GB2166297A

GB2166297A - Antenna exciter for at least two frequency bands

Info

Publication number: GB2166297A
Application number: GB08526009A
Authority: GB
Inventors: Paul Thiele; Detlef Block; Wolfgang Kohnen
Original assignee: Kabelmetal Electro GmbH
Current assignee: Kabelmetal Electro GmbH
Priority date: 1984-10-27
Filing date: 1985-10-22
Publication date: 1986-04-30
Also published as: DE3439414A1; IT8548721A0; IT1182940B; GB8526009D0; FR2572593A1; BR8505309A

Abstract

An antenna excitor (2) for two different frequency bands comprises two polarising diplexers (3,4) into each of which two mutually perpendicular linearly polarised electromagnetic waves are fed through waveguides 5, 6, 7 and 8. Different internal cross-sectional shapes and cross-sectional dimensions are adopted in the two diplexers (3,4) to ensure that the waves, on the one hand, do not mutually interfere and, on the other hand, propagate in the correct direction. As described, the front part of diplexer 3 has a circular cross-section, the second part has a cross-section which is smaller and somewhat rectangular, whilst the cross-section of the diplexer 4 is circular and even smaller. <IMAGE>

Description

SPECIFICATION Antenna exciter for at least two frequency bands This invention relates to an antenna excitor for at least two different frequency bands, comprising a substantially tubular component in which at least two polarising diplexers are disposed one behind another, each diplexer having two waveguides so connected to it that each diplexer will (in use) carry two electromagnetic waves which are polarised at right angles to each other, a first diplexer, intended for a lower frequency band, having greater clear dimensions than the second diplexer. In this connection reference may be made to U.S. Patent Specification 4, 410,866.

An antenna excitor as just specified may be used, for example, for illuminating a directional antenna having a parabolic reflector for directional communication, satellite communication or radio direction-finding. In this field, the excitor can be used for the direct illumination of the reflector, or instead for illuminating it via a subreflector (Cassegrain principle). In this context, the word "illumination" is employed to include both directions of transmission of the electromagnetic waves, that is to say both waves to be radiated and waves to be received.

Polarising diplexers for illuminating reflectors are known, for example, from U.S. Patent Specification 3, 864,688. They are used for decoupling two electromagnetic waves, carried through connected waveguides, in such a manner that they do not interfere with each other. In this known polarising diplexer, a cylindrical tube section is used for this purpose, into which two waveguides open next to each other. The two waves are decoupled by a number of mutually offset pins or a twisted metal strip, disposed in the tube section between the connecting points of the two waveguides. This causes one wave to be rotated by 90 , so that the two waves are perpendicular to each other.The requirement for interference-free guidance of two orthogonally polarised waves of the same frequency band can thus be met, with a certain degree of effort and expense, by this known arrangement.

The antenna excitor of U.S. Patent Specification 4, 410,866, as initially indicated, has two polarising diplexers, each designed for a different frequency band. This antenna excitor can carry simultaneously two orthogonal waves of the 3.7 to 4.2 GHz frequency band (called the "4-GHz band" hereinafter) and two orthogonal waves of the 5.925 to 6.425 GHz frequency band (called the "6-GHz band" hereinafter), for example. In the tubular po lapsing diplexer for the 4-GHz band which is used in this arrangement, filters are installed which are intended to act as a short circuit for the 4-GHz band to prevent the waves from propagating in the wrong direction. In contrast, the waves of the 6 GHz band are not intended to be affected by the filters.The provision of these filters, made from beryllium oxide, and installation of the filters entail a considerable effort and expense, particularly since the filters necessitate high-precision manufacturing procedures. Between the two polarising diplexers, a conical adaptor is also provided, which makes the antenna excitor longer and heavier. This makes it more difficult to install in an antenna system. In addition, this adaptor too necessitates highprecision manufacturing procedures if no interfering reflections are to occur.

It is an object of the present invention to provide an antenna excitor for at least two frequency bands, the construction of which is simpler than the known design.

According to the present invention, there is provided an antenna excitor for at least two different frequency bands, comprising a substantially tubular component in which at least two polarising diplexers are disposed one behind another, each diplexer having two waveguides so connected to it that each diplexer will (in use) carry two electromagnetic waves which are polarised at right angles to each other, a first diplexer, intended for a lower frequency band, having greater clear dimensions than the second diplexer; in which excitor: the first diplexer (for the lower frequency band) comprises an unround part which is directly connected to the second diplexer, the internal crosssection of the unround part having different dimensions in two mutually perpendicular planes, and also comprises a symmetrical part which is connected to the unround part in the axial direction, the symmetrical part having a symmetrical internal cross-section; the first diplexer has one waveguide connected to its unround part and the other wave guide connected to its symmetrical part, each waveguide extending in a radial direction; the clear dimensions of the unround part are greater than the clear width of the second diplexer, at least in the plane perpendicular to the direction of polarisation of the wave fed into the unround part; and the clear dimensions of the symmetrical part are greater than the smallest dimension of the unround part and at least great enough to permit propogation of the fundamental mode of the wave fed thereinto.

