JP5871647B2 - Decoupling circuit - Google Patents

Description

  The present invention relates to a decoupling circuit connected to a plurality of antennas mounted on a wireless communication device or the like, and more particularly to a decoupling circuit that reduces coupling between two antennas.

  In recent years, with the increase in speed and quality of wireless communication systems, there is an increasing demand for multi-antenna technology that uses a plurality of antennas for transmission and reception in order to apply diversity and MIMO (Multiple Input Multiple Output). In order for diversity and MIMO to be effective, it is necessary to reduce the coupling between a plurality of antennas as much as possible and to lower the antenna correlation.

  However, in general, when a plurality of antennas are mounted in a small area such as a small communication terminal, a sufficient distance between the antennas cannot be secured, so that coupling between antennas becomes strong and communication performance deteriorates. In order to solve this problem, a method is known in which a decoupling circuit is connected to the antenna, and the coupling via the antenna is canceled by coupling via the circuit.

  For example, by configuring a decoupling circuit with two transmission lines and reactance elements that connect the lines, no matter what the amplitude or phase of the coupling between antennas (for any shape antenna), It is known that mutual coupling between antennas can be reduced (see, for example, Non-Patent Document 1 below). Further, it is known that the decoupling circuit is composed of ten lumped constant elements, so that the mutual coupling between antennas can be reduced regardless of the amplitude and phase of coupling between antennas (for example, the following non-patent documents). Reference 2). Further, there is a method of reducing the coupling between antennas by devising the shape of two antennas and connecting the antennas with a connection circuit (reactance circuit) (see, for example, Patent Document 1 below).

JP 2011-205316 A

SC Chen, YS Wang, and SJ Chung, “A decoupling technique for increasing the port isolation between two strongly coupled antennas”, IEEE Trans. Antennas Propag., Vol.56, no.12, pp.3650-3658, 2008 December Kazuhiro Aizawa and Naoki Honma, “Proposal of multiband decoupling circuit that suppresses coupling between antennas with close frequency”, 2010 IEICE, B-1-208, March 2010

  However, in the decoupling circuit of Non-Patent Document 1, it is necessary to determine the transmission line length according to the coupling between the antennas, and the maximum length of the transmission line is an electrical length and a half wavelength is required. There was a problem of becoming. Further, the decoupling circuit of Non-Patent Document 2 has a problem that the circuit becomes complicated because ten lumped constant elements are required and a crossing structure of lines is required. Furthermore, the structure of Patent Document 1 has a problem that the coupling can be reduced only for a limited antenna shape, and the coupling cannot be reduced only by installing a connection circuit between the antennas when the antenna shape changes.

  The present invention has been made to solve the above-described problems, and is to obtain a small and simple decoupling circuit capable of reducing coupling between antennas regardless of the amplitude and phase of coupling between antennas. Objective.

とし、前記第３のサセプタンス回路のサセプタンスを、

とした、ことを特徴とする減結合回路等にある。 The present invention provides a first susceptance circuit having one end connected to a first input / output terminal, a second susceptance circuit having one end connected to a second input / output terminal, and other than the first susceptance circuit a third susceptance circuit connected between the other end of the end and the second susceptance circuit, the other end to the third connection point and the third input of the susceptance circuit of said first susceptance circuit A first matching circuit connected between the second terminal and the second susceptance circuit, and a fourth input / output terminal connected between the connection point of the third susceptance circuit and the fourth input / output terminal. Two matching circuits, and a coupling amount between the first antenna connected to the first input / output terminal and the second antenna connected to the second input / output terminal is reduced, and In the first and second input / output terminals, the first and second The antenna side viewed, the first input-output terminal and the second coupling the S _{a21 =} .alpha.e ^j.phi input and output terminals, the coupling between the antenna amplitude alpha, phi between the antennas binding phase, the Y ₀ When standardized admittance is used, the susceptance of the first and second susceptance circuits is

And the susceptance of the third susceptance circuit,

The decoupling circuit is characterized by that.

  According to the present invention, it is possible to provide a small and simple decoupling circuit capable of reducing coupling between antennas regardless of the amplitude and phase of coupling between antennas.

