EP0419892B1 - Microwave polarisation filter - Google Patents

Abstract

The invention relates to a broadband polarisation filter with a symmetrical double branch (D) to which in each case two identically constructed symmetrical series branches (SV1, SV2) are connected via a pair of filter arm sections (A1, A2; A3, A4). The filter arm sections having bends (E1-E10; E11-E20) exclusively in the E-plane are arranged and designed such that, on the one hand, precise phase symmetry is produced between and within the two pairs, and, on the other hand, it is possible to produce the filter completely using numerically controlled milling technology. The polarisation filter according to the invention can be used for supplying directional radio and satellite radio reflector antennas. <IMAGE>

Description

The invention relates to a microwave polarization filter according to the preamble of claim 1.

Polarization switches, which consist of an electrically symmetrical double branch and two mutually identical, in themselves electrically symmetrical series branches and in which the double branch and the two series branches are interconnected via four mutually identical connections, are known for example from DE-OS 27 03 878. An essential area of application of such polarization switches is satellite radio, in which the available transmission and reception frequency bands are occupied by right and left rotating circular polarization and can thus be used twice with the same bandwidth. For the implementation of antenna feed systems, for example, such polarization switches are required that their two passageways in the transmit and in the receive band should be as low-reflection as possible and in exact phase synchronization. In practical implementation, however, coaxial lines are still used in this known polarization switch in order to achieve the exact phase symmetry. However, if the transmission of large microwave powers is carried out via such polarization switches, difficulties are to be expected because waveguide-coaxial junctions and coaxial lines cannot be subjected to high power.

So-called phase-symmetrical polarization switches are also known, in which the phase symmetry is only approximated by a mostly relatively difficult phase adjustment. The generation of pure circular polarization, however, requires the exact phase synchronization of both passes of the polarization switch. A polarization switch which can be phase-symmetrized by such an adjustment process is, for example from DE-OS 27 08 271, but also from the symmetrical double branch described in detail in DE-PS 28 42 576.

DE-PS 30 10 360 discloses the only polarization switch whose two passageways are exactly phase-symmetrical in a wide frequency range and which can also be loaded with a high microwave power, i.e. which does not require coaxial line transitions. This polarization switch has four spatially oblique EH offsets, which, however, cannot disadvantageously be milled with numerically controlled machine tools.

Such a millable, initially not phase-symmetrical polarization switch is known from European patent application 0 196 065. With this switch, a round or square waveguide running in the axial direction is branched by means of a double branch into two pairs of rectangular waveguides which are respectively opposite one another. The first pair, consisting of two opposing rectangular waveguides, is fed by a symmetrical waveguide fork with straight arms. The second pair, which consists of the two other rectangular waveguides lying opposite one another, is fed by a second, in itself electrically symmetrical, waveguide fork with partial arms bent (E-bends) over their broad sides. The preamble of claim 1 is based on the polarization switch known from this European patent application, which, however, is not of phase symmetry.

The object of the invention is to provide an exactly phase-symmetrical broadband polarization switch, which consists exclusively of waveguides and which can be produced entirely in cost-effective machine tool-controlled milling technology.

This task is in a broadband generic Microwave polarization switch solved by the features specified in the characterizing part of claim 1.

Appropriate and advantageous refinements and developments are specified in the subclaims.

Fig. 1

die Seitenansicht auf einen einfachen, zwei E-Knicke aufweisenden E-Hohlleiterversatz,

Fig. 2

die Seitenansicht auf einen vier E-Knicke aufweisenden Doppel-E-Hohlleiterversatz mit der gleichen Versatzstrecke wie bei der Anordnung nach Fig. 1,

Fig. 3

die Seitenansicht auf eine streckenlängenmäßige Nachbildung der Hohlleiteranordnung nach Fig. 2, aber ohne seitlichen Versatz,

Fig. 4

eine Querschnittsansicht der Polarisationsweiche nach der Erfindung durch das nicht spiegelbildsymmetrisch zur Doppelverzweigungslängsachse verlaufende Paar der Weichenarmabschnitte,

Fig. 5

eine darauf senkrecht stehende Querschnittsansicht durch die Polarisationsweiche nach der Erfindung und zwar durch das spiegelbildsymmetrisch zur Doppelverzweigungslängsachse verlaufende Paar der Weichenarmabschnitte.

