EP1699107B1 - 3 dB coupler - Google Patents

Description

The invention relates to a 3dB coupler having at least a first and a second electrical conductor which are spaced apart and which are capacitively and inductively coupled together, wherein the first conductor represents the primary side and the second conductor represents the secondary side of a transformer.

In the field of laser excitation or plasma processes, high-frequency amplifiers with the usual industrial frequencies of 13.56 MHz and 27.12 MHz and output powers of 1 kW to 50 kW are known. The use of high frequency amplifiers of higher power and higher frequencies is desired, but can be difficult to realize for various reasons.

One reason is the nonlinearity and dynamic, often unpredictable, change in the load impedances of laser excitation or plasma processes. These dynamic changes in impedance create reflections that cause losses in the amplifier. High reactive energies, which are stored in the dummy elements of the amplifiers, in the leads and in dummy elements of matching networks, can thereby discharge and build up to high voltages or currents and excite the amplifier to oscillate or destroy components.

Such load impedance changes occur, for example, when igniting the laser excitation or plasma processes or when arcing in the plasma process. In addition, it must be taken into account that high-frequency-driven laser excitations and, to an increasing extent, high-frequency excitations Plasma processes are operated pulsed, so the high-frequency amplifier with pulse frequencies of, for example, 100Hz to 300kHz on and off or be switched between two power ranges. With each switching process then arise short-term reflections, which are for the most part in the amplifiers in loss energy, ie heat development, implemented.

Output stages of such high-frequency amplifiers are already realized with transistors for small powers (1-6kW), tubes are usually used for larger powers. Tubes are more robust to reflections and can dissipate the energy dissipation better than transistors, but are more expensive and subject to operational wear. Besides, they are relatively big. Together with control circuit and cooling, tube high-frequency amplifiers are offered in control cabinets in sizes of approx. 0.8m x 1m x 2m.

Therefore, it is increasingly trying to equip high-frequency amplifier of greater power with transistor output stages. The use of transistorized amplifiers has greatly increased the use of switched amplifiers operating in resonant mode. The transistors are switched so that only a very low energy loss is produced. This makes it possible to build amplifiers with very small dimensions and comparatively high power. 13.56MHz 3kW amplifiers with sizes of approx. 0.3m x 0.2m x 0.2m can be realized. Such amplifiers can be better integrated into plasma systems or laser excitation arrangements due to their size.

Great performance with transistorized output stages can be achieved with the interconnection of several synchronously running high-frequency amplifiers. The interconnection is done by so-called combiners. There are different types of such combiners.

A combiner commonly used in microwave technology or radio transmitter technology is the so-called 90 ° hybrid, which is also referred to as a 3dB coupler. The 3dB coupler is a four-port.

When using the 3dB coupler as a combiner, a high-frequency power amplifier with the same internal resistance, the same output frequency and a 90 ° phase-shifted output signal is connected to two ports. At a third gate, a load with a load resistor is connected. At the fourth gate a load balancing resistor is connected. Load resistance, load balancing resistance and internal resistance of the amplifiers are the same. The exclusively passive components of the 90 ° hybrid (lines, capacitors, transformers or inductors) are designed so that the power of the two amplifiers is combined at the load, that no power is delivered at the load balancing resistor and that the two amplifiers are decoupled and mutually exclusive can not influence. The 90 ° hybrid itself is ideally lossless, that is, the power of the two high-frequency amplifiers is fully supplied to the load applied to the third port.

The 3dB couplers known from microwave technology are constructed as Leltungskoppler with line lengths of λ / 4. This line coupling technique is very unfavorable for 13 and 27 MHz, because the size would be a few meters with λ / 4 lengths, which would mean a step backwards in view of the desired reduction of the generators.

Alternatively, a 3dB coupler may be constructed of discrete components, with the 3dB coupler typically having at least one Capacitive coupling capacitance and a transformer with a coupling inductance for inductive magnetic coupling has.

$${\mathrm{C}}_{\mathrm{K}}=\mathrm{1}/\left(\mathrm{2}{\mathrm{\pi fZ}}_{\mathrm{0}}\right)\mathrm{.}$$

wobei gilt:

• L_k = Koppelinduktivität
• C_k = Koppelkapazität
• Z₀ = Wellenwiderstand
• f = Frequenz

