The invention relates to a circularly polarized antenna coupling structure for emitting and receiving of mm wavelength radar signals. It has a multilayer unit consisting of one or more layers of non-conductive printed circuit board, at least one microwave cover layer arranged on one surface of the carrier layer of the printed circuit board, and a current-conducting excitation line arranged on the cover layer. The multilayer unit is clamped between an upper clamping element and a lower clamping element. The material of the upper clamping element and/or the lower clamping element is at least partially electrically conductive. The upper clamping element and the lower clamping element are attached to each other in such a way as to ensure current conduction. In the upper clamping element, a resonator cavity is provided for its excitation, and in the lower clamping element a microwave channel corresponding to the wavelength is formed. Furthermore, it contains a connection area and an antenna preferably made of conductive material or coated with conductive material joined to the connection area. In addition, the excitation line — in order to pass the radar signals — is placed on the cover layer in the connection area. A recess is formed in the printed circuit board opposite the microwave channel.

The mm-wave level measurement in the field of waste water discharge measurement has developed greatly in recent years due to the universal acceptance of the polluter pays principle. The discharge of waste water has a significant impact on the environment. For this reason, the measurement of waste water emissions has been introduced in many countries at major emitters under official supervision. The polluter pays the waste water treatment fee based on the amount of waste water it emits, i.e., the polluter pays principle applies. The amount of emission can be measured with a level measuring radar in an open-channel flow measurement arrangement. An important breakthrough occurred in technical life, because cheap and extremely accurate level-measuring radar chips in the 77-81 GHz band appeared.

With the help of these radar chips, the tank level measuring radar can be made in the case of a suitable antenna adapter unit. Until now, 77-81 GHZ band radars have typically been implemented with the help of expensive one or more layers of ceramic or sapphire substrate thin-layer integrated circuits. Fitting this to a circularly polarized supply line with a circular cross-section is an easy task, due to the high dimensional accuracy of the thin-film integrated circuit.

Patent application No. US9212942 describes an antenna coupling that is used to couple an electromagnetic signal from a high-frequency thin film module to an antenna. The antenna coupling includes: a planar radiating element arranged on a circuit board and configured to emit the signal; a housing comprising a rear wall and an antenna extending through the rear wall, wherein the antenna is designed to transmit the emitted signal from a volume defined by the initial range of the antenna (overmode design) to a volume defined by the main range of the antenna (single mode) by modus transformation along volume; and a dielectric sealing element placed in the antenna. The planar radiating element may be one of the following: it is arranged (a) in the starting region or (b) immediately before the starting region. The inner diameter of the starting region in a transition region is the same as the inner diameter of the main region and increases towards the planar radiating element. The circuit board is attached to the housing to seal the housing. The circuit board, the housing, the antenna and the dielectric sealing element form an internal cavity within the housing, which is gas-tightly sealed from the environment by the circuit board and the dielectric sealing element.

The antenna coupler solution described in this document uses a coupler mounted on a printed circuit board, which is primarily suitable for attaching a thin film carrier. In this solution, the antenna is formed on a thin layer chip substrate and it is connected to the power line with a broadband overmode transition, unlike the embodiment described in our solution. A serious disadvantage of the solution is that it only works properly on a thin layer substrate, as this is the only way to ensure the tuning of the resonator cavity. If the coupler was designed on the printed circuit board, it would be out of tune due to thermal expansion and moisture absorption.

Patent application No. US7498896 B2 discloses a high-frequency electric antenna device for coupling it to a current conductor formed from a narrow strip. The equipment includes: an antenna with a generally rectangular wall; a printed circuit board with a current conducting sheet at ground potential on one side and a current conductor formed from a narrow strip ending in a dot on the other side. The dot resonates with the antenna, which transmits predetermined high-bandwidth radio frequency signals in the equipment. The end of the antenna is connected perpendicularly to the substrate surrounding it, and essentially the dot is in the center of the device.

