Testing of 30-GHz low noise receivers

NASA-sponsored studies of the growth in communications traffic have indicated that the frequency spectrum allocated to fix-service satellites at the C and Ku bands will reach saturation by the early 1990's. The next higher frequency bands allocated for communications satellties are 27.5 to 30 GHz for the uplink and 17.7 to 20.2 GHz for the downlink. Current plans for developing satellite systems that use these bands include a NASA demonstration satellite (ACTS). One of the components identified as critical to the success of that mission is a 27.5 to 30 GHz satellite receiver. In response to that identification, NASA has sponsored the development of such a receiver to the proof-of-concept (POC) level. Design and fabrication of such POC model receivers was carried out under parallel contracts awarded to LNR Communications, Inc. of Hauppauge, New York and to ITT Defense Communications Division of Nutley, New Jersey. The most significant of the performance goals were a 5 db maximum noise figure, a 2.5 GHz passband, and e0 dB Rf to If gain. Following delivery of hardware from each of the contractors, an in-house test program was undertaken at NASA's Lewis Research Center in order to verify the contractor-reported performance and to provide a comparison of the two receivers under identical test conditions. The present paper reports the results of those tests

Range imager performance comparison in homodyne and heterodyne operating modes

Range imaging cameras measure depth simultaneously for every pixel in a given field of view. In most implementations the basic operating principles are the same. A scene is illuminated with an intensity modulated light source and the reflected signal is sampled using a gain-modulated imager. Previously we presented a unique heterodyne range imaging system that employed a bulky and power hungry image intensifier as the high speed gain-modulation mechanism. In this paper we present a new range imager using an internally modulated image sensor that is designed to operate in heterodyne mode, but can also operate in homodyne mode. We discuss homodyne and heterodyne range imaging, and the merits of the various types of hardware used to implement these systems. Following this we describe in detail the hardware and firmware components of our new ranger. We experimentally compare the two operating modes and demonstrate that heterodyne operation is less sensitive to some of the limitations suffered in homodyne mode, resulting in better linearity and ranging precision characteristics. We conclude by showing various qualitative examples that demonstrate the system’s three-dimensional measurement performance

Test results for 27.5- to 30-GHz communications satellite receivers

Five proof of concept receivers are tested. The receivers operate in the 27.5 to 30 GHz uplink band for communications satellites and produce an output at C band. Receiver requirements and test results are given. Test methods are discussed and results are compared with the contractor's test results

Análisis mediante modelos de multiestados del impacto de la viruela aviar sobre una población de Verdecillos (Serinus serinus): la importancia de estimar las tasas de recaptura

Disease is one of the evolutionary forces shaping populations. Recent studies have shown that epidemics like avian pox, malaria, or mycoplasmosis have affected passerine population dynamics, being responsible for the decline of some populations or disproportionately killing males and larger individuals and thus selecting for specific morphotypes. However, few studies have estimated the effects of an epidemic by following individual birds using the capture–recapture approach. Because avian pox can be diagnosed by direct examination of the birds, we are here able to analyze, using multistate models, the development and consequences of an avian pox epidemic affecting in 1996, a population of Serins (Serinus serinus) in northeastern Spain. The epidemics lasted from June to the end of November of 1996, with a maximum apparent prevalence rate > 30% in October. However, recapture rate of sick birds was very high (0.81, range 0.37–0.93) compared to that of healthy birds (0.21, range 0.02–0.32), which highly inflated apparent prevalence rate. This was additionally supported by the low predicted transition from the state of being uninfected to the state of being infected (0.03, SE 0.03). Once infected, Serin avian pox was very virulent with (15–day) survival rate of infected birds being of only 0.46 (SE 0.17) compared to that of healthy ones (0.87, SE 0.03). Probability of recovery from disease, provided that the bird survived the first two weeks, however, was very high (0.65, SE 0.25). The use of these estimates together with a simple model, allowed us to predict an asymptotic increase to prevalence of about 4% by the end of the outbreak period, followed by a sharp decline, with the only remaining infestations being infected birds that had not yet recovered. This is in contrast to the apparent prevalence of pox and stresses the need to estimate recapture rates when estimating population dynamics parameters.Las enfermedades infecciosas son una de las fuerzas evolutivas que modulan a las poblaciones animales. Estudios recientes han puesto de manifiesto como epidemias como la viruela aviar, la malaria o la mycoplasmosis afectan a la dinámica de las poblaciones de passeriformes, siendo responsables de dramáticas reducciones en el tamaño de algunas poblaciones, o de la muerte desproporcionada de machos o de los individuos de mayor tamaño, seleccionando de ese modo en favor de determinados morfotipos. Sin embargo, pocos estudios han estimado los efectos de una epidemia mediante el seguimiento de los distintos individuos utilizando las técnicas de captura–recaptura. Debido al hecho de que la viruela aviar puede ser diagnosticada mediante el examen directo de los individuos, hemos podido analizar, utilizando modelos de multiestado, el desarrollo y consecuencias de una epidemia de viruela aviar que afectó en 1996, a una población de Verdecillos en el nordeste de España. La epidemia afectó a los Verdecillos desde junio hasta finales de noviembre, con una prevalencia aparente máxima de > 30% en octubre. Sin embargo, la tasa de recaptura de los individuos enfermos fue muy alta (0,81, rango 0,37–0,93), comparada con la de los individuos sanos (0,21, rango 0,02–0,32), lo cual exageraba en gran medida la tasa de prevalencia aparente. Este resultado estaba adicionalmente apoyado por la baja tasa estimada de transición del estado de no infectado al estado de infectado (0,03, SE 0,03). Una vez un Verdecillo quedaba infectado, la viruela aviar resultó muy virulenta, siendo la tasa de supervivencia (a 15 días) de los individuos enfermos de tan solo 0,46 (SE 0,17), comparada con la de los individuos no infectados (0,87, SE 0,03). La probabilidad de recuperación de la enfermedad, siempre y cuando el individuo hubiera sobrevivido las dos primeras semanas, fue sin embargo, muy alta (0,65, SE 0,25). Estos valores fueron utilizados para construir un modelo que permitió predecir el valor real de prevalencia de la enfermedad. Según el modelo, el porcentaje de individuos infectados después del brote debió incrementarse de forma asintótica hasta el 4%, manteniéndose en ese valor, hasta que se produjo una abrupta reducción en el número de individuos infectados al final de la epidemia, siendo estos los individuos que todavía no se habían recuperado de la enfermedad. Estos valores contrastan con los valores aparentes de prevalencia de la viruela y enfatiza la necesidad de estimar la tasa de recaptura cuando se realizan estimaciones de los distintos parámetros de dinámica de poblaciones

