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Instantaneous model of a MESFET for use in linear and nonlinear circuit simulations

A formal approach for nonlinear modeling of FETs is presented. The intrinsic transistor is described by current and charge generators, that are instantaneously dependent on the two internal voltages. The extrinsic parasitic elements are also included. This instantaneous model is obtained from the small signal equivalent circuit computed at a number of bias points, by integration of the bias dependent elements. A program for using this model in nonlinear circuit analysis has been developed. The process has been carried out for two transistors, one being of low noise, and the other a power MESFET. Good agreement has been observed when comparing the nonlinear analysis with measured data. A solid-state power amplifier at 28 GHz has been designed using the power transistor, delivering 21 dBm at 1 dB compression point.Peer ReviewedPostprint (published version

Unidad externa para una estación terrena del experimento CODE

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Detecció de mascaretes en cares mitjançant visió per computador

Es presenta el disseny i la implementació d’un sistema de detecció de cares amb i sense mascareta, preparat per poder ser exportat en diferents plataformes. S’ha desenvolupat amb TensorFlow i amb la llibreria OpenCV mitjançant els llenguatges de programació Python i C++. El model prèviament entrenat SSD MobileNet V2 FPNLite 320x320 ha estat la base de l’entrenament de la xarxa neuronal. L’entrenament s’ha dut a terme a partir d’una base d’imatges àmplia i diversa, construïda gràcies a la creació d’un procés automatitzat que, donades imatges de cares sense mascareta, es generen cares amb mascareta de diferents tipus, colors i contrasts. A més a més, s’ha augmentat aquesta base d’imatges amb altres processos automatitzats, com el canvi aleatori de la brillantor de la imatge o el redimensionament i col·locació de les cares amb mascareta generades sobre fons aleatoris. Aquestes accions permeten aconseguir més robustesa per a imatges amb múltiples il·luminacions, així com per a cares de diverses mides i col·locades en diferents parts de la imatge. La situació de la pandèmia de la COVID-19 fa que l’eina pugui tenir diverses aplicacions mentre l’ús de les mascaretes sigui obligatori en espais tancats. Des de control de l’entrada en una porta automàtica a aportar informació a una persona amb visibilitat reduïda.Se presenta el diseño y la implementación de un sistema de detección de caras con y sin mascarilla, preparado para poder ser exportado en diferentes plataformas. Se ha desarrollado con TensorFlow y con la librería OpenCV mediante los lenguajes de programación Python y C++. El modelo previamente entrenado SSD MobileNet V2 FPNLite 320x320 ha sido la base del entrenamiento de la red neuronal. El entrenamiento se ha llevado a cabo a partir de una base de imágenes amplia y diversa, construida gracias a la creación de un proceso automatizado que, dadas imágenes de caras sin mascarilla, se generan caras con mascarilla de diferentes tipos, colores y contrastes. Además, se ha aumentado esta base de imágenes con otros procesos automatizados como el cambio aleatorio del brillo de la imagen o el redimensionamiento y la colocación de las caras con mascarilla generadas sobre fondos aleatorios. Estas acciones permiten conseguir mas robustez para imágenes con múltiples iluminaciones, así como para caras de varios tamaños y colocadas en diferentes partes de la imagen. La situación de la pandemia de la COVID-19 hace que la herramienta pueda tener varias aplicaciones mientras el uso de las mascarillas sea obligatorio en espacios cerrados. Desde control de la entrada en una puerta automática a aportar información a una persona con visibilidad reducida.The design and implementation of a face wearing and not wearing a face mask detection system are presented, prepared to be exported for different platforms. It has been developed with TensorFlow and with the OpenCV library using the Python and C++ program languages. The pre-trained model SSD MobileNet V2 FPNLite 320x320 has been the basis of neural network training. The model has been trained from a wide and diverse dataset, built by the creation of an automated process which, given images of faces not wearing a face mask, generate faces wearing a face mask of different types, colors, and contrasts. In addition, this dataset has been increased with other automated processes, such as random change in image brightness or resizing and placing faces with a mask on random backgrounds. These actions provide more robustness for images with multiple illuminations, as well as for faces of various sizes and placed in different parts of the image. The situation of the COVID-19 pandemic makes the tool able to have several applications while the use of masks is mandatory in enclosed spaces. From input control on an automatic door to provide information to a person with reduced visibility.Objectius de Desenvolupament Sostenible::3 - Salut i Benesta

