Articles de revista
http://hdl.handle.net/2117/653
Tue, 25 Oct 2016 07:05:14 GMT2016-10-25T07:05:14ZNodal sampling: a new image reconstruction algorithm for SMOS
http://hdl.handle.net/2117/90880
Nodal sampling: a new image reconstruction algorithm for SMOS
Gonzalez Gambau, Verónica; Turiel, Antonio; Olmedo Casal, Estrella; Martinez, Justino; Corbella Sanahuja, Ignasi; Camps Carmona, Adriano José
Soil moisture and ocean salinity (SMOS) brightness temperature (TB) images and calibrated visibilities are related by the so-called G -matrix. Due to the incomplete sampling at some spatial frequencies, sharp transitions in the TB scenes generate a Gibbs-like contamination ringing and spread sidelobes. In the current SMOS image reconstruction strategy, a Blackman window is applied to the Fourier components of the TBs to diminish the amplitude of artifacts such as ripples, as well as other Gibbs -like effects. In this paper, a novel image reconstruction algorithm focused on the reduction of Gibbs -like contamination in TB images is proposed. It is based on sampling the TB images at the nodal points, that is, at those points at which the oscillating interference causes the minimum distortion to the geophysical signal. Results show a significant reduction of ripples and sidelobes in strongly radio-frequency interference contaminated images. This technique has been thoroughly validated using snapshots over the ocean, by comparing TBs reconstructed in the standard way or using the nodal sampling (NS) with modeled TBs. Tests have revealed that the standard deviation of the difference between the measurement and the model is reduced around 1 K over clean and stable zones when using NS technique with respect to the SMOS image reconstruction baseline. The reduction is approximately 0.7 K when considering the global ocean. This represents a crucial improvement in TB quality, which will translate in an enhancement of the retrieved geophysical parameters, particularly the sea surface salinity.
Wed, 19 Oct 2016 14:42:51 GMThttp://hdl.handle.net/2117/908802016-10-19T14:42:51ZGonzalez Gambau, VerónicaTuriel, AntonioOlmedo Casal, EstrellaMartinez, JustinoCorbella Sanahuja, IgnasiCamps Carmona, Adriano JoséSoil moisture and ocean salinity (SMOS) brightness temperature (TB) images and calibrated visibilities are related by the so-called G -matrix. Due to the incomplete sampling at some spatial frequencies, sharp transitions in the TB scenes generate a Gibbs-like contamination ringing and spread sidelobes. In the current SMOS image reconstruction strategy, a Blackman window is applied to the Fourier components of the TBs to diminish the amplitude of artifacts such as ripples, as well as other Gibbs -like effects. In this paper, a novel image reconstruction algorithm focused on the reduction of Gibbs -like contamination in TB images is proposed. It is based on sampling the TB images at the nodal points, that is, at those points at which the oscillating interference causes the minimum distortion to the geophysical signal. Results show a significant reduction of ripples and sidelobes in strongly radio-frequency interference contaminated images. This technique has been thoroughly validated using snapshots over the ocean, by comparing TBs reconstructed in the standard way or using the nodal sampling (NS) with modeled TBs. Tests have revealed that the standard deviation of the difference between the measurement and the model is reduced around 1 K over clean and stable zones when using NS technique with respect to the SMOS image reconstruction baseline. The reduction is approximately 0.7 K when considering the global ocean. This represents a crucial improvement in TB quality, which will translate in an enhancement of the retrieved geophysical parameters, particularly the sea surface salinity.CI de microondas. Tecnologías
http://hdl.handle.net/2117/87861
CI de microondas. Tecnologías
Artal, Eduardo; Comerón Tejero, Adolfo; Corbella Sanahuja, Ignasi
Los circuitos integrados monolíticos de microondas presentan ventajas potenciales respecto de los circuitos híbridos habituales en cuanto a fiabilidad, reducido tamaño y peso, banda ancha y bajo coste. Se describe el estado actual y desarrollo en los últimos años, los aspectos tecnológicos de diseño y fabricación, las aplicaciones y los productos comerciales existentes.