The invention is explained in more detail below with reference to five figures. Show it:

Fig. 1

the side view of a simple, two E-bend E-waveguide offset,

Fig. 2

the side view of a four E-bend double E waveguide offset with the same offset distance as in the arrangement according to FIG. 1,

Fig. 3

2 shows the side view of a path length simulation of the waveguide arrangement according to FIG. 2, but without lateral offset,

Fig. 4

2 shows a cross-sectional view of the polarization switch according to the invention through the pair of switch arm sections which does not run mirror-image symmetrically to the double branching longitudinal axis,

Fig. 5

a cross-sectional view perpendicular to it through the polarizing switch according to the invention, namely through the mirror image symmetrical to the double branching longitudinal axis of the pair of switch arm sections.

1 is based on a waveguide arrangement with an E offset, which is used in non-phase-symmetrical polarization switches, as are known from European patent application 0 196 065. This E-offset resulting in an offset distance consists of two E-bends E21 and E22, the waveguide axis running obliquely upwards after the E-bend E21 with the axis elongated vertically upwards in FIG. 1 in front of the bend E21 which is clockwise positive counted kink angle + α and the waveguide axis running vertically upwards after the E-Kink E22 the axis elongated in FIG. 1 in front of the bend E22 forms the bend angle - α (directed counterclockwise). The E-bends E21 and E22 thus have mutually opposing bend angles and are connected by an oblique, straight rectangular waveguide section H9. For large bandwidths of low reflection, angle pieces and intermediate lines with aspect ratios a = 4b are particularly favorable, with a representing the broad side dimension and b the narrow side dimension. A first step in the direction of the invention now consists in that the intermediate line formed by the rectangular waveguide section H9 in FIG. 1 is separated in the middle of its length by a cut S1. A short rectangular waveguide section B13 with a vertical axis direction is then introduced at this interface, as shown in FIG. 2. A further E-Knick E23 or E24 is connected to both sides of it, again with the opposite direction of buckling and at the same buckling angle as in Fig. 1. The E-Knick E23 thus has a buckling angle - α and the E-Knick E24 has a buckling angle + α . In the arrangement according to FIG. 2, the oblique waveguide section H9 from FIG. 1 consists of two half as long rectangular waveguide sections H10 and H11. This results in the double-E waveguide offset according to FIG. 2 with the same offset distance v as in FIG. 1 and with a somewhat greater height. The length of the short rectangular waveguide section B13 is L _s .

As a further step in the direction of the invention, there follows a horizontal section S2 in the waveguide arrangement according to FIG. 2, namely in the area of the new, perpendicular, short rectangular waveguide section B13 and a 180 ° rotation of the cable run above or below the section S2 about the waveguide axis Y. This creates the line structure shown in FIG. 3. It differs geometrically from the double E offset according to FIG. 2 in that the axes X1 and X2 of their accesses are no longer offset (v = 0). Despite this difference, the line structure in Fig. 3, compared to that of Fig. 2, meets the requirement that it be accurate same line locations always contains the same elements. However, this requirement is not sufficient for the desired exact phase symmetry of the line structures shown in FIGS. 2 and 3; because in the unusable case that the length L _{s of} the short rectangular waveguide section B13 is made too small, for example L _s = 0, the double offset shown in FIG. 2 changes into the single offset according to FIG. 1. 3 contains an additional E-bend with the bend angle -2 α because the two middle E-bends E27 and E28 for the case that the short rectangular waveguide section B14 has a length L _s = 0 Add length L _s = 0 of the short rectangular waveguide section B14 in FIG. 3 with their articulation angles. Accordingly, the lines of the waveguide arrangements according to FIG. 1 and FIG. 3 (the latter with L _s = 0) are roughly different in phase despite the middle paths having the same length.

