JP2000124711A - High isolation wilkinson circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve isolation between a second terminal and a third terminal. SOLUTION: For this Wilkinson circuit, a resistor connected between the second terminal 12 and the third terminal 13 is constituted of serially connected first resistance element R1 and second resistance element R2 and an LC parallel resonance circuit is connected between the connection point and the ground. The resonance frequency of the LC parallel resonance circuit is turned to the center frequency of a using frequency band and the LC parallel resonance circuit is prevented from adversely affecting the Wilkinson circuit. When the LC parallel resonance circuit is connected, the isolation between the second terminal 12 and the third terminal 13 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Wilkinson circuit that outputs a distributed output and has good isolation between a second terminal and a third terminal to which a combined input is input.

[0002]

2. Description of the Related Art A Wilkinson circuit is known as a distributor / combiner of an RF signal. As a distributor / combiner of an RF signal, a rat race circuit, a hybrid ring circuit, a 3 dB coupler, etc. are known in addition to the Wilkinson circuit. ing. The rat race circuit, the hybrid ring circuit, and the circuit of the 3 dB coupler are four-terminal circuits, and the configuration is complicated, but the Wilkinson circuit has three terminals.
There is an advantage that the configuration can be simplified.

[0003]

FIG. 5 shows a conventional Wilkinson circuit. As shown in FIG. 5, the Wilkinson circuit has a first terminal 111 and a second terminal 11.
It has three terminals, a third terminal 113 and the impedance of each terminal is Zo. The first terminal 111 has a first distributed constant line 114 and a second distributed constant line 1
One end of 15 is connected. The impedance of the first distributed constant line 114 and the second distributed constant line 115 is √2Zo, and the length is １ ／ wavelength of the center frequency of the operating frequency band. Further, the second terminal 1
A resistor 116 having an impedance of 2Zo is connected between the terminal 12 and the third terminal 113.

In the Wilkinson circuit configured as described above, the signal power input to the first terminal 111 is divided and output to the second terminal 112 and the third terminal 113 by そ れ ぞ れ each. Become like Also, the second
The signal powers input from the third terminal 113 and the third terminal 113 are combined by about ず つ each and output from the first terminal 111. Note that the power consumed by the resistor 116 is the second output on the output side when used as a distributor.
The reflected power generated when the load impedance between the terminal 112 and the third terminal 113 becomes unbalanced is consumed. When used as a synthesizer, the second terminal 11
Each half of the signal power input from the second and third terminals 113 is consumed.

In the Wilkinson circuit shown in FIG.
When the impedance Zo of the first terminal 111 to the third terminal 113 is set to 50Ω, the first distributed constant line 114
And the impedance of the second distributed constant line 115 is approximately 7
0.71Ω, and the resistance value of the resistor 116 becomes 100Ω. The first terminal 1 in such a Wilkinson circuit
11 input VSWR, second terminal 112 and third terminal 1
13 output VSWR, from the first terminal 111 to the second terminal 11
FIG. 6 shows each characteristic of the 2 / pass loss to the third terminal 113 and the isolation between the second terminal 112 and the third terminal 113. In this case, the used frequency band is 130 to 170 MHz.
z, and its center frequency is 150 MHz. Such a Wilkinson circuit having each terminal of 50Ω is used, for example, in a bidirectional amplifier for loss compensation of a leaky coaxial cable.

FIG. 7 shows a schematic configuration of a bidirectional amplifier. The bidirectional amplifier 100 shown in FIG.
1, the signal input from the main line 120 is amplified by the bidirectional amplifier 100 and output to the main line 121, and the signal input from the main line 121 is
It is amplified at 00 and output to the main line 120. The signal flow in this case is indicated by a solid arrow line. That is, the trunk line 12
The signal input from 0 is split by the first splitter / combiner 122 and input to the downstream amplifier 123. Downstream amplifier 12
3 is supplied to the second distributor / combiner 124
And output to the trunk line 121. In addition, trunk line 12
The signal input from 1 is split by the second splitter / combiner 124 and input to the upstream amplifier 125. Up amplifier 12
5 is output to the first distributor / combiner 122
And output to the main line 120. The first distribution /
As the combiner 122 and the second distributor / combiner 124, a Wilkinson circuit as shown in FIG. 5 is used.

