFIE)
with the recently proposed Taylororthogonal (TO) and divergenceTaylororthogonal (divTO) basis functions. These new schemes, which we call stable, unlike the recently published divergence TO discretization of the
EMFIE, which we call standard, result in impedance matrices with stable condition number in the very low frequency regime. More importantly, we show for sharpedged objects of moderately small dimensions that the
computed RCS with the stable EMFIE schemes show improved accuracy with respect to the standard EMFIE scheme. The computed RCS for the sharpedged objects tested becomes much closer to the RCS computed with the RWG discretization of the electricfield integral equation (EFIE), which is wellknown to provide good RCS accuracy in these cases. To provide best assessment on the relative performance of the several implementations, we have cancelled the main numerical sources of error in the RCS computation: (i) we implement the EMFIE so that the nonnull static quasisolenoidal
current does not contribute in the far
field computation; (ii) we compute with machineprecision the strongly singular Kernelcontributions in the impedance elements with the direct evaluation method.
20130903T10:33:27Z

Optically beamformed wideband array performance
http://hdl.handle.net/2117/20072
Title: Optically beamformed wideband array performance
Authors: Jofre Roca, Lluís; Stoltidou, Chysavgi; Blanch Boris, Sebastián; Mengual, Teresa; Vidal, Borja; Marti, Javier; Mckenzie, Iain; Cura, J.M. del
Abstract: Optical beamforming networks (OBFNs) are an interesting alternative for the design of wideband antenna arrays, mainly due to their low losses and weight, their high parallel processing capabilities and their electromagnetic immunity. Nevertheless, for a practical implementation, different technological and architectural tradeoffs need to be assessed. In this paper, the performance of an OBFN system is analytically studied and experimentally demonstrated. The study forms part of the optical beamforming network project, a multigroup research project supported by the European Space Agency (ESA). Differently from bulky freespace geometries, the architecture is based on fiberoptic delay lines for the time delays generation and on a spatial light modulator for the phase shifts generation. Experimental results for an Xband prototype are provided, showing beam steering accuracy, multibeam capability, amplitude distribution weighting and wideband operation.
Description: IEEE Antennas and Propagation Society
Research Awards for 2009
20130826T08:40:19Z

Accelerated direct solution of the methodofmoments linear system
http://hdl.handle.net/2117/19930
Title: Accelerated direct solution of the methodofmoments linear system
Authors: Heldring, Alexander; Tamayo, J.M.; Úbeda Farré, Eduard; Rius Casals, Juan Manuel
Abstract: This paper addresses the direct (noniterative) solution of the methodofmoments (MoM) linear system, accelerated through blockwise compression of the MoM impedance matrix. Efficient matrix block compression is achieved using the adaptive crossapproximation (ACA) algorithm and the truncated singular value decomposition (SVD) postcompression. Subsequently, a matrix decomposition is applied that preserves the compression and allows for fast solution by backsubstitution. Although not as fast as some iterative methods for very large problems, accelerated direct solution has several desirable features, including: few problemdependent parameters; fixed time solution avoiding convergence problems; and high efficiency for multiple excitation problems [e.g., monostatic radar cross section (RCS)]. Emphasis in this paper is on the multiscale compressed block decomposition (MSCBD) algorithm, introduced by Heldring , which is numerically compared to alternative fast direct methods. A new concise proof is given for the N2 computational complexity of the MSCBD. Some numerical results are presented, in particular, a monostatic RCS computation involving 1 043 577 unknowns and 1000 incident field directions, and an application of the MSCBD to the volume integral equation (VIE) for inhomogeneous dielectrics.
20130711T14:38:23Z

Sparsified adaptive cross approximation algorithm for accelerated method of moments computations
http://hdl.handle.net/2117/19928
Title: Sparsified adaptive cross approximation algorithm for accelerated method of moments computations
Authors: Heldring, Alexander; Tamayo Palau, José María; Simon, C.; Úbeda Farré, Eduard; Rius Casals, Juan Manuel
Abstract: This paper presents a modification of the adaptive cross approximation (ACA) algorithm for accelerated solution of the Method of Moments linear system for electrically large radiation and scattering problems. As with ACA, subblocks of the impedance matrix that represent the interaction between well separated subdomains are substituted by “compressed” approximations allowing for reduced storage and accelerated iterative solution. The modified algorithm approximates the original subblocks with products of sparse matrices, constructed with the aid of the ACA algorithm and of a subsampling of the original basis functions belonging to either subdomain. Because of the sampling, an additional error is introduced with respect to ACA, but this error is controllable. Just like ordinary ACA, sparsified ACA is kernelindependent and needs no problemspecific information, except for the topology of the basis functions. As a numerical example, RCS computations of the NASA almond are presented, showing an important gain in efficiency. Furthermore, the numerical experiment reveals a computational complexity close to N logN for sparsified ACA for a target electrical size of up to 50 wavelengths.
20130711T14:21:54Z

