The invention relates to a multi-stage broadband directional coupler in accordance with the preamble of claim 1.
In high-frequency systems, it is often necessary to split a signal, for example of a power P, into two signals in any given power split. In special cases, it may be desirable to split the power into 50% in each case. Hybrid ring couplers are often used for this purpose. Hybrid ring couplers of this type are known inter alia from Zinke Brunswig “Hochfrequenztechnik”, Springer-Verlag, 6th edition, 2000, in particular page 192.
These hybrid ring couplers are frequently constructed using microstrip conductor technology.
Further, however, high-frequency couplers are also known in which the degree of coupling is generally set via lines coupled on the end or longitudinal faces. For higher coupling levels, such as are required for a power splitter, these distances are often very small, or even so small that they can no longer be produced economically.
Thus, for example, a directional coupler is also known from U.S. Pat. No. 6,946,927 B2, which is constructed using suspended substrate technology. In other words, a coupling path using stripline technology is provided on one side of a substrate and is connected to two first and second terminals, also constructed using stripline technology, on the substrate. On the opposite side of the substrate, a second coupling path is further arranged, which leads to a third and fourth output or terminal. In a plan view, the two coupling paths are arranged so as to overlap at least in part.
A high-frequency coupler which is even further improved, in particular in the form of a narrow-band coupler or power splitter, is known for example from EP 1 867 003 B9. According to this publication, an improvement is also achieved by providing interdigital capacitors, which are each coupled between a coupling path and the earth, in the longitudinal direction of the two coupling paths.
The main drawbacks of the directional couplers using coplanar line technology relate inter alia to the required minimum distances between the conductor paths coupled on the longitudinal faces and to the coupling factor, which is thus also limited. Further, the coupling factor is highly tolerance-dependent (etching tolerances and fluctuations in the dielectric constant of the substrate material have a disadvantageous effect). Further, a coupler using coplanar line technology is non-optimal as regards dielectric losses.
An ideal separation of forward and backward waves is additionally only possible using directional couplers which permit propagation of TEM waves. Directional couplers using microstrip conductor or coplanar line technology do not make propagation of pure TEM waves possible. Therefore, directional couplers using coaxial line technology are used.
However, directional couplers or power splitters using coaxial line technology are of a relatively complex construction. Thus, in conventional directional couplers of this type, extremely precisely milled housings have to be manufactured, which have to have very different housing interior widths for the different stages of the coupler. Thus, the arrangement, in particular at the transition from one coupling stage to the next, is highly critical, since precise dimensions have to be adhered to here both as regards the coupling lines and as regards the distance from the inner housing walls. Even minimal deviations here can lead to relatively strongly altered electrical characteristic values.
A directional coupler largely similar to the described prior art is also known from EP 0 669 671 A1. It comprises two coupling paths, which each extend between two terminals on different paths. Each of the two coupling paths has a coupling portion, the two coupling paths extending mutually in parallel at a predetermined distance in the region of the respective single coupling portions thereof, so as to produce the desired coupling effect in this case.
An arrangement which is comparable in this regard is also known from U.S. Pat. No. 4,797,643. The special feature in this case is that two directional coupler arrangements which produce a coupling effect are arranged in a shared housing. The actual coupling path is formed by two coupling portions that extend perpendicularly at a distance from one another and belong to the two coupling paths.
After passing through an intermediate path approximately ten times as long as the coupling portion, the two coupling paths cross a second time. At this second crossing point, the two coupling paths likewise again extend at an equal distance from one another, and form the next two interacting coupling portions there.
JP 5-191113 discloses a directional coupler in which each coupling path has just one coupling portion between the respectively associated terminals thereof, which portion interacts with a corresponding coupling portion, extending in parallel therewith, of the second coupling path.
The prior publication MOHAMED M FAHMI: “Multilayer Multi-Section Broadband LCC Stripline Directional Couplers”, 1 Jun. 2007, XP031111873, describes a coupler device, specifically a directional coupler having four terminal ports. However, this is a stripline coupler which is fundamentally of a completely different construction from the above-described coaxial couplers, which have intercoupled signal lines accommodated in a housing which serves as an external conductor.
