Balun circuit

Abstract

To reduce deviation from simulation in a balun circuit using semi-rigid cables.SOLUTION: A balun circuit comprises: a substrate having a first input port, a second input port, an output port, and a through-hole in a predetermined size; and a first semi-rigid cable and a second semi-rigid cable which are fixed onto the through-hole, and which are electrically connected to a circuit formed on the substrate. An outer conductor of the first semi-rigid cable is electrically connected to an inner conductor on one end side of the second semi-rigid cable. An outer conductor of the second semi-rigid cable is electrically connected to an inner conductor on one end side of the first semi-rigid cable.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a balun circuit.

Background Art

[0002] A Wilkinson synthesizer for synthesizing two high-frequency signals into one high-frequency signal and a Wilkinson divider for dividing one high-frequency signal into two high-frequency signals are known (see, for example, Patent Documents 1 and 2). It is also known that such a Wilkinson synthesizer and Wilkinson divider can be configured with a balun circuit using a semi-rigid cable (see, for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, a balun circuit using a semi-rigid cable as in Patent Document 3 can obtain good characteristics in simulation, but when actually constructing a circuit and measuring input / output characteristics, there may be a large deviation between the measurement result and the simulation.

[0005] Therefore, the present invention has been made in view of these points, and an object thereof is to reduce the deviation from simulation in a balun circuit using a semi-rigid cable.

Means for Solving the Problems

[0006] In a first aspect of the present invention, there is provided a substrate having a first input port, a second input port, an output port, and a through-hole of a predetermined size, and a first semi-rigid cable and a second semi-rigid cable fixed on the through-hole and electrically connected to a circuit formed on the substrate. The outer conductor of the first semi-rigid cable is electrically connected to the inner conductor on one end side of the second semi-rigid cable, and the outer conductor of the second semi-rigid cable is electrically connected to the inner conductor on one end side of the first semi-rigid cable. The output port is electrically connected to the inner conductor on the other end side opposite to one end of the first semi-rigid cable and the inner conductor on the other end side opposite to one end of the second semi-rigid cable, providing a balun circuit.

[0007] The balun circuit further includes a resistor element having one end electrically connected to the first input port and the other end opposite to one end electrically connected to the second input port. The first input port may be electrically connected to the outer conductor of the first semi-rigid cable, and the second input port may be electrically connected to the outer conductor of the second semi-rigid cable.

[0008] The balun circuit may further include a first input-side semi-rigid cable electrically connecting the first input port and the outer conductor of the first semi-rigid cable, a second input-side semi-rigid cable electrically connecting the second input port and the outer conductor of the second semi-rigid cable, a first output-side semi-rigid cable electrically connecting the output port and the inner conductor on the other end side opposite to one end of the first semi-rigid cable, and a second output-side semi-rigid cable electrically connecting the output port and the inner conductor on the other end side opposite to one end of the second semi-rigid cable.

[0009] The balun circuit further includes a terminator electrically connected to an internal conductor on one end side of the first semi-rigid cable and an outer conductor of the second semi-rigid cable, and the outer conductor of the first semi-rigid cable and the outer conductor of the second semi-rigid cable may be electrically connected to a predetermined reference potential.

[0010] The balun circuit may further include a first input-side semi-rigid cable electrically connecting the first input port and an internal conductor on the other end side opposite to one end of the first semi-rigid cable, a second input-side semi-rigid cable electrically connecting the second input port and an internal conductor on the other end side opposite to one end of the second semi-rigid cable, a first output-side semi-rigid cable electrically connecting the output port and an internal conductor on the other end side opposite to one end of the first semi-rigid cable, and a second output-side semi-rigid cable electrically connecting the output port and an internal conductor on the other end side opposite to one end of the second semi-rigid cable.

Effect of the Invention

[0011] According to the present invention, in a balun circuit using a semi-rigid cable, there is an effect that the deviation from the simulation can be reduced.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0013] <First Configuration Example of Balun Circuit 10> FIG. 1 shows a first configuration example of the balun circuit 10 according to this embodiment. The balun circuit 10 shown in FIG. 1 shows an example of a Wilkinson synthesizer for synthesizing two high-frequency signals into one high-frequency signal. The balun circuit 10 includes a substrate 20, a first input-side semi-rigid cable 31, a second input-side semi-rigid cable 32, a first semi-rigid cable 41, a second semi-rigid cable 42, a first output-side semi-rigid cable 51, a second output-side semi-rigid cable 52, and a resistive element 60.

