EP2506363B1 - Waveguide coupling - Google Patents

Description

The present invention relates to a waveguide coupling, in particular for a radar level gauge, with a waveguide, a support plate and at least one feed line, wherein the feed line is guided on and / or in the carrier plate in the inner region of the waveguide and the feed line with one end in the inner region of the waveguide ends, wherein the carrier plate is continuously extending into the inner region of the waveguide and thus beyond the end of the feed line, wherein in the vicinity of the end of the feed line and / or in the carrier plate, an electrically conductive coupling element is arranged, so that the coupling element with the feed line is coupled and the coupling element of the coupling of guided via the feed line in the waveguide electromagnetic waves in the waveguide, wherein the coupling element has a longitudinal ridge and a crosspiece, said longitudinal ridge and the crosspiece arrange crosswise et, wherein the feed line is aligned substantially straight to the center of the inner cross-sectional area of the waveguide and wherein the longitudinal web of the coupling element is arranged in extension of the feed line.

Such waveguide couplings have long been known in high frequency engineering and they are used as an interface between an electronic device generating an electromagnetic signal and the supply of the line-guided signal in the interior of the waveguide. In waveguide couplings known from the prior art, the carrier plate usually consists of a board known from circuit technology, wherein the feed line is often designed as a microstrip line and is guided through a recess in the waveguide in the interior of the waveguide, where the conducted electromagnetic wave of the feedline separates and propagates as a guided electromagnetic wave in the waveguide. In the example given application in the context of a radar level gauge, the guided electromagnetic wave can ultimately leave the waveguide as a free space wave, either immediately after exiting the waveguide or after passing through an adjoining the waveguide radiator, often to achieve a certain radiation characteristic is provided; in the latter case, the waveguide serves quasi only as a transition element. The shape of the waveguide as well as the injected electromagnetic signal decide which modes of an electromagnetic wave ultimately propagate in the waveguide. Usually, electromagnetic waves with frequencies in the GHz range are used for radar applications.

A generic waveguide coupling is from the US 2,829,348 A known, which is dedicated to the coupling of a strip conductor to a waveguide. The US 2010/0225410 A1 shows an arrangement in which two microstrip conductors are guided into the interior of a waveguide. The EP 0 071 069 A2 shows a waveguide coupling, coincide in the feed line and coupling element. Further waveguide couplings are in US 2006/0255875 A1 and JP 2007-13450A disclosed.

From the prior art it is known that the material surrounding the feed line in the inner region of the waveguide material of the carrier plate is removed - for example by milling - so that the end of the feed line is practically exposed. This process is comparatively complicated, since the resulting structures are small and therefore mechanically sensitive, especially in the case of high-frequency electromagnetic waves, so that high demands must be placed on the precision of the milling work to be performed. Such constructions are known, for example Brumbi, D .: "Fundamentals of radar technology for level measurement", 3rd revised edition, 1999 ,

It is therefore an object of the invention to provide such a waveguide coupling, which has a greater stability and is easy to manufacture.

The previously derived object is achieved in the waveguide coupling described above in that the waveguide is mounted on a first side of the support plate on the support plate, that the coupling element is capacitively coupled to the feed line, that the support plate on its first side on which the waveguide is placed, or in an intermediate layer, the feed line, the coupling element and an electrically conductive screen surface, that the support plate on its first side opposite the second side or in an intermediate layer a large area has further electrically conductive shielding surface and that outside of the region opposite to the inner cross-sectional surface of the waveguide that the shielding surface and / or the further shielding surface protrudes with an influencing extension in the inner cross-sectional area of the waveguide and that the influencing extension to the center of the inner cross-sectional area of the waveguide is aligned tapered, and is arranged in alignment with the feed line.

The fact that the support plate is continuously extending into the inner region of the waveguide, so practically represents a continuous plate, eliminates the operation of the exemption of that end of the feed line, which ends in the interior of the waveguide, also mechanically sensitive structures are avoided. By the electrically conductive coupling element in the vicinity of the end of the feed line, it is possible to adjust the waveguide coupling electromagnetically and, for example, to influence the bandwidth to the desired center frequency of the leading electromagnetic waves.

