Showing papers in "Past & Present in 1996"

Phased array antenna with temperature compensating capability

Abstract: Generally, a variation of temperature at the installation site causes a phased array antenna radiation pattern to degrade. This paper describes the temperature characteristics of various components of the phased array antenna and degradations of the radiation pattern originating from temperature variations. It is effective to measure the phase distribution on the aperture and correct it, as the occasion demands, to prevent such degradations. Also, we propose a simple and effective algorithm for the measurement of the current distribution on the aperture, and present the evaluation test results of a phased array antenna with temperature compensation obtained by applying the algorithm.

Pregnancy, childbirth and the female body in early modern germany

Abstract: Cet article explore les assomptions communes dans l'Allemagne du debut des temps modernes sur la sensiblite des femmes pendant la grossesse et l'accouchement, et sur les connections entre les aspects physique et psychologique de leur bien-etre physique, sur l'usage qu'elles faisaient de leur etat dans les relations conjugales et sociales et sur l'impact des croyances concernant les risques de fausse-couche

The concept of the household-family in eighteenth-century england

Abstract: On nous dit que dans l'Angleterre des 17 e et 18 e siecles la structure familiale etait typiquement nucleaire. Jusqu'en 1960 il a ete clairement defini que le groupe dosmetique etendu n'etait pas la forme predominante en Angleterre au debut de l'Epoque Moderne : les familles completes n'etaient pas larges, les groupes domestique n'etaient ni larges ni complexes. Mais quelles conceptions de la famille les gens avaient-ils aux 17 e et 18 e siecles ? Il semblerait qu'ils ne consideraient pas uniquement l'unite familiale nucleaire. Le terme de «family» pouvait signifier le groupe domestique incluant diverses personnes a charges tels que les serviteurs, apprentis ou parents co-residents : « les personnes vivants dans la meme maison ». L'A. s'attache plus particulierement a la construction du concept de «household family» a travers l'usage linguistique qui en est fait dans les textes de l'epoque

State and religion in islamic societies

Abstract: L'A. s'interroge sur la nature des relations entre Etat et religion dans les societes islamiques. Au-dela du sens commun qui souvent dans l'Islam identifie pouvoir politique et institutions religieuses, l'A. entend nuancer cette vision des choses en montrant les limites de l'idee europeenne et occidentale de separation des pouvoirs executif, legislatif et judiciaire. Il s'agit pour lui de presenter une vue historique de la situation moyen-orientale sur ces questions pour montrer que l'Islam sait differencier Etat et institutions religieuses meme si la forme de cette separation peut etre surprenante pour un occidental

Payment and participation: welfare and state-formation in britain 1900–1951

Abstract: THE development of the British state in the twentieth century, James Cronin has recently suggested, was limited rather than rising inexorably, constrained both by the ‘anti-state logic’ of the Conservatives' appeal to the taxpaying public, and by the ‘self-denying tendencies inherent in the unique structure of the British state’, most obviously the role of the Treasury and its allies in the City in limiting spending. As a result, he suggests, priority was given to the interests of taxpayers rather than to the beneficiaries of expenditure on welfare. Such an emphasis on limitations to the expansion of the state carries a normative assumption that the state could and should have been bigger, yet the share of GNP taken in taxation in Britain was not noticeably lower than in other countries. Indeed, the striking feature of the British fiscal system in the first half of the twentieth century is not so much the level of taxation as its structure , with a high reliance on direct taxation of personal income and profits, a narrow base of indirect taxes, and a low level of social security contributions from employers and workers. The precise way in which revenue was extracted was an important influence on the form of the state, helping to define the boundaries between the central and local state, and between the state, market and voluntary organizations. Influences, of course, worked in two directions: the wider institutional structure influenced the tax system as well as being shaped by it.