It also has an opening next to the printed circuit board through which the current conductor extends through the wall of the antenna. It contains several parallel conductors attached to the wall of the antenna. Thus, the antenna is electrically connected to the current-conducting sheet on ground potential. The current-conducting sheet on ground potential essentially covers the entire area of the printed circuit board. The antenna coupling solution outlined in US7498896 B2 describes a carrier backplane integrated on a printed circuit board, which is a composite single-carrier solution difficult to manufacture. The tuning cavity is also integrated into the printed circuit board, but the printed circuit board sealing the end of the tuning cavity is not stretched. The solution is very sensitive to dimensional accuracy. It is not suitable for mm-wave circuit technology, because it is sensitive to warping of the substrate, which is unavoidable given its absorbent properties.

The solutions according to US 10616996 B2 and European patent No. EP 3492881 B1 describe a printed circuit board for a radar level measuring device. The microwave signal is coupled to an antenna via a microwave conductor, an excitation line. The connection area on the top layer of the printed circuit board is used to receive the microwave guide/excitation line. The shape of the resonator shell is reversely created by forming an annular circumferential recess on the backside of the printed circuit board substrate, the wall of which has an electromagnetically reflective coating. The ring-shaped peripheral recess on the back, together with the area surrounded by the recess, forms a resonator for the introduced microwave signals.

This construction is a difficult-to-produce composite single-substrate solution, on which the tuning cavity is also integrated on the printed circuit board, but the printed circuit board is not stretched and rigid. The solution is very sensitive to dimensional accuracy. The printed circuit board absorbs moisture, which causes the device to go out of tune. Replacing the layer of the printed circuit board under the excitation line with ceramics would be an expensive and complicated solution. In addition to the fact that stiffening with synthetic resin requires complicated processing, it is expected that the synthetic resin will also absorb moisture, which can deform the dimensional accuracy and also the printed circuit board. The antenna coupling solution described in patent application US2019/0063983 uses an antenna chip coupling solution mounted on a printed circuit board, which can only be realized with an expensive ceramic or sapphire substrate. Gluing and soldering a support is expensive. This solution applies to the use of a radar level measuring device.

Patent application US 7752911 B2 relates to an antenna coupling solution. In this, a level-measuring radar suitable for determining the filling level of tanks is described. The radar includes an antenna for radiating and/or receiving electromagnetic waves, and a signal transmission device for conducting the electromagnetic waves to the antenna. The signal transmission device includes an antenna/excitation line for transmitting the electromagnetic waves between the antenna and a wave guide. The signal transmission device includes an antenna junction for detaching the electromagnetic waves into the antenna. The antenna connection includes: a printed circuit board, wherein the printed circuit board includes a first layer, a second layer, and the power line on the underside or within the second layer for transmitting electromagnetic waves, a detaching unit containing a coupling element and a resonant field for transmitting the electromagnetic waves to the antenna. The resonance space is integrated into the first layer as a recess. The first and second layers contain insulating material. A metal layer is formed on the lower side of the first layer in the form of a third layer, this metal layer is the ground potential of the power supply and its wall acts as an antenna in the resonance space. The metal layer is arranged between the first layer and the second layer. The second layer is arranged below the first layer to cover the resonance space.

The solution discussed in this document differs from the solution according to the present invention in several features. The metallic front antenna coupler wave guide and rear antenna tuning cavity are connected to both sides of the full-thickness printed circuit board. In such a design, the tolerance and temperature dependence of the fullthickness carrier size detunes the tuning cavity. Furthermore, if the carrier absorbs moisture, it detunes the tuning cavity even more.

The solution according to the present invention, on the other hand, forms the excitation line on the thinned membrane of the carrier layer. This high-frequency membrane is laminated together with the FR4 substrate. The lower and upper metal clamping element (and the detuning cavity in it) rests only on the thin high-frequency membrane. The thin membrane containing the high-frequency excitation line can absorb much less moisture because of its small thickness, and results in a smaller size deviation and change. Due to technological reasons, the laminated production of the excitation line carrier membrane and FR4 carrier is not necessarily of uniform quality. This quality problem occurs both in the solution of US 7752911 and the present patent. However, in the solution according to US 7752911 , the full-thickness gripping of the carrier system with the lower and upper metallic clamps results in detuning of the tuning cavity due to metallization and manufacturing irregularities.