Thu, 09 Jun 2016 16:03:58 GMThttp://hdl.handle.net/2117/878612016-06-09T16:03:58ZArtal, EduardoComerón Tejero, AdolfoCorbella Sanahuja, IgnasiLos circuitos integrados monolíticos de microondas presentan ventajas potenciales respecto de los circuitos híbridos habituales en cuanto a fiabilidad, reducido tamaño y peso, banda ancha y bajo coste. Se describe el estado actual y desarrollo en los últimos años, los aspectos tecnológicos de diseño y fabricación, las aplicaciones y los productos comerciales existentes.Full wave analysis of the image hybrid dielectric/HTS resonator
http://hdl.handle.net/2117/87021
Full wave analysis of the image hybrid dielectric/HTS resonator
Sans, C; O'Callaghan Castellà, Juan Manuel; Sancho, D; Pous Andrés, Rafael; Fontcuberta, J; Ji-Fuh, Liang; Guo-Chun, Liang
An analysis of the image hybrid dielectric/HTS resonator is carried out. A full-wave radial mode-matching method is used to obtain the electromagnetic fields inside the resonator for single TE01 and dual HE11 modes. The resonator power-handling capability is estimated from the field at the surface of the HTS film, assuming a certain value for the critical field of the HTS film
Thu, 12 May 2016 14:01:11 GMThttp://hdl.handle.net/2117/870212016-05-12T14:01:11ZSans, CO'Callaghan Castellà, Juan ManuelSancho, DPous Andrés, RafaelFontcuberta, JJi-Fuh, LiangGuo-Chun, LiangAn analysis of the image hybrid dielectric/HTS resonator is carried out. A full-wave radial mode-matching method is used to obtain the electromagnetic fields inside the resonator for single TE01 and dual HE11 modes. The resonator power-handling capability is estimated from the field at the surface of the HTS film, assuming a certain value for the critical field of the HTS filmOptimum carrier to signal power ratio for remote heterodyne DD-OFDM in PONs
http://hdl.handle.net/2117/86700
Optimum carrier to signal power ratio for remote heterodyne DD-OFDM in PONs
Cano Valadéz, Iván Nicolás; Santos Blanco, M. Concepción; Prat Gomà, Josep Joan
The carrier to signal power ratio (CSPR) in a directdetection
optical orthogonal frequency division multiplexing
(OFDM) system based on remote heterodyne scheme is optimized
in a passive optical network (PON) downlink. A numerical
investigation shows that nonlinearities in fiber have the effects
of increasing the optimum CSPR and making the system more
vulnerable to CSPR changes.
Fri, 06 May 2016 12:51:55 GMThttp://hdl.handle.net/2117/867002016-05-06T12:51:55ZCano Valadéz, Iván NicolásSantos Blanco, M. ConcepciónPrat Gomà, Josep JoanThe carrier to signal power ratio (CSPR) in a directdetection
optical orthogonal frequency division multiplexing
(OFDM) system based on remote heterodyne scheme is optimized
in a passive optical network (PON) downlink. A numerical
investigation shows that nonlinearities in fiber have the effects
of increasing the optimum CSPR and making the system more
vulnerable to CSPR changes.Closed-form expressions for the optimization of high speed electro-optical modulators
http://hdl.handle.net/2117/86698
Closed-form expressions for the optimization of high speed electro-optical modulators
Ibarra Fusté, Jose Antonio; Santos Blanco, M. Concepción
Compact closed-form mathematical expressions for the propagation parameters (characteristic impedance,
effective permittivity and attenuation) of coplanar waveguides (CPW) are presented. The
formulas take into account asymmetric structures, thick electrodes and two-layered substrates, and
thus are perfectly tailored for the optimization of electro-optical modulators. Excellent agreements,
within a range of frequencies up to 100 GHz, are found with full-wave finite elements results from
commercial software (HFSS) and with measures reported in the literature, for material and geometrical
CPW parameters of practical relevance for the design of electro-optical modulators
Fri, 06 May 2016 12:39:59 GMThttp://hdl.handle.net/2117/866982016-05-06T12:39:59ZIbarra Fusté, Jose AntonioSantos Blanco, M. ConcepciónCompact closed-form mathematical expressions for the propagation parameters (characteristic impedance,
effective permittivity and attenuation) of coplanar waveguides (CPW) are presented. The
formulas take into account asymmetric structures, thick electrodes and two-layered substrates, and
thus are perfectly tailored for the optimization of electro-optical modulators. Excellent agreements,
within a range of frequencies up to 100 GHz, are found with full-wave finite elements results from
commercial software (HFSS) and with measures reported in the literature, for material and geometrical
CPW parameters of practical relevance for the design of electro-optical modulatorsImpact of the local oscillator calibration rate on the SMOS measurements and retrieved salinities
http://hdl.handle.net/2117/86692
Impact of the local oscillator calibration rate on the SMOS measurements and retrieved salinities
Gabarró Prats, Carolina; Gonzalez Gambau, Verónica; Corbella Sanahuja, Ignasi; Torres Torres, Francisco
The local oscillators (LOs) of the Soil Moisture and
Ocean Salinity mission payload are used to shift the operating
frequency of the 72 receivers to an optimal intermediate frequency
needed for the signal processing. The LO temperature variations
produce phase errors in the visibility, which result in a blurring of
the reconstructed brightness temperature (Tb) image. At the end
of the commissioning phase, it was decided to calibrate the LO
every 10 min while waiting for a more in-depth analysis. During
short periods of time, the LOcalibration has been performed every
2 min to assess the impact of a higher calibration rate on the
quality of the data. In this paper, by means of a decimation experiment,
the relative errors of 6- and 10-min calibration interval
data sets are estimated using the 2 min as a reference. A noticeable
systematic across- and along-track pattern of amplitude ±0.3 K is
observed for Tb differences between 10 and 2 min, whereas this is
reduced between 6 and 2 min. A simulation experiment confirms
that the nature of such systematic pattern is due to the visibility
phase errors induced by the LO calibration rate. Such pattern is
propagated into the sea surface salinity (SSS) retrievals. Overall,
the SSS error increase (relative to the 2min SSS data) is about 0.39
and 0.14 psu for the 10- and 6-min data sets, respectively. This
paper shows that a LO calibration rate of at least 6 min would
noticeably improve the SSS retrievals.
