GB2161027A - Corrugated rectangular waveguide horns - Google Patents

Abstract

A four wall corrugated rectangular waveguide horn has the corrugations in adjacent walls (1, 2) axially offset from each other so that the corrugation slots S in each wall are aligned with the ribs R between the corrugation slots S in the two adjacent walls. Preferably the width of each slot S in each wall of the horn is less than that of the aligned ribs R on the adjacent walls so that the slot is axially separated from the preceding and succeeding slots in the adjacent walls by portions (5) of the aligned ribs R. The construction is intended to reduce or prevent cross-coupling between the slots in adjacent walls of the horn. <IMAGE>

Description

SPECIFICATION Corrugated rectangular waveguide horns This invention relates to corrugated rectangular waveguide horns in which all four walls are corrugated.

Such horns are able to generate a beam with a non circular symmetry, e.g. an elliptical beam, and are therefore potentially very suitable for antenna systems which are designed to operate with such beams, such as in some satellite communication or radar systems. Also a cartesian (rectangular) waveguide feed system enables a tracking capability to be realised more easily than a circular system.

Conventional four wall corrugated rectangular horns have the corrugation slots in each wall aligned with the slots in its adjacent walls so that the corresponding slots of adjacent walls lie in the same transverse plane, and the design is generally based on a modal analysis of superimposed two wall corrugated rectangular waveguides. The validity of this design approach has never been properly established and in practice the radiation performance of conventional four wall corrugated rectangular horns has proved to be less than satisfactory, particularly over relatively wide frequency bands of 20% or more.In particular, the horns are susceptible to over-moding at specific frequencies, with the result that high levels of cross polarisation and deformation of the co-polar main beam can occur at these frequencies, and it has been found that this occurs whether the slots are continuous around the horn or are corner filled. One reason subscribed for this is that cross coupling occurs at the junctions between the slots in adjacent walls of the horn, even with corner filling, producing unwanted mode conversions and giving rise to cross polarisation.

With the aim of overcoming the problem, according to the invention, we propose a corrugated rectangular waveguide horn which has all four walls corrugated and in which the corrugation slots in each wall are aligned with the ribs between the corrugation slots in the two adjacent walls.

With this arrangement the slots in each wall of the horn are not aligned with the slots in the adjacent walls as in conventional four wall corrugated rectangular horns, but are axially displaced relative thereto so that their ends are blocked by the ribs on the adjacent walls.

This substantially prevents cross coupling between the slots in adjacent walls and avoids unwanted mode conversion, and it is considered that the utilisation of this construction will greatly improve the radiation performance, particularly with regard to the cross polar characteristics, of a four wall corrugated rectangular horn.

The width of each slot in each wall of the horn may be the same as the width of the aligned ribs on the adjacent walls. In this case the ribs of each wall of the horn are effectively interleaved with the ribs of the adjacent walls, with the result that the slots in each wall alternate with the slots in the adjacent walls with the leading face of each slot lying in the same transverse plane as the trailing face of a slot in each adjacent wall.

Preferably, however, the width of each slot in each wall of the horn is less than that of the aligned ribs on the adjacent walls so that the slot is axially separated from the preceding and succeeding slots in the adjacent walls by portions of the aligned ribs. It is thought that this construction should prevent crosscoupling between the slots in adjacent walls still further.

Generally the slot and rib widths will each be uniform throughout the horn, although the slot depth may be varied in accordance with known practice, taking into account the optimum slot depth (A 9/4) at the aperture of the horn and the optimum slot depth (A 9/2) for matching purposes at the throat of the horn.

Two examples of a four wall corrugated rectangular horn in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic perspective view, partly in section, of a first example, in which, for the sake of clarity, corrugations have been shown on two adjacent walls only; Figure 2 is a perspective view to a larger scale of a portion of the horn shown in Fig. 1, showing more clearly the junction between two adjacent corrugated walls; and, Figure 3 is a view similar to that of Fig. 2, but showing the junction between two adjacent corrugated walls of the second example.

In the example shown in Figs. 1 and 2, the horn is a linearly flared rectangular horn having four corrugated walls 1, 2, 3 and 4. The corrugations in the bottom wall 1 of the horn comprise a series of transverse slots S of uniform width separated from each other by ribs R of the same width as the slots. The adjacent side wall 2 of the horn contains a series of corrugations which is identical to that of the bottom wall 1, but which is displaced relative thereto, in the axial direction z of the horn by a distance which is half the corrugation period and which in this case is equal to the width of a slot S or rib R.The ribs R of the corrugations in the bottom wall 1 of the horn are thus interleaved with the ribs R of the corrugations in the side wall 2, with the result that, at the junction between the walls 1 and 2, each corrugation slot S in each wall is aligned with and terminated by a rib R of the other wall.

Although not shown, the arrangement of the corrugations in the top wall 3 and the other side wall 4 of the horn are arranged in an identical manner to those in the walls 1 and 2 respectively, such that the arrangement of the ribs and slots at each of the junctions between two adjacent walls is the same as that shown in Fig. 2. It follows therefore that the ribs and slots of the corrugations in the top and bottom walls 1 and 3 of the horn are directly opposite each other, and that the ribs and slots of the corrugations in the two side walls 2 and 4 are also directly opposite each other but offset in the axial direction z of the horn with respect to the corrugations in the top and bottom walls 1 and 3 by the spacing between the slots (i.e. the width of the ribs).

The example illustrated in Fig. 3 is of a horn which is the same as that shown in Figs.

1 and 2 except that the width of the ribs R is greater than that of the slots S. In this case the axial offset of the corrugations in adjacent walls is such that, as shown in Fig. 3, the centre line of each slot S in the wall 1 intersects the center line of a rib R of the adjacent wall 2 at the junction between the two walls, and because the ribs R are of greater width than the slots S the ribs R of the wall 1 overlap the offset ribs R of the wall 2 at the junction between the walls. The overlapping portions 5 of the ribs R separate axially the slots S of the wall 1 from the slots S of the wall 2, and since the other two walls of the horn (not shown) are mirror images of the walls 1 and 2, each pair of opposite slots in one pair of opposite walls will be separated from an adjacent pair of opposite slots in the opposite pair of walls by a smooth walled portion of the horn formed by the intervening overlapping portions 5 of the ribs R aligned with the relevant slots.

Claims (5)

1. A corrugated rectangular waveguide horn which has all four walls corrugated and in which the corrugation slots in each wall are aligned with the ribs between the corrugation slots in the two adjacent walls.

2. A horn according to Claim 1, in which the width of each slot in each wall of the horn is the same as the width of the aligned ribs on the adjacent walls.

3. A horn according to Claim 1, in which the width of each slot in each wall of the horn is less than that of the aligned ribs on the adjacent walls so that the slot is axially separated from the preceding and succeeding slots in the adjacent walls by portions of the aligned ribs.

4. A horn according to Claim 2 or Claim 3, in which the width of the slots in each wall of the horn is the same as that of the slots in the adjacent walls.

5. A horn according to Claim 1, substantially as described with reference to Figs. 1 and 2, or Fig. 3, of the accompanying drawings.