GB2303253A

GB2303253A - Polarization filter for illuminating an antenna

Info

Publication number: GB2303253A
Application number: GB9614607A
Authority: GB
Inventors: Karl-Heinz Reimann
Original assignee: Alcatel Kabel AG and Co
Current assignee: Nexans Deutschland GmbH
Priority date: 1995-07-12
Filing date: 1996-07-11
Publication date: 1997-02-12
Anticipated expiration: 2016-07-11
Also published as: DE29511273U1; GB2303253B; GB9614607D0

Abstract

A polarization filter 2 for illuminating the parabolic reflector comprises a waveguide section 5 which is suitable for simultaneously transmitting two orthogonal, linearly polarized electromagnetic waves and is sealed at one end face 9. First and second waveguides 3 and 4 are connected to the waveguide section with its end face impinging in a radial direction. The second waveguide 4 is rotated by 90{ with respect to the first 3. In order to avoid reflections, the wall of the waveguide section has a cutout 8 diametrically opposite the connecting point 7 of the second waveguide, whose central axis M coincides with the lengthened central axis of the second waveguide. A plurality of pins 10 are situated between input apertures of the feeders in the main section for short-circuiting.

Description

Polarization filter for illuminating an antenna Description The invention relates to a polarization filter for illuminating the parabolic reflector of a directional antenna, comprising a waveguide section, which is suitable for simultaneously transmitting two orthogonal, linearly polarized electromagnetic waves, is sealed at one end face and to which two waveguides are connected which guide the two electromagnetic waves separately and have different dimensions in two mutually perpendicular axes, in which filter the first waveguide is connected in the course of the waveguide section, with its end face impinging thereon in a radial direction, to said waveguide section in such a way that its major axis runs parallel to the axis of the waveguide section, in which filter the second waveguide is connected to the waveguide section in such a way that its major axis is situated at right angles to the axis thereof, and in which filter a short-circuiting element is arranged in the interior of the waveguide section between the connecting points on the two waveguides (DE-C-3 241 890).

Directional antennas serve the purpose of wireless transmission of electromagnetic waves from one place to another. They are used in this, for example, for radio relay, satellite radio and radio-determination, and are to have as high as possible an efficiency. They are equipped for this purpose with driven dipoles which have for the antennas a very high damping of the minor lobes in the disturbing directions, good matching and high gain. The driven dipoles, which are fitted as a rule with a feed horn, are arranged at the focal point in the case of parabolic antennas. A feed line is connected to the driven dipole. Also known are antennas which are used for two mutually separated electromagnetic waves. In such antennas, use is made as driven dipole of a polarization filter in which two feed lines end which guide the two waves separately.

In the case of such a polarization filter known from US-A-3 864 688, the two feed lines, which are constructed as waveguides, are connected in the same plane to the tubular polarization filter. As a result, they can easily be guided one behind another in a plane.

However, such a connection is attended by the disadvantage that the separation of the two electromagnetic waves in the polarization filter requires a substantial outlay on precision manufacture, since one wave must be rotated by 900 with low reflection without disturbing the other wave. For this purpose, in this known polarization filter there are arranged between the feed points of the two waveguides pins which are virtually offset in the axial direction and in the circumferential direction, or a sheet-metal strip turned in on itself.

In the polarization filter according to the initially mentioned DE-C-3 241 890, the two waves are separated with less outlay. The second waveguide is connected for this purpose, running in the radial direction with respect to the polarization filter, to an end face of the latter. This end face is sealed by the second waveguide. The two waveguides are thereby connected to the polarization filter with polarization directions which are mutually offset by 900. The two waves are therefore fed in directly at right angles to one another.

They are decoupled in this way acceptably without additional parts. This polarization filter has proved itself in practice. Taking the second waveguide at the end face on the polarization filter still requires an increased outlay, however.

It is the object of the invention to configure in a simpler way the polarization filter sketched at the beginning.

This object is achieved according to the invention when - the second waveguide is also connected in the course of the waveguide section, with its end face imping ing thereon in the radial direction, to the said waveguide section, and - when there is provided in the wall of the waveguide section at a point diametrically opposite the con necting point of the second waveguide a cutout whose central axis coincides with the lengthened central axis of the second waveguide.

This polarization filter is particularly simple to produce. All that is required is to prepare the two connecting points for the two waveguides on the waveguide section and then, for example, to solder the waveguides to them. This requires only flat surfaces to be produced - for example by milling - on the waveguide section, and correctly dimensioned holes to be provided as apertures in the wall of the waveguide section. The cutout situated directly opposite the connecting point of the second waveguide can be produced equally easily, for example by means of a face mill which is guided through the hole, provided for connecting the second waveguide, in the wall of the waveguide section. After the two waveguides have been fastened to the waveguide section, the waves guided by the latter are decoupled in the polarization filter without additional elements.

An exemplary embodiment of the subject-matter of the invention is represented in the drawings, in which Figure 1 shows a diagrammatic representation of an antenna with a polarization filter according to ths invention, and Figures 2 and 3 show two different views of the polarization filter in an enlarged representation.

1 denotes the reflector of a parabolic antenna at whose focal point is arranged a polarization filter 2 whose design emerges more precisely from Figures 2 and 3.

Connected to the polarization filter 2 are two waveguides 3 and 4 which are fixed with their free ends to the reflector 1 and are guided through the latter. Waveguides leading further can be connected to the ends projecting from the reflector 1.

