GB2078070A

GB2078070A - Microwave oven

Info

Publication number: GB2078070A
Application number: GB8114793A
Authority: GB
Original assignee: Bosch Siemens Hausgerate GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 1980-05-28
Filing date: 1981-05-14
Publication date: 1981-12-23
Also published as: GB2078070B; JPS56167295A; DE3118136C2; FR2484758B1; SE446561B; DE3118136A1; SE8102750L; FR2484758A1; NL8102278A; JPS6110953B2; CH653510A5

Abstract

A microwave oven comprises a heating chamber (10), a high frequency oscillator (14), a waveguide (15) and a rotary antenna (17) for leading high frequency energy from the waveguide (15) to the interior of the heating chamber (10). The rotary antenna comprises a vertical segment (18) and a horizontal segment (19). The vertical segment (18) is disposed in the heating chamber (10) at or near a location at which the electric field assumes its minimum intensity in a resonant mode. <IMAGE>

Description

SPECIFICATION A high frequency heating appliance The present invention relates to a high frequency heating appliance of the type, in which high frequency energy is fed into the interior of a heating chamber by means of a rotary antenna.

The simplest form of such a rotary antenna is an "L" shaped rotary antenna, but generally has the disadvantage that high frequency radiation from its horizontal segment is relatively low and the performance of the rotary antenna is poor because of the "L" shapedantenna being of the vertical electric field coupling type, wherein the majority of high frequency energy is radiated from its vertical segment.

In accordance with the present invention, there is now provided a high frequency heating appliance comprising a heating chamber, a high frequency oscillator, a waveguide and a rotary antenna for leading high frequency energy from the waveguide to the interior of the heating chamber, the rotary antenna comprising a vertical segment and a horizontal segment, the vertical segment being disposed in the heating chamber at or near a location, at which an electric field assumes its minimum intensity in a resonant mode.

The heating chamber is thus so dimensioned as to set up one or more resonant modes. This configuration enhances the performance of the rotary antenna by inhibiting leakage of high frequency radiation from the vertical segment of the antenna as much as possible and increasing high frequency radiation from the horizontal segment of the antenna, thus providing improved high frequency distribution.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a high frequency heating appliance embodying the present invention, Figure 2 is a cross-sectional view of the appliance in side elevation and Figure 3 is an enlarged plan view of an essential feature of the appliance.

Referring now to the drawings, Figure 1 shows a heating appliance in the forms of an electric cooker of the built-in type with four electric heating elements 1 on its top for cooking purposes. The electric heating elements 1 are controlled by knobs 2 on a front panel of the heating appliance, which panel also carries control knobs 3 for operation of an oven of the heating appliance. Ventilating apertures 4 for cooling air are provided below the control panel and above a door 6 provided with a handle 5. A drawer 7 is provided below the main body of the heating appliance for receiving attachments or other small articles.

Referring now to Figure 2, the door 6 is mounted to be slidable on a rail 8. The door 6 is provided at its inner face with a shelf 9, on which food or the like may be carried.

It is thus very convenient to introduce and remove food, since the shelf 9 pulls out with the door 6. The oven is formed by heating chamber 10, which is provided with an upper heater 11 substantially parallel with the top wail of the oven and a lower heater 11' at the outer bottom wall 9f the oven for heating or cooking food.

A hot air circulating fan 12 is installed behind the heating chamber 10 to render the temperature distribution more uniform within the heating chamber. A heat insulator 13 is provided on the periphery of the heating chamber 10 to reduce loss of heat through the outer walls of the heating chamber and promote a higher degree of efficiency. A high frequency oscillator 14, such as a magnetron, is adapted to supply high frequency energy through a Z-shaped waveguide 15, one end of which is in communication with a feeding aperture 16 formed substantially in the centre of the top wall of the heating chamber 10. A rotary antenna 17 extends through the feeding aperture 16. The rotary antenna 17 comprises a vertical segment 18 and a horizontal segment 19.One end of the vertical segment 18 of the rotary antenna 17 is coupled to an antenna driving shaft 20 of low loss dielectric material such as alumina ceramic. The antenna driving shaft 20 is driven buy a motor 24 mounted across a top wall of the waveguide 15.

A seal plate 27 of low loss dielectric material extends across the feeding aperture 16 for the purpose of preventing hot air in the heating chamber 10 from entering the magnetron 14 by way of the waveguide 15.

The rotary antenna 17 is journalled in the seal plate 27 and in the top wall of the waveguide 15 for rotation.

As illustrated in Figure 3, the heating chamber 10 is so dimensioned as to set up a specific resonant mode (the 503 mode in the illustrated embodiment) and the vertical segment 18 of the rotary antenna 17 is coupled with the heating chamber at a location, at which an electric field assumes its minimum intensity in the specific mode. The respective dimensions of the heating chamber for setting up the specific mode are given by

wherein X is the wavelength of the high frequency energy, a, b and care respective dimensions of the heating chamber and m, n and p are the numbers of peaks of standing waves. Therefore, this mode is not excited at the vertical segment of the antenna, but excited when the horizontal segment of the rotating antenna passes the location, at which the electric field assumes its maximum intensity.

With such an arrangement, high frequency radiation from the vertical segment of the rotary antenna is very small and high frequency radiation from the horizontal segment is relatively increased. Thus, thb rotary antenna demonstrates increased performance and improved high frequency distribution while rotating.

A cooling fan 32 is provided to cool the magnetron 14 by drawing and discharging air through an air guide 33 and the ventilating apertures 4.

High frequency radiation from the magnetron 14 is introduced into the interior of the heating chamber 10 by way of the Z-shaped waveguide 15 and the rotary antenna 17 driven by the motor 24. Cooling air for the magnetron 14 is drawn through the ventilating apertures 4 and discharged forwardly through the ventilating apertures 4 after cooling the magnetron 14.

Although in the illustrated embodiment only the single mode is present in the heating chamber, the vertical segment of the rotary antenna may be located at or near a location, at which the electric field assumes its minimum intensity in all of a plurality of modes which are excited at the same time.

Claims

1. A high frequency heating appliance comprising a heating chamber, a high frequency oscillator, a waveguide and a rotary antenna for leading high frequency energy from the waveguide to the interior of the heating chamber, the rotary antenna comprising a vertical segment and a horizontal segment, the vertical segment extending through wall means of the heating chamber at or near a location, at which an electric field assumes its minimum intensity in a resonant mode.

2. A high frequency heating appliance as claimed in claim 1, wherein the high frequency oscillator is arranged to generate energy at a wavelength given by

wherein Xis the wavelength, a, band care the dimensions of the heating chamber and m, n and p the number of the maxima of the standing waves in the respectively associated dimension.

3. A high frequency heating appliance substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.