It is a figure which shows the decoupling circuit which concerns on Embodiment 1 of this invention. It is a figure which shows the structural example of the matching circuit of FIG. It is a figure which shows the decoupling circuit based on Embodiment 2 of this invention. It is a figure which shows the decoupling circuit which concerns on Embodiment 2 at the time of comprising a matching circuit with a saddle type circuit.

  Hereinafter, a decoupling circuit according to the present invention will be described with reference to the drawings according to each embodiment. In each embodiment, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

Embodiment 1 FIG.
1 is a diagram showing a decoupling circuit according to Embodiment 1 of the present invention. FIG. 2 shows a configuration example of the matching circuits 201 and 202 of FIG.

  In FIG. 1, the decoupling circuit is provided with input / output terminals 1 to 4, susceptance elements 101 to 103, connection portions 11 and 12, and matching circuits 201 and 202. The first antenna 51 is connected to the input / output terminal 1 of the decoupling circuit, and the second antenna 52 is connected to the input / output terminal 2.

  One end of the susceptance element 101 is connected to the side of the input / output terminal 1 opposite to the first antenna 51, and one end of the susceptance element 102 is connected to the side of the input / output terminal 2 opposite to the second antenna 52. Further, the other end of the susceptance element 101, one end of the matching circuit 201, and one end of the susceptance element 103 are connected to the connection portion 11. The other end of the susceptance element 102, one end of the matching circuit 202, and the other end of the susceptance element 103 are connected to the connection unit 12. Further, the other end of the matching circuit 201 is connected to the input / output terminal 3, and the other end of the matching circuit 202 is connected to the input / output terminal 4.

The operation of this decoupling circuit will be described. The magnitude of the high-frequency signal reflected at the input / output terminal 1 when the high-frequency signal is input from the input / output terminal 1 to the first antenna 51, that is, the reflection amplitude | _Sa11 | The magnitude of the high frequency signal reflected by the input / output terminal 2 when the high frequency signal is input from the input / output terminal 2 to the second antenna 52, that is, the reflection amplitude | _Sa22 | In addition, when a high frequency signal is input from the input / output terminal 1 to the first antenna 51, coupling to the input / output terminal 2 via the antenna (that is, the first and second input / output terminals 1 and 2 at the first and second input / output terminals 1 and 2). 2 is a combination of the first input / output terminal 1 and the second input / output terminal 2), and S _a21 = αe ^jφ . That is, α represents the amplitude of coupling between antennas, and φ represents the phase of coupling between antennas. Further, the normalized admittance and _{Y 0.}

At this time, the susceptance B ₁ of the susceptance elements 101 and 102 is

And the susceptance B ₂ of the susceptance element 103 is

  And

If the susceptances B ₁ and B _{2 of the} susceptance elements 101, 102, and 103 are set according to the equations (1) and (2), the coupling is performed in the S parameter as viewed from the reference plane A of the decoupling circuit in FIG. Can be zero.
However, the reflection amplitude of the S parameter as viewed from above the reference plane A does not become zero. Therefore, impedance matching is performed by the matching circuit 201 and the matching circuit 202. Since the coupling amount of the S parameter viewed from the upper side from the reference plane A is 0, the matching circuit 201 and the matching circuit 202 can be adjusted independently to achieve matching.

As described above, the magnitude of the high-frequency signal transmitted from the input / output terminal 3 to the input / output terminal 4 when the high-frequency signal is input from the input / output terminal 3 to the decoupling circuit, that is, the coupling amount | S ₄₃ | Intercoupling can be reduced. Further, the magnitude of the high frequency signal reflected at the input / output terminal 3 when the high frequency signal is input from the input / output terminal 3 to the decoupling circuit, that is, the reflection amplitude | S ₃₃ | can be reduced. Furthermore, the magnitude of the high frequency signal reflected at the input / output terminal 4 when the high frequency signal is input from the input / output terminal 4 to the decoupling circuit, that is, the reflection amplitude | S ₄₄ | can be reduced.

  FIG. 2 is a configuration example of the matching circuits 201 and 202. (a) is a saddle type circuit composed of lumped constant elements 211, 212, and 213, and (b) is a T type circuit composed of lumped constant elements 214, 215, and 216. The lumped constant elements 211 to 216 are capacitors, inductors, or jumpers (0Ω). If the matching circuits 201 and 202 are saddle type circuits or T type circuits, any reflection amplitude and phase can be matched. Note that the lumped constant elements 211, 213, and 214 may be opened without being installed.

