JP4759870B2 - High frequency heating device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-frequency heating apparatus that dielectrically heats an object to be heated, and more particularly to the configuration and radiation control of a high-frequency radiation unit in a heating chamber.
[0002]
[Prior art]
The high-frequency heating device is an indispensable device in daily life because it can directly heat an object to be heated and does not require preparation of a pan. However, since the heating chamber that houses the object to be heated is not a structure whose shape can be changed, the electrical characteristics of the heating chamber change depending on the presence of the object to be heated. This change in electrical characteristics in the heating chamber affects the characteristics of the high-frequency generating means that generates the high frequency supplied into the heating chamber and the high-frequency distribution in the heating chamber. The influence received by the high frequency generation means is represented by changes in the oscillation frequency and the oscillation output. In addition, the high-frequency distribution may cause local heating due to a synergistic effect of the shape of an object to be heated and its physical characteristics.
[0003]
The ideal characteristics of the high-frequency heating device are summarized in that the high-frequency energy generated by the high-frequency generating means is supplied to the object to be heated with maximum efficiency and the object to be heated is uniformly heated.
[0004]
From the viewpoint of high-efficiency utilization of high-frequency energy, the measurement method of the high-frequency output displayed on the high-frequency heating device is stipulated in the JIS standard and IEC standard, and the amount of the heated object used for the high-frequency output measurement is 2000 cc of water And 1000 cc, which is different from the amount of the object to be heated generally (about 200 cc to 400 cc) in daily life. Due to the influence of the amount of the object to be heated, the high-frequency output with respect to the general amount of the object to be heated has a utilization efficiency of about 60 to 80% of the output value displayed on the apparatus.
[0005]
As a technique for improving such a high frequency characteristic, a matching technique at a high frequency is used. In the first place, the high-frequency heating device maximizes the high-frequency energy generated by the high-frequency generating means for the object to be heated specified in the standard, and transmits the metal post into the waveguide to optimize the matching state. In general, it is designed. Of course, if the arrangement position and shape of the metal post are changed, an optimum alignment state can be achieved for any object to be heated. However, in order to move the metal post, a complicated and expensive structure is required. It has become a practical issue.
[0006]
It is also known that this matching metal post affects the high frequency distribution in the heating chamber. Accordingly, the arrangement of the metal post for matching has been determined to be a practical configuration while achieving both effective use of high-frequency energy and optimization of the high-frequency distribution.
[0007]
On the other hand, from the viewpoint of uniformly heating an object to be heated, there is a prior art relating to a method of causing high-frequency radiation into the heating chamber, in addition to a method of rotating the object to be heated and a method of stirring the high frequency in the heating chamber.
[0008]
Conventional techniques related to high-frequency radiation include a configuration in which a plurality of high-frequency generation means are provided, and the high-frequency energy generated by the high-frequency generation means is radiated from radiation sections provided on different wall surfaces of a substantially rectangular parallelepiped heating chamber. There exists a thing of a structure provided with several radiation | emission part on the same wall surface with respect to a means.
[0009]
Moreover, in the radiation | emission part structure which uses the opening provided in the wall surface of the heating chamber as a radiation opening, the shape of this opening is a rectangular shape normally. On the other hand, Japanese Patent Laid-Open No. 2000-164341 discloses a configuration in which a square-shaped radiation port and a rectangular radiation port are provided.
[0010]
[Problems to be solved by the invention]
However, the configuration of the conventional radiating unit is provided with a square-shaped radiating port as a secondary, and does not exhibit a special radiating effect due to synergy with the main radiating port, but has a plurality of radiating ports. It is the same operation and effect as the one. In addition, as shown in FIGS. 7, 8 and 11 disclosed in the publication, a rectangular radiation port is arranged on the waveguide wall surface on the short-circuit surface side of the waveguide around the output antenna of the high frequency generating means. However, there is a problem that a spark is generated at the radiation opening due to a standing wave generated in the vicinity of the output antenna under the influence of a high frequency wave reflected from the heating chamber side and returned into the waveguide.
