JPH0216558B2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention is applicable to ISM (industrial, scientific, medical) applications, for example.
This application concerns the improvement of heating chambers when using high-frequency heating devices that use the 915 MHz band, which is one of the frequency bands, and is made of solid-state active elements such as transistors that are particularly susceptible to reflected power.

Conventional configurations and their problems In recent years, with advances in transistor technology, high-frequency generators have been constructed with solid-state active elements such as transistors, instead of the conventionally widely used magnetrons.
Aiming for lower voltage, lighter weight, smaller size, and longer life is being considered. In the case of microwave ovens, which are conventionally widely used as high-frequency heating devices for consumer use, most of them operate at 2450MHz, which is one of the ISM frequencies.
is using. However, it is generally said that the performance of a transistor decreases in proportion to the first to the second power of the operating frequency f, and it is extremely difficult to produce a transistor with high output and high efficiency at 2450 MHz. Therefore, even with current technology, it is necessary to use another ISM frequency band for transistorization.
Currently, we have no choice but to use the low frequency of the 915MHz band.

However, when using a high-frequency generator constructed of solid-state active elements such as transistors using a frequency in the 915 MHz band according to the present invention, as shown in FIG. It has been common practice to have a configuration in which a circulator 4 and a non-reflection termination 5 are interposed between the emitting antenna 3. Thus, it is generally not used in high-frequency heating devices that use a magnetron at 2450MHz.
Using expensive parts such as circulators is
This is due to the following two reasons.

The first reason is that the frequency of 915MHz according to the present invention is about three times the wavelength of 2450MHz, and the free space wavelength is 33 cm. The reason is that the wavelength roughly corresponds to the size of the heating chamber. Therefore, compared to 2450MHz, the number of modes that can resonate in heating chamber 2 is greatly reduced, and therefore, when the load, which is the object to be heated, changes, the impedance of antennas 3 to 5 when looking at the heating chamber 2 side increases. It fluctuates widely. Therefore, when designing the heating chamber 2, efforts are made to achieve impedance matching over a wide range of loads as much as possible, but it is generally difficult to keep the standing wave ratio low even under empty or light load conditions close to empty. It is. Therefore, during such light loads, most of the radio waves are reflected. On the other hand, a high-frequency heating device using a transistor is more susceptible to reflected power than a magnetron, and therefore a circulator 4 is used to absorb the reflected power to the non-reflection terminal 5 to prevent it from returning to the high-frequency generator 1. It is.

However, this circulator 4 is not only an expensive component, but also has the problem that it is very large and poorly made in the case of a high-power microwave oven of hundreds of watts, such as a general microwave oven.

OBJECTS OF THE INVENTION The present invention solves these conventional problems and aims to reduce the reflected power to the high frequency generator without using expensive parts such as circulators.

Structure of the Invention In order to achieve the above object, the present invention provides, in addition to an output antenna that guides the high frequency waves generated by the high frequency generator into the heating chamber, a second antenna that takes out the reflected radio waves from the heating chamber, and a second antenna that takes out the radio waves taken out by this antenna. It has a configuration with a non-reflection termination that absorbs.

With this configuration, when the amount of radio waves absorbed by the load decreases when the load is light, the radio waves are absorbed to the non-reflection termination through the second antenna, and the reflection to the high frequency generator can be suppressed to a small level without using a circulator.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 2, 7 is the second antenna, 8
6 is a non-reflective termination, and 6 is an object to be heated.

When the heated object 6 serving as a load is large, most of the radio waves emitted from the antenna 3 are absorbed by the heated object 6 and the electric field strength inside the heating chamber 2 is small, so that the electric power absorbed from the antenna 7 to the non-reflection terminal 8 is small. is small. On the other hand, as the heated object 6 becomes smaller and the radio waves absorbed by the heated object 6 decrease,
The electric field strength inside the heating chamber 2 increases, and the antenna 7
The power absorbed into the non-reflection termination 8 increases.
As a result, the reflected power to the high-frequency oscillator 1 can be kept low even when the object to be heated 6 is small and under light load, while when the object to be heated 6 is large, the power absorbed by the non-reflection terminal 8 is small, and there is no reduction in efficiency. few.

Effects of the Invention As explained above, according to the present invention, it is possible to suppress the reflected power to the high frequency generator to a small level even during light loads without using expensive and complicated components such as circulators as in the past. Therefore, an inexpensive and highly reliable high-frequency heating device can be realized by a high-frequency generating device using solid-state active elements such as transistors.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional high-frequency heating device using a high-frequency generator using solid-state active elements such as transistors, and FIG. 2 is a block diagram of a high-frequency heating device according to an embodiment of the present invention. 1... High frequency generator, 2... Heating chamber, 3...
Output antenna, 4... Circulator, 5... Non-reflection termination, 6... Heated object, 7... Power receiving antenna, 8... Non-reflection termination.

Claims (1)

[Claims] 1: a high-frequency generator comprising a solid-state active element such as a transistor that generates a high-frequency wave; a heating chamber that stores an object to be heated; a first antenna that guides the high-frequency wave generated by the high-frequency generator to the heating chamber; A high-frequency heating device comprising a second antenna that extracts indoor high-frequency waves and a non-reflection termination that absorbs the extracted high-frequency waves.