EP0370811A2

EP0370811A2 - Microwave ovens

Info

Publication number: EP0370811A2
Application number: EP89312176A
Authority: EP
Inventors: Michael John Dickinson; Christopher Gregson; Gordon Thomas Andrews
Original assignee: New World Domestic Appliances Ltd
Current assignee: New World Domestic Appliances Ltd
Priority date: 1988-11-24
Filing date: 1989-11-23
Publication date: 1990-05-30
Also published as: GB2227913A; GB8827429D0; EP0370811A3

Abstract

A microwave oven comprises a waveguide system (1) which constitutes the top surface of an oven cavity (2), the waveguide system (1) affording a pair of waveguides (6) and (7) which are disposed at right angles to one another and by means of which microwave energy is launched into the oven cavity (2) from a magnetron assembly (13) which is located to one side of the oven cavity (2), thereby enabling a further cavity (not shown) to be located immediately over the oven cavity (2).

Description

This invention relates to microwave ovens which may be of conventional form or may be combination microwave ovens which incorporate a gas or electric heater in addition to the microwave energy source.
It is becoming increasingly popular to provide a microwave oven or a combination microwave oven as part of a stacked unit, with, for example, a grill or oven cavity disposed over the microwave oven cavity. Such a stacked unit places constraints on the amount of space which can be provided between the bottom of the grill or oven cavity and the top of the microwave oven cavity and where a top microwave energy launch system is required, there is often insufficient space to use either the normal direct launch system or conventional waveguide launch systems.
It is an object of the present invention to provide a microwave oven with an improved microwave launch system which may be located in the top of a microwave oven which forms part of a stacked unit but which may also be located elsewhere in the microwave oven e.g. in the back or side walls.
According to the present invention there is provided a microwave oven comprising an oven cavity, a source of microwave energy for said oven cavity, and a waveguide system coupled to said source for launching microwave energy into said oven cavity, said waveguide system comprising a pair of angularly disposed waveguides disposed adjacent and parallel to a surface of said oven cavity.
In a preferred form of microwave oven in accordance with the present invention, the pair of waveguides will be disposed substantially at right angles to one another, it being conveniently arranged that the pair of waveguides are each of generally oblong rectangular cross-section, the major surfaces of each waveguide being disposed parallel to said surface of said oven cavity.
It may be arranged that the pair of waveguides are disposed along adjacent edges of said surface, at least spart of the inner minor surface of each waveguide being open for launching microwave energy into said oven cavity.
It may further be arranged that one of said waveguides is provided with an extension thereof in the vicinity of the junction of the pair of waveguides, a microwave antenna which is coupled to said source of microwave energy being disposed in said extension for launching microwave energy into said waveguides, and at least one of said waveguides may be provided with a tuning plate along the length thereof, and/or with a tuning stub for matching the waveguide to said cavity.
Conveniently, a mode stirrer or a re-radiating antenna may be provided disposed between said pair of waveguides.
In an especially preferred form of microwave oven the waveguide system will be disposed in the top surface of the oven cavity.
An exemplary embodiment of the invention will now be described, reference being made to the accompanying single figure drawing which is a fragmentary view of part of a microwave oven cavity incorporating a waveguide system in accordance with the present invention.
In the drawing there is depicted a waveguide system 1 which forms the top surface of a microwave oven cavity depicted diagrammatically at 2. It will be appreciated that the oven cavity 2 will normally be provided with a front opening to allow access thereto, and it should also be appreciated that the microwave oven of which the oven cavity 2 and the waveguide system 1 forms a part, may be a conventional microwave oven, or it may take the form of a combination microwave oven which incorporates a gas and/or electric heater in addition to the normal microwave energy source.
The arrangement shown in the drawing is particularly designed to enable a second cavity, which may take the form of a grill and/or conventional oven, to be positioned above the oven cavity 2, with a minimum of spacing between the two cavities.
The waveguide system 1 shown in the drawing consists of a generally rectangular, box shaped upper member 3 having a side extension 4 and a lower, generally "T" shaped, member 5 which is secured to the upper member 3. The lower member 5, together with the upper member 3 and side extension 4 define a pair of waveguides 6 and 7 which are disposed at right angles to one another and each of which is of oblong rectangular cross-section, the major surfaces of which are parallel to the top surface of the oven cavity 2. The waveguides 6 and 7 extend along respective adjacent edges 8 and 9 of the upper member 3 and their inside (minor) surfaces 10 and 11 respectively are open and afford launch "windows" through which microwave energy is launched into the oven cavity 2 via an open area 12 in the upper member 3 which extends between the waveguides 6 and 7 and the opposed edges of the upper member 3.
Attached to the upper surface of the side extension 4 of the waveguide system 1 is a magnetron assembly 13 which is provided with a microwave antenna 14 which extends into the waveguide 6 and by means of which microwave energy is coupled into the waveguides 6 and 7.
In order to provide matching of the magnetron assembly 13 to the waveguides 6 and 7, and also matching between the waveguides 6 and 7 and the oven cavity 2, each waveguide is provided with an optional tuning plate 15, the position of which is chosen to effect the required matching, and one or more tuning stubs 16 may also be provided.
In order to effect even distribution of the microwave energy within the oven cavity 2, a mode stirrer 17 is provided in the open area 12 between the waveguides 6 and 7, and this may be air blown or motor driven. Instead of a mode stirrer 17 a re-radiating antenna may be used.
It is envisaged that in some applications the open area 12 of the waveguide system 1 may be provided with a heat resistant, microwave transparent cover between the waveguide system 1 and the oven cavity 2.
By making use of the waveguide system 1 as described, top launch of microwave energy into the oven cavity 2 is obtained even though the magnetron assembly 13 is located to one side of the oven cavity, thereby enabling a further cavity e.g. a grill and/or conventional oven, to be located immediately over the oven cavity 2.
Although in the embodiment described, the waveguide system 1 constitutes the top surface of the oven cavity, it should be appreciated that it could equally well constitute other surfaces e.g. a back, side or bottom surface of the oven cavity.

