Filtering circuit and balun circuit

Abstract

A filter circuit includes a branch-line coupler having first to fourth terminals and a balun circuit connected to one of the second and third terminals, the balun circuit having an input terminal connected to one of the second and third terminals for input of a high-frequency signal, a first transmission line having one end connected to the input terminal and having a length equivalent to 1 / 4 of the high-frequency signal, a second transmission line having one end connected to the input terminal and having a length equivalent to 1 / 4, a third transmission line having one end connected to the other end of the second transmission line and having a length equivalent to 1 / 4, and a fourth transmission line having one end connected to the other end of the third transmission line, electromagnetically coupled to the first transmission line, and having a length equivalent to 1 / 4, the other end of the first transmission line and the other end of the fourth transmission line being either both connected to a ground or both left open or connected to two terminal resistors having equal resistance values, respectively.

Description

Technical Field

[0001] This invention relates to filter circuits and balun circuits. Background Technology

[0002] Conventionally, there exists a one-terminal circuit having a coupling line and a transmission line, wherein the through terminal and isolation terminal of the coupling line are grounded, and the transmission line is connected between the input terminal and the coupling terminal of the coupling line (for example, see Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-158245

[0006] Furthermore, the aforementioned one-terminal circuit is a circuit for reducing phase noise, rather than a circuit for suppressing the reflection of signals at the desired frequency. Summary of the Invention

[0007] Therefore, the object of the present invention is to provide a filter circuit and a balun circuit that can suppress the reflection of signals of a desired frequency.

[0008] Solution for solving the problem

[0009] The filtering circuit disclosed herein includes: a branch-line coupler having a first terminal, a second terminal, a third terminal, and a fourth terminal connected in a loop by conductor lines, with the first terminal serving as an input port and the fourth terminal serving as an output port; and a first balun circuit connected to either the second terminal or the third terminal, the first balun circuit having: a first input terminal connected to either the second terminal or the third terminal for receiving a high-frequency signal; and a first transmission line having one end connected to the first input terminal and having an electrical length corresponding to the frequency of the high-frequency signal. The first transmission line has a length of one-quarter of the electrical length; a second transmission line has one end connected to the first input terminal and has a length equivalent to one-quarter of the electrical length; a third transmission line has one end connected to the other end of the second transmission line and has a length equivalent to one-quarter of the electrical length; and a fourth transmission line has one end connected to the other end of the third transmission line and electromagnetically coupled to the first transmission line, having a length equivalent to one-quarter of the electrical length, wherein the other ends of the first transmission line and the other ends of the fourth transmission line are both connected to ground, or both are set to open circuit, or are respectively connected to two terminating resistors having equal resistance values.

[0010] Invention Effects

[0011] The present invention provides a filter circuit and a balun circuit that can suppress the reflection of signals of a desired frequency. Attached Figure Description

[0012] Figure 1 This is a diagram illustrating an example of a filter circuit 100 according to an implementation method.

[0013] Figure 2 This is a diagram representing the balanced-to-unbalanced converter circuit 120.

[0014] Figure 3 This is a graph showing the frequency characteristics of the S11 parameter of the balun-to-unbalance converter circuit 120.

[0015] Figure 4 This is a diagram showing the operating characteristics of the filter circuit 100.

[0016] Figure 5 This is a diagram showing the operating characteristics of the filter circuit 100.

[0017] Figure 6 This is a diagram showing a modified example of the implementation of the filter circuit 100A.

[0018] Figure 7This is a diagram showing a modified example of the implementation of the filter circuit 100B.

[0019] Figure 8 This is a diagram showing a modified example of the balanced-unbalanced switching circuit 120M.

[0020] Figure 9 This is a graph showing the frequency characteristics of the S11 parameters of the 120M balanced-to-unbalanced converter circuit.

[0021] Figure 10 This is a graph showing the frequency characteristics of the S11 parameters of the 120M balanced-to-unbalanced converter circuit.

[0022] Figure 11 This is a diagram showing a modified example of the filter circuit 100C of the implementation method.

[0023] Figure 12 This is a diagram showing a modified example of the implementation of the filter circuit 100D.

[0024] Figure 13 This is a graph representing the frequency characteristics of the S11 and S21 parameters of the first simulation model.

[0025] Figure 14 This is a graph representing the frequency characteristics of the S11 and S21 parameters of the second simulation model.

[0026] Explanation of reference numerals in the attached figures

[0027] 10: Substrate

[0028] 100, 100A, 100B, 100C, 100D: Filter circuits

[0029] 110, 110M: Branch line coupler

[0030] 110A, 110B, 110C, 110D: Conductor circuits

[0031] 111, 112, 113, 114, 115, 116, 117, 118: terminals

[0032] 120, 120A, 120B, 120C, 120D, 120M, 120MA, 120MB: Balanced-to-Unbalanced Conversion Circuits

[0033] 120IN: Input terminal

[0034] 121, 122, 123, 124: Transmission lines

[0035] 130: Line. Detailed Implementation

[0036] The implementation method will be described below.

[0037] [Description of embodiments of this disclosure]

[0038] [1] A filtering circuit according to one embodiment of the present disclosure includes: a first branch line coupler having a first terminal, a second terminal, a third terminal, and a fourth terminal sequentially connected by a loop-shaped first conductor line, wherein the first terminal is used as a first input port and the fourth terminal is used as a first output port; and a first balun circuit connected to either the second terminal or the third terminal, the first balun circuit having: a first input terminal connected to either the second terminal or the third terminal for inputting a high-frequency signal; and a first transmission line having one end connected to the first input terminal and having a first electrical length corresponding to the frequency of the high-frequency signal. A first transmission line having a length of one-quarter; a second transmission line having one end connected to the first input terminal and having a length equivalent to one-quarter of the first electrical length; a third transmission line having one end connected to the other end of the second transmission line and having a length equivalent to one-quarter of the first electrical length; and a fourth transmission line having one end connected to the other end of the third transmission line and electromagnetically coupled to the first transmission line, having a length equivalent to one-quarter of the first electrical length, wherein the other ends of the first transmission line and the other ends of the fourth transmission line are both connected to ground, or both are set to open circuit, or are respectively connected to two terminating resistors having equal resistance values.

