EP0284911B1 - Broad-band polarizing junction - Google Patents

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

The invention relates to a broadband. Polarization switch for microwaves with a waveguide that carries two orthogonally linear polarizations, from which two arms that form a symmetrical waveguide fork are branched off at opposite points at an acute angle, each of which has a first E-bend, an area with a parallel guide, in each case a second E-bend and a series branching into a first, with respect to its longitudinal axis with the waveguide aligning the two orthogonal polarizations aligned waveguide arm rectangular cross-section are transferred, and from which a second waveguide arm extends in the axial direction, which has a rectangular cross-section over an E-bend is led out laterally from the space between the two arms.

Such a polarization switch is known from DE-OS 33 45 689. However, this known polarizing switch has a relatively large overall length and is also not structurally designed so that it can be used with less complex manufacturing methods, e.g. with simple numerically controlled milling machines.

The object of the invention is to provide a very broadband polarizing switch of the type mentioned, but which is designed so that it can be produced inexpensively using simple methods and can be designed to be particularly small in terms of its transverse dimensions and overall length.

According to the invention, this object is achieved in that in the second waveguide arm provided with a right-angled E-bend is anchored in its transition zone to the waveguide guiding the two orthogonal polarizations, a central plate extending over its entire broad side dimension, which is approximately half as wide as its narrow side dimension and thus divides it fork-like into two symmetrical arms in this transition zone, taking into account an exact constant maintenance of the wave resistances.

The polarization switch according to the invention can be formed in two parts with the exception of the access to the second waveguide arm, which has a rectangular cross-section, the mirror image being the same, the plane of the game being formed by the cross-current-free central plane of the two partial arms of the waveguide fork of the first waveguide arm. These two parts can be made by milling control in a single plane. An essential commercial value for the polarizing filter according to the invention can thus be seen in the fact that it consists of only two main parts which are largely mirror-like and which can be produced very inexpensively using simple numerically controlled automatic milling machines.

Advantageous and expedient developments and refinements of the invention are described in the subclaims.

• FIG 1 eine Breitband-Polarisationsweiche nach der Erfindung in Draufsicht,
• FIG 2 die Breitband-Polarisationsweiche der FIG 1 in einer Seitenansicht.

The invention is explained below with reference to an embodiment shown in two figures. Each shows in a sectional view:

• 1 shows a broadband polarization switch according to the invention in plan view,
• 2 shows the broadband polarization switch of FIG 1 in a side view.

aufgeteilt. In FIG 1 sind die Rechteckhohlleiterarme 1 und 2 mit den Seitenabmessungen a=2b₁ gezeichnet. Sie können aber auch mit b₁ < a/2 ausgeführt werden. An jedem der Teilarme 20, 21 ist im Abstand l_K von E-Knicken der Serienverzweigung 22 ein E-Knick 23 bzw. 24 mit gleichem Knickwinkel, allerdings in entgegengesetzter Knickrichtung, angeschlossen. Der Abstand l_K ist so gewählt, daß zwischen den innenleigenden Breitseitenwänden der durch die beiden Teilarme 20 und 21 gebildeten Hohlleitergabel der andere Rechteckhohlleiterarm 2 Platz hat. Die parallel zueinaner verlaufenden Bereiche der beiden Teilarme 20 und 21 werden dann durch je einen weiteren E-Knick 5 bzw. 5ʹ spiegelsymmetrisch zur Längsachse der Polarisationsweiche hin abgewinkelt. In den Querschnitten 3, 3ʹ beginnt die Durchdringung mit dem Hohlleiterarm 2. Vom Zugang des Hohlleiterarms 1 bis zu diesen Querschnitten 3, 3ʹ ist die Hohlleitergabel exakt wellenwiderstandshomogen. Im Querschnitt 6 münden die Teilarme 20 und 21 in einen aus einem Innenleiter 10 kreisrunden Querschnitts und einem Außenleiter 11 runden Querschnitts bestehenden Koaxialwellenleiter 4, dessen Wellenwiderstand an den Wellenwiderstand der beiden in Serie geschalteten Teilarme 20 und 21 angeglichen ist. Die hinsichtlich des Wellenwiderstands inhomogene Zone ist also bei dieser Polarisationsweiche auf einen sehr kurzen Bereich zwischen den Querschnitten 3, 3ʹ einerseits und 6 andererseits reduziert, was eine Anpassungsarbeit wesentlich erleichtert.The in Figures 1 and 2 in top or Side view broadband polarization switch has a first waveguide arm 1 rectangular cross-section with the side lengths a and b₁. This waveguide arm 1, as shown in FIG. 1, is fitted with an adapted series branch 22, which consists of two narrow profile E-bends set in mirror symmetry, in two partial arms 20, 21 with halved waveguide height ${\text{b}}_{\text{T}}\text{= b₁ = a / 4}$

