EP0285879B1 - Broad-band polarizing junction - Google Patents

Abstract

Measures are provided in two waveguides (7) carrying two orthogonal linear polarisations, e.g. the incorporation of an inner conductor (8) and/or of symmetrically arranged metal longitudinal webs, as a result of which its characteristic impedance can be approximated to (or, if necessary, matched to) the characteristic impedances of the two polarisation-selective rectangular waveguide arms (10, 11). In this case, two conditions must be met, namely, firstly matching the cross-section factors in the characteristic impedance equations of the waveguides to be matched to one another and secondly, matching the limit frequencies of the wave types which are to be merged. Residual reactances in the junction passages can then be matched, in a broadband manner, in a very short space without difficulties. The measures specified in the invention can be used in the case of broadband polarising junctions for satellite radio and directional radio antennas. <IMAGE>

Description

The invention relates to a broadband polarization switch for separating orthogonally linearly polarized electromagnetic microwaves with a branching device which divides a waveguide guiding the two orthogonal polarizations into two rectangular waveguide arms which each only carry one of these polarizations and which have the same line impedance.

) besteht bei allen bekannten Polarisationsweichen nach der Wellenwiderstandsgleichung

ein Wellenwiderstandssprung Z_rund bwz. Z_Quadrat / Z_Rechteck ≈ 2. In der vorstehenden Gleichung ist Z der Leitungswellenwiderstand, b . K / a der Querschnittsfaktor für die jeweilige Welle im Rechteckhohlleiter, Z_o der Feldwellenwiderstand einer ebenen Welle im freien Raum, λ_o die Wellenlänge im freien Raum und λ_k die jeweilige kritische Wellenlänge, die auch Grenzwellenlänge des betrachteten Wellentyps genannt wird. Eine breitbandige Anpassung des Wellenwiderstandssprungs zwischen den Leitungen ist - jedenfalls über große Bandbreiten von einer Oktave und mehr - prinzipiell unmöglich.Practically all known polarization switches lack the basic prerequisite for a real broadband adaptation, namely the wave resistance homogeneity along the two passages of such a switch; because between each of the two polarization-selective switch connections, which are always designed as rectangular waveguides with the aspect ratio a ≈ 2b, and the waveguide has a circular or square cross-section ( $\text{a = b}$

) exists in all known polarization switches according to the wave resistance equation

a wave resistance jump Z _around bwz. Z _square / Z _rectangle ≈ 2. In the above equation, Z is the line impedance, b. K / a the cross-sectional factor for the respective wave in the rectangular waveguide, Z _o the field wave resistance of a plane wave in free space, λ _o the wavelength in free space and λ _k the respective critical wavelength, which is also called the cut-off wavelength of the wave type under consideration. A broadband adaptation of the wave resistance jump between the lines is - in principle over wide bandwidths of one octave and more - impossible.

Attempts have been made to make the diagnosed surge in wave resistance at least narrow-band (up to approx. 20%) with low reflection with steady transitions, with deflection and short-circuit plates of the most varied cut of both end faces, with diaphragms, screw accumulations and the like.

From US-A-3 150 333 a polarization switch for separating two orthogonally linearly polarized electromagnetic waves using a branching device is known which divides a horn radiator guiding the two orthogonal polarizations into two rectangular waveguide arms which each only carry one of these polarizations. The latter two arms have equally large line wave resistance values. By arranging a pyramid-shaped metal core inside the horn, with the pyramid tip in the aperture area of the horn and the pyramid base in the interior of the branching area at the feed end of the horn, a gradual, steady impedance transformation from the wave resistance value of the rectangular waveguide arms guiding both polarizations to the wave resistance value of the horn radiator in the area reached its aperture. With this known steady-state impedance transition, the wave resistance jump is only made narrow-band with low reflection. This transition is not suitable for a broadband application.

The polarization switch known from GB-A-2 175 145 behaves in a similar manner and just as disadvantageously, in which the transition zone to the wave resistance transformation does not contain an ideal pyramid-shaped core, but rather a core which is often stepped in the manner of a staircase and consists of a series of parallelepipedic elements of square cross-section consists.

