Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/654
Sat, 22 Oct 2016 03:56:00 GMT2016-10-22T03:56:00ZScattering and emissivity of rain events using boundary element method
http://hdl.handle.net/2117/89163
Scattering and emissivity of rain events using boundary element method
Duffo Ubeda, Núria; Vall-Llossera Ferran, Mercedes Magdalena; Camps Carmona, Adriano José; Corbella Sanahuja, Ignasi; Bara Temes, Francisco Javier; Torres Torres, Francisco
The theory of thermal microwave emission from a bounded medium containing random nonspherical discrete scatters is studied. It is known that for a medium of constant temperature the emissivities can be related to the bistatic scattering coefficients. Such relations hold for the four Stokes parameters. The down-welling polarimetric emission of the rain can be computed by means of the radiative transfer equation, which contains the four Stokes parameters. In order to apply the above equation to a realistic rain event, raindrop shapes have to be taken into account in the computation of the scattering amplitudes. Those shapes were obtained by Pruppacher and Pitter and are quite different from a sphere when the size increases. In this paper a procedure based in the Boundary Element Method (B.E.M.) is presented to compute the scattering amplitudes for each drop shape. Results are then averaged for all drop radii with a weighting function given by the Laws-Parson law. This law establishes the relationship between the drop size distribution and the rain intensity. A Gaussian distribution of the drop canting angle due to the wind has been also considered. Finally, some numerical results are presented. The scenario consists of a rain cell of 4 Km height at a uniform temperature, considering the wind effect. The values of the rain intensity and wind speed and direction have been obtained from realistic measurements recorded by a meteorological station located in campus. In order to validate these results, the four Stokes parameters obtained with these simulations were compared with the ones measured by a X-band polarimetric radiometer developed in our laboratory.
Mon, 25 Jul 2016 12:40:49 GMThttp://hdl.handle.net/2117/891632016-07-25T12:40:49ZDuffo Ubeda, NúriaVall-Llossera Ferran, Mercedes MagdalenaCamps Carmona, Adriano JoséCorbella Sanahuja, IgnasiBara Temes, Francisco JavierTorres Torres, FranciscoThe theory of thermal microwave emission from a bounded medium containing random nonspherical discrete scatters is studied. It is known that for a medium of constant temperature the emissivities can be related to the bistatic scattering coefficients. Such relations hold for the four Stokes parameters. The down-welling polarimetric emission of the rain can be computed by means of the radiative transfer equation, which contains the four Stokes parameters. In order to apply the above equation to a realistic rain event, raindrop shapes have to be taken into account in the computation of the scattering amplitudes. Those shapes were obtained by Pruppacher and Pitter and are quite different from a sphere when the size increases. In this paper a procedure based in the Boundary Element Method (B.E.M.) is presented to compute the scattering amplitudes for each drop shape. Results are then averaged for all drop radii with a weighting function given by the Laws-Parson law. This law establishes the relationship between the drop size distribution and the rain intensity. A Gaussian distribution of the drop canting angle due to the wind has been also considered. Finally, some numerical results are presented. The scenario consists of a rain cell of 4 Km height at a uniform temperature, considering the wind effect. The values of the rain intensity and wind speed and direction have been obtained from realistic measurements recorded by a meteorological station located in campus. In order to validate these results, the four Stokes parameters obtained with these simulations were compared with the ones measured by a X-band polarimetric radiometer developed in our laboratory.Modelo de transistores MESFET en régimen no lineal
http://hdl.handle.net/2117/88876
Modelo de transistores MESFET en régimen no lineal
Corbella Sanahuja, Ignasi; Legido, Jm; Pradell i Cara, Lluís
Tue, 19 Jul 2016 07:29:03 GMThttp://hdl.handle.net/2117/888762016-07-19T07:29:03ZCorbella Sanahuja, IgnasiLegido, JmPradell i Cara, LluísMethod of moments applied to the analysis of rough surfaces modelled by fractals
http://hdl.handle.net/2117/88555
Method of moments applied to the analysis of rough surfaces modelled by fractals
Vall-Llossera Ferran, Mercedes Magdalena; Duffo Ubeda, Núria; Camps Carmona, Adriano José; Corbella Sanahuja, Ignasi; Bara Temes, Francisco Javier; Torres Torres, Francisco
The Scattering and Emissivity of rough surfaces involve solutions to non-linear differential equations. Different approaches have been used in the literature to obtain approximate solutions under some hypothesis. For example Kirchhoff solution is used when the roughness is gentle on the scale of the wavelength.
