Analysis of satellite multibeam antennas’ performances
- Paper number
IAC-05-B3.1.04
- Author
Mr. Guido Sterbini, University of Rome "La Sapienza", Italy
- Year
2005
- Abstract
The growing request of wideband mobile communications moves space technologies towards more ambitious design scenarios: the development effort will realize the convergence of multimedia applications with mobility need. In this work, we discuss the application of the concept of frequency reuse (cellular coverage) in satellite communications, stressing the importance for a design-oriented mathematical model as first step for dimensioning antenna systems. We consider in particular multibeam reflector antennas: the antenna farm is composed by three or four reflectors; each reflector has a cluster of feeds and, correctly interleaving feeds and reflectors on the satellite, we can build a cellular coverage in far field. Generally we refer to a hexagonal mesh of the coverage with a cell size ranging between half and one degree. There are several problems to cope with in this approach: high antenna gain, high isolation between iso-frequency beams, high beam pointing stability, all respecting the limitations linked to satellite project (weight limit, space limit etc.) and to the feasibility of the feed cluster. We focus on these aspects because they lead to communication channel reliability and to the relaxation of the mobile terminal constraints, such as sensibility (high antenna gain) and robustness to noise (high isolation, high beam pointing stability). For fulfilling the request of high isolation we should consider a far field radiation pattern with low side-lobes. For obtaining it, we can taper the illumination on the reflectors: we need high efficiency feeds, that is to say feeds with an uniform illumination, but they make worse the antenna-spillover efficiency. This solution introduces other parameters in the design environment and, in order to manage this complexity, we propose an efficient mathematical model for conducting the project. The first part of the work consists in reorganizing, making uniform and completing the models already developed in the scientific literature. In particular, we express the loss due to the beam pointing error, the feed diameter, and the reflector taper as functions of what we consider the fundamental quantities of the design (the project specifications), that is the structure and dimension of the cellular coverage, the number of reflectors used, the central frequency of the transmission, and so on. In doing it, we adopt the multidimensional Taylor-development formalism. For computing the spillover efficiency of the antenna, we consider different feed illuminations and we propose a completely original mathematical model, obtained by the interpolation of simulator results. The second part of the work is dedicated to characterize the secondary far field pattern, that is the half power beamwidth, the maximum and minimum directivity on the cell, the position of the first null, the maximum of the first side-lobe, and so on. Combining this model together with the information on the cellular coverage geometry is possible to evaluate the isolation and the minimum directivity on the cell, which are the fundamental specifications of communication performance. As third part of the work, in order to test the model and his analysis and synthesis capabilities, we implement a software tool that helps the designer in the rapid tuning of the fundamental quantities for the optimization of the performances, through parametric plots. This tool can compile the source files for an electromagnetic simulation of the problem: the proposed model show an optimum agreement with the results of the simulations. An example of analysis and synthesis of the performance of an antenna farm with the software tool developed should be the subject of a poster session or the topic of a demonstration.
- Abstract document
- Manuscript document
IAC-05-B3.1.04.pdf (🔒 authorized access only).
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