Conceptual design of a 1-MW CW X-band transmitter for planetary radar

A proposed conceptual design to increase the output power of an existing X-band radar transmitter used for planetary radar exploration from 365 kW to 1 MW CW is presented. The basic transmitter system requirements as dictated by the specifications for the radar are covered. The characteristics and expected performance of the high-power klystrons are considered, and the transmitter power amplifier system is described. Also included is the design of all of the associated high-power microwave components, the feed system, and the phase-stable exciter. The expected performance of the beam supply, heat exchanger, and monitor and control devices is also presented. Finally, an assessment of the state-of-the-art technology needed to meet system requirements is given and possible areas of difficulty are summarized

Shape and deformation measurement using heterodyne range imaging technology

Range imaging is emerging as a promising alternative technology for applications that require non-contact visual inspection of object deformation and shape. Previously, we presented a solid-state full-field heterodyne range imaging device capable of capturing three-dimensional images with sub-millimetre range resolution. Using a heterodyne indirect time-of-flight configuration, this system simultaneously measures distance (and intensity), for each pixel in a cameras field of view. In this paper we briefly describe our range imaging system, and its principle of operation. By performing measurements on several metal objects, we demonstrate the potential capabilities of this technology for surface profiling and deformation measurement. In addition to verifying system performance, the reported examples highlight some important system limitations. With these in mind we subsequently discuss the further developments required to enable the use of this device as a robust and practical tool in non-destructive testing and measurement applications

A power-saving modulation technique for time-of-flight range imaging sensors

Time-of-flight range imaging cameras measure distance and intensity simultaneously for every pixel in an image. With the continued advancement of the technology, a wide variety of new depth sensing applications are emerging; however a number of these potential applications have stringent electrical power constraints that are difficult to meet with the current state-of-the-art systems. Sensor gain modulation contributes a significant proportion of the total image sensor power consumption, and as higher spatial resolution range image sensors operating at higher modulation frequencies (to achieve better measurement precision) are developed, this proportion is likely to increase. The authors have developed a new sensor modulation technique using resonant circuit concepts that is more power efficient than the standard mode of operation. With a proof of principle system, a 93–96% reduction in modulation drive power was demonstrated across a range of modulation frequencies from 1–11 MHz. Finally, an evaluation of the range imaging performance revealed an improvement in measurement linearity in the resonant configuration due primarily to the more sinusoidal shape of the resonant electrical waveforms, while the average precision values were comparable between the standard and resonant operating modes

Aplicación de la modelación integrada bayesiana y de los métodos Monte Carlo basados en cadenas de Markov para la conservación de una especie recolectada