3, the outer E-bends are designated E25 and E26 and the rectangular waveguide sections between the bends E25 and E27 or E26 and E28 are designated H12 or H13.

mit $$\text{λ}{\text{}}_{{\text{KE}}_{\text{11}}}\text{=}\frac{\text{2 ab}}{\sqrt{\text{a² + b²}}}\text{.}$$

For the desired exact phase symmetry of the cable runs, which are shown in FIGS. 2 and 3, the following further condition must be met. The length L _{s of} the vertical line sections B13 and B14 must be so large that the E₁₁ interference fields of the adjacent E-bends E23, E24 and E27, E28 do not interlock. The criterion for the strength of the decay of the E₁₁ interference fields in the rectangular waveguide is its aperiodic E₁₁ attenuation: $$\text{a}{}_{{\text{apE}}_{\text{11}}}\text{=}\frac{{\text{2πL}}_{\text{s}}}{\text{λ}{}_{{\text{KE}}_{\text{11}}}}\sqrt{\text{1 -}{\left(\frac{\text{λ}{}_{{\text{KE}}_{\text{11}}}}{{\text{λ}}_{\text{O}}}\right)}^{\mathrm{2nd}}}\text{Np}$$

With $$\text{λ}{}_{{\text{KE}}_{\text{11}}}\text{=}\frac{\text{2 from}}{\sqrt{\text{a² + b²}}}\text{.}$$

In these equations, λ _{KE 11 is} the cut-off wavelength of the E ₁ 1 wave in the rectangular waveguide with the broad side dimension a and the narrow side dimension b and λ _o the operating wavelength.

The highest operating frequency is always decisive here; it is sufficient here relatively small lengths L _s ≈ b (≈ a / 4) for sufficiently high E₁₁ attenuation values around 25 dB.

The sufficient conditions for the double E offset according to FIG. 2 and the cable pull according to FIG. 3 to be phase-symmetrical exactly and broadband, i.e. 3 that an exact electrical replica of the double E offset according to FIG. 2 with respect to exactly the same phase and reflection is now clarified and can also be easily implemented. These cables can therefore be used as follows.

A polarization switch which is not phase-symmetrical per se and which, with the foregoing prior knowledge, is particularly suitable for expanding to exact phase symmetry, is known from European patent application 0 196 065. It consists of a straight mirror image symmetrical and a rectangular waveguide fork, which runs obliquely to the side and is not mirror image symmetrical, which fit into each other without penetration. These two forks feed a double branching switch head described in more detail in DE-PS 28 42 576, whereby e.g. in a circular waveguide two mutually perpendicular polarized H₁₁ waves E₀₁ and H₂₁ are excited without interference waves.

With the help of the double-E offset in FIG. 2 and its simulation in FIG. 3, a polarization switch can be created which, in contrast to the switch described in patent application 0 196 065, is exactly phase-symmetrical with regard to the switch arm pairs and thus the entire polarization switch.

4 and 5 show two mutually perpendicular cross-sectional side views through this new, through the invention achieved polarization switch, Fig. 4 shows a section through the non-mirror-symmetrical switch arm pair and Fig. 5 shows a section through the mirror-symmetrical switch arm pair of the switch. The polarization switch according to the invention has a symmetrically constructed five-armed double branch D, which contains an arm lying in the double branch longitudinal axis direction L for connecting a further waveguide with a round or square cross section and four identically designed partial arm connections with a rectangular cross section, which are each offset by 90 ° and offset run at the same angle with respect to the double branching longitudinal axis L in the opposite direction to the connecting arm of the further waveguide. In each case two opposing partial arm connections of the double branch D are of mutually equal length, each forming a pair of switch arm sections A1, A2 (FIG. 4) and A3, A4 (FIG. 5) with the two partial arms T1, T2 (FIG. 4) and T3 , T4 (FIG. 5) each one of two identically designed, symmetrical series connections SV1 (FIG. 4) or SV2 (FIG. 5), which are located in the same plane with their connecting flanges.

