High frequency heating apparatus

The present invention is a high frequency heating apparatus which has a high frequency oscillator for radiating high frequency energy when energized by a high voltage, a waveguide for propagating the high frequency energy from the high frequency oscillator to a heating cavity or heating chamber of the apparatus in which an object to be heated is placed, and an electric wave radiating member provided between and extending into the waveguide and the heating chamber. The electric wave radiating member both couples, through electric waves, the waveguide with the heating chamber and also radiates the high frequency energy into the heating chamber for uniform heat distribution within the heating chamber.

BACKGROUND OF THE INVENTION 
The present invention relates to a high frequency heating apparatus and 
more particularly, to a high frequency heating apparatus wherein 
improvements are made in the microwave feeding method and microwave 
radiator or antenna for varying the electric wave radiation pattern into 
the heating cavity with respect to time, thus advantageously achieving a 
more uniform heat distribution in space, facilitation of apparatus design 
through the possibility of separate analysis of the electric field 
distribution and the electric wave output, and an improved efficiency of 
electric wave output during small load operation. 
When a conventional high frequency heatin apparatus, for example, a 
microwave oven, is investigated, there are various problems which have not 
been fully studied. 
Firstly, one such problem is that the electric field distribution within 
the heating cavity is not sufficiently uniform. In other words, when 
electric waves are radiated into the heating cavity composed of 
electrically conductive material, standing waves are developed, with the 
cavity acting as a resonant cavity through interference between the 
incident waves radiated from the oscillator and the electric waves 
reflected through insufficient absorption thereof by the load. The modes 
of these standing waves are mainly determined by the dimensions of the 
heating cavity and the position at which the oscillator is installed. 
Meanwhile, the high frequency electric waves are radiated onto the load, 
with a radiation pattern corresponding to directivity of the electric wave 
radiator or antenna, the main components of which radiation pattern is 
determined by configuration and dimensions of the antenna. Since both the 
standing waves and radiation pattern are substantially fixed in space 
unless some particular countermeasures are taken, portions having a strong 
electric field and portions having a weak electric field are 
simultaneously present in the heating cavity, thus resulting in uneven 
heat distribution therein. 
In order to cope with the above described problems, there have 
conventionally been proposed and put into practice a variety of 
countermeasures, the outstanding ones of which are installation of 
stirrers or employment of a rotatable table to place the object to be 
heard thereon. Neither of these, however, is a fundamental resolution of 
the problems. 
Secondly, another problem involved in the conventional high frequency 
heating apparatus is that the degree of heating tends to differ between 
the upper portion and lower portion of the object to be heated such as 
food. For example, when milk or the like kept in a bottle is heated, it is 
often experienced that the milk in the upper portion of the bottle is too 
hot to drink, while the milk at the lower portion remains cold. This 
inconvenience is attributable to the radiation pattern described above, 
and mainly caused by the oscillating portion of the heating apparatus 
being strongly heated due to the installation of the oscillator at the 
upper part of the apparatus. To overcome the above described 
disadvantages, provision of the oscillating portion at the lower portion 
of the apparatus is considered. This arrangement, however, still has a 
disadvantage that since the distance between the oscillating portion and 
the object to be heated must be short for efficient utilization of the 
heating cavity. It is extremely difficult to make the electric field 
distribution on a planar or flat surface uniform, thus the concept is 
actually applied only to limited kinds of apparatus. 
Thirdly, there is a further problem involved in the designing of such a 
known high frequency heating apparatus. This problem is that the analysis 
required to make the heating uniform cannot be separated from that to 
improve the electric wave efficiency through proper adjustment of the 
working point of the oscillator. When the problem as described above is 
considered, for example, with respect to a heating apparatus having 
stirrers or rotatable tables mentioned earlier, with these stirrers being 
designes mainly for uniform heat distribution, the configuration or mode 
or movement of the stirrer simultaneously causes variations with time of 
the substantial impedance, thus resulting in a large deviation from the 
optimum working point as observed from the oscillator. These drawbacks 
consequently bring about further problems such as insufficient output in 
spite of relatively favorable distribution or unsatisfactory distribution 
despite ample output, thus at the present state of the art making it 
necessary for the design to be a suitable compromise between these 
factors. 
Fourthly, a still further problem of efficiency reduction is involved in 
the known high frequency heating apparatus. In the general practice, the 
rated electric wave output of a microwave oven is specified by the 
electric power consumed during a temperature rise with respect to a water 
load of 2000 c.c. It is commonly known in this line of industry, however, 
that when a water load of 100 c.c. is reached, the electric wave output is 
reduced to 50 to 60% of the rated output. Such a discrepancy may be 
avoided through an intended reduction of the rated output. These 
countermeasures, however, are not desirable from the view point of 
efficient utilization of the energy, and thus do not present fundamental 
resolution of the problems involved. 