[0039] In a filtering circuit of one embodiment of this disclosure, the signal at one end of the first transmission line of a first balanced-to-unbalanced converter circuit connected to either the second or third terminal of the first branch line coupler is 180 degrees out of phase with the signal at one end of the fourth transmission line. Therefore, reflection of the signal at the first input terminal of the first balanced-to-unbalanced converter circuit is effectively suppressed. Consequently, the reflection coefficient of the high-frequency signal transmitted in the first branch line coupler at a frequency equal to a quarter wavelength of the lengths of the first and fourth transmission lines can be effectively suppressed and removed from the high-frequency signal transmitted in the first conductor line of the first branch line coupler. Therefore, a filtering circuit capable of suppressing reflection of signals at a desired frequency can be provided.

[0040] [2] In [1], the first conductor line of the first branch line coupler is a rectangular loop conductor line, and the first terminal, the second terminal, the third terminal, and the fourth terminal are connected to the corners of the rectangular loop first conductor line. Since the first conductor line is a rectangular loop, the line length and line width are easily set, and the impedance of the first branch line coupler is easily set. Therefore, a filter circuit that allows for easy setting of the impedance of the first branch line coupler and suppresses reflections of signals at the desired frequency can be provided.

[0041] [3] In either [1] or [2], the first balun circuit may be disposed within the region enclosed by the first conductor line. By disposing the first balun circuit within the region enclosed by the first conductor line, miniaturization can be achieved. Therefore, a filter circuit that can be miniaturized and suppress reflections of signals at a desired frequency can be provided.

[0042] [4] It can be that, in any of [1] to [3], the lengths of the first transmission line, the second transmission line, the third transmission line, and the fourth transmission line are equal to each other. By making the lengths of the first to fourth transmission lines equal, the frequency characteristics of the first to fourth transmission lines are identical, which can more effectively suppress the reflection coefficient in the frequency band where the lengths of the first to fourth transmission lines are a quarter wavelength, and remove it from the high-frequency signals transmitted in the conductor lines of the branch line coupler. Therefore, a filter circuit that can more effectively suppress the reflection of signals at the desired frequency can be provided.

[0043] [5] May be any of [1] to [3], wherein the lengths of the first transmission line and the fourth transmission line are equal, the lengths of the second transmission line and the third transmission line are equal, and the lengths of the first transmission line and the fourth transmission line are different from the lengths of the second transmission line and the third transmission line. By creating a difference in length between the first and fourth transmission lines and the second and third transmission lines, a deviation is generated in the frequency characteristics of the first and fourth transmission lines compared to the second and third transmission lines, thus widening the frequency band at which reflections can be suppressed by the first balanced-to-unbalanced converter circuit. Therefore, a filter circuit capable of suppressing reflections of signals at a desired frequency over a wider frequency band can be provided.

[0044] [6] May be any one of [1] to [5], in which the first transmission line and the fourth transmission line extend close to and parallel to each other. By extending the first transmission line and the fourth transmission line close to and parallel to each other, stronger electromagnetic coupling between the first transmission line and the fourth transmission line can be obtained, and the reflection coefficient in the frequency band of a quarter wavelength of the length from the first transmission line to the fourth transmission line can be more effectively suppressed and removed from high-frequency signals transmitted in the conductor lines of the branch line coupler. Therefore, a filter circuit that can more effectively suppress the reflection of signals at the desired frequency can be provided.

[0045] [7] In any of [1] to [6], the filter circuit further includes: a second balun circuit connected to either the second terminal or the third terminal, the second balun circuit having: a second input terminal connected to either the second terminal or the third terminal for inputting the high-frequency signal; a fifth transmission line having one end connected to the second input terminal and having a length equivalent to one-quarter of the electrical length at the frequency of the high-frequency signal; a sixth transmission line having one end connected to the second input terminal and having a length equivalent to one-quarter of the electrical length; a seventh transmission line having one end connected to the other end of the sixth transmission line and having a length equivalent to one-quarter of the electrical length; and an eighth transmission line having one end connected to the other end of the seventh transmission line and electromagnetically coupled to the fifth transmission line, having a length equivalent to one-quarter of the electrical length, the other ends of the fifth transmission line and the other ends of the eighth transmission line being connected to ground, or both being open circuits, or respectively connected to two terminating resistors having equal resistance values.

[0046] The signal at one end of the fifth transmission line of the second balun (balanced-to-unbalanced) converter circuit, which is connected to either the second or third terminal of the first branch line coupler, is 180 degrees out of phase with the signal at one end of the eighth transmission line. Therefore, reflection of the signal at the second input terminal of the second balun (balanced-to-unbalanced) converter circuit is effectively suppressed. Thus, reflection of signals with frequencies equal to a quarter wavelength of the lengths of the first, fourth, fifth, and eighth transmission lines in the high-frequency signal transmitted in the first branch line coupler can be effectively suppressed at both the second and third terminals, and removed from the high-frequency signal transmitted in the first conductor line of the first branch line coupler. Therefore, a filter circuit that can more effectively suppress reflections of signals at desired frequencies can be provided.

[0047] [8] In any of [1] to [6], the filter circuit further includes: a second branch line coupler having a fifth terminal, a sixth terminal, a seventh terminal, and an eighth terminal connected sequentially by a loop-shaped second conductor line, with the fifth terminal serving as a second input port and the eighth terminal serving as a second output port; and a second balun converter circuit connected to either the sixth terminal or the seventh terminal, the second balun converter circuit having: a second input terminal connected to either the sixth terminal or the seventh terminal for inputting a high-frequency signal transmitted by the second branch line coupler; and a fifth transmission line having one end connected to the second input terminal and having a function equivalent to being coupled by the second branch line. The transmission line has a length equal to one-quarter of the second electrical length at the frequency of the high-frequency signal transmitted by the device; a sixth transmission line has one end connected to the second input terminal and has a length equivalent to one-quarter of the second electrical length; a seventh transmission line has one end connected to the other end of the sixth transmission line and has a length equivalent to one-quarter of the second electrical length; and an eighth transmission line has one end connected to the other end of the seventh transmission line and electromagnetically coupled to the fifth transmission line, having a length equivalent to one-quarter of the second electrical length, wherein the other ends of the fifth transmission line and the other ends of the eighth transmission line are both connected to ground, or both are set to open circuit, or are respectively connected to two terminating resistors having equal resistance values.

