AU613607B2

AU613607B2 - Broad-band polarisation duplexer

Info

Publication number: AU613607B2
Application number: AU13398/88A
Authority: AU
Inventors: Eberhard Schuegraf
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1987-03-24
Filing date: 1988-03-23
Publication date: 1991-08-08
Anticipated expiration: 2008-03-23
Also published as: AU1339888A; EP0284911A1; ATE77004T1; EP0284911B1; DE3871586D1

Abstract

The invention relates to a broadband, compact polarising junction which can be manufactured using milling techniques and has a waveguide (4) carrying two orthogonal linear polarisations, a first rectangular waveguide arm (1) of which, which runs at its end axially with respect to the waveguide carrying the two orthogonal polarisations, is branched via a first waveguide fork, designed symmetrically with two partial arms (20, 21), and a second waveguide arm (2) of which originates in the axial direction and is led out laterally, with a rectangular cross-section, via an E-bend (12) from the space between the waveguide fork partial arms (20, 21) and, in whose transition zone to the waveguide carrying the two orthogonal polarisations, there is anchored a centre plate (8), extending over the complete broad side dimension (a) of the waveguide, which is approximately half as wide as the narrow side (b1) of the waveguide and which thus splits the waveguide in this transition zone, in the manner of a fork, into two partial arms (14, 15), taking into account that the characteristic impedances are kept precisely constant. A broadband polarising junction constructed according to the invention can be used in satellites and directional radio antennas. <IMAGE>

Description

0g I Mef 51593 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name and Address of Applicant: Siemens Aktiengesellschaft Nittelsbacher Platz 2 8000 Muenchen FEDERAL REPUBLIC OF GERMANY Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Broad-Band Polarisation Ouplexer The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/3 1 v ir L 2 BROAD-BAND POLARISATION DUPLEXER The present invention relates to a broad-band polarisation duplpxer for microwaves.

Polarisation duplexers are known in the art and examples of such devices can be found in U.S Patent No. 4,700,154 and German Patent Specification DE-O OS 33 45 689. The latter has a number of disadvantages in that the duplexer has a relatively large overall length and has a construction that is not suited to inexpensive production especially by numerically-controlled automatic milling machines.

It is an object of the present invention to substantially overcome the abovementioned problems through provision of a polarisation duplexer that operates over a broad-band, and is designed so that it may be produced relatively inexpensively by simple methods and most preferably having small transverse dimensions and overall length.

In accordance with the present invention there is disclosed a broad-band polarisation duplexer for microwaves, said duplexer comprising: a primary waveguide adapted to conduct two orthogonal linearly polarised waves; first and second partial arms forming a substantially symmetrical waveguide fork branching at an acute angle from said primary waveguide at positions mutually offset from the primary waveguide longitudinal axis, said first and second partial arms forming via corresponding first elbow bends, parallel arms extending to corresponding second elbow bends which connect said arms to a common series trunk comprising a first waveguide of substantially rectangular cross-section extending from said arms and aligned with said primary waveguide longitudinal axis, said first and second partial arms being adapted to convey one of said orthogonally pclarlsed waves to and from said first waveguide; a second waveguide of substantially rectangular cross-section extending via a third elbow bend from said primary waveguide substantially perpendicular to said primary waveguide longitudinal axis, said third elbow being located between said first and second partial arms of said waveguide fork, said second waveguide being adapted to convey the other one of said orthogonally polarised waves; and IAD/103$6 I_ J -Y 2A a central plate of generally isosceles triangular configuration having its apex aligned with said primary waveguide longitudinal axis, its substantially equal side edges forming, in part, said substantially symmetrical waveguide fork, and the substantially flat opposite surfaces of said central plate being substantially equally spaced from the interior surfaces of said third elbow bend by a distance substantially equal to one IAD/10350 3 half the smaller dimension of said second rectangular waveguide, whereby said plate defines a transition zone between said pri \ry waveguide and said first and second waveguides which maintains the impedances of all three waveguides substantially constant.

A preferred embodiment of tie present invention will now be described with reference to the drawings in which: Fig. 1 is a perspective view of the preferred embodiment; Fig. a, is a perspective view of the central plate adapted for insertion into the duplexer of Fig. 1; Fig. 3 is a cross-section of the preferred embodiment taken along line Ill-Ill of Fig. 4; and Fig. 4 is a cross-section taken along the line IV-IV of Fig. 3.