Most of the foregoing problems in the known high frequency heating 
apparatuses are mainly attributable to the power supplying systems for 
supplying electric waves into the heating cavity. Typical power supplying 
systems are briefly described hereinbelow. The known power supplying 
systems currently put into actual use may be broadly divided into a direct 
coupling system wherein the oscillator is directly coupled to the heating 
cavity or heating chamber, such as those disclosed in U.S. Pat. Nos. 
2,763,757 and 2,813,185, a coaxial power supplying system, for example, 
those described in U.S. Pat. Nos. 2,632,090 and 3,221,132, and a wave 
guide power supplying method such as those detailed in U.S. Pat. Nos. 
2,761,942 and 2,909,635. These prior art power supply systems, however, 
have merits and demerits as described hereinbelow. 
Reference is made to FIGS. 1 to 3 showing schematic side sectional views of 
conventional microwave ovens (outer casings removed for clarity) employing 
the above described known power supply systems. In the heating apparatus 
of FIG. 1 employing the direct coupling system, an oscillator or magnetron 
m is directly mounted on the top wall ha of the oven walls defining the 
heating cavity or heating chamber h with an antenna a of the magnetron m 
extending into the heating cavity h for supplying high frequency energy 
thereinto. This arrangement, however, has a serious disadvantage in that 
matching or tuning of the oscillator and the load cannot be properly 
achieved when the dimensions of the heating cavity h as a resonant cavity 
and the position of the antenna a are defined, although advantageous in 
that a higher efficiency may be expected due to the absence of loss factor 
such as a waveguide (not shown) and that the antenna portion a having a 
rod-like shape is readily analyzed for its radiation pattern and exciting 
mechanism. This implies that it becomes extremely difficult in designing 
to simultaneously achieve uniform heat distribution in the heating cavity 
h and utilization of the oscillator m at a high efficiency. 
In the waveguide power supplying system shown in FIG. 2, the electric waves 
radiated from the antenna a of the magnetron m which is mounted at one end 
of the waveguide w are propagated through the waveguide w disposed on the 
top wall ha of the heating chamber h and supplied into the chamber h 
through a rectangular opening wo formed in the other end of the waveguide 
w disposed on the top wall ha of the heating chamber h and supplied into 
the chamber h through a rectangular opening wo formed in the other end of 
the waveguide w. This opening wo has its width approximately equal to the 
width of the waveguide w. In the above arrangement, although the problems 
encounted may be smaller since the matching or tuning can be controlled 
outside of the heating cavity h, control of the radiation pattern is 
difficult because the radiation is effected through the opening wo of the 
waveguide w. More specifically, even if the opening wo is formed in the 
central portion of the wall ha of the heating cavity h, the radiation 
characteristics are still asymmetrical, thus making it extremely difficult 
to arrange the electric field to be evenly distributed within the heating 
cavity h. 
Meanwhile, in the coaxial power supplying system of FIG. 3, the electric 
waves from the magnetron M are propagated through space between an outer 
conductor wa and an inner conductor wb into the heating cavity h for 
supplying high frequency energy thereinto. Although the above described 
coaxial power supplying system is advantageous as compared with the 
foregoing two systems of FIGS. 1 and 2 in the ease of matching and 
adjustment of the radiation pattern, the same system has disadvantages in 
that accurate dimensions of the outer conductor wa and inner conductor wb 
are particularly required due to the continuous construction of the inner 
conductor wb from the antenna of the oscillator m to the interior of the 
heating chamber h. The assembly of a number of components, i.e., the outer 
conductor wa, the inner conductor wb and the oscillator m in a 
predetermined relation gives rise to a further serious problem especially 
in the case of mass-production, thus adversely affecting the working 
efficiency. 
Similarly, there have conventionally been proposed various arrangements for 
uniformly heating the object placed in the heating cavity, such as the 
stirrer method employing a vane or disk to be rotated in the heating 
cavity or the rotating table method for rotating, within the heating 
cavity, the object to be heated which is placed on the table. Each of 
these countermeasures, however, is of a secondary nature, and are not 
sufficient for the purpose of achieving the uniform heating of the object 
to be heated. 