In the present invention, this problem is solved by making the lower and upper metal clamping elements (and the tuning cavity inside) rest only on the thin high-frequency membrane, since the clamping elements can be manufactured much more precisely and reproducibly and thus detune the cavity less.

Overall, compared to the solution described in US7752911 , the solution according to the present invention is unique because the lower and upper clamping elements rest on the membrane formed on the carrier. This results in the printed circuit board being deformed by the clamping effect of the clamping elements. Although this deformation is very small (it can be as much as a micron), but on the one hand the board is compressed, and on the other hand it bends very slightly, because the surface of one of the clamping elements in contact with the circuit board exceeds the other surface of the other clamping element in contact with the circuit board. Because of this deformation, the membrane is stretched like a drum on one of the tensioning elements. The tuning cavity is formed in the tensioning element, which is much less detuned by the excitation line implemented on a membrane-like support. The US 7752911 solution is not membrane-like in design and its design is not suitable for stretching the membrane because it does not contain any elements that would stretch the membrane. That is, the antenna coupling solution disclosed in the US patent describes a carrier backplate integrated on a printed circuit board, which is a composite single-carrier solution that is difficult to manufacture. The tuning cavity is also integrated on the printed circuit board, but not stretched. The solution is very sensitive to dimensional accuracy. It is expensive to produce.

The international patent application WO2021/262044A1 describes a waveguide coupling adapter for mm wavelength signals. The adapter contains a multi-layer unit with a printed wiring board, conductive excitation line and connection area. In this solution a microwave channel is formed opposite to which an opening is formed on the board with printed wiring. The multilayer unit is clamped between two metallic clamping elements, one of which has a resonator cavity, and the other has a microwave channel. Above the excitation line, opposite to it, a groove is formed in one of the clamping elements, which is wider than the excitation line. The clamping elements are clamped together in a current-conducting manner.

The lower metallic clamping element and the upper clamping element formed from printed circuit board according to the solution of document WO 2021/262044A1 do not rest directly on a membrane of reduced thickness. Therefore, gripping the entire carrier system with the lower metallic clamping element and with the back plate formed in the upper printed circuit plate in its full thickness results in uncontrollable detuning of the tuning cavity. Another reason for this is the absorption of moisture by the plastic carrier and the unevenness of the lateral metallization of the rear clamping element formed from the circuit board, as well as the positioning error resulting from the lack of mounting holes and fixings arranging the clamping elements. There is only one opening for passing the excitation line. This does not in any way ensure stepped or continuous transition impedance transformer matching of the excitation line.

European patent document EP 1744 395 A1 describes a microwave power divider/combiner for microwave wavelength signals on a microwave substrate. The device contains a multi-layer unit with a printed circuit board, a conductive excitation line, a connection area and a metallic stiffening backplate. The multilayer unit is clamped between two metal clamps. A resonator cavity is formed in one of the clamping elements, and a microwave channel shorter than the wavelength is formed in the other. Above the excitation line, opposite to it, in one of the clamping elements, a groove is formed, which is wider than the excitation line. The clamping elements are connected to each other in a current-conducting manner.

The lower and upper metallic clamping elements of the solution according to document EP 1744 395 A1 are connected from above to the FR4 printed circuit substrate and from below to the metallic support back plate laminated to the substrate. Therefore, gripping the entire carrier system with the lower and upper metallic clamping elements in full thickness results in the fact that the tuning cavity is difficult to control, because the FR4 carrier extends into the metallic back panel. This can be realized by layer milling, which is critical from the point of view of production. This solution results in detuning due to the moisture absorption of the plastic carrier and the inadequate limitability of the carrier in the coupling cavity. Furthermore, the FR4 material extending into the coupling cavity with increased thickness results in a very critical and difficult to control coupling loss from a processing point of view. This disadvantage of the solution of EP 1744395 A1 is also eliminated by the solution according to the present invention.

The advantages of the present solution compared to previously known solutions illustrated in the Figures "Prior art 1 and Prior art 2" are shown and supported by Figure 1A representing a part of the present invention. The reference numbers used in the Figures "Prior art 1 and Prior art 2" correspond to the reference numbers increased by one hundred used in the present invention.

