Directional coupler

Abstract

A directional coupler according to one embodiment of the present invention comprises: a first line having both ends connected to a coupling terminal and an isolation terminal; a second line disposed on a different plane from the first line and having both ends connected to an input terminal and an output terminal; a first ground substrate disposed on the first line among the first line and the second line and grounding the first line; and a second ground substrate disposed under the second line among the first line and the second line and grounding the second line, wherein at least a portion of the first line and the second line are disposed to overlap each other, and the first ground substrate and the second ground substrate preferably have different sizes and shapes.

Description

Directional coupler

[0001] The present invention relates to a directional coupler, and more particularly, to a directional coupler capable of achieving high directivity by controlling the phase velocities of even and odd modes to be similar.

[0002] The function of a directional coupler generally used in a wireless communication base station is to detect a signal induced in a coupling line by providing a coupling line close to the main line through which the signal is transmitted in order to isolate the signal source required for diagnosis and control in a wireless communication system.

[0003] An example of how directional couplers can be used is in digital pre-distortion (DPD) technology used in base stations. In this case, the power amplifiers used in base stations use nonlinear power amplifier technology rather than linear power amplifier technology to maximize efficiency. However, nonlinear amplifiers cannot be used in mobile communication systems that require very high linearity. Therefore, linearization technology is used to input a signal that can compensate for the nonlinear characteristics of the nonlinear power amplifier of the base station. At this time, a portion of the power of the output signal of the nonlinear power amplifier of the base station is coupled to the directional coupler and fed back to the DPD system, and the DPD generates an input signal that can linearize the nonlinear power amplifier of the base station.

[0004] An ideal directional coupler should exhibit a zero value, meaning no power at the isolation terminal. However, the practical implementation of a directional coupler imposes limitations on the appearance of some power, and the inevitable reflections from the isolation terminal are transmitted to the coupling terminal, distorting the purely induced forward coupled signal. This can cause errors in forward power measurements, and if a distorted signal is input to the DPD system, it can cause fatal problems in the linearization of the base station power amplifier.

[0005] Accordingly, in general, for high directivity, the phase velocity of the even mode and the odd mode can be designed to have approximately the same value to improve directivity. However, since the difference between the characteristic impedance of the even mode of the directional coupler and the impedance of the odd mode is greater, a value indicating greater coupling can be obtained. Therefore, it is difficult to design the phase velocity of the even mode and the phase velocity of the odd mode to have the same value in order to improve coupling, and it is also difficult to obtain high directivity.

[0006] Therefore, a technology that can improve both coupling and directivity may be required.

[0007] The problem to be solved in the present invention is to provide a directional coupler that is easy to control so that the phase velocity of the even mode and the phase velocity of the odd mode have the same value.

[0008] Another problem to be solved by the present invention is to provide a highly directive directional coupler capable of achieving coupling of less than -10 dB even when two lines are placed on different layers.

[0009] A directional coupler according to one embodiment of the present invention includes a first line having both ends connected to a coupling terminal and an isolation terminal, a second line disposed on a different plane from the first line and having both ends connected to an input terminal and an output terminal, a first ground substrate disposed above the first line between the first line and the second line, and a second ground substrate disposed below the second line between the first line and the second line, wherein at least a portion of the first line and the second line are disposed to overlap each other, and it is preferable that the first ground substrate and the second ground substrate differ from each other in at least one of a size and a shape.

[0010] Furthermore, it is preferable that the device further includes a first inductor disposed between the input terminal and the second line, a second inductor disposed between the output terminal and the second line, a third inductor disposed between the isolation terminal and the first line, and a fourth inductor disposed between the coupling terminal and the first line, and at least some of the first to fourth inductors have different inductances.

[0011] Furthermore, it is preferable that at least some of the first length, which is the distance between the second line and the first inductor, the second length, which is the distance between the second line and the second inductor, the third length, which is the distance between the first line and the third inductor, and the fourth length, which is the distance between the first line and the fourth inductor, are different from each other.

