Strip-loaded hollow dielectric H-plane sectoral horn antennas for square radiation pattern

The radiation characteristics of a new type of hollow dielectric H-plane sectoral horn antenna are presented. Metallic strips of optimum length are loaded on the H-walls of the sectoral horns. The effects of strip loading for producing square patterns in the H plane are discussed.

Beam shaping of sectoral electromagnetic horn antennas using corner reflector technique

In the present thesis, possibility of beam shaping of sectoral horns and corner reflector systems'has been studied in detail. The experimental results obtained in the above two cases are compared. As far as the flanged sectoral horns are concerned, the special advantage is that the gain is increased without impairing impedance conditions. An intense study on corner reflector antennas shows that the been broadening or focussing will be possible by adjusting parameters involved. Beam tilting by imposing asymmetries is another interesting property of the systems. A comprehensive study of these fields has been presented in Chapter II. Chapter III is exclusively for describing the experimental techniques used in the present investigation. In Chapter IV, experimental results on flanged sectoral horns and corner reflector eyetses are presented. A comparative analysis of the experimental results obtained with flanged sectoral horns and corner reflector systems is presented in the Chapter V. The similarity and close resemblance in each aspects are shown by presenting typical results from these two eysteee. Theoretical aspects of both types of antennas are considered in Chapter VI. Attempts are made for co-ordinating the theoretical aspects and drawing a final conclusion. In Chapter VII. the final conclusion that the flanged sectoral horn may be considered as a corner reflector system has been drawn. The importance of the conclusions and usefulness are pointed out. The scope for further work in these lines has been indicated.

Corrugated flange technique for beam shaping of sectoral electromagnetic horn antennas

The need for improved feed systems for large reflector antennas employed in Radio Astronomy and Satellite tracking spurred the interest in horn antenna research in the 1960's. The major requirements were to reduce spill over, cross-polarisation losses,and to enhance the aperture efficiency to the order of about 75-8O%L The search for such a feed culminated in the corrugated horn. The corrugat1e 1 horn triggered widespread interest and enthusiasm, and a large amount of work(32’34’49’5O’52’53’58’65’75’79)has already been done on this type of antennas. The properties of corrugated surfaces has been investigated in detail. It was strongly felt that the flange technique and the use of corrugated surfaces could be merged together to obtain the advantages of both. This is the idea behind the present work. Corrugations are made on the surface of flange elements. The effect of various corrugation parameters are studied. By varying the flange parameters, a good amount of data is collected and analysed to ascertain the effects of corrugated flanges. The measurements are repeated at various frequencies, in the X— and S-bands. The following parameters of the system were studied: (a) beam shaping (b) gain (c) variation of V.S.U.R. (d) possibility of obtaining circularly polarised radiation from the flanged horn. A theoretical explanation to the effects of corrugated flanges is attempted on the basis of the line-source theory. Even though this theory utilises a simplified model for the calculation of radiation patterns, fairly good agreement between the computed pattern and experimental results are observed.

Formation of elliptically polarized beam from h-plane sectoral horns using corrugated flanges

The flange technique, suggested by Reynolds72 is simple technique to improve antenna characteristics. Using flange technique we can trim the antenna characteristic by suitably adjusting the flange parameters75. Later corrugated flanges87 are used for beam shaping. The important parameters of the corrugated flanges are (a) flange angle, (b) flange width, (c) flange position, (d) conductivity of the flange, (e) amplitude excitation of the flange elements, (f) period of corrugation etc. Compared to a compound horn the flange technique offers great convenience in trimming antenna characteristics. Horns are commonly used as a feed in radar and satellite communications. A large number of work had been done to improve the characteristics of horn antennas. It is an established fact that grooved walls on the inner surface of a horn can improve the antenna characteristics44. Corrugated comb surface can be used for the circular polarization98, tilt of polarization99 etc. This suggests the possibility to combine these two phenomena and to obtain a resultant beam. This thesis presents the result of an investigation to study the possibility of controlling different antenna characteristics like polarization, beam shaping, matching etc, using corrugated flange techniques.

Investigations on the radiation characteristics of flanged sectoral horn antennas and corner reflector systems

Antennas play an important role in determining the characteristics of any electronic system which depends on free space as the propagation medium. Basically, an antenna can be considered as the connecting link between free space and the transmitter or receiver. For radar and navigational purposes the directional properties of an antenna is its most basic requirement as it determines the distribution of radiated energy. Hence the study of directional properties of antennas has got special significance and several useful applications.

Seguros de desempleo: revisión de literatura y propuesta para Colombia

En este artículo se estudia la posibilidad de introducir seguros de desempleo en Colombia. En una primera parte, se propone una revisión de literatura de los seguros de desempleo en la cual se exponen las ventajas generadas por una cobertura contra este riesgo, así como sus inconvenientes. En una segunda parte, se estudian varios escenarios para introducir seguros de desempleo en Colombia. Después de haber presentado el contexto del mercado laboral y de las normas que lo vigilan, se proponen varios diseños que abordan la gestión y la administración del riesgo de desempleo en Colombia. Igualmente se presentan algunas consideraciones teóricas para la valoración del costo del aseguramiento, las cuales incorporan los efectos del riesgo moral sobre la duración y la incidencia del desempleo.

Short Term Health Shocks and School Attendance: The Case of a Dengue Fever Outbreak in Colombia.

