Broadband directional coupler

Abstract

Broadband directional coupler for measuring the power of a forward or reflected high-frequency signal on a coaxial line (1) with a voltage divider consisting of a first resistor (8) and a second resistor (12), wherein a first terminal (6) of the first resistor (8) is connected to an inner conductor (2) of the coaxial line (1), and to a third resistor (18), characterized by that the third resistor (18) is ring-shaped and is arranged concentrically to the inner conductor (2) in a plane oriented orthogonally to the inner conductor and that the first resistor (8) rests outside its first and second terminals (7,9) on a large-area counter-support (37) in a third cavity (36) free of electromagnetic fields in a housing (21) of the broadband directional coupler arranged in a substantially rotationally symmetrical manner around the inner conductor (2).

Description

[0001] The invention relates to a directional coupler for measuring the power of a forward high-frequency signal and / or a reflected high-frequency signal on a coaxial cable over a wide frequency range, preferably from 9 kHz to 1 GHz.

[0002] Directional couplers are primarily used on a high-frequency link between a broadband power amplifier and a complex load, preferably a transmitter antenna, to identify a mismatch between the power amplifier and the complex load by measuring the forward high-frequency signal and the reflected high-frequency signal, and to switch off the power amplifier in a targeted and rapid manner when a guideline value for the mismatch is exceeded.

[0003] Such a directional coupler is known, for example, from DE 10 2010 009 227 A1. The directional coupler has a symmetrical design, in that it splits the coaxial cable at a single point for both the forward and reflected high-frequency signals and performs a measurement of the inner-line voltage and a measurement of the inner-line current at each point. In the case of the forward high-frequency signal, the voltages measured for the inner-line voltage and current are superimposed additively, while in the case of the reflected high-frequency signal, the voltages measured for the inner-line voltage and current are superimposed subtractively. In the case of a perfect match, the subtraction of the voltages measured for the inner-line voltage and current results in an ideal value of zero. In the case of a mismatch, the voltage difference is not zero.With an infinite VSWR (Voltage Standing Wave Ratio), the superimposed voltage determined for the forward high-frequency signal and for the reflected high-frequency signal is equal.

[0004] Such a directional coupler is less suitable for broadband applications because parasitic electromagnetic interference from the coaxial cable into the individual measuring units—shunt resistor for measuring the inner-line current, resistive voltage divider for measuring the inner-line voltage, measuring leads and circuits for adding or subtracting the two measured voltages—superimposes interference voltages on the individual measured voltages. These interference voltages are phase-shifted relative to the measured voltages and are frequency-dependent. Consequently, the forward and reflected high-frequency signals each exhibit frequency-dependent and differing amplitude and phase responses. Therefore, such a directional coupler does not provide directivity over a wide frequency range.

[0005] DE 10 2010 009 227 A1 discloses a broadband directional coupler for measuring the power of a forward and / or a reflected high-frequency signal on a line.

[0006] US Patent 6 066 994 A discloses a directional coupler for RF power measurement with a capacitive voltage divider connected to the center conductor of a length of a transmission line.

[0007] The object of the invention is therefore to create a directional coupler that exhibits a high directional characteristic over the widest possible frequency range.

[0008] The problem is solved by a broadband directional coupler according to the invention with the features of claim 1. Advantageous technical extensions of the invention are listed in the respective dependent claims.

[0009] The measuring arrangement according to the invention for measuring the inner conductor current and the inner conductor voltage, consisting of a first resistor, the first terminal of which is preferably connected to the inner conductor of the coaxial line and the second terminal of which is preferably connected to a measuring unit and the first terminal of a second resistor, and a third resistor, the first terminal of which is preferably connected to an outer conductor of the coaxial line and the second terminal of the second resistor and the second terminal of which is preferably connected to a ground, is optimized according to the invention bythat the third resistor is, on the one hand, ring-shaped and, on the other hand, arranged concentrically to the inner conductor of the coaxial cable in a plane oriented orthogonally to the inner conductor, and that the first resistor rests outside its first and second terminals on a large-area counter-support in a third cavity free of electromagnetic fields in a housing of the broadband directional coupler arranged essentially rotationally symmetrically around the inner conductor.