[0011]
The present invention solves the above problems, and provides a device for efficiently and uniformly high-frequency heating an object to be heated by devising the shape of the radiant port so that the radiation distribution to the heating chamber has a radiation characteristic different from the conventional one. For the purpose.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, a high-frequency heating device of the present invention has a heating chamber for storing an object to be heated, high-frequency generating means for generating a high frequency, two high-frequency generating ports mounted on one end and the high-frequency generating means on one end. Is provided with a waveguide for transmitting the high frequency to the heating chamber, and each of the two radiation ports has a portion parallel to a tube axis of the waveguide and a portion perpendicular to the tube axis. L-shaped, provided point-symmetrically with respect to a point on the tube axis of the waveguide, from the end face of the other end of the waveguide to a position approximately ½ of the transmission wavelength of the high frequency It is the structure provided in between .
[0013]
According to the above invention, by arranging a plurality of L-shaped radiation ports symmetrically, the directions of the electric fields exciting the radiation ports are different from each other, and the high frequency radiated from each radiation port is near the radiation port. A wide radiation distribution is formed around the radiation aperture by combining or repelling. This behavior near the radiation port mitigates the influence on the high-frequency generating means due to the difference in the amount and shape of the object to be heated, and allows the high-frequency generating means to operate stably for various objects to be heated. Use efficiency can be increased.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
According to the first aspect of the present invention, the heating chamber for storing the object to be heated, the high frequency generating means for generating a high frequency, the high frequency generating means is mounted at one end, and two radiation ports are provided at the other end. A waveguide for transmitting a high frequency to the heating chamber, and the two radiation ports are L-shaped each having a portion parallel to a tube axis of the waveguide and a portion perpendicular to the tube axis. Provided point-symmetrically with respect to a point on the tube axis of the waveguide, and provided between the end face of the other end of the waveguide and a position approximately ½ of the transmission wavelength of the high frequency By arranging two L-shaped radiation ports symmetrically, the direction of the electric field exciting each radiation port is different, and the high frequency radiated from each radiation port is coupled in the vicinity of the radiation port. To produce a wide radiation distribution around the radiation opening. This behavior near the radiation port mitigates the influence on the high-frequency generating means due to the difference in the amount and shape of the object to be heated, and allows the high-frequency generating means to operate stably for various objects to be heated. Use efficiency can be increased.
[0015]
In addition, the maximum distance in the tube axis direction of the waveguide of the two radiation ports is set to approximately ½ of the transmission wavelength of the high frequency transmitted through the waveguide, so that the direction of the high-frequency electric field across each radiation port can be changed. The directions can be defined in opposite directions, and the omnidirectional radiation direction can be reliably achieved.
[0016]
According to a second aspect of the invention, in particular, in the invention described in claim 1, with the configuration annexed to the vicinity to the capacitance component of the points of the point symmetry, each emission opening by concentrating the high frequency in the vicinity of the point symmetry point Can be maintained stably.
[0017]
According to a third aspect of the present invention, in particular, in the first aspect of the present invention, the two radiation ports are configured not to cross the tube axis of the waveguide, and the radiation located on the high frequency generating means side. The radiation energy from the mouth can be suppressed and high frequency excitation of each radiation mouth can be guaranteed.
[0018]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0019]
Example 1
1 is a cross-sectional configuration diagram of a high-frequency heating apparatus showing Embodiment 1 of the present invention, FIG. 2 is a configuration diagram of a waveguide of FIG. 1, and FIG. 3 is a high-frequency electric field distribution by a radiation port of FIG.
[0020]
In the figure, 10 is a heating chamber for storing an object to be heated, 11 is a waveguide, and a high frequency generating means 12 is attached to one end. A radiation port 13 provided on the wall surface of the heating chamber 10 is disposed at the other end of the waveguide 11. Reference numeral 14 denotes a mounting tray on which an object to be heated is placed, 15 is a turntable, and 16 is a drive motor for the turntable.
