Directional coupler

Abstract

Directional coupler (1) which is at least partially formed in a particularly multilayer printed circuit board (2), having a main line (3) for transmitting power and at least one secondary line (6, 7) which is arranged in a coupling region with a coupling section (4, 5) parallel to and spaced from the main line (3), wherein the main line (3) is arranged in the interior of the printed circuit board (2) in the coupling region, wherein m first additional coupling lines (12 - 15), m ≥ 1, are provided, which have a coupling section (8 - 11) which runs parallel to and spaced from the coupling section (4, 5) of the at least one secondary line (6, 7), wherein the first additional coupling lines (12 - 15) have a terminal (16 - 19) which is arranged on the outside of the printed circuit board (2) for connection to ground or an external circuit, characterized in that a. the at least one secondary line (6, 7) is arranged inside the printed circuit board (2), b. several coupling sections (8 - 11) of the first additional coupling lines (12 - 15) are provided in the longitudinal direction of the coupling section (4, 5) of the at least one secondary line (6, 7) and c. that n second additional coupling lines (24 - 27), n ≥ 1, are provided, which have a coupling section (20 - 23) which runs parallel and at a distance from the main line (3) and which are electrically connected in parallel to the at least one secondary line (6, 7).

Description

The invention relates to a directional coupler which is at least partially formed in an in particular multi-layer printed circuit board.The invention also relates to a method for tuning a directional coupler.High frequency generators are used to generate and supply high frequency power to a load. Possible loads are, for example, plasma processes, such as plasma coating and plasma etching, or laser processes (laser excitation). Since the impedance of the load can change and thus (partial) reflection of the power supplied by the high-frequency generator can occur in the event of a mismatch, the entire power supplied by the high-frequency generator is often not absorbed in the load (the plasma). In order to be able to accurately adjust the high frequency power supplied to the load, it is desirable to determine the power absorbed in the load.It is known to use a directional coupler for measuring / determining the high-frequency power absorbed in a load, wherein the absorbed high-frequency power results from the difference between the power generated by the high-frequency generator and the reflected power. This makes it possible to control the high-frequency generator so that the power absorbed in the load can be set and kept constant with high accuracy.In order to be able to detect both the high-frequency power supplied in the direction of the load and the reflected power, it is known to use directional couplers which have two secondary lines in addition to a main line via which the high-frequency power is transmitted in the direction of the load. In this case, the power supplied in the direction of the load can be measured via one auxiliary line and the reflected power can be measured via the other auxiliary line. Due to the supply of the high-frequency power via the main line, electromagnetic fields are generated, which are coupled to the auxiliary lines, so that a measurement signal can be detected at the auxiliary lines, which is related to the power on the main line.The term directional sharpness (directivity) describes the quality of the measurement. The aim is to detect on one bypass line as few as possible portions of the power supplied in the direction of the load and to detect with the other bypass line as few as possible portions of the reflected power. However, in practice this is not fully achieved. This means that with the one bypass line, with which only the power supplied in the direction of the load is to be detected, a small proportion of the reflected power is always detected. The directional sharpness refers to the ratio of the power detection of the desired signal to the power detection of the undesired signal. The directional sharpness should be as high as possible.Directional couplers are frequently implemented on printed circuit boards. However, such directional couplers are subject to manufacturing variations, the effects of which are evident only after production with the checking of the function. If the coupling structure is located on an inner layer in multilayer printed circuit card directional couplers, the geometry of the coupler structure can no longer be adapted subsequently, for example by laser trimming. The tolerances must thus be accepted, which leads to a lower dynamic range of a measurement.US 2005 / 0017821 A1 discloses a directional coupler having a main line, bypass lines and additional coupling lines, it being possible for the main line to be arranged in a printed circuit board.It is the object of the present invention to further develop a directional coupler in such a way that effects of manufacturing tolerances can be counteracted or these can be compensated.According to the invention, this object is achieved by a directional coupler which is formed at least partially in an in particular multilayer printed circuit board, having a main line for transmitting a power and at least one secondary line which is arranged in a coupling region having a coupling section parallel and at a distance from the main line, wherein the main line and the at least