The polarization filter 2 is represented and enlarged in Figure 2. It comprises a waveguide section 5 - termed "driven dipole 5" below for shortness - which can have a circular or square cross-section. One end A, facing the reflector 1 of the driven dipole 5 is open, while the other end B is sealed at the end face. The waveguides 3 and 4 are of rectangular construction. They could, however, also be elliptical. The two waveguides 3 and 4 thus have different dimensions in the polarization direction, on the one hand, and in the direction at right angles thereto, on the other hand, that is to say along two mutually perpendicular axes.

The two waveguides 3 and 4 are connected to the driven dipole 5 in such a way that they are fixed to the latter with their end faces such that they run up to said driven dipole radially. The major axis of the first waveguide 3 runs parallel in this case to the axis of the driven dipole 5, while the major axis of the second waveguide 4 is situated perpendicular thereto. The second waveguide 4 is consequently rotated at its connecting point on the driven dipole 5 by 900 with respect to the first waveguide 3. It is connected to the driven dipole 5 between the first waveguide 3 and the sealed end B of said driven dipole.

Provided at the connecting points of the two waveguides 3 and 4 in the wall of the driven dipole 5 are holes or apertures 6 and 7. A clear cross-section of the latter emerges, for example, from Figure 3. A cutout 8 is provided in the wall of the driven dipole 5 on the side thereof diametrically opposite the second waveguide 4 or the aperture 7. The central axis M of the cutout 8 coincides with the lengthened central axis of the second waveguide 4. The cutout 8 is produced, for example, by means of a face mill which is guided through the aperture 7. It serves as an earth equalizer conductor for the purpose of avoiding reflections in transmitting the electromagnetic waves. In the sealed end face of the driven dipole 5 at the end B thereof, there is fitted an adjustable short-circuiting element 9 which projects into the driven dipole 5. In the exemplary embodiment represented, the short-circuiting element 9 simultaneously serves as seal for the driven dipole 5.

In the sketched arrangement of the waveguides 3 and 4 on the driven dipole 5, the two electromagnetic waves, which are supplied separately via the latter, are fed into the driven dipole 5 offset by 900 in their polarization directions. This is indicated by the arrows drawn in in Figure 3. In this way, the waves are already acceptably decoupled when fed in, with the result that no more elements are required for decoupling in the driven dipole 5 itself. Only elements which ensure the waves are decoupled without reflection or interference are provided on or in the driven dipole 5.

A short circuiting element comprising, for example, pins 10 can be provided for this purpose between the feed-in points of the two waveguides 3 and 4. The short-circuiting element can also be designed as a metal sheet. The result of this is that the wave fed in by the first waveguide 3 can propagate only in the direction of the open end A of the driven dipole 5.

The polarization filter 2 can be produced by connecting the waveguides 3 and 4 as feed lines along the entire length to the driven dipole 5. However, it is also possible in accordance with the representation in Figure 2 to provide the driven dipole 5 in one piece with relatively short waveguide connections which have at their free ends connecting flanges 11 and 12 to which the actual feed lines can be connected. This results in the advantage that the component represented in Figure 2 can be produced, for example as galvanoplastic, in one piece and with high dimensional accuracy, so that feeding in the waves with low reflection can be even further improved.

The two waveguides 3 and 4 can also be guided one behind the other as feed line in a plane, with the result that the shading of the antenna is slight. This shading can be further reduced by rotating the second waveguide 4 by 900 only at its end connected to the driven dipole 5, with the result that the two waveguides are then situated one above another at their narrow sides in the feed line.

The polarization filter 2 is sketched in the preceding for the case in which two waves are transmitted simultaneously, that is to say are to be radiated by the reflector 1. However, it is equally well suited for simultaneously receiving two waves rotated in their polarization directions by 900. This polarization filter can also be used for simultaneously transmitting and receiving one each of these waves.

Claims

Patent Claims

1. Polarization filter for illuminating the parabolic reflector of a directional antenna, comprising a waveguide section, which is suitable for simultaneously transmitting two orthogonal, linearly polarized electromagnetic waves, is sealed at one end face and to which two waveguides are connected which guide the two electromagnetic waves separately and have different dimensions in two mutually perpendicular axes, in which filter the first waveguide is connected in the course of the waveguide section, with its end face impinging thereon in a radial direction, to said waveguide section in such a way that its major axis runs parallel to the axis of the waveguide section, in which filter the second waveguide is connected to the waveguide section in such a way that its major axis is situated at right angles to the axis thereof, and in which filter a short-circuiting element is arranged in the interior of the waveguide section between the connecting points of the two waveguides, characterized in that - the second waveguide (4) is also connected in the course of the waveguide section (5), with its end face impinging thereon in the radial direction, to the said waveguide section, and - in that there is provided in the wall of the waveguide section (5) at a point diametrically opposite the connecting point of the second waveguide (4) a cutout (8) whose central axis (M) coincides with the lengthened central axis of the second waveguide.

2. Polarization filter according to Claim 1, characterized in that the second waveguide (4) is connected to the waveguide section (5) between the first waveguide (3) and the sealed end (B) of said waveguide section.

3. Polarization filter according to Claim 1 or 2, characterized in that a short-circuiting element (9) is fitted at the sealed end (B) of the waveguide section (5), in the end face thereof and in a fashion projecting therein.