A microwave oven is a cooking apparatus, which generates a microwave to heat foods with electricity as a power source. The microwave oven is very suitable to cook an unbaked food to be cooked with ingredients or a precooked food such as an instant food.
Recently, a composite heating microwave oven is well known, which heats a food therein by an additional heater in a cavity as well as by microwave.
The additional heater of the composite heating microwave oven is fixed on a ceiling or a lower portion of a cavity of the oven. Accordingly, when a food is placed on a tray of the cavity and cooked, the additional heater works at a fixed location regardless of the amount or the volume of the food. However, in this case, the heat from the additional heater cannot be used efficiently and the food is not cooked very well.
FIG. 1 is a perspective view of a microwave oven provided with a heating apparatus according to the related art.
Referring to FIG. 1, the related art heating apparatus includes a cavity 1, an upper plate 3 and an upper heater 2. The cavity 1 receives a food to cook. The upper plate 3 constitutes a ceiling of the cavity 1. The upper heater 2 is installed under the upper plate 3 and heats the food.
A rotation tray 5 is installed at the lower portion of the cavity 1, and is rotatable in a state that a food is placed thereon. A separate lower heater 4 is installed under the rotation tray 5.
Here, the upper heater 2 is fixed in the vicinity of the upper plate 3 positioned at an upper portion of the cavity 1. The tray 5 and the lower heater 4 are installed at the lower portion of the cavity 1.
In this related art microwave oven, when it is intended to heat a food by using the heaters, the microwave oven is turned on and the upper and lower heaters 2 and 4 generate heat.
The heat is merged into the airflow circulating inside the cavity 1 to form a thermal current, so that the heat is delivered to the food by convection.
Accordingly, the upper heater 2 heats a comparatively distant upper surface of the food while the lower heater 4 heats a comparatively near lower surface of the food. Also, the microwave oven heats the food by microwave of magnetron (not shown).
However, since the upper and lower heaters 2 and 4 and the rotation tray 5 are fixed to the upper and lower portions of the cavity 1 respectively, the distances between the food on the rotation tray 5 and the heaters 2 and 4 are always constant regardless of the type and the size of the food. Accordingly, it is limited to optimize a cook condition of the food.
In addition, since the lower heater 4 is near to the food but the upper heater 5 is comparatively distant from the food as shown in FIG. 1, some of the thermal current generated by the upper heater 2 is not utilized to heat the food.