[0010] Due to the design of the third resistor, which acts as a shunt resistor for measuring the line current and thus the inner conductor current, as a ring-shaped individual resistor, it exhibits a negligibly small inductive impedance compared to a parallel connection of a multitude of individual resistors arranged in a circle according to the aforementioned prior art. This inductive impedance is connected in series with the resistive component of the third resistor. The negligibly small inductive impedance and the concentric arrangement of the third resistor in a plane orthogonal to the inner conductor of the coaxial cable prevent electromagnetic induction of a stray voltage from the inner conductor of the coaxial cable into the ring-shaped third resistor. Furthermore, the ring-shaped design of the third resistor allows for a more extensive and uniform distribution of heat losses along the resistor ring.

[0011] If the third resistor is preferably designed with a low resistance, then, in combination with its negligible inductive impedance, it prevents undesirably strong attenuation and phase distortion of the high-frequency signal in the high-frequency link. In this way, the broadband directional coupler according to the invention can also be advantageously used in a high-frequency link in which high-frequency signals with high power levels are transmitted.

[0012] The third resistor is preferably applied to a conductive layer on the first side of a ceramic disk, which is mounted gaplessly between two machined end faces of two halves of a housing for the broadband directional coupler arranged substantially rotationally symmetrically around the inner conductor of the coaxial cable. Since the third resistor preferably has a smaller axial dimension than its radial dimension, the end face of a housing half facing the third resistor only needs to have a shallow milled groove in the area of ​​the third resistor to accommodate it and simultaneously ensure gapless mechanical contact between the housing half and the ceramic disk in the remaining area of ​​the disk.The ceramic disc additionally has a bore in its center, preferably for a cylindrical first cavity to guide the inner conductor of the coaxial cable. This bore is not metallized.

[0013] Preferably, firstly, the housing of the broadband directional coupler is made of an electrically conductive material, e.g., aluminum; secondly, a highly permeable toroidal core is preferably inserted in a second cavity, which is arranged concentrically and at a certain distance from the first cavity in a housing half facing the third resistor; thirdly, the ohmic component of the third resistor is more preferably significantly lower than the resistance of the housing (with toroidal core); and fourthly, the ceramic disk more preferably has an electrical connection between the two housing halves in the area outside the annular third resistor, so that a large part of the outer conductor current of the coaxial cable flows on the inside of the housing, i.e.,in the area between the first and second cavity, via the third resistor applied to the ceramic disk through the electrical connection to the housing half of the broadband directional coupler that faces away from the third resistor, and finally to the inside of the housing half facing away from the third resistor.

[0014] The preferred use of aluminium as the conductive material for the housing of the broadband directional coupler also achieves the best possible heat dissipation at higher power coaxial conductor currents while maintaining low weight.

[0015] The highly permeable toroidal core, preferably inserted in the second cavity, whose mean diameter is smaller than the mean diameter of the annular third resistor, forces a large part of the outer conductor current of the coaxial cable to flow on the inside of the housing in the area between the first and second cavities.

[0016] Due to the preferred gap-free mounting of the ceramic disk between the two halves of the housing, there is direct mechanical and electrical contact between the two housing halves and the ceramic disk. Furthermore, by applying a conductive layer to the side of the ceramic disk where the third resistor is located – hereinafter referred to as the first side of the ceramic disk – there is also direct electrical contact between the housing half of the broadband directional coupler, in which the high-permeability toroidal core is located, and the first side of the ceramic disk, and thus between the first side and the third resistor located there.

[0017] The electrical connection in the ceramic disk between the two adjacent halves of the housing is preferably realized via many vias which can be arranged in a specific angular grid on a circle concentric to the annular third resistor and located outside the annular third resistor.

[0018] The voltage across the third resistor, which corresponds to the outer conductor current and thus the inner conductor current of the coaxial cable, is preferably routed via a wire that is contacted with the conductive layer on the ceramic disk inside the annular third resistor to the second terminal of the second resistor of the measuring arrangement. To prevent unwanted electromagnetic interference from the inner conductor of the coaxial cable to the wire connection, and thus an unwanted superimposed interference voltage, the wire is routed to the second terminal of the second resistor in an electromagnetic-field-free channel of the housing.

[0019] The first resistor, whose first terminal is connected to the inner conductor of the coaxial cable, is preferably located in a third cavity of the broadband directional coupler housing. This third cavity has only one slot leading to the first cavity, allowing the connection between the inner conductor of the coaxial cable and the first terminal of the first resistor to be made. This ensures that the first resistor is located in a cavity free from the electric field of the inner conductor and that no unwanted interference voltages are generated between the first resistor and the housing.

