Ka-band payloads are becoming more and more popular for satellite communication. The wider band width in Ka-band allows a better satisfaction of the increasing demand for capacity. In addition to the use of more resources, a more efficient use of the available resources will become key for a successful development of satellite communication services. Modern antenna concepts allow a high frequency reuse scheme and, therefore, an extreme efficient use of the most rare resource in satellite communication, the frequency band width. In this paper, we describe the design and the use of different types of such antennas.
Die Quergleitung von Schraubenversetzungen im kubisch-flächenzentrierten Gitter wird als einfacher Elementarprozeß mit eindeutigem Reaktionsweg und definiertem Sattelpunkt behandelt. Die Aktivierungsenergie für diesen Prozeß wird für die vorderste, unmittelbar an einer LOMER-COTTRELL-Versetzung anliegende Versetzung einer Versetzungsgruppe berechnet. Dazu wird das Spannungsfeld der Versetzungsgruppe in der primären Gleitebene und seine Wirkung auf die Aufspaltung der quergleitenden Versetzung untersucht. Die kritische Länge 2 lDas Ergebnis der Rechnung ist ein linearer Zusammenhang zwischen der Aktivierungsenergie U und dem Logarithmus der äußeren Spannung τ für eine bestimmte Zahl n von Versetzungen in der Versetzungsgruppe und für einen bestimmten Wert der spezifischen Stapelfehlerenergie γ. Der Proportionalitätsfaktor A ist von n wenig, von γ stark abhängig. Der Vergleich mit dem Experiment ermöglicht die experimentelle Bestimmung der Stapelfehlerenergie von kubisch-flächenzentrierten Metallen.
This paper describes the development of a 4 GHz transmit antenna generating six shaped beams for covering main areas of Africa. Design and optimisation, hardware activities and performance data are presented. Two polarisation sensitive gridded single offset reflectors (diameter 2..15 m) are fed by two orthogonally polarised feed arrays with 16 and 20 feeds respectively. The antenna generates three independent beams for each polarisation. Frequency reuse by polarisation diversity and by space diversity between two far displaced beams allows for 30 channels in total to be transmitted. A flexible channel to beam allocation is possible (reconfiguration) with a slightly reduced channel number. The three horizontally polarised beams are partly overlappling with five of the 16 feeds to be shared. These feeds are excited via dual mode subnetworks. This feedsystem consisting of 16 compact, high efficiency SCRIMP-Horns, a dual mode beam forming network in barline technique has been manufactured and tested. Measurement results are compared with pattern predictions on the level of primary as well as secondary pattern. The correspondence is in both cases very close. Mutual, coupling between horns has been included exactly into the analysis. This is mandatory for a realistic cross-polar prediction as it is demonstrated by comparison with the measurements.
A new compact multimode horn for multifeed application is presented, the principle of operation is described and starting values for a first design iteration are given.Furthermore measurement results of a radiator element with an aperture diameter of 1.7 lambda, fed by a four probe polarizer, are presented.
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