In this paper the Method of Moments is used to analyze the scattering of arbitrary surfaces. No approximation about the scale roughness is necessary. Both Gaussian and Fractal surfaces have been modeled and compared. The introduction of fractal geometry provides a new tool to describe natural rough surfaces. A first inside to the properties and parameters that describe fractal geometry has been done in order to characterize them statistically. It has been demonstrated that geometrical and scattering characteristics are controlled by Fractal descriptors, including fractal dimension.
As a first step, our simulations refer to a (topological) one-dimensional (1-D) profile embedded in a two-dimensional (2-D) space. Physically, this corresponds to assume that both the electromagnetic field and the surface height are constant along a fixed direction. Extension to the case of a 2-D surface embedded in a three-dimensional (3-D) space is not conceptually difficult, but any simulation run requires a much longer computational time. Furthermore, scattering results obtained for 1-D profiles give also a good indication of scattering dependence on 2-D surface parameters.
Wed, 06 Jul 2016 13:26:55 GMThttp://hdl.handle.net/2117/885552016-07-06T13:26:55ZVall-Llossera Ferran, Mercedes MagdalenaDuffo Ubeda, NúriaCamps Carmona, Adriano JoséCorbella Sanahuja, IgnasiBara Temes, Francisco JavierTorres Torres, FranciscoThe Scattering and Emissivity of rough surfaces involve solutions to non-linear differential equations. Different approaches have been used in the literature to obtain approximate solutions under some hypothesis. For example Kirchhoff solution is used when the roughness is gentle on the scale of the wavelength.
In this paper the Method of Moments is used to analyze the scattering of arbitrary surfaces. No approximation about the scale roughness is necessary. Both Gaussian and Fractal surfaces have been modeled and compared. The introduction of fractal geometry provides a new tool to describe natural rough surfaces. A first inside to the properties and parameters that describe fractal geometry has been done in order to characterize them statistically. It has been demonstrated that geometrical and scattering characteristics are controlled by Fractal descriptors, including fractal dimension.
As a first step, our simulations refer to a (topological) one-dimensional (1-D) profile embedded in a two-dimensional (2-D) space. Physically, this corresponds to assume that both the electromagnetic field and the surface height are constant along a fixed direction. Extension to the case of a 2-D surface embedded in a three-dimensional (3-D) space is not conceptually difficult, but any simulation run requires a much longer computational time. Furthermore, scattering results obtained for 1-D profiles give also a good indication of scattering dependence on 2-D surface parameters.Evaluation of MIRAS space borne instrument performance: snap shot radiometric accuracy and its improvement by means of pixel averaging
http://hdl.handle.net/2117/88554
Evaluation of MIRAS space borne instrument performance: snap shot radiometric accuracy and its improvement by means of pixel averaging
Camps Carmona, Adriano José; Torres Torres, Francisco; Bara Temes, Francisco Javier; Corbella Sanahuja, Ignasi; Martín Neira, Manuel
Wed, 06 Jul 2016 13:19:37 GMThttp://hdl.handle.net/2117/885542016-07-06T13:19:37ZCamps Carmona, Adriano JoséTorres Torres, FranciscoBara Temes, Francisco JavierCorbella Sanahuja, IgnasiMartín Neira, ManuelCalibration procedures in 2-D large interferometric radiometers study applied to the MIRAS/SMOS instrument
http://hdl.handle.net/2117/88084
Calibration procedures in 2-D large interferometric radiometers study applied to the MIRAS/SMOS instrument
Torres Torres, Francisco; Camps Carmona, Adriano José; Corbella Sanahuja, Ignasi; Bará Temes, Francisco Javier; Vall-Llossera Ferran, Mercedes Magdalena; Duffo Ubeda, Núria
