Designing latest-generation antennae for communications satellites
For his PhD thesis, the engineer, Jorge Teniente Vallinas, has developed a method for designing antennas used in satellites such as Hispasat. The PhD, at the Public University of Navarre, was awarded the second prize in the latest edition of the Rosina Ribalta Awards from the Epson Ibérica Foundation for the best PhD thesis in the field of Information and Communications Technology.
The aims of this doctoral thesis were, on the one hand, to establish the bases for the design of Gaussian profiled corrugated antennae which has been worked on by the Public University of Navarre Antennae Group since 1995 and, on the other, to devise and design cutting edge technology of antennae, reducing machining costs and size, at the same time as maintaining the excellent radiation features, all this based on the experience acquired in the design of Gaussian profiled corrugated antennae.
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The Gaussian profiled corrugated antennae are currently the best possible solution for obtaining very high gain radiation patterns. More specifically, the advantages over the classic corrugated horn antennae are twofold: firstly, it is possible to design lateral lobe antennae much lower than with any other type of corrugated profile and, also, they are somewhat shorter than the rest of the corrugated antennae.
Classical corrugated antennae, that normally have been used in high-performance applications, apart from illuminating the zone covering its target area, have lateral lobes that illuminate other zones to such an extent that they may interfere with other antennae or instruments present in these areas. However, Gaussian profiled antennae can reduce the power radiated by the lateral lobes of classical antennae – in which the power is 1000 times less than that at the main surface. The new antennae can achieve between 10 and 100 times even less than this.
The Gaussian profiled antennas have similar behaviour to the metallic end opening or horn of a wind musical instrument but, instead of transporting acoustic waves, they are designed to transport electromagnetic radiation; this is why they are also called “horn antennae”. With these antennae, radiation at microwave or millimetric frequencies enter via the narrowest, posterior part and the antennae shapes the guided waves within its interior in such a way that they come out into open space with certain characteristics, according to their profile. Corrugated antennae -with rectangular metallic folds in its interior – unlike the smooth ones, achieve an internal field shape with two characteristics: firstly, they discriminate very well between polarisations, by which each antenna can work in two channels per frequency and, secondly, the radiated surface is much more like a pure surface of free space.
Since the first patents of this type of antennae were produced at a national, at the Public University of Navarre in 1995 and 1996, it has been incorporated into a number of satellites. For example, in 1998, when this technology was still emerging, the antenna currently used by Hispasat 1C to serve Europe was designed and developed. This same antenna was also to be used, some years later, in Hispasat 1D.
In 2000, two millimetric-wave frequency antennae (about 350 GHz) were designed for the European Space Agency’s MARSCHALS project. These were instruments installed in aircraft with the aim of scanning at these frequencies the upper troposphere and the lower stratosphere, given the importance of these layers of the atmosphere for the global climate.
Since 1999, other researchers from around the world, taking advantage of the fact that the registered patents only covered national territory, have been using this type of antennae proposed by the Public University of Navarre. Thus, a group of English researchers has employed the same techniques to develop the high-frequency instrument for use in the future PLANCK satellite and another, Italian research group has used the same idea for a low-frequency instrument for use in the same satellite. Both research groups have received advice from the researchers at the Navarre-based university.
Finally, in 2002, a new design for this type of antennae, shorter and more compact, with very low lateral lobes and maintaining good levels of discrimination of polarisation and wide moderate bandwidth, was marketed by the UK company, Flann Microwave. Regarding this design, there is a request for an international patent to avoid the uncontrolled marketing by researchers from outside the Public University of Navarre.
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