The preferred embodiment shown in the drawings includes a coaxial waveguide 4 consisting of an inner guide 10 of circular cross-section and an outer guide 11 of round cross-section. The coaxial waveguide 4 is adapted to conduct two orthogonal linearly polarised waves and also defines the longitudinal axis 13 of the polarisation duplexer.

Extending, in one polarisation plane from the coaxial waveguide 4, are two partial arms 30 and 31 forming a substantially symmetrical waveguide fork that branches at an acute angle from the coaxial waveguide 4 at positions mutually offset from the longitudinal axis 13. Elbow bends and 5 respectively connect to the partial arms 30 and 31 form parallel arms 21 and 20. The parallel arms 20 and 21 extend to corresponding elbow bends 23 and 24 which connect the arms 20 and 21 to a common series trunk 22 connected to a first waveguide 1.

The waveguide 1 is of substantially rectangular cross-section having side lengths and The parallel arms 20 anc 21 preferably have a bisected waveguide height "bT b 1 /2 a/4".

Extending from the waveguide 4 between the partial arms 30 and 31 is c. second waveguide 2 adapted to conduct linearly polarised waves orthogonal to those conducted by the first waveguide 1.

In the illustrated embodiment, the rectangular waveguides 1 and 2 are shown with side dimensions "a 2bl". However, as understood by those skilled in the art they can be constructed with "b a/2".

Furthermore, the distance "LK" from the common series trunk 22 to the IAD/10350 i I 4elbow bends 23 and 24 is chosen so that the second rectangular waveguide 2 has space between the inner broadside walls of the waveguide fork and the parallel arms 20 and 21.

As seen in Fig. 3, the second waveguide 2 penetrates the partial arms 30 and 31 at cross-sections 3 and The correct location of the point of penetration of the waveguides provides for substantially exact matching of the waveguide impedances, Cross-section 6 defines the point at which the partial arms 30 and 31 open into the coaxial waveguide 4. This achieves matching of the wave impedances of the partial arms 30 and 31. Thus, the illustrated duplexer comprises only a short region between the cross-sections 3 and and the cross section 6 in which the transition zone between waveguides is inhomogenous with respect to wave impedances.

Such a situation necessitates a matching operation, The second waveguide 2 extends from between the parallel arms 20 and 21 by means of a 900 elbow bend 12. As seen in Fig. 4, the elbow bend 12 is constructed with a 90° corner projection 7 instead of a standard oblique outer corner, in order to facilitate production.

The waveguide 2 is internally divided by a central plate 8 extending over its broad side dimension and having a thickness of approximately "b 1 The central plate 8 thus forms within the waveguide 2, two partial arms 14 and 15 which have wave impedances kept precisely constant.

The lateral displacement of the waves in the second waveguide 2 caused by insertion of the central plate 8 is compensated by optimising the distance between the front surface 17 of the central plate 8 and the plane of a step 16 formed in the waveguide 2. Because of the division into partial arms 14 and 15, the reactance at the position of transition 6 with the coaxial waveguide 4, is matched in terms of wave impedances, thus the reactance becomes smaller and therefore capable of better compensation.

Furthermore, the inner guide 10 is secured to the rear surface 18 of the central plate 8. The plate 8 is firmly anchored in the narrow-side walls of the second waveguide 2 by means of two tab surfaces 9 and 9'.

Such a mode of fitting and mounting the inner guide 10 to the central plate IAD/1035o 5 8 can also be beneficially transferred to many other known polarisation duplexers.

With reference to Fig. 4, it will seen by those skilled in the art that the polarisation duplexer is, with the exception of the exiting second waveguide 2, divided symmetrically in mirror image terms about the longitudinal axis 13. Such an arrangement lends itself for production by a milling machine having control in a single plane.

As shown at the bottom in Figs. 3 and 4, the coaxial waveguide 4 with the inner guide 10 and the outer guide 11 can be continued homogenously after the cross-section 6, as far as a downstream load, a horn radiator for example. Alternatively, if the inner guide 10 is not required, then such an arrangement can be achieved by means of a constant or stepped transition.

In Figs. 3 and 4, a two-stage, rotationally-symmetrical quarter-wavelength transformer with a stepped inner guide 19 and an oppositely-stepped outer guide 25 (constant H 11 limiting frequency, frequency-independent wave impedance stages) is shown in broken lines. It is also possible to shift the transformer further into th. bifurcation zone of the polarisation duplexer upwards in Figs. 1 and so that only the lowest transformer stage is still constructed as a coaxial waveguide.