Fri, 06 May 2016 12:19:48 GMThttp://hdl.handle.net/2117/866922016-05-06T12:19:48ZGabarró Prats, CarolinaGonzalez Gambau, VerónicaCorbella Sanahuja, IgnasiTorres Torres, FranciscoThe local oscillators (LOs) of the Soil Moisture and
Ocean Salinity mission payload are used to shift the operating
frequency of the 72 receivers to an optimal intermediate frequency
needed for the signal processing. The LO temperature variations
produce phase errors in the visibility, which result in a blurring of
the reconstructed brightness temperature (Tb) image. At the end
of the commissioning phase, it was decided to calibrate the LO
every 10 min while waiting for a more in-depth analysis. During
short periods of time, the LOcalibration has been performed every
2 min to assess the impact of a higher calibration rate on the
quality of the data. In this paper, by means of a decimation experiment,
the relative errors of 6- and 10-min calibration interval
data sets are estimated using the 2 min as a reference. A noticeable
systematic across- and along-track pattern of amplitude ±0.3 K is
observed for Tb differences between 10 and 2 min, whereas this is
reduced between 6 and 2 min. A simulation experiment confirms
that the nature of such systematic pattern is due to the visibility
phase errors induced by the LO calibration rate. Such pattern is
propagated into the sea surface salinity (SSS) retrievals. Overall,
the SSS error increase (relative to the 2min SSS data) is about 0.39
and 0.14 psu for the 10- and 6-min data sets, respectively. This
paper shows that a LO calibration rate of at least 6 min would
noticeably improve the SSS retrievals.Superconducting Multiplexer Filter Bank for a Frequency-Selective Power Limiter
http://hdl.handle.net/2117/86589
Superconducting Multiplexer Filter Bank for a Frequency-Selective Power Limiter
Padilla Díaz, Alberto; Mateu Mateu, Jordi; Orloff, Nathan D.; O'Callaghan Castellà, Juan Manuel; Collado Gómez, Juan Carlos; Booth, James C.; Rocas Cantenys, Eduard
This work proposes a superconducting multiplexer filter bank configuration to be used as a frequency-selective power limiter. The proposed configuration limits narrowband high-power signals within a single frequency band without degrading the signal performance in the rest of the frequency bands. To accomplish this, we need to calculate the limiting power of superconducting filters implemented by means of half-wavelength transmission line resonators. The limiting power is obtained as a function of the resonator geometry, filter bandwidth, and filter order. Practical issues occurring in superconducting filters operating at high power, such as the reduction of the quality factors and de-tuning, are also analyzed and shown to not adversely affect the overall multiplexer power limiter performance.