The pair of switch arm sections A1 and A2 shown in FIG. 4, which is not mirror image symmetrical to the double branching longitudinal axis L, has, starting from the double branching D, first in each switch arm section A1 or A2 a short waveguide section B1 or B2 running parallel to the double branching longitudinal axis L. The two short waveguide sections B1 and B2 are followed by a longer waveguide section H1 or H2 via an E-bend E1 or E2 with an angle + α. The longer waveguide sections H1 and H2 in the two switch arm sections A1 and A2 are followed by a short waveguide section B3 and B4 running parallel to the double branching longitudinal axis L via an E-bend E3 and E4 each with an angle α relative to the direction of the double branching longitudinal axis L. . A longer waveguide section H3 or H4 is connected to the short waveguide sections B3 and B4 via a further E-bend E5 or E6, each with an angle + α. The switch arm sections A1 and A2 then continue via bends E7 and E8 with an angle -α in short waveguide sections B5 and B6 running parallel to the double branching longitudinal axis L. The short waveguide section B5 is connected via an E-bend E9 with an angle + α ′ = + α to one arm T1 of the series branch SV1, whereas the other arm T2 of this series branch SV1 is connected via an E-bend E10 from the angle -α ′ = -α is connected to the short waveguide section B6.

The pair of switch arm sections A3 and A4 shown in FIG. 5, mirror image symmetrical to the double branching longitudinal axis L, has a short waveguide section B7 and B8 running parallel to the double branching longitudinal axis L, starting from the double branching D in each switch arm section A3 or A4. This is followed by a longer waveguide section H5 in the switch arm section A3 via an E-bend E11 with an angle -α relative to the direction of the axis L and in the switch arm section A4 via an E-bend E12 with an angle + α relative to the axis L also a longer waveguide section H6 . This is followed by a short waveguide section B9 in the switch arm section A3 via an E-bend E13 with the angle + α and in the switch arm section A4 via an E-bend E14 with the angle -α also a short waveguide section B10. The short waveguide sections B9 and B10 run parallel to the double branching longitudinal axis L. Then a longer waveguide section H7 follows in the switch arm section A3 via an E-bend E15 with an angle + α and in the switch arm section A4 also an longer waveguide section via an E-bend with an angle -α H8. This is followed by a short waveguide section B11 in the switch arm section A3 via an E-bend E17 with an angle -α and in the switch arm section A4 via an E-bend E18 with an angle + α also a short waveguide section B12. The two short waveguide sections B11 and B12 run parallel to the double branching longitudinal axis L. Then, in the switch arm section via an E-bend E19 with an angle + α ′ = + α, one arm T3 of the series branch SV2 is connected, while in the other switch arm section A4 via an E. -Kink E20 with one Angle - α ′ = -α of the partial arm T4 follows the series branch SV2.

All longer waveguide sections H1 to H8 have the same length in the switch arm sections A1 to A4 of the two pairs of forks. The short waveguide pieces B1, B2, B7 and B8 with the length L _s ˝, the short waveguide pieces B3, B4, B9 and B10 with the length L _s and the short waveguide pieces B5, B6, B11 and B12 are also dimensioned with each other with the same length the length L _s '. All short waveguide pieces B1 to B12 of the four switch arm sections A1 to A4 are dimensioned at least so long that there is sufficient E₁₁ interference field attenuation at the highest operating frequency.

In the cross-sectional view of FIG. 4, two parallel double E offsets of FIG. 2, which are placed next to one another in parallel, are interconnected with a broadband rectangular waveguide series branch SV1 known from European patent application 0 196 065 to form a new fork which is not mirror-symmetrical. The lateral offset distance v must be somewhat larger than the broad side a of all rectangular waveguides used, so that both pairs A1, A2 and A3, A4 of the switch arm sections fit into one another without penetration. The pair of switch arm sections A1 and A2 shown in Fig. 4 is symmetrical in itself, for which the lengths L _s ' and L _s ˝ must meet the same, already quantified requirements as the length L _s .