The use of the inner guide 10 creates the possibility of reducing or entirely eliminating disturbing wave impeaance jumps along the two passages of the polarisation duplexer. Whilst the transmission wave impedances of the rectangular polarisation duplexer waveguides 1 and 2 with their side ratios "a 2bl" are essentially predetermined, the transmission wave impedance of the round, outer waveguide Ti is not specified, and is therefore freely selectable. This creates the possibility of reducing the transmission wave impedance of the outer waveguide 11, and thus approximating that transmission wave impedance to the transmission wave impedances of the rectangular waveguides 1 and 2. Ideal matching conditions prevail when the transmission wave impedances of the outer waveguide 11 are matched, over a broad band, to those of the rectangular waveguides 1 and 2.

The matching of the wave impedances achieved over very large bandwidths if the following two conditions are fulfilled. Firstly, the IAD/10350 /0 i\

B

6 matching of the cross-section factors in the wave impedance equations of the waveguides to be maLched to one another and secondly, the matching of the limiting frequencies of the wave types to be converted into one another. In this case, any remaining reactance jumps in the waveguides can then be matched by transformation measures requiring only short overall lengths. The application of this principle leads to a substantially enlarged bandwidth with little reflection.

The use of the inner guide 10 achieves not only the desired reduction in wave impedance, but, in addition, a substantial reduction of the ambiguity range in the coaxial waveguide 4. For even narrower ambiguity ranges, other cross-sectional shapes of the inner guide 10 are possible, e.g. a cross-shaped or a square cross-section. The inner guide 10 gives rise to very low supplementary losses and brings a series of further advantages. The inner guide 10 extended beyond the polarisation duplexer is capable of improving the performance of a load connected to the polarisation duplexer, e.g. the bandwidth of the reflection freedom on a grooved horn and its cross polarisation properties in relation to the horn supply. In this case, the inner guide 10 can end in the horn throat, in the grooved region, outside the horn aperture, in a stepped configuration or discontinuously. Furthermore, in an inner guide 10 designed to be hollow, space can be created for waves of the same or a different type with the same or a different frequency compared to those waves already present outside the inner guide 10. In addition, the interior space of the inner guide 10 can be provided in a suitable manner with conductive material or with dielectric. Furthermore, coupling uevices for waves which are coupled out of the space outside the inner guide 10 into its interior and coversely can be disposed in the interior space of the inner guide and/or near its surface.

The preferred embodiment can be constructed in two parts which are identical enantiomorphically, except for the fact that th& a"^of the second waveguide 2 exhibits a rectangular cross-section. In this connection, a mirror plane is formed in the central nlane of the two parallel arms 20,21 of the waveguide fork and the first waveguide 1, which is free from cross-currents. These two parts can be produced by IAD/10350 L -7 controlling a milling cutter in a single plane. Thus, a substantial commercial value for the polarisation duplexer can be seen in that it consists of only two main parts, which are to a large extent symmetrical in mirror-image terms, and which can be produced very inexpensively by simple numerically-controlled automatic milling machines.

The foregoing describes only one embodiment of the present invention and other embodiments, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.

LN

I'4, IAD/1035o I

Claims

1. A broad-band polarisation duplexer for microwaves, said duplexer comprising: a primary waveguide adapted to conduct two orthogonal linearly polarised waves; first and second partial arms forming a substan' ally symmetrical waveguide fork branching at an acute angle from said primary waveguide at positions mutually offset from the primary waveguide longitudinal axis, said first and second partial arms forming via corresponding first elbow bends, parallel arms extending to corresponding second elbow bends which connect said arms to a common series trunk comprising a first waveguide of substantially rectangular cross-section extending from said arms and aligned ,iith said primary waveguide longitudinal axis, said first and second partial arms being adapted to convey one of said orthogonally polarised waves to and from said first waveguide; a second waveguide of substantially rectangular cross-section extending via a third elbow bend from said primary waveguide substantially perpendicular to said p-imary waveguide longitudinal axis, said third elbow being located between said first and second partial arms of said waveguide fork, said second waveguide being adapted to convey the other one of said orthogonally polarised waves; and a central plate of generally Isosceles triangular configuration having its apex aligned with said primary waveguide longitudinal axis, its substantially equal side edges forming, in part, said substantially symmetrical waveguide fork, and the substantially flat opposite surfaces of said central plate being substantially equally spaced from the interior surfaces of said third elbow bend by a distance substantially equal to one half the smaller dimension of said second waveguide, whereby said plate defines a transition zone between said primary waveguide and said first and second waveguides which maintains the impedances of all three waveguides substantially constant.