Claims

1. A microwave oven comprising an oven cavity, a source of microwave energy for said oven cavity, and a waveguide system coupled to said source for launching microwave energy into said oven cavity, said waveguide system comprising a pair of waveguides disposed substantially at right angles to one another and positioned adjacent and substantially parallel to a surface of said oven cavity, each of said waveguides being of generally rectangular cross-section, with a pair of opposed surfaces which are substantially parallel to said surface and a pair of opposed surfaces which are substantially perpendicular to said surface, characterised in that inner adjoining surfaces of said waveguides which are substantially perpendicular to said surface are open along at least part of their length for launching said microwave energy into said oven cavity.

2. A microwave oven as claimed in claim 1, in which the pair of waveguides are disposed along adjacent edges of said surface.

3. A microwave oven as claimed in claim 1 or claim 2, in which one of said waveguides is provided with an extension thereof in the vicinity of the junction of the pair of waveguides, a microwave antenna which is coupled to said source of microwave energy being disposed in said extension for launching microwave energy into said waveguides.

4. A microwave oven as claimed in claim 3, in which at least one of said waveguides is provided with a tuning plate along the length thereof for matching the waveguide to said cavity.

5. A microwave oven as claimed in claim 3 or claim 4, in which at least one of said waveguides is provided with a tuning stub for matching the waveguide to said cavity.

6. A microwave oven as claimed in any preceding claim, comprising a mode stirrer disposed between said pair of waveguides.

7. A microwave oven as claimed in any of claims 1 to 5, comprising a re-radiating antenna disposed between said pair of waveguides.

8. A microwave oven as claimed in any preceding claim, in which the waveguide system is disposed in the top surface of the oven cavity.