Fractalshaped antennas and their application to GSM 900/1800
http://hdl.handle.net/2117/19687
Title: Fractalshaped antennas and their application to GSM 900/1800
Authors: Puente Baliarda, Carles; Anguera Pros, Jaume; Romeu Robert, Jordi; Borja, C.; Navarro, Mónica; Soler, Jordi
20130626T17:05:35Z

Multiport small integrated antenna impedance matrix measurement by backscattering modulation
http://hdl.handle.net/2117/19568
Title: Multiport small integrated antenna impedance matrix measurement by backscattering modulation
Authors: Monsalve, Beatriz; Blanch Boris, Sebastián; Romeu Robert, Jordi
Abstract: A method to characterize small antennas in their actual operating conditions is presented. The proposed procedure is based on the radar cross section (RCS) measurement technique using backscattering modulation. A theoretical description of the measurement setup based on the signal flow graph representation is presented. The experimental validation includes the measurement of one and two port antennas, as well as the measurement of a small integrated antenna. Results show how the effect of the environment on the antenna impedance can be adequately measured with the proposed system.
20130618T12:19:09Z

Determination of the overlap factor and its enhancement for mediumsize tropospheric lidar systems: a raytracing approach
http://hdl.handle.net/2117/18353
Title: Determination of the overlap factor and its enhancement for mediumsize tropospheric lidar systems: a raytracing approach
Authors: Kumar, Dhiraj; Rocadenbosch Burillo, Francisco
Abstract: The problem of overlap factor (OVF) computation and its nearrange sensitivity for
mediumsize aperture (
f
∕
10
,
f
∕
11
) biaxial tropospheric lidar systems using raytracing sim
ulation software is presented. The method revisits both detector and fiber optics coupling alter
natives at the telescope focalplane along with the insertion of a field lens. A sensitivity analysis
is carried out as a function of laser divergence, field lens, and detector/fiber positions, detector
size, and the fiber
’
s core diameter and numerical aperture. The raytracing approach presented
here is straightforward and a comparatively much simpler solution than analyticalbased meth
ods. Parametric simulations are carried out to show that both approaches are coincident. Insertion
of a field lens proves to be an elegant and low sensitivity solution for OVF enhancement, par
ticularly, in the nearrange of the lidar
20130315T15:03:19Z

Study on aerosol properties over Madrid (Spain) by multiple instrumentation during SPALI10 lidar campaign
http://hdl.handle.net/2117/17647
Title: Study on aerosol properties over Madrid (Spain) by multiple instrumentation during SPALI10 lidar campaign
Authors: Molero, Francisco; Sicard, Michaël; Navas Guzmán, Francisco; Preissler, J.; Amodeo, Aldo; Freudenthaler, Volker; Fernández, J.A.; Tomás Martínez, Sergio; Granados, M.; Wagner, F.; Giunta, Aldo; Mattis, I.; Pujadas, Manuel; Comerón Tejero, Adolfo; Alados Arboledas, Lucas; Guerrero Rascado, Juan Luis; D'Amico, Giuseppe; Lange, Diego; Kumar, Dhiraj; Pappalardo, Gelsomina; Giner Nos, Joaquín José; Muñoz Porcar, Constantino; Rocadenbosch Burillo, Francisco
Abstract: Cuatro sistemas lidar Raman multifrecuencia (Madrid, Granada, Barcelona y Evora), tomaron
medidas simultáneamente a un sistema de referencia (Potenza) para verificar su funcionamiento
durante la campaña de intercomparación: SPALI10, (SPAin Lidar Intercomparison 2010) que tuvo
lugar en Madrid entre el 18 de Octubre y el 5 de Noviembre de 2010. Estos sistemas lidar Raman
multifrecuencia proporcionan propiedades ópticas de los aerosoles con resolución vertical. Los
perfiles suministrados por los sistemas lidar se compararon con información complementaria
proporcionada por otra instrumentación, tal como la distribución de tamaños de los aerosoles
medida de manera continua a nivel de superficie o la caracterización de la columna de aerosoles
20130212T09:56:33Z