The object of the invention is to provide a possibility with which the interfering jumps in wave resistance in the case of broadband polarization switches to be used are reduced or completely eliminated.

According to the invention, which relates to broadband polarization switches of the type mentioned, this object is achieved in that the waveguide carrying the two polarizations has a line impedance whose value corresponds at least approximately to that of the two rectangular waveguide arms, for which two conditions are met, namely on the one hand, the approximation of the cross-sectional factors in the wave resistance equations of the waveguides to be matched to one another and, on the other hand, the approximation of the cut-off frequencies of the wave types to be merged into one another in these waveguides, and that transformation measures requiring only short lengths to adapt remaining reactances in the waveguides are provided. The invention is based on the idea that the line wave resistances of the rectangular crossover waveguide arms with their aspect ratio a ≈ 2 b are fixed, whereas the line wave resistance of the waveguide carrying the two orthogonal polarizations is not fixed and can therefore be freely selected. This opens up the previously unused possibility of lowering the line wave resistance of the waveguide guiding the two orthogonal polarizations by the specified measures and thus at least approximating the line wave resistances of the rectangular waveguide arms. Ideal adaptation conditions prevail if the line wave resistances of the waveguide carrying the two orthogonal polarizations are broadband matched to those of the rectangular waveguide arms. By fulfilling the specified two conditions, namely on the one hand Alignment of the cross-sectional factors in the wave resistance equations of the waveguides to be matched to one another, for example the factor b according to the wave resistance equation given above. K / a for the H₁₀ wave in the rectangular waveguide, and the approximation of the cut-off frequencies of the wave types to be converted into one another, an adaptation of the wave resistances over very wide bandwidths is achieved. Both passes of such wave resistance-homogenized polarization switches then no longer contain any jumps in wave resistance, but only reactances which, as is known - in contrast to jumps in wave resistance - can be adapted very broadband. This principle of wave resistance homogenization can be applied to practically all known polarization switches. The result is always a wide range of reflection poor compared to previously much wider.

In the subclaims, advantageous and expedient implementation options of the invention for achieving a wave resistance homogeneity along the two passages of a broadband polarization filter are specified.

Fig. 1

zwei wellenwiderstandssenkende Maßnahmen im die beiden Orthogonalpolarisationen führenden Wellenleiter,

Fig. 2

eine Anzahl von Querschnittsmöglichkeiten bei einem die beiden Orthogonalpolarisationen führenden Wellenleiter jeweils mit einem Innenleiter mit reduziertem Wellenwiderstand und erweiterten Frequenz-Eindeutigkeitsbereichen,

Fig.3

einen meßtechnisch gewonnenen, quantitativen Zusammenhang zwischen dem Wellenwiderstand eines Koaxialwellenleiters mit rundem Innenleiter und seinem Durchmesserverhältnis von Innen- zu Außenleiterdurchmesser,

Fig. 4

ein Diagramm, bei dem für das Durchmesserverhältnis eines jeweils betrachteten Koaxialwellenleiters der Durchmesser desjenigen gedachten Rundhohlleiters ermittelt wird, der die gleiche H₁₁-Grenzfrequenz hat wie der Koaxialwellenleiter,

Fig. 5

ein Diagramm, in dem Frequenz-Eindeutigkeitsbereiche in Koaxialwellenleitern abhängig von ihrem Durchmesserverhältnis dargestellt sind,

Fig. 6

in einer Querschnittsdarstellung eines Koaxialwellenleiters das E-Feld der H₃₁-Störwelle,

Fig. 7

in einer Schrägansicht die Struktur einer Zweiband-Polarisationsweiche mit einem Innenleiter zur Reduzierung der Wellenwiderstandssprünge.