In a preferred embodiment of the invention, it has been found to be advantageous if the coupling element is arranged substantially in the center of the waveguide and / or in the carrier plate. If previously it is mentioned that the feed line is guided on and / or in the carrier plate, or that the coupling element is arranged on and / or in the carrier plate, then it is meant that the electrically conductive elements are not necessarily on a surface of the Carrier plate must be realized, but rather can be realized as conductive structures in a printed circuit board, as is known for example from multilayer boards.

As a particularly suitable structure for the coupling element according to the invention a cross shape has been found, so that the coupling element thus has a longitudinal web and a transverse web, wherein the longitudinal web and the crosspiece are arranged in a cross shape. Of course, the longitudinal web and the crosspiece do not have to be distinguishable as individual, overlapping structures, but rather may also be present as a single structure in which only a geometrical distinction is made between a longitudinal web and a transverse web can be. The cross shape of the coupling element brings an unexpected positive effect in terms of achievable and achieved bandwidth with it. While with conventional constructions bandwidths are achieved with an adaptation of better than 15 dB of usually not more than about 10% of the carrier frequency, with the described cross-shaped coupling element bandwidths of about 20% of the carrier frequency can be achieved, which brings a significant advantage.

By varying the length of the longitudinal web and the length of the transverse web, for example, the bandwidth can be varied, with which an adaptation above a predetermined attenuation is achieved by a desired center frequency.

The coupling element is preferably designed such that the characteristic dimensions of the coupling element are in the range of one quarter of the wavelength of the electromagnetic waves to be emitted. By "characteristic dimensions" is meant, for example, the longitudinal and transverse extent of the coupling element, in the case of the cross-shaped configuration of the coupling element so the extension of the longitudinal web and the transverse web of the coupling element. In any case, however, account must be taken here of the effective relative permittivity of the design - resulting, for example, from the relative permittivities of the support plate and ambient air - since this is a scaling factor, the scaling factor being more precisely the reciprocal of the root from the actual relative permittivity.

According to the invention, the carrier plate has on its first side, on which the waveguide is mounted, or on its second side opposite the first side, or in an intermediate layer, the feed line, the coupling element and an electrically conductive shielding surface. Of course, the electrically conductive shielding surface and the feed line are realized separately from one another, wherein the feed line, the coupling element and the shielding surface are realized in particular as a metallization of the carrier plate. It makes sense to photolithographically make the production of these electrically conductive structures in a known manner, since it is here It is also possible to carry out the required precision in the execution of the structures even in the area of millimeter fractions.

According to an advantageous development, the electrically conductive shielding surface contacts the waveguide on its end face, wherein the shielding surface surrounds the waveguide in particular over a large area. Since the electrically conductive waveguide is connected at its end face to the likewise electrically conductive shielding surface, it is possible in a very simple manner to place the shielding surface and waveguide at a common electrical potential, for example at ground potential.

It has also been found to be advantageous if the support plate according to the invention on its first side, on which the waveguide is placed, or on its second side opposite the first side or in an intermediate layer has a large area further electrically conductive screen surface and preferably outside the range , which is opposite to the inner cross-sectional area of the waveguide, wherein the further screen surface is in turn realized in particular as a metallization of the carrier plate or as a metallic intermediate layer. In this way, the entire surface of the support plate can be provided in a simple manner with a defined potential and can suppress interference emissions.

In the context of the invention it has been recognized that it is possible in a surprisingly simple manner to suppress unwanted modes in the waveguide. This can be achieved by projecting the shielding surface and / or the further shielding surface into the inner cross-sectional surface of the waveguide with an influencing extension, wherein the influencing extension is aligned with the center of the inner cross-sectional surface of the waveguide and is aligned with the feedline. In this case, despite its orientation in the direction of the center of the inner cross-sectional area of the waveguide, the influencing extension remains in the vicinity of the circumference of the inner cross-sectional area of the waveguide, ie preferably does not protrude into the region of the coupling element.