[0021]
The radiation port 13 has a waveguide end face 17 far from the side on which the high frequency generating means 12 of the waveguide 11 is mounted, and a distance of about ½ of the transmission wavelength of the frequency transmitted from the end face 17 to the waveguide 11. It is placed on the wall between the remote location. The radiant aperture 13 has radiant apertures 13a and 13b made up of two L-shaped openings arranged symmetrically. The point-symmetrical position is on the tube axis 18 of the waveguide 11 and is indicated by 19 in FIG. The opening of each radiation port 13a, 13b has a portion parallel to the tube axis 18 and a portion perpendicular to the tube axis 18, and the openings are arranged so as not to cross the tube axis 18. In addition, a metal post 20 is provided to which a capacitive component is added and an impedance matching action is added to a waveguide wall surface facing the radiation port at a point-symmetrical position of the radiation port. Reference numeral 21 denotes a connection hole into which the output antenna of the high frequency generator 12 is inserted. Further, 22 shows an example in which the transmission wavelength in the waveguide is a standing wave distribution, but it is not necessary to limit the length of the waveguide 11 to resonate in the waveguide as shown.
[0022]
Next, the main operation of the above configuration will be described. A high-frequency current as indicated by arrows 23 to 26 in FIG. 2 flows through the waveguide wall surface, and a high-frequency electric field in the direction indicated by arrows 23 to 26 is similarly generated at the L-shaped radiation ports 13a and 13b. The direction of the high-frequency electric field is distributed in all directions, thereby producing a high-frequency electric field distribution as shown in FIG. That is, the region where the electric field is strong appears at the point-symmetrical position of the L-shaped radiation port, and the high-frequency wave propagates in the direction perpendicular to the tube axis of the waveguide 11. The strong field intensity at the point-symmetrical position is due to the high frequency radiated from each radiation port being coupled in the vicinity of the radiation port, thereby forming a wide radiation distribution around the radiation port. Due to the behavior near the radiation port, the influence on the high-frequency generating means due to the difference in the amount and shape of the object to be heated is mitigated, and the high-frequency generating means can be stably operated with respect to the object to be heated in various ranges. Energy utilization efficiency can be increased.
[0023]
In FIG. 3, the reason that the high-frequency electric field distribution is not symmetric with respect to the tube axis of the waveguide is that the radiation energy from the radiation port on the high-frequency generating means side is strong, and the opening shape of this radiation port. It is possible to improve the symmetry by reducing.
[0024]
(Example 2)
Next, a second embodiment of the present invention will be described with reference to FIGS. The difference between the second embodiment and the first embodiment is that the placing plate on which the object to be heated is placed is a square plate and has a non-rotating configuration, and an opening is provided on the wall surface of the heating chamber provided with a radiation port. Is provided with means for changing the high-frequency impedance of the part.
[0025]
That is, in FIG. 4, 30 is a mounting plate made of a ceramic material, and 31 and 32 are openings provided on the wall surface forming the heating chamber 10. Further, impedance varying means 50 shown in FIG. 5 is disposed outside the heating chamber 10 so as to close the openings 31 and 32.
[0026]
In FIG. 5, the impedance varying means 50 has a box-shaped portion 51 made of a metal member as a main body, and is configured to form a groove portion by being assembled and mounted on the heating chamber wall surface. In the box-shaped part 51, a rotating plate 52 having a plate-like structure is provided. Rotating shafts 53 and 54 for rotating the rotating plate 52 are provided at both ends of the rotating plate 52, and the rotating shaft 53 is inserted into a hole provided in the wall surface of the box-shaped portion 51 and is rotatably supported by the hole. On the other hand, the rotary shaft 54 is connected to an output shaft of a stepping motor 55 which is a means for rotating the rotary plate 52. Reference numeral 56 denotes a light shielding portion for detecting the rotation angle provided on the rotation shaft 54, and a photo interrupter (not shown) is used as the rotation angle detecting means. Reference numerals 57 to 60 are heating chamber mounting flanges which are spot-welded and assembled to the heating chamber wall surface. 61 is a hole for mounting the rotating plate 52 in the box-shaped part 51. As specific dimensions of the box-shaped part 51, the width is 80 mm, the length is La + Lb, and the height is 20 mm. La and Lb dimensions are the lengths from the center of the rotating plate 52 to the respective end faces of the box-shaped part 51. When the impedance variable means having such a configuration is mounted in the heating chamber, the opening 62 (31, 32 in FIG. 4) is arranged at a predetermined position on the La dimension side of the box-shaped part 52. As a result, the end of the groove portion formed by the box portion 51 and the heating chamber wall surface is a wall surface 63 forming the box portion 51 in FIG. The support angle of the rotating plate 52 defines the state where the wide surface 52a of the rotating plate 52 is substantially parallel to the wall surface 63 as 0 degree.