Criterios y métodos de reducción del ruido de fase en osciladores de microondas con MESFET

This paper gives several building criteria for the design of microwave oscillators with MESFET (MESFET-MWO) in order to achieve low phase noise. From device low frequency noise model and identification of phase noise mechanisms generation and sources in MESFET-MWO, a novel expression of 1Hz single side noise power ro carrier power relation or ~(t) function is obtained. A low cost X band oscillator with high efficiency and medium power is built to prove the methods of phase noise reduction derived of that expression. The phase noise measured of the built oscillator allows us to doubt of the device noise model used.Peer ReviewedPostprint (published version

The correlation of visibility noise and its impact on the radiometric resolution of an aperture synthesis radiometer

The correlation between the visibility samples' noise of an aperture synthesis radiometer are required for the computation of the recovered temperature noise of a given pixel and of the improvement introduced by baseline redundance. A general expression for this correlation and noise examples for a linear array are presented.Peer ReviewedPostprint (published version

Ocean salinity observations with SMOS mission

The purpose of this paper is to present the capabilities of SMOS (Soil Moisture and Ocean Salinity mission) for the global mapping of ocean salinity from space. SMOS has been selected by the European Space Agency as the second Earth Explorer Opportunity with a launch date in June 2005. The sensor embarked on SMOS is MIRAS, a Microwave Imaging Radiometer with Aperture Synthesis. MIRAS works at L-band, in the two-polarisations, and has full polarimetric capability. The measurement of sea surface salinity (SSS) is one of the challenges of SMOS. This paper presents first the scientific requirements for a number of oceanographic applications. The scientific requirements are then translated into instrument accuracy, sensitivity, stability and spatial resolution. Major sources of error in the retrieval of ocean salinity will be addressed through an experimental campaign which is described.Peer ReviewedPostprint (published version

Exact representation of antenna system diversity performance from input parameter description

A simplc formulation Io compute thc envelope correlation of an antenna divemiry system is dcrired. 11 is shown how to compute the envelope correlation hom the S-parameter descnplian of the antenna system. This approach has the advantage that i t does not require the computation nor the measurement of the radiation panem of the antenna system. It also offers the advantage of providing a clca understanding ofthe effects ofmutual coupling and input match on the diversity performance of the antcnnii system

Processing and initial comparison of PSR data from CAMEX-3 to SSM/I and TMI data

A multiband Polarimetric Scanning Radiometer (PSR) was integrated on a NASA DC-8 aircraft and flown from August through September of 1998 during the third Convection and Moisture Experiment (CAMEX-3). The PSR is a new conically-scanning imaging radiometer with channels at 10.7, 18.7, 21.5, 37.0 and 89.0 GHz, including both vertical and horizontal polarizations at each of these frequencies. These channels correspond to several key sensing bands of the DMSP (Defense Meteorological Satellite Program) SSM/I (Special Sensor Microwave Imager) and the NASA TRMM (Tropical Rainfall Measuring Mission) TMI (TRMM Microwave Imager). The PSR was developed by Georgia Institute of Technology and the NOAA Environmental Technology Laboratory and is the first airborne imaging radiometer to provide a research quality dataset of high spatial resolution multiband polarimetric microwave imagery within and around a hurricane. The authors describe the processing and calibration of the PSR CAMEX-3 dataset. They also provide a qualitative analysis and comparison of the PSR imagery to the SSM/I and TMI with specific regard to the spatial structure of a hurricane eyewall and surrounding rainbands.Peer ReviewedPostprint (published version

Compensation of elevation angle variations in polarimetric brightness temperature measurements from airborne microwave radiometers

This paper presents a method for compensating the elevation angle fluctuations occurring in airborne radiometry due to aircraft roll and pitch. The correction is based on a radiative transfer model, and is demonstrated by real data from conical scans over the ocean, showing good results.Peer Reviewe