Wed, 04 May 2016 14:54:11 GMThttp://hdl.handle.net/2117/865892016-05-04T14:54:11ZPadilla Díaz, AlbertoMateu Mateu, JordiOrloff, Nathan D.O'Callaghan Castellà, Juan ManuelCollado Gómez, Juan CarlosBooth, James C.Rocas Cantenys, EduardThis work proposes a superconducting multiplexer filter bank configuration to be used as a frequency-selective power limiter. The proposed configuration limits narrowband high-power signals within a single frequency band without degrading the signal performance in the rest of the frequency bands. To accomplish this, we need to calculate the limiting power of superconducting filters implemented by means of half-wavelength transmission line resonators. The limiting power is obtained as a function of the resonator geometry, filter bandwidth, and filter order. Practical issues occurring in superconducting filters operating at high power, such as the reduction of the quality factors and de-tuning, are also analyzed and shown to not adversely affect the overall multiplexer power limiter performance.A General approach for the calculation of intermodulation distortion in cavities with superconducting endplates
http://hdl.handle.net/2117/86367
A General approach for the calculation of intermodulation distortion in cavities with superconducting endplates
Mateu Mateu, Jordi; Collado Gómez, Juan Carlos; Menéndez, O; O'Callaghan Castellà, Juan Manuel
We report on a general procedure to calculate intermodulation distortion in cavities with superconducting endplates that is applicable to the dielectric-loaded cavities currently used for measurement of surface resistance in high-temperature superconductors. The procedure would enable the use such cavities for intermodulation characterization of unpatterned superconducting films, and would remove the uncertainty of measuring intermodulation on patterned devices, in which the effect of patterning damage might influence the outcome of the measurements. We have verified the calculation method by combining superconducting and copper endplates in a rutile-loaded cavity
Thu, 28 Apr 2016 12:02:43 GMThttp://hdl.handle.net/2117/863672016-04-28T12:02:43ZMateu Mateu, JordiCollado Gómez, Juan CarlosMenéndez, OO'Callaghan Castellà, Juan ManuelWe report on a general procedure to calculate intermodulation distortion in cavities with superconducting endplates that is applicable to the dielectric-loaded cavities currently used for measurement of surface resistance in high-temperature superconductors. The procedure would enable the use such cavities for intermodulation characterization of unpatterned superconducting films, and would remove the uncertainty of measuring intermodulation on patterned devices, in which the effect of patterning damage might influence the outcome of the measurements. We have verified the calculation method by combining superconducting and copper endplates in a rutile-loaded cavityReduced microwave losses YBa2Cu3O7-d thin films on electro-optic LiNbO3 crystals
http://hdl.handle.net/2117/86351
Reduced microwave losses YBa2Cu3O7-d thin films on electro-optic LiNbO3 crystals
Fàbrega Sanchez, Lourdes; Rubi, R; Fontcuberta, J; Sanchez, F; Ferrater Lambarri, Carlos; Garcia-Cuenca, M V; Varela, M; Collado Gómez, Juan Carlos; Mateu Mateu, Jordi; Menéndez, O; O'Callaghan Castellà, Juan Manuel
Thu, 28 Apr 2016 10:44:36 GMThttp://hdl.handle.net/2117/863512016-04-28T10:44:36ZFàbrega Sanchez, LourdesRubi, RFontcuberta, JSanchez, FFerrater Lambarri, CarlosGarcia-Cuenca, M VVarela, MCollado Gómez, Juan CarlosMateu Mateu, JordiMenéndez, OO'Callaghan Castellà, Juan ManuelNonlinear RF spurious in a cylindrical cavity with superconducting endplates
http://hdl.handle.net/2117/86344
Nonlinear RF spurious in a cylindrical cavity with superconducting endplates
Mateu Mateu, Jordi; Collado Gómez, Juan Carlos; Shaw, T J; O'Callaghan Castellà, Juan Manuel
We have developed a method to calculate the distribution of fundamental and spurious fields in a metallic cylindrical cavity with superconducting endplates in which signals at two different frequencies are injected. The nonlinearity in the superconductor produces the typical intermodulation effects if the frequencies of the injected signals are sufficiently close to each other and near a resonant mode. Our method uses harmonic balance to match the fields in the cavity with the currents on the endplates. The method can be used for a variety of nonlinear models of the superconducting endplate, and could be the base for a nondestructive procedure to extract the nonlinear parameters of an HTS sample from RF measurements. Our analysis is restricted to the TE011 mode, but the method can be applied to any propagating mode in the cylindrical cavity. Closed-form equations for the case of square-law nonlinearities in the superconductor are derived and used to check the validity of the harmonic balance calculation.
Thu, 28 Apr 2016 10:33:28 GMThttp://hdl.handle.net/2117/863442016-04-28T10:33:28ZMateu Mateu, JordiCollado Gómez, Juan CarlosShaw, T JO'Callaghan Castellà, Juan ManuelWe have developed a method to calculate the distribution of fundamental and spurious fields in a metallic cylindrical cavity with superconducting endplates in which signals at two different frequencies are injected. The nonlinearity in the superconductor produces the typical intermodulation effects if the frequencies of the injected signals are sufficiently close to each other and near a resonant mode. Our method uses harmonic balance to match the fields in the cavity with the currents on the endplates. The method can be used for a variety of nonlinear models of the superconducting endplate, and could be the base for a nondestructive procedure to extract the nonlinear parameters of an HTS sample from RF measurements. Our analysis is restricted to the TE011 mode, but the method can be applied to any propagating mode in the cylindrical cavity. Closed-form equations for the case of square-law nonlinearities in the superconductor are derived and used to check the validity of the harmonic balance calculation.