EP0670609B1 - Multibeam antenna capable of receiving/transmitting same frequency signals, from/to one or more coplanar directions, simultaneously - Google Patents

Description

This invention concerns a multibeam antenna capable of receiving/transmitting same frequency signals from/to one or more coplanar directions simultaneously.

The invention consists of one or more radiating elements and of a parabolic reflector with square aperture. Essential detail for the achievement of optimal performance is that one of the four vertices of the square, which circumscribes the reflector, must be placed close to the vertex of the paraboloid. A more detailed explanation will be provided later on herein.

With this invention the Inventors intend to meet the need of obtaining an antenna capable of simultaneously receiving/transmitting signals at the same frequency, from/to several coplanar directions, while ensuring at the same time a sufficient degree of isolation between signals, in the case that these directions are aligned and in proximity one with the other.

The successful results which the owner Company wishes to patent were reached in the attempt to respond to future demands in the via satellite reception of TV signals. Due to the increase in the crowding of the stationary orbit, one will soon receive signals from a satellite while trying at the same time to filter as much as possible the signals coming from adjacent satellites. The attenuation of these disturbing signals is necessary because, since they occupy the same frequency band as those one wishes to receive, they are noise.

In the previous techniques, the same problem was solved by using oversized reflectors. This system often met only partially the needs mentioned above, since it provided not simultaneous reception of these signals through a resighting mechanism. This implied technical problems as well as, obviously, greater costs.

As indicated in the document EP-A-0.275.062, prior art, the antenna comprising a parabolic reflector has radiating elements located at different positions of focusses at opposite sides with respect to the center axis of the antenna, while in the present invention, the radiating elements, are aligned on a line parallel to the diagonal of the quadrangular parabolic reflector and are placed close to one of the four vertices of the reflector.

This invention finds its application in the technical field of space and non-space antenna electronics. It may be conveniently applied especially in the field of space antennas, most of all for TV signals.

The invention subject of this application for patent refers to an antenna studied for Direct Broadcasting System (DBS) type applications, namely a direct TV signal reception system via satellite.

The invention illustrated herein ensures, in case of "single reflector" configuration adoption, the achievement of optimal performance in terms of:

• maximum isolation between operating directions, at the same antenna gain;
• minimum size of the reflecting surface - in fact, the square configuration allows to reduce packaging problems and therefore facilitates antenna assembly transportation.

The invention will now be described by way of illustration and not in a limiting manner, according to the version currently preferred by the inventors and referred to the figures attached hereto:

Fig. 1 - Schematic drawing of the plan view of the antenna reflector

Fig. 2 - Schematic drawing of the side view of the antenna reflector

Fig. 3 - Assembly of the plan view a), of the side view b) and of front view c)

Fig. 4 - Schematic drawing of the radiation patterns of the antenna.

As regards Fig. 4, notice how, at the peak of each one of the three beams, the directivity of the other two is very low.

Fig. 1 shows one of the aperture shapes, of reflector (1), which can be assigned to the antenna in question, in which (3) indicates the rim, (4) indicates one of the four vertices close to which passes the focal axis (5). The focal axis is visible in Fig. 2, while in Fig. 1 it coincides with point (2). The radiating elements (2) are aligned on a line parallel to the diagonal (6); said radiating elements (2) and the optimal operating directions (represented by the diagonals (6) of the reflector) are coplanar and can be placed on two orthogonal planes.

The antenna, subject of the invention submitted herein, has therefore been studied, as mentioned before, for DBS type applications and in particular it meets the requirements the parameters of which are illustratively indicated by, but not limited to, the following:

• angular distance between generated beams = 3.3°
• projected square surface area < 800 x 800 mm²
• total isolation from adjacent satellites (copolar and crosspolar polarisation) and within the same satellite (crosspolar) > 27 dB.

The antenna receives the TV signal coming from continguous satellites on the stationary orbit. The angular distance, which today is expected for these satellites, is about 3.3°. The Inventors have taken this requisite into account in their invention.

The electro-magnetic energy coming from each satellite is reflected by the reflector's surface and directed towards the corresponding radiating element (2).

The most significant result of the invention is represented by the capacity of not receiving unwanted signals coming from other directions. Essentially, this considerable advantage is due to the fact that the antenna has a square configuration and it is used in directions aligned with the diagonals.

It is possible to exploit the actually greater width of the aperture in those directions and a greater power tapering at the ends. These two characteristics, once combined, cause very low side lobes.

Claims (3)

1. Multibeam antenna comprising a parabolic reflector (1) having a quadrangular shaped aperture and radiating elements (2) disposed on the focal plane (5), characterised in that said radiating elements (2) are aligned on a line parallel to a diagonal (6) of the quadrangular parabolic reflector .
2. Multibeam antenna according to the claim 1, wherein the radiating elements (2) are placed close to one of the four vertices of the quadrangular parabolic reflector (1).
3. Multibeam antenna according to claim 1 or 2 wherein :

   angular distance between generated beams is more or less 3.3°

   projected square surface area is smaller than 800 x 800 mm².

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