one secondary line are arranged in the interior of the printed circuit board in the coupling region, wherein m first additional coupling lines, m≥1, are provided which have a coupling section which runs parallel and at a distance from the coupling section of the at least one secondary line, wherein the first additional coupling lines have a connection which is arranged on the outer side of the printed circuit board for connection to ground or an external circuit. Furthermore, the directional coupler is designed such that a. the at least one auxiliary line is arranged in the interior of the printed circuit board, b. a plurality of coupling sections of the first auxiliary coupling lines are provided in the longitudinal direction of the coupling section of the at least one auxiliary line, and c. n second auxiliary coupling lines, n≥1, are provided, which have a coupling section which runs parallel to and at a distance from the main line and which are electrically connected in parallel to the at least one auxiliary line.Preferably, the first additional coupling lines are connected to ground. Thus, the coupling can be reduced. In particular, positive thickness tolerances of the printed circuit board material can be compensated in this way, for example. Both the coupling and the decoupling can be influenced by the additional coupling lines. This allows the required adjustment range of subsequent sump circuits to be reduced in order to maximize the isolation of the directional coupler. The disadvantages of the prior art, which lead to lower measurement dynamics, can be avoided. In particular, the measurement dynamics of the entire measurement system can be improved by the measure according to the invention. In the directional coupler, tolerance-induced scattering is improved.In particular, by means of suitable additional coupling lines, the measurement signal can either be attenuated or amplified in order to compensate for the effects of manufacturing tolerances.The coupling section of the first additional coupling lines can be shorter than the coupling section of the at least one auxiliary line. In particular, a plurality of coupling sections of the first additional coupling lines can be provided in the longitudinal direction of the coupling section of the at least one auxiliary line. For example, two first additional coupling lines can be provided, wherein the length of the coupling sections of the first additional coupling lines corresponds to approximately half the length of the coupling section of the at least one auxiliary line.The coupling sections of the first additional coupling lines can have a distance <2 mm, in particular a distance <1 mm, from the coupling section of the at least one secondary line. The small distance from the coupling section of the at least one auxiliary line can ensure that the coupling sections of the additional coupling lines also become effective.The coupling sections of the first additional coupling lines can be arranged on a side of the coupling section of the at least one secondary line facing away from the main line. Thus, they influence the interaction between the main line and the at least one secondary line in a controlled manner.The coupling sections of the first additional coupling line can have a smaller distance from the coupling section of the at least one auxiliary line than the coupling section of the at least one auxiliary line has from the main line. In this way, a particularly good fine tuning of the directional coupler can be effected.N second additional coupling lines, n≥1, can be provided, which have a coupling section which runs parallel to and at a distance from the main line and which are connected electrically in parallel to the at least one auxiliary line. As a result, the coupling can be increased. Too little coupling, e.g. due to negative thickness tolerances of the printed circuit board material, can thereby be compensated.By suitably selecting the number n and m and the interconnection of the additional coupling lines, the coupling can be set so finely that the change in the coupling due to manufacturing tolerances becomes minimal.The coupling sections of the second additional coupling lines can be arranged outside the coupling region. In particular, the coupling sections of the second additional coupling lines can be arranged in front of and / or behind the coupling section of the auxiliary line, as viewed in the longitudinal direction of the coupling section of the at least one auxiliary line.In order to ensure that the signal of interest is coupled out mainly by the at least one auxiliary line, it can be provided that the coupling sections of the second auxiliary coupling lines are shorter than the coupling section of the at least one auxiliary line.The coupling sections of the first additional coupling lines can be arranged in the same layer. The coupling sections of the second additional coupling lines can also be arranged in the same layer. In particular, the coupling sections of the first and second additional coupling lines can be arranged in the same or different layers.Furthermore, it can be provided that the coupling sections of all lines are arranged in the same layer. A directional coupler configured in this way can be produced particularly easily, since all lines or their coupling sections can be produced in one or the same processing step of the printed circuit board.The at least one auxiliary line and the auxiliary coupling lines can be designed as conductor