divided up. In Figure 1, the rectangular waveguide arms 1 and 2 are drawn with the side dimensions a = 2b₁. But they can also be performed with b₁ <a / 2. An E-bend 23 or 24 with the same bend angle, but in the opposite bend direction, is connected to each of the partial arms 20, 21 at a distance l _K from E-bends of the series branch 22. The distance l _K is selected so that the other rectangular waveguide arm 2 has space between the inner broad side walls of the waveguide fork formed by the two partial arms 20 and 21. The regions of the two partial arms 20 and 21 running parallel to one another are then angled mirror-symmetrically to the longitudinal axis of the polarization switch by a further E-bend 5 or 5ʹ. In the cross sections 3, 3ʹ the penetration begins with the waveguide arm 2. From the access of the waveguide arm 1 to these cross sections 3, 3ʹ, the waveguide fork is exactly homogeneous in terms of the wave resistance. In cross section 6, the partial arms 20 and 21 open into a coaxial waveguide 4 consisting of an inner conductor 10 with a circular cross section and an outer conductor 11 with a round cross section, the characteristic impedance of which is matched to the characteristic impedance of the two partial arms 20 and 21 connected in series. The inhomogeneous zone with respect to the wave resistance is thus reduced to a very short area between the cross sections 3, 3ʹ on the one hand and 6 on the other hand with this polarization switch, which considerably facilitates adaptation work.

The second waveguide arm 2 of rectangular cross-section is angled in the longitudinal direction with a normal profile E-bend 12, the E-bend 12 being formed with a 90 ° corner projection 7 instead of with an inclined outside corner to facilitate production. Furthermore, the waveguide arm 2 with a central plate 8, the entire broad side dimension a is sufficient and which has a thickness dimension of approximately b 1/2, divided into two partial arms 14 and 15, the wave resistances being kept exactly constant. The adjustment of the lateral offset is carried out by optimizing the distance bʹ between the front end face 17 of the middle plate 8 and the level of a gradation 16. By dividing into two partial arms 14 and 15 it is achieved that the reactance at the transition point 6 to the wave resistance adapted, from the inner conductor 10 and the outer conductor 11 existing coaxial waveguide 4 is smaller and therefore easier to compensate. In addition, the inner conductor 10 is fastened to the rear face 18 of the plate 8, which is firmly anchored in the narrow side walls of the waveguide arm 2 by means of two surfaces 9, 9ʹ. This type of attachment and mounting of an inner conductor can also be used to transfer many other known polarization switches.

According to FIG. 2, the polarization switch according to the invention is divided by the parting plane 13 into two mirror-symmetrical parts with the exception of the switch access on the waveguide arm 2, which parts can be produced by milling control in a single plane.

