Microwave heating device

1. A microwave heating device comprising:

a microwave oscillation portion including plural phase-locked loops connected to a single reference-signal oscillator and having plural outputs;

plural amplification portions for amplifying the respective outputs from the microwave oscillation portion;

plural radiation portions which are adapted to be supplied with outputs from the amplification portions and to radiate microwaves to a heating chamber; and

a control portion for controlling the microwave oscillation portion, wherein

each of the radiation portions has plural microwave feeding points,

the respective outputs from the amplification portions are supplied to the respective microwave feeding points,

the radiation portions are antennas having a substantially-disc shape,

the radiation portions are placed on the same wall surface of the heating chamber, wherein the radiation portions are not placed on the rest of wall surfaces of the heating chamber,

the radiation portions and the microwave feeding points in the radiation portions placed on the same wall surface of the heating chamber are placed symmetrically with respect to a line passing through an approximate center of the wall surface;

one microwave feeding point in the respective radiation portions is placed on a line connecting a respective center points of the respective radiation portions to each other, and

another microwave feeding point of the respective radiation portions is placed on a respective lines which pass through the center points and are orthogonal to the line connecting the respective center points to each other.

2. The microwave heating device according to claim 1 , wherein

the microwave oscillation portion includes a phase variable portion for changing, in phase, an oscillating signal outputted from the reference-signal oscillator, whereby microwaves supplied to the plural microwave feeding points in each of the radiation portions are set to have phases having a predetermined phase difference therebetween.

3. The microwave heating device according to claim 2 , wherein the at least two microwave feeding points in each of the radiation portions are adapted such that lines connecting the respective microwave feeding points to a center point of this radiation portion form an intersection angle of 90 degrees, and microwaves fed to the respective microwave feeding points are made to have a phase difference of 90 degrees, therebetween, at a center frequency within a used microwave frequency range.

4. The microwave heating device according to claim 2 , wherein the at least two microwave feeding points in each of the radiation portions are adapted such that lines connecting the respective microwave feeding points to a center point of this radiation portion form an intersection angle of 90 degrees, and at a center frequency within a used microwave frequency range, with respect to the phase of microwaves fed to one of the microwave feeding points, which is defined as a reference, the phase of microwaves fed to the other microwave feeding point is changed over between 90 degrees and −90 degrees.

5. The microwave heating device according to claim 2 , wherein the at least two microwave feeding points in each of the radiation portions are placed such that a line connecting the respective microwave feeding points in this radiation portion to each other passes through a center point of this radiation portion, and microwaves fed to the at least two microwave feeding points are made to have a phase difference of 180 degrees, therebetween, at a center frequency within a used microwave frequency range.

6. The microwave heating device according to claim 1 , wherein

the microwave oscillation portion includes a phase variable portion for changing, in phase, an oscillating signal outputted from the reference-signal oscillator, whereby microwaves radiated from at least two radiation portions, out of the radiation portions, are made variable in phase difference therebetween.

7. The microwave heating device according to claim 1 , wherein the at least two microwave feeding points in each of the radiation portions are adapted such that lines connecting the respective microwave feeding points to a center point of this radiation portion form an intersection angle of 90 degrees, and microwaves fed to the respective microwave feeding points are made to have a phase difference of 90 degrees, therebetween, at a center frequency within a used microwave frequency range.

8. The microwave heating device according to claim 1 , wherein the at least two microwave feeding points in each of the radiation portions are adapted such that lines connecting the respective microwave feeding points to a center point of this radiation portion form an intersection angle of 90 degrees, and at a center frequency within a used microwave frequency range, with respect to the phase of microwaves fed to one of the microwave feeding points, which is defined as a reference, the phase of microwaves fed to the other microwave feeding point is changed over between 90 degrees and −90 degrees.

9. The microwave heating device according to claim 1 , wherein the at least two microwave feeding points in each of the radiation portions are placed such that a line connecting the respective microwave feeding points in this radiation portion to each other passes through a center point of this radiation portion, and microwaves fed to the at least two microwave feeding points are made to have a phase difference of 180 degrees, therebetween, at a center frequency within a used microwave frequency range.

10. The microwave heating device according to claim 1 , wherein

the control portion has a function of controlling the outputs of the microwave oscillation portion and is adapted to perform control for stopping feeding of microwaves to at least a single microwave feeding point out of the plural microwave feeding points in each of the radiation portions.