Meanwhile, an apparatus having a positive countermeasure of a primary 
nature for effecting the uniform heating has conventionally been proposed, 
for example, by U.S. Pat. No. 2,961,520. In that apparatus which has a 
coaxial power supplying system, as is clear from the statement in column 
2, line 27 and after of the specification thereof, the junction between 
the fixed inner conductor extending from the magnetron and the inner 
conductor rotating at the heating cavity comes into question. More 
specifically, the arrangement of said U.S. Pat. No. 2,961,520 still 
presents various problems arising from limitations of the power supplying 
system, such as undesirable spark discharge at the junction, complicated 
choke construction, the necessity of precise dimension control and the 
countermeasures required upon adhesion of dirty matter to the junction. 
Furthermore, in the conventional microwave ovens referred to in the 
foregoing description, it is a general disadvantage that, during heating 
through electric waves, the heat source is not visible with the eyes, thus 
psychologically giving rise to some uneasiness on the part of the user. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to provide a 
high frequency heating apparatus wherein improvements are made in the 
uniformity of horizontal heat distribution as well as in the heat 
distribution in a vertical direction with respect to a long and narrow 
object such as liquid contained in a bottle. 
Another important object of the present invention is to provide a high 
frequency heating apparatus of the above described type wherein the 
improvements of uniform heat distribution and electric wave output can be 
separately analyzed for efficient design of the heating apparatus. 
A further object of the present invention is to provide a high frequency 
heating apparatus of the above described type in which the efficiency of 
electric wave output is improved for a small load, with simultaneous 
efficient operation of the oscillator even at the rated output. 
A still further object of the present invention is to provide a high 
frequency heating apparatus of the above described type wherein the 
electric power required for the heating apparatus on the whole is 
effectively utilized for efficient heating operation, with arrangements 
for the improvements of the heat distribution and working efficiency being 
adapted to be observed by eye during use. 
Another object of the present invention is to provide a high frequency 
heating apparatus of the above described type which is accurate in 
functioning and simple in construction, with a consequently high 
manufacturing efficiency at low cost. 
According to a preferred embodiment of the present invention, a high 
frequency heating apparatus in the form of a microwave oven includes a 
high frequency oscillator or generator which radiates high frequency 
energy upon energization thereof by a high voltage, a waveguide having the 
high frequency oscillator disposed at one end portion thereof for 
propagating the high frequency energy from the high frequency oscillator 
to the heating cavity or heating chamber of the microwave oven in which an 
object to be heated, for example a food article, is placed, and an 
electric wave radiating member provided between and extending into the 
waveguide and the heating chamber through a supporting member of 
dielectric material. The electric wave radiating member both couples, 
through electric waves, the waveguide with the heating chamber and also 
radiates the high frequency energy from the high frequency oscillator into 
the heating chamber. By this arrangement, the high frequency energy is 
uniformly distributed within the heating chamber both in horizontal and 
vertical directions, with substantial elimination of the disadvantages 
inherent in the conventional high frequency heating apparatus. 
These and other objects and features of the present invention will become 
apparent from the following description taken in conjunction with the 
preferred embodiment thereof with reference to the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 4 to 6, there is shown a high frequency heating 
apparatus as applied to a microwave oven M according to one embodiment of 
the present invention. The microwave oven M includes an outer casing 1 
having a cubic box-like configuration open at the front side thereof. The 
outer casing 1 has a double-walled structure and includes inner walls S of 
steel plates or similar material which defines the heating cavity or 
heating chamber H. These inner walls include a horizontal base plate Sa, 
vertical side walls Sb, a top wall Sc and a rear wall Sd, and thus define 
an access opening 0 at the front of the oven M. As is seen from FIG. 5, 
the outer surfaces of these walls Sa, Sb, Sc and Sd are spaced from the 
corresponding walls of the outer casing 1 to provide spaces therebetween. 
The outer casing 1 further includes an outside front wall portion 1a 
immediately above the access opening O, on which front wall portion 1a, 
there is mounted a control panel 3 carrying a timer knob 6, operating 
buttons 7 and the like. The microwave oven M further includes a door 2 
having a handle 5 adjacent to one edge thereof remote from the hinge (not 
shown) with which the door 2 is supported at the lower edge thereof to the 
lower front edge of the casing 1 in a position corresponding to the access 
opening 0 for pivotal upward or downward movement so as to selectively 
open and close the access opening 0. Furthermore, the door 2 has a 
rectangular opening 4 formed in the central portion thereof, in which 
opening 4 a transparent plate member and a shielding plate such as a 
punched metal plate or the like (not shown) for shielding the microwave 
are closely fitted to form an observation window 4a in the door 2 for 
observation of an object (not shown) placed within the heating chamber H. 