As shown in FIGS. 1 and 2 below, the coaxial waveguide 4 with the inner conductor 10 and the outer conductor 11 according to the cross section 6 can be passed along in a longitudinally homogeneous manner to a subsequent consumer, for example a horn antenna. If, on the other hand, the inner conductor 10 is to disappear, this can be accomplished with a steady or stepped transition will. In Figures 1 and 2, a two-stage, rotationally symmetrical quarter-wave transformer with a stepped inner layer 19 and an oppositely stepped outer conductor 25 (constant H₁₁ cut-off frequency, frequency-independent wave resistance levels) is shown in dashed lines. It is also possible to push the transformer further into the bifurcation zone of the polarization switch - in Figures 1 and 2 - so that only the lowest transformer stage is designed as a coaxial waveguide.

By using the inner conductor 10, it is possible to reduce or completely eliminate the disturbing wave resistance jumps along the two passages of the polarization switch. While the line wave resistances of the rectangular polarizing waveguide arms 1 and 2 with their aspect ratios a≈2b₁ are fixed, the line wave resistance of the round waveguide 11 is not fixed and therefore freely selectable. This opens up the possibility of lowering the line wave resistance of the round waveguide 11 and thus approximating the line wave resistance of the rectangular waveguide arms 1 and 2. Ideal adaptation conditions prevail when the line wave resistances of the round waveguide 11 are broadband matched to those of the rectangular waveguide arms 1 and 2.

This adjustment of the wave resistances is achieved over very large bandwidths if the following two conditions are met, namely on the one hand the adjustment 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 adjustment of the cut-off frequencies of the wave types to be merged, with the remaining reactance jumps then can be adapted in the waveguides by means of transformation measures requiring only short overall lengths. Using this principle results in a significantly increased range of reflection poor.

Through the use of the inner conductor 10, in addition to the desired reduction in wave resistance, a substantial expansion of the uniqueness range of the coaxial waveguide 4 is also achieved. For even broader areas of uniqueness, other cross-sectional shapes of the inner conductor 10 are possible, e.g. a cross-shaped or a square cross-section. The inner conductor 10 causes very little additional losses and brings a number of further advantages. The inner conductor 10, which is extended beyond the polarization switch, is suitable for improving the behavior of a consumer connected to the polarization switch, e.g. the bandwidth of the low reflection of a grooved horn and its cross-polarization properties compared to horn feeding. In this case, the inner conductor 10 can end in the horn neck, in the groove area or outside the horn aperture in a stepped, stepped or abrupt manner. Furthermore, space can be created in a hollow inner conductor 10 for waves of the same or different type with the same or different frequency as those waves already present outside the inner conductor 10. For this purpose, the interior of the inner conductor 10 can be provided in a suitable manner with conductive material or with dielectric. Coupling devices for waves can also be arranged in the interior of the inner conductor 10 and / or near its surface, which are coupled from the space outside the inner conductor 10 into its interior and vice versa.

Claims (14)