[0027]
The rotating plate 52 has a heat resistant temperature of 200 ° C. or higher and a non-metallic material of a resin material or an inorganic material having a low dielectric loss characteristic in a frequency band used by the apparatus, and the base material has a predetermined plate thickness. In addition, each is formed or fired. Next, the operation and action of the impedance varying means 50 will be described. The impedance variable means can be configured such that La = 30 mm and Lb = 20 mm to vary the phase value of the voltage reflection coefficient S11 at the opening 62 in a range of approximately ± 180 degrees to approximately −30 degrees. That is, in this case, by rotating the rotating plate 52, an impedance in which the capacitive reactance component is changed can be formed in the opening 62. Further, by adopting the configuration of La = 50 mm and Lb = 20 mm, the phase value of the voltage reflection coefficient S11 at the opening can be varied from approximately +90 degrees to ± 180 degrees through approximately −135 degrees. That is, in this case, when the rotating plate 52 is rotated, the inductive reactance component (phase value range: +90 degrees to ± 180 degrees) and the capacitive reactance component (phase value range: ± 180 degrees are approximately − 135 degrees) value can be present. Furthermore, by adopting a configuration of La = 70 mm and Lb = 20 mm, the phase value of the voltage reflection coefficient S11 at the opening 62 can be varied from approximately +0 degrees to +90 degrees to a range of approximately ± 180 degrees. That is, in this case, by rotating the rotating plate 52, the opening 62 can have an impedance in which the inductive reactance component changes.
[0028]
When the phase value of the voltage reflection coefficient at the opening is approximately ± 180 degrees, that is, when the impedance of the opening is approximately zero, the opening can be operated in the same manner as the metal wall surface.
[0029]
When the support angle of the rotating plate 52 is changed, the impedance of the opening 62 is changed, and the phase difference between the high frequency incident wave and the reflected wave at the opening 62 can be changed. The phase difference between the high frequency incident wave and the reflected wave on the metal wall surface of the heating chamber 10 is 180 degrees. On the other hand, the phase difference between the incident wave and the reflected wave at the opening provided on the metal wall surface is 180 degrees when the impedance value of the opening is zero, 0 degrees when the impedance value is infinite, and in the case of inductive reactance. The phase of the reflected wave is delayed with respect to the incident wave, and the phase is advanced in the case of capacitive reactance. The apparent size of the heating chamber changes with the change in phase between the incident wave and the reflected wave. In the case of inductive reactance, the size of the heating chamber is apparently larger than the radio wave effect, whereas in the case of capacitive reactance, it is reduced. This is, for example, to change the apparent distance between the object to be heated housed in the heating chamber and the radiation port. By utilizing this phenomenon, the heating area on the plane of the object to be heated can be changed, or the heating area in the height direction of the object to be heated can be changed, and the object to be heated can be moved without moving the object to be heated. Uniform heating can be achieved.
[0030]
Further, the openings are arranged as shown in FIG. 4 and the rotation plate of the impedance varying means is controlled to rotate corresponding to each opening, thereby deflecting the high-frequency distribution in the heating chamber in the vertical and horizontal directions of the heating chamber. Can be made. By utilizing these action phenomena, it is possible to variably control the heating region of the object to be heated without rotating the object to be heated, thereby heating the object to be heated uniformly.
[0031]
Next, actual heating characteristics of the high-frequency heating device shown in FIG. 4 will be described with reference to FIGS. 6 and 7.
FIG. 6 shows the ratio of the heating power absorbed by water calculated from the temperature rise value of each amount of water and the ratio of the heating power to the input power of the apparatus as efficiency. In FIG. 6, 71 is a heating power characteristic and 72 is efficiency with respect to the radiation port shown in FIG. 4, while 73 is a heating power characteristic and 74 is efficiency with respect to the conventional rectangular radiation port. From the same characteristics, the use efficiency of the high-frequency energy can be improved as a whole by using the radiation port of the present invention, and the use efficiency for a small load can be greatly improved. The impedance values of the openings 31 and 32 are substantially zero.