[0048] The filter circuit also includes a second branch-line coupler identical to the first branch-line coupler and a second balun circuit identical to the first balun circuit. This effectively suppresses the reflection coefficient of the high-frequency signal transmitted in the first and second conductor lines of the two branch-line couplers at frequencies corresponding to the first and second balun circuits, and removes it from the high-frequency signal transmitted in the first conductor line of the first branch-line coupler. Therefore, a filter circuit capable of suppressing reflections of signals at desired frequencies in the two branch-line couplers can be provided.

[0049] [9] It may be that, in [8], the length of the first conductor line of the first branch line coupler is different from the length of the second conductor line of the second branch line coupler, the length of the first transmission line and the fourth transmission line of the first balun converter is different from the length of the fifth transmission line and the eighth transmission line of the second balun converter, and the length of the second transmission line and the third transmission line of the first balun converter is different from the length of the sixth transmission line and the seventh transmission line of the second balun converter.

[0050] Because the first and second branch-line couplers have different sizes, and the first and second baluns have different sizes, the reflection coefficient of the high-frequency signal transmitted through the first branch-line coupler at the frequency corresponding to the first baluns, and the reflection coefficient of the high-frequency signal transmitted through the second branch-line coupler at the frequency corresponding to the second baluns, can be suppressed. Therefore, a filter circuit that can suppress the reflection of signals at desired frequencies that are different from each other in the two branch-line couplers can be provided.

[0051]

[10] One embodiment of the balanced-unbalanced converter circuit of this disclosure may include: an input terminal for a high-frequency signal input; a first transmission line having one end connected to the input terminal and having a length equivalent to one-quarter of the electrical length at the frequency of the high-frequency signal; a second transmission line having one end connected to the input terminal and having a length equivalent to one-quarter of the electrical length; a third transmission line having one end connected to the other end of the second transmission line and having a length equivalent to one-quarter of the electrical length; and a fourth transmission line having one end connected to the other end of the third transmission line and electromagnetically coupled to the first transmission line, having a length equivalent to one-quarter of the electrical length, wherein the other ends of the first transmission line and the other ends of the fourth transmission line are both connected to ground, or both are set to open circuit, or are respectively connected to two terminating resistors having equal resistance values.

[0052] In one embodiment of the balanced-to-unbalanced converter circuit disclosed herein, the signal at one end of the first transmission line is 180 degrees out of phase with the signal at one end of the fourth transmission line. Therefore, signal reflection at the input terminals of the balanced-to-unbalanced converter circuit is effectively suppressed. Consequently, the reflection coefficient of a specific frequency in the high-frequency signal corresponding to the lengths of the first and fourth transmission lines can be effectively suppressed. Thus, a balanced-to-unbalanced converter circuit capable of suppressing reflections of signals at a desired frequency can be provided.

[0053] [Details of the embodiments of this disclosure]

[0054] The embodiments of this disclosure will now be described in detail, but these embodiments are not limited thereto. It should be noted that in this specification and drawings, sometimes repeated descriptions are omitted by labeling constituent elements that have substantially the same functional configuration with the same reference numerals.

[0055] <Implementation Method>

[0056] [The configuration of filter circuit 100]

[0057] Figure 1 This is a diagram illustrating an example of the filter circuit 100 in the implementation method. Hereinafter, the XYZ coordinate system will be defined for explanation. Furthermore, in the following explanation, "top view" refers to viewing the XY plane. For ease of explanation, the -Z direction side will be referred to as the lower side or "down," and the +Z direction side will be referred to as the upper side or "up," but this does not represent a general vertical relationship.

[0058] The filter circuit 100 includes a substrate 10, a branch line coupler 110, and two baluns 120A and 120B. Baluns 120A and 120B are examples of a first balun and a second balun, respectively. Hereinafter, unless otherwise specified, the two baluns 120A and 120B will simply be referred to as balun 120. Furthermore, for balun 120, in addition to using… Figure 1 In addition to using Figure 2 Please provide an explanation. Figure 2 This is a diagram representing the balanced-to-unbalanced converter circuit 120.

[0059] [Structure of substrate 10]

[0060] As an example, substrate 10 is an FR4 (Flame Retardant type 4) wiring substrate. A branch line coupler 110 and two baluns (120A, 120B) are provided on the upper surface of substrate 10. As an example, the branch line coupler 110 is formed with a metallic pattern on the surface of substrate 10, and the two baluns (120A, 120B) are chip components mounted on the surface of substrate 10. In addition to the branch line coupler 110 and the two baluns (120A, 120B), as an example, high-frequency circuitry for processing high-frequency signals may also be mounted on substrate 10. As an example, the frequency of the high-frequency signal is 5GHz to 40GHz, which falls within the millimeter-wave band.

[0061] [The structure and operation of the branch line coupler 110]

[0062] Branch line coupler 110 is a four-terminal circuit having conductor lines 110A, 110B, 110C, 110D and terminals 111, 112, 113, 114. Conductor lines 110A to 110D are an example of the first conductor lines connected in a rectangular loop when viewed from above. Terminals 111, 112, 113, and 114 are examples of the first, second, third, and fourth terminals, respectively, and are connected sequentially by conductor lines 110A to 110D when viewed from above. It should be noted that conductor lines 110A to 110D can also be in shapes other than a rectangular loop (e.g., a circular loop).

[0063] Terminal 111 is an input port, and terminal 114 is an output port. Terminal 112 is connected to the input terminal 120IN of the balun 120A, and terminal 113 is connected to the input terminal 120IN of the balun 120B. Terminal 111, as an input port, and terminal 114, as an output port, are connected to high-frequency circuits or the like outside the filter circuit 100. High-frequency signals are input from terminal 111, and high-frequency signals that have undergone filtering by the filter circuit 100 are output from terminal 114.

[0064] As an example, conductor lines 110A to 110D are implemented using microstrip lines. The microstrip lines are implemented using metal lines, such as copper foil, patterned on the surface (upper surface) of the substrate 10, and ground layers on the inner or lower surface of the substrate 10. Here, the metal lines, such as copper foil, patterned on the surface (upper surface) of the substrate 10, are represented as conductor lines 110A to 110D. Furthermore, to facilitate understanding of the configuration of the branch line coupler 110, terminals 111 to 114 are represented as extending from the corners of conductor lines 110A to 110D. However, terminals 111 to 114 can be located at the corners of conductor lines 110A to 110D, or they can be extended; either is acceptable. In the case of extensions, microstrip lines or the like can be used.