The invention and exemplary embodiments thereof are explained below with reference to seven figures. Show it

Fig. 1

two measures reducing the wave resistance in the waveguide guiding the two orthogonal polarizations,

Fig. 2

a number of cross-sectional possibilities in the case of a waveguide guiding the two orthogonal polarizations, each with an inner conductor with reduced wave resistance and extended frequency uniqueness ranges,

Fig. 3

a quantitative relationship between the wave resistance of a coaxial waveguide with a round inner conductor and its diameter ratio of inner to outer conductor diameter,

Fig. 4

a diagram in which the diameter of the imaginary circular waveguide is determined for the diameter ratio of a respective coaxial waveguide which has the same H₁₁ cut-off frequency as the coaxial waveguide,

Fig. 5

1 shows a diagram in which frequency uniqueness ranges in coaxial waveguides are shown depending on their diameter ratio,

Fig. 6

in a cross-sectional view of a coaxial waveguide, the E field of the H₃₁ interference wave,

Fig. 7

in an oblique view, the structure of a two-band polarization switch with an inner conductor to reduce the jumps in wave resistance.

To achieve the desired reduction in wave resistance in a waveguide having a round or square cross-section with an outer conductor 1 and having both orthogonal polarizations, either a symmetrical arrangement of at least four metal webs 2, 3, 4 and 5 on the inner surface of the wall of the outer conductor is suitable according to the left representation of FIG 1 or / and, as shown in the right-hand illustration of FIG. 1, a concentrically arranged inner conductor 6. In practice, the inner conductor 6 is easier to manufacture than the conductive webs 2, 3, 4 and 5 extending in the longitudinal direction of the waveguide. The inner conductor 6 is arranged in the central longitudinal axis of the outer conductor 1 and thus runs concentrically. The inner conductor 1 is preferably fixed in the bifurcation zone of the three polarization switch waveguides with the outer conductor contours, i.e. conductive, connected. This specially created attachment can be used universally and can be used for reflection compensation of both polarizations.

The simplest form of an inner conductor 6 is the circular cross-sectional shape shown in the right-hand illustration of FIG. 1. In addition to the desired reduction in wave resistance, a significant expansion of the uniqueness range for the coaxial waveguide is also achieved, for which quantitative information will follow in the further course of the description.

For even broader _{ranges of} uniqueness f _kE11 / f _kH11 , f _kH31 / f _kH11 and f _kE21 / f _kH10 , cheaper cross-sectional _{shapes of} the Inner conductor 6 possible, which are shown in Fig. 2 in detail. Thereafter, the inner conductor 6 can be, for example, cruciform, and combinations with a round or square outer conductor 1 without or with conductive longitudinal webs 2, 3, 4 and 5 are also possible.

According to the article by W. Baier: "Wave types in cables with a rectangular cross-section" from the magazine "AEÜ", volume 22 (1968), number 4, pages 179-185, in particular pages 184-185, the inner conductor 6 causes very little additional loss and brings the following additional advantages. The inner conductor 6, which is extended beyond the polarization switch, is suitable for improving the behavior of a consumer connected to the polarization switch, e.g. to improve the bandwidth of the low reflection of a grooved horn and its cross-polarization properties compared to horn feeding through a pure waveguide - i.e. without an inner conductor. In this case, the inner conductor 6 can end in the horn neck, in the groove area or outside the horn aperture in a steady, stepped or abrupt manner. Furthermore, space can be created in a hollow inner conductor 6 for waves of the same or different type with the same or different frequency as those waves already present outside the inner conductor 6. For this purpose, the interior of the inner conductor can in turn be suitably provided with conductive material or with a dielectric. In the interior of the inner conductor 6 and / or near its surface, coupling devices for waves can also be arranged, which are coupled from the space outside the inner conductor to its interior and vice versa.

Irrespective of its respective cross-sectional shape and that of the associated outer conductor 1, the inner conductor 6 predominantly increases the transverse capacitance in the wave resistance equivalent circuit diagram for H waves. Thus, the wave resistance of the H₁₁ wave or the H₁₀ wave - as intended - and the associated cutoff wavelengths increase.