The casing 1 is provided with legs 8 for stable positioning of the 
microwave oven M. 
It should be noted here that the configuration and construction of the 
outer casing 1 are not limited to those described above with reference to 
the microwave oven M of FIG. 1, but may be suitable changed to any other 
shape and construction within the scope of the arrangements according to 
the invention which are detailed hereinbelow. 
Referring particularly to FIG. 5, in the space defined by the top wall Sc 
of the heating cavity S and the corresponding top wall of the casing 1, 
there is disposed, on the top wall Sc, a waveguide 9 which is formed by 
part of said top wall Sc and a cober member 9a. One end 9c of the 
waveguide 9 extends into the space between the rear wall Sd of the heating 
cavity H and the corresponding rear wall of the casing 1. At the end 9c of 
the waveguide 9, on the under surface of a base plate 9b thereof 
integrally formed with the top wall Sc of the heating chamber H, there is 
mounted a magnetron 10 which is energized by a high voltage source (not 
shown) upon depression of the operating button 7. Its antenna 10a extends 
upwardly into the waveguide 9 through a small opening formed in the base 
plate 9b and with the axis of the antenna 10a being spaced from a rear 
wall 9e of the waveguide 9 by a distance l2. Generally at the central 
portion of the top wall Sc of the heating chamber H which forms part of 
the base plate 9b of the waveguide 9, there is formed a small opening h in 
which a circular supporting member d of low loss dielectric material 
having a concentric small opening da therein is fitted. An electric wave 
radiating member of antenna 11 is inserted into the concentric small 
opening da and supported by the supporting member d to extend both into 
the waveguide 9 and the heating chamber H. The vertical axis of the 
antenna 11 is spaced from the front wall 9f at the other end 9d of the 
waveguide 9 by a distance l1. On the under surface of the top wall Sc of 
the chamber H in a position between the antenna 11 and the rear wall Sd, 
there is rotatably mounted a stirrer fan 12 which is driven by suitable 
driving means (not shown) for stirring the high frequency energy in the 
heating chamber H. 
By this arrangement, the high frequency energy generated by the magnetron 
10 energized by a high voltage upon depression of the operating button 7 
and radiated by the antenna 10a is propagated through the waveguide 9 and 
supplied into the heating chamber H through the electric wave radiating 
means or antenna 11 and is further stirred by the stirrer 12 for efficent 
heating of the object (not shown), preferrably contained in a vessel (not 
shown) and placed on the bottom wall Sa of the chamber H. 
It should be noted here that the small opening h formed in the top wall Sc 
between the waveguide 9 and the heating chamber H should not be so large 
in diameter as to permit loose coupling between the waveguide portion 9 
and the heating chamber H in the absence of the antenna 11. More 
specifically, the relation between the waveguide 9 and the heating chamber 
H should be so arranged in design that high frequency energy is hardly 
supplied into the heating chamber H through the opening h alone as in the 
punched metal employed for the observation window 4a of the door 4, but 
that when an electrically conductive material, for example, a metallic rod 
is inserted into the opening h, a large amount of the high frequency 
energy is supplied into the chamber H. By arranging the apparatus in the 
manner as described above, it becomes possible to readily control the heat 
distribution as in the direct coupling method, since the electric field 
distribution in the heating chamber H is conveniently determined only on 
the basis of the configuration of the antenna 11 within the chamber H. In 
this case, the opening h of small circular shape, unlike the conventional 
waveguide arrangement, advantageously eliminates the possibility of 
developing directivity in the radiating characteristics. It is another 
advantage of the above described arrangement that the electrical output of 
the oven M can be analyzed almost independently of the electric field 
distribution within the heating chamber H. More specifically, it is 
possible to arbitrarily control the working point of the magnetron 10 
through alterations of the distances l1, from the antenna 11' to the front 
wall 9f, and l2, from the antenna 10a and the rear wall 9e of the 
waveguide 9, and also the length of the antenna 11 extends into the 
waveguide 9. As is seen from the above description, the metallic rod 11 
serves a combined purpose as an electric wave coupling member between the 
heating chamber H and the waveguide 9, and also as the electric wave 
radiating member, i.e., antenna. 