In order for the desired behavior of the 3dB coupler to be established, the coupling inductance and the coupling capacity should fulfill the following conditions: $${\mathrm{L}}_{\mathrm{K}}={\mathrm{Z}}_{\mathrm{0}}/\left(\mathrm{2}\mathrm{\pi f}\right)$$

$${\mathrm{C}}_{\mathrm{K}}=\mathrm{1}/\left(\mathrm{2}{\mathrm{\pi fZ}}_{\mathrm{0}}\right)\mathrm{,}$$

where:

• L _k = coupling inductance
• C _k = coupling capacity
• Z ₀ = characteristic impedance
• f = frequency

At 13 MHz and Z ₀ = 50Ω, a coupling inductance L _k of approximately 600 nH and a coupling capacitance C _k of approximately 200 pF are obtained.

The construction of a 3dB coupler from discrete components always requires a high expenditure of precise components, which under certain circumstances also have to be adjusted. This is always very expensive, especially for larger outputs (more than 1kW).

The coupling capacity by means of two spaced electrical conductors with a defined surface and a defined distance from each other can be realized easily, inexpensively and very precisely reproducible. In most cases, however, the required inductance is not achieved by means of two such conductors. It must therefore be increased appropriately. One possibility is to increase the inductance exclusively with inductance-increasing elements, eg ferrites. To come to the necessary inductance at high powers are Inductor elements with large dimensions and high costs necessary.

From the US 2003/0025573 A1 a delay line has become known for operation at upper 100 MHz.

The EP 0 456 212 A2 discloses a common mode choke for filtering common mode signals. In the known common mode choke a purely inductive coupling is sought.

The US 2004/0207482 A1 further discloses a microwave coupler. The coupling takes place for microwave signals with a frequency of more than 1 GHz.

The US 2003/0218516 A1 shows a directional coupler, in which a part of a power to be determined is coupled out for measurement purposes. A capacitive coupling should be avoided.

From the EP 0 715 392 A1 an inductive battery charging system has become known. The known battery charging system is operated at a frequency of 75 kHz.

The EP 0 964 525 A1 discloses an analog-to-digital converter with a coupler acting as an adder. The coupling in the coupler is made by inductive coupling with two magnetic cores.

From the EP 0 506 091 A1 a power detector for portable telephones has become known. The Lelstungsdetektor is operated at frequencies of 800 MHz to 1 GHz.

From the publication " Designing VHF Lumped Element Couplers with MW Office "by Steve Maas; Applied Wave 1999 ; It has become known to construct couplers with discrete components.

Furthermore, it is from the US 2003/0137363 A1 have become known to provide a two-conductor based coupler for frequencies greater than 2 GHz.

Finally, the reveals WO 01/43283 A1 a 90 ° power controller. The known power divider is formed of discrete components.

In contrast, the object of the present invention is to further form a 3dB coupler in such a way that a good capacitive and inductive coupling of the primary and the secondary side of the transformer can be realized with a small overall size.

This object is achieved with a 3dB coupler of the type mentioned with the features of claim 1. The dependent claims indicate preferred developments. The object is further achieved by the use of such a 3dB coupler for coupling RF power at a frequency in the range 1 MHz - 80 MHz and at powers greater than 1 kW.

In this case, the first and the second conductor each have a number of turns n> 1. By this simple measure, the inductance can be increased in a simple manner. The inductance increases with the number of turns squared, with a doubling of the number of turns, the inductance therefore increases by a factor of four. The size of an inductance-increasing element can therefore be reduced by a factor of 4 when the number of turns is doubled. Thus, the size can be reduced by using more than one turn. At a sufficiently high number of turns can ideally be dispensed with further inductance-increasing measures.

By an increased number of turns but also the length of the inductance generating conductor can be reduced. This advantageously also causes a more symmetrical phase Aufaufstellung. Ideally, the phase offset between the input signal at one input port and a first output signal of a first output port should be + 45 ° and between the input signal and a second output signal of a second output port should be -45 °. However, with only one turn, a phase offset of e.g. + 40 ° at one exit gate compared to the entrance gate and -50 ° at the other exit gate. For shorter conductor lengths deviations from the ideal phase are smaller.

The inventive 3dB coupler can be used to couple RF power at a frequency in the range 1-80 MHz, in particular at about 1 MHz; about 2 MHz; 13.56 MHz; 27.12 MHz or about 60 MHz and be used at powers greater than 1kW. In this area, the use of 3dB couplers was previously unknown.