[0032]
FIG. 7 shows a heating distribution when 180 g of ad hair synthetic paste is put in a commercially available sake bottle and subjected to high-frequency heating. The radiation port is as shown in FIG. 4, where (a) shows that the impedance values of the openings 31 and 32 are substantially zero, and (b) shows that the impedance values of the openings 31 and 32 are almost infinite. It is the heating distribution at the time. From the characteristics shown in the figure, it was recognized that the heating region can be changed in the vertical direction by changing the impedance of the opening. It was also recognized that uniform heating can be realized by controlling the impedance of the opening for the object to be heated, which can be made uniform by heating from below, such as milk and sake lees.
[0033]
(Example 3)
Next, Embodiment 3 of the present invention will be described with reference to FIG. The difference between the third embodiment and the second embodiment is a configuration in which the positions of the openings are arranged corresponding to the radiation distribution from the radiation port.
[0034]
That is, in FIG. 8, the longitudinal directions of the openings 75 and 76 are arranged so as to be parallel to the tube axis of the waveguide 11 in accordance with the radiation distribution shown in FIG. According to such an arrangement of the openings, the high-frequency distribution in the heating chamber 10 can be deflected in the left-right direction in FIG. 8 by changing the impedance of the openings. This is particularly effective for promoting uniform heating in flat heating objects such as frozen okonomiyaki or simultaneous heating of a plurality of heating objects.
[0035]
Example 4
Next, Embodiment 4 of the present invention will be described with reference to FIGS. The difference between the fourth embodiment and FIG. 2 of the first embodiment is the configuration of the radiation port.
[0036]
That is, in FIG. 9, the radiation port provided in the waveguide 11 that transmits a high frequency is a rectangular radiation port 100 and diagonals 101 and 102 of the radiation port 100, and is in the tube axis direction 18 of the waveguide 11. Each of the connecting radiation ports 103 and 104 extends. The opening shape of the rectangular radiation port 100 is configured to resonate in a high frequency band that transmits the waveguide 11. That is, when the frequency is 2455 MHz, it is a square shape with a side length of about 61 mm.
[0037]
The distance between the terminal ends of the coupling radiation ports 103 and 104 (indicated by 105 in FIG. 9) is set to ½ or more of the high-frequency transmission wavelength transmitted through the waveguide in the tube axis direction 18 of the waveguide. Specifically, when the frequency is 2455 MHz and the width dimension of the waveguide H surface is 80 mm, the transmission wavelength in the waveguide is about 190 mm, and the distance between the terminal ends of the coupling radiation ports 103 and 104 is 95 mm or more. Therefore, the opening shape of the connection radiation port is, for example, 20 mm wide and 30 mm long (17 mm or more in calculation).
[0038]
According to the radiation port having such a configuration, a high-frequency electric field indicated by arrows 106 to 109 in FIG. 9 is generated by a high-frequency current flowing through the waveguide wall surface. That is, the excitation direction of the rectangular-shaped radiation port 100 can be a direction crossing the tube axis of the waveguide, and this excitation form generates a high-frequency electric field distribution as shown in FIG. From this high-frequency electric field distribution, the high-frequency radiation direction by the radiation port configuration shown in the fourth embodiment can be made to cross the tube axis of the waveguide. Thereby, a high frequency can be radiated in the direction of the diagonal line of the heating chamber in the substantially rectangular parallelepiped heating chamber, and a bulky object to be heated can be heated uniformly.
[0039]
(Example 5)
Next, a fifth embodiment of the present invention will be described with reference to FIG. The fifth embodiment is different from the third embodiment in the arrangement of the opening on the wall surface of the heating chamber.
[0040]
That is, in FIG. 11, 110 is an opening provided on the wall surface of the heating chamber 10. The opening 110 is provided at a predetermined position based on the high-frequency electric field distribution of FIG. 10 so that the longitudinal direction of the opening 110 is parallel to the line connecting the starting points 101 and 102 of the coupling radiation port. . Further, an impedance variable means 50 shown in FIG. 5 is disposed outside the heating chamber 10 so as to close the opening 110.
