EP0374720B1 - Mode converter - Google Patents

Description

The present invention relates to an arrangement for converting a wave of the H11 mode in a circular waveguide into a wave from the basic mode for a rectangular or elliptical waveguide and vice versa, wherein a coupling opening is arranged in the wall of the circular waveguide so that the magnetic plane of one connected rectangular or elliptical waveguide coincides with the magnetic plane of the shaft of the H11 mode in the circular waveguide, the coupling opening has an inductively and / or capacitively acting diaphragm and a separating plate is inserted in the circular waveguide in the direction of the electrical plane of the H11 shaft, that begins in the area of the coupling opening and extends in the circular waveguide into the area where said H11 wave is to be prevented from spreading.

Such an arrangement, which is part of a polarization switch, is evident from DE-A-32 41 890 and GB-A-2 130 444. From these publications it can be seen that tuning means are required in order to achieve the lowest possible reflection between the rectangular and round waveguides. Tuning elements increase the effort both for the manufacture of the waveguide component and for its adjustment.

In the case of polarization switches known from BE-A-677 286 and US-A-3 201 717, rectangular waveguides are coupled to a round waveguide over their full opening cross section. Separating plates arranged in the area of the coupling openings gradually change from a small width to a width adapted to the diameter of the circular waveguide. In order to achieve the lowest possible reflection coupling of the rectangular waveguide to the circular waveguide, adapter rods or conductive sheets are inserted into the rectangular waveguide, as is apparent from US Pat. No. 3,201,717.

GB-A-965 244 shows that a separating plate in a waveguide excites higher shaft types. To counteract this, the separating plate is provided with slots.

The invention is based on the object of specifying a shaft type converter of the type mentioned at the outset, which can be produced with as little effort as possible, for example by machining processes.

This object is achieved according to the invention by the features of claim 1, and expedient embodiments of the invention emerge from the subclaims.

An important advantage of the invention is that the wave type converter does not require any tuning elements in order to adapt the rectangular or elliptical input or output waveguide to the central circular waveguide over a broad band. Above all, it proves to be advantageous that no adjustment elements are required in the input or output waveguide in order to have a low-reflection (r ≦ 0.015) wave coupling or decoupling in a fairly wide frequency band (eg 10.75 - 12.5 GHZ) to enable. For this reason, the central circular waveguide does not need to be equipped with an input or output waveguide section which is intended to accommodate adjustment elements. That is to say, only a flange plane has to be provided on the circular waveguide, to which a conventional rectangular or elliptical waveguide leading, for example, to a transmitter or a receiver can be flanged. A wave type converter of the type according to the invention can thus be produced with little effort from a hollow body with a round inner cross-section, which forms the central circular waveguide, by machining, in the wall of the hollow body, a coupling opening with an aperture for a rectangular or elliptical waveguide to be connected and around this Coupling opening is milled around a flange level directly on the hollow body. It is therefore not necessary to mill a rectangular or elliptical waveguide section branching off the round waveguide from the hollow body wall in a complex process, nor is it necessary to subsequently solder such a waveguide section to the round waveguide. The separating plate required for the shaft type converter on which the invention is based leaves can be easily manufactured by punching or etching and then inserted into the circular waveguide. Grooves embedded in the inner waveguide wall are helpful for the introduction and fastening of the separating plate in the circular waveguide. These grooves are arranged exactly in the polarization plane of the shaft (H11) which is spreading in the circular waveguide and is to be converted into another type of shaft (e.g. H10 or H01), so that a separating plate inserted into the grooves immediately provides the correct orientation for the shaft to be decoupled. Since the invented wave type converter does not require any tuning elements and therefore no adjustment measures are necessary, it is highly reproducible. This shaft type converter also comes with a short overall length, which meets the requirements for the lowest possible damping.

Fig. 1

zeigt eine teilweise längsgeschnittene, aus zwei Wellentypwandlern gebildete Polarisationsweiche.

Fig. 2

zeigt einen Querschnitt A-A durch die Polarisationsweiche und

Fig. 3

ein Reflexionsfaktordiagramm.

Based on an embodiment shown in the drawing, the invention is explained in more detail below.

Fig. 1

shows a partially longitudinally cut polarization switch formed from two wave type converters.

Fig. 2

shows a cross section AA through the polarization switch and

Fig. 3

a reflection factor diagram.