Referring now to FIG. 7, there is shown a modification of the embodiment of 
FIGS. 5 and 6. In this modification, the metallic rod 11 for the antenna 
described as employed in the microwave oven of FIGS. 5 and 6 is replaced 
by an electric wave radiating member 11' having an L-shaped portion 11'b 
at one end thereof extending into the heating chamber H, with the other 
end 11'a thereof extending upwardly through an opening h1 formed in the 
top wall Sc of the chamber H into waveguide 9 being further connected, 
through a supporting rod 13 of a dielectric material, to the driving shaft 
of a motor M mounted on the cover member 9a of the waveguide 9 for 
rotation of the radiating member 11' within the heating chamber H upon 
energization of the motor M. By the above arrangement, the effect to be 
obtainable when the radiating member moves about in the heating chamber H 
is readily achieved through rotation of the member 11', thus contributing 
greatly to the uniform distribution of the electric field within the 
heating chamber H. Although the stirrer 12 is dispensed within the 
modification of FIG. 7, it is needless to say that such a stirrer may be 
further provided for further improvement of the even distribution of the 
electric field. Furthermore, the waveguide 9 described as constituted by a 
part of the top wall Sc of the heating chamber H and the cover member 9a 
may be replaced by a waveguide separately prepared and mounted on the top 
wall Sc of the chamber H. Similarly, the opening h1 formed in the top wall 
Sc for insertion of the radiating member 11' therethrough may further be 
fitted with a member similar to a support member d of low loss dielectric 
material as in the embodiment of FIGS. 4 to 6. The remainder of the 
construction and function of the microwave oven of FIG. 7 is similar to 
those described with reference to the oven of FIGS. 4 to 6, so that 
detailed description thereof is omitted. 
Referring now to FIGS. 8 and 9, there is shown another modification of the 
microwave oven of FIGS. 4 to 6. In this modification wherein the outer 
casing 1 of the oven is removed fro clarity of description, the waveguide 
9 described as mounted on the top wall Sc of the heating chamber H in the 
oven of FIGS. 4 to 6 is replaced by a waveguide 9' mounted to the under 
surface of the bottom wall Sa of the chamber H in a space between the wall 
Sa and the corresponding bottom plate of the casing 1 (not shown). At the 
end 9'c of the waveguide 9' in a position adjacent to the magnetron 10, 
there is mounted a fan or blower 14 suitably coupled with a driving motor 
(not shown) for cooling the magnetron 10. Approximately, in the central 
portion of the bottom wall Sc of the chamber H, there is formed an opening 
h2 in which a bearing 14 of low loss dielectric material is received. An 
electric wave radiating member 11" of L-shape is inserted, at its end 
11"a, into the bearing 14 and supported on the bearing 14 by a ring member 
15 of similar low loss dielectric material fixed to the radiating member 
11" for permitting rotation of the member 11" in the bearing 14. The 
radiating member 11" is further provided with a plurality of blades 16 of 
low loss dielectric material which are secured to the member 11" through 
corresponding arms 17 also of low loss dielectric material to form an 
impeller V around the radiating member 11". Above the impeller V, a 
support plate 18 is disposed within the heating chamber H to divide the 
chamber H into two portions Ha and Hb, on which support plate 18, the 
object to be heated, for example, food f place in a vessel U is placed. 
The heating chamber H is formed with ventilation openings a1 to a4 in the 
walls adjacent to the corner portions thereof and is further provided with 
a duct portion 19 fixed at one side. The duct 19, the opening a1, the 
heating chamber Hb for the impeller V, the opening a3, the upper heating 
chamber Ha and the opening a4 are communicated with one another for the 
circulation of air flow in the directions shown by arrows. 
By the above arrangement, when the blower 14 is operated, the air flow 
developed thereby is directed through the opening a1 and the chamber Hb 
after having cooled the magnetron 10, thus rotating the impeller V 
together with the electric wave radiating member 11". The air flow is 
further led into the heating chamber Ha through the openings a2, the duct 
19 and the opening a3 and finally is discharged, through the opening a4, 
out of the chamber Ha together with vapor generated in said chamber H 
during heating. Supplying the electric power from the lower side according 
to the invention as described above has various advantages over known 
arrangements in that influence due to radiation is larger than that by 
resonance since the electric wave radiating member or antenna is disposed 
close to the object to be heated. By such an arrangement, the distribution 
of the electric field is readily improved by controlling the radiation 
pattern through analysis made into the configuration of the electric wave 
radiating member. Furthermore, because the electric power is supplied from 
the lower portion of the heating chamber H, the temperature difference 
between the upper and lower portions of a long and narrow object, for 
example, the liquid contained in a bottle, can be minimized rather easily. 
Additionally, efficient utilization of the magnetron is achieved since the 
impedance variations resulting from rotation angle of the radiating member 
can be reduced through negligible influence of resonance by the heating 
cavity and through designing to accumulate energy in the electric wave 
radiating portion. Similarly, output reduction at the time of small load 
can also be prevented. 