[0065] Conductor lines 110A to 110D have an electrical length λe1 that is equivalent to 1 / 4 of the wavelength at the design frequency f1 (transmission suppression frequency) of the branch line coupler 110. The lengths of conductor lines 110A to 110D are equal. Here, "equivalent to 1 / 4 of the electrical length λe1" means not only λe1 / 4, but also includes lengths slightly shorter or slightly longer than λe1 / 4 considering impedance matching, etc.

[0066] Furthermore, the line widths of face-to-face conductor lines 110A and 110C are equal, as are those of face-to-face conductor lines 110B and 110D. However, the line widths can differ between conductor lines 110A and 110C, and between conductor lines 110B and 110D. This is to adjust the impedance. It should be noted that the line width refers to the width along the length of the rectangular loop extending from conductor lines 110A to 110D.

[0067] In such a branch-line coupler 110, the difference between the path length traversed from conductor lines 110A, 110B, and 110C and the path length traversed only from conductor line 110D between terminals 111 and 114 is λe1 / 2. Therefore, the signal traversed from conductor lines 110A, 110B, and 110C and the signal traversed only from conductor line 110D are transmitted to terminal 114 with a phase difference of 180 degrees.

[0068] When a signal containing the frequency band of frequency f1 is input to terminal 111 without the balun circuits 120A and 120B connected to terminals 112 and 113 respectively, the signal containing frequency f1 and the frequency band near frequency f1 centered on frequency f1 (hereinafter referred to as the frequency band of frequency f1) is canceled out in the paths traversed by conductor lines 110A, 110B, 110C and traversed by conductor line 110D. As a result, a signal with the signal level of the frequency band of frequency f1 in the input signal's frequency band is suppressed and output from terminal 114. That is, the branch line coupler 110 suppresses the transmission of signals in the frequency band of frequency f1 by design.

[0069] [The structure and operation of the balanced-to-unbalanced converter circuit 120]

[0070] like Figure 2 As shown, the balun circuit 120 has an input terminal 120IN and transmission lines 121, 122, 123, and 124. Input terminal 120IN is an example of a first input terminal. Transmission lines 121, 122, 123, and 124 are examples of a first transmission line, a second transmission line, a third transmission line, and a fourth transmission line, respectively. As an example, the balun circuit 120 is a chip formed on a GaAs (gallium arsenide) substrate and mounted on the surface of the substrate 10 in a flip-chip configuration. It should be noted that... Figure 1 The internal representation of the balanced-unbalanced conversion circuits 120A and 120B in the chip represents the connection relationship of the transmission lines 121, 122, 123, and 124 within the chip, rather than representing the extension direction of the transmission lines 121, 122, 123, and 124 in the XYZ coordinate system.

[0071] The balun circuit 120 is a circuit that suppresses the reflection of a desired frequency f0 in the frequency band of the signal input to the input terminal 120IN. In other words, the balun circuit 120 is a circuit that absorbs the desired frequency f0 in the frequency band of the signal input to the input terminal 120IN. Therefore, the balun circuit 120 can also be understood as a reflection suppression circuit or an absorption circuit.

[0072] Transmission lines 121 to 124 each have a length equivalent to 1 / 4 of the electrical length λe0 at the desired frequency f0. Here, "equivalent to 1 / 4 of the electrical length λe0" means not only λe0 / 4, but also includes lengths slightly shorter or slightly longer than λe0 / 4 considering impedance matching, etc. As an example, transmission lines 121 to 124 have the same length.

[0073] Furthermore, the line widths of transmission lines 121 to 124 can be set to an appropriate width considering impedance, etc. However, from the perspective of circuit symmetry, it is preferable that the line widths of transmission lines 121 and 124 are equal, and the line widths of transmission lines 122 and 123 are equal. Here, as an example, it is assumed that the line widths of transmission lines 121 to 124 are all equal.

[0074] Transmission lines 121 to 124 extend parallel to each other. One end of transmission line 121 is connected to input terminal 120IN, and the other end is connected to GND (ground). One end of transmission line 122 is connected to input terminal 120IN, and the other end is connected to one end of transmission line 123. Transmission line 122 is positioned next to transmission line 121.

[0075] Transmission line 123 is positioned next to transmission line 124, with its other end connected to one end of transmission line 124. Transmission line 124 is positioned next to transmission line 121, close to transmission line 121 in a manner that allows for a certain degree of electromagnetic coupling, and extends parallel to transmission line 121. The other end of transmission line 124 is connected to GND (ground).

[0076] Transmission line 124 is connected to the input terminal via transmission lines 122 and 123. The lengths of transmission lines 122 and 123 are λe0 / 2, therefore, signals with a 180-degree phase difference appear at the desired frequency f0 at one end of transmission line 121 and one end of transmission line 124. For example... Figure 2 As shown, when the signal at one end of transmission line 121 is set to 0 degrees, the phase of the signal at one end of transmission line 124 is 180 degrees.

[0077] Therefore, transmission lines 121 and 124 transmit signals that are 180 degrees out of phase with each other. Furthermore, since transmission lines 121 and 124 are configured close together to achieve a certain level of electromagnetic coupling, the signals transmitted by transmission lines 121 and 124 are combined. Because the signals with a 180-degree phase difference are combined, the signals transmitted by transmission lines 121 and 124 cancel each other out. As a result, the desired frequency f0 signal is not reflected to input terminal 120IN. More specifically, the signal level of the desired frequency f0 signal reflected to input terminal 120IN is very low, and the reflection is suppressed to become essentially equivalent to no reflection. In other words, the desired frequency f0 signal in the signal input to input terminal 120IN is absorbed by the balun circuit 120 and is not output from input terminal 120IN.

[0078] Therefore, if the impedance of the balun circuit 120 as seen from the input terminal 120IN is, for example, 50Ω, the balun circuit 120 can be considered essentially the same as a 50Ω terminating resistor for the desired frequency f0. The proximity of transmission lines 121 and 124 refers to the degree to which the electromagnetic coupling is strong enough that the signals transmitted by transmission lines 121 and 124 are combined. It should be noted that, here, a circuit configuration is shown where the other ends of transmission lines 121 and 124 are both connected to GND (ground), but it is also possible for the other ends of transmission lines 121 and 124 to be both open circuits, or for the other ends of transmission lines 121 and 124 to be connected to two terminating resistors with equal resistance values. That is, the other ends of transmission lines 121 and 124 can be terminated in the same state. As an example, any one of the following is acceptable: both connected to GND, both open circuits, or each connected to two terminating resistors with equal resistance values.