In the bidirectional amplifier 100 having such a configuration, when a signal leaks as indicated by a broken line, the bidirectional amplifier 100 oscillates. That is, the first distribution / combiner 122 and the second distribution / combiner 124
The isolation characteristics between the output terminals are required to be good values and at least 20 dB or more, depending on the amplification degree of the downstream amplifier 123 and upstream amplifier 125. The Wilkinson circuit shown in FIG. 5 has a minimum isolation value of 22.6 dB in the operating frequency band as shown in FIG. 6, but when used as a distributor / combiner of a bidirectional amplifier, the downstream amplifier 123 In addition, there is a problem that oscillation may occur depending on the amplification degree of the upstream amplifier 125. Therefore, an object of the present invention is to provide a high-isolation Wilkinson circuit having an improved isolation value.

[0008]

In order to achieve the above object, a high isolation Wilkinson circuit according to the present invention has one end connected to a first terminal and the other end connected to a second terminal, A first distributed constant line having a length of about 1/4 wavelength at a center frequency of a used frequency band;
A second distributed constant line having one end connected to the first terminal and the other end connected to the third terminal, and having a length of about １ ／ wavelength at a center frequency of a used frequency band; A Wilkinson circuit including a resistor connected between the second terminal and the third terminal, wherein the resistor is configured by connecting two resistor elements in series, and a connection point between the two resistor elements is provided. An LC parallel resonance circuit that is in a substantially parallel resonance state at the center frequency of the operating frequency band is connected between the ground and the ground.

Further, another high isolation Wilkinson circuit according to the present invention has one end connected to the first terminal and the other end connected to the second terminal, and at the center frequency of the operating frequency band, about 1 /. A first distributed constant line having a length of 4 wavelengths, one end connected to the first terminal and the other end connected to the third terminal, and about 1 / A Wilkinson circuit including a second distributed constant line having a length of four wavelengths, and a resistor connected between the second terminal and the third terminal, wherein the resistor connects two resistance elements in series. A parallel resonance circuit composed of a capacitor and a distributed constant line, which are in a substantially parallel resonance state at the center frequency of the operating frequency band, is connected between a connection point between the two resistance elements and the ground.

According to the present invention, a substantially parallel resonance state is established between the connection point between the two resistance elements connected between the second terminal and the third terminal and the ground at the center frequency of the operating frequency band. Is connected, the isolation between the second terminal and the third terminal can be improved. In addition, since heat generated by the two resistance elements is transmitted to the ground via the parallel resonance circuit, the heat radiation effect of the resistance element floating from the ground in the past can be improved, and the Wilkinson with higher power can be used. It can be a circuit.

[0011]

FIG. 1 shows a circuit example of a high isolation Wilkinson circuit according to an embodiment of the present invention. However, in this circuit example, the impedance of the three terminals is 50Ω, the used frequency band (center frequency 150 MHz) is 130 MHz to 170 MHz, and the distribution (synthesis) ratio is 1: 1. It is a circuit example. The high isolation Wilkinson circuit of the present invention shown in FIG. 1 has an impedance Zo (≒ 50).
Ω), a first terminal 11, a second terminal 12, and a third terminal 13. In this case, the first terminal 11
Input from the second terminal 12 with a distribution ratio of 1: 1.
Is distributed to the third terminal 13 and output. Also, the second
The power input from the terminal 12 and the power from the third terminal 13 are respectively combined in half, and the combined power is output from the first terminal 11.

The first terminal 11 has an impedance of Z
11 (≒ 70.71Ω), a first distributed constant line 14 having a phase amount θ11 of approximately 90 °, and an impedance Z1
2 (≒ 70.71Ω), one end of a second distributed constant line 15 having a phase amount θ12 of about 90 ° is connected, and the other end of the first distributed constant line 14 and the other end of the second distributed constant line 15 are connected to each other. Are connected to the second terminal 12 or the third terminal 13, respectively. Further, between the other end of the first distributed constant line 14 and the second distributed constant line 15 (the second terminal 12 and the third terminal 13
Between them, a first resistance element R1 (≒ 50Ω) and a second resistance element R2 (≒ 50Ω) are connected in series. Further, an LC parallel resonance circuit is connected between a connection point between the first resistance element R1 and the second resistance element R2 and the ground.
This LC parallel resonance circuit has an inductor Lo (# 25.0
2nH) and a capacitor Co (≒ 45 pF),
The resonance frequency fo is substantially set to the center frequency 150 MHz of the used frequency band.