Against this background, the object of the present invention is to provide an improved directional coupler, in particular a 3 dB coupler, which is improved by comparison with conventional solutions in terms of costs, losses and manufacturing tolerances.
The object is achieved according to the invention in accordance with the features set out in claim 1. Advantageous embodiments of the invention are set out in the dependent claims.
The directional coupler according to the invention has major advantages over the prior art.
The directional coupler according to the invention is distinguished primarily by having a low tolerance-sensitivity whilst maintaining very good electrical values. In addition, the housing of the coupler according to the invention can be produced in a convenient manner. Overall, the coupler according to the invention is simple to manufacture and calibrate, making possible manufacture which is more cost-effective overall than conventional solutions.
The directional coupler according to the invention comprises a housing as an external conductor, which may preferably be manufactured as an injection-moulded part. Although injection-moulded parts of this type undergo or have to undergo subsequent machining in relation to the housing interior, the manufacture of an injection-moulded housing of this type is much more cost-effective than a housing which previously had to be milled in accordance with the prior art. The housings previously had to be milled because directional couplers of this type were highly tolerance-dependent, and the required precision could only be adhered to using a milled housing.
Further, the directional coupler according to the invention is distinguished in that the coupling portions of the two coupling paths of the multi-stage broadband directional coupler are defined with respect to one another by transition regions, which are also referred to as discontinuities for simplicity, even though the transition need not be exactly abrupt but rather takes place gradually over some distance. At these transition points, the coupling portions have an altered line cross section, i.e. the line thickness and/or line width thereof changes and/or the coupling distance changes, i.e. the distance between the two adjacent but galvanically separated coupling lines. Subsequently, capacitively acting shields are provided in the interior of the coupler housing in this region as a compensation device for the aforementioned transition regions.
In the context of the invention, it is thus ultimately also possible for the coupler housing to be able to have a more or less equal housing interior width over the coupling path or for this housing interior width only to vary relatively little over the length of the housing. In conventional multi-stage directional couplers, the housing interior width varies greatly in relation to the individual coupling portions. It was perfectly normal for the housing interior width to have to be configured 2 to 3 times larger from an initial coupling portion to a subsequent or central coupling portion. The interior ratios and dimensions still had to be adhered to extremely precisely, in particular at the transition regions from one coupling portion to the next.
In a preferred embodiment of the invention, it is further possible for the coupling distance, in particular between the coupling portions positioned closest together, to subsequently be able to be fine-tuned slightly by the possibility of inserting and/or fixing dielectric spacers (for example in the form of a plastics material plate etc.), which may be of small dimensions, between the coupling portions positioned closest together.
Also, one or the many further advantages in the context of the invention is that the coupler housing can be separated into two equal coupler housing halves along a separating plane. Each of the two coupler housing halves comprises one of the basically two coupling paths. Thus, each housing half can be mounted along with the associated coupling path, and subsequently the complete coupler housing can be finished by putting the two coupler housing halves together.
Further advantages, details and features of the invention can be seen in the following from the embodiment described by way of drawings, in which, in detail:
The multi-stage directional coupler shown in the drawings is formed for example as a 3 dB directional coupler. However, the coupling path may also be configured differently, in such a way that power splits other than 50:50 are also possible at any time.
The drawings show the directional coupler according to the invention having a coupler housing 1, which in the embodiment shown comprises coupler housing halves 1a and 1b formed identically in terms of size.
In other words, the two coupler housing halves 1a, 1b are of the same length, the same width and the same height transverse to the separating plane 3 thereof.
Two adjacent coupler housing halves 1a and 1b, visible from the opening faces 5 thereof, are formed identically (or formed substantially identically) and can be placed with the opening faces 5 thereof against one another by rotation through 180°, in such a way that the housing half contact planes 7, each positioned at the separating plane 3, of the two coupler housing halves 1a, 1b come to be positioned against one another, including the coupling path(discussed further below) provided in the housing interior 9.