"Prior art 1" represent the solution according to documents WO 2021/262044 A1 and EP 1744395 A1 , while "Prior art 2" represents the solutions of EP 3492881 B1 ; US 10616996 B2 and US 7752911 B2. A significant disadvantage of the latter documents is that the metal layer cannot be applied to the wall of the cavity sufficiently evenly for forming a smooth surface, due to production technology reasons. This detunes the resonator cavity, causing a loss of performance. For the same reason, the cover layer cannot be stretched, because the appropriate amount of tension would deform the printed circuit board and this would distort the geometry of the resonator cavity. In the solution according to the present invention, such a loss of performance does not occur.

Figure 1 A shows the essential recognition and innovation of the present invention in a clear way compared to previous solutions. The present solution is different from the previous state of the art. The essential novelty of the present invention compared to the existing patents is that the thick insulating layer carrier of the resonator cavity which characterized the previously known solutions is eliminated. In this way, the size accuracy can be better controlled and the loss factor is smaller. The latter is an important aspect, since the insulating substrate has significant attenuation in the mm wavelength range. The additional advantage of the thin layer used in the present solution is that the attenuation loss is lower.

The documents described above that are closest to our invention do not provide instructions for the implementation of the solution according to our invention. The solutions included in them refer to clamping of the entire carrier system in its full thickness with lower and upper metallic clamping elements or they use an intermediate support layer. Detuning of the tuning cavity is difficult to control due to metallization unevenness and the absorption of moisture by the thick plastic carrier, as well as due to plastic material processing distortion, and its production is difficult and expensive. The inventors recognized that if the lower clamping element and the upper clamping element (having the tuning cavity in it) are directly connected to the thin high-frequency membrane carrying the excitation line, the resonator and the tuning cavity formed in the clamping elements can be manufactured in a much more precise and a well- reproducible way and with this solution detuning of the cavity does not occur and can be produced cost-effectively owing to the stretched solution.

The disadvantages of the solutions described above and the solutions used in practice are that a significant part of them were developed for high-stability thin-film circuits, and the laminated microwave plastic layered versions are not suitable for the 77-81 GHZ frequency, mm wavelength application, because of their low manufacturing accuracy, and the adaptive cavity is greatly affected by the deviation of the size (the tuning perturbation is large). At the same time, the dimensional accuracy due to the warping of the plastic carrier also detunes the adaptive cavity.

By developing the solution according to the patent, our goal was to create an antenna coupling device operating in the mm-wave range, which enables reproducible mass production in the case of a cheap laminated microwave plastic carrier.

During the innovation process, it has been realized how the expensive thin-film integrated circuit can be replaced with cheap industrial integrated circuit and laminated microwave plastic substrate in case of a special design. In order to be able to reproducibly connect the signal from a laminated plastic microwave carrier having a smaller dimensional accuracy to the circularly polarized antenna having circular crosssection compared to the thin layer carrier circuit - especially in the case of several layers - the laminated plastic carrier must be designed in such a way that its connecting part should be as thin as a membrane, since then the adaptive cavity is only affected to a very small extent by its size deviation (the tuning perturbation is minimal). At the same time, due to the warping of the plastic carrier, the dimensional accuracy is increased by fixing it circularly on both sides, stretching the membrane-thin coupling part in a drum-like manner.

For this solution, we used a laminate that can be made by printed circuit board manufacturers on the market. The production technology of printed circuit board manufacturers is not necessarily the same. The printed circuit board manufacturing company ELTOS (Eltos S.p.A. Strada E, 44 - San Zeno - 52100 Arezzo, Italy) manufactures the composite circuit substrate by applying a perforated NOFLOW PREPREG layer to the perforated pre-manufactured FR4 type board drilled through under the excitation wire, and ISOLA MT77 high-frequency carrier membrane is also applied. This is baked together under pressure at 150 degrees. After that, the layers of the hole are joined with copper and gold. The printed circuit board manufacturers MMAB (MMAB Group Kft. Madarasz Viktor utca 47-49 H-1138 Budapest, Hungary) and TCL (TCL ELEKTRONIKA Hungary 1149 Budapest Angol u. 38.) manufacture the composite circuit board in such a way that the FR4 plate and the high-frequency carrier membrane (ISOLA MT77) are laminated together in one step and baked together at 150 degrees. With precision depth milling (Z-axis milling), the hole is deepened from the FR4 to the high-frequency carrier membrane.