The present antenna excitor employs only two polarising diplexers, which are directly connected to each other. No adaptors are needed between these two diplexers, nor is a separate short-circuit element needed for the first diplexer, for suppressing propagation in the wrong direction of the waves fed into the first diplexer. The antenna excitor is accordingly of simple construction, and axially it is as short as it could be. Thus not only is it simple and economical in production but also its weight can be reduced in comparision with the known design, and its installation is simpler. Separate short-circuit elements, which in the prior art have always been required, are no longer needed because the first polarising diplexer is made unround internally at the transition point, so that waves fed into this unround part cannot enter the second polarising diplexer.Similarly waves fed into the symmetrical part of the first polarising diplexer cannot enter the unround part because of the different cross-sectional shapes of the two parts of this polarising diplexer.

One embodiment of the invention is shown in the accompanying diagrammatic drawings, in which: Figure 1 is a side view of an antenna arrangement having an antenna excitor according to the invention, Figure 2 shows the antenna excitor itself on an enlarged scale, Figure 3 is an end view of the antenna excitor of Figure 2 taken in the direction of the arow A in Figure 2, and Figure 4 is a cross-sectional view of the same antenna excitor taken at the line IV-IV in Figure 2.

In the present description and claims, "excitor" is used to mean "antenna excitor", and "diplexer" is used to mean "polarising diplexer".

In Figure 1, the parabolic reflector of an antenna system, which is mounted, for example, at the tip of a mast, is designated by 1. At the focus of the reflector 1, an excitor 2 is provided which comprises two diplexers 3 and 4. Two wave guides 5 and 6 open into the diplexers 3, and two wave guides 7 and 8 open into the diplexer 4. The excitor 2 can have an opening 9 which expands in the direction of the reflector 1. The installation and arrangement of the individual parts of such an antenna system are familiar to those skilled in the art.

For this reason, they will not be discussed in detail.

In the case of Figure 1, excitor 2 is used for the direct illumination of the reflector 1. In principle, however, it is also possible to use the excitor 2 for an antena system having subreflectors.

The diplexers 3 and 4 are both constructed in such a manner that they carry, in decoupled manner, in each case, two mutually perpendicular waves of the same frequency band. In this arrangement, diplexer 3 is called the first diplexer, for the 4-GHz band. Into the diplexer 3, the two waveguides 5 and 6 open radially with respect to the tubular diplexer. The junctions of the two waveguides can be mutually offset by 90" in the peripheral direction, thus directly ensuring that the directions of polarisation of the two waves fed in are perpendicular to each other.

The dimensions of the internal space of diplexer 3 are non-uniform; it is subdivided into a symmetrical part 10 and an unround part 11, which are so designed, however, that the diplexer 3 can be produced as a single component. The subdividing is indicated by the dashed line 12. As shown in Figure 3, the symmetrical part 10 can have, for example, a cylindrical internal space, so that it has a circular cross-sectional form. But symmetry is also obtained if the part 10 is made polygonal, e.g.

square. The wave guide 5 opens into the symmetrical part 10.

The internal space of the unround part 11 has an unround cross-sectional shape having different dimensions in two mutually perpendicular directions.

As shown in Figure 4, this cross-section shape may, for example, be that of a rectangle whose narrow sides bulge outwards. But the internal space of the unround part 11 may instread have an elliptical or a true rectangular shape. The narrow sides could bulge inwards, or have an arbitrary shape. The waveguide 6 opens into the unround part 11.

The planes of polarisation of the two waves fed into diplexer 3 via wave guides 5 and 6 are perpendicular to each other. In this connection, the cross-sectional shape of the unround part 11 has been so designed that projections 13 and 14, emphasised in Figure 3 by stippling, provided at the transition from the symmetrical part 10 to the unround part 11, act as a short circuit or block for the wave fed in by the waveguide 5. The wave thus cannot propagate in the direction of the unround part 11, but only in the correct direction, which is towards the reflector 1. The diplexer 3 thus needs no additional short-circuit element.