[0012] Furthermore, it is preferable that the respective inductance values ​​formed by the first to fourth lengths are different from each other.

[0013] Furthermore, it is preferable that a capacitance is formed between the first inductor and the fourth inductor, and a capacitance is formed between the second inductor and the third inductor.

[0014] Furthermore, it is preferable that an area is formed between the first line and the second line that does not overlap with the first ground substrate and the second ground substrate.

[0015] Furthermore, it is preferable that the lengths of the first line and the second line are different from each other.

[0016] Furthermore, it is preferable that a capacitance is formed between the first line and the first ground substrate so that the first line and the first ground substrate are electrically connected, and that a capacitance is formed between the second line and the second ground substrate so that the second line and the second ground substrate are electrically connected.

[0017] Furthermore, it is preferable that the directional coupler further includes a mounting ground substrate disposed below the first line and having the input terminal, the output terminal, the coupling terminal, and the isolation terminal disposed on an upper surface thereof.

[0018] Furthermore, it is preferable that the first ground substrate is electrically connected to the mounting ground substrate through a via hole or a side electrode.

[0019] The present invention can achieve high directivity by designing to facilitate phase control of even and odd modes.

[0020] In addition, the directivity of the directional coupler can be further improved to achieve coupling of less than -10 dB.

[0021] Figure 1 is a drawing for explaining the characteristics of a directional coupler.

[0022] Figure 2 is a drawing for explaining a strip line directional coupler.

[0023] Figure 3 is a diagram for explaining the electric field characteristics and equivalent circuit in even mode.

[0024] Figure 4 is a diagram for explaining the electric field characteristics and equivalent circuit in odd mode.

[0025] Figure 5 is a schematic diagram of a directional coupler according to a comparative example.

[0026] Figure 6 is a perspective view of a combined directional coupler according to one embodiment of the present invention.

[0027] Figure 7 is a schematic exploded perspective view of a grounding substrate and a line of a directional coupler according to one embodiment of the present invention.

[0028] Figure 8 is an exploded perspective view of a directional coupler according to one embodiment of the present invention.

[0029] Figure 9 is a cross-sectional view of a directional coupler according to one embodiment of the present invention.

[0030] Fig. 10 is a graph for explaining the directivity of a directional coupler according to one embodiment of the present invention.

[0031] The bandpass filter of the present invention will now be described in detail with reference to the accompanying drawings. The drawings presented below are provided as examples to ensure that those skilled in the art can fully grasp the spirit of the present invention. Therefore, the present invention is not limited to the drawings presented below and may be embodied in other forms. Furthermore, like reference numerals designate like elements throughout the specification.

[0032] At this time, if there is no other definition in the technical and scientific terms used, they have the meaning commonly understood by a person of ordinary skill in the technical field to which this invention belongs, and the description of known functions and configurations that may unnecessarily obscure the gist of the present invention in the following description and attached drawings are omitted.

[0033] Figure 1 is a drawing for explaining the characteristics of a directional coupler.

[0034] A directional coupler is a device with four ports that can induce a specific wave propagating on an arbitrary line with a specific impedance to another line, and has four ports (P1, P2, P3, P4) composed of two transmission lines coupled in such a way that the direction of propagation of the induced wave is determined according to the direction of propagation of the induced wave.

[0035] At this time, the formula that can determine each characteristic of the directional coupler is as follows.

[0036] Insertion loss characteristic = 10*log(P1 / P2) = -20*log(|S21|)

[0037] Isolation = 10*log(P1 / P4) = -20*log(|S41|)

[0038] Coupling = 10*log(P1 / P3) = -20*log(|S31|)

[0039] Directionality = 10*log(P3 / P4) = 20*log(|S31| / |S41|)

[0040] Directional couplers utilize the above characteristics to monitor the wave characteristics of the wave incident on the input terminal at the output terminal through the coupling terminal. For example, assuming that the incident power is 10 watts at a specific frequency, using a 20 dB directional coupler will result in 1 / 100th of the power being displayed at the coupling terminal, resulting in a power level of 0.1 watts, which can be measured with a commercial signal analyzer (spectrum analyzer).