Accordingly, the present invention is a circularly polarized antenna coupling structure for emitting and receiving of mm wavelength radar signals. It has a multilayer unit consisting of one or more layers of non-conductive printed circuit board, at least one microwave cover layer arranged on one surface of the carrier layer of the printed circuit board, and a current-conducting excitation line arranged on the cover layer. The multilayer unit is clamped between an upper clamping element and a lower clamping element. The material of the upper clamping element and/or the lower clamping element is at least partially electrically conductive. The upper clamping element and the lower clamping element are attached to each other in such a way as to ensure current conduction. In the upper clamping element, a resonator cavity is provided for its excitation, and in the lower clamping element a microwave channel corresponding to the wavelength is formed. Furthermore, it contains a connection area and an antenna preferably made of conductive material or coated with conductive material and joined to the connection area. In addition, the excitation line — in order to pass the radar signals — is placed on the cover layer in the connection area. A recess is formed in the printed circuit board opposite the microwave channel. The cover layer has a size that exceeds the cross-section of the recess, preferably between 0.1 and 0.4 mm thick. The cover layer is stretched over the recess forming a membrane, with the multilayer unit being clamped between the upper clamping element and the lower clamping element clamped directly from the lower clamping element. Furthermore, in the clamping element on the side of the excitation line, along the length of the excitation line, a groove with a constant or variable cross-section, which exceeds the crosssection of the excitation line, and has a conical or stepped design is formed.

Some advantageous embodiments of the present invention are described in the depended claims.

The antenna coupling structure according to the invention will be described with reference to the accompanying drawings.

Figure 1 A shows the portion “A” of the embodiment of the antenna coupling structure according to Figure 1 B, partly in section;

Figure 1 B shows the portion “I” of the embodiment of the antenna coupling structure according to Figure 3, partly in section;

Figure 2 is an exploded view of the antenna coupling structure according to Figure 3;

Figure 3 is the side view of a possible embodiment of the antenna coupling structure partly in section, where the lower clamping element itself also is the antenna;

Figure 3a is the perspective view of the portion “III” of Figure 2 showing a possible embodiment of the groove;

Figure 3b is the perspective view of the portion “III” of Figure 2 showing another possible embodiment of the groove;

Figure 4 shows the portion “IV” of the antenna coupling structure according to Figure 6 partly in section;

Figure 5 is an exploded view of the antenna coupling structure of Figure 6; and

Figure 6 shows the side view of another possible embodiment of the antenna coupling structure partly in section, where the lower clamping element and the antenna are separate workpieces. The circularly polarized antenna coupler structure 20 is used to emit and receive mm wavelength radar signals (Figures 3, 6). The antenna coupling structure 20 contains a multilayer unit 22, which consists of a single or multilayer non-conductive printed circuit board 6, at least a microwave cover layer 1 arranged on one surface 15 of the carrier layer of the printed circuit board 6 and a current-conducting excitation line 12 arranged on the cover layer 1 (Figures 1a, 1b, 2, 5 and 6). The recess 19 is formed in the printed circuit board 6, which defines the connection area 16 (Figures 1b, 2, 4 and 5). It also includes an antenna 3 - preferably made of conductive material or coated with conductive material - joined to the connecting area 16 (Figures 1 b - 6). One surface 15 of the printed circuit board 6 on the antenna side 3 is sealed with the cover layer 1 (Figures 1a, 1 b - 6). The multilayer unit 22 can also be placed in reverse between the clamping elements 4, 5, so that the cover layer 1 and the excitation line 12 are placed under the upper clamping element 5. In this case, the groove 11 is formed in the upper clamping element 5 and the resonator cavity 18 is formed deeper in the upper clamping element 5. Furthermore, the elastic sealing 9, for example, the insulating "O" ring, is also placed between the lower clamping element 4 and the printed circuit board 6. For this, obviously, the shoulders of the lower clamping element 4 connecting to the fastening element 8 are chosen to be wider. This embodiment has not been shown for reasons of clarity. The cover layer 1 is larger than the cross-section of the recess 19, preferably between 0.1 and 0.4 mm thick, and is laminated on the printed circuit board 6. The printed circuit board 6 is an FR4 single or multi-layer board. Printed circuit board 6 provided with FR4 cover layer 1 or printed circuit boards with similar properties are commercially available. In order to transmit the radar signals, the excitation line 12 is placed on the cover layer 1. The cover layer 1 is stretched over the recess 19 in a membrane-like manner so that the multilayer unit 22 is clamped between the upper clamping element 5 and the lower clamping element 4. Advantageously, the surface of the resonator cavity 18 and the channel 17 are made of a conductive, but not magnetizable material. In addition, the lower clamping element 4 and the upper clamping element 5 with the help of the flexible seal 9 serve to fix the printed circuit board 6 in the correct position and to prevent overstretching of the membrane, and are attached to the side of the printed circuit board 6 opposite to the cover layer 1. The drum-like stretching of the cover layer 1 is ensured by clamping the upper clamping element 5 and the lower clamping element 4 together (Figures 1 b, 4). This is achieved with the - advantageously conductive - fastening elements 8. Preferably, the fastening elements 8 are screws with an internal keyhole. The size of the cover layer 1 can be at least as large as to extend beyond the clamping elements 4, 5 (Figure 5), but it can also be as large as to cover one surface 15 of the printed circuit board 6 entirely (Figure 2).