FIGS. 1 and 2 show two views of a polarization filter formed from two wave type converters. The central element of this polarization switch is a hollow body with a round inner cross section, which serves as a round waveguide RH. The round waveguide RH is provided with means such that for the application of the polarization switch two orthogonally polarized waves of the H11 mode in the round waveguide RH into two separate ones Waves of the H10 or H01 mode for rectangular waveguides or the corresponding basic mode for elliptical waveguides can be converted. Since the polarization switch is a reciprocally operable microwave component, two basic mode waves orthogonally oriented to one another and fed in via rectangular or elliptical waveguides are converted into two H11 waves polarized orthogonally to one another. For this purpose, two rectangular or elliptical coupling openings K1 and K2 are milled in the wall of the circular waveguide RH in the axial direction and radially offset from one another by 90 °. In fact, each of the coupling openings K1, K2 is arranged in such a way that the magnetic planes of a rectangular or elliptical waveguide connected to them coincide with the magnetic planes of the H11 wave assigned to them in the circular waveguide RH. A flange plane FE1, FE2 is milled around each coupling opening K1, K2 on the outside of the circular waveguide RH. It enables the rectangular or elliptical waveguide to be coupled to be flanged directly to the hollow body serving as a round waveguide RH without any adaptation devices. Such adaptation devices, for example tuning pins, which are usually arranged in waveguide sections branching off from the coupling openings, to which the further waveguides are flanged, are unnecessary due to the following easy-to-implement means.

With each coupling opening K1, K2, a dividing plate TB1, TB2 is inserted in the circular waveguide RH, which lies in the electrical plane of the H11 shaft that is to be coupled to the coupling opening K1, K2 associated with it. The partition plate TB1, TB2 causes the desired H11 shaft to be deflected to the coupling opening and thereby converted into the basic mode for the rectangular or elliptical waveguide. For a low reflection transition for the To achieve the H11 wave on the basic mode wave in a rectangular or elliptical waveguide or vice versa, the divider plate TB1, TB2 begins in the area of the coupling opening K1, K2 with a narrow width and expands continuously or step-wise to the internal dimensions of the round waveguide RH adjusted width. The shape with which the separating plate TB1, TB2 widens in width has an influence on the frequency range in which there is a low-reflection transition. The partition plate TB1, TB2 partially extends into the area of the circular waveguide RH, where the shaft to be deflected by this partition plate is to be prevented from spreading. In this area, the partition plate TB1, TB2 is provided with a plurality of slots S1, S2. They suppress resonances caused by the partition plate TB1, TB2. A tongue-like extension V1, V2 present at the opposite narrow end of the separating plate TB1, TB2 also serves the same purpose. It is very well suited for receiving a compensation element KE, for example in the form of a short pencil. However, in the case of two wave type converters arranged one behind the other, which together form a polarization switch, only that partition plate TB1 needs to be provided with such a compensation element KE, whose associated coupling opening K1 represents a certain disturbance for the H11 wave not to be coupled here. In the present exemplary embodiment, an H11 wave, which is assigned with its polarization direction to the separating plate TB2 and the associated coupling opening K2, experiences a malfunction through the coupling opening K1 located in front of it. This disturbance is compensated for by a pin KE which extends in the E plane of the disturbed H11 shaft and is arranged on the tongue-like extension V1 of the separating plate TB1. The interference compensation by the KE pin is so good that for the second wave type converter connected downstream to generate a polarization filter, its geometry is identical to that of the first wave type converter, in terms of amount, the same reflection factor is achieved as if it were operated as the sole wave type converter - without another wave type converter connected upstream of it.

The second wave type converter of a polarizing filter does not have to be the same as the first. It can also be replaced by another waveguide or coaxial transition that excites an H11 shaft in the round waveguide.

As can be seen in FIG. 2, the two separating plates TB1 and TB2 are inserted in grooves N11, N12 and N21, N22, which are milled into the inner wall of the circular waveguide RH. That is, for each partition plate TB1 and TB2 there are a pair of grooves N11, N12 and N21, N22 running in the axial direction of the circular waveguide. The position of the grooves is exactly based on the polarization planes of the H11 waves, so that the separating plates TB1, TB2 used in the grooves N11, N12 and N21, N22 are aligned precisely with the polarization planes. The coupling openings K1 and K2 have capacitively and / or inductively acting diaphragms B1 and B2, which can be produced together with the coupling openings in a milling process. The dimensions of these diaphragms B1, B2 and the shape and position of the separating plates TB1, TB2 relative to the coupling opening are decisive for the adaptation of the round waveguide RH to the coupled rectangular or elliptical waveguide. In detail, it should now be explained once again, by means of which three simple, highly reproducible measures, which make the tuning elements and each test field adjustment superfluous, enable the circular waveguide to be optimally adapted to the rectangular or elliptical waveguide.