FIGS. 10 and 11 refer to a comparison between the conventional microwave 
oven of the stirrer type and the microwave oven according to the present 
invention. A heat distribution test was carried out, with vessels U' each 
containing 100 c.c. of water disposed on the bottom plates within the 
heating chambers of the conventional oven of the stirrer type and the oven 
of the invention in the symmetrical positions as shown in FIG. 10. Both of 
the ovens were then energized to reach a predetermined maximum temperature 
for subsequent temperature difference measurements between the water 
containing vessels U' in each of the ovens. As a result, in the case of 
the conventional oven of the stirrer type, temperature difference of 
7.degree. C. was detected between the water in these vessels, while in the 
oven of the present invention the temperature difference was as small as 
2.degree. C. 
Furthermore, under conditions similar to above, milk bottles m each 
containing 200 c.c. of water were disposed in the same positions as in the 
above described test, and another test measuring the temperature 
difference between the upper and lower portions of water in each of the 
bottles m was carried out. As a result of which test, a temperature 
difference of 23.degree. C. was measured in the conventional oven of the 
stirrer type, while the oven of the invention gave temperature difference 
of 2.degree. C. 
FIG. 11 shows a comparison of the characteristics for a small load between 
the conventional microwave oven of the stirrer type and the microwave oven 
of the present invention. A difference of ten-odd percent is noticed at 
the water load of 100 c.c. 
It should be noted here that, in the microwave oven of FIG. 8 of the 
invention, if the supporting plate for the object or food f to be heated 
is made of a light transmitting material, such as a transparent or 
semi-transparent material, with a suitable light source 20 for 
illumination being disposed in a position below the supporting plate, 
favorable psychological effect on the part of the user can be expected. In 
other words, in the conventional microwave ovens, there has been some 
uncertainty that the user cannot directly see conditions of the heat 
source by eye. This psychological uneasiness is advantageously eliminated 
by the above described arrangement, since the movement of the electric 
wave radiating member in the heating chamber can be observed, thus 
permitting the user to actually feel that the electric waves being 
radiated. 
Referring now to FIGS. 12 and 13, there are shown further modifications of 
the microwave oven of FIG. 8. In these modifications, reflectors for the 
electric waves are incorporated for further improvement of the electric 
field distribution. 
In the microwave oven of the modification of FIG. 12, the blades 16 for the 
impeller V described as composed of low loss dielectric material in the 
oven of FIG. 8 are replaced by blades 16' of metallic material for an 
impeller V' for also serving as a reflector of the electric waves. This 
arrangement is particularly effective for improving the electric field 
distribution in cases where favorable radiation pattern is not obtainable 
through adjustment of the configuration of the radiating member 11" alone. 
In the microwave oven shown in FIG. 13, the impeller V' described as fixed 
to and rotating in synchronism with the radiating member 11" by the arms 
17' in the arrangement of FIG. 12 is replaced by an impeller V" having 
blades 16" and rotatably mounted through the arms 17" for rotation 
independent of the rotation of radiating member 11". The member 11" is 
suitable connected, at one end thereof, to a driving shaft of the motor M' 
mounted on the lower surface of the waveguide 9' for being driven by the 
motor M', while the impeller V" is driven through the air flow caused by a 
suitable blower means (not shown). 
It should be noted here that the configuration of the electric wave 
radiating member 11" is not limited to one shown in FIGS. 12 and 13, but 
may be suitably altered to take any other shapes, for example, those shown 
in FIG. 5 or 7 provided that the same sufficiently meet the purpose of 
efficient heat distribution within the heating chamber. 
It should also be noted that, although in the modifications of FIGS. 12 and 
13, blower means, ventilation openings and the like are not particularly 
shown, it is needless to say that such blower means, ventilation openings, 
are duct and the like may be incorporated as detailed with reference to 
FIG. 8. 
Referring now to FIGS. 14 and 15, there is shown a further modification of 
the microwave oven of FIG. 7. In this modification, the electric wave 
radiating member 11' described as employed in the microwave oven of FIG. 7 
is replaced by an antenna 11s of spiral shape as an electric wave 
radiating member which is connected, at the central end portion thereof 
through a supporting rod 13' of dielectric material, to the driving shaft 
of the motor M for rotation as shown. By rotating the spiral radiating 
member 11s upon energization of the motor M, uniformity of heat 
distribution is further improved in the microwave oven of the invention. 
Features of the antenna having the spiral configuration are described in 
U.S. Pat. No. 3,493,709, so that reference should be made thereto for 
details thereof. 