[0020] The first resistor is preferably implemented as a resistive layer printed onto a ceramic substrate. The first resistor preferably rests, in the region of its first and second terminals, on a large-area counter-support, e.g., made of aluminum, belonging to the third cavity. This arrangement ensures optimal heat dissipation from the first resistor. The first resistor is exposed above and below its resistive layer, thereby simultaneously achieving optimal electrical insulation and heat dissipation to the housing of the broadband directional coupler, and minimizing parasitic capacitances relative to the housing.

[0021] The measuring unit for determining the power of a forward high-frequency signal or a reflected high-frequency signal is preferably housed in a field-free fourth cavity of the housing or in an additional housing on a printed circuit board that is shielded from electromagnetic fields and directly connected to the housing of the broadband directional coupler.

[0022] The measuring unit for determining the power of an incoming high-frequency signal is preferably galvanically isolated from the measuring unit for determining the power of a reflected high-frequency signal. This prevents mutual galvanic coupling of the measurement signals.

[0023] Finally, the end faces of opposing housing halves preferably each have an annular groove, the diameter of which is slightly smaller than the outer diameter of the essentially rotationally symmetrical housing of the broadband directional coupler and in which special springs for electromagnetic shielding of the measuring arrangement of the broadband directional coupler against electromagnetic interference from the outside are inserted.

[0024] Exemplary embodiments of the broadband directional coupler according to the invention are explained in detail below with reference to the drawing. The figures in the drawing show: Fig. 1 a circuit diagram with the broadband directional coupler according to the invention Fig. 2A a representation of a cross-section and a top view of a first housing half of a broadband directional coupler according to the invention with integrated shunt measuring resistor, Fig. 2B a representation of a cross-section and a top view of a second housing half of a broadband directional coupler according to the invention with integrated shunt measuring resistor, Fig. 3 A top view of a ceramic disk with integrated shunt measuring resistor, Fig. 4 a three-dimensional representation of one housing half of an embodiment of the broadband directional coupler with integrated voltage measuring resistor, Fig. 5 a top view of a voltage measuring resistor, Fig. 6 a three-dimensional representation of an embodiment of the broadband directional coupler, Fig. 7A a circuit diagram of a measuring unit for detecting a leading high-frequency signal, Fig. 7B a circuit diagram of a measuring unit for detecting a reflected high-frequency signal, Fig. 8 a basic representation of the course of the line current in a broadband directional coupler according to the invention and Fig. 9 a basic representation of the waveforms of all currents occurring in a broadband directional coupler according to the invention.

[0025] Before the broadband directional coupler according to the invention is presented in detail, the basic measurement setup with the broadband directional coupler according to the invention, which is essential for understanding the broadband directional coupler according to the invention, is described using the following examples: Fig. 1 explained.

[0026] In Fig. Figure 1 shows the measuring setup for measuring the voltage and current of the inner conductor of a coaxial cable, which is identical for measuring a forward and a reflected high-frequency signal. The coaxial cable 1 consists of an inner conductor 2 and an outer conductor 3 concentric with the inner conductor 2. The outer surface of the outer conductor 3 is, as shown in Fig. As indicated in 1, one side is connected to ground potential. The inner conductor 2 is typically connected at its input terminal 4 to a Fig. 1 not shown broadband power amplifier and at its output terminal 5 with a in Fig. 1. A complex load not shown, typically a transmitting antenna, is connected.

[0027] On the input side, the inner conductor 2 is connected at a node 6 to the first terminal 7 of a first resistor 8 belonging to a voltage divider, for measuring the voltage of the inner conductor 2. This resistor is designed with a relatively high resistance to accommodate a high division factor between the voltage to be measured at the inner conductor 2 and a measurement voltage to be processed by a measuring unit (to be explained later). For a voltage difference of 1000:1 between the voltage to be measured at the inner conductor and the measurement voltage to be processed in the measuring unit, and for a broadband directional coupler designed in the kilowatt range, a resistance value of 50 kΩ is typically recommended for the first resistor 8. This resistor must also be designed to withstand a high voltage of approximately 1200 volts RMS.