Like any directional coupler, the directional coupler comprises at least three ports, but generally four ports. In the embodiment shown, a coaxial interface 11, 13, 15, 17 visible on the housing exterior is provided in each of the ports, each coupler housing half 1a, 1b having a coaxial interface 11, 13 or 15, 17 on each of the two opposing longitudinal faces 19. Equally, however, corresponding lines connected in the interior of the housing, in particular coaxial cables, may also be guided out of the housing. For simplicity, reference is made to ports in this case too. The two coaxial interfaces 11, 13 associated with one of the two coupler housing halves 1a, 1b form the two ports, which are connected to one of the coupling paths described in the following, whilst the other two coaxial plug couplings 15, 17, which are provided on the other coupler housing half 1b, are connected to the second coupling path. Generally speaking, the connection of the coupling paths at the ends thereof is ultimately provided by way of a coaxial line system, for example in the form of a coaxial line.
As is known, the electrical mode of operation is such that an electromagnetic wave input at one coaxial coupling plug is output at the two opposite coaxial plug couplings forming the outputs with a corresponding power split, in accordance with the coupling ratio, whereas ideally no energy is output at the remaining fourth port on the input side.
From the cross-sectional view of
From the drawings, it can be seen that the two coupling paths 21 and 23 are of a multi-stage construction, and in the embodiment shown are subdivided into three coupling portions, specifically coupling portions 21a, 21b and 21c for the first coupling path 21 and corresponding coupling portions 23a, 23b and 23c for the second coupling path 23.
The first and third coupling portion of each coupling path 21, 23 are each configured symmetrically about a central vertical plane E, at least over the majority of the length thereof.
Each of the coupling portions has a line width LB and a line thickness LD (perpendicular to the plane 3 in a vertical direction), in other words a specific material cross section. In addition, in each case each of the three coupling portions is characterised by a coupling distance KA between the two adjacent coupling portions 21a and 23a or 21b and 23b or 21c and 23c.
Transition regions 27, in which the material cross section of the coupling paths 21, 23, i.e. the coupling width and/or the coupling thickness and/or the coupling distance between the two adjacent coupling portions changes, are formed between the successive coupling portions 21a, 21b, 21c or 23a, 23b, 23c of each of the two coupling paths 21, 23.
The length of the individual coupling portions substantially corresponds at least approximately to λ/4 for the mid-band operating frequency of the coupler.
Further, it can also be seen from
In the embodiment shown, two shield webs 29′ are provided for each transition region 27, and each protrude from two opposing longitudinal inner faces 31 in the housing interior 9 in the direction of the coupling path 21, 23, preferably protruding perpendicularly from the longitudinal inner faces 31 and ending in the transition region 27 at a small distance from the side flanks (side wall portions) of the relevant coupling path.
These shield webs 29′ may each extend as far as the base 33 of the relevant coupler housing half 1a, 1b defining the housing interior 9, where they are connected to the material of the associated housing half 1a, 1b, in particular in a material fit. However, it is also possible for the shields or shield webs 29, 29′ to end before the base 33 or the base face 33 formed thereby so as to form a gap.
The shields 29 visible in the drawings, i.e. the shield webs 29′, end at least shortly before the separating plane 3, in other words the peripheral housing edge 3′, in such a way that the two housing halves can be joined together securely, lying against one another at the peripheral housing rim 3′ thereof.
In addition or alternatively, the shields 29 may also be formed in such a way that the shield webs 29′ are not arranged to the side of the coupling paths 21, 23 which are arranged above one another (as shown in
As can be seen from the plan view of each of the coupler housing halves 1a, 1b, the housing interior 9 for each of the two coupler housing halves 1a, 1b is configured with more or less the same interior width IB over the length of the housing interior 9. The inner and longitudinal faces 31 which define the housing interior 9 only transition into inner end faces 32 at the end-face regions of the housing interior, specifically preferably via rounded wall portions 34.