When the LC parallel resonance circuit resonates in parallel, its impedance becomes theoretically infinite, which is equivalent to the absence of the LC parallel resonance circuit between the resistance elements R1 and R2. . Since the inductance of the inductor Lo is set to a small value (．25.02 nH), the number of turns is several turns. When such an LC parallel resonance circuit is connected between the resistance elements R1 and R2, even if power is consumed in the resistance elements R1 and R2 and heat is generated, the generated heat is grounded via the inductor Lo. Be transmitted. Therefore, a high-power Wilkinson circuit can be provided without taking any special heat radiation measures for the resistance elements R1 and R2.

The input VSW of the first terminal 11 in the high isolation Wilkinson circuit of the present invention shown in FIG.
R, the output VSWR of the second terminal 12 and the third terminal 13,
FIG. 2 shows the characteristics of the passage loss from the first terminal 11 to the second terminal 12 / third terminal 13, and the isolation between the second terminal 12 and the third terminal 13. In this case, the used frequency band is 130 to 170 MHz, and its center frequency is 15 MHz.
0 MHz. Since the isolation between the second terminal 12 and the third terminal 13 in this operating frequency band is at least 38.8 dB, oscillation occurs even when used in a bidirectional amplifier for compensating for loss of a leaky coaxial cable. A bidirectional amplifier having stable characteristics without any problem can be obtained.

Referring to FIG. 2, although the output VSWR is deteriorated compared to the conventional one, the operating frequency band of the Wilkinson circuit is determined by the value of the input VSWR whose characteristic value is worse than that of the output VSWR. In the high isolation Wilkinson circuit of the present invention, as shown in FIG. 2, the output VSWR has a better value than the input VSWR. There is no negative effect of this. By the way, in the conventional Wilkinson circuit, the second
Since the resistor provided between the third terminal and the third terminal floats from the ground, if the resistor is simply attached to the heat sink, a stray capacitance or the like is generated between the resistor and the ground, deteriorating high-frequency characteristics. For this reason, it was difficult to take measures against heat dissipation to the resistor. Therefore, in the high isolation Wilkinson circuit of the present invention, the fact that the power can be increased without deteriorating the high frequency characteristics is an excellent feature that the conventional Wilkinson circuit cannot achieve.

Next, another circuit example of the high isolation Wilkinson circuit according to the embodiment of the present invention is shown in FIG. However, the circuit example shown in FIG. 3 is a circuit in which the inductor Lo of the parallel resonance circuit in the high isolation Wilkinson circuit of the present invention shown in FIG. Therefore, even in the high isolation Wilkinson circuit shown in FIG. 3, the impedance of the first terminal 21, the second terminal 22, and the third terminal 23 is 50.
And the operating frequency band (center frequency 150
MHz) is 130 MHz to 170 MHz, and the distribution (synthesis) ratio is 1: 1.

In FIG. 3, the first terminal 21 has an impedance Z21 (≒ 70.71Ω) and a phase amount θ21.
Is connected to one end of a second distributed constant line 25 whose impedance is Z22 (≒ 70.71Ω) and whose phase amount θ22 is approximately 90 °. The first distributed constant line 24 and the second distributed constant line 2
The other end of 5 is a second terminal 22 or a third terminal 23, respectively. Further, between the other end of the first distributed constant line 24 and the second distributed constant line 25 (the second terminal 22 and the third
Between the terminals 23), the first resistance element R1 (≒ 50Ω)
And the second resistance element R2 (≒ 50Ω) are connected in series. Further, a parallel resonance circuit is connected between the connection point between the first resistance element R1 and the second resistance element R2 and the ground. This parallel resonance circuit has an impedance Zo (# 5
0Ω), a distributed constant line 26 having a phase amount θo (≒ 25.25 °) and a capacitor Co (≒ 45 pF), and its resonance frequency fo is substantially equal to the center frequency 15 of the used frequency band.
0 MHz.

When the parallel resonance circuit resonates in parallel,
The impedance is theoretically infinite, which is equivalent to the fact that no parallel resonance circuit is provided between the resistance elements R1 and R2. When the distributed constant line 26 is formed of a microstrip line, the center frequency is 150 MHz, depending on the wavelength reduction ratio of the microstrip line.
Is about 7 cm long. When such a parallel resonance circuit is connected between the resistance elements R1 and R2, even if power is consumed in the resistance elements R1 and R2 and heat is generated, the generated heat is grounded via the distributed constant line 26. Will be transmitted to Therefore, the resistance elements R1, R2
A high-power Wilkinson circuit can be provided without taking special heat radiation measures.