[0041] Figure 2 is a drawing for explaining a strip line directional coupler.

[0042] Figure 3 is a diagram for explaining the electric field characteristics and equivalent circuit in even mode.

[0043] Figure 4 is a diagram for explaining the electric field characteristics and equivalent circuit in odd mode.

[0044] The electrical characteristics of a directional coupler can be completely determined from the propagation velocity along the transmission line and the effective capacitance between the lines.

[0045] Meanwhile, the electrical characteristics of the directional coupler can be determined by the propagation speed on the transmission line and the effective capacitor value between the lines.

[0046] For example, if we take a directional coupler using a strip line as shown in Fig. 2, the capacitor C 12 represents the capacitor between two strip conductors without considering the ground conductor, and C 11 Wow C 22 represents a capacitor between one strip conductor and ground without considering the other strip conductors.

[0047] At this time, in general, to achieve high directivity, the phase velocities of the even mode and odd mode should be made approximately equal.

[0048] Next, Fig. 3 shows the electric field direction and equivalent circuit in even mode. At this time, no current flows between the two strip conductor lines, C 12 exhibits open circuit characteristics. In even mode, the capacitor on each line to ground is C e = C 11 = C 22 If the size and position of the two strip conductors are the same, the impedance and phase velocity (v) of the even mode pe ) and effective permittivity (ε ree ) and the propagation velocity (C) in free space has the following equation.

[0049]

[0050]

[0051] Next, Fig. 4 shows the electric field direction and equivalent circuit in odd mode. The voltage zero of the electromagnetic field exists between the two conductors, and the capacitor C 12 It can be assumed that the grounding is through the center of gravity. At this time, the effective capacitor is C o = C 11 + 2C 12 =C 22 +2*C 12 If the size and position of the two strip conductors are the same, the impedance and phase velocity (v) of the odd mode po ), effective permittivity (εreo ) and the propagation velocity (C) in free space has the following equation.

[0052]

[0053]

[0054] Accordingly, the coupling amount considering the phase velocities of even and odd modes can be expressed as follows.

[0055]

[0056] In this way, the greater the difference between the characteristic impedance of the even mode and the impedance of the odd mode, the greater the coupling value can be obtained. That is, C 22 We can see that the larger the value of , the greater the coupling value can be obtained.

[0057] Meanwhile, in the case of microstrip coupled lines, the effective permittivity (ε) of the even mode ree ) is the effective permittivity (ε) of odd modes. reo ) can be large. At this time, looking at the above formula, it can be seen that the larger the effective permittivity, the smaller the phase velocity.

[0058] In this way, the phase velocity of the even mode and the phase velocity of the odd mode are inversely proportional to the size of the capacitance Ce of the even mode and the capacitance Co of the odd mode. Therefore, to obtain a large coupling, C 22 As the value increases, the difference between the capacitance Ce of the even mode and the capacitance Co of the odd mode increases. Therefore, C 22 Regardless of the size of the mode, the phase velocity of the even mode is the same, but the phase velocity of the odd mode becomes more different, which may further deteriorate the directivity.

[0059] That is, no matter what coupling is obtained, C 22 Due to the difference in phase speed, the phase speeds of the even mode and the odd mode cannot be the same, making it difficult to obtain high directivity.

[0060] Figure 5 is a schematic diagram of a directional coupler according to a comparative example.

[0061] Meanwhile, when using a structure in which two lines overlap, such as the directional coupler according to the comparative example of Fig. 5, there is an advantage in that a device with a small mounting area can be created. However, the capacitor value (C) between the two lines 12 ) is very large, so that coupling can occur when the distance between the first and second lines is very close, and the size of the strategy can be implemented to be larger than the output power. Therefore, it can be applied as a wideband divider rather than a coupler. In addition, the above structure has a characteristic that the phase of the output port and the coupling port is 90 degrees different. However, even in this case, C 11 , C 22 C is very large compared to 12 It can be seen that it is impossible to obtain similar directivity due to this.

