CA1201173A

CA1201173A - Microwave heating apparatus comprising semiconductor microwave oscillator

Info

Publication number: CA1201173A
Application number: CA000412906A
Authority: CA
Inventors: Shigeru Kusunoki; Tomotaka Nobue
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1982-10-06
Filing date: 1982-10-06
Publication date: 1986-02-25

Abstract

ABSTRACT
This invention relates to a microwave heating apparatus, wherein the output from a single semi-conductor oscillator (1) is divided into two parts by a power distributor, the parts are amplified by amplifiers (3, 4), respectively, and the amplified parts are fed into a heating chamber (7) by two antennas (A2, A3), the phase of microwaves being adjusted to combine power in the heating chamber (7).

Description

SPECIFICATION

TITLE: Microwave Heating Apparatus MECHANICAL FIELD
This invention relates to a microwave heating appa-ratus wherein the output from a senliconductor microwave oscillator is divided into two parts b~ a power distributor and the parts are respectively amplified by power ampli-fiers and microwaves are fed into a heating chamber by two antennas. The invention is intend to control the phase o microwaves to effect combination of power in the heating chamber.

BRIEF DESCRIPTION OF T~IE DR~WINGS
Fig. 1 is a block diagram showing a conventional semiconductor microwave generator;
Fig. 2 is a block diagram showing a microwave heating apparatus according to this invention; and Fig. 3 shows the positional relation between anten-nas and a heating chamber in the prlncipal portion of the apparatus.

BACKGROUND ART
Such a conventional apparatus, as shown in Fig. 1, consists in distributing the output from a semiconductor oscillator 1, i.e., distributing the output from a

- 2 terminal a be~ween terminals b and c on the same energy level by a divider 2, respectively amplifying the parts by semiconductor amplifiers 3 and 4, combining them by a power combiner 5, and feeding the resultant to the hea-ting chamber by a slngle antenna Al. In addition, the powers from the terminals e and f are combined and delivered from the terminal ~. The terminals d and h are inte~connected at their terminal ends.
This arrangement, however, has such drawbacks as requiring a heavy duty power combiner 5 and this producing high power loss~

DISCLOSURE OF TIIE INVENTION
~ccordingly, the invention provides an arrangement consisting in dividing the output from a single semi-conduc-tor power oscillator into two parts by a power distributor, respe~tively amplifying them by power amplifiers, and feeding them by two antennas into a heating chamber serving as an microwave resonator, said heating chamber also serving as a power combiner, thereby making the arrangement highly efficient and inexpensive. An embodiment of the invention will now be described with re~erence to the drawings.

~5 BEST MODE OF CARRYING OUT. THE INVENTION
In Fig. 2 the power from a semiconductor microwave oscillator 1 enters the terminal a o a distributor .. ~, 2 and. is equally distributed among and delivered from the terminals b and c. The d terminal is ended at the termination. In addition, the microwaves delivered Erom th~ distributor 2 are, generally, in phase and 180 out of phase with each other at the terminals b and c.
The outputs from the distributor 2 are amplified by semiconductor amplifiers 3 and 4 and fed to two antennas A2 and A3. One of the two has a phase shifter 6 connected thereto, as required for phase shift, in relation to a heater to be described below.
Fig~ 3 shows the relation between the heating chamber and the antennas. The heating chamber 7 is defined by metal walls and serves as a cavity resonator with respect to microwaves. The figure shows an example of a standing wave mode (2, 0, 1), That is, standing wave electric fields chanye in intensity by 2, 0 and 1 in the directions of x, y and z r respectively. In this case, the antennas A2 and A3 are located at 1/4 and 3/4 positions in the _ direction and at the middle in the z direction on the x-z plane, whereby microwave oscilla-tion is effected in the highest intensity region of electric field in the standing wave mode (2, 0, 1), so that microwaves can be efficiently fed into the heating chamber.
The outputs from the antennas are 1~0 out of phase with each other because of the relation to the time phase of the standing wave mode.

Let ~ be said phase, ~ be the propagation constant and 1 be the distance from the power amplifier to the antenna. Then, ~ = ~1 In order to obtain a phase shift of 180, the power is fed to the antenna with the use oE a phase shifter 6 if the distributor 2 is in phase but without the use of a phase shifter if it is 180 out of phase.

INDUSTRIAL A:PPLICABI~ITY
As described above, according to the present inven-tion, since combination of power is possible in the heating chamber cavity even in the absence of a power combiner, it is possible to avoid more than 10% of the power loss caused where a power combiner is used.
While combination of high power is difficult to achieve in the case of strip wires often used in semi-conductor power systems because of problems of heat dissi-pation and electric discharge, the invention basically solves these problems.
Further, since antennas are provided on a single wall surface, as compared with an arrangement providing antennas on two separate wall surfaces, there are merits that the ineffective volume of the heating chamber can be reduced and that the arrangement of the microwave lines for feeding power to the respective antenna is planar and simple.

Claims

CLAIMS:

1. A microwave heating apparatus using a semi-conductor microwave generator wherein the output from a single semiconductor oscillator is branched by a power distributor, and the branched power parts are respective-ly amplified by semiconductor amplifiers, the amplified power parts being fed into a heating chamber by two antennas provided on a single wall surface of the heating chamber in such a manner that they are 180° out of phase with each other.

2. A microwave heating apparatus as set forth in Claim 1, wherein an in-phase distributor is used as said power distributor, and a phase shifter for phase-shifting microwaves by 180° is installed in one of the microwave wires leading to the antennas.

3. A microwave heating apparatus as set forth in Claim 1, using a power distributor wherein micro-waves at the output ends differ in phase by 180°.

4. A microwave heating apparatus as set forth in Claim 1, wherein the resonance mode in the heating chamber has a standing wave (2, 0, 1) and two antennas are installed at 1/4 and 3/4 positions, respectively, in the x direction and at the middle in the z direction on the x-z wall surface.