[0014] The substrate 20 is a circuit board formed of a dielectric or the like. The substrate 20 has, for example, circuit patterns formed of metal films such as wiring patterns and ground patterns. The substrate 20 has a first input port 21, a second input port 22, an output port 23, and a through hole 24 having a predetermined size.

[0015] High-frequency signals in the range of several hundred MHz to several GHz are respectively input to the first input port 21 and the second input port 22. The output port 23 outputs a combined signal obtained by combining the signals input to the first input port 21 and the second input port 22, respectively. Each port has a connector, a terminal, a core wire of a cable, etc. for exchanging electrical signals with the outside.

[0016] The through-hole 24 is a hole formed by drilling a part of the substrate 20. The through-hole 24 is formed in the region where the first semi-rigid cable 41 and the second semi-rigid cable 42 are located. In other words, the first semi-rigid cable 41 and the second semi-rigid cable 42 are fixed on the through-hole 24 and are electrically connected to the circuit formed on the substrate 20. In FIG. 1, the region where the through-hole 24 of the substrate 20 is formed is indicated by a dotted line.

[0017] The first input-side semi-rigid cable 31, the second input-side semi-rigid cable 32, the first semi-rigid cable 41, the second semi-rigid cable 42, the first output-side semi-rigid cable 51, and the second output-side semi-rigid cable 52 are fixed to the substrate 20 and constitute at least a part of the circuit formed on the substrate 20.

[0018] The semi-rigid cable is a coaxial cable in which an outer conductor covers the periphery of an inner conductor (center conductor) via an insulator. The semi-rigid cable is known to have excellent high-frequency characteristics because the outer conductor forms a seamless metal tube. It is desirable that the impedance of the semi-rigid cable is unified to a predetermined value. The impedance of the semi-rigid cable is, for example, 50 Ω or 100 Ω.

[0019] The first input-side semi-rigid cable 31 electrically connects the first input port 21 and the outer conductor of the first semi-rigid cable 41. In other words, the first input port 21 is electrically connected to the outer conductor of the first semi-rigid cable 41.

[0020] The second input-side semi-rigid cable 32 electrically connects the second input port 22 and the outer conductor of the second semi-rigid cable 42. In other words, the second input port 22 is electrically connected to the outer conductor of the second semi-rigid cable 42. The first input-side semi-rigid cable 31 and the second input-side semi-rigid cable 32 are, for example, about 100 mm in length.

[0021] The outer conductor of the first semi-rigid cable 41 is electrically connected to the inner conductor on one end side of the second semi-rigid cable 42. In FIG. 1, the inner conductor on one end side of the first semi-rigid cable 41 is defined as the inner conductor 43b. Also, the outer conductor of the second semi-rigid cable 42 is electrically connected to the inner conductor on one end side of the first semi-rigid cable 41. In FIG. 1, the inner conductor on one end side of the second semi-rigid cable 42 is defined as the inner conductor 43c. The lengths of the first semi-rigid cable 41 and the second semi-rigid cable 42 are, as an example, about 10 mm in length.

[0022] The first output-side semi-rigid cable 51 electrically connects the output port 23 and the inner conductor on the other end side opposite to one end of the first semi-rigid cable 41. In FIG. 1, the inner conductor on the other end side opposite to one end of the first semi-rigid cable 41 is defined as the inner conductor 43a.

[0023] Also, the second output-side semi-rigid cable 52 electrically connects the output port 23 and the inner conductor on the other end side opposite to one end of the second semi-rigid cable 42. In FIG. 1, the inner conductor on the other end side opposite to one end of the second semi-rigid cable 42 is defined as the inner conductor 43d.

