GB2162727A - Microwave oven - Google Patents

Abstract

A microwave oven has an oven cavity, 4, defined by conductive walls. A waveguide, 1, opens into an upper portion of a side wall of the oven cavity, 4, and an antenna of a magnetron, 2, is inserted horizontally into said waveguide. Thus a compact oven construction is achieved, in which the total height of the oven is reduced to the height of the oven cooking cavity. <IMAGE>

Description

SPECIFICATION Microwave oven Background of the invention This invention relates to microwave oven heating apparatus and particularly,-to the structure and the position of a waveguide in the microwave oven.

Microwave ovens have found wide acceptance in the home market for the preparation of a wide variety of foods in extremely fast cooking times. The energy source of a microwave oven is the magnetron. The magnetron energy generator conventionally operates from a regular line source of low frequency and low voltage which is stepped up to a very high voltage. The output of the magnetron is directed into the oven cooking cavity by a waveguide.

Usually in order to attain a good match between the load impedance in the oven cooking cavity and the magnetron, the waveguide has to be placed on the outside top surface of the oven cooking cavity and requires a substantial length. As a result, the whole microwave oven will stand taller than the oven cooking cavity due to the thickness of the waveguide structure. Furthermore, an oven cover is required to enclose the waveguide and the oven cooking cavity.

If the waveguide is shortened and inserted into the oven cooking cavity from the side wall of the oven cooking cavity, using ordinary design methods, the length of waveguide will be restricted by the total length of the microwave oven and it is difficult to achieve a good match between the load impedance and the magnetron.

Accordingly, an object of the present invention is to achieve the function of the waveguide efficiently.

Another object of the present invention is to achieve a good match between the load impedance and the magnetron with a saving in the material required for the oven body structure.

According to the invention there is provided a microwave oven having an oven cavity and a waveguide which opens into an upper portion of a side wall of the oven cavity and extends vertically downward along said side wall of said oven cavity, an antenna of a magnetron being inserted horizontally into said waveguide.

Thus, an advantage of the invention is that the waveguide is placed on the side wall of the oven cooking cavity, the dimensions of the waveguide being suitably selected to obtain a good match between the load impedance and the magnetron, with an arrangement which will not increase the length of the microwave oven. A further advantage is that the height of the microwave oven is reduced.

Certain embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a microwave oven with a waveguide embodying the present invention.

Figure 2 is a sectional front view of Figure 1.

Figure 3 is a perspective view of an alternative embodiment of the present invention.

Figure 4 is another view of Figure 3.

Figure 5 is a perspective view of another alternative embodiment of the present invention.

Figure 6 is a sectional front view of Figure 5.

Description of the preferred embodiments Referring to Figures 1- and 2, a microwave oven generally includes a hollow oven cooking cavity 4 defined by conductive walls. The dimensions of the oven cooking cavity 4 are selected to excite numerous modes of microwave energy at a frequency of 2450 MHz. The food 15 required to be cooked is placed on the oven cavity 4 through an opening 5 which is provided on the front of the microwave oven. The opening 5 is closed by means of a sidehinged door assembly 10. The door assembly has a window to permit the food to be seen during the process of cooking. A metal shield is used to prevent the microwave energy from passing out directly through the window from the oven cavity 4.

Moreover good seals are provided between the door assembly 10 and the oven cavity 4 to prevent the microwave energy from escaping around the periphery of the opening when the microwave oven is in operation. A latch is mounted on the door assembly 10 and engages a mating dot in a peripheral front plate surround the access opening 5.

The microwave energy, which is used to cook the food, is generated by a magnetron 2 placed beside a waveguide 1. The waveguide 1 is a rectangular block structure, extending vertically downward from the top of the side wall 8 of the oven cavity 4 and fixed on the side wall 8 by spot welding. From Figure 2, it can be seen that the waveguide 1 has a length within the extent h. It is well known in the art that the magnetron's characteristics are mostly affected by load impedance in a practical situation. To obtain the desired operating point of the magnetron on its performance and characteristic curve, the dimensions of the waveguide 1 must be suitably selected. With this embodiment of the present invention, it is possible to find a length of waveguide 1 within the distance h such that a good match between the load impedance and the magnetron is achieved.Referring to Figure 2, the magnetron 2 has an antenna 9 which is inserted into the waveguide 1. The microwave energy is emitted from the antenna 9 and is directed into the waveguide 1. The microwave energy enters the oven cavity 4 through the entry 11 which is an opening in the top of the side wall 8 of the oven cavity 4. The entry 11 is enclosed by the waveguide 1. A stirrer 3 is installed in the top of the oven cavity 4. The stirrer 3 is used to reflect the microwave entering from the entry 11 uniformly on the food 15. A stream of air used to cool the magnetron 2 is directed into the oven cavity 4 through the air entry 13 on the side wall 8 of the oven cavity 4 to blow the stirrer 3 to rotate.

