GB2096399A

GB2096399A - Improvements relating to corrugated horns

Info

Publication number: GB2096399A
Application number: GB8207512A
Authority: GB
Original assignee: ERA Patents Ltd
Current assignee: ERA Patents Ltd
Priority date: 1981-03-31
Filing date: 1982-03-15
Publication date: 1982-10-13
Also published as: GB2096399B

Abstract

A corrugated feed horn for a reflector antenna has its corrugations formed by a series of grooves having a common depth D and in which there are at least two different groups of grooves 1,2, which are interspersed with each other. The shape of the grooves 1 of any one group is different from the shape of the grooves 2 of any other group, and are such that the horn is capable of operating under balanced hybrid conditions in at least two different frequency bands. When there are only two groups of grooves as shown the grooves of one group preferably alternate with the grooves of the other group. <IMAGE>

Description

SPECIFICATION Improvements relating to corrugated horns This invention relates to corrugated feed horns for reflector antennae such as are used in high frequency radar and communications systems, particularly in satellite communications.

Conventional corrugated horns, in which the corrugations are formed by a series of similar grooves, usually of generally rectangular cross sectional shape or profile, operate relatively efficiently to radiate purely polarised energy with low cross-polar components (essential for accurate and undistorted signal transmission and reception), but only at a single frequency or frequency band. This frequency dependence has the disadvantage that when transmission and reception is required at two or more widely differing frequencies (for example satellite systems commonly receive in the twelve GHZ band and transmit in the eighteen GHz band) more than one conventional horn is necessary.With a view to overcoming this problem, U.K. patent no. 1,498,905 has proposed a corrugated horn in which the corrugations are formed by a series of grooves or slots of at least two different depths, grooves of one common depth being interspersed with grooves of another common depth whereby the horn radiates a balanced hybrid mode at at least two different frequencies. In particular patent no. 1,498,905 describes a corrugated horn having a series of grooves in which alternate grooves are of different depths but are otherwise of conventional form having a substantially rectangular profile.

We have now found that the problem can also be solved by suitably varying the cross sectional shape of the corrugations instead of their depth. According to the invention therefore, in a corrugated feed horn for a reflector antenna, the corrugations are formed by a series of grooves having a common depth and comprising at least two different groups of grooves interspersed with each other, the grooves of each group having a profile which is of different shape from that of the grooves of the other group or groups, and the groove profiles being such that the horn is capable of operating under balanced hybrid conditions in at least two different frequency bands.

In the case where there are only two groups of grooves, the grooves of one group preferably alternate with the grooves ofthe other group. When there are more than two groups, the grooves are preferably arranged so that the series comprises a number of successive identical sequences each containing one groove of each group.

The invention is applicable to sectoral, pyramidal, and conical horns, whether having linear or nonlinear internal surface profiles, but preferably the horn in accordance with the invention is a conical horn (i.e. having a circular cross-section) having its internal surface profiled so that it has a curvature which approximates to a raised cosine shape. With a linear conical horn a relatively small flare angle is necessary in order to achieve wind-band performance (i.e. very low cross-polarisation levels over as wide a frequency spectrum as possible).At high fiare angles there is a tendency for mode conversion into the cross-polar EH12 mode to take place at the throat of the horn.With a horn having a curved internal profile as described above, the curvature provides the horn with an initial low flare angle, and also provides conversion to the HE12 mode, permitting the gain of the horn to be increased and substantially equal beam width to be obtained in the two different frequency bands.

A variety of different profiles may be used for the different groups of grooves, but those selected will generally be governed by the ease with which a corrugated horn having such grooves can be manufactured as well as by the operating efficiency of the horn. For example, the grooves of one group may have a profile which is wider at the mouth of the groove (i.e. at the internal surface of the horn) than at the base, the profile preferably converging continuously towards the base, and the grooves of another group may have a profile which is narrower at the mouth of the groove than at the base, the profile preferably diverging continuously towards the base. Such groups may be interspersed with each other and/or with a group in which the groove profile is a conventional substantially rectangular shape.

Three examples of corrugation profiles which may be used in horns in accordance with the present invention for operation over two different frequency bands are illustrated diagramatically in the accompanying drawings, in which: Figure 1 is an axial section through part of the horn wall showing the first example, the internal configuration of the horn being formed by the surface of revolution of the section about the horn axis X; and, Figures 2 and 3 are views similar two that of Figure 1 but showing the second and third examples respectively.

In the drawings the internal wall S of each horn as diverging linearly from the throat end of the horn, although if preferred the wall may diverge following a curve approximating to a raised cosine shape.

In the first example shown in Figure 1 the corrugations in the horn wall S are formed by a series of two differently shaped grooves 1 and 2 which are arranged alternately along the length of the horn wall S and each of which has the same overall depth D. In each of the grooves 1 the upstream wall (i.e. the wall nearer the throat of the horn) is straight and the downstream wall (i.e. the wall nearerthe aperture of the horn) includes a right angled step 3 so that the groove has a wide entrance portion and a narrow base portion as shown. In contrast, in each of the grooves 2 the downstream wall is straight and the upstream wall has a right angled undercut 4 so that the groove has a narrow entrance portion and a wide base portion as shown.

In the example of Figure 2, the horn corrugations are again formed by a series of two differently shaped grooves 5 and 6 which are arranged alternately along the horn wall S and each of which has the same overall depth D. The grooves have trapezoidal profiles, the opposite walls of each groove 5 diverging towards the base, and the opposite walls of each groove 6 converging towards the base. The angles of divergence and convergence are the same so that the opposite walls of each section 7 of the horn between adjacent grooves are parallel to each other as shown. Horns having this configura tion are relatively easy to manufacture since the grooves 5 and 6 may be formed initially with rectan gular profiles as is conventional, the sections 7 between the grooves subsequently being bent to mod ifs the groove profiles as shown.

The example illustrated in Figure 3 also comprises a series of two differently shaped grooves 8 and 9 arranged alternately along the horn wall S and each having the same overall depth D. In this case, the grooves 8 have a conventional substantially rectangular profile, and the grooves 9 have a V-shaped profile. This example is also relatively easy to man ufactu re.

Claims

1. A corrugated feed horn for 2 reflector antenna, in which the corrugations are formed by a series of grooves having a common depth and comprising at least two different groups of grooves interspersed with each other, the grooves of each group having a profile which is of different shape from that of the grooves of the other group or groups, and the groove profiles being such that the horn is capable of operating under balanced hybrid conditions in at least two different frequency bands.

2. A horn according to claim 1, in which there are two groups of grooves, and the grooves of one group alternate with the grooves of the other group.

3. A horn according to claim 1, in which there are more than two groups of grooves, and the grooves are arranged so that the series comprises a number of successive identical sequences each containing one groove of each group.

4. A horn according to any one of claims 1 to 3, having a circular cross section and its internal surface profiled along the length of the horn so that it follows a curvature which approximates to a raised cosine shape.

5. A horn according to any one of the preceding claims, in which the grooves of one group have a profile which is wider at the mouth of the groove than at the base, the profile converging continuously towards the base.

6. A horn according to claim 5, in which the grooves of a second group have a profile which is narrower at the mouth of the groove than atthe base, the profile diverging continuously towards the base.

7. A horn according to claim 5 or claim 6, in which the grooves of another group have a profile which is substantially rectangular.

8. A horn according to claim 1, in which the grooves have profiles substantially as described with reference to any one of Figures 1 to 3 of the accompanying drawings.