As shown in the drawing, the symmetrical part 10 is made circular. Its clear diameter D must always be larger than the clear dimension K of the unround part 11, to enable projections 13 and 14to be provided. Preferably the diameter D is equal to the largest dimension G of the unround part 11. It must be at least large enough for the fundamental mode of the wave fed into the symmetrical part 10 to be able to propagate (1.7 x D).

Diplexer 4 is provided as the second diplexer, for carrying the 6-GHz band. Here, too, the junctions of the two wave guides 7 and 8 can be mutually offset by 90" in the peripheral direction. However, diplexer 4 can be of an arbitrary or optional design in certain respects. Thus, it can also contain a short circuit element 15 which prevents the propagation in the wrong direction of the wave supplied by the wave guide 7. Again, it is possible to place the feed point of the waveguide 8 at the otherwise closed face 16 of the diplexer 4, so that the shortcircuit element can be omitted. Such a diplexer is described, for example, in German Offenlegungsschrift 3,241,890.

Diplexer 4 is directly connected to diplexer 3.

Since its dimensions are smaller than those of the diplexer 3, there is a discontinuity, as shown in Figure 5, at the point of transition. The second diplexer 4 has, for example, a circular drilling 17 at the point of opening into the first diplexer 3, whereas the unround part 11 of the first diplexer 3 is approximately rectangular, as shown in Figure 4.

The direction of polarisation of the wave fed in at the unround part 11 is indicated by arrows 18. Because of the different cross-sectional shapes and cross-sectional dimensions of the two diplexers 3 and 4, this wave cannot enter the second diplexer 4 since the projecting area, emphasised by stippling, acts as a block.

At the openings of the excitor 2, to which the waveguides 5 and 8 are connected, orthodox filters (known from the prior art) can be provided. This does not affect the remainder of the structure of the excitor 2.

In the case illustrated, the excitor 2 is presented as a two-frequency-band excitor. It can also be used for three or more frequency bands, by appropriate extension. For example, for a third frequency band, one more diplexer, only, comparable to the first diplexer 3, needs to be connected.

The excitor 2 can be used not only for the two frequency bands specified, namely the 4-GHz band and the 6-GHz band, but also, in principle, for any combination of two or more different frequency bands.

The preceding description has been concerned with an arrangement in which the electromagnetic waves are supplied via the waveguides 5 to 8 and are radiated by the reflector 1. However, the excitor 2 is also operable in the converse arrangement in which electromagnetic waves are received by the reflector 1 and are carried via the excitor 2 into the waveguides 5 to 8.

In addition, it will of course be understood that the present invention has been described above purely by way of example, and that various modifications of detail can be made within the ambit of the invention.

Claims

1. An antenna excitor for at least two different frequency bands, comprising a substantially tubular component in which at least two polarising diplexers are disposed one behind another, each diplexer having two waveguides so connected to it that each diplexer will (in use) carry two electromagnetic waves which are polarised at right angles to each other, a first diplexer, intended for a lower frequency band, having greater clear dimensions than the second diplexer; in which excitor: the first diplexer (for the lower frequency band) comprises an unround part which is directly connected to the second diplexer, the internal crosssection of the unround part having different dimensions in two mutually perpendicular planes, and also comprises a symmetrical part which is connected to the unround part in the axial direction, the symmetrical part having a symmetrical internal cross-section; the first diplexer has one waveguide connected to its unround part and the other wave guide connected to its symmetrical part, each waveguide extending in a radial direction; the clear dimensions of the unround part are greater than the clear width of the second diplexer, at least in the plane perpendicular to the direction of polarisation of the wave fed into the unround part; and the clear dimensions of the symmetrical part are greater than the smallest dimension of the unround part and at least great enough to permit propagation of the fundamental mode of the wave fed thereinto.

2. An excitor according to claim 1, wherein the unround part of the first diplexer has a substantially rectangular cross-section whose narrow sides bulge outwards.

3. An excitor according to claim 1, wherein the unround part of the first diplexer has an elliptical cross-section.

4. An excitor according to claim 1, wherein the unround part of the first diplexer has a rectangular cross-section.

5. An excitor according to any of claims 1 to 4, wherein the symmetrical part of the first diplexer has a circular cross-section.

6. An excitor according to any of claims 1 to 4, wherein the symmetrical part of the first diplexer has a polygonal cross-section.

7. An excitor according to any of claims 1 to 6, wherein the two waveguides connected to the first diplexer are connected to it at two points which are mutually offset by 90" in the peripheral direction.

8. An excitor according to claim 1, substantially as described with reference to any Figure or Figures of the accompanying drawings.