[0028] The second terminal 9 of the first resistor 8 is connected via a node 10 on one side to the first terminal 11 of a second resistor 12 belonging to the voltage divider and on the other side via a suitably dimensioned output resistor 13 to the output terminal 14, which is connected to the measuring unit to be explained later. The second terminal 15 of the second resistor 12 is connected via a further node 16 to the first terminal 17 of a third resistor 18, which, as a shunt measuring resistor, measures the outer conductor current of the coaxial cable 1, which is approximately identical to the inner conductor current, and on the other side to the inner surface 19 of the outer conductor 3 of the coaxial cable 1. The second terminal 20 of the third resistor 18 is connected to ground. Additional parasitic capacitances, such as those found in such a measuring arrangement and described in DE 10 2010 009 227 A1, are omitted for the sake of simplicity. Fig. 1 not shown.

[0029] To prevent inductively and capacitively generated interference voltages in the measuring arrangement and thus achieve a more accurate measurement result, the necessary design features are presented below, in particular those of the third resistor 18, which serves as a shunt current-measuring resistor, and the first resistor 8, which is positioned on the high-voltage side of the voltage divider and serves as a voltage-measuring resistor. The second resistor 12, positioned on the low-voltage side of the voltage divider, and the output coupling resistor 13 are located within a measuring unit, which will be discussed later and is equipped with suitable electromagnetic shielding measures, and therefore do not require a separate design.

[0030] First, the constructive design of the third resistor 18, which provides a voltage proportional to the current in the coaxial line, is described using the Fig. 2A, Fig. 2B, Fig. 3, Fig. 6, Fig. 8 and Fig. 9 described.

[0031] The third resistance 18 is, as from Fig. The outer conductor 3 of the coaxial cable 1, which emerges from the 1, is galvanically connected at its first terminal 17 to the inner surface 19 of the outer conductor 3 of the coaxial cable 1, on which the return current, identical to the inner conductor current of the coaxial cable 1, flows, and at its second terminal 20 to ground. To measure the inner conductor current of the coaxial cable 1, the coaxial cable 1 is cut in a section of the broadband directional coupler, and the outer conductor 3 of the coaxial cable 1 is replaced by a housing 21. This housing has good electrical conductivity for conducting the outer conductor current and good thermal conductivity for dissipating the heat generated in the individual resistors, and is therefore preferably made of aluminum. Like the outer conductor 3 of the coaxial cable 1, the housing 21 has a rotationally symmetrical shape.

[0032] For measuring the inner conductor current of the forward high-frequency signal and the inner conductor current of the reflected high-frequency signal, the housing 21 is enclosed by a ceramic disk 22, preferably made of aluminum nitride with a comparatively high thermal conductivity of 180-190 W / m. 2 K and a dielectric constant ε r of 9.5 with a third resistance 18 of preferably 47 mΩ applied to the first side of the ceramic disk 22, which is fixed firmly and without gaps between two halves 231 and 232 or 232 and 233 of the housing 21.

[0033] In order to achieve a gap-free fixation of the ceramic disc 22, which is largely flat on both sides, within each of the two halves 231 and 232 or 232 and 233 of the housing 21, the end faces of the individual halves 231 and 232 or 232 and 233 of the housing 21 are turned flat. In order to reduce or completely eliminate the effect of any unevenness that may occur on the planar surfaces of the ceramic disk 22 and on the end faces of the housing halves 231 and 232 or 232 and 233 on the clearance between the respective ceramic disk 22 and the associated housing halves 231 and 232 or 232 and 233, concentrically arranged, annular countersunk grooves 41 are provided in one of the end faces of a housing half 231 or 233 opposite the first side of the respective ceramic disk 22, in which contact springs 24 are provided for mechanical contact between the housing halves 231 or 233.233 and the respective ceramic disc 22 are inserted. The opposing housing halves 231 and 232, and 232 and 233, respectively, are connected to each other by screws 43, which are guided in axially aligned bores 44 on the end faces of the housing halves 231 and 232, and 232 and 233, respectively. The housing halves 231 and 232 and 233 facing the coaxial cables 1 are also fastened to the coaxial cables 1 by screws 43 guided in axially aligned bores 44 in the housing halves 231 and 233.