Thu, 16 Jun 2016 12:42:55 GMThttp://hdl.handle.net/2117/880842016-06-16T12:42:55ZTorres Torres, FranciscoCamps Carmona, Adriano JoséCorbella Sanahuja, IgnasiBará Temes, Francisco JavierVall-Llossera Ferran, Mercedes MagdalenaDuffo Ubeda, NúriaNew radiometers: SMOS-a dual pol L-band 2D aperture synthesis radiometer
http://hdl.handle.net/2117/88045
New radiometers: SMOS-a dual pol L-band 2D aperture synthesis radiometer
Kerr, Yann H.; Waldteufel, Philippe; Camps Carmona, Adriano José; Bará Temes, Francisco Javier; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Núria; Vall-Llossera Ferran, Mercedes Magdalena
Since the mid 1980s, aperture synthesis interferometric radiometers have received increased attention to monitor the Earth at low microwave frequencies (L-band), where there is a maximum sensitivity to soil moisture and ocean salinity. At L-band, classic radiometers require large steerable antennas to meet the spatial resolution requirements (30-50 km at most, 10-20 km wished for), from a low polar orbit platform. During the 1990s, technological studies were conducted by the ESA with an eye to design a 2D synthetic aperture L-Band radiometer (the Microwave Imaging Radiometer by Aperture Synthesis project: MIRAS). In 1998, in answer to a call for Earth Explorer Opportunity Missions issued by ESA, the Soil Moisture and Ocean Salinity Mission proposal (SMOS), based upon a radiometer concept derived from the MIRAS studies, was submitted, In 1999, following a selection procedure, ESA approved the SMOS mission for an extended phase. This paper summarize part of the work carried out on the interferometric radiometry concept and the optimization of the instrument configuration.
Wed, 15 Jun 2016 15:08:06 GMThttp://hdl.handle.net/2117/880452016-06-15T15:08:06ZKerr, Yann H.Waldteufel, PhilippeCamps Carmona, Adriano JoséBará Temes, Francisco JavierCorbella Sanahuja, IgnasiTorres Torres, FranciscoDuffo Ubeda, NúriaVall-Llossera Ferran, Mercedes MagdalenaSince the mid 1980s, aperture synthesis interferometric radiometers have received increased attention to monitor the Earth at low microwave frequencies (L-band), where there is a maximum sensitivity to soil moisture and ocean salinity. At L-band, classic radiometers require large steerable antennas to meet the spatial resolution requirements (30-50 km at most, 10-20 km wished for), from a low polar orbit platform. During the 1990s, technological studies were conducted by the ESA with an eye to design a 2D synthetic aperture L-Band radiometer (the Microwave Imaging Radiometer by Aperture Synthesis project: MIRAS). In 1998, in answer to a call for Earth Explorer Opportunity Missions issued by ESA, the Soil Moisture and Ocean Salinity Mission proposal (SMOS), based upon a radiometer concept derived from the MIRAS studies, was submitted, In 1999, following a selection procedure, ESA approved the SMOS mission for an extended phase. This paper summarize part of the work carried out on the interferometric radiometry concept and the optimization of the instrument configuration.Banco automatizado para la medida de parámetros S, de ruido y características DC de transistores en oblea
http://hdl.handle.net/2117/88024
Banco automatizado para la medida de parámetros S, de ruido y características DC de transistores en oblea
Pradell i Cara, Lluís; Purroy, Francesc; Subirats, M.; Ballester, A.; Torres Torres, Francisco; O'Callaghan Castellà, Juan Manuel; Corbella Sanahuja, Ignasi
The AMR Group has an automatized bench for the measurement of DC-characteristics, [S] parameters (45 MHz- 40 GHz) and noise parameters (2-26.5 GHz) of microwave on-wafer transistors. The hardware configuration is described, as well as the software applications developed. The measurement procedures are commented in detail, in particular those concerning the noise-parameters extraction techniques. Experimental results show the bench performances.