Lambs into lions : Explaining early Christian intolerance

Abstract: Au IV e siecle de notre ere, les relations entre le christianisme et les religions mediterraneennes que l'on designe sous le terme de paiennes connaissent une mutation. A la fin du siecle, des bandes de chretiens militants encouragees par les plus hautes figures du gouvernement imperial, detruisaient les temples et s'en prenaient avec une impunite presque totale a ceux qui croyaient aux anciens dieux. L'A. s'interesse aux conditions qui ont permis aux militants chretiens de s'imposer a ceux qui pronaient des moyens plus pacifiques pour atteindre leurs objectifs

Wraiths, revenants and ritual in medieval culture

Abstract: Les communautes medievales europeennes definissaient la vie et la mort de deux manieres : le modele spirituel, caracteristique des traditions des elites et le modele materialiste associe a la sphere culturelle populaire de l'Europe du Nord. Si la doctrine du « spiritus » comme principe de vie s'opposait a l'idee d'une « virtus » physique residant dans la chair et les os, les groupes s'accordaient pour definir la « bonne » et la « mauvaise » mort. Il existait un concept de vie apres la mort : pour le modele spirituel, cette vie apres la mort est une existence spectrale et les mouvements d'un corps apres la mort ne peut avoir lieu qu'avec l'intervention d'un esprit (demon possedant le corps). Pour le modele materialiste, la vie apres la mort apparait sous la forme d'un revenant plutot que sous celle d'une apparition. En ce qui concerne l'equilibre entre les mondes des vivants et des morts, la doctrine ecclesiale promouvait les prieres pour ceux qui se trouvaient au purgatoire pour apaiser le tourment des ancetres. Quant aux communautes de l'Europe du Nord elles etaient en relation avec leurs morts a travers les rituels de danse

Capabilities of printed reflectarray antennas

Abstract: This article presents an advanced antenna technology, namely the printed reflectarray, that has the potential for providing an enhanced communication capability with relatively low cost, small size and small mass. It has application in the commercial and military arenas as well as in space exploration.

Phased array radars in France: present and future

Abstract: The beam agility of phased arrays eases fast time sharing between search, acquisition and tracking modes for radars in a varying environment. For ground or surface applications requiring full azimuth coverage, Thomson-CSF designers chose rotating antennas instead of multi-faceted ones. Innovative designs, such as the RADANT prism, have been developed for the to-day phased arrays. To achieve high reliability and improved performance, active arrays are developed, using solid state T/R modules. Furthermore, by processing digitally the transmitted signals and/or the received ones, such arrays permit space/time signal processing for better parasitic signal cancellation, target resolution and non-cooperative recognition. These present and future technologies are illustrated by existing equipment (ARABEL, FLAIR, RBE2) and ongoing developments (RIAS), two of them conducted on an international basis (COBRA, AMSAR).

High gain antenna systems for millimeter wave radars with combined electronical and mechanical beam steering

Abstract: Antenna systems for millimeter waves (MMW), considered in this paper, are large plane phased array antennas, installed on two axis angular positioners. This combination provides mechanical scanning in the upper hemisphere along with electronical scanning in a given conical scan sector. The modular (subarray) structure is the basis of designing the arrays described. The array architecture and achievable performances are discussed. Key elements developed for Ka-band arrays are presented.

Scots, indians and empire: the scottish politics of civilization 1519–1609

Abstract: Comment concevoir la civilisation ecossaise des origines a l'epoque moderne. L'A. passe en revue la perception des populations ecossaises selon les sources historiographiques britanniques disponibles. La politique de civilisation britannique, l'imperialisme, a insuffle un nouvel elan a la vie politique et intellectuelle ecossaise. Les contrastes socioculturels entre Highlanders et Lowlanders se sont affirmes plus profondement a partir de la fin du Moyen-Age. L'A. souligne les contributions de John Mair et James VI sur ce dernier point, notamment par leurs etudes des rapprochements fait entre Indiens du Nouveau Monde et Highlanders et de la politique de civilisation britannique. Il presente ensuite la vision politique de George Buchanan sur la civilisation des «tribus» ; travaux qui anticipaient les etudes Celtiques du 18 e siecle, Buchanan abandonnant l'approche en termes de mythes fondateurs pour privilegier une approche congitiviste de l'histoire et qui, anticipant Montaigne, ne reussit pas a trouver un modele de civilisation dans le Nouveau Monde