The dimensions of the 3dB coupler for frequencies below 100 MHz can be significantly reduced. They can be smaller than λ / 4, in particular smaller than λ / 8 and preferably even smaller than λ / 10. With these quantities, the influences of the line theory of high-frequency technology have no meaning. It should be expressly mentioned here again that the 3dB coupler according to this invention is not a line coupler, as known from the prior art for higher frequencies, ie the character of the 3dB coupler is not (exclusively) by the Cable length determined. Rather, the coupling between the electrical conductors corresponds to a capacitive coupling with a fixed predetermined and set capacitance between the conductors at a given fundamental frequency f and predetermined characteristic impedance Z ₀ . The capacity can be adjusted by the area and the distance of the conductors. Furthermore, the coupling of an inductive coupling with a fixed predetermined and set inductance of the transformer at a given fundamental frequency f and predetermined wave resistance Z ₀ corresponds. The inductance is set, for example, depending on the length of the conductors, in particular the conductor sections. In one embodiment of the invention, at least one inductance-increasing element is provided in the coupling region for increasing the inductance of the conductor. The values for the inductance and the capacitance are calculated from the formulas given above as a function of frequency and characteristic impedance.

In this case, the inductance-increasing element may have any shape. Preferably, it surrounds the conductors in the coupling region at least partially. It can e.g. lying parallel to them. This allows a particularly simple and effective coupling can be achieved. Preferably, the Induktivitätserhöhüngselement the conductors in the coupling region is annularly surrounded. In this case, by annular is meant that the conductor sections are surrounded in the coupling region by a largely closed geometery, they may be circular, ellipsoidal, rectangular or otherwise shaped. The advantage of an annular geometry is the reduction of stray fields. In a rectangular construction of the ring shape, the heat that arises in the inductance-increasing element, particularly good to a heat sink, especially a flat cooling plate, be dissipated. In general, the inductance-increasing element may have a heat sink or be in heat exchange connection with such or may itself be embodied as a heat sink.

The rectangular shape of the inductance-increasing element may be composed of several parts, for example, four cuboids or two U-shaped parts or a U-shaped part and a cuboid. In the assembled from several parts designs a simplified production is possible, also can be provided to adjust the inductance adjustable gaps between the parts.

Preferably, the at least one inductance-increasing element is formed of ferritic material. In particular, one or more conductors may be provided at least in sections, advantageously in the coupling region encompassing ferrite rings.

Depending on the power to be coupled, ferrite rings with relatively high or low magnetic losses can be used. While ferrite rings with still relatively high magnetic losses can be used at comparatively low powers, ferrite material with extremely low magnetic losses must be used for high powers. With the same size ferrite body with low magnetic losses usually also lower A _L values, which is why to achieve the same inductance correspondingly more ferrite must be used.

Thus, while ferrite rings with a high A _L value of, for example, 200 nH can be used at comparatively low powers, and thus only a few ferrite rings are required to achieve the necessary inductance of, for example, 600 nH, for high powers (eg 5 kW) with correspondingly large currents Ferrite rings with a lower A _L value can be used in the conductors because otherwise correspondingly high ferromagnetic losses occur in the ferrite cores. As is known, the magnetic or even gyromagnetic losses in the ferrite core increase depending on the material at certain frequencies up to a magnetic resonance frequency. If this ferromagnetic resonance frequency is too low and too close to the operating frequency, the losses heat the ferrite.

Therefore, at high powers, preference is given to using ferrite rings with a lower A _L value and, correspondingly, a correspondingly higher number. Thus, with a power of up to 10kW and an operating frequency of 13.56MHz, 90 ° hybrids with a footprint of 5cm X 10cm or smaller can be realized. The height in both cases is less than or equal to 5cm. However, the higher the number of turns, the less inductance-increasing elements are needed. This is desirable for a particularly space-saving and inexpensive construction, since the inductance-increasing elements makes the reproducibility of the inductance more difficult.

In a particularly preferred embodiment, the first and the second conductor each have a number of turns n = 2. This number of turns represents a good compromise, in particular when using an inductance-increasing element at the same time. The design effort for the 3dB coupler is limited. The inductance and the capacitance can be reproduced well and ohmic losses can be kept low. Stray sufferers have no great influence. When ferrites are used as inductance enhancement elements, their number or extent can be reduced to 25% of what is needed with a turn number of n = 1. This can save expensive ferrites. In addition, reproducibility is better when fewer ferrites are used, as the 10-20% tolerances used to make ferrites are less significant.