In the upper clamping element 5, a resonator cavity 18 with the same cross-section as the cross-section of the connecting end 23 of the antenna 3 is provided, and in the lower clamping element 4 there is a microwave channel 17 with the same cross-section as the cross-section of the antenna 3 (Figures 1 , 3, 4 and 6). In a special case, the antenna 3 itself can be the lower clamping element 4 (Figure 3). In the surface of the lower clamping element 4 facing the excitation line 12, a groove 11 with a cross-section exceeding the cross-section of the excitation line 12 is formed along the length of the excitation line 12 (Figures 2 and 5).

The groove 11 running along the length of the excitation line 12 can be tapered or stepped for impedance matching (Figures 3a and 3b). The impedance of the millimeterwavelength coplanar waveguide can be formed by the continuous conical or stepped design of the groove 11 running along the excitation line 12 in such a way that the higher modes formed due to the excitation line 12 can also be suppressed with it, i.e. , it matches the excitation line 12 to the drive circuit more precisely. The antenna 3 is attached to the channel 17 formed in the lower clamping element 4.

The cross section of the connection area 16, the resonator cavity 18 and the microwave channel 17 is circular or polygonal. Advantageously, the material of the upper clamping element 5 and the lower clamping element 4 is non-magnetizable metal or a suitable material coated with a non-magnetizable material, for example plastic or conductive plastic.

In the case of one possible design shown in Figure 6, the antenna 3 is not formed as part of the lower clamping element 4, but is attached as a separate element to the antenna coupling structure 20.

The antenna coupling structure 20 suitable for tank level measurement according to the present invention can be connected to the radar chips via the excitation line 12 in the already known manner, ensuring bidirectional signal transmission. The measurement can be performed by transmitting the signals emitted from the radar chips to the excitation line 12 and by transmitting the signals received via the excitation line 12 to a central processing unit. Given that the application of the antenna coupling structure 20 is well within the knowledge of a person skilled in the art, a more detailed description of this is unnecessary.

The detailed description of our solution also serves as an example of implementation. It provides appropriate information for persons skilled in the art to implement the solution according to the present invention.

The advantages of our invention compared to other mm-wave circularly polarized antenna coupling structures, which are made with expensive sapphire or ceramic thin layer substrates, are that in the solution according to the present invention, the coupling structure is implemented with a microwave laminated plastic substrate that can be mass-produced simply and cost-effectively. The technical solution tolerates the wide size deviation of the thin membrane, because the thin membrane layer detunes the matching resonator cavity less than the previously used solutions. The present design tolerates the warping properties of the microwave laminated plastic substrate because it stretches the membrane better. The appropriate stretching is ensured by the use of lower and upper clamping elements according to the present invention. In addition, the wall of the resonator cavity does not need to be provided with another conductive layer, because the wall of the upper clamping element provides adequate shielding.