[0024] In other words, the output port 23 is electrically connected to the inner conductor 43a of the first semi-rigid cable 41 and the inner conductor 43d of the second semi-rigid cable 42. The first output-side semi-rigid cable 51 and the second output-side semi-rigid cable 52 are, as an example, about 30 mm in length.

[0025] One end of the resistance element 60 is electrically connected to the first input port 21, and the other end opposite to the one end is electrically connected to the second input port 22. In other words, one end of the resistance element 60 is electrically connected to the inner conductor of the first input-side semi-rigid cable 31, and the other end opposite to the one end is electrically connected to the inner conductor of the second input-side semi-rigid cable 32.

[0026] At the connection point between the resistive element 60 and the semi-rigid cable, for example, a wiring connected to the resistive element 60 and an inner conductor exposed by removing a part of the outer conductor of the semi-rigid cable are connected by soldering or the like. The resistive element 60 is provided on the substrate 20, for example. The resistive element 60 is 100 Ω as an example.

[0027] In the above-described balun circuit 10, it is desirable that the connection points of two or more semi-rigid cables connect the inner conductors and the outer conductors to each other by soldering or the like. Also, the connection points of two or more semi-rigid cables may be a connection using a connector. Further, it is desirable that the outer conductors of the semi-rigid cables excluding the first semi-rigid cable 41 and the second semi-rigid cable 42 are connected to the reference potential.

[0028] The balun circuit 10 according to the above-described embodiment has a configuration in which the balun-connected semi-rigid cables are fixed to the substrate 20 and through holes 24 are formed in a part of the region of the substrate 20 corresponding to the balun connection portion. In order to explain the input / output characteristics of such a balun circuit 10, first, the input / output characteristics of a circuit to be compared with the balun circuit 10 will be explained. The circuit to be compared is a circuit that does not have the through holes 24 in the substrate 20 in the balun circuit 10 described with reference to FIG. 1. Therefore, the following description of the circuit to be compared will be made using the same reference numerals as those of the balun circuit 10 described with reference to FIG. 1.

[0029] <Input / Output Characteristics of the Circuit to be Compared> FIG. 2 shows an example of the transmission loss of the circuit to be compared. FIG. 2 shows the transmission loss when a signal input to the first input port 21 is output from the output port 23. The horizontal axis in FIG. 2 indicates the frequency of the input signal, and the vertical axis indicates the value of the transmission loss. The solid line in the figure is the measured value, and the dotted line is the simulation result.

[0030] Figure 3 shows a first example of the reflection loss of the circuit to be compared. Figure 3 shows the reflection loss of the signal input to the first input port 21 of the circuit to be compared. Also, Figure 4 shows a second example of the reflection loss of the circuit to be compared. Figure 4 shows the reflection loss of the signal input to the output port 23. The horizontal axis in Figures 3 and 4 indicates the frequency of the input signal, and the vertical axis indicates the value of the reflection loss. Note that the solid line in the figure is the measured value, and the dotted line is the simulation result.

[0031] As can be seen from Figure 2, the value of the through loss becomes larger as it reaches -4 dB. Also, it can be seen that there is a large difference between any of the measured values and the simulation results when comparing the through loss in Figure 2, and the reflection losses in Figures 3 and 4. Therefore, it can be understood that it is difficult to accurately design the input / output characteristics of the circuit to be compared using simulation before constructing the circuit.

[0032] <Input / Output Characteristics of the Balun Circuit 10> Figure 5 shows an example of the through loss of the balun circuit 10 according to the present embodiment. Figure 5 shows the through loss when the signal input to the first input port 21 is output from the output port 23. The horizontal axis in Figure 5 indicates the frequency of the signal, and the vertical axis indicates the value of the through loss. Note that the solid line in the figure is the measured value, and the dotted line is the simulation result.

[0033] Figure 6 shows a first example of the reflection loss of the balun circuit 10 according to the present embodiment. Figure 6 shows the reflection loss of the signal input to the first input port 21 of the balun circuit 10 according to the present embodiment. Also, Figure 7 shows a second example of the reflection loss of the balun circuit 10 according to the present embodiment. Figure 7 shows the reflection loss of the signal input to the output port 23. The horizontal axis in Figures 6 and 7 indicates the frequency of the signal, and the vertical axis indicates the value of the reflection loss. Note that the solid line in the figure is the measured value, and the dotted line is the simulation result.

