Symmetrical Flexible Waveguide

Abstract

A waveguide twistable of the type which can be wound on a drum for simultaneously transmitting two mutually perpendicular linearly polarized electromagnetic waves comprises a metal tube which has a constant cross-sectional profile along its length. The profile is approximately square and has rounded corners and includes thin wall portions which extend along the entire length of the tube. The thin wall portions are appropriately shaped to maintain the profile substantially symmetrical with respect to imaginary mutually perpendicular lines drawn across the said profiles from the center of each square side when the waveguide is bent about a given radius of curvature, or twisted through a given torsional angle.

Description

BACKGROUND OF THE INVENTION

This invention relates to waveguides for the simultaneously transmission of two perpendicular, linearly polarized electromagnetic waves, and more particularly, to such a waveguide which has an effective inner periphery which is approximately square, has rounded corners, and which is twistable and can be wound on a drum.

There is increasing need for communication systems which permit multiple use of given equipment. It is known to simultaneously transmit over the antenna of a radio link communications utilizing two perpendicularly linearly polarized waves. To feed such antennas, two waveguide trains are normally required. Even if a waveguide with square cross section is used in which two mutually perpendicular polarized electromagnetic waves may be transmitted the expenditures for such a feeder line are relatively high. This is because a plurality of angles and elbows are required which are combined with the straight waveguide pieces by means of flange connections. Furthermore, each flange point increases total reflection factor of the feeder line in an undesirable manner.

Among the objects of the present invention is the provision of a waveguide which may simultaneously transmit two differently polarized waves, and which does not exhibit the above-mentioned drawbacks.

SUMMARY OF THE INVENTION

Briefly stated this and other objects of the invention are accomplished by forming the waveguide as a seamless metal tube whose wall thickness is sufficiently thin along a constant cross-sectional profile so that the tube may remain substantially symmetrical with respect to imaginary mutually perpendicular lines drawn across the profiles from the center of each square side when the waveguide is bent about a given radius of curvature or twisted through a given torsional angle.

BRIEF DESCRIPTION OF THE DRAWINGS

The single FIGURE of the drawing is a cross-sectional view through a waveguide constructed according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The waveguide of the present invention is formed from a seamless drawn aluminum tube. The inner periphery of the cross section of the waveguide has a constant profile which is substantially square with strongly rounded corners having a radius of curvature r. The two perpendicular cross-sectional axes A and B are of the same length. The wall has a different thickness at different points about the cross-sectional profile. Preferably the walls are thicker in the area of the rounded corners and thinner in the area between the corners. In the illustrated embodiment the minimum wall thickness marked d.sub.1 which is located in the middle of one of the square sides gradually increases to the maximum thickness d.sub.2 located at the corners. The outer edges of the waveguide are constructed in a continuous pattern. The inner surface 10 of the tube has straight wall portions 12 which are substantially planar, or curved slightly outwardly in a similar manner to portions 14, and curved portions 14 which are substantially round. The curved portions 14 have a radius of curvature r, and continue until they meet the straight wall portions 12. The curved sections 16 of the outer surface 18 have a radius of curvature R. These curved sections 16 continue in any way until they meet the other curved section of the outer surface 18.

The inner straight wall portions 12 on opposite sides of the waveguide cross section are parallel to each other. Curved portions 14 and 16 are curved symmetrically relative to axes A and B and remain symmetrical to these axes during bending or twisting. The cross section also remains uniform through the deformed section.

The possibility of bending or twisting such a waveguide is naturally highest for any given size if the shape of the cross section of its inner periphery is circular. The inner periphery deviates from the circular only to the extent that undesirable rotation of the fed-in waves is prevented.

In order to assure necessary decoupling of the mutually perpendicular waves, care must be taken during the manufacture and the installation of the waveguide to avoid interference with the symmetry of the cross section to the greatest extent possible.

The waveguide may be constructed as a seamless, extruded aluminum tube. Furthermore, it can be utilized for the rapid construction of radio links as a feeder waveguide for antennas without requiring the use of elbows, angular pieces or the like. Accordingly it may be quickly and simply installed. The reflection points which occurred in known feeder lines constructed from a plurality of partial sections are eliminated.

The following table shows exemplary parameters of a waveguide according to the present invention: ---------------------------------------------------------------------------

A or B 40 mm. r 22 mm. R 28 mm. d.sub.1 2 mm. d.sub.2 Band Width 10% Maximum Torsional Angle 90% Minimum Radius of Curvature 600 mm. ---------------------------------------------------------------------------

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations.

Claims

I claim:

1. A twistable flexible waveguide of the type which can be wound on a drum for the simultaneous transmission of two mutually perpendicular, linearly polarized electromagnetic waves comprising:

a thin-walled seamless aluminum tube having a cross-sectional profile which is constant along its length; said cross-sectional profile of said tube having an inner periphery which is approximately square and has rounded corners, and an outer periphery which is formed with a continuous pattern; said thin wall of said tube having a thickness which varies along its cross-sectional profile so that it has a maximum thickness in the region of said rounded corners and a minimum thickness midway therebetween, whereby said cross-sectional profile is maintained substantially symmetrical with respect to imaginary mutually perpendicular lines drawn across said cross-sectional profile from the center of each square side when the waveguide is bent about a given radius of curvature or twisted through a given torsional angle.

2. The combination of claim 1 wherein the opposite sides of the inner periphery of said cross-sectional profile includes surface portions which are parallel to each other.

3. The combination of claim 1 wherein the opposite sides of the inner periphery of said cross section includes symmetrical curved surfaces.

4. The combination of claim 3 wherein said curved surfaces form an inner periphery which deviates from the circular shape only sufficiently to constitute means for preventing undesired rotation of the fed-in waves.