Processing and evaluation of multichannel airborne radar measurements (MCARM) measured data

Abstract: Rome Laboratory's (RLs) Multichannel Airborne Radar Measurements (MCARM) program has collected clutter and target data employing an L-band airborne phased array radar testbed. The data collection is at the output of an electronically steered active array mounted on BAC1-11 aircraft. The MCARM array has 16 columns, each consisting of two four-element subarrays. Each subarray has its own output or is combined into a single output per column with up to 24 outputs for the array. Space-time adaptive processing (STAP) techniques simultaneously combine the signals from the elements of an array antenna and pulses of a radar waveform to suppress interference and provide target detection. To obtain adequate clutter power with the limited power-aperture product of the array for STAP analysis, the transmit mainlobe power can be focused in the receive beam sidelobe region or the transmit beam can be spoiled for broader angular coverage. In addition, the data is collected at different platform altitudes and radar waveforms over different terrain. The performance improvement achievable against Doppler-spread clutter that can be achieved with STAP using the L-band data is demonstrated. We present processing results of representative MCARM data files to demonstrate that the adaptive processing can help to detect targets in a nonhomogeneous environment. The limitations of the number of independent clutter samples in estimating the covariance matrix and its impact on target cancellation are examined by processing files with real and synthetic targets.

Scheduling of tasks in phased array radar

Abstract: This paper presents two approaches for scheduling update and search tasks in a phased array antenna radar system. The first approach is based on dynamic programming from the operations research theory. The other is a temporal reasoning scheme based on temporal logic with a background in artificial intelligence. This algorithm is registered by the Swedish Patent Office. The computational schemes of the two approaches are analyzed and compared.

The design, development and testing of the THAAD (Theater High Altitude Area Defense) solid state phased array (formerly ground based radar)

Abstract: This paper describes the Theater High Altitude Area Defense (THAAD) solid state phased arrays design, development and testing. It is the largest most complex solid state phased array built in the world, employing more than 25,000 active radiators each with a corresponding gallium arsenide (GaAs) transmit/receive (T/R) module. The array operates in several aperture illumination modes, is self calibrating in the field, transportable and designed to be "fail soft". The array's performance has been verified on a near-field range and during radar search and track missions of satellites and missiles at White Sands Missile Range (WSMR).

Usury, dearth and famine in western India

Abstract: En Inde occidentale, le systeme d'usure (« sahukari ») etait largement repandu dans la fourniture et le commerce des graines alimentaires. Il etablissait ainsi des rapports entre l'usurier et le paysan qui attendait d'etre aide lors des disettes et famines. Mais la plupart du temps l'aide n'etait pas attribuee et cette non-aide se developpa avec l'Etat colonial. Les paysans ripostaient par des soulevements. Des elements de cette « economie morale » rentrent dans le domaine du surnaturel. En effet, les paysans croyaient que les stockeurs avaient le pouvoir magique d'engendrer la disette qui pouvait ainsi devenir la base de mouvements populaires a forte connotation religieuse

Time, slavery and plantation capitalism in the ante-bellum american south

Abstract: Les specialistes du sud des Eatst-Unis d'avant la guerre de secession consideraient que les populations d'esclaves resistaient a l'imposition d'un temps de travail regulier et routinier bases sur des horaires du fait qu'ils suivaient traditionnellement les rythmes de la nature. Cet article documente l'emergence d'une conscience du temps dependante de l'heure aupres des esclaves du Sud pendant et apres les annees 1830. Il postule que l'application d'horaires et d'horloges au travail des esclaves des plantations revele le debut d'une impulsion capitaliste chez les maitres du sud pre-secessionniste

An experimental S-band digital beamforming antenna

Abstract: This paper describes a 12 channel S-band digital beamforming antenna aimed at radar applications. It has a 2.8-3.3 GHz agile band and the signal is sampled at IF. The design of the antenna elements, calibration network, receiver modules and signal processing ASIC are discussed. Calibration procedures and experimental results, showing very good performance, are also presented. The purpose of the work has been to evaluate design parameters, requirements and limitations.