3 shows a reflection diagram in which several locus curves of a wave type converter of the type described here are drawn in different positions A, B, C, D with respect to the real axis Re and the imaginary axis Im. With · the center frequency, with o the lower and with x the upper frequency of the frequency band for which the wave type converter is adapted, is marked. The position of the center frequency of this frequency band can be determined solely by the angle α (see FIG. 1) with which the partition plate expands. For an angle α in the range of 110 ° ... 130 °, the center frequency can be varied in a frequency range of f _c (1.1 ... 1.25), where f _{c is} the cut-off frequency of the H11 mode.

Regardless of the setting of the center frequency, the real part of the reflection factor of the wave type converter can be freely selected by moving the separating plate TB1 or TB2 in the direction of the longitudinal axis z of the circular waveguide RH. As indicated in FIG. 3, this measure allows the locus to be shifted in parallel in the direction of the real axis Re of the reflection factor diagram from position B via A to C and vice versa. An independent shift of the locus in the direction of the imaginary axis Im from position D via A to E and vice versa can be carried out by appropriately dimensioning the broad side of the aperture B1 or B2.

(f_c = Grenzfrequenz des H11-Mode) höchstens 0,01 ... 0,04 dB.With a suitable dimensioning of the diaphragms B1, B2 and the separating plates TB1, TB2, for example in the frequency range 10.75 GHz ÷ 12.5 GHz, an adaptation with a reflection factor of r ≈ 0.015 with a relative one can be made for each polarization Achieve a bandwidth of approximately 0.15. Such a polarization filter has a polarization decoupling of more than 50 dB, and its maximum attenuation is depending on the operating frequency ${\text{f = f}}_{\text{c}}\text{· (1.1 ... 1.25)}$

(f _c = cut-off frequency of the H11 mode) at most 0.01 ... 0.04 dB.

Claims (6)

1. Arrangement for the converting of a wave of the H11 mode in a circular waveguide into a wave of fundamental mode for a rectangular or an elliptical waveguide and conversely, wherein a coupling opening is so arranged in the wall of the circular waveguide that the magnetic plane of a rectangular or an elliptical waveguide connected thereto coincides with the magnetic plane of the wave of the H11 mode in the circular waveguide, the coupling opening has an inductively-acting and/or capacitvely-acting aperture, and inserted into the circular waveguide is a partition plate which lies in the direction of the electrical plane of the H11 wave and which starts in the region of the coupling opening and extends in the circular waveguide into the region where a propagation of the said H11 wave shall be prevented, characterised thereby that the partition plate (TB1, TB2) starts, at its end disposed in the region of the coupling opening (K1, K2), with a narrow width and widens out towards its other end to a width, which is matched to the inner dimensions of the circular waveguide (RH), at such an angle (α) that a desired operating centre frequency for the arrangement is set, and that let into the partition plate (TB1, TB2) are several slots (S1, S2) which are so arranged and dimensioned that disturbing resonances caused by the partition plate (TB1, TB2) are suppressed.
2. Arrangement according to claim 1, characterised thereby that the narrow end of the partition plate (TB1, TB2) has a tongue-like prolongation (V1, V2).
3. Arrangement according to claim 1, characterised thereby that let into the inner wall of the circular waveguide (RH) are two grooves (N11, N12), which are disposed opposite one another in direction of the electrical plane of the H11 wave, extend in longitudinal direction of the circular waveguide and serve for the reception of the partition plate (TB1).
4. Arrangement according to claim 1, characterised thereby that for two waves of the H11 mode polarised orthogonally to each other the circular waveguide (RH) has two coupling openings (K1, K2) which are provided with apertures (B1, B2) and which are offset relative to one another axially with respect to the circular waveguide longitudinal axis and radially according to the polarisation directions of the two H11 waves.
5. Arrangement according to claim 1, characterised thereby that two groove pairs (N11, N12; N21, N22) extending in longitudinal direction of the circular waveguide are let in, wherein the grooves of each pair lie opposite one another in the polarisation direction of a respective one of the two H11 waves, and that each groove pair (N11, N12; N21, N22) serves for the reception of a partition plate (TB1, TB2).
6. Arrangement according to claim 4, characterised thereby that that separating plate (TB1), which is disposed at a coupling opening which represents a disturbance for the H11 wave passing it and associated with the other opening (K2), is provided at its tongue-like prolongation (V1) with an element (KE) compensating for this disturbance.

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