To make the inductive transformer of the 3dB coupler, a close inductive coupling is necessary, ie at least sections of the primary and the secondary line must be as close to each other as possible. In particular, conductor sections of the primary and the secondary side may overlap or mesh with each other. Furthermore, the extend Conductor or sections thereof advantageously at least in sections, preferably in the coupling region, parallel to each other.

In order to achieve a reproducible capacity, at least one spacer, in particular an insulator, can be provided, which holds portions of the at least one first and the at least one second conductor at a predetermined distance. It is particularly preferred if the conductors extend at least in sections, preferably in the coupling region, in parallel planes.

According to a preferred embodiment, areal spacers or insulators may be provided between adjacent conductor sections. The insulators are preferably made of an insulating material with an ε _r in the range 2 - 2.6, preferably from about 2.33, and a thickness of about 0.5mm to 3mm provided. The insulators may extend throughout the coupling region.

For high quality and high dielectric strength, polytetrafluoroethylene (PTFE), as known under the trade name "Teflon", may be used as the insulating material. A low loss factor tan δ of the insulating material is advantageous. tan δ should be less than 0.005 to minimize losses in the insulating material. RT / duorit 5870 from ROGERS Corp. has been found to be particularly suitable in the first experiments. exhibited a tan δ of 0.0005 - 0.0012 and an ε _r of 2.3.

A space-saving arrangement, which at the same time allows easy to reproduce capacities, results when the conductors are formed at least in the coupling region as a flat conductor tracks.

In this context, it is particularly advantageous when the at least one spacer is formed flat and a conductor portion of the first conductor on the one and a conductor portion of the second conductor mounted on the opposite side of the spacer, in particular the spacer with a conductor portion of the first and second Printed conductor, coated or laminated. The spacer serves as a carrier material for the conductors or conductor tracks and may be formed as a printed circuit board.

Several of these arrangements may be stacked on top of each other. As already mentioned above, it is thus possible to ensure a defined, constant distance between the conductors or interconnects. In particular, portions of the first and second conductors can thereby be arranged in the coupling region in a conductor stack, wherein adjacent conductor segments are spaced apart, in particular, by an insulator.

In an advantageous embodiment, a plurality of spacers, in particular printed circuit boards, provided on both sides with conductor sections are stacked, wherein the conductor sections of opposing rare adjacent spacers are essentially congruent. The conductor tracks with a dielectric as a carrier layer can be easily realized by means of a board design and circuit board production.

In a preferred embodiment of the invention, a first circuit board is provided which has a recess which is surrounded by a respective conductor track on the top and bottom of the circuit board. At least two essentially T-shaped printed circuit boards are provided, each of which has a conductor track on the upper and lower sides, the printed conductors being connected to two separate windings. The recess can receive a ring-shaped ferrite, for example, where the tees can be inserted into the breakthrough of the ferrite.

The operating frequency is not limited to the industry frequency of 13.56 MHz, but may be in the range 1 to 100MHz. the big advantage This arrangement is, however, that the principle is applicable to even much lower frequencies. Well the track sections do not work as a line coupler, but as coupling capacitances and coupling inductances. If the printed conductors or printed conductor sections were to work as line couplers, at least one line length of λ \ 4 would have to be used. However, such line lengths are longer, the lower the frequency. This would mean ever larger designs for line couplers. According to the concept of the invention, however, the design does not have to be lengthened with the reduction of the frequency, only the kapetity and inductance values, for example by influencing the number of turns, have to be adapted.

Fig. 1a

die Oberseite einer ersten Leiterplatte, die Teil eines 3dB-Kopplers ist;

Fig. 1b

die Unterseite der Leiterplatte der Fig. 1a;

Fig. 2a

die Oberseite einer zweiten Leiterplatte, die Ober der ersten Leiterplatte anzuordnen ist;

Fig. 2b

die Unterseite der zweiten Leiterplatte;

Fig. 3a

die Oberseite einer dritten Leiterplatte, die Ober der zweiten Leiterplatte anzuordnen ist;

Fig. 3b

die Unterseite der dritten Leiterplatte

Fig. 4

eine Frontalansicht einer ersten Ausführungsform eines 3dB-Kopplers;

Fig. 5

eine weitere Ausführungsform eines 3dB-Kopplers.