This paper makes use of a short, sharp, unexpected health shock in the form of the 2010 Colombian Dengue outbreak to examine the direct and indirect impact of negative health shocks on behaviour of households in affected areas. Our analysis combines data from several sources in order to obtain a comprehensive picture of the influence of the outbreak, and furthermore to understand the underlying mechanisms driving the effects. Our initial analysis indicates that the outbreak had a substantial negative effect on the health status of adults and adversely affected their ability to function as usual in their daily lives. In our aggregated school data, in areas with high levels of haemorrhagic Dengue we observe a reduction innational exam attendance (last year of secondary school) and on enrolment rates in primary education. Further analysis aims to exploit detailed individual level data to gain a more in depth understanding of the precise channels through which this disease influenced the behaviour and outcomes of the poor in Colombia.

Evidence of induced innovation in US Sectoral Capital’s Shares

We use annual data on capital’s share and relative factor prices from 35 US industries from 1960 to 2005 to test the induced innovation hypothesis. We derive, from a production function framework, testable implications for the effect of contemporaneous and lagged factor price ratios on capital’s share of production. The predicted effect is positive or negative depending on the elasticity of substitution between labor and capital. From panel regressions, the estimated effect of the contemporaneous factor price ratio implies an elasticity of substitution that is less than unity, consistent with the consensus from the literature. Based on this, our negative estimated effects for lagged price ratios are both statistically significant and consistent with the induced innovation hypothesis.

International propagation of shocks: an evaluation of contagion effects for some Latin American countries

In this paper we analyze the spread of shocks across assets markets in eight Latin American countries. First, we measure the extent of markets reactions with the Principal Components Analysis. And second, we investigate the volatility of assets markets based in ARCH-GARCH models in function of the principal components retained in the first stage. Our results do not support the existence of financial contagion, but of interdependence in most of the cases and a slight increase in the sensibility of markets to recent shocks.

Elasticity of Substitution in the U.S. Market with Endogenous Transport Costs: a Sectoral Approach.

En este artículo se presentan estimaciones de la elasticidad de sustitución de bienes importados al mercado de los EEUU en el periodo 1990 - 2003, siguiendo a Anderson y Wincoop (2004). Estas estimaciones aprovechan la disponibilidad de la información sobre costos de transporte de bienes publicada por la Oficina del Censo de los Estados Unidos, desagregándola a seis digitos. Se obtienen dos estimaciones diferentes de la elasticidad de sustitución: una a nivel agregado promedio y otra a nivel sectorial. Como puede esperarse, las estimaciones que tienen en cuenta la endogeneidad de los costos de transporte son estadisticamente diferentes en un punto porcentual a los resultados obtenidos cuando no se contempla la estructura de los costos de transporte. Esta diferencia es incluso superior cuando comparamos los resultados obtenidos utilizando la clasificacion sectorial a nivel de dos digitos de la clasificacion ISIC revisión 2.

Sectoral investment composition, capital services measurement and growth in Colombia

This is mainly a discussant paper on measurement criteria upon sector’s investment and capitalservices and the way these composition and measurement issues come to have an impact ongrowth figures for some major sectors of the Colombian economy. The main focus is on distinctionmatters regarding the measurement of capital stock and capital services in the productionprocess. The availability of appropriate data, widely discussed throughout the document, impliesthat major affirmations are more hypothetic than indicative or descriptive in style. Moststatements are established as a motivation device for studies on sector’s activities with a focus onconsistency with aggregate figures.

Respuesta dinámica a los shocks monetarios en un modelo de búsqueda en el mercado de trabajo.

Este artículo analizar la respuesta dinámica de unas cuantas variables macroeconómicas clave ante tres choques exógenos: uno monetario, otro relacionado con el gasto del gobierno, y otro de tipo tecnológico. Mediante el uso de un modelo de efectivo adelantado con dos fricciones de mercado, una relacionada con la intermediación de fondos a préstamo, y otra relacionada con el mercado de trabajo, analizamos la habilidad del modelo en relación a simular información relacionada con el mismo tipo de respuesta dinámica a shocks observados en información histórica (estimamos multiplicadores dinámicos con respecto al choques exógenos mediante la estimación de un modelo VARX aplicada a nuestros dos bases de datos). Detectamos evidencia sobre los efectos expansionistas de corto plazo de la política monetaria, y resaltamos la importancia de estudiar la dinámica de las tasas real y nominal de interés. En relación a la primera de ellas observamos un movimiento contracíclico del dinero y las tasas de interés, que no se presenta con respecto a la segunda. También encontramos buen desempeño del modelo en su capacidad de simular la respuesta dinámica del producto luego de los choques. Reproduce bien la dinámica de la inversión y el empleo ante choques tecnológicos o de gasto público. Ofrecemos un estudio de caso para el uso de esta tecnología de validación como técnica alternativa para la evaluación de modelos de equilibrio general dinámicos calibrados.

Economic shocks and crime: evidence from the crash of ponzi schemes

In November 2008, Colombian authorities dismantled a network of Ponzi schemes, making hundreds of thousands of investors lose tens of millions of dollars throughout the country. Using original data on the geographical incidence of the Ponzi schemes, this paper estimates the impact of their break down on crime. We find that the crash of Ponzi schemes differentially exacerbated crime in affected districts. Confirming the intuition of the standard economic model of crime, this effect is only present in places with relatively weak judicial and law enforcement institutions, and with little access to consumption smoothing mechanisms such as microcredit. In addition, we show that, with the exception of economically-motivated felonies such as robbery, violent crime is not affected by the negative shock.