[0062] Figure 6 is a perspective view of a combined directional coupler according to one embodiment of the present invention.

[0063] Figure 7 is a schematic exploded perspective view of a grounding substrate and a line of a directional coupler according to one embodiment of the present invention.

[0064] Figure 8 is an exploded perspective view of a directional coupler according to one embodiment of the present invention.

[0065] Figure 9 is a cross-sectional view of a directional coupler according to one embodiment of the present invention.

[0066] A directional coupler according to one embodiment of the present invention includes a first line (120) having both ends connected to a coupling terminal (230) and an isolation terminal (240), a second line (150) disposed on a different plane from the first line (120) and having both ends connected to an input terminal (210) and an output terminal (220), a first grounding substrate (130) disposed on the first line (120) between the first line (120) and the second line (150) and grounding the first line (120), and a second grounding substrate (140) disposed below the second line (150) between the first line (120) and the second line (150) and grounding the second line (150).

[0067] At this time, at least a portion of the first line (120) and the second line (150) are arranged to overlap each other, and it is preferable that the first ground substrate (130) and the second ground substrate (140) have different sizes and shapes.

[0068] A directional coupler according to one embodiment of the present invention may further include a mounting ground substrate (110) disposed below the first line (120) and having an input terminal (210), an output terminal (220), a coupling terminal (230), and an isolation terminal (240) disposed on the upper surface.

[0069] At this time, the input terminal (210), the output terminal (220), the coupling terminal (230), and the isolation terminal (240) can be placed on the same plane by the mounting grounding substrate (110).

[0070] The first ground substrate (130) can be electrically connected to the mounting ground substrate (110) through a via hole or a side electrode.

[0071] Meanwhile, it is preferable that the lengths of the first line (120) and the second line (150) are different from each other.

[0072] And, it is preferable that a capacitance is formed between the first line (120) and the first ground substrate (130) so that the first line (120) and the first ground substrate (130) are electrically connected, and a capacitance is formed between the second line (150) and the second ground substrate (140) so that the second line (150) and the second ground substrate (140) are electrically connected.

[0073] A directional coupler according to one embodiment of the present invention comprises two transmission lines overlapping each other in different layers rather than in the same plane, and having different ground layers, with the two ground layers positioned between the first transmission line and the second transmission line. Thus, the directivity of the directional coupler can be maximized to -10 dB or less.

[0074] Referring to FIGS. 6 to 9, a first ground substrate (130) is placed on a first line (120), a second ground substrate (140) is placed on the first ground substrate (130), and a second line (150) is placed on the second ground substrate (140).

[0075] Although there is an advantage in that the layout space of the directional coupler can be reduced by the structure in which two lines overlap, the capacitance between the first line (120) and the second line (150) can be very large, and it may be impossible to implement a coupling of -10 dB or less (e.g., -20 dB coupling).

[0076] Accordingly, by placing the first ground substrate (130) and the second ground substrate (140) between the first line (120) and the second line (150), the capacitance can be reduced. However, the first line (120) and the second line (150) placed on different layers may inevitably have different propagation velocities in the even mode and the odd mode due to the difference in the length of the lines for impedance matching and the difference in the height of the first to fourth connecting portions (Via1, Via2, Via3, Via4) such as via holes.

[0077] Accordingly, a directional coupler according to one embodiment of the present invention further includes a first inductor (L1) disposed between an input terminal (210) and a second line (150), a second inductor (L2) disposed between an output terminal (220) and the second line (150), a third inductor (L3) disposed between an isolation terminal (240) and the first line (120), and a fourth inductor (L4) disposed between a coupling terminal (230) and the first line (120).

[0078] At this time, it is preferable that at least some of the first to fourth inductors (L1, L2, L3, L4) have different inductances.