For example, when the frequency is 900 MHz and a high frequency signal is input from the input / output terminal 1 to the first antenna 51, the amplitude α of the coupling S _a21 via the antenna to the input / output terminal 2 is −6 dB, and the phase φ is −150. Degree. Further, | S _a11 | = | S _a22 | = 0. At this time, when the susceptance B ₁ of the susceptance elements 101 and 102 is obtained from the above formula (1), B ₁ = 0.035 [S] (6.13 pF) is obtained, and the susceptance B ₂ of the susceptance element 103 is calculated from the formula (2). When calculated, B ₂ = 0.012 [S] (2.13 pF). If the susceptances B ₁ and B ₂ of the susceptance elements 101, 102, and 103 are set in this way, the coupling amount of the S parameter viewed from the upper side from the reference plane A can be set to zero.

Further, the matching circuits 201 and 202 are respectively the saddle type circuits of FIG. 2A, and the lumped constant elements 211, 212, and 213 are respectively 18 nH, 8.2 nH, and no lumped constant elements are open (open). In this way, the reflection amplitudes | S ₃₃ | and | S ₄₄ | become −20 dB, and matching can be achieved. The bond amount | S ₄₃ | is zero.

  In FIG. 1, each of the susceptance elements 101 to 103 is one element. However, the susceptance element of each susceptance element may be composed of a plurality of lumped constant elements to form a susceptance circuit.

  Further, the first matching circuit 201 and the second matching circuit 202 are not limited to the saddle type circuit and the T type circuit, and matching circuits having various configurations can be applied.

  The susceptance of the susceptance elements 101 to 103 does not have to be exactly the same as the expressions (1) and (2), and the antenna coupling can be reduced if they are almost equal.

  As described above, the decoupling circuit is composed of the susceptance elements 101 to 103 and the matching circuits 201 and 202, so that the coupling between the antennas can be reduced regardless of the amplitude and phase of the coupling between the antennas. It has the effect that a decoupling circuit is obtained.

Embodiment 2. FIG.
In the second embodiment, a matching circuit and a transmission line are respectively installed between the input / output terminal 1 and the susceptance element 101 and between the input / output terminal 2 and the susceptance element 102 of the decoupling circuit according to the first embodiment. The effect of the first embodiment will be clarified.

  FIG. 3 shows a decoupling circuit according to Embodiment 2 of the present invention. FIG. 4 is a diagram illustrating a decoupling circuit according to the second embodiment when the matching circuits 201 to 204 are configured as saddle type circuits.

  3, in the decoupling circuit according to the second embodiment, a matching circuit 203 and a transmission line 151 are connected in series between the input / output terminal 1 and the susceptance element 101 of the decoupling circuit according to the first embodiment. A matching circuit 204 and a transmission line 152 are connected in series between the input / output terminal 2 and the susceptance element 102.

  One end of the matching circuit 203 is connected to the input / output terminal 1 opposite to the first antenna 51, and the other end of the matching circuit 204 is connected to the input / output terminal 2 opposite to the second antenna 52. The other end of the matching circuit 203 is connected to one end of the transmission line 151, and the other end of the matching circuit 204 is connected to one end of the transmission line 152. Further, the other end of the transmission line 151 is connected to one end of the susceptance element 101, and the other end of the transmission line 152 is connected to one end of the susceptance element 102.

In the decoupling circuit according to the first embodiment, the reflection amplitudes | S _a11 | and | S _a22 | of the antenna need to be sufficiently small, but may not be matched depending on the antenna shape. Thus, when | S _a11 | and | S _a22 | are not sufficiently small, matching is _achieved by connecting matching circuit 203 to first antenna 51 and connecting matching circuit 204 to second antenna 52. be able to.

  In general, the first antenna 51 and the second antenna 52 are arranged with a certain interval in order to reduce coupling between antennas or for convenience of layout. If the lengths of the transmission line 151 and the transmission line 152 are determined according to the installation positions of the first antenna 51 and the second antenna 52, the susceptance elements 101 to 103 are interposed between the first antenna 51 and the second antenna 52. And the coupling between antennas can be reduced by a decoupling circuit.