Design aspects of compact high power multiport unequal power dividers

Abstract: Array antennas for radar require low sidelobe patterns to avoid jamming. Also, arrays used for airborne radar application are required to have very low sidelobes as the radar operates on a clutter limited mode rather than noise limited mode. In order to achieve low sidelobe antennas, the feeder network must be designed such that it should provide the required unequal power division. Corporate feeds are the preferred choice from the bandwidth point of view. But the feeder network will be very complex for larger arrays. Alternatively, a group of elements can be combined suitably and then they can be fed from a relatively simpler corporate feeder which may be a optimum solution. In either of the approaches, high power unequal power dividers are required. Waveguides can handle high powers and hence the high power dividers are to be designed using them. For equal power division, either E-plane tee, H-plane tee or Magic tee can be used. But, for unequal power division there are two ways, one is by slot couplers and the other is by the use of a septum. We discuss the design details of a septum based unequal power divider with multiple ports. We also cover the types of fabrication techniques adapted and their effect on the performance of the power dividers. Tables of results are included to bring out the close correlation between the design and measured results. Comments on the bandwidth performance of these power dividers are included with the results of studies on the effect of errors in these power dividers for low sidelobe antennas.

Limitations and capabilities of directions-of-arrival estimation techniques using an array of antennas: a mobile communications perspective

Abstract: Application of antenna array processing has been suggested for mobile communication systems to overcome the problem of limited channel bandwidth and to satisfy an ever growing demand that the large number of mobiles put on the channel. Application of the array processing requires either a knowledge of a reference signal or the direction of the desired signal source to achieve its desired objectives. There exists a range of schemes to estimate the direction of arrival with conflicting demands of accuracy and processing power. This paper provides a tutorial treatment of direction-of-arrival estimation schemes covering a review of many existing direction-of-arrival (DOA) estimation methods including their performance, sensitivities and limitations.

Matrix method for near-field diagnostic techniques of phased arrays

Abstract: Near-field measurements can be used as diagnostic tools to reconstruct the aperture field distribution of planar array antennas and to locate their possible defective elements. A method for obtaining the individual element excitation of an array antenna from measured near-fields is presented. A computer simulation is performed to evaluate the effect of various near-field parameters such as the measurement distance and the sample spacing on the reconstruction of the excitation. The validity of the approach has been verified using both synthetic and actual measurements data. Good results have been obtained.

Design and construction of a broadband wide-scan angle phased-array antenna with 4096 radiating elements

Abstract: Phased-array radar must provide a multifunction capability and offer a high degree of flexibility to the users. A broadband wide-scan phased array antenna with 4096 elements was designed and constructed. The array can be used over a wide frequency band of 0.3f/sub 0/. The agreement between the measured and the predicted data is very good. In addition, the position errors of the array elements were measured. The additional RMS sidelobe level due to these errors is negligible.

Two low-cost phased arrays

Abstract: One of the most versatile antennas used in radar is the phased array. In a phased array antenna, the phase shifters (or T/R modules in an active aperture phased array) with their beam-steering control circuitry along with the feed network account for the major hardware cost. This paper presents two antenna array configurations that use simpler feed, simpler phase-shifting and beam-steering control circuitry for realizing low-cost phased arrays. Both are lens configurations. The first one uses a Radant lens, which provides a medium that is loaded with diodes and provides the needed phase shift by switching the diodes on and off. The other configuration employs a ferroelectric dielectric material whose dielectric constant can be varied with an applied DC bias voltage. It is shown that the ferroelectric lens may have further advantages of smaller thickness, simpler beam-steering controls and lower cost.

Low profile phased array of dielectric resonator antennas

Abstract: A novel high gain, C-Band, low profile phased array is being developed with electronic beam steering capability in the azimuth plane The radiating elements consist of dielectric resonator antennas (DRAs) of rectangular cross-section, fed from a microstrip line by proximity coupling Challenging issues in this research project, include achieving wide bandwidth performance, low sidelobe levels, and wide angle scan coverage Preliminary results on sub-array performance will be presented