Preferred embodiments of the invention are shown schematically in the drawing and are explained below with reference to the figures of the drawing. It shows:

Fig. 1a

the top of a first circuit board that is part of a 3dB coupler;

Fig. 1b

the underside of the PCB Fig. 1a ;

Fig. 2a

the top of a second circuit board to be placed above the first circuit board;

Fig. 2b

the bottom of the second circuit board;

Fig. 3a

the top of a third circuit board to be placed above the second circuit board;

Fig. 3b

the underside of the third circuit board

Fig. 4

a frontal view of a first embodiment of a 3dB coupler;

Fig. 5

another embodiment of a 3dB coupler.

The FIGS. 1a, 1b show the top 1a and bottom 1b of a first circuit board 1. Die FIGS. 2a, 2b show the top 2a and bottom 2b of a second circuit board 2. Die FIGS. 3a, 3b show the top 3a and bottom 3b of a third circuit board 3. Through the circuit boards 1, 2, 3, an inventive 3 dB coupler 100 can be formed, as shown in the Fig. 4 is shown.

The terminals 11, 16, 21, 26 of the printed circuit board 1 are the inputs and outputs (gates) of the 3dB coupler. The terminals 12 and 12a are congruent when the printed circuit boards 1 and 2 are placed on each other, and are electrically connected to each other in composite 3dB coupler. Same glit for the terminals 13, 13a; 14, 14a; 15, 15a; 22, 22a; 23, 23a; 24, 24a and 25, 25a. The 3dB coupler has a transformer, wherein the inductance of the primary side (vertically shaded areas) has two turns that run through the inductance-increasing element 4 designed as ferrite. The course of the two turns is indicated by reference numerals and arrows in the Figures 1a - 3b explained. The first inductance runs from 11 to 12, further to 12a, further to 13, further to 13a, further to 14, further to 14a, further to 15, further to 15a and finally to the terminal 16.

The inductance of the secondary side (diagonally hatched areas) also continues in two turns through the inductance-increasing element 4, namely from terminal 21 to 22, further to 22a, continuing to 23 after 23a continue to 24 continue to 24a continue to 25 continue to 25a and finally to connection 26.

The trained 3dB coupler 100 ( Fig. 4 ) The capacitance is so substantially only between the conductive surfaces of the top 1a, 2a, 3a and bottom 1b, 2b, 3b each of a printed circuit board 1, 2nd , 3 trained. The upper side 1a of the printed circuit board 1 and the lower side 2b of the printed circuit board 2 have printed conductors 27a, 28b of the same inductance, and the upper side 2a of the printed circuit board 2 and the lower side 3b of the printed circuit board 3 have printed conductors 28a, 29b of the other inductor. Since a voltage is formed across the inductance, the circuit boards 1, 2, 3 must be spaced apart from each other, in particular by spacers, for example by Isoller plates or films, be isolated from each other separated. The whole arrangement of three circuit boards 1, 2, 3 can also be integrated into a multi-layered (in this case six-layered) multilayer board, which allows a more precise and cost-optimized production. The inductance-increasing elements 4 must then be inserted in the form of two half-shells.

With the dimensions of 10 cm in length and 5 cm in width (printed circuit board 1) and 4cm in height (determined by the designed as a ferrite ring inductance increasing element 4) so a 3dB coupler for the merger of twice 2.5kW RF power at 13.56MHz to 5kW can be achieved.

If the capacitance needs to be adjusted or increased, a discrete capacitor can be connected in parallel or the area can be increased on both sides, eg on the PCB 1

In the Fig. 4 the arrangement of the printed circuit boards 1, 2, 3 to the 3dB coupler 100 is shown. You can see the terminals 16, 26. Above the circuit board 1, the circuit boards 2, 3 are arranged, wherein the T-shaped circuit boards 2, 3 are inserted into the free space 4a of the formed as a ferrite Induktivitätserhöhungselements 4. This means that the coupling region 101 is surrounded by the inductance-increasing element 4. The printed circuit boards 1, 2, 3 have printed conductors 27a, 27b, 28a, 28b, 29a, 29b on their upper side 1a, 2a, 3a and lower side 1b, 2b, 3b. The conductor tracks 27a, 27b, 28a, 28b, 29a, 29b on different sides of a printed circuit board 1, 2, 3 are spaced apart by the carrier material of the printed circuit board 1, 2, 3. The carrier material is an insulator and serves as a spacer. The opposing trace portions of adjacent circuit boards 1,2,3 are spaced by spacers. The inductance-increasing element 4 is placed on a heat sink 103, which in turn sits on a support plate 104. Between the heat sink 103 and the element 4, a heat conduction-improving layer 105 is arranged.