[0079] In addition, Figure 2 The circuit shown is called a balanced-to-unbalanced converter circuit 120 because: when the signal at one end of transmission line 121 (the end on the +X direction side) is set to 0 degrees, the signal at one end of transmission line 124 (the end on the +X direction side) has a phase of 180 degrees. Internally, signals with phases of 0 degrees and 180 degrees are generated, which can be understood as a general balanced-to-unbalanced converter. The balanced-to-unbalanced converter circuit 120 in this embodiment has… Figure 2 The configuration shown and the features described above are sufficient; it is not necessary to have the characteristics required by a typical balun.

[0080] [S11 parameters of the balanced-to-unbalanced converter circuit 120]

[0081] Figure 3This is a graph showing the frequency response of the S11 parameter (reflection coefficient) of the balun 120. The frequency response of the S11 parameter was calculated in a circuit simulator with input terminal 120IN as port 1. Figure 3 In the diagram, the horizontal axis represents frequency (GHz), and the vertical axis represents the S11 parameter (dB). Here, as an example, the desired frequency f0 is 22GHz.

[0082] like Figure 3 As shown, a very low S11 parameter value was obtained in the frequency band centered at the desired frequency f0. The S11 parameter value at the desired frequency f0 is approximately 0.05 dB, and a good value below 0.8 dB was obtained in a wide bandwidth from approximately 17 GHz to approximately 28 GHz. Figure 3 The simulation results confirm that the balanced-to-unbalanced converter circuit 120 can suppress the reflection of the signal at the desired frequency f0.

[0083] [Operating characteristics of filter circuit 100]

[0084] Figure 4 and Figure 5 This is a diagram showing the operating characteristics of the filter circuit 100. Figure 4 This represents the frequency response of parameter S11. Figure 5 The frequency characteristics of parameter S21 are represented. Here, the lengths of the conductor lines 110A to 110D of the branch line coupler 110 and the lengths of the transmission lines 121 to 124 of the balun circuits 120A and 120B are explained as follows: The lengths of conductor lines 110A to 110D are each one-quarter of the electrical length λe1 when the frequency f1 is 15 GHz. Furthermore, the lengths of transmission lines 121 to 124 are each one-quarter of the electrical length λe0 when the desired frequency f0 is 20 GHz.

[0085] Furthermore, the S11 parameter of the filter circuit 100 is calculated by setting terminal 111 of the branch line coupler 110 as port 1 and using a circuit simulator. Furthermore, the S21 parameter of the filter circuit 100 is calculated by setting terminal 111 of the branch line coupler 110 as port 1 and terminal 114 as port 2 and using a circuit simulator.

[0086] like Figure 4 As shown, regarding the S11 parameters, characteristics of less than -20dB in the frequency band from approximately 18GHz to approximately 22GHz and less than -10dB in the frequency band from approximately 16GHz to approximately 25GHz were obtained, and characteristics of suppressed reflection at around 20GHz were also obtained. Furthermore, as... Figure 5As shown, with regard to the S21 parameter, the characteristic of achieving a transmission suppression of less than -10dB is obtained in the frequency bands of approximately 11 GHz to approximately 16 GHz, approximately 18 GHz to approximately 20 GHz, and approximately 28 GHz to approximately 30 GHz.

[0087] As described above, the desired frequency f0 of the balun circuits 120A and 120B is set to 20 GHz, and the frequency f1 of the branch line coupler 110 is set to 15 GHz. Therefore, it can be inferred that the main reason for the decrease in the value of parameter S11 around 20 GHz is that reflections at the input terminals 120IN of the balun circuits 120A and 120B are suppressed, and the frequency band component around 20 GHz in the signal transmitted by the branch line coupler 110 is absorbed by the balun circuits 120A and 120B. As a result, the value of parameter S21 around 20 GHz will decrease, and the frequency band around 20 GHz in the signal transmitted from terminal 111 to terminal 114 of the branch line coupler 110 will not be transmitted.

[0088] Furthermore, the low value of the S21 parameter at around 15 GHz can be attributed to the fact that, since it falls within the frequency band of the branch line coupler 110's frequency f1, the signal is canceled out in the paths traversed by conductor lines 110A, 110B, 110C, and traversed by conductor line 110D. Similarly, the low value of the S21 parameter at around 30 GHz can be attributed to the fact that, since it falls within the frequency band of the second harmonic of the branch line coupler 110's frequency f1, the signal is canceled out in the paths traversed by conductor lines 110A, 110B, 110C, and traversed by conductor line 110D.

[0089] As described above, it can be confirmed that by connecting the balun circuits 120A and 120B to terminals 112 and 113 of the branch line coupler 110, respectively, a frequency band of approximately 20 GHz in the signal transmitted by the branch line coupler 110 can be removed. This is because the balun circuits 120A and 120B suppress the reflection of signals in the desired frequency band f0 at the input terminal 120IN. Thus, the balun circuit 120 absorbs signals in the desired frequency band f0, thereby suppressing the reflection of signals in the desired frequency band f0 in the branch line coupler 110, and also suppressing transmission.

[0090] Therefore, a filter circuit 100 and a balun circuit 120 can be provided to suppress reflections of signals at the desired frequency. Furthermore, a filter circuit 100 and a balun circuit 120 can be provided to suppress transmissions of signals at the desired frequency. By adjusting the lengths of the transmission lines 121 to 124 of the balun circuit 120, the desired frequency f0 can be removed from the signal transmitted by the branch line coupler 110.

[0091] Furthermore, when it is desired to divide the frequency band of the signal transmitted by the branch line coupler 110, it is sufficient to divide it so that the desired frequency f0 is included in the non-transmittable frequency band. If this is done, the frequency band of the signal transmitted by the branch line coupler 110 can be divided into the frequency band of the desired frequency f0. This is particularly suitable for applications where interference between adjacent frequency bands is to be suppressed.

[0092] Furthermore, since the two baluns 120A and 120B are connected to terminals 112 and 113 of the branch line coupler 110, which has a symmetrical circuit configuration, the overall circuit is well balanced. The desired frequency f0 can be removed from the signal transmitted by the branch line coupler 110 through the two baluns 120A and 120B, and the reflection of the desired frequency f0 signal can be suppressed more effectively.