It should be noted here that any metallic material such as a solid rod, 
hollow pipe or dielectric material having metallic coating on the surface 
and the like may be employed as the electric wave radiating member in the 
microwave ovens of FIGS. 5, 6, 7, 8, 12 or 13. 
It should also be noted that the circular opening h in the wall between the 
waveguide and the heating chamber for radiating the electric wave 
therethrough should preferably be located in the central portion of such a 
wall of the heating chamber, and that the same wall having said opening 
therein and the wall opposite to it should preferably be of square shape 
since variation of impedance due to rotational angle of the electric wave 
radiating member is small in the above arrangement. 
Referring back to FIG. 7, the dimensions of the heating cavity H to which 
the arrangement of the invention is applied should preferably be of 
non-resonating dimensions. More specifically, in the electric wave 
radiating member having configuration as shown in FIG. 7, it is desirable 
to suppress radiation of electric waves at the portions A and B of the 
radiating member 11', with the electric waves being mainly radiated from 
the end portion C thereof. When the oscillating frequency and the 
dimensions of the heating cavity are determined, the kind of standing 
waves likely to be developed in the heating cavity are readily found 
through simple calculations as disclosed, for example, on pages 28 to 32 
of Microwave Power Engineering Vol. 2 edited by E. C. OKress, Academic 
Press. As well known in the art, if the distance between the A and B 
portions and the oven wall is less than 1/4 wavelength, the A and B 
portions will not be efficient radiators and will be only loosely coupled 
as radiators to the heating cavity. Accordingly, if such loose coupling is 
made between the A and B portions of the electric wave radiating member 
11' and the standing wave likely to be developed, the non-resonating 
condition is established, and by facilitating radiation of electric waves 
from the portion C of the radiating member 11', it is possible to obtain 
still higher uniformity of heat distribution. 
Another example of the heating cavity dimensions is the so-called 
complementary cavity. As is seen from the literature mentioned above, the 
mode of the standing waves developed in a rectangular cavity is generally 
represented as TEm.n.p. by the number of electric fields each varying in 
the direction of x, y, or z. In the presence of two modes, for example, 
TEm.sub.1 .multidot.n.sub.1 .multidot.p.sub.1 and TEm.sub.2 
.multidot.n.sub.2 .multidot.p.sub.2, if m.sub.1 and m.sub.2, n.sub.1 and 
n.sub.2, and p.sub.1 and p.sub.2 are in the relation of even number in one 
hand and of odd number in the other respectively, both are referred to as 
complementary modes. 
Referring to FIG. 16, there are shown such modes TE340 and TE250 for 
example. The marks .DELTA. represent the maximum points of electric field 
of the mode TE340, while the marks O denote that of the mode TE250. With 
the cavity designed to develop such standing waves, if the portion of a 
radiating member equivalent to the portion C of the member 11' of FIG. 7 
is moved through a locus as shown by a circle with an arrow in FIG. 16, a 
heating pattern wherein the two modes are combined is obtained with 
further improvement of the uniformity of heating distribution. 
Referring also to FIGS. 17 and 18, there are shown still further 
modifications of the electric wave radiating member 11 such as the one 
employed in the modifications of FIGS. 7 and 8. It has also been found by 
the experiments conducted by the present inventors with respect to the 
finishing of the extreme end 11'a of the electric wave radiating member 
11' within the waveguide 9 that such extreme end is effectively finished 
for prevention of spark discharge and for stabilization of the working 
point in the manner as described with reference to FIGS. 17 and 18. In 
FIG. 17, the extreme end of the end portion 11'a of the electric wave 
radiating member 11' extending into the waveguide 9 through the dielectric 
member d' fitted around the opening h' is rounded either by beveling or by 
forming the extreme end itself into a spherical shape, which arrangement 
is particularly effective for preventing electrical discharge between the 
wall of the waveguide 9 and the radiating member 11'. In the modification 
of FIG. 18, the extreme end of the radiating member 11' is not rounded as 
in FIG. 17, but is formed into an inverted cone shape, which arrangement 
is also effective for improving the stability of the working point of the 
magnetron (not shown). 