[0034] In order to additionally achieve an electrical contact between the housing halves 231 or 233 and the first side of the respective ceramic disk 22, the ceramic disk 22 is coated on its first side inside and outside of the ring-shaped third resistor 18 with a conductive layer, preferably with silver palladium.

[0035] The rotationally symmetrical housing halves 231, 232, and 233 each have an axial inner bore serving as the first cavity 25, in which the inner conductor 2 of the coaxial cable 1 is guided. The inner conductor 2 is supported on the inside of the housing 21 by a support disk 42. The first cavity 25 in the housing halves 231 and 233 facing the first side of the individual ceramic disks 22 is stepped, with the inner diameter of the first cavity 25 in the area of ​​the ceramic disk 22 being smaller than the inner diameter of the first cavity 25 in the area of ​​the connection of the coaxial cable 1 and corresponding to the inner diameter of an inner bore 26 provided in the ceramic disk 22.

[0036] In the area of ​​the smaller inner diameter of the first cavity 25 recessed in the housing halves 231 and 233, a second cavity 27 is provided at a certain distance from the first cavity 25. This second cavity is arranged concentrically to the first cavity 25 and is designed in an annular form. It is in direct contact with the respective ceramic disk 22 and contains a ring core 28 with a high permeability, preferably a nanocrystalline ring core with an inductance of 120 pH.

[0037] Two adjacent housing halves 231 and 232, and 232 and 233 respectively, are electrically connected to each other in the area of ​​the respective ceramic disk 22 by several special springs 29, which are embedded in annular milled grooves 30 on the end faces of the respective housing halves 231 and 232, and 232 and 233. The diameter of the annular milled grooves 30 is slightly smaller than the largest radial dimension of the rotationally symmetrical housing 21 and serves, on the one hand, as electromagnetic shielding of the coaxial cable 1 and the entire broadband directional coupler according to the invention from external electromagnetic fields and, on the other hand, for guiding common-mode currents that flow on the outside of the outer conductor 3 of the coaxial cable 1.

[0038] The first side of a ceramic disk 22 is electrically connected to the opposite second side of the ceramic disk 22 via several vias 31. The vias 31 are arranged in a specific angular grid corresponding to the number of vias on a circle whose diameter is larger than the outer diameter of the annular third resistor 18. The inner diameter of the annular third resistor 18 is larger than the outer diameter of the toroidal core 28, while the outer diameter of the annular third resistor 18 is smaller than the diameter of the hole circle of the vias.

[0039] The voltage potential applied to node 16 is tapped at the electrically conductive coating on the surface 33 of the first side of the ceramic disk 22, located on the inner side of the annular third resistor 18, via a soldered connection to a wire 32 and supplied to the second terminal 15 of the second resistor 12, which is located in a measuring unit to be described later. To prevent electromagnetic interference on the wire 32 and thus a superimposed interference voltage on the voltage potential measured at node 16, the wire 32 is guided in a recess 34 free of electromagnetic fields, preferably in a milled channel free of electromagnetic fields, within the housing 21.

[0040] The measurement of the inner conductor current of coaxial cable 1, which is based on a measurement of the outer conductor current of coaxial cable 1 corresponding to the inner conductor current, is described below using the following: Fig. 3, Fig. 8 and Fig. 9 explained. Fig. For the sake of simplicity, the measuring unit 39 and the measuring arrangement for measuring the voltage on the inner conductor of the coaxial cable are not shown in Figure 9.

[0041] The outer conductor current of the coaxial cable 1, which flows along the inside of the housing half 231 of the housing 21 due to the skin effect (see the path of the outer conductor current marked with arrows and a solid line in the Fig. 8 and Fig. 9), meets the electrically conductive coating on the surface 33 located on the inside of the first side of the ceramic disk 22, which is adjacent to the ring-shaped third resistor 18.Since the impedance of the annular third resistor 18 is many times smaller than the impedance of the housing 21 (with the toroidal core 28 arranged in the cavity 17), the outer conductor current will not flow on the inside of the housing 21 in the area of ​​the first cavity 25 to the next housing half 232, but will instead flow via the conductive coating on the inner surface 23 of the first side of the ceramic disk 22, the annular third resistor 18, the conductive coating on the surface 35 of the first side of the ceramic disk 22 located outside the annular third resistor 18, the vias 31 between the first and second sides of the ceramic disk 22, and via the second side of the ceramic disk 22 back to the inside of the housing half 232 of the housing 21 in the area of ​​the first cavity 25.