The input VSW of the first terminal 21 in the high isolation Wilkinson circuit of the present invention shown in FIG.
R, the output VSWR of the second terminal 22 and the third terminal 23,
FIG. 4 shows respective characteristics of the passage loss from the first terminal 12 to the second terminal 22 / third terminal 23 and the isolation between the second terminal 22 and the third terminal 23. In this case, the used frequency band is 130 to 170 MHz, and its center frequency is 15 MHz.
0 MHz. Since the isolation between the second terminal 22 and the third terminal 23 in this use frequency band is at least 37.5 dB, oscillation occurs even when used in a bidirectional amplifier for loss compensation of a leaky coaxial cable. A bidirectional amplifier having stable characteristics without any problem can be obtained. In the above description, the distributed constant line is a distributed constant line using a microstrip line, but the present invention is not limited to this, and may be a distributed constant line using a coaxial cable or the like.

[0020]

As described above, the present invention is substantially parallel to the center frequency of the operating frequency band between the connection point between the two resistance elements connected between the second terminal and the third terminal and the ground. Since the parallel resonance circuit that is in the resonance state is connected, the isolation between the second terminal and the third terminal can be improved. This makes it possible to provide a stable bidirectional amplifier that does not generate oscillation or the like even when the high isolation Wilkinson circuit according to the present invention is applied to the bidirectional amplifier. In addition, since heat generated by the two resistance elements is transmitted to the ground via the parallel resonance circuit, the heat radiation effect of the resistance element floating from the ground in the past can be improved, and the Wilkinson with higher power can be used. It can be a circuit. In the high isolation Wilkinson circuit of the present invention, the fact that high power can be achieved with a simple configuration without deteriorating high-frequency characteristics is an excellent feature that the conventional Wilkinson circuit cannot achieve.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a circuit example of a high isolation Wilkinson circuit according to an embodiment of the present invention.

FIG. 2 is a table showing various electrical characteristics of the high isolation Wilkinson circuit according to the embodiment of the present invention.

FIG. 3 is a circuit diagram showing a circuit example of a high isolation Wilkinson circuit according to another embodiment of the present invention.

FIG. 4 is a table showing various electrical characteristics of a high isolation Wilkinson circuit according to another embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a conventional Wilkinson circuit.

FIG. 6 is a table showing various electrical characteristics of a conventional Wilkinson circuit.

FIG. 7 is a diagram schematically illustrating a bidirectional amplifier to which a Wilkinson circuit is applied.

[Explanation of symbols]

11, 12, 13, 21, 22, 23, 111, 11
2,113 terminal 14,15,24,25,26,114,115 distributed constant line 100 bidirectional amplifier 116 resistor 120,121 trunk line 122,124 distributor / combiner 123 combiner 123,125 amplifier Co capacitor Lo inductor R1, R2 resistance element

Claims (2)

[Claims] A first terminal connected to the first terminal and a second terminal connected to the second terminal;
And a first distributed constant line having a length of about １ ／ wavelength at the center frequency of the operating frequency band, and one end connected to the first terminal and the other end connected to the third terminal. And a second distributed constant line having a length of about 1/4 wavelength at the center frequency of the operating frequency band, and a second distributed constant line connected between the second terminal and the third terminal. A Wilkinson circuit comprising a resistor, wherein the resistor is formed by connecting two resistor elements in series, and between a connection point between the two resistor elements and the ground, in a substantially parallel resonance state at a center frequency of a used frequency band. A high isolation Wilkinson circuit, wherein an LC parallel resonance circuit is connected. 2. One end is connected to the first terminal and the other end is connected to the second terminal.
And a first distributed constant line having a length of about １ ／ wavelength at the center frequency of the operating frequency band, and one end connected to the first terminal and the other end connected to the third terminal. And a second distributed constant line having a length of about 1/4 wavelength at the center frequency of the operating frequency band, and a second distributed constant line connected between the second terminal and the third terminal. A Wilkinson circuit comprising a resistor, wherein the resistor is formed by connecting two resistor elements in series, and between a connection point between the two resistor elements and the ground, in a substantially parallel resonance state at a center frequency of a working frequency band. A high isolation Wilkinson circuit, wherein a parallel resonance circuit including a capacitor and a distributed constant line is connected.