If the length of waveguide 1 required to get a good match between the load impedance and the magnetron is greater than the distance h, the alter native embodiment of the present invention shown in Figures 3 and 4 can-be adopted. The waveguide 1 with length h is placed vertically on the side wall 8 of the oven cavity 4. At the lower portion, the waveguide 1 is turned 180 and extends vertically upward to increase the length of waveguide 1 by distance y. It appears that there are two wave guides, one with length h and the other with length y, placed side by side on the side wall 8 of oven cavity 4 and joining at the lower portions.

The antenna 9 of magnetron 2 is inserted into the portion near the end of waveguide 1. The microwave energy emitted from the antenna 9 travels downward through a distance y. It then turns 180 and travels vertically upward through a distance h.

Finally the microwave energy enters the oven through the entry 11 on the top of the side wall 8 of the oven cavity 4. With this embodiment of the present invention the effective length of wave guide 1 is h + y, which is greater than h, and a greater extent for the adjustment of the dimen sions of waveguide 1 is achieved, in order to obtain a good match between the load impedance and the magnetron.

Referring to Figure 5, which is another alternative embodiment of the present invention, the wav eguide 1 is placed on the side wall 8 of oven cavity 4 and extends vertically downward from the top of the side wall 8 of the oven cavity 4. The antenna 9 of the magnetron 2 is inserted into the lower portion of waveguide 1 as can be seen clearly from Figure 6. Another auxiliary waveguide 14 extends horizontally outward from the upper portion of the waveguide 1. Referring to Figure 6, the waveguide 1 is joined with the auxiliary waveguide 14 in a "right-angled" manner. The length of the auxiliary waveguide 14 is d which is measured from the outside edge of the waveguide 1 to the end of the auxiliary waveguide 14. The provision of the auxil iary waveguide 14 contributes a means to achieve a good match between the load impedance and the magnetron 2.A length d of the auxiliary waveguide 14 can- be selected to achieve the re quired results. To vary the length 1 of the auxiliary waveguide 14 is better than to varythe length of the waveguide 1 because the position of the mag netron 2 need not be changed.

Referring to Figures 2, 3 and 6, with embodi ments pf the inventions, it can be seen that the waveguides 1 only utilize the space beside the oven cavity 4. no waveguides are placed on the top surface of the oven cavity 4 and the height of waveguides 1 or 14 are smaller than or equal to the height of oven cavity 4. Therefore a reduction in the height of the microwave oven is obtained.

Moreover the top plate of the oven cavity 4 can act as- a part of the oven cover, and hence a smaller oven cover is required to enclose the right hand portion of the microwave oven thus reducing the amount of material needed. The length of the microwave oven has not increased because all the high voltage components such as transformers can be placed beneath or beside the waveguides.

Claims (5)

1. A microwave oven having an oven cavity and a waveguide which opens into an upper portion of a side wall of the oven cavity and extends vertically downward along said side wall of said oven cavity, an antenna of a magnetron being inserted horizontally into said waveguide.

2. A microwave oven as claimed in claim 1 in which said waveguide extends vertically downward from one end towards the bottom of said side wall of said oven cavity, turns through 180 and extends vertically upward to said upper portion of said side wall, and said antenna of said magnetron is inserted horizontally into a suitable position of said waveguide near said one end of said waveguide.

3. A microwave oven as claimed in claim 1 or 2 in which said waveguide extends horizontally away from said upper portion of said side wall of said oven cavity to form an auxiliary waveguide.

4. A microwave oven as claimed in any preceding claim wherein said waveguide is installed on said side wall of said oven cavity, and wherein the top panel of said oven cavity acts as a cover for said microwave oven.

5. Microwave ovens substantially as hereinbefore described with reference to any of the Figures of the accompanying drawings.