[0093] Furthermore, since the conductor lines 110A to 110D of the branch line coupler 110 are rectangular loops, it is easy to set the line length and line width, and it is easy to set the impedance of the branch line coupler 110.

[0094] Furthermore, since the transmission lines 121 to 124 of the balun 120 are of equal length, the reflection coefficient in the desired frequency band of the transmission line 121 to 124, which is a quarter wavelength in length, can be suppressed more effectively and removed from the high-frequency signals transmitted in the conductor lines 110A to 110D of the branch line coupler 110.

[0095] Furthermore, since the transmission lines 121 and 124 of the balun circuit 120 extend close to and parallel to each other, stronger electromagnetic coupling can be achieved, and the signals transmitted by the transmission lines 121 and 124 are combined with each other. Therefore, the reflection coefficient in the desired frequency band of a quarter wavelength of the length of the transmission lines 121 to 124 can be suppressed more effectively, and removed from high-frequency signals transmitted in the conductor lines 110A to 110D of the branch line coupler 110.

[0096] It should be noted that the above description illustrates the scheme of connecting the balun 120 to the branch line coupler 110 to construct the filter circuit 100. However, the balun 120 can also be connected to circuits other than the branch line coupler 110. That is, the application of the balun 120 is not limited to the filter circuit 100. If the balun 120 is connected to a circuit other than the branch line coupler 110, it can absorb signals in the desired frequency band f0 from the connected circuit. Absorbing signals in the desired frequency band f0 means suppressing the reflection of the desired frequency band f0 to the outside of the balun 120.

[0097] Furthermore, the above describes the scheme of connecting the balun circuits 120A and 120B to terminals 112 and 113 of the branch line coupler 110, respectively. However, the filter circuit 100 may also be configured to include a balun circuit 120.

[0098] [Composition of filter circuits 100A and 100B]

[0099] Figure 6 and Figure 7 These are diagrams showing filter circuits 100A and 100B, respectively, of modified embodiments of the implementation. For example, as... Figure 6 As shown, it can also be a filter circuit 100A formed by connecting the balun circuit 120 to terminal 112 of the branch line coupler 110. Furthermore, as... Figure 7 As shown, a filter circuit 100B can also be formed by connecting the balun 120 to terminal 113 of the branch line coupler 110. In such filter circuits 100A and 100B, the balun 120 also absorbs signals in the frequency band of the desired frequency f0 from the signal transmitted by the branch line coupler 110. Therefore, filter circuits 100A and 100B can provide filtering circuits that can suppress reflections of signals at the desired frequency.

[0100] [Construction and frequency characteristics of a 120MHz balanced-to-unbalanced converter circuit]

[0101] Furthermore, the above describes a scheme where the transmission lines 121 to 124 of the balun 120 have equal lengths, but the lengths can also be different. Figure 8 This is a diagram illustrating a modified embodiment of the balancing-unbalancing converter circuit 120M. The balancing-unbalancing converter circuit 120M differs from the circuit in that the lengths of transmission lines 121 and 124 are longer than the lengths of transmission lines 122 and 123. Figure 2The balun circuit 120 shown is different. It should be noted that the transmission lines 121 and 124 are of equal length, and the transmission lines 122 and 123 are of equal length.

[0102] Figure 9 This is a graph showing the frequency characteristics of the S11 parameters of the 120M balanced-to-unbalanced converter circuit. Figure 10 This is a graph showing the frequency response of the S11 parameters of a 120MHz balanced-to-unbalanced converter circuit. As an example, Figure 9 This refers to the frequency characteristics of the S11 parameters calculated using a circuit simulator, where the lengths of transmission lines 121 and 124 are set to 1 / 4 of their electrical length at 20 GHz, and the lengths of transmission lines 122 and 123 are set to 1 / 4 of their electrical length at 26 GHz. As an example, Figure 10 This indicates the frequency characteristics of the S11 parameters calculated using a circuit simulator, where the length of transmission lines 121 to 124 is set to 1 / 4 of the electrical length at 20 GHz.

[0103] If Figure 9 and Figure 10 By comparison, we can see that: with Figure 10 In comparison, Figure 9 In this circuit, the minimum value of parameter S11 is given at a frequency offset of approximately 22 GHz, and the value of parameter S11 becomes a slightly wider bandwidth below -10 dB. The configuration where the lengths of transmission lines 121 and 124 in the balun circuit 120M are longer than the lengths of transmission lines 122 and 123 is achieved by shortening transmission lines 122 and 123 compared to the balun circuit 120.

[0104] It is conceivable that in the balun 120M, by shifting the transmission loss generated in transmission lines 122 and 123 to the high-frequency side by 3 GHz, a wideband can be achieved, and the frequency at which the minimum value of parameter S11 is given is shifted. Thus, by configuring the lengths of transmission lines 121 and 124 in the balun 120M to be longer than the lengths of transmission lines 122 and 123, a balun 120M that achieves a wideband with a frequency band that suppresses reflections can be obtained. It is conceivable that if such a balun 120M is used to replace... Figure 1 The balanced-to-unbalanced converter circuits 120A and 120B also widen the bandwidth of the signal output from terminal 114 of the branch line coupler 110, which is around 22 GHz where transmission is suppressed.

[0105] [Composition of filter circuit 100C]

[0106] Furthermore, the above describes the arrangement of the balun circuits 120A and 120B on the outside of the branch line coupler 110, but the balun circuits 120A and 120B can also be arranged on the inside of the branch line coupler 110. Figure 11 This is a diagram showing a modified example of the filter circuit 100C of the implementation method.

[0107] The filter circuit 100C includes a substrate 10, a branch line coupler 110, and baluns 120MA and 120MB. The baluns 120MA and 120MB are disposed on the upper surface of the substrate 10 inside the rectangular area enclosed by the conductor lines 110A to 110D of the branch line coupler 110.

[0108] The input terminals 120IN of the baluns 120MA and 120MB are connected to terminals 112 and 113, respectively. The circuit configurations of the baluns 120MA and 120MB are the same; therefore, the balun 120MA will be described here.

[0109] The connection relationship and length of the 120mA transmission lines 121-124 of the balun-to-unbalance converter circuit are related to... Figure 2 The transmission lines 121 to 124 of the balun 120A shown have the same connection relationship and length, but for miniaturization, the transmission lines 121 to 124 of the balun 120MA are bent. Transmission line 121 extends in a rectangular spiral at the center of the balun 120MA. Transmission lines 122 and 123 extend along the end edges of the balun 120MA. Transmission line 124 extends in a rectangular spiral along transmission line 121. It should be noted that the part shown by the dashed line is the intersection of transmission lines 121 and 124, which is disposed in the inner layer of the substrate of the chip of the balun 120MA.