  As the matching circuits 203 and 204, for example, a saddle type circuit and a T type circuit shown in FIG. 2 can be considered, but the present invention is not limited to this, and matching circuits having various configurations can be considered. FIG. 4 is a diagram illustrating a decoupling circuit according to the second embodiment when the matching circuits 201 to 204 are all configured as saddle type circuits. In FIG. 4, reference numerals 221 to 232 denote lumped constant elements.

In the S parameter as viewed from the reference plane B of the decoupling circuit of FIG. 3, the coupling amplitude is α, the phase is φ, the normalized admittance is Y ₀ , and the susceptance B ₁ of the susceptance elements 101 and 102 is expressed by the above formula (1 If the susceptance B ₂ of the susceptance element 103 is obtained by the above equation (2) and the susceptances B ₁ and B ₂ are set, respectively, the coupling between the antennas can be reduced.

  As described above, the decoupling circuit is configured by the susceptance elements 101 to 103 and the matching circuits 201 and 202, and the matching circuit 203 and the transmission line 151 are installed between the input / output terminal 1 and the susceptance element 101, By installing the matching circuit 204 and the transmission line 152 between the terminal 2 and the susceptance element 102, a small and simple decoupling circuit that can reduce the coupling between the antennas regardless of the amplitude and phase of the coupling between the antennas. It has the effect of being obtained.

  1-4 Input / output terminal, 11, 12 connection part, 51 1st antenna, 52 2nd antenna, 101-103 susceptance element, 151, 152 transmission line, 201-204 matching circuit, 211-216, 221-232 Lumped constant element.

Claims (4)

A first susceptance circuit having one end connected to the first input / output terminal;
A second susceptance circuit having one end connected to the second input / output terminal;
A third susceptance circuit connected between the other end of the first susceptance circuit and the other end of the second susceptance circuit;
A first matching circuit connected between a connection point between the other end of the first susceptance circuit and the third susceptance circuit and a third input / output terminal;
A second matching circuit connected between a connection point between the other end of the second susceptance circuit and the third susceptance circuit and a fourth input / output terminal;
Reducing the amount of coupling between the first antenna connected to the first input / output terminal and the second antenna connected to the second input / output terminal ,
When the first and second input / output terminals are viewed from the first and second antenna sides, the coupling between the first input / output terminal and the second input / output terminal is ^expressed as S _a21 = αe ^jφ , α When the amplitude of coupling between antennas, φ is the phase of coupling between antennas, and Y ₀ is normalized admittance,
The susceptance of the first and second susceptance circuits;

And the susceptance of the third susceptance circuit,

And
A decoupling circuit characterized by that. 2. The decoupling circuit according to claim 1 , wherein the first and second matching circuits are saddle type circuits or T type circuits. A first susceptance circuit having one end connected to the first input / output terminal;
A second susceptance circuit having one end connected to the second input / output terminal;
A third susceptance circuit connected between the other end of the first susceptance circuit and the other end of the second susceptance circuit;
A first matching circuit connected between a connection point between the other end of the first susceptance circuit and the third susceptance circuit and a third input / output terminal;
A second matching circuit connected between a connection point between the other end of the second susceptance circuit and the third susceptance circuit and a fourth input / output terminal; and the first input / output terminal; A series circuit of a third matching circuit and a first transmission line connected between the first susceptance circuit;
A series circuit of a fourth matching circuit and a second transmission line connected between the second input / output terminal and the second susceptance circuit;
Reducing the amount of coupling between the first antenna connected to the first input / output terminal and the second antenna connected to the second input / output terminal ,
A connection between the third matching circuit, the first transmission line series circuit and the first susceptance circuit, the fourth matching circuit, the second transmission line series circuit, and the second susceptance circuit. In the connection unit, when the first and second antennas are viewed, the coupling is S _a21 = αe ^jφ , α is the amplitude of coupling between antennas, φ is the phase of coupling between antennas, and Y ₀ is normalized admittance. ,
The susceptance of the first and second susceptance circuits;

And the susceptance of the third susceptance circuit,

And
A decoupling circuit characterized by that. 4. The decoupling circuit according to claim 3 , wherein the first to fourth matching circuits are saddle type circuits or T type circuits.

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