[0034] As can be seen from FIG. 5, the insertion loss of the balun circuit 10 is -3.5 dB or more, and it can be understood that flat and good characteristics are obtained in a wide band of 1000 MHz. Also, it can be seen that the difference between the measured value and the simulation result of the insertion loss in FIG. 5 and the reflection loss in FIGS. 6 and 7 is small compared to the circuit being compared.

[0035] The substrate 20 of the balun circuit 10 has a through hole 24 formed at the position of the semi-rigid cable connected in a balun configuration compared to the substrate of the circuit being compared. Therefore, the value of the parasitic capacitance generated between the outer conductor of the semi-rigid cable connected in a balun configuration and the substrate 20 can be reduced. Thus, it is considered that the balun circuit 10 can reduce the deviation between the measured value and the simulation. Therefore, according to the balun circuit 10 according to the present embodiment, after designing using simulation, a balun circuit 10 having good frequency characteristics, a circuit using the balun circuit 10, etc. can be configured.

[0036] The balun circuit 10 according to the above-described present embodiment has been described by taking the circuit configuration shown in FIG. 1 as an example, but is not limited thereto. As long as it is a circuit configuration having a circuit connected in a balun configuration with a semi-rigid cable, it can be applied as the balun circuit 10 according to the present embodiment by forming a through hole in a part of the substrate corresponding to the circuit connected in a balun configuration. Therefore, an example of a circuit configuration different from the circuit configuration shown in FIG. 1 will be described next.

[0037] <Balun Circuit 10 of the Second Configuration Example> FIG. 8 shows a second configuration example of the balun circuit 10 according to the present embodiment. In the balun circuit 10 of the second configuration example, components that operate substantially the same as those of the balun circuit 10 of the first configuration example shown in FIG. 1 are given the same reference numerals, and redundant explanations are omitted. The balun circuit 10 of the second configuration example further includes a terminator 70.

[0038] The terminator 70 is electrically connected to the internal conductor 43b on one end side of the first semi-rigid cable 41 and the outer conductor of the second semi-rigid cable 42. The terminator 70 has, for example, a terminating resistor with one end connected to the internal conductor 43b and the outer conductor of the second semi-rigid cable 42, and the other end opposite to the one end connected to the reference potential. The resistance value of the terminating resistor is, as an example, 50 Ω. It is desirable that the terminator 70 is formed on the substrate 20.

[0039] The outer conductor of the first semi-rigid cable 41 and the outer conductor of the second semi-rigid cable 42 are electrically connected to a predetermined reference potential. In this case, the internal conductor 43c on one end side of the second semi-rigid cable 42 is also connected to the reference potential. The reference potential is, for example, the ground potential (0 V) formed on the substrate 20.

[0040] The first input-side semi-rigid cable 31 electrically connects the first input port 21 and the internal conductor 43a on the other end side opposite to one end of the first semi-rigid cable 41. The second input-side semi-rigid cable 32 electrically connects the second input port 22 and the internal conductor 43d on the other end side opposite to one end of the second semi-rigid cable 42.

[0041] The first output-side semi-rigid cable 51 electrically connects the output port 23 and the internal conductor 43a on the other end side opposite to one end of the first semi-rigid cable 41. The second output-side semi-rigid cable 52 electrically connects the output port 23 and the internal conductor 43d on the other end side opposite to one end of the second semi-rigid cable 42.

[0042] In such a balun circuit 10 of the second configuration example, by forming the through hole 24 in the region of the substrate 20 indicated by the dotted line, the value of the parasitic capacitance generated between the balun-connected circuit and the substrate 20 can be reduced. And the passing loss of the balun circuit 10 can be reduced, and the deviation between the measured value and the simulation can be reduced.

[0043] In the balun circuit 10 according to the above-described embodiment, an example in which a part of the substrate 20 corresponding to the circuit connected in a balun manner is formed as the through hole 24 has been described, but the present invention is not limited to this. A part of the substrate 20 corresponding to the circuit connected in a balun manner may be made of only a dielectric without forming a metal. Even with such a configuration, the value of the parasitic capacitance generated between the circuit connected in a balun manner and the substrate 20 can be reduced.