[0110] If the miniaturized balanced-to-unbalanced converter circuits 120MA and 120MB are arranged inside the rectangular area enclosed by the conductor lines 110A to 110D of the branch line coupler 110, a filter circuit 100C that can suppress the reflection of signals of the desired frequency and achieves miniaturization can be provided.

[0111] [Construction of filter circuit 100D]

[0112] Figure 12This is a diagram showing a modified example of a filter circuit 100D. The filter circuit 100D includes a substrate 10, branch line couplers 110 and 110M, balun circuits 120A, 120B, 120C, and 120D, and a line 130. The branch line coupler 110 and the balun circuits 120A and 120B are connected to... Figure 1 The same as shown. Branch line coupler 110M has terminals 115, 116, 117, 118 and four conductor lines identical to the conductor lines 110A-110D of branch line coupler 110 (in... Figure 12 (Figure reference numerals omitted). The balun circuits 120C and 120D have the same four transmission lines 121-124 as the balun circuits 120A and 120B (in... Figure 12 (The reference numerals in the accompanying drawings are omitted).

[0113] Branch line coupler 110 is an example of a first branch line coupler, and branch line coupler 110M is an example of a second branch line coupler. The four conductor lines of branch line coupler 110M are an example of the second conductor lines. Terminals 115, 116, 117, and 118 are examples of the fifth, sixth, seventh, and eighth terminals, respectively. Balanced-to-unbalanced converter circuits 120A and 120B are examples of a first balanced-to-unbalanced converter circuit, and balanced-to-unbalanced converter circuits 120C and 120D are examples of a second balanced-to-unbalanced converter circuit. The four transmission lines of balanced-to-unbalanced converter circuits 120C and 120D are examples of the fifth, sixth, seventh, and eighth transmission lines, respectively.

[0114] Terminal 115 of branch line coupler 110M is connected to terminal 114 of branch line coupler 110 via line 130. The input terminals 120IN of baluns and baluns circuits 120C and 120D are connected to terminals 116 and 117, respectively. It should be noted that, as an example, line 130 is a microstrip line.

[0115] The dimensions of branch line coupler 110M differ from those of branch line coupler 110. Branch line coupler 110M is smaller than branch line coupler 110, and its designed frequency f2 is higher than that of branch line coupler 110. Furthermore, the dimensions of balun circuits 120C and 120D differ from those of balun circuits 120A and 120B. The lengths of the four transmission lines in balun circuits 120C and 120D are shorter than the lengths of transmission lines 121 to 124 in balun circuits 120A and 120B. Therefore, the desired frequency f3 of balun circuits 120C and 120D is higher than that of balun circuits 120A and 120B.

[0116] In such a filter circuit 100D, the desired frequency band of the signal input to the branch line coupler 110 is absorbed by the balun circuits 120A and 120B, and the signal in the frequency band of f1 is canceled at the branch line coupler 110. Furthermore, the desired frequency band of the signal input from the branch line coupler 110 to the branch line coupler 110M via line 130 is absorbed by the balun circuits 120C and 120D, and the signal in the frequency band of f2 is canceled at the branch line coupler 110M. As a result, the signal after removing the frequency bands of f0, f1, f2, and f3 from the signal input to the branch line coupler 110 is output from terminal 118 of the branch line coupler 110M.

[0117] If two branch line couplers 110 and 110M, and baluns 120A and 120B and baluns 120C and 120D connected to the branch line couplers 110 and 110M respectively, are used to set the frequencies f0, f1, f2 and f3, then the high-frequency signal can be divided into five frequency bands.

[0118] Furthermore, the branch line couplers 110 and 110M have different sizes, as do the baluns 120A and 120B and the baluns 120C and 120D. Therefore, the reflection coefficient of the high-frequency signal transmitted by the branch line coupler 110 at frequencies corresponding to those of the baluns 120A and 120B can be suppressed, and the reflection coefficient of the high-frequency signal transmitted by the branch line coupler 110M at frequencies corresponding to those of the baluns 120C and 120D can also be suppressed. Thus, a filter circuit 100D can be provided that can suppress the reflection of signals at desired frequencies that are different from each other in the two branch line couplers 110 and 110M.

[0119] Furthermore, the filter circuit 100D has a configuration where a small branch line coupler 110M is connected to the subsequent stage of a large branch line coupler 110, but the reverse is also possible. Here, the results of a simulation of a first simulation model in which the lengths of each part in the filter circuit 100D are set as follows are explained. The lengths of the conductor lines 110A to 110D of the branch line coupler 110 are set to 1 / 4 of the electrical length at 27 GHz. The lengths of the transmission lines 121 and 124 of the balun circuits 120A and 120B are set to 1 / 4 of the electrical length at 16.5 GHz, and the lengths of the transmission lines 122 and 123 are set to 1 / 4 of the electrical length at 30 GHz. The lengths of the four conductor lines of the branch line coupler 110M are set to 1 / 4 of the electrical length at 25 GHz. The lengths of transmission lines 121 and 124 in the balun circuits 120C and 120D are set to one-quarter of the electrical length at 14 GHz, and the lengths of transmission lines 122 and 123 are set to one-quarter of the electrical length at 26 GHz. Furthermore, to achieve overall impedance balance, 0.18 pF capacitors are inserted in series between terminal 114 and line 130, and between line 130 and terminal 115.

[0120] [Frequency characteristics of parameters S11 and S21 in the first simulation model]

[0121] Figure 13 This is a graph representing the frequency characteristics of the S11 and S21 parameters of the first simulation model. Figure 13 In the diagram, the dashed line represents the frequency characteristics of parameter S11, and the solid line represents the frequency characteristics of parameter S21.

[0122] Regarding parameter S11, it is known that reflection can be reduced to below -10dB in the frequency bands of approximately 24GHz to approximately 27GHz and approximately 29GHz to approximately 34GHz. Furthermore, regarding parameter S21, it is known that reflection is below -10dB over a wide range, and even when judged at -20dB, transmission is only observed in the frequency band of approximately 24GHz to approximately 35GHz. Thus, it can be confirmed that in the first analog model including two branch line couplers 110, 110M and four baluns 120A to 120D, reflection in the desired frequency band can be reduced, and signals in the desired frequency band can be transmitted.