The series branches SV1 and SV2 are designed with the correct wave resistance, the partial arms T1 to T4 having an aspect ratio between the broad side a and the narrow side b of approximately 4: 1. The waveguide feed access Z1 and Z2 of the two series branches SV1 and SV2 has an aspect ratio between the broad side a and the narrow side b _o of approximately 2: 1.

All E-bends E1 to E20 are provided with a symmetrical corner flattening F on the outer broad side bend of the waveguide.

The clear width w between the switch arm sections A3 and A4 of the mirror-symmetrically designed switch arm pair in Fig. 5 must be dimensioned somewhat larger than the broad side a of all rectangular waveguides, so that the switch arm section pair shown in Fig. 4 between the switch arm sections A3 and A4 of the one shown in Fig. 5 Arrangement has space. For reasons of the same length of partial arms T1 and T2 or T3 and T4 of the series branches SV1 and SV2, the width w is also adopted for the switch arm sections A1 and A2 of the arrangement shown in FIG. 4. Since all switch arm components are mutually exactly phase-symmetrical, this also applies to the complete switch arm pairs under the conditions mentioned above. Then the interconnection with the double branching D, which is likewise exactly symmetrical, represents an exactly phase-symmetrical polarization switch.

The remaining phase error Δφ of this polarization switch depends only on the dimensional tolerances; the more precisely the important electrical dimensions are adhered to, the better the approximation to the ideal case Δφ = 0. With sufficiently small dimensional tolerances, there is no need for adjustment, both for the series products and from the start of development, as has already been explained.

A major advantage of the polarization switch according to the invention is that the two pairs (Gabein) of the switch arm sections A1, A2 and A3, A4 can be completely milled. For this purpose, each of the two forks is divided by a plane that cuts all rectangular waveguides of the respective fork along the center lines of their broad sides - that is to say without cross current and therefore without loss. The two division levels are perpendicular to each other and divide the fork block into four quadrants. With regard to these parting planes, all waveguide walls are exactly cylindrical and can therefore be manufactured inexpensively and with very small tolerances using a two-dimensionally numerically controlled milling machine. This is compared to the previous one galvanoplastic manufacturing technology achieved an enormous cost reduction.

A crossover can be connected to the waveguide feed accesses Z1 and Z2 of the two series branches SV1 and SV2.

Claims (8)