Since, unlike in the art, the housing according to the invention thus more or less has an evenly formed housing interior width IB over the entire interior length thereof, the housing according to the invention or the coupler housing halves according to the invention may also be formed as cast parts. In this case, the housing inner faces and the base face can be post-machined if necessary. As a result of this, and also as a result of the lower tolerance-sensitivity than in conventional solutions, it is possible to use a coupler housing manufactured as a cast part.
The coupling level can be influenced and changed by the formation of the coupling paths, i.e. by corresponding changes of cross section in the individual coupling portions and/or by changes in the coupling distance KA, in particular between the two coupling portions extending closest together, i.e. between the two central coupling portions 21b and 23b in the embodiment shown.
In this case, so as to carry out precise distance tuning and/or to change the coupling factor if desired, an insulator or dielectric 35 may be interposed at this point, optionally inserted into a hole so as to be held captively. A spacer rim of the insulator, protruding beyond the hole 37 in the coupling portion 21b or 23b, thus defines the minimum distance between the two coupling portions 21b, 23b.
In the embodiment shown, the two coupling paths 21, 23 are each held by way of two spacers or support devices in the form of an insulator or dielectric, specifically spacers or support devices 39a and 39b for the first coupling path 21 and spacers or support devices 41a and 41b for the second coupling path 23. These support elements 39a, 39b and 41a, 41b for holding and adjustment may for example be pin-shaped, and are inserted into corresponding internal housing holes 43, opposing shoulders of the support elements engaging in corresponding coupling portion holes 45. In turn, a material shoulder 45a protruding radially beyond the hole diameter is provided therebetween, and is positioned both on the base face of the respectively adjacent base 33 of the coupler housing half 1a, 1b and on the coupling portion base face 25 adjacent thereto, as can be seen in particular from
This internal conductor connection piece 47 is subsequently held in a braced manner by means of an insulator plate 50 against a housing hole 51, in the axial extension of which the external conductor 53 of the associated coaxial interface 11 is arranged, preferably being screwed on by way of a threaded connection on the associated coupler housing half, i.e. a housing shoulder 1′a or 1′b integrally connected to the coupler housing half there. In the region of the outwardly facing coaxial interface 11, the associated internal conductor connection piece 47 is configured for example in the form of a coaxial plug coupling in the manner of a conventional internal conductor 55 which makes a coaxial plug-in connection possible. However, in a deviation from this, a coaxial cable connection may also for example be guided out to the outside directly from the interior of the housing 9 or of the housing half 1a or 1b, without the aforementioned interface formation. Completely different configurations and solutions are also possible in this regard.
As a result of this arrangement, in principle each of the two coupling paths 21, 23 can be held in the associated coupler housing half 1a, 1b even without the aforementioned spacers or support elements 39a, 39b or 41a, 41b.
The broadband coupler according to the invention has been described with reference to two coupling paths, which are each subdivided into three coupling portions, as well as the two transition regions each between two successive coupling regions. However, in a deviation from this, more or fewer coupling portions may also be provided in each of the coupling paths. In principle, whilst taking into account the configuration according to the invention, a coupler may also be implemented which for example only comprises two coupling paths, which are each subdivided into two successive coupling portions only having one interposed transition region. Likewise, the coupling paths may also have more than three coupling portions, for example 4, 5 etc. coupling portions in succession, which are preferably likewise distinguished by corresponding transition regions of varying material cross section and/or by a coupling distance changed to this effect between two successive coupling portions.
Additionally, an advantage of the directional coupler according to the invention is that two coupler housing halves of the same dimensions can be used. They may preferably both consist of a cast part. However, it is also possible to use a coupler housing of a height in which both coupling paths can be accommodated. This coupler housing may also preferably consist of a cast part, for example of an aluminium cast part. In this case, all that would remain would be to place a possibly planar cover on the opening face 9 of the box-shaped coupler housing. In this case, a cover of this type need not necessarily consist of a cast part.
Number | Date | Country | Kind |
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10 2014 004 007.0 | Mar 2014 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2015/000451 | 2/26/2015 | WO | 00 |