1. Broadband polarisation filter for microwaves, having a waveguide (4) which conducts two mutually orthogonal linear polarisations, and from which two partial arms (20, 21) forming a symmetrical waveguide fork are branched off at mutually opposite positions at an acute angle, which partial arms are conducted via a first E-bend (5; 5') in each case, a region with mutually parallel guidance in each case, a second E-bend (23; 24) and a series junction (22) in each case over into a first waveguide arm (1) of rectangular cross-section which is flush with respect to its longitudinal axis with the waveguide (4) conducting the two orthogonal polarisations, and from which a second waveguide arm (2) proceeds in the axial direction, which second waveguide arm, with rectangular cross-section, is led laterally via an E-bend (12) out of the space between the two partial arms (20, 21), characterised in that, a central plate (8) extending over its entire broad-side dimension a is anchored in the second waveguide arm (2), which is provided with a rectangular E-bend (12), in its transition zone to the waveguide (4) conducting the two orthogonal polarisations, which central plane is approximately half as thick as its narrow-side dimension (b₁) and thus divides it in this transition zone into two symmetrical partial arms (14, 15) in the manner of a fork, while taking account of keeping the characteristic impedances exactly constant.
2. Polarisation filter according to Claim 1, characterised in that given spatially symmetrical excitation of both linear polarisations with an electrically symmetrical rectangular waveguide fork in each case, the fork partial arms (20, 21 and 14, 15) merge with half of the narrow-side dimension b₁ of the outer entrances to the rectangular waveguide arms (1, 2) and with unchanged broad side (a) into the waveguide (4) conducting the two orthogonal polarisations.
3. Polarisation filter according to Claim 1 or 2, characterised in that the narrow-side dimension (b₁) of the second waveguide arm (2) has a step (16) between the central plane end and the rectangular E-bend (12), and in that the lateral offset is compensated by optimising the distance (b') between the front end face (17) of the central plate (8) and the plane of the step (16).
4. Polarisation filter according to one of Claims 1 to 3, characterised in that the rectangular E-bend (12) of the second waveguide arm (2) is provided with a 90° corner projection (7) of the outer corner directed into the interior.
5. Polarisation filter according to one of the preceding claims, characterised in that an inner guide (10) for the waveguide having a round or square outer guide (11) and conducting the two orthogonal polarisations is secured to the rear end face (18) of the central plate (8) so that a coaxial waveguide (4) is formed, this inner guide being dimensioned such that the originally approximately double line characteristic impedance of the round or square waveguide is matched to the inherently equal line characteristic impedances of the two rectangular waveguide arms (1, 2), for which two conditions must be fulfilled, namely on the one hand the matching of the cross-section factors in the characteristic impedance equations of the waveguides to be matched to one another, and on the other hand the matching of the limit frequencies of the wave modes requiring transition into one another, remaining reactances in the waveguides being matched by transformation measures requiring only short overall lengths.
6. Polarisation filter according to one of Claims 1 to 4, characterised in that, in a waveguide having a round or square outer guide and conducting the two orthogonal polarisations, there is secured to the rear end face (18) of the central plate (8) an inner guide (19), which tapers gradually or in steps and thus forms a part of a quarter-wavelength transformer, whose outer guide (25), which is formed by the circular or square outer guide (11), is formed to run gradually or in steps counter thereto.
7. Polarisation filter according to Claim 5 or 6, characterised in that the entrances to the two rectangular waveguide arms (1, 2) are designed with substantially reduced narrow-side dimension compared with the normal narrow-side dimension $\text{b₁ = a/2,}$

   

   and in that the line characteristic impedance of these rectangular waveguide arm entrances reduced with respect to the waveguide narrow-side dimension is compensated by increased capacitive loading by means of thicker inner guides (10 and 19 respectively) in the waveguide (4) conducting the two orthogonal polarisations and/or with longitudinal metal webs on the inside of the outer wall thereof.
8. Polarisation filter according to Claim 5 or 7, characterised in that the inner guide (10) is continued longitudinally homogeneously beyond the actual polarisation filter region to a load, for example a horn radiator.
9. Polarisation filter according to one of Claims 5 to 8, characterised in that the inner guide (10, 19) has a circular cross-section.
10. Polarisation filter according to one of Claims 5 to 8, characterised in that the inner guide (10, 19) has a cross-shaped or a square cross-section.
11. Polarisation filter according to one of Claims 5 to 8, characterised in that the inner guide (10, 19) has a circular cross-section with symmetrically arranged longitudinal webs.
12. Polarisation filter according to one of the preceding claims, characterised by a design in two mirror-symmetrical identical parts with the exception of the entrance to the second waveguide arm (2), the mirror plane being formed by the cross-current-free central plane (13) of the waveguide fork having two symmetrical partial arms (20, 21) for the first waveguide arm (1).
13. Polarisation filter according to one of the preceding claims, characterised by production using milling technology, in which the preferably numerical cutter control is executed in a single plane.
14. Polarisation filter according to one of the preceding claims, characterised in that there is connected to the two polarisation-selective rectangular waveguide arms (1, 2) in each case one frequency separating filter via a long line in each case, which is designed as an overmodulated rectangular waveguide provided with appropriate transitions.

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