When endeavoring to make informed decisions, conservation biologists must frequently contend with disparate sources of data and competing hypotheses about the likely impacts of proposed decisions on the resource status. Frequently, statistical analyses, modeling (e.g., for population projection) and optimization or simulation are conducted as separate exercises. For example, a population model might be constructed, whose parameters are then estimated from data (e.g., ringing studies, population surveys). This model might then be used to predict future population states, from current population estimates, under a particular management regime. Finally, the parameterized model might also be used to evaluate alternative candidate management decisions, via simulation, optimization, or both. This approach, while effective, does not take full advantage of the integration of data and model components for prediction and updating; we propose a hierarchical Bayesian context for this integration. In the case of American black ducks (Anas rubripes), managers are simultaneously faced with trying to extract a sustainable harvest from the species, while maintaining individual stocks above acceptable thresholds. The problem is complicated by spatial heterogeneity in the growth rates and carrying capacity of black ducks stocks, movement between stocks, regional differences in the intensity of harvest pressure, and heterogeneity in the degree of competition from a close congener, mallards (Anas platyrynchos) among stocks. We have constructed a population life cycle model that takes these components into account and simultaneously performs parameter estimation and population prediction in a Bayesian framework. Ringing data are used to develop posterior predictive distributions for harvest mortality rates, given as input decisions about harvest regulations. Population surveys of black ducks and mallards are used to obtain stock–specific estimates of population size for both species, for inputs into the population life–cycle model. These estimates are combined with the posterior distributions for harvest mortality, to obtain posterior predictive distributions of future population status for candidate sets of regional harvest regulations, under alternative biological hypotheses for black duck population dynamics. These distributions might then be used for both the exploration of optimal harvest policies and for sequential updating of model posteriors, via comparison of predictive distributions to future survey estimates of stock–specific abundance. Our approach illustrates advantages of MCMC for integrating disparate data sources into a common predictive framework, for use in conservation decision making.En el momento de tomar decisiones bien fundamentadas, es habitual que los biólogos conservacionistas deban enfrentarse a fuentes de datos dispares e hipótesis alternativas acerca de los impactos probables que tendrán las decisiones propuestas en el estado del recurso. A menudo, tanto los análisis estadísticos, como la modelación (para la proyección poblacional, por ejemplo) y la optimización o simulación, se llevan a cabo como ejercicios independientes. Así, es posible que se construya un modelo poblacional, cuyos parámetros se estimen a partir de datos (como estudios de anillamiento y estudios poblacionales). Posteriormente, cabe la posibilidad de que este mismo modelo se emplee para predecir situaciones demográficas futuras a partir de las estimaciones de población actuales, utilizando para ello un sistema de gestión determinado. Por último, el modelo parametrizado también puede emplearse para evaluar posibles decisiones de gestión alternativas, a través de la simulación, la optimización, o ambos procedimientos. Si bien este enfoque resulta eficaz, no aprovecha al máximo la integración de datos y los componentes de los modelos para la predicción y actualización. En este estudio proponemos un contexto bayesiano jerárquico que permite efectuar dicha integración. En el caso del ánade sombrío americano (Anas rubripes), los gestores deben enfrentarse a la labor de intentar extraer una recolección sostenible de la especie, al tiempo que mantienen los stocks de individuos por encima de umbrales aceptables. El problema se ve agravado por la heterogeneidad espacial que presentan las tasas de crecimiento y la carga cinegética de los stocks de ánades sombríos, el movimiento entre los stocks, las diferencias regionales en la intensidad de la presión recolectora y la heterogeneidad en el grado de competencia por parte de un congénere cercano —el ánade real (Anas platyrynchos)— entre los stocks. Hemos formulado un modelo del ciclo vital de la población que toma en consideración estos componentes, al tiempo que permite llevar a cabo una estimación de los parámetros y una predicción de la población en un marco bayesiano. Los datos de anillamiento se emplean para desarrollar distribuciones predictivas posteriores para las tasas de mortalidad durante la recolección, expresadas como decisiones de entrada acerca de la normativa sobre recolecciones. Los estudios poblacionales del ánade sombrío y del ánade real se emplean para obtener estimaciones sobre el tamaño poblacional específicas de los stocks de ambas especies, que se emplearán como entradas para el modelo del ciclo vital de la población. Dichas estimaciones se combinan con las distribuciones posteriores para la mortalidad durante la recolección, con el propósito de obtener distribuciones predictivas posteriores de la situación demográfica futura para posibles conjuntos de normativas regionales acerca de la recolección, de acuerdo con hipótesis biológicas alternativas relativas a la dinámica poblacional del ánade sombrío. En una fase posterior, tales distribuciones pueden utilizarse tanto para la investigación de políticas óptimas en materia de recolección, como para la actualización secuencial de distribuciones posteriores del modelo mediante la comparación de distribuciones predictivas para estimaciones en estudios futuros acerca de la abundancia poblacional presente de forma específica en los stocks. Nuestro enfoque ilustra las ventajas que presentan las técnicas de Montecarlo basadas encadenas de Markov (MCMC) para integrar fuentes de datos dispares en un marco predictivo común, con vistas a su utilización en la toma de decisiones sobre conservación