2. A polarisation duplexer as claimed in claim 1 wherein the apex of said central plate is suLstantially rectangular in shape to form said symmetrical waveguide fork so as to also include a rec qular fork IAD/1035 0 'rvaf -I I; 1~1 ;i I-LIP L~- i I- I~ 9 having third and fourth partial arms of substantially rectangular cross-section, said central plate being sized such that said transition zone between said primary waveguide and said third and fourth partial arms is substantially rectangular having its smaller dimension substantially equal to one half the smaller dimension of said first waveguide.

3. A polarisation duplexer as claimed in claim 1 or 2 wherein the width of the narrow side of said second waveguide between said third elbow bend and said central plate exhibits a step enabling cancellation of capacitive reactance in said second waveguide by optimisation of the distance between the respective opposite surfaces of said plate and the plane of the step.

4. A polarisation duplexer as claimed in any one of the preceding claims wherein said third elbow bend Is a 90° bend and is provided with a corner projection directed into the interior of the bend from its outer corner.

A polarisation duplexer as claimed in any one of the preceding claims wherein said primary waveguide comprises either a round or square outer guide and an inner guide secured to the surfaces of said central plate to form a coaxial primary waveguide, said inner guide being dimensioned such that the transmission wave impedance of the primary waveguide is matched to the wave impedance of the first waveguide and to the wave impedance of the second wavegulde, and thus satisfying two conditions, namely the matching of the cross-section factors in the wave impedance equations of the waveguldes, and the matching of the limiting frequencies of the remaining reactances in the waveguides, the latter being matched by transformation means requiring only short overall lengths,

6. A polarisation duplexer as claimed In any one of riaims 1 to 4 wherein the primary waveguide comprises either a round or square outer guide and an inner guide secured to the surfaces of the central plate, said inner guide tapering constantly or in a stepped configuration to form a quarter-wavelength transformer together with said outer guide shaped or stepped in a correspondingly opposite manner.

7. A polarisation duplexer as claimed in claim 5 or 6, in which entrances to said third and fourth arms are constructed with their smaller dimension being substantially reduced compared with the smaller 10350 rris -ra~~ 10 dimension of said first and second waveguides such that the transmission wave impedance of said entrances is matched by intensified capacity of loading through provision of a thicker said inner guide and/or by internal longitudinal metal webs at the outer wall thereof.

8. A polarisation duplexer as claimed in claim 5 or claim 7, wherein said inner guide is continued, homogenously beyond the actual polarisation duplexer region as far as a load such as a horn radiator.

9. A polarisatlon duplexer as claimed in any une of claims 5 to 8, wherein said Inner guide exhibits a circular cross-section.

A polarisation duplexer as claimed in any one of claims 5 to 8, wherein said inner guide exhibits a cross-shaped or a square cross-section.

11. A polarisation duplexer as claimed in any one of claims 5 to 8, wherein said inner guide exhibits a circular cross-section with symmetrically disposed longitudinal webs.

12. A polarisation duplexer as claimed in any one of the preceding claims, wherein the duplexer is constructed from two parts which are identical in mirror-image terms with the exception of an entrance of the second waveguide, the mirror plane being formed by the cross-current-free central plane of the waveguide fork, exhibiting said first and second partial arms, for the first waveguide.

13, A polarisation duplexer as claimed in claim 12, in which production has been effected using milling technology and numerical control of the milling cutter taking place In a single plane.

14. A polarisation duplexer as claimed in any preceding claim, in which a respective frequency duplexer is connected to each of said first and second waveguides via a respective long line, which is constructed as an over-moded rectangular waveguide provided with appropriate transitions. A polarisation duplexer substantially as described with reference to Figures 1, 2, 3 and 4 of the drawings. DATED this TWENTY-THIRD day of MAY 1991 Siemens Aktiengesellschaft Patent Attorneys for the Applicant SPRUSON FERGUSON i 4 0* .IW