For the simple, practical interesting case of the coaxial waveguide with a circular inner and outer conductor 3 shows the quantitative relationship between the characteristic impedance of this coaxial waveguide and its diameter ratio d / D _k from inner conductor diameter d to outer conductor diameter D _k . The measurements are carried out in such a way that, for coaxial waveguides with specific values of the diameter ratios (d / D _K ) _n , that rectangular waveguide with its aspect ratio (b / a) _{n is} determined, which results in broadband adaptation at the abrupt transition between the respective coaxial waveguide and the rectangular waveguide. Here, the limit frequencies of the H₁₀ wave in the rectangular waveguide and the H₁₁ wave in the coaxial waveguide are made the same. For this purpose, for the diameter ratio d / D _{k of} the respective coaxial waveguide from FIG. 4 according to Meinke, Gundlach: "Taschenbuch der Hochfrequenztechnik", 2nd edition, Springer-Verlag, page 309, the diameter D _o of the imaginary circular waveguide that determines the has the same H₁₁ cutoff frequency as the coaxial waveguide. The limit wavelength of the coaxial _{waveguide thus} results as λ _kH11 = 1.706 D _o and from this the desired broad side a of the rectangular waveguide with the matched H₁₀ limit wavelength 2a = 1.706 D _o .

In addition, in these measurements the reactance remaining at the cross-sectional jump is compensated for by a suitable longitudinal offset of the beginning of the inner conductor relative to the jump point. Such abrupt transitions from the rectangular waveguide to the coaxial waveguide require practically no overall length. They reach bandwidths of poor reflection up to an octave, and over 50% bandwidth their reflection is less than 1%. An important basic component of wave resistance homogeneous polarization switches is thus available.

Based on the quantitative relationships of the diameter ratios d / D _k of coaxial waveguides with their wave resistances, shown in Fig. 3, and their H₁₁ cut-off frequencies, shown in Fig. 4, can initially for the mostly given rectangular waveguide with a = 2b with respect to the wave resistance and the H₁₁ cutoff frequency to match Determine the coaxial waveguide. In this context, reference is made to the left column of the calculation table at the end of the description. In addition, there are completely new concept perspectives for the realization of polarization switches with extremely wide bandwidths due to the introduction of lower rectangular waveguides with b <a / 2 and the coaxial waveguides adapted to them with relatively thick inner conductors. For this purpose, the examples a = 3b and a = 4b are evaluated in the calculation table given at the end of the description. To assess the associated coaxial waveguide, their theoretical uniqueness ranges are then determined in view of the E₁₁ interference wave that occurs first with symmetrical H₁₁ excitation. The limiting frequency _ratios f _kE11 / f _kH11 depending on the diameter _ratio d / D _{k of} the coaxial waveguide according to FIG. 5 from Meinke, Gundlach: "Taschenbuch der Hochfrequenztechnik", Springer-Verlag, 2nd edition, 1962, page 309 are quantitative in character for lower-selected rectangular waveguides with b <a / 2 and the matching coaxial waveguides with relatively thick inner conductors, ambiguity ranges f _kE11 / f _kH11 , which become extremely rapidly wider with increasing diameter _ratio d / D _K and whose width for d / D _K → 1 against ∞ go.

Then the E₁₁-following H₃₁ interference wave according to Fig. 6 is also included in the observation. The H₃₁ interference wave is excited despite symmetrical excitation next to the H₁₁ fundamental wave, because according to Fig. 6 e.g. the E field strengths of the H₁₃ wave at diametrically opposite points on the circumference in the coaxial waveguide always have the same direction as the E fields of the H₁₁ wave.

With the introduction of the inner conductor, in addition to the broadband adjustment of the wave resistances, the range of uniqueness f _kH31 / f _{kH11 is} also expanded. According to FIG. 5, the coaxial waveguide matched to the rectangular waveguide with a = 2b with d / D _K = 0.37 has a usable uniqueness range f _kH31 / f _kH11 = 2.73 (compared to the usable uniqueness range f _kE11 / f _kH11 = 2.08 for the round waveguide without inner conductor). Because of the necessary distances between the operating frequencies and the limit frequencies, f _kH31 / f _kH11 = 2.73 corresponds to a usable bandwidth of f _h / f _n = 2.5 maximum. 5, the coaxial waveguide at d / D _K = 0.77 reaches a maximum of the width of the uniqueness range at f _kH31 / f _kH11 = 3.09 corresponding to a usable bandwidth of at most f _h / f _n = 2.8.