[0079] Additionally, a capacitance may be formed between the first inductor (L1) and the fourth inductor (L4), and a capacitance may be formed between the second inductor (L2) and the third inductor (L3).

[0080] It is preferable that at least some of the first length (a), which is the distance between the second line (150) and the first inductor (L1), the second length (b), which is the distance between the second line (150) and the second inductor (L2), the third length (c), which is the distance between the first line (120) and the third inductor (L3), and the fourth length (d), which is the distance between the first line (120) and the fourth inductor (L4), are different from each other.

[0081] It is preferable that the respective inductance values ​​formed by the first to fourth lengths (a, b, c, d) are different from each other.

[0082] In order to form coupling at the input terminal (210), the output terminal (220), the coupling terminal (230), and the isolation terminal (240), the first to fourth connecting portions (Via1, Via2, Via3, Via4) used for impedance matching of the first line (120) and the second line (150) may need to form first to fourth inductors (L1, L2, L3, L4).

[0083] At this time, the propagation speed due to the first length (a) and the first inductor (L1), the propagation speed (V1) due to the first length (a) and the first inductor (L1), the propagation speed (V2) due to the second length (b) and the second inductor (L2), the propagation speed (V2) due to the third length (c) and the second inductor (L2), and the propagation speed (V4) due to the fourth length (d) and the fourth inductor (L4) are inevitably different from each other.

[0084] Therefore, to compensate for different propagation speeds, C 11 Wow C 22 Appropriate C with different values 12 It can be configured to have a value. For example, the lengths of the first line (120) and the second line (150) can be different from each other, the size and shape of the first ground substrate (130) and the second ground substrate (140) can be different from each other, the second ground substrate (140) can be placed on the first ground substrate (130), and the second line (150) can be placed on the second ground substrate (140).

[0085] An area (A) that does not overlap with the first ground substrate (130) and the second ground substrate (140) can be formed between the first line (120) and the second line (150).

[0086] The amount of coupling of the first line (120) and the second line (150) can be adjusted by the distance between the area (A) where neither the first ground substrate (130) nor the second ground substrate (140) overlaps between the first line (120) and the second line (150) and the first to fourth connecting portions (Via1, Via2, Via3, Via4) connecting the first line (120) and the second line (150) to the input terminal (210), the output terminal (220), the coupling terminal (230), and the isolation terminal (240).

[0087] For example, the larger the area (A) between the first line (120) and the second line (150) where neither the first ground substrate (130) nor the second ground substrate (140) overlaps, and the narrower the first line (120) and the second line (150), the more the coupling amount and directivity can be controlled.

[0088] As we have seen earlier, C 22 As C increases, the phase velocity of the even mode does not change, but the phase velocity of the odd mode increases. In the case of a microstrip coupled line, referring to the effective permittivity approximation of Kirschning and Jansen, it can be seen that the effective permittivity of the even mode is greater than that of the odd mode. Thus, the larger the effective permittivity, the smaller the phase velocity, and in some cases, this C 22 Directivity can be improved by adjusting the value, but conversely, directivity may also be further reduced.

[0089] Accordingly, in the present invention, by configuring the first to fourth inductors (L1, L2, L3, L4) to have different inductances, it is possible to control the phase velocity of the even mode and the phase velocity of the odd mode to be similar to each other in a specific desired frequency band, and a directional coupler with high directivity can be achieved.

[0090] Fig. 10 is a graph for explaining the directivity of a directional coupler according to one embodiment of the present invention.

[0091] In Fig. 10, the input to isolation characteristic 1 curve is an example graph showing the non-optimized isolation characteristic of the propagation velocity (v1) due to the first length (a) + the first inductor (L1), the propagation velocity (v2) due to the second length (b) + the first inductor (L1), the propagation velocity (v3) due to the third length (c) + the third inductor (L3), and the propagation velocity (v4) due to the fourth length (d) + the fourth inductor (L4).

