Wilkinson-type combiner and RF generator
A low-cost, small-size Wilkinson-type combiner that suppresses the risk of damaging an isolation resistor due to combination loss is provided. The combiner comprises first and second input terminals to which RF signals are input; an output terminal; a wiring line that combines the RF signals input to the first and second input terminals, and outputs the combined signal to the output terminal; an isolation unit provided between the first and second input terminals and formed by a first isolation resistor, a transformer, and a second isolation resistor connected in series; a detection circuit connected to a secondary coil of the transformer and configured to detect a current flowing in the secondary coil; and a determination circuit that outputs a control signal to block input of RF signals to the first and second input terminals if the current flowing in the isolation unit and detected by the detection circuit is higher than or equal to a prescribed value.
1. A Wilkinson-type combiner comprising:
a first input terminal and a second input terminal to which RF signals are input;
an output terminal;
a wiring line configured to combine the RF signals input to the first input terminal and the second input terminal and output a combined RF signal to the output terminal;
an isolation unit provided between the first input terminal and the second input terminal and formed by a first isolation resistor, a transformer, and a second isolation resistor connected in series;
a detection circuit connected to a secondary coil of the transformer and configured to detect a current flowing in the secondary coil; and
a determination circuit configured to output a control signal for blocking input of the RF signals to the first input terminal and the second input terminal when the current flowing in the isolation unit detected by the detection circuit is higher than or equal to a predetermined value.
2. The Wilkinson-type combiner of claim 1 , wherein a corona ring is provided on each of the first isolation resistor and the second isolation resistor.
3. The Wilkinson-type combiner of claim 2 , further comprising:
a GND plate to which a reference potential is applied; and
an insulating substrate disposed on the GND plate and configured to insulate the isolation unit from the GND plate,
wherein each of the first isolation resistor and the second isolation resistor includes a flange portion connected to a wiring line of the isolation unit, and
the corona ring is disposed on the insulating substrate so as to surround the flange portion or the wiring line of the isolation unit connected to the flange portion.
4. The Wilkinson-type combiner of claim 3 , wherein the corona ring includes an upper insulating substrate, a lower insulating substrate, and a conductor pattern interposed between the upper and lower insulating substrates,
the lower insulating substrate is disposed to be in contact with the insulating substrate,
a connection opening configured to expose the conductor pattern is formed in the upper insulating substrate, and
the wiring line of the isolation unit and the conductor pattern are electrically connected in the connection opening.
5. The Wilkinson-type combiner of claim 3 , further comprising:
an insulating resistor presser configured to press the first isolation resistor, the second isolation resistor, or the wiring line of the isolation unit connected to the flange portion of the first isolation resistor or the second isolation resistor against the insulating substrate; and
an insulating corona ring presser configured to press the corona ring against the insulating substrate.
6. An RF generator comprising:
an excitation amplifier circuit configured to generate an RF signal;
a first power amplifier circuit and a second power amplifier circuit configured to amplify power of the RF signal generated by the excitation amplifier circuit;
a combiner to which outputs of the first and second power amplifier circuits are input; and
a control circuit,
wherein the combiner is the Wilkinson-type combiner of claim 1 ,
each of the outputs of the first and second power amplifier circuits is input to a corresponding one of the first input terminal and the second input terminal, and
the control circuit receives the control signal from the determination circuit to block input of the RF signals to the first and second input terminals.