An embodiment without Induktivitätserhöhungselement is in the Fig. 5 shown. The conductors 110, 111 designed as strip conductors are shaped as spirals. The spirals made of conductive material are applied to both sides of a circuit board, laminated example beispielse. It is largely congruent a conductor 110 mounted on the top and a conductor 111 on the underside of the circuit board. The conductors 110, 111 represent the inductances of the primary side and the secondary side of a transformer of a 3dB coupler. They each have a winding number n = 4.

If the terminals 112-115 are desired as vias, they must be made offset, as in the Fig. 5 implied is. However, it is also conceivable to form the connections 112-115 respectively on the top and bottom side and to arrange the 3dB coupler, for example, between two amplifiers.

Again, an inductance-enhancing element, e.g. a ferrite e.g. conceivable as a disk, pin or pot core. Possibly. in the middle of the spiral, a recess, e.g. a bore for a ferrite can be provided.

Claims (12)

1. Coupler (100) in the form of a 3dB coupler which couples two input signals, which are phase-shifted by 90°, to an output signal, comprising at least one first and one second electrical conductor (110, 111) which are spaced apart from each other and are capacitively and inductively coupled to each other, wherein the first conductor (110) represents the primary side and the second conductor (111) represents the secondary side of a transformer, and wherein the first and the second conductor (110, 111) each have a winding number n > 1 and the coupler (100) is designed as a four-port device, wherein the coupler is designed to have a predetermined coupling capacitance C_K and coupling inductance L_K, wherein C_K=1/(2πf Z₀), L_K= Z₀/(2πf), Z₀ is a predetermined wave impedance and f is a predetermined basic frequency, wherein the coupler is designed to couple RF power at a frequency in the range between 1 and 80 MHz and at powers > 1 kW.
2. 3dB coupler according to claim 1, characterized in that the first and second conductors each have a winding number of n=2.
3. 3dB coupler according to any one of the preceding claims, characterized in that at least one inductance increasing element (4) is provided in a coupling region (101) to increase the inductance of the conductors.
4. 3dB coupler according to claim 3, characterized in that the at least one inductance increasing element (4) surrounds the conductors (110, 111) in the coupling region (101) at least partially.
5. 3dB coupler according to claim 3 or 4, characterized in that the at least one inductance increasing element (4) has an annular shape.
6. 3dB coupler according to any one of the claims 3 to 5, characterized in that the at least one inductance increasing element (4) comprises at least one adjustable gap.
7. 3dB coupler according to any one of the claims 3 to 6, characterized in that the at least one inductance increasing element (4) is formed from ferritic material.
8. 3dB coupler according to any one of the preceding claims, characterized in that the length of the at least one first and/or second conductor (110, 111) is < λ/4, preferably < λ/8, with particular preference <λ/10.
9. 3dB coupler according to any one of the preceding claims, characterized in that at least one spacer is provided which keeps sections of the at least one first and the at least one second conductor at a predetermined separation, wherein the at least one spacer has a laminar configuration and one conductor section of the first conductor is disposed on one side of the spacer and one conductor section of the second conductor is disposed on the opposite side of the spacer, in particular, that a conductor section of the first and second conductor is printed, coated or laminated on the spacer.
10. 3dB coupler according to any one of the claims 3 to 9, characterized in that the inductance increasing element (4) comprises a cooling body (103) or is in contact therewith, thereby exchanging heat, or is itself designed as cooling body (103).
11. 3dB coupler according to any one of the preceding claims, characterized in that a first circuit board (1) is provided comprising a recess which is surrounded by one strip conductor (27a, 27b) each on the upper and lower sides (1a, 1b) of the circuit board (1), at least two substantially T-shaped circuit boards (2, 3) are provided which comprise one strip conductor (28a, 28b, 29a, 29b) each on the upper and lower sides (2a, 3a, 2b, 3b), wherein the strip conductors (27a, 27b, 28a, 28b, 29a, 29b) are connected to form two separate windings.
12. The use of a 3dB coupler according to any one of the preceding claims for coupling RF power at a frequency in the range between 1 and 80MHz, in particular at 1MHz; 2MHz; 13.56MHz; 27.12MHz or 60MHz and at powers of more than 1kW.

Images