Matching device and matching method

1. A matching device comprising:

a directional coupler configured to detect a travelling wave and a reflected wave;

a matching circuit including an input terminal, an output terminal, a first variable capacitance capacitor having one end connected to the input terminal through a first transmission line and the other end that is grounded, a second variable capacitance capacitor having one end connected to the output terminal through a second transmission line and the other end that is grounded, and an inductance having one end connected to said one end of the first variable capacitance capacitor and the other end connected to said one end of the second variable capacitance capacitor; and

a control unit configured to control a capacitance value of the first variable capacitance capacitor and a capacitance value of the second variable capacitance capacitor based on the travelling wave and the reflected wave detected by the directional coupler,

wherein the control unit calculates a reflection coefficient based on the travelling wave and the reflected wave detected by the directional coupler, changes the capacitance of the second variable capacitance capacitor such that the capacitance of the second variable capacitance capacitor goes to a circle described by a trace of the reflection coefficient which passes through a matching point on a Smith chart, calculates and predicts an intersection point with the circle, and determines a direction of fine-tuning of the capacitance of the first variable capacitance capacitor based on the predicted intersection point (expected point on circumference),

wherein the control unit fine-tunes the capacitance of the first variable capacitance capacitor such that the capacitance of the first variable capacitance capacitor is increased when an imaginary part of the expected point on circumference is negative and fine-tunes the capacitance of the first variable capacitance capacitor such that the capacitance of the first variable capacitance capacitor is decreased when the imaginary part of the expected point on circumference is positive,

the control unit changes the capacitance of the first variable capacitance capacitor such that the calculated reflection coefficient becomes close to zero when a distance between the calculated reflection coefficient and the circle becomes a predetermined value or less, and

the control unit fine-tunes the capacitance of the second variable capacitance capacitor such that the capacitance of the second variable capacitance capacitor is decreased in the case of outward deviation from the circle and fine-tunes the capacitance of the second variable capacitance capacitor such that the capacitance of the second variable capacitance capacitor is increased in the case of inward deviation from the circle.

2. The matching device of claim 1 , wherein the expected point on circumference is set by calculating an intersection point between the circle and a straight line extending from two points of the reflection coefficient obtained by changing the capacitance of the second variable capacitance capacitor.

3. The matching device of claim 1 , wherein the expected point on circumference is set by calculating an intersection point between the circle and three points of the reflection coefficient obtained by changing the capacitance of the second variable capacitor.

4. The matching device of claim 1 , wherein the distance smaller than or equal to the predetermined value is a distance between a concentric circle greater than the circle and a concentric circle smaller than the circle.

5. A matching method in a matching device including: a directional coupler configured to detect a travelling wave and a reflected wave; and a matching circuit including an input terminal, an output terminal, a first variable capacitance capacitor having one end connected to the input terminal through a first transmission line and the other end that is grounded, a second variable capacitance capacitor having one end connected to the output terminal through a second transmission line and the other end that is grounded, and an inductance having one end connected to said one end of the first variable capacitance capacitor and the other end connected to said one end of the second variable capacitance capacitor, the method comprising:

setting a circle described by a trace of a reflection coefficient which passes through a matching point on a Smith chart along the first transmission line;

calculating the reflection coefficient based on a traveling wave and a reflected wave detected by the directional coupler;

changing a capacitance of the second variable capacitance capacitor such that the capacitance of the second variable capacitance capacitor goes to the circle, calculating and predicting an intersection point with the circle, determining a direction of fine-tuning of the capacitance of the first variable capacitance capacitor based on the predicted intersection point (expected point on circumference), fine-tuning the capacitance of the first variable capacitance capacitor such that the capacitance of the first variable capacitance capacitor is increased when an imaginary part of the expected point on circumference is negative, and fine-tuning the capacitance of the first variable capacitance capacitor such that the capacitance of the first variable capacitance capacitor is decreased when the imaginary part of the expected point on circumference is positive; and

changing the capacitance of the first variable capacitance capacitor such that the calculated reflection coefficient becomes close to zero when a distance between the calculated reflection coefficient and the circle becomes a predetermined value or less, performing fine-tuning such that the capacitance of the second variable capacitance capacitor is decreased in the case of outward deviation from the circle, and performing fine-tuning such that the capacitance of the second variable capacitance capacitor is increased in the case of inward deviation from the circle.