Wed, 15 Jun 2016 13:11:03 GMThttp://hdl.handle.net/2117/880242016-06-15T13:11:03ZPradell i Cara, LluísPurroy, FrancescSubirats, M.Ballester, A.Torres Torres, FranciscoO'Callaghan Castellà, Juan ManuelCorbella Sanahuja, IgnasiThe AMR Group has an automatized bench for the measurement of DC-characteristics, [S] parameters (45 MHz- 40 GHz) and noise parameters (2-26.5 GHz) of microwave on-wafer transistors. The hardware configuration is described, as well as the software applications developed. The measurement procedures are commented in detail, in particular those concerning the noise-parameters extraction techniques. Experimental results show the bench performances.Modelado físico de transistores MESFET y HEMT
http://hdl.handle.net/2117/87997
Modelado físico de transistores MESFET y HEMT
Lázaro, A; Pradell i Cara, Lluís; Torres Torres, Francisco
Models are developed for the de I-V curves and microwave small-signal parameters of the GaAs MESFET and HEMT. In the first step, the concept of a local small-signal equivalent circuit is introduced. In the second step, a formulation of the
Tue, 14 Jun 2016 15:58:42 GMThttp://hdl.handle.net/2117/879972016-06-14T15:58:42ZLázaro, APradell i Cara, LluísTorres Torres, FranciscoModels are developed for the de I-V curves and microwave small-signal parameters of the GaAs MESFET and HEMT. In the first step, the concept of a local small-signal equivalent circuit is introduced. In the second step, a formulation of theMezclador autooscilante con FET de AsGa en banda X. Consideraciones de diseño
http://hdl.handle.net/2117/87739
Mezclador autooscilante con FET de AsGa en banda X. Consideraciones de diseño
Corbella Sanahuja, Ignasi; de los Reyes, Elías; Elias Fusté, Antonio
Using a single active device as a non linear element both oscillating and mixing functions are acomplished. A method of design that uses a dielectric resonator as a frequency selective network is given.
Mon, 06 Jun 2016 14:51:30 GMThttp://hdl.handle.net/2117/877392016-06-06T14:51:30ZCorbella Sanahuja, Ignaside los Reyes, ElíasElias Fusté, AntonioUsing a single active device as a non linear element both oscillating and mixing functions are acomplished. A method of design that uses a dielectric resonator as a frequency selective network is given.A large signal nonlinear MODFET model from small signal S-parameters
http://hdl.handle.net/2117/87376
A large signal nonlinear MODFET model from small signal S-parameters
O'Callaghan Castellà, Juan Manuel; Beyer, Jb
A general technique for predicting the MODFET large signal performance has been developed. The technique is based entirely on experimental data (small signal S-parameters at different biased points) and therefore is independent of the structure of the FET. Software requirements include a program to fit an equivalent circuit to S parameter data; a simple least-square polynomial approximation program; and SPICE for nonlinear time-domain simulations. Hardware requirements are basically limited to a network analyzer to carry out the small-signal S parameter measurements. Measurements at 10 GHz confirm the validity of the model.
Thu, 26 May 2016 14:17:31 GMThttp://hdl.handle.net/2117/873762016-05-26T14:17:31ZO'Callaghan Castellà, Juan ManuelBeyer, JbA general technique for predicting the MODFET large signal performance has been developed. The technique is based entirely on experimental data (small signal S-parameters at different biased points) and therefore is independent of the structure of the FET. Software requirements include a program to fit an equivalent circuit to S parameter data; a simple least-square polynomial approximation program; and SPICE for nonlinear time-domain simulations. Hardware requirements are basically limited to a network analyzer to carry out the small-signal S parameter measurements. Measurements at 10 GHz confirm the validity of the model.