[0042] Additionally, a very small parasitic current flows in the outer conductor - in Fig. 9 is represented by a dashed line with arrows - from the inside of the housing half 231 of the housing 21 along the end face of the housing half 231 of the housing 21 to the second cavity 27, along the inner surfaces of the second cavity 27, the countersunk groove 41 recessed in the end face of the housing half 231 of the housing 21, via the contact spring 24 located in the countersunk groove 41, via the vias 31 between the first and second sides of the ceramic disk 22 and via the second side of the ceramic disk 22 back to the inside of the housing half 232 of the housing 21 in the area of ​​the first cavity 25.

[0043] Due to the effect of the toroidal core 28 with its high permeability, a large part of the outer conductor current flowing on the inside of the housing half 231 of the housing 21 is guided via the electrical coating of the ceramic disk 23 and the annular third resistor 18 applied as a layer resistor on the ceramic disk 33, and only a small part of the outer conductor current is guided as parasitic outer conductor current past the annular third resistor 18 on the exposed inner surfaces of the housing half 231 of the housing 21.

[0044] The potential on the coated surface 33 of the first side of the ceramic disk 22, which is positioned on the inside of the ring-shaped third resistor 18 and is guided to a measuring unit via the wire 32, corresponds to the positive voltage drop of the outer conductor current at the third resistor 18 relative to the outside of the housing 21, which is at ground potential, and serves to measure the leading high-frequency signal.

[0045] As from Fig. As can be seen in Figure 8, the outer conductor current flows from the inside of the housing half 232 of the housing 21 via the second side of the further ceramic disk 22 located between the two housing halves 232 and 233, the vias 31 of this ceramic disk 22, the surface 35 of the first side of the ceramic disk 22 positioned on the outside of the annular third resistor 18, the annular third resistor 18 applied to the ceramic disk 23 as a film resistor, the surface 35 of the first side of the ceramic disk 22 positioned on the inside of the annular third resistor 18 to the inside of the housing half 233 of the housing 21.

[0046] The potential on the coated surface 33 of the first side of the ceramic disk 22 located between the two housing halves 232 and 233, which is positioned on the inside towards the ring-shaped third resistor 18, is conveyed via a wire 32 to a measuring unit, thus corresponds to the negative voltage drop of the outer conductor current at the third resistor 18 relative to the outside of the housing 21 which is at ground potential and serves to measure the reflected high-frequency signal.

[0047] The following describes the constructive design of the first resistor 8, which detects the voltage on the inner conductor 2 of the coaxial line 1 and divides it to a lower measuring voltage, based on the Fig. 4, Fig. 5 and Fig. 8 described.

[0048] The first resistor 8 for dividing the voltage of the inner conductor 2 of the coaxial line 1 to a suitable voltage level for the measuring unit 39 is, as shown in Fig. The resistor 8, shown in Figure 1, is connected at its first terminal 7 to the inner conductor 2 of the coaxial cable 1 and at a second terminal 9 to the node 10. The first resistor 8 is a resistive layer on a special ceramic substrate, preferably made of aluminum oxide (Al2O3) – e.g., with a thermal conductivity of 26 W / m. 2 K and a dielectric constant ε r of 9.0 -, realized. The first resistor 8 is designed for voltages up to a maximum of 1200 V RMS and powers up to 8000 W and typically has a resistance of 50 kΩ.

[0049] The first resistor 8 is according to Fig. 8 is housed in a third cavity 36 within the housing 21, preferably within the housing half 232. The resistive layer of the first resistor 8 is exposed above and below the inner walls of the third cavity 36. The first resistor 8 is arranged according to Fig. 5 in the area outside its first and second connections 7 and 9, each is supported in a counter bearing 37. These counter bearings (support surfaces) 37 are made of a material with high thermal conductivity, preferably aluminum, due to the sometimes very high thermal loads of the first resistor 8, which depend on the standing wave ratio, in order to optimally dissipate the heat generated in the resistive layer of the first resistor 8. With a power of 8000 W to be transmitted on the coaxial cable 1 and a standing wave ratio of 10, approximately 25 W of heat must be dissipated from the first resistor 8. The first resistor 8, located centrally in the third cavity 36, is according to Fig. 4 and Fig. 8 is separated from the first cavity 25 only by a slot 38. The extent of the slot 38 corresponds to the cross-section of the connecting line between the inner conductor 2 of the coaxial line 1 located in the first cavity 25 and the first resistor 8. In this way, the build-up of a capacitive interference voltage between the resistive layer of the first resistor 8 and the inner walls of the third cavity 36, originating from the power line of the broadband directional coupler, i.e., from the inner conductor 2 of the coaxial line 1, which would otherwise be superimposed on the voltage drop across the first resistor 8, is prevented.