tracks, wherein the coupling sections of the auxiliary coupling lines are narrower than the coupling section of the at least one auxiliary line. By suitably selecting the widths of the coupling portions, the characteristics of the directional coupler can be influenced.The coupling sections of the additional coupling lines can be arranged in a different position than the coupling section of the at least one auxiliary line. This creates further adjustment possibilities.The directional coupler can be constructed symmetrically with respect to a center plane of the main line. In particular, bypass lines and respectively associated additional coupling lines can be provided on both sides of the main line.The scope of the invention also includes a method for tuning a directional coupler according to the invention, wherein one or more first additional coupling lines are connected to ground and one or more second additional coupling lines are electrically connected in parallel to the at least one auxiliary line for tuning, according to claim 16.Further features and advantages of the invention are evident from the following detailed description of exemplary embodiments of the invention, on the basis of the figures of the drawing, which shows details essential to the invention, and from the claims. The features shown there are not necessarily to be understood to scale and are represented in such a way that the features according to the invention can be made clearly visible. The various features can be realized individually or in any combination in variants of the invention.Exemplary embodiments of the invention are illustrated in the schematic drawing and are explained in more detail in the following description.The following are shown: FIG. 1 shows a plan view of a position of a directional coupler; FIG. 2 shows a sectional illustration through a directional coupler.FIG. 1 shows a plan view of a layer of a directional coupler 1. the directional coupler consists of a multilayer printed circuit board material 2, a main line 3 being arranged in the interior of the directional coupler 1. The main line 3 serves for the transmission of power, for example from left to right in the exemplary embodiment shown, from a high-frequency power generator to a load or from right to left when the power of a load is reflected. Coupling sections 4, 5 of secondary lines 6, 7 run parallel to the main line 3. The length of the coupling portions 4, 5 defines a coupling region. In a fully manufactured directional coupler 1, the main line 3 and the secondary lines 6, 7 are covered by further printed circuit board material, so that they are located in the interior of the directional coupler 1. The coupling structure comprising the main line 3 and the secondary lines 6, 7 is thus no longer accessible from the outside. A different material, for example prepreg, can be provided between the main line 3 and the coupling sections 4, 5 of the secondary lines 6, 7 than the remaining printed circuit board material, for example Arlon TC350 or Rogers RO4350B.Coupling sections 8 to 11 of first additional coupling lines 12 to 15 run at a small distance and parallel to the coupling sections 4, 5 of the auxiliary lines 6, 7. The first additional coupling lines 12 to 15 have connections 16 to 19 on the outside of the printed circuit board 2, which connections are provided for connection to ground or an external circuit. By connecting one or more of the connections 16 to 19 to ground, the coupling of the directional coupler 1 can be adjusted or production tolerances corrected. The length of the coupling sections 8 to 11 corresponds to approximately half the length of the coupling sections 4, 5.Furthermore, FIG. 1 shows coupling sections 20 to 23 of second additional coupling lines 24 to 27, which can be electrically connected in parallel with the auxiliary lines 4, 5, which is indicated by the switches shown. In this case, the coupling sections 20 to 23 are arranged at a distance from the main line 3. They are arranged in particular at a greater distance from the main line 3 than the coupling sections 4, 5. In particular, they are arranged in front of and behind the coupling sections 4, 5, as seen in the direction of extension of the coupling sections 4, 5.All coupling sections of the additional coupling lines have a smaller width than the coupling sections 4, 5 of the auxiliary lines 6, 7. All coupling sections are formed narrower than the main line 3.FIG. 2 shows a sectional illustration through the directional coupler 1 along the line II-II of FIG. 1, wherein no additional coupling lines are visible here. The secondary lines 6, 7 are arranged next to the main line 3. Between the main line 3 and the auxiliary lines 6, 7 there is a material 35 which differs from the material 36 of the remaining printed circuit board 2; in particular, the material 35 is prepreg. By suitable selection of the material 35, the coupling of the directional coupler 1 can also be influenced.It can also be seen from FIG. 2 that the entire coupler structure is arranged in the interior of the directional coupler 1 or the printed circuit board 2 and is therefore no longer accessible from the outside after the production of the directional coupler. On the underside, the printed circuit board 2 has a metallic plate, in particular a copper layer. This metallic plate is in particular a ground layer. The metallic plate can conduct away the heat arising as a result of power loss in the direction of an underlying cooling plate.