[0123] [Frequency characteristics of parameters S11 and S21 in the second simulation model]

[0124] Furthermore, for the second analog model formed by connecting two of the aforementioned first analog models in series, the frequency characteristics of parameters S11 and S21 are also calculated using a circuit simulator. The series connection of the two first analog models refers to connecting terminal 118 of the first-stage first analog model to terminal 111 of the second-stage first analog model. Parameter S11 is calculated using terminal 111 of the first-stage first analog model as port 1, and parameter S21 is calculated using terminal 111 of the first-stage first analog model as port 1 and terminal 118 of the second-stage first analog model as port 2.

[0125] Figure 14 This is a graph representing the frequency characteristics of the S11 and S21 parameters of the second simulation model. Figure 14 In the diagram, the dashed line represents the frequency response of parameter S11, and the solid line represents the frequency response of parameter S21. In the second analog model, compared to the first analog model, parameter S21 is particularly improved, with the difference between the approximately 24 GHz to approximately 35 GHz band and other peak values ​​being approximately 30 dB. Thus, it can be confirmed that the second analog model, including four branch line couplers 110, 110M and four baluns 120A to 120D, can reduce reflections in the desired frequency band and increase signal transmission in the desired frequency band.

[0126] The filter circuit and balun circuit of the present invention have been described above according to exemplary embodiments. However, the present invention is not limited to the specific embodiments disclosed, and various modifications and alterations can be made without departing from the claims.

Claims

1. A filter circuit, comprising: The first branch line coupler has a first terminal, a second terminal, a third terminal and a fourth terminal connected in a loop by a first conductor line, wherein the first terminal is used as a first input port and the fourth terminal is used as a first output port; as well as A first balanced-to-unbalanced converter circuit is connected to either the second terminal or the third terminal. The first balanced-to-unbalanced converter circuit has: The first input terminal is connected to either the second terminal or the third terminal for high-frequency signal input; The first transmission line has one end connected to the first input terminal and has a length equivalent to one-quarter of the first electrical length at the frequency of the high-frequency signal; The second transmission line has one end connected to the first input terminal and has a length equivalent to one-quarter of the length of the first electrical line; The third transmission line has one end connected to the other end of the second transmission line and has a length equivalent to one-quarter of the length of the first transmission line; as well as The fourth transmission line has one end connected to the other end of the third transmission line and electromagnetically coupled to the first transmission line, and has a length equivalent to one-quarter of the length of the first transmission line. The other end of the first transmission line and the other end of the fourth transmission line are both connected to ground, or both are set to open circuit, or are respectively connected to two terminating resistors with equal resistance values. The first balanced-to-unbalanced conversion circuit is disposed within the area enclosed by the first conductor line.

2. The filter circuit according to claim 1, wherein, The first branch line coupler has a first terminal, a second terminal, a third terminal, and a fourth terminal, which are formed by sequentially connecting the first conductor lines into a rectangular ring circuit.

3. The filter circuit according to claim 1 or 2, wherein, The lengths of the first transmission line, the second transmission line, the third transmission line, and the fourth transmission line are equal.

4. The filter circuit according to claim 1 or 2, wherein, The lengths of the first transmission line and the fourth transmission line are equal, the lengths of the second transmission line and the third transmission line are equal, and the lengths of the first transmission line and the fourth transmission line are different from the lengths of the second transmission line and the third transmission line.

5. The filter circuit according to claim 1 or 2, wherein, The first transmission line and the fourth transmission line extend close to each other and parallel to each other.

6. The filter circuit according to claim 1 or 2, Also includes: A second balanced-to-unbalanced converter circuit is connected to either the second terminal or the third terminal. The second balanced-to-unbalanced converter circuit has: The second input terminal is connected to either the second terminal or the third terminal, for inputting the high-frequency signal; The fifth transmission line has one end connected to the second input terminal and has a length equivalent to one-quarter of the length of the first electrical line; The sixth transmission line has one end connected to the second input terminal and has a length equivalent to one-quarter of the length of the first electrical line; The seventh transmission line has one end connected to the other end of the sixth transmission line and has a length equivalent to one-quarter of the length of the first transmission line; as well as The eighth transmission line, having one end connected to the other end of the seventh transmission line and electromagnetically coupled to the fifth transmission line, has a length equivalent to one-quarter of the first electrical length. The other end of the fifth transmission line and the other end of the eighth transmission line are either connected to ground, or both are set to open circuit, or are respectively connected to two terminating resistors with equal resistance values.

7. The filter circuit according to claim 1 or 2, further comprising: The second branch line coupler has a fifth terminal, a sixth terminal, a seventh terminal, and an eighth terminal that are connected in a ring by a second conductor line in sequence, with the fifth terminal serving as the second input port and the eighth terminal serving as the second output port; as well as The second balanced-to-unbalanced converter circuit is connected to either the sixth terminal or the seventh terminal. The second balanced-to-unbalanced converter circuit has: The second input terminal is connected to either the sixth terminal or the seventh terminal, and is used for high-frequency signal input transmitted by the second branch line coupler; The fifth transmission line has one end connected to the second input terminal and has a length equivalent to one-quarter of the second electrical length at the frequency of the high-frequency signal transmitted by the second branch line coupler; The sixth transmission line has one end connected to the second input terminal and has a length equivalent to one-quarter of the second electrical length; The seventh transmission line has one end connected to the other end of the sixth transmission line and has a length equivalent to one-quarter of the second electrical length; as well as The eighth transmission line, having one end connected to the other end of the seventh transmission line and electromagnetically coupled to the fifth transmission line, has a length equivalent to one-quarter of the second electrical length. The other end of the fifth transmission line and the other end of the eighth transmission line are either connected to ground, or both are set to open circuit, or are respectively connected to two terminating resistors with equal resistance values.

8. The filter circuit according to claim 7, wherein, The length of the first conductor line of the first branch line coupler is different from the length of the second conductor line of the second branch line coupler. The lengths of the first and fourth transmission lines of the first balanced-to-unbalanced converter circuit are different from the lengths of the fifth and eighth transmission lines of the second balanced-to-unbalanced converter circuit. The lengths of the second and third transmission lines of the first balanced-to-unbalanced converter circuit are different from the lengths of the sixth and seventh transmission lines of the second balanced-to-unbalanced converter circuit.

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