[0050] The measuring voltage tapped at the third resistor 18 at node 16 and transmitted via wire 32, which is proportional to the outer conductor current of the coaxial line 1, and the measuring voltage tapped at node 10, which represents the voltage detected and divided at the inner conductor 2 of the coaxial line 1 by the first resistor 8, are used to measure the forward high-frequency signal and the reflected high-frequency signal of a measuring unit 39 according to the Fig. 7A and Fig. 8 in the case of measuring the preceding high-frequency signal and according to the Fig. 7B and Fig. 8 supplied for the case of measuring the reflected high-frequency signal.

[0051] The measured voltages detected at the two contacts 10 and 16 are supplied to the first terminal 11 and the second terminal 15 of the second resistor 12 in the measuring unit 39. The second resistor 12 is shown in the diagram of the Fig. 7A and Fig. 7B is implemented by a parallel connection of a fixed-value resistor 12 and a variable resistor 12'. The operating point of the measuring voltage at contact 10 can be set using the variable resistor 12' of the second resistor 12. They primarily serve to compensate for voltage errors caused by tolerances of the two ceramic resistors 16 and 8.

[0052] As from the Fig. 7A and Fig. As can be seen from 7B, the voltage U across the third resistor 18 is due to the capacitor 44, which is connected between node 16 and ground. I a voltage that is proportional to the outer conductor current and thus to the inner conductor current of coaxial cable 1. The voltage U across the second resistor 12 is located between nodes 10 and 16. Va voltage proportional to the voltage across the inner conductor 2 of the coaxial line 1. Thus, across capacitor 45, which is connected between node 10 and ground, in the case of measurement of the leading high-frequency signal according to Fig. 7A and equation (1) the sum U V + U I the voltage U dropping across the second resistor 12 V and the voltage drop U across the third resistor 18 I on. In the case of measuring the reflected high-frequency signal according to Fig. 7B and equation (2) the difference U lies at capacitor 45 V - U I the voltage U dropping across the second resistor 12 V and the voltage drop U across the third resistor 18 I to. UV+UI=k⋅Peffective⋅(VSWR+1VSWR) UV−UI=k⋅Peffective⋅(VSWR−1VSWR)

[0053] In equations (1) and (2), the variable P represents WirkThe active power transmitted by the broadband directional coupler according to the invention, the variable VSWR the voltage standing wave ratio of the coaxial line 1 and the variable k a proportionality factor.

[0054] The sum of the stresses or the stress difference according to equations (1) and (2) includes the stress that is in Fig. 7A and Fig. 7B The parasitic voltage drop shown in dashed lines across the third resistor 18 from the inner conductor 2 of the coaxial line 1 is not included, as it is negligibly small.

[0055] The voltage drop across capacitor 45 is fed to a filter circuit connected in parallel with the second resistor 12 for frequency compensation. This filter circuit is implemented as a π-circuit and consists of the parallel connection of capacitor 46 with a fixed capacitance and capacitor 47, whose capacitance is adjustable, resistor 48, and capacitor 50 with a fixed capacitance and capacitor 49, whose capacitance is adjustable. The filter circuit is connected to the output 40 of the filter circuit, and thus to the measuring unit 39, via the coupling resistor 13. A measuring voltage proportional to the forward or reflected high-frequency signal can be tapped at output 40, which is implemented as a coaxial cable connection, typically an SMP or SMA connector.

[0056] The broadband directional coupler according to the invention is not limited to the embodiment shown. In particular, the invention covers all combinations of all features claimed in the respective claims, all features disclosed in the description, and all features illustrated in the figures of the drawing.