In order to achieve a conclusion of the waveguide in the direction opposite to the direction of radiation, either a conductive cap on the second side of the support plate in geometrical continuation of the waveguide to be placed, the electrically conductive cap then with its end face in particular those on the second side of the support plate arranged large screen area or the other screen contacted. Alternatively, however, it can also be provided that the support plate has on its first side opposite the second side - or again in an intermediate layer - in continuation of the waveguide an electrically conductive layer as the conclusion of the waveguide. In both variants, a distance from the end of the waveguide is preferably realized to the coupling element, which is also a quarter of the wavelength of the guided electromagnetic waves.

In a further preferred embodiment of the invention it is provided that the waveguide and / or the cap are filled with a potting compound, wherein the permittivity of the dielectric used as potting compound is to be considered in the dimensioning of those structures in the generation and guidance of the desired electromagnetic Waves are involved. In a filled with a potting compound waveguide, it is particularly advantageous if the support plate in the region of the inner cross-sectional area of the waveguide has at least one recess - for example in the form of a bore - as can spread over these recesses an initially liquid potting compound in all areas of waveguide coupling ,

Fig. 1

eine aus dem Stand der Technik bekannte Hohlleitereinkopplung in Seitenansicht und in Draufsicht,

Fig. 2

eine Trägerplatte einer Hohlleitereinkopplung von der ersten Seite und von der zweiten Seite in Draufsicht,

Fig. 3

eine Trägerplatte für eine Hohlleitereinkopplung,

Fig. 4

ein Ausführungsbeispiel einer Trägerplatte für eine erfindungsgemäße Hohlleitereinkopplung und

Fig. 5

eine Explosionsdarstellung einer Hohlleitereinkopplung.

In particular, there are a variety of ways to design and further develop the waveguide coupling according to the invention. Reference is made on the one hand to the claims subordinate to claim 1, on the other hand, to the following description of embodiments in conjunction with the drawings. In the drawing shows

Fig. 1

a known from the prior art waveguide coupling in side view and in plan view,

Fig. 2

a carrier plate of a waveguide coupling from the first side and from the second side in plan view,

Fig. 3

a carrier plate for a waveguide coupling,

Fig. 4

an embodiment of a carrier plate for a waveguide coupling according to the invention and

Fig. 5

an exploded view of a waveguide coupling.

In Fig. 1 a waveguide coupling 1 known from the prior art is shown, wherein Fig. 1a a waveguide 2, a support plate 3 and a feed line 4 has. The waveguide 2 is placed in the assembled state on the first side 5 of the support plate 3 on the support plate 3, which in Fig. 1a is indicated by a dashed line.

The feed line 4 is guided on the support plate 3 in the inner region 5 of the waveguide, in any case, this applies to the mounting state. Accordingly, the feed line 4 terminates at one end 7 in the inner region 6 of the waveguide 2, the end 7 of the feed line 4 projecting into the inner region 6 of the waveguide 2 in the axial direction of the waveguide 2, ie actually at an outer end in the irradiation region of the waveguide 2 is provided. In Fig. 1b is good to see that the one end 7 of the feed line 4 in the inner region 6 of in Fig. 1b itself not shown waveguide ends and there is free, namely protruding into a milled recess 8. It is readily conceivable that the end 7 of the feed line 4 is cumbersome to produce and, moreover, is mechanically very sensitive.

