WO1986005326A1

WO1986005326A1 - Constant e-plane beamwidth horn

Info

Publication number: WO1986005326A1
Application number: PCT/AU1986/000047
Authority: WO
Inventors: Kenneth Martin Harvey
Original assignee: The Commonwealth Of Australia Care Of The Secretar
Priority date: 1985-03-01
Filing date: 1986-02-27
Publication date: 1986-09-12

Abstract

A constant E-plane beamwidth horn having spaced apart H-plane walls (1) and spaced apart E-plane walls (2) radiating from a throat (3) to a mouth (4) has E-plane walls (2) curve outwardly from the throat (3) to the mouth (4) in a generally arcuate preferably radiused (R) form whereby a small variance in beamwidth across a wide frequency is achieved, and optionally terminate in a common plane at the mouth or continue outwardly at a lesser radius (r).

Description

CONSTANT E-PLANE BEAMWIDTH HORN

This invention relates to a constant E-plane beamwidth horn and in particular it relates to a horn of the type which normally involves a long microwave pyramidal horn fed from a rectangular 5. waveguide.

To fully understand the basis of the invention reference may be had to the reference in the "Transactions on IEEE Antennas and Propagation, Vol AP-30 No. A, July, 1982" which shows a horn 10. of this general characteristic and shows how the horn is generally constructed to have straight sides expanding outwardly to a curved termination at the end. i It is known that the beamwidths in the

15. E and H planes vary inversely with frequency and that this relationship can be modified in the . H-plane by markedly increasing the flare angle and the aperture size simultaneously. This increases the phase change across the H-plane aperture which

20. effectively reduces the change in beamwidth as frequency increases. By judicious choice of H-plane aperture size and H-plane flare angle it is possible to design a horn that has a near constant H-plane beamwidth over at least an octave bandwidth.

25. The above procedure cannot however be adopted for achieving a constant E-plane beamwidth of such a horn because the aperture amplitude distribution in the E-plane is uniform whereas in the H-plane it is cosinυsoidal.

30. The present invention relates to a method of achieving a near constant E-plane beamwidth by the simple means of curving the E-plane sides of the horn. The invention comprises a constant E-plane beamwidth horn having spaced apart H-plane walls and spaced apart E-plane walls radiating from a throat to a mouth, characterised in that the E-plane 5. walls curve outwardly from the throat to the mouth in generally arcuate form whereby a small variance in beamwidth across a wide frequency is achieved.

The walls are preferably radiused from the throat, and can be terminated at the mouth by 10. continuations formed on a smaller radius.

FIG. 1 is a perspective front view of the horn showing the H and E plane;

FIG. 2 is a front elevation;

. FIG. 3 is a section on line 3-3 of 15. FIG. 2 to show particularly the "H" plane configuration, and

FIG. is a section on line 4-4 of FIG. 3 particularly the "E" plane configuration.

Although prior art has described a horn 20. with curved extremities, as shown in the prior art document referred to earlier herein, this was only for reducing the side-lobe level.

By using curved sides at or near the throat of the horn, it is possible to vary the wavefront 25. curvature at various points along the horn, this together with diffraction from the curved sides that varies with frequency, produces a horn that has, in simple terms only :- (a) an effective aperture that changes slightly with frequency;

(b) an effective wavefront curvature that changes slightly with frequency;

5. (c) an aperture amplitude distribution that is tapered.

This tapering of the amplitude distribution together with the high degree of wave curvature enables a horn to be designed having minimal variations 10. in beamwidth over a frequency band of up to 2.4:1.

Referring to the drawings, FIG. 1 shows the horn formed by the two H-plane walls 1 that is the walls that form the boundries of the H-plane cross section and the two E-plane walls 2, the H-plane walls 15. being relatively planar and spaced apart, the E-plane walls being outwardly curved from the throat 3 to the mouth 4. A waveguide 5 is shown in FIG.

1 joined to the throat 3.

In a preferred form the E-plane walls are 20. radiused about the points R, the E-plane walls

2 being positioned to give a smooth entrance curvature at the throat 3 from the waveguide 5, the walls conveniently continuing to flare into a plane at the mouth 4.

25. The continuations 6 are optional and as shown in FIG. 4 are curved about radius points r to reduce edge diffraction at the extreme ends of the curved sides (2).

The H-plane walls 1 can similarly have flare 30. extensions 7 as shown in dotted lines in FIG. 3. As an example, a horn having B - 8.2 mm and R - 55 mm was found to exhibit a minimum beamwidt of 39.1° and a maximum beamwidth of 47.9 over the frequency band 8 to 18 GHz.

5. This design also showed in the E-plane a side-lobe level considerably lower than a conventional horn.

In explanation of the principle of the inventi curved sides at or near _the throat of the horn 10. and extending out to the furthest edge gives rise to two consequences. Firstly, edge diffraction is either eliminated or reduced. Ray contribution to the far field is from the direct wave plus extende diffraction from the curved sides. This is equivalen

15. . to an amplitude distribution across the effective aperture that is tapered. Secondly, the wave front across the effective aperture is curved to a marked degree. It is therefore now possible to achieve a horn design that has small variance in beamwidth

20. across a wide frequency band as was possible in the H-plane. The principle is an extension of the work described in the cited reference whereby the aperture and flare angle are optimised specifical for constant beamwidth properties.

25. The horn shown has central ridges 8 on the E-plane walls which reduce in height outwardly toward the mouth 4.

It is to be remembered from the foregoing that while radii have been referred to, the curvature

30. can be varied to suit conditions but the invention resides in using curved side walls in the E-plane of the horn such that there is a gradual expansion instead of a elongated straight-sided expanded horn with perhaps a flare at the end.

Claims

_CLAMS.

1. A constant E-plane beamwidth horn having spaced apart H-plane walls (1) and spaced apart E-plane walls (2) radiating from a throat (3) to a mouth (4), characterised in that the E-plane

5 walls (2) curve outwardly from the throat (3) to the mouth (4) in a generally arcuate form whereby a small variance in beamwidth across a wide frequency is achieved.

2. A constant E-plane beamwidth horn according to claim 1 wherein the said E-plane walls (2) are radiused from the throat (3) to the mouth (4).

3. A constant E-plane beamwidth horn according to claim 2 wherein the E-plane walls (2) are curved about radius points (R) positioned to give a smooth entrance curvature at the throat (3) from a waveguide

5. (5).

4. A constant E-plane bandwidth horn according to claim 3 wherein the walls flare into a plane at the mouth (4) .

5. A constant E-plane bandwidth horn according to claim 1 wherein the E-plane walls (2) have continuations at (6) at the mouth (4) formed at a more acute curvature than the curvature of the E-plane walls (2) .

6. A constant E-plane bandwidth horn according to claim 5 wherein the continuations (6) are curved about a radius point (r), said radius being smaller than the radius of the E-plane walls (2).

7. A constant E-plane bandwidth horn according to claim 1 wherein the H-plane walls (1) are tapered and have outwardly directed flare extensions (7) at the mouth.

8. A constant E-plane bandwidth horn according to claim 1 wherein the throat (3) and the mouth

(4) are rectangular in cross-section and the E-plane walls (2) have central ridges (8) reducing in height _# outwardly toward the mouth 4.

9. A constant E-plane bandwidth horn constructed and operating substantially as described and illustrate in the accompanying drawings.