Referring now to FIGS. 19 and 20, there are shown still further 
modifications of the microwave ovens of FIGS. 5 and 7 respectively. In the 
modifications of FIG. 19, a turntable for placing thereon the object (not 
shown) to be heated is further incorporated. This turntable t is rotatably 
mounted generally at the central portion on the bottom wall Sa of the 
heating chamber H. It is suitably coupled for rotation, through a central 
shaft to thereof, to the motor M", with a plurality of roller members r 
being rotatably disposed between the under surface of the turntable t 
adjacent to peripheral edge thereof and the bottom wall Sa for 
stabilization of the table t during rotation of said turntable t. Although 
the stirrer fan 12 described as employed in the oven of FIG. 5 is 
dispensed within the arrangement of FIG. 19, such a fan may of course be 
incorporated depending on the necessity. Meanwhile, in the microwave oven 
of FIG. 20, which is another modification of the oven of FIG. 7, the 
turntable t is further incorporated in a manner similar to that in the 
modification of FIG. 19. In the arrangements of FIGS. 19 and 20, the 
effect of even heating is further obtained by the employment of the 
turntable in addition to the favorable effect described with reference to 
FIGS. 5 and 7. 
Referring now to FIGS. 21 and 22, there is shown another modification of 
the microwave oven of FIG. 13. In this modification, the electric wave 
radiating member 11" of approximately L-shape described as employed in the 
oven of FIG. 13 is replaced by the radiating member 11' of the type as 
detailed in the oven of FIG. 7. The impeller V" of FIG. 13 is dispensed 
with, and the radiating member 11' is adapted to be driven for rotation by 
the motor M'. In the lower heating chamber Hb, four rectangular plates Z, 
each secured to inner walls S of the heating chanber H in directions 
perpendicular to the bottom wall Sa of the chamber H and facing the 
corresponding corners of the chamber H, are provided to form a polygonal 
space surrounding the radiating member 11' in the lower heating chamber Hb 
as shown. By this arrangement, impedance variations following rotation of 
the radiating member 11' are advantageously reduced, thus efficient 
utilization of the magnetron 10 is achieved. 
It should be noted here that the space described as formed in the lower 
heating chamber Hb of the microwave oven of FIG. 21 is not required to be 
octagonal, but may be of any configuration such as an ellipse, circle and 
the like so long as such a space is effective for reducing the impedance 
variations due to rotation of the electric wave radiating member 11'. 
It should also be noted that the configuration of the radiating member is 
not limited to that of the member 11', but may be suitably altered to any 
other shape depending on the necessity. 
Referring now to FIGS. 23 and 24, there is shown a still further 
modification of the microwvae oven of FIG. 21. In this modification, the 
plates Z described as employed in the oven of FIG. 21 are dispensed with, 
while the electric wave radiating member 11' is also replaced by a 
coupling member 110 of metallic material or the like. 
It should be noted here that, although in the foregoing embodiments and 
modifications thereof, the metallic conductor 11 is mainly described as 
functioning both as a coupling member between the waveguide and the 
heating chamber, and also as the electric wave radiating member, the 
modification of FIG. 23 is characterized in that the metallic conductor 
110 functions only as a coupling member. In FIG. 23, the metallic 
conductor 110 in the shape of a rod is coupled at one end to the shaft of 
the driving motor M' for rotation through a dielectric member 3 and at its 
other end, into the heating chamber H' through the opening h" formed in 
the wall Sa between the waveguide 90 and the heating chamber H' and also 
through an opening 112a formed in a corresponding wall of a reradiation 
chamber 112 of a rectangular box-like configuration which is disposed 
above the wall Sa in spaced relation to said wall Sa. The extreme upper 
end of the conductor 110 is secured to the top wall 112b of the acting 
cavity 112 through an insulating spacer 111 by a fixing screw 111a. The 
top wall 112b of the reradiation chamber 112 is further provided with a 
plurality of slots 113a to 113f formed diagonally in said wall 112b in 
parallel and spaced relation to each other as is most clearly seen in FIG. 
24. In this arrangement, the metallic conductor rod 110 has the function 
to couple through electric waves the waveguide 90 with the heating cavity 
H', with the electric waves being radiated into the heating cavity H' 
through the slots 113a to 113f formed in the top wall 112b of the 
reradiation chamber 112. 
It should be noted here that the number of the slots 113 is not limited to 
six, and the configurations of the slots or acting cavity may also be 
modified to any other shapes provided that the electric waves are 
efficiently radiated into the heating cavity therethrough. 
It should also be noted here that, although the present invention is mainly 
described with reference to the microwave ovens in the foregoing 
embodiment and modifications therefor, the concept of the present 
invention is not limited in its application to microwave ovens, but may 
also be applicable to any other types of high frequency heating apparatus. 
Although the present invention has been fully described by way of example 
with reference to the attached drawings, it is to be noted that various 
changes and modifications are apparent to those skilled in the art. 
Therefore, unless such changes and modifications depart from the scope of 
the present invention, they should be construed as included therein.