In the Fig. 2 to 5 waveguide couplings 1 and components of such waveguide couplings 1 are shown. Unlike the out Fig. 1 known waveguide couplings is in the embodiments according to the Fig. 2 to 5 the support plate 3 extends continuously into the inner region 6 of the waveguide 2, so that therefore the end of the 7th the feed line 4 is not exempted, so no to the contour of the end 7 of the feed line 4 adapted recess in the inner region of the waveguide in the support plate 3 is provided. It therefore eliminates the time-consuming processing step of producing a precise opening of the support plate 3. Further, in the Fig. 2 to 5 recognizable that in the vicinity of the end 7 of the feed line 4 on the support plate 3, an electrically conductive coupling element 9 is provided, wherein the indication "in the vicinity of the end 7 of the feed line 4" is to be understood that the coupling element 9 capacitively with the Feed line 4 and is coupled to the end 7 of the feed line 4 and the coupling element 9 of the coupling of guided via the feed line 4 in the waveguide 6 electromagnetic waves in the waveguide 6 is used.

The shape of the coupling element 9 is crucial for the adaptation of the waveguide coupling, wherein it is advantageous regardless of the shape of the coupling element 9, if - as in the Fig. 2 to 5 shown - the coupling element 9 is arranged substantially in the center of the waveguide 2 on the support plate 3; the electromagnetic waves emitted by the coupling element 9 are thus emitted practically symmetrically with respect to the wall of the waveguide 2.

In the embodiments, it is provided that the coupling element 9 has a longitudinal web 9a and a transverse web 9b, wherein the longitudinal web 9a and the transverse web 9b form a total of a cross. A good adaptation of the waveguide coupling 1 is realized primarily by the longitudinal web 9a, 9b further, but not so significant improvements of the adjustment are achieved with the cross bar.

In the illustrated embodiments, the characteristic dimensions of the coupling element 9 are in the range of one quarter of the wavelength of the electromagnetic waves to be emitted, wherein the characteristic dimensions in the present case in each case the longitudinal extent of the longitudinal web 9a and the cross bar 9b.

In the Fig. 2a and 3 to 5 It can be seen that the feed line 4 is aligned substantially tapered straight to the center of the inner cross-sectional area of the waveguide 2, that is, in the case of the circular waveguide 2 radially extends, wherein the longitudinal web 9a of the coupling element 9 is arranged in extension of the feed line 4.

The in the Figures 2 and 4 illustrated examples and embodiments are characterized in that the support plate 3 on its first side 5, to which the waveguide is mounted in the assembled state - not shown in the Fig. 2 and 4 - The feed line 4, the coupling element 9 and a - in the Fig. 2 and 4 not shown - waveguide on its end face 10 contacting, the waveguide in particular a large area surrounding electrically conductive shielding surface 11, wherein the feed line 4, the coupling element 9 and the shield surface 11 are realized as metallization of the support plate 3. In the Fig. 2 , in particular the Fig. 2b It is shown that the carrier plate 3 on its first side 5 opposite the second side 12 has a large area further electrically conductive screen surface 13 and that outside of the area opposite the inner cross-sectional area of the waveguide, wherein the further shield surface 13 also as a metallization of the support plate 3rd is realized.

The waveguide coupling 1 in Fig. 5 shows an exactly opposite structure of the assignment of the first page 5 and the second side 12 of the support plate 3. In the embodiment shown there, the waveguide 2 is indeed also placed on the first side 5 of the support plate 3, but the feed line 4 and the coupling element realized on the second side 12 of the support plate 3 as a metallization, which works just as well; Both solutions shown are technically equivalent and equally easy to manufacture.

In the example according to Fig. 3 No extended screen surface is provided, but only an electrically conductive contacting surface 14, on which the waveguide can be placed. In the support plate 3 according to Fig. 4 According to the invention, the electrically conductive shielding surface 11 protrudes with an influencing extension 14 into the inner cross-sectional area of the waveguide, wherein the influencing extension 14 is arranged on the center of the inner cross-sectional area of the waveguide, in the present case in alignment with the feed line 4. The feed line 4, the longitudinal web 9a and the influencing extension 14 are quasi in line.

In Fig. 5 is further shown that on the second side 12 of the support plate 3 in continuation of the waveguide 2, an electrically conductive cap 15 is placed as a conclusion of the waveguide 2, wherein the electrically conductive cap 15 consists of an electrically conductive base portion 15a and an electrically conductive terminating element 15b wherein the end element 15b can be inserted into the base part 15a.