[0092] In Fig. 10, the input to isolation characteristic 2 curve is an example graph in which the isolation characteristic is improved by optimizing the propagation velocity (v1) due to the first length (a) + the first inductor (L1), the propagation velocity (v2) due to the second length (b) + the first inductor (L1), the propagation velocity (v3) due to the third length (c) + the third inductor (L3), and the propagation velocity (v4) due to the fourth length (d) + the fourth inductor (L4).

[0093] As shown in Fig. 10, it can be seen that even if the first line (120) and the second line (150) are placed on different layers, a coupling of -10 dB or less can be implemented, and it can also be seen that a high directivity coupler of -20 dB or less can be implemented.

[0094] As described above, although the present invention has been described through limited embodiments and drawings, these are provided only to help with the overall understanding of the present invention, and the present invention is not limited to the above embodiments, and various modifications and variations are possible from the technical idea of ​​the present invention by a person having ordinary knowledge in the technical field to which the present invention belongs.

[0095] Therefore, the idea of ​​the present invention is not limited to the described embodiments, and all things that have equivalent or equivalent modifications to the claims described below are considered to fall within the scope of the idea of ​​the present invention.

[0096]

[0097] [Explanation of symbols]

[0098] 110: Grounding board for mounting 120: First line

[0099] 130: First ground board 140: Second ground board

[0100] 150: Second track

[0101] 210: Input terminal 220: Output terminal

[0102] 230: Coupling terminal 240: Isolation terminal

[0103] L1: First inductor L2: Second inductor

[0104] L3: Third inductor L4: Fourth inductor

[0105] Via1: First connection Via2: Second connection

[0106] Via3: Third connection Via4: Fourth connection

[0107] a: first length b: second length

[0108] c: 3rd length d: 4th length

Claims

1. A first line having both ends connected to a coupling terminal and an isolation terminal; A second line arranged on a different plane from the first line and having both ends connected to the input terminal and the output terminal; A first grounding substrate disposed above the first line between the first line and the second line; and A second grounding substrate is included, which is disposed between the first line and the second line and below the second line, At least a portion of the first line and the second line are arranged to overlap each other, A directional coupler wherein the first ground substrate and the second ground substrate have at least one different size and shape.

2. In paragraph 1, A first inductor disposed between the input terminal and the second line; A second inductor disposed between the output terminal and the second line; A third inductor disposed between the isolation terminal and the first line; and Further comprising a fourth inductor disposed between the coupling terminal and the first line, A directional coupler, wherein at least some of the first to fourth inductors have different inductances.

3. In paragraph 2, A directional coupler, wherein at least some of a first length, which is a distance between the second line and the first inductor, a second length, which is a distance between the second line and the second inductor, a third length, which is a distance between the first line and the third inductor, and a fourth length, which is a distance between the first line and the fourth inductor, are different from each other.

4. In paragraph 3, A directional coupler, wherein each inductance value formed by the first to fourth lengths is different from each other.

5. In paragraph 2, A capacitance is formed between the first inductor and the fourth inductor, A directional coupler in which a capacitance is formed between the second inductor and the third inductor.

6. In paragraph 1, A directional coupler, wherein an area that does not overlap with the first ground substrate and the second ground substrate is formed between the first line and the second line.

7. In paragraph 1, A directional coupler wherein the lengths of the first line and the second line are different from each other.

8. In paragraph 1, A capacitance is formed between the first line and the first ground substrate, so that the first line and the first ground substrate are electrically connected, A directional coupler in which a capacitance is formed between the second line and the second ground substrate, so that the second line and the second ground substrate are electrically connected.

9. In paragraph 1, A directional coupler further comprising a mounting ground substrate disposed below the first line and having the input terminal, the output terminal, the coupling terminal, and the isolation terminal disposed on the upper surface.

10. In paragraph 9, A directional coupler in which the first ground substrate is electrically connected to the mounting ground substrate through a via hole or a side electrode.

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