Abstract: The oven cavity (1) of a microwave oven includes an apertured launch wall (3) on the external side of which a launch box (5) is mounted so as to cover the aperture. Two three or four magnetrons supply microwave energy to the launch box (5), and hence into the oven cavity, via corresponding waveguides (10a, 10b, 10c) each in communication with a respective side of the launch box (5). In another aspect of the invention, a microwave oven cavity (1) includes an apertured launch wall (3), means for supplying microwave energy to the cavity (1) through the aperture and a match plate (26) mounted in the cavity so as to be spaced a small distance from the launch wall (3) and in registration with the aperture. The match plate and the launch wall (3), define a slot for coupling microwave energy into the cavity (1), and at least one hole (27) in the match plate (26), in use, enables microwave energy to be coupled to resonant modes in the centre of the cavity.

Abstract: A microwave oven comprises a magnetron for delivering microwave power to a cavity of the oven, a rotatable phase modular (19) an electrical resistance heating element (12) and a rotatable fan (20) for forcing air over the resistance heating element (12) and though the cavity. The phase modulator (19) and the fan (20) are mounted on a common driveshaft (18). A matchplate (9) is mounted in the cavity.

Abstract: A microwave oven has an oven cavity in which a launch site for delivering microwave energy into the oven cavity is provided by a hole (6) in a wall (2) of the cavity and a match plate (10). In order to improve the distribution of microwave energy in the cavity, the oven also has a second wall (4) partially covered on its internal side by a second match plate (30) which acts as a second resonator. The second wall may include a hole which, with the second match plate, forms a second launch site for delivering microwave energy into the oven cavity, in which case the two holes are interconnected by a waveguide via which said microwave energy is supplied from at least one magnetron.

Abstract: A microwave oven has a food-receiving cavity and a magnetron for delivering microwave power to the cavity. The magnetron is supplied with a high voltage through a transformer, and a variable impedance is connected in series with the primary winding of the transformer. The resistive heating effect produced by primary current is utilized to heat the air in the oven cavity, and the magnitude of the impedance is variable to vary the output of the magnetron.

Abstract: A microwave oven has a food-receiving cavity the rear panel of which is apertured to provide a launch area for the entry of microwave power to the cavity from a magnetron. A metal plate is positioned in front of a launch area, a central area of the plate having apertures. A forced hot air system comprising a fan and an electrical resistance heating element are positioned between the launch area and the plate. In use, the plate acts as a baffle plate for the hot air system and also as a mis-match plate for the microwave power, so that the dielectric load of food items placed in the cavity determines the microwave power coupled to the loaded oven from the magnetron.

Abstract: A microwave oven has a magnetron 26 cooled by a fan 30 which generates a flow of air which is admitted to the oven cavity 10 through an inlet aperture 32, leaving the cavity through an outlet aperture 36. A grill element 22 is located in the upper part of the cavity 10 and a turntable 24 is positioned in the lower part of the cavity 10. Where the air respectively enters and leaves the cavity, thermocouples monitor air inlet (Ti) and air outlet (To) temperatures. After cooking commences, the air inlet and air outlet temperatures are monitored. After a time dependent on the load of the food item being cooked, the plot of air outlet temperature against time crosses the plot of air inlet temperature against time. The crossover point 44 of the air inlet and air outlet temperatures is used to control the remaining cooking time and the duration of energisation of the magnetron and the grill element during the remaining cooking time.

Abstract: A microwave oven has electrical resistance heating elements (38a, 38b), a fan (36) for passing air over the heating elements and through the oven cavity (10) and a magnetron for delivering microwave power to the oven cavity. The oven is intended for use in commercial establishments such as cafes, petrol filling stations or railway stations and is capable of occupying a stand-by mode pending insertion of a foot item into the oven cavity (10). During the stand-by mode the electrical resistance heating elements are energized at a lower power level (continuously or in pulses) in order to provide a reservoir of heat which speeds the cooking process. The oven is capable of occupying the stand-by mode continuously.

Abstract: A microwave oven defrosts a food item by subjecting the food item to a first defrosting stage during which a flow of air is forced through the oven cavity by a fan, and microwave power is simultaneously delivered to the cavity, ceasing the first stage when the temperature of the air flow reaches a threshold value and subjecting the food item to a second defrosting stage during which the air flow is maintained continuously and the microwave power is pulsed in accordance with a pre-set program.

Abstract: A microwave oven has a magnetron for delivering microwave power to the oven cavity, and a fan (36) and electrical resistance heating element (38) for recirculating hot air through the cavity. The oven cooks cakes by subjecting the cakes to a first cooking stage during which hot air but no microwave power is produced, and a second cooking stage during which microwave power is produced but the electrical resistance heating element (38) is not energized, and a third cooking stage during which hot air power is applied and microwave power is produced for a certain proportion of the third cooking stage. The transitions between the stages are determined by the recirculated air temperature as detected by a thermocouple (40) positioned to detect the temperature of the air as the latter leaves the oven cavity.

Abstract: A microwave oven having a cavity for receiving a food item to be cooked, primarily meat items, a magnetron for delivering microwave power to the cavity, and a forced hot air system, including a fan and an electrical resistance heating element which are both disposed in a compartment separated from the cavity by a dividing panel. The oven has a first thermistor for monitoring air temperature drawn from the oven cavity after a predetermined time, between eight and fifteen minutes, dependent upon the nature of the food item to be cooked. When the predetermined time is reached, a microprocessor determines the remaining cooking time to complete cooking by referring to an internal program that relates to the particular food item to be cooked. A second thermistor monitors temperature near the heating element and, through the microprocessor, controls the heating element.