In Fig. 5 is further shown that an electrically conductive connection between the waveguide 2 and the cap 15 is made by a plurality of vias 16, which are embedded in the support plate 3. The plated-through holes 16 make an electrically conductive connection between the electrically conductive screen surface 11 on one side of the carrier plate 3 and the further electrically conductive screen surface 13 on the other side of the carrier element 3. As already mentioned, it is not critical for the technical function whether the feed line 4, the coupling element 9 and the shielding surface 11 are provided on the side of the waveguide 2 of the support member 3 or on the side of the termination 15, just as it is of crucial importance, whether the further shield surface 13 on the waveguide 2 facing side of the support plate 3 is provided or on the other, the end 15 facing side of the support plate 3. Vias 16 are also in Fig. 3 shown.

This in Fig. 2 illustrated example is designed for the coupling of electromagnetic waves with a center frequency of 80 GHz, in this case for coupling a linearly polarized electromagnetic wave, wherein the waveguide is made round and with an inner diameter of 2.6 mm, the longitudinal web 9a and the transverse web 9b of Einkoppelelements 9 have a length of 0.84 mm, and the support plate 3 has an edge length of about 6 mm. Due to the clever choice of the shape and the dimensions of the coupling element 9, it is possible a Adjustment better than 15 dB for a bandwidth of about 17 GHz or 21% of the center frequency to achieve. It should be noted here that the specifications apply to a design without encapsulation; in the case of encapsulation, the relative permittivity of the encapsulant must also be taken into account when dimensioning

The example according to Fig. 3 is optimized for a coupling of a linearly polarized electromagnetic wave with a center frequency of 6 GHz, wherein the - not shown waveguide - is designed round and with an inner diameter of 21.6 mm, the longitudinal web 9a of the coupling element 9 has a length of 5.5 mm and the transverse web 9b of the coupling element 9 has a length of 7.4 mm and wherein the carrier plate 3 has an edge length of about 32 mm. In this example, a potting compound with a relative permittivity of about 4 is used, which has also been taken into account in the aforementioned interpretation. If the potting is omitted or replaced by a potting with a different relative permittivity, the dimensions must be adjusted accordingly. In Fig. 3 it is further shown that the support plate in the region of the inner cross-sectional surface of the waveguide recesses 17a, 17b, which serve above all the better Verfüllbarkeit the waveguide 1 with a potting compound and are designed as holes. These holes are easy to manufacture and reduce the advantage of the illustrated embodiment of a waveguide coupling 1 with an otherwise continuous support plate 3, since holes are very easy to manufacture compared to a milled exemption of the feed line 4.

Claims (10)