These numerical values apply to coaxial waveguides with round inner and outer conductors. Even larger useful bandwidths can be expected with coaxial waveguides, the cross-sectional variants of which are outlined in FIG. 2. The design of these cross-sections aims at the highest possible capacitive load on the H₁₁ wave - that is, on a low H₁₁ cutoff frequency - with the lowest possible capacitive load on the H₃₁ wave and a consequently high H₃₁ cutoff frequency. With these methods it seems possible, e.g. to master the practically interesting combination of the two directional radio ranges from 3.4 to 4.2 GHz and from 10.7 to 11.7 GHz with a single polarization switch.

As a practical application of the invention, a broadband polarization filter of a two-band antenna system for the directional radio frequency ranges 3.58 to 4.2 GHz and 6.425 to 7.125 GHz is explained below with reference to FIG. 7. For this frequency quotient f _h / f _n = 1.99, the circular waveguide 7 is unsuitable as a polarization waveguide as well as a horn waveguide because of its “multi-ripple” over frequency ranges which, including the necessary cut-off frequency _spacings f _kE11 / f _kH11 = 2.08. The inevitable expansion of the uniqueness range succeeds with the introduction of an inner conductor 8, so that according to FIG. 7, for example from the article by E. Schuegraf "Novel microwave switches for two-band antennas" from "NTZ", volume 38 (1985), number 8, pages 554 to 560 known double branch 9, which serves the E₁₁ and H₂₁ interference wave-free excitation of both polarizations, a coaxial waveguide, consisting of the inner conductor 8 and the outer conductor 7, is connected. Its uniqueness can be expanded to f _kE11 / f _kH11 = 2.274 with a relatively thin inner conductor 8 of d = 7.3 mm in outer conductor 7 with D _K = 52.2 mm. This means that f _kH11 = 3.21 GHz (11% below f _n = 3.58 GHz) and f _kE11 = 7.3 GHz, ie 2.5% above f _h = 7.125 GHz, at which there is sufficient interference field attenuation for the E₁₁ wave results. Thus, on the one hand, the E₁₁ interference field of the double branch 9 is sufficiently attenuated; and - since the inner conductor 8 is extended into the vicinity of the first groove of a connected grooved horn - the E₁₁ useful excitation in the groove region is decoupled from the horn waveguide with the aperiodic E₁₁ damping as desired. In addition, the shape of the inner conductor 8 has a very decisive influence on the horn reflection and also on the cross-polarization suppression, even with very small changes.

The rectangular waveguide accesses 10 and 11 of the polarization switch shown in FIG. 7 are designed with a = 2 b = 46 mm. Both waveguide forks 12, 12' and 13, 13' and the double branch 9 are impedance homogeneous, and matching coaxial waveguide has. 3 and 4 D _K = 43 mm and d = 16 mm according to FIG. This dimensioning represents the prototype of the wave resistance-homogeneous polarization switch according to the invention.

In the arrangement in FIG. 7, the remaining jump in wave resistance between the previously determined coaxial waveguide (d = 16 mm, D _K = 43 mm) and that leading to the horn with D _K = 52.2 mm and d = 7.3 mm is advantageously on 1.6 reduced and is bridged by λ _H / 4 transformation stages with little reflection. The rotationally symmetrical transformer offers many, easily implemented correction options that always have the same effect for both polarizations.

The polarization switch shown in the exemplary embodiment according to FIG. 7 has a very large useful bandwidth. Therefore, it is particularly suitable for the fact that on its rectangular waveguide arms 10 and 11 a crossover for two or more microwave radio frequency ranges different frequency position is connected (directly). In addition, the connection between the two rectangular waveguide arms 10 and 11 of the polarization crossover shown in FIG. 7 and the two crossovers can also be established by two long lines, which are designed, for example, as having corresponding transitions, overmoded, bendable rectangular waveguides and by all conceivable measures are suitable to expand their clear transmission frequency range, more than one directional radio range of the same polarization from the location of the crossovers, e.g. at the foot of the antenna tower, low attenuation, reflection and delay distortion to the broadband polarization switch arranged directly on the antenna, i.e. for example on the tower and vice versa.