Claims

[1] Broadband directional coupler for measuring the power of a forward or reflected high-frequency signal on a coaxial line (1) comprising a voltage divider consisting of a first resistor (8) and a second resistor (12), wherein a first terminal (6) of the first resistor (8) is connected to an inner conductor (2) of the coaxial line (1), and to a third resistor (18), characterized by , that the third resistor (18) is ring-shaped and is arranged concentrically to the inner conductor (2) in a plane oriented orthogonally to the inner conductor and that the first resistor (8) rests outside its first and second terminals (7,9) on a large-area counter-support (37) in a third cavity (36) free of electromagnetic fields in a housing (21) of the broadband directional coupler arranged in a substantially rotationally symmetrical manner around the inner conductor (2). [2] Broadband directional coupler according to claim 1, characterized by , that the second terminal (9) of the first resistor (8) and the first terminal (11) of the second resistor (12) is connected to a measuring unit (39), and / or that a first terminal (17) of the third resistor (18) is connected to an outer conductor (19) of the coaxial line (1) and the second terminal (15) of the second resistor (12) and the second terminal (20) of the third resistor (18) is connected to a ground. [3] Broadband directional coupler according to claim 1 or 2, characterized by , that the third resistor (18) is designed to be low-resistance and has a comparatively small extent in the axial direction compared to the radial direction. [4] Broadband directional coupler according to one of claims 1 to 3, characterized by, that the third resistor (18) is applied to a first side of a ceramic disk (22) coated with a conductive layer, which is fixed without gaps between two plan-turned end faces of two halves (231,232,233) of a housing (21) of the broadband directional coupler arranged substantially rotationally symmetrical around the inner conductor (2) and whose center has a bore for a cylindrical first cavity (25) for guiding the inner conductor (2). [5] Broadband directional coupler according to claim 4, characterized by , that the housing (21) is made of an electrically conductive material, preferably aluminium, with a conductivity lower than that of the third resistor (18). [6] Broadband directional coupler according to one of claims 4 or 5, characterized by, that a highly permeable toroidal core (28) is arranged in a second cavity (27), which is arranged concentrically and at a certain distance to the first cavity (25) in a half (231,233) of the housing (21) facing the third resistor (18). [7] Broadband directional coupler according to claim 6, characterized by , that the mean diameter of the ring core (28) is smaller than the mean diameter of the annular third resistor (18). [8] Broadband directional coupler according to one of claims 4 to 7, characterized by , that the first side of the ceramic disk (22) outside the annular third resistor (18) is conductively connected to a second side of the ceramic disk (22) via several vias (31) arranged on a circle, in particular in a specific angular grid. [9] Broadband directional coupler according to any one of claims 4 to 8, characterized by, that the conductive layer (33) of the ceramic disk (22) located inside the ring-shaped third resistor (22) is connected to a second terminal (15) of the second resistor (12) via a wire (32) which is guided in a recess (34) of the housing free of electromagnetic fields. [10] Broadband directional coupler according to any one of claims 4 to 9, characterized by , that the internal outer conductor impedance of the housing (21) of the broadband coupler is orders of magnitude larger than the impedance of the third resistor (18). [11] Broadband directional coupler according to any one of claims 1 to 10, characterized by , that the first resistor (8) is a low-resistance resistive layer printed on a ceramic substrate. [12] Broadband directional coupler according to claim 11, characterized by , that the first resistor (8) is hollow below and above the resistance layer. [13] Broadband directional coupler according to claim 4, characterized by, that the third cavity (36) has a slot (37) to the first cavity (25) which has the extent of a galvanic connection between the inner conductor (2) and the first resistor (8). [14] Broadband directional coupler according to claim 2, characterized by , that the measuring unit (39) is arranged in a fourth cavity free of electromagnetic fields in a housing (21) of the broadband directional coupler or in an additional housing directly connected to the housing (21) of the broadband directional coupler and shielding electromagnetic fields. [15] Broadband directional coupler according to claims 1 to 14, characterized by , that a measuring unit (39) for measuring the power of a forward high-frequency signal is galvanically isolated from a measuring unit (39) for measuring a reflected high-frequency signal. [16] Broadband directional coupler according to any one of claims 4 to 10, characterized by, that springs (29) for electromagnetic shielding are inserted in an annular groove (30) on the end faces of the halves (231, 232, 233) of the housing (21) of the broadband directional coupler, the diameter of which is slightly smaller than the outer diameter of the housing (21).

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