1. Waveguide coupling (1), in particular for a radar fill level measuring device, having a waveguide (2), a carrier plate (3) and at least one feed line (4), wherein the feed line (4) is guided on and/or in the carrier plate (3) into the inner region (6) of the waveguide (2) and the feed line (4) ends with one end (7) in the inner region (6) of the waveguide (2), wherein the carrier plate (3) also extends continuously into the inner region (6) of the waveguide (2) and thus beyond the end (7) of the feed line (4), wherein an electrically conductive coupling element (9) is arranged on and/or in the carrier plate (3) in the vicinity of the end (7) of the feed line (4), so that the coupling element (9) is coupled to the feed line (4) and the coupling element (9) serves to couple electromagnetic waves led in the waveguide (6) via the feed line (4) into the waveguide (6), wherein the coupling element (9) has a longitudinal bar (9a) and a cross bar (9b), wherein the longitudinal bar (9a) and the cross bar (9b) are arranged in a cross shape, wherein the feed line (4) is aligned substantially straight towards the center of the inner cross section area of the waveguide (2), and wherein the longitudinal bar (9a) of the coupling element (9) is arranged in extension of the feed line (4),
   wherein the waveguide (2) is placed on the carrier plate (3) on a first side (5) of the carrier plate (3), wherein the coupling element (9) is capacitively coupled to the feed line (4), wherein the carrier plate (3) has on its first side (5), on which the waveguide (2) is placed, or, in an intermediate layer, the feed line (4), the coupling element (9) and the screen face (11), wherein the carrier plate (3) has, on its second side (12) opposite the first side (5) or in an intermediate layer, a large-area further electrically conductive screen face (13) outside the region, which is opposite the inner cross section area of the waveguide (2), wherein the screen face (11) and/or the further screen face (13) extends into the inner cross section area of the waveguide (2) with an influencing extension (14), and wherein the influencing extension (14) is aligned towards the center of the inner cross section area of the waveguide (2) and is arranged in line with the feed line (4).
2. Waveguide coupling (1) according to claim 1, characterized in that the coupling element (9) is arranged substantially in the center of the inner cross section area of the waveguide (2) on and/or in the carrier plate (3).
3. Waveguide coupling (1) according to claim 1 or 2, characterized in that the characteristic dimensions of the coupling element (9), taking into account the effective relative permittivity of the waveguide coupling, are in the range of one quarter of the wavelength of the electromagnetic waves to be emitted, wherein the effective relative permittivity results from the relative permittivities of the carrier plate (3) and of the medium surrounding the carrier plate (3).
4. Waveguide coupling (1) according to any one of the claims 1 to 3, characterized in that the electrically conductive screen face (11) contacts the waveguide (2) at its end face (10) and the screen face (11) surrounds the waveguide (2) in particular over a large area.
5. Waveguide coupling (1) according to one of claims 1 to 4, characterized in that the feed line (4), the coupling element (9) and the screen face (11) and/or the further screen face (13) is/are implemented as metallization of the carrier plate (3).
6. Waveguide coupling (1) according to any one of claims 1 to 5, characterized in that an electrically conductive cap (15a, 15b) is placed on the second side (12) of the carrier plate (3) in geometrical continuation of the waveguide (2) as a closure of the waveguide (2), the electrically conductive cap (15) contacts with its end face (16), in particular, the screen face (11) arranged on the second side (12) of the carrier plate (3) or the further screen face (13), or that the carrier plate has, on its second side (12) opposite the first side (5) or in an intermediate layer in continuation of the waveguide (2), an electrically conductive layer as a termination of the waveguide.
7. Waveguide coupling (1) according to claim 6, characterized in that an electrically conductive connection is produced between the waveguide (2) and the cap (15a, 15b) or between the waveguide (2) and the conductive layer serving as termination of the waveguide (2), in particular by means of at least one through-plating (16) through the carrier plate (3).
8. Waveguide coupling (1) according to any one of claims 1 to 7, characterized in that for the coupling in of a linearly polarized electromagnetic wave with a center frequency of 80 GHz, the waveguide (2) is designed round and with an inner diameter of approximately 2.6 mm, the longitudinal bar (9a) and the transverse bar (9b) of the coupling element (9) each having a length of approximately 0.84 mm and the carrier plate (3) preferably having an edge length of approximately 6 mm.
9. Waveguide coupling (1) according to any one of claims 1 to 7, characterized in that, in order to couple in a linearly polarized electromagnetic wave with a center frequency of 6 GHz, the waveguide (2) is designed round and with an inner diameter of approximately 21.6 mm, the longitudinal bar (9a) of the coupling element (9) having a length of approximately 5.5 mm and the transverse bar (9b) of the coupling element (9) having a length of approximately 7.4 mm and the carrier plate (3) preferably having an edge length of approximately 32 mm, wherein there is a casting of the waveguide coupling (1) with a casting compound having a relative permittivity of approximately 4.
10. Waveguide coupling (1) according to any one of claims 1 to 9, characterized in that the waveguide (2) and/or the cap (15a, 15b) are filled with a casting compound, and in that the carrier plate has at least one recess in the region of the inner cross section area of the waveguide, in particular for better filling with a casting compound, in particular in the form of at least one bore.

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