It is pointed out that the inner conductor shown in Figure 7 of the already mentioned article by E. Schuegraf in the magazine "NTZ", volume 38 (1985), number 8, pages 554-560 is not a round inner conductor in the Acting with the invention, with which a wave resistance homogenization is achieved along the two passages of a polarization filter, but rather a λ / 4 transformer. The inner conductor shown in FIGS. 2a and 2b of DE-C2-28 42 576 also represents a narrow-band λ / 4 transformer network with additional reactances, which are specifically designed for good adaptation in two narrow frequency ranges that are relatively far apart (scarce Octave), specially cut and cannot be compared with an inner conductor dimensioned according to the invention.

Dazu wird jeweils derjenige Koaxialwellenleiter ermittelt, der bei rundem Außen- und Innenleiter die gleiche H₁₁-Grenzfrequenz und frequenzunabhängig gleiche Welllenwiderstände aufweist wie die Rechteckhohlleiterarme. Aus dem b/a-Wert des Rechteckhohlleiterarms folgt nach Fig. 3 das Durchmesserverhältnis des wellenwiderstandsgleichen Koaxialwellenleiters zu

Für den jeweiligen d/D_K-Wert des Koaxialwellenleiters folgt aus Fig. 4 das Durchmesserverhältnis (D_K / D_o) mit D_o als Durchmesser desjenigen Rundhohlleiters, der die gleiche H₁₁-Grenzfrequenz hat wie der jeweilige Koaxialwellenleiter

Für den jeweiligen Koaxialwellenleiter mit d / D_K ergibt sich nach Fig. 5 aus Meinke, Gundlach "Taschenbuch der Hochfrequenztechnik", 2. Auflage, Seite 309 der Eindeutigkeitsbereich f_kE11 / f_kH11 bzw. f_kH31 / f_kH11:

Als konkretes Beispiel werden für den 4-GHz-Rechteckhohlleiter mit a = 58,17 mm und den obigen Seitenverhältnissen folgende vollständige Dimensionierungen angegeben.

According to the principles of the invention, new polarization switches can now be dimensioned, each of which has two rectangular waveguide arms, for example, with the following aspect ratios (calculation table):

For this purpose, the coaxial waveguide is determined in each case which has the same H₁₁ cutoff frequency and frequency-independent same waveguide resistances as the rectangular waveguide arms in the case of a round outer and inner conductor. According to FIG. 3, the diameter ratio of the coaxial waveguide, which is the same as the wave resistance, follows from the b / a value of the rectangular waveguide arm

For the respective d / D _K value of the coaxial waveguide follows from Fig. 4, the diameter ratio (D _K / D _o ) with D _o as the diameter of that circular waveguide that has the same H₁₁ cut-off frequency as the respective coaxial waveguide

According to FIG. 5 from Meinke, Gundlach "Taschenbuch der Hochfrequenztechnik", 2nd edition, page 309, the uniqueness range f _kE11 / f _kH11 or f _kH31 / f _kH11 results for the respective coaxial waveguide with d / D _K :

As a concrete example, the following complete dimensions are given for the 4 GHz rectangular waveguide with a = 58.17 mm and the above aspect ratios.

Claims (17)

