Mutual locking of quasi identical R.F. heating magnetrons (preliminary results)

The conditions for the mutual locking of twoPeer 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

Millimeter-wave aperture synthesis radiometry for snow and ice mapping

An outline design for a dual-band mm-wave polarimetric SAIR has been presented and is considered to be tractable. The envisaged application is for snow and ice mapping and ocean wind vector measurement. The vastly increased complexity of the high-frequency waveband may not be justified by the scientific benefit and operation at an additional lower frequency such as 18 GHz may give improved classification, though with reduced spatial resolution. The authors describe the outline design for a polarimetric, mm-wave SAIR. One-dimensional aperture synthesis employs a hybrid technique in which a long linear array of real-aperture stick antennas form over-lapping fan beams on the ground and aperture synthesis within the fan beams enables synthesis of the mm-wave image. Critical aspects for building a high-resolution, mm-wave ESTAR are system calibration and the construction of stick antennas that will be 3 m long and about half a wavelength wide.Peer ReviewedPostprint (published version

Baseline redundancy and radiometric sensitivity: a critical review

When computing the radiometric resolution of an interferometric radiometer the correlation among the errors of different baselines is usually assumed negligible. ln this way: a) the radiometric sensitivity turns out to be pixel independent (except for antenna pattern effects), and b) the error of the average of P redundant baselines is reduced by a factor of (P)1/2. While this may be the case in radioastronomy applications, for an on-board instrument where all the baselines are measured at the same time interval the errors will actually be correlated. This has two effects: a) The radiometric resolution changes from pixel to pixel and b) the radiometric resolution improvement introduced by redundance is reduced as compared with the case of independent errors. In this paper this correlation is computed and the results obtained are applied, first, to a fully redundant (all possible baselines are actually measured) filled linear array to analyze the actual radiometric improvement, and, next, to the same array without redundance to investigate the dependence of sensitivity on pixel information.Peer ReviewedPostprint (published version

La Misión de oportunidad SMOS de la serie Earth Explorer. Radiometría por síntesis de apertura para la medida de la humedad del suelo y la salinidad del océano

Desde medi ados de los años 80, di versas Agencias Espaciales han prestado una atención a los ll amados radiómetros interferométricos por síntesis de apertura. Estos in strumentos ofrecen por primera vez un salto cuantitativo importante en resolución espac ial como para permitir monitorizar la superfi cie terrestre a frecuencias bajas de microondas (banda L). En esta banda de frecuencias (1.4 GHz) existe la máxima sensibilidad de la temperatura de brillo tanto a la humedad del terreno, como a la salinidad del océano. En los radiómetros clásicos, la resolución espacial viene dada por el ancho de haz de la antena que, al ser escaneada, forma la imagen de temperatura de brillo. Por ello, para alcanzar la resolución espacial deseada (30-50 km como máximo, 10-20 km ideal) 'desde un satélite en órbita baja, las antenas requeridas tienen unas dimensiones inaceptablemente grandes: entre 10 y 20 metros de diámetro. Durante los años 90, la Agencia Europea del Espacio (ESA) llevó a cabo una serie de estudios tecnológicos con vistas a desarrollar un radiómetro por síntesis de apertura bidimensional en banda L. A este proyecto se le llamó MIRAS (Microwave Imaging Radiometer by Aperture Synthesis). En Noviembre de 1998, la mi sión SMOS (Soil Moisture and Ocean Salinity) basada en el concepto derivado de los estudios del proyecto MIRAS, fue propuesta como respuesta a un anuncio de «Misiones de Oportunidad Earth Exploren) lanzado por la ESA [1). En Mayo de 1999, después de un proceso de selección de 27 propuestas, la ESA aprobó la mi sión SMOS en segundo lugar para una fase A extendida. Este artículo describe brevemente la moti vación de esta misión , los principios de funcionamiento de dicho in strumento y las actividades en las que ha participado y participa un grupo de profesores del Departament de Teoria del Senyal i Comunicacions, de la Universitat Politecnica de Catalunya.Peer Reviewe

Scattering and emissivity of rain events using boundary element method

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.Peer ReviewedPostprint (published version

Efecto de la reducción simétrica del plano de tierra en líneas microstrip

The variations of the characteristic impedance and wavelength of a symmetrical biplate line with the width of the upper plate held constant are studied, for several widely used dielectrics, by the method of moments with a nonuniform distribution of pulse basis functions. Results presented show that, for plastic substrates, a lower plate as narrow as twice the width of the upper results in a Z0 that differs from the corresponding microstrip impedance by less than a 4%.Peer ReviewedPostprint (published version

Ondas electromagnéticas en comunicaciones

Este libro está dedicado al estudio de las ondas electromagnéticas, sus peculiaridades en frecuencias ópticas, y los principios básicos de su interacción con la materia. Su principal objetivo es facilitar la adquisición de conceptos y procedimientos que permitan el estudio posterior de sus aplicaciones en ingeniería de comunicaciones (antenas, microondas, comunicaciones, ópticas). Contiene muchos ejemplos extraídos de la vida cotidiana o de aplicaciones técnicas sencillas. El libro realiza un planteamiento original, a partir de la postulación de los campos radiados por una carga acelerada, lo que permite al lector trabajar de forma rigurosa con ondas desde el principio. Su utilización puede ser de interés para estudiantes de ingeniería interesados en comunicaciones y que hayan seguido un curso básico de electricidad y magnetismo

Circuitos de microondas con líneas de transmisión

El libro propone una introducción a las microondas sin recurrir al análisis electromagnético. Comienza por las líneas de transmisión, la carta de Smith y sus aplicaciones, y continua por la descripción de los circuitos de microondas mediante los parámetros de dispersión (scattering), inversores de impedancias, atenuadores, filtros, divisores y combinadores de potencia, acopladores direccionales e híbridos, y circuitos basados en líneas de transmisión acopladas

Algunos aspectos del secado de azulejos cerámicos por microondas

The results of tests performed on the drying of unfired tiles by the action of microwaves are presented. These results show that a reduction of more than 5% humidity can be achieved in less than 5 minutes in a well designed system. Some aspects concerning the difficulties met at the static tests are also given. Some effects of the changing properties of the tiles during the drying are described, along with measurements of their dielectric constant. These compare favourably with data obtained from a simple formula for a mixture of dielectric materials.Peer ReviewedPostprint (published version