Claims

Directional coupler (1) which is formed at least partially in an in particular multilayer printed circuit board (2), having a main line (3) for transmitting a power and at least one secondary line (6, 7) which is arranged in a coupling region having a coupling section (4, 5) parallel to and at a distance from the main line (3), wherein the main line (3) is arranged in the interior of the printed circuit board (2) in the coupling region, wherein m first additional coupling lines (12-15), m ≥ 1, are provided which have a coupling section (8-11) which runs parallel to and at a distance from the coupling section (4, 5) of the at least one secondary line (6, 7), wherein the first additional coupling lines (12-15) have a connection (16-19) which is arranged on the outer side of the printed circuit board (2) for connection to ground or an external circuit, characterized in that a. the at least one secondary line (6, The additional coupling elements (8-11) of the first additional coupling lines (12-15) are arranged in the interior of the printed circuit board (2), b. in the longitudinal direction of the coupling section (4, 5) of the at least one auxiliary line (6, 7), and c. that n second additional coupling lines (24-27), n≥1, are provided, which have a coupling section (20-23), which runs parallel to and spaced apart from the main line (3) and which are electrically connected in parallel to the at least one auxiliary line (6, 7).Directional coupler according to Claim 1, characterized in that the coupling section (8-11) of the first additional coupling lines (12-15) is shorter than the coupling section (4, 5) of the at least one secondary line (6, 7).Directional coupler according to one of the preceding claims, characterized in that the coupling sections (8-11) of the first additional coupling lines (12-15) have a distance of <2 mm, in particular <1 mm, from the coupling section (4, 5) of the at least one secondary line.Directional coupler according to one of the preceding claims, characterized in that the coupling sections (8-11) of the first additional coupling lines (12-15) are arranged on a side of the coupling section (4, 5) of the at least one secondary line (6, 7) which side is remote from the main line (3).Directional coupler according to one of the preceding claims, characterized in that the coupling sections (8-11) of the first additional coupling line (12-15) have a smaller distance from the coupling section (4, 5) of the at least one secondary line (6, 7) than the coupling section (4, 5) of the at least one secondary line (6, 7) has from the main line (3)Directional coupler according to one of the preceding claims, characterized in that the coupling sections (20-23) of the second additional coupling lines (24-27) are arranged outside the coupling region.Directional coupler according to one of the preceding claims, characterized in that the coupling sections (20-23) of the second additional coupling lines (24-27) are arranged before and / or behind the coupling section (4, 5) of the secondary line (6, 7) as viewed in the longitudinal direction of the coupling section (4, 5) of the at least one secondary line (6, 7).Directional coupler according to one of the preceding claims, characterized in that the coupling sections (20-23) of the second additional coupling lines (24-27) are shorter than the coupling section (4, 5) of the at least one secondary line (6, 7).Directional coupler according to one of the preceding claims, characterized in that the coupling sections (8-11) of the first additional coupling lines (12-15) are arranged in the same position.Directional coupler according to one of the preceding claims, characterized in that the coupling sections (20-23) of the second additional coupling lines (24-27) are arranged in the same position.Directional coupler according to one of the preceding claims, characterized in that the coupling sections (8-11, 20-23) of the first and second additional coupling lines (12-15, 24-27) are arranged in the same or different layers.Directional coupler according to one of the preceding claims, characterized in that the coupling sections (4, 5, 8-11, 20-23) of all lines (3, 6, 7, 12-15, 24-27) are arranged in the same position.Directional coupler according to one of the preceding claims, characterized in that the at least one secondary line (6, 7) and the additional coupling lines (12-15, 24-27) are designed as conductor tracks, wherein the coupling sections (8-11, 20-23) of the additional coupling lines (12-15, 24-27) are narrower than the coupling section (4, 5) of the at least one secondary line (6, 7).Directional coupler according to one of the preceding claims, characterized in that the coupling sections (8-11, 20-23) of the additional coupling lines (12-15, 24-27) are arranged in a different position than the coupling section (4, 5) of the at least one secondary line (6, 7).Directional coupler according to one of the preceding claims, characterized in that the directional coupler (1) is constructed symmetrically with respect to a centre plane (30) of the main line (3).Method for tuning a directional coupler (1) according to one of the preceding claims, characterized in that, for tuning, m, m ≥ 1, first additional coupling lines (12-15) are connected to ground and n, n ≥ 1, second additional coupling lines (24-27) are electrically connected in parallel with the at least one auxiliary line (6, 7), wherein n and m are selected to be suitable for setting the coupling, so that the change in the coupling on account of manufacturing tolerances becomes minimal.

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