[0044] In the balun circuit 10 according to the above-described embodiment, an example in which the first input port 21, the second input port 22, and the output port 23 are connected to the circuit connected in a balun manner (the first semi-rigid cable 41 and the second semi-rigid cable 42) by semi-rigid cables has been described, but the present invention is not limited to this. Among the connections between the first input port 21, the second input port 22, and the output port 23 and the circuit connected in a balun manner, at least one connection may be a transmission line formed on the substrate.

[0045] In the balun circuit 10 according to the above-described embodiment, an example in which the Wilkinson synthesizer is configured has been described, but the present invention is not limited to this. The balun circuit 10 may be configured as a Wilkinson divider. In this case, the first input port 21 functions as the first output port, the second input port 22 functions as the second output port, and the output port 23 functions as the input port.

[0046] As described above, the present invention has been described using embodiments. However, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist. For example, all or part of the device can be configured by functionally or physically dispersing and integrating it in an arbitrary unit. Further, a new embodiment generated by an arbitrary combination of a plurality of embodiments is also included in the embodiments of the present invention. The effects of the new embodiment generated by the combination have the effects of the original embodiments combined.

Description of Reference Numerals

[0047] 10 Balun circuit 20 Substrate 21 First input port 22 Second input port 23 Output port 24 Through hole 31 First input side semi-rigid cable 32 Second input side semi-rigid cable 41 First semi-rigid cable 42 Second semi-rigid cable 43 Internal conductor 51 First output side semi-rigid cable 52 Second output side semi-rigid cable 60 Resistor element 70 Terminator

Claims

1. A substrate having a first input port, a second input port, an output port, and a through hole of a predetermined size, a first semi-rigid cable and a second semi-rigid cable fixed on the through hole and electrically connected to a circuit formed on the substrate, comprising: The external conductor of the first semi-rigid cable is electrically connected to the internal conductor on one end side of the second semi-rigid cable, The external conductor of the second semi-rigid cable is electrically connected to the internal conductor on one end side of the first semi-rigid cable, The output port is electrically connected to the internal conductor on the other end side opposite to one end of the first semi-rigid cable and the internal conductor on the other end side opposite to one end of the second semi-rigid cable, a balun circuit.

2. Further comprising a resistive element having one end electrically connected to the first input port and the other end opposite to the one end electrically connected to the second input port, The first input port is electrically connected to the external conductor of the first semi-rigid cable, The second input port is electrically connected to the external conductor of the second semi-rigid cable, The balun circuit according to claim 1.

3. a first input side semi-rigid cable electrically connecting the first input port and the external conductor of the first semi-rigid cable, a second input side semi-rigid cable electrically connecting the second input port and the external conductor of the second semi-rigid cable, a first output side semi-rigid cable electrically connecting the output port and the internal conductor on the other end side opposite to one end of the first semi-rigid cable, a second output side semi-rigid cable electrically connecting the output port and the internal conductor on the other end side opposite to one end of the second semi-rigid cable, The balun circuit according to claim 1 or 2, further comprising:

4. Further comprising a terminator electrically connected to the internal conductor on one end side of the first semi-rigid cable and the external conductor of the second semi-rigid cable, The external conductor of the first semi-rigid cable and the external conductor of the second semi-rigid cable are electrically connected to a predetermined reference potential, The balun circuit according to claim 1.

5. A first input-side semi-rigid cable that electrically connects the first input port and an inner conductor on the other end side opposite to one end of the first semi-rigid cable. A second input-side semi-rigid cable that electrically connects the second input port and an inner conductor on the other end side opposite to one end of the second semi-rigid cable. A first output-side semi-rigid cable that electrically connects the output port and an inner conductor on the other end side opposite to one end of the first semi-rigid cable. A second output-side semi-rigid cable that electrically connects the output port and an inner conductor on the other end side opposite to one end of the second semi-rigid cable. The balun circuit according to claim 4, further comprising the above.

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