1. Broadband polarisation junction for separating orthogonally linearly polarised electromagnetic microwaves, comprising a branching device which divides a waveguide (7) carrying the two orthogonal polarisations into two rectangular waveguide arms (10,11), in each case now only carrying one of these polarisations, of mutually identical characteristic line impedance, characterised in that the waveguide (7) carrying the two polarisations exhibits a characteristic line impedance, the value of which at least approximately corresponds to that of the two rectangular waveguide arms (10,11), for which purpose two conditions are met, namely, on the one hand, matching the cross-sectional factors in the characteristic impedance equations of the waveguides to be matched to one another and, on the other hand, matching the cut-off frequencies of the wave types to be changed into one another in these waveguides, and in that transformation measures requiring only short constructional lengths are provided for matching remaining reactances in the waveguides.
2. Polarisation junction according to Claim 1, characterized in that, in the case of a spatially symmetric excitation of both linear polarisations with in each case one electrically balanced rectangular waveguide fork (12,12',13,13'), in each case consisting of two fork part arms, the fork part arms open with half the height b of the external accesses to the rectangular waveguide arms and with unchanged wide side a into the waveguide (7) carrying the two orthogonal polarisations.
3. Polarisation junction according to Claim 1, characterised in that at least four metal ribs (2,3,4,5) are symmetrically arranged in the longitudinal direction of the waveguide on the inside surface of the outer wall (1), constructed to be circular or square, of the waveguide carrying the two polarisations.
4. Polarisation junction according to one of the preceding claims, characterised in that, in the inner space of the outer conductor (1) of the waveguide of circular or square cross-section, an inner conductor (6), which is arranged concentrically, that is to say on the centre longitudinal axis, is provided which is cross-sectionally dimensioned and possibly stepped in such a manner that the given conditions for homogeneous approximation or homogenisation of the characteristic impedance are met.
5. Polarisation junction according to Claim 4, characterised in that the accesses to the two rectangular waveguide arms (10,11) are constructed with a height which is significantly reduced compared with the normal height $\text{b = a/2}$

   

   , and in that the characteristic line impedance of the waveguide (7) carrying the two orthogonal polarisations is matched to the characteristic line impedance of these rectangular waveguide arm accesses, reduced in waveguide height, by increased capacitive loading by means of a thicker inner conductor (8) in the waveguide carrying the two orthogonal polarisations and/or by means of longitudinal metal ribs on the inside on its outer wall.
6. Polarisation junction according to Claims 4 or 5, characterised in that the inner conductor (8) is mounted in the forking zone of the three polarisation junction waveguides, for example at a double branch (9), and is there permanently, that is to say conductively, connected to the waveguide contours.
7. Polarisation junction according to one of Claims 4 to 6, characterised in that the inner conductor (8) exhibits a circular cross-section.
8. Polarisation junction according to one of Claims 4 to 6, characterised in that the inner conductor (6) exhibits a cruciform cross-section.
9. Polarisation junction according to one of Claims 4 to 6, characterised in that the inner conductor (6) exhibits a square cross-section.
10. Polarisation junction according to one of Claims 4 to 6, characterised in that the inner conductor (6) exhibits a circular cross-section with symmetrically arranged longitudinal ribs.
11. Polarisation junction according to one of Claims 4 to 10, characterised in that the inner conductor (8) is extended in the outer conductor (7) with circular or square cross-section past the actual polarisation junction area in the direction of the connected load.
12. Polarisation junction according to Claim 11, characterised in that the inner conductor terminates gradually, stepped or abruptly in the load, for example a horn radiator, particularly a corrugated horn radiator, in the horn radiator neck, in the corrugated area or outside the horn radiator aperture.
13. Polarisation junction according to one of Claims 4 to 12, characterised in that the inner conductor is constructed to be hollow so that waves of the same or different type and having the same or a different frequency as those waves already existing outside the inner conductor can be carried therein.
14. Polarisation junction according to Claim 13, characterised in that the hollow inner space of the inner conductor, in turn, is suitably provided with conductive and/or dielectric material.
15. Polarisation junction according to Claim 12 or 14, characterised in that in the hollow inner space of the inner conductor and/or near to its surface, coupling devices for waves are arranged which are coupled out of the space outside the inner conductor into its interior and conversely.
16. Polarisation junction according to one of the preceding claims, characterised in that one frequency filter each is directly connected to both polarisation-selective rectangular waveguide arms (10,11).
17. Polarisation junction according to one of Claims 1 to 15, characterised in that one frequency filter each is connected to both polarisation-selective rectangular waveguide arms (10,11) via in each case a long line which is constructed as overmoded rectangular waveguide provided with corresponding transitions.

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