1. Microwave polarization splitter having a symmetrically constructed five-segmented double junction which contains a segment, lying in the longitudinal axis direction of the double junction, for connection of a continuing waveguide of round or square cross-section and four identically designed partial segment connectors of rectangular cross-section, which are in each case offset by 90° with respect to one another and in each case extend at the same angle with respect to the double junction longitudinal axis in the opposite direction to the connection segment of the continuing waveguide, and of which, in each case, two mutually opposite partial segment connectors are connected, via splitter segment sections having the same length as one another, in each case form a pair and are provided exclusively with bends over the wide sides of the waveguide (E bends), to the two partial segments of in each case one of two identically designed, symmetrical series junctions, the connection flanges of which lie in one and the same plane, one pair of the splitter segment sections having, in the same position and extending exclusively opposite, E bends which cause this pair to extend with mirror symmetry with respect to the double junction longitudinal axis, and the other pair of the splitter segment sections, which does not extend with mirror symmetry with respect to the double junction longitudinal axis, having, extending parallel and in the same position, E bends which produce an offset of the associated series junction with respect to the double junction longitudinal axis of at least a length such that the two pairs of splitter segment sections can engage in one another without penetration, characterized in that the pair of splitter segment sections (A1, A2) which does not extend with mirror symmetry with respect to the double junction longitudinal axis (L) has, starting from the double junction (D), first, in each splitter segment section, a short waveguide piece (B1, B2) extending parallel to the double junction longitudinal axis, and thereafter, consecutively one after another, in each case one E bend (E1, E2) having an angle +α (+α is the clockwise angle and -α is the anticlockwise angle between the extended waveguide axis before the corresponding E bend and the waveguide axis after this E bend), a longer waveguide piece (H1, H2), an E bend (E3, E4) having an angle -α, another short waveguide piece (B3, B4), extending parallel to the double junction longitudinal axis, an E bend (E5, E6) having an angle +α, another longer waveguide piece (H3, H4), an E bend (E7, E8), having an angle -α, and another short waveguide piece (B5, B6), extending parallel to the double junction longitudinal axis, followed, via an E bend (E9, E10) having an angle +α′ or -α′, respectively (the definition of the sense of α also applies to α′), by in each case one partial segment (T1, T2) of the associated series junction (SV1), in that the pair of splitter segment sections (A3, A4) which extends with mirror symmetry with respect to the double junction longitudinal axis, has, starting from the double junction, first, in each splitter segment section, likewise a short waveguide piece (B7, B8), extending parallel to the double junction longitudinal axis, and thereafter, following one after another, E bends (E11, E12), having an angle -α and +α, respectively, which cause the two splitter segment sections to spread out from one another, a longer waveguide piece (H5, H6), an E bend (E13, E14) having an angle +α or -α, respectively, another short waveguide piece (B9, B10), extending parallel to the double junction longitudinal axis, an E bend (E15, E16) having an angle +α or -α, respectively, another longer waveguide piece (H7, H8), an E bend (E17, E18) having an angle -α or +α, respectively, and another short waveguide piece (B11, B12), extending parallel to the double junction longitudinal axis, followed, via an E bend (E19, E20) having an angle +α′ or -α′, respectively, by in each case one partial segment (T3, T4) of the associated series junction (SV2), in that the longer waveguide pieces (H1 to H8) in both splitter segment section pairs have the same length, specifically so that the splitter segment section pair not designed with mirror symmetry produces a lateral offset distance (v) which is somewhat larger than the wide side (a) of the rectangular waveguide used, and in that the short waveguide pieces (B1 to B12) are at least long enough for sufficient E₁₁ interference-field attenuation to be produced at the highest operating frequency, at least all those short waveguide pieces which in each case have the same offset separation from the double junction having the same length as one another.
2. Polarization splitter according to Claim 1, characterized in that the side ratio between the wide side (a) and the narrow side (b) of the rectangular waveguide of the splitter segment sections (Al to A4) is approximately 4:1.
3. Polarization splitter according to Claim 1 or 2, characterized in that the series junctions (SV1, SV2) are designed with the correct characteristic impedance with partial segments (T1 to T4) with the side ratio between the wide side (a) and the narrow side (b) of approximately 4:1 starting from a waveguide feed input (Z1, Z2) having a side ratio of approximately 2:1 between the wide side (a) and the narrow side (b₀).
4. Polarization splitter according to one of the preceding claims, characterized in that the E bends (E1 to E20) are provided with a symmetrical corner flat (F), in each case on the outer wide-side bend.
5. Polarization splitter according to one of the preceding Claims, characterized by implementation using a preferably numerically tool-controlled milling technique.
6. Polarization splitter according to Claim 5, characterized in that each of the two splitter segment section pairs (A1, A2; A3, A4) is divided by a plane which intersects all of the rectangular waveguides of the corresponding pair along the mid-lines of their wide sides, so that the two dividing planes are perpendicular to one another and divide the entire splitter unit into four quadrants, and in that the waveguide walls which extend exactly cylindrically relative to these dividing planes are produced by using a two-dimensionally numerically controlled automatic milling machine.
7. Polarization splitter according to one of the preceding claims, characterized in that the angle α′ corresponds with the angle α.
8. Polarization splitter according to one of the preceding claims, characterized in that a frequency filter is in each case connected to the waveguide feed inputs (Z1, Z2) of the two series junctions (SV1, SV2).

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