Abstract: A microwave oven having a cavity for receiving a food item to be cooked, a magnetron for delivering microwave power to the cavity, and a forced hot air system including a fan and an electrical resistance heating element which are disposed in a compartment separated from the cavity by a dividing panel. The oven has a thermistor for monitoring the variation of hot air temperature over time and for determining the particular time at which the hot air temperature reaches a predetermined value. When the hot air temperature reaches the predetermined value, a microprocessor: (1) determines the remaining cooking time to complete cooking by referring to an internal program that relates the time of measurement with total cooking time, and (2) determines a maximum hot air temperature to be maintained from the time of measurement to the end of cooking by reference to a second internal program which relates the values of the time of measurement with the maximum desirable hot air temperature.

Abstract: A microwave oven having a cavity for receiving food items to be cooked, primarily baked goods and frozen foods, a magnetron for delivering microwave power to the cavity, and a forced hot air system, including a fan and an electrical resistance heating element which are both disposed in a compartment separated from the cavity by a dividing panel. The oven has a thermistor for monitoring air temperature drawn from the oven cavity after a predetermined time, between four and eight minutes, from the commencement of cooking. Dependent upon the sensed temperature being below or above a predetermined threshold temperature between 130.degree. C. and 140.degree. C., a microprocessor determines a category for the food item being cooked with a corresponding final cooking temperature to be attained for completion of cooking by referring to an internal program that relates to the particular food item to be cooked.

Abstract: A microwave oven has a magnetron which launches microwave power into a cavity of the oven through an aperture in the base of the cavity. A metal tray, which may be a shelf or a rotatable turntable is supported above the aperture in a predetermined disposition so that the oven when devoid of food presents a poor power match with the magnetron in terms of effectiveness of power transfer from the magnetron into the oven cavity. As a result, the dielectric load of food items placed in the oven determines the power coupled to the loaded oven from the magnetron and the power transfer automatically increases in proportion to the dielectric food load in the oven. A forced hot air system blows hot air through the cavity, so that food items on the tray are cooked by the simultaneous application of microwave power and the hot air.

Abstract: A microwave oven has a magnetron for producing microwave power and a resistance heating element over which air is forced by a fan to produce a forced flow of hot air through the oven cavity. A thermistor in the hot air flow senses the temperature of the hot air. Microwave power and hot air are produced simultaneously until the sensed hot air temperature reaches a predetermined threshold temperature (T1). For baked food items this represents the end of the cooking process, but for meat items there is a final cooking stage during which no hot air is forced through the cavity, the level of microwave power being doubled during the final stage. The end of the final stage occurs when the sensed temperature drops to a predetermined threshold (TS).

Abstract: A microwave oven has a magnetron for supplying microwave power to a cavity of the oven, and an electrical resistance heating element over which air is blown by a fan to provide a forced flow of hot air through the cavity. The variation in hot air temperature is monitored, and the slope of the temperature/time variation is sensed after a predetermined time interval from the commencement of cooking with the oven in a cold condition. The sensed slope is then used to predict the time period it will take the hot air temperature to reach a predetermined threshold, and the microwave power and the hot air are discontinued after the predicted time period has elapsed.

Abstract: An oven system comprises a grill unit and a microwave oven unit built into a standard kitchen unit framework or other structure for receiving same with the grill unit surmounting the microwave oven unit. A duct extends from the rear of the microwave oven unit, upwardly past the rear of the grill unit, over the top of the grill unit to a front exit. The rear wall of the cavity of the microwave oven unit has a vent communicating with the duct, and the rear wall of the cavity of the grill unit has a vent communicating with the duct. The microwave oven unit has a magnetron cooled by a blower which directs a flow of air through the duct, this flow being capable of venting both cavities.

Abstract: A portable microwave oven is designed to be powered from a domestic power socket having a standard maximum power rating. The oven has two side walls, a base, a top wall, a rear wall and a closable front door together defining an oven cavity, a magnetron for supply microwave power to the cavity of the oven, a blower motor for generating a flow of cooling air for the magnetron, a rotatable turntable on the base of the cavity for supporting food thereon, a port in one of the side walls of the cavity, a vent in the rear wall of said vent leading to a vent outlet at the rear of the oven, a shutter mounted adjacent the port and movable between an open position in which the port is open and air is blown through the port and into the cavity by the blower motor and a closed position in which the port is closed by the shutter which prevents air delivered by the blower motor from reaching said cavity.

Abstract: A microwave oven delivers microwave power to the oven cavity simultaneously with thermal power provided by a circulation of hot air forced through the cavity by a fan. A temperature sensor in the cavity and timing means monitor the temperature/time variation. If a predetermined maximum temperature (e.g. 250.degree. C.) is reached in the cavity in a predetermined time (e.g. 30 minutes) from commencement of cooking with the oven in a cold condition, the oven automatically switches off to finish the cooking process. Most food items other than large meat or casserole dishes will be cooked within the predetermined time by this method. For larger meat and casserole dishes, where the maximum temperature is reached after the predetermined time, the delivery of microwave power is increased and the delivery of thermal power decreased when the maximum temperature is reached in order to complete cooking of these denser food items.