[0041]
According to this configuration, uniform high frequency heating can be performed without changing the object to be heated by changing the high frequency distribution in the heating chamber by changing the impedance of the opening. Further, by providing the longitudinal direction of the opening parallel to the line connecting the starting points of the connection radiation ports, the impedance change of the opening can be reliably applied to the change of the high-frequency distribution in the heating chamber. Furthermore, the high frequency distribution in the heating chamber can be changed in the vertical direction or the horizontal direction with only one impedance variable means.
[0042]
In addition, it is desirable from the viewpoint of processing and suppressing the occurrence of sparks by the edge portion that the corner portion of each radiation port is appropriately rounded. Further, the radiating portion and the opening are sealed with a mica material or the like in order to avoid the scattering of the heated object. The range of change in the impedance of the opening is not limited to the above description. For example, when the support angle of the rotating plate is 90 degrees, the impedance of the opening is made substantially zero so that only the inductive component is variable. Or, when the support angle of the rotating plate is approximately 45 degrees, the variable impedance range including both the inductive component and the capacitive component can be set by setting the impedance of the opening to substantially zero. Furthermore, you may attach an impedance variable means to the heating chamber of the structure which rotates a mounting tray.
[0043]
【The invention's effect】
As described above, according to the present invention, by arranging a plurality of L-shaped radiation ports in point symmetry, the directions of the electric fields that excite the radiation ports are different from each other, and the high frequencies radiated from the radiation ports are different. Are combined or repelled in the vicinity of the radiation aperture to form a wide radiation distribution around the radiation aperture. This behavior near the radiation port mitigates the influence on the high-frequency generating means due to the difference in the amount and shape of the object to be heated, and allows the high-frequency generating means to operate stably for various objects to be heated. Use efficiency can be increased.
[0044]
In addition, an opening provided on the wall surface of the heating chamber at a position different from the radiation port and impedance variable means for changing the high-frequency impedance in the opening can be provided to change the impedance of the opening so as to change the high frequency from the radiation port. The uniform heating can be promoted without changing the radiation direction and moving the object to be heated.
[0045]
In addition, by including a rectangular radiation port provided in the waveguide that transmits high frequency, and a connection radiation port that extends in the tube axis direction of the waveguide starting from the diagonal of the radiation port, The excitation direction of the rectangular radiation port can be set to a direction that intersects the tube axis of the waveguide, and the excitation direction can be set to the direction that intersects the tube axis of the waveguide. Thereby, a high frequency can be radiated in the direction of the diagonal line of the heating chamber in the substantially rectangular parallelepiped heating chamber, and a bulky object to be heated can be heated uniformly.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of a high-frequency heating device according to a first embodiment of the present invention. FIG. 2 is a configuration diagram of a waveguide of the high-frequency heating device. FIG. 5 is a cross-sectional configuration diagram of a high-frequency heating device according to a second embodiment of the present invention. FIG. 5 is a configuration diagram of impedance variable means of the high-frequency heating device. FIG. 8 is a cross-sectional configuration diagram of the high-frequency heating device according to the third embodiment of the present invention. FIG. 9 is a cross-sectional configuration diagram of the high-frequency heating device according to the fourth embodiment of the present invention. High-frequency electric field distribution diagram of high-frequency heating device [FIG. 11] Cross-sectional configuration diagram of high-frequency heating device of Example 5 of the present invention [Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Waveguide 12 High frequency generation means 13, 13a, 13b Radiation port 18 Tube axis 19 Point symmetry position 20 Metal post (capacitance component)
31, 32, 62, 75, 76, 110 Opening 50 Impedance variable means 100 Rectangular radiation port 101, 102 Diagonal origin 103, 104 Linked radiation port

Claims (3)

A heating chamber for storing an object to be heated, a high-frequency generating means for generating a high frequency, and a high-frequency generating means mounted at one end and two radiation ports provided at the other end, thereby transmitting the high-frequency to the heating chamber. A wave tube, and each of the two radiation openings has an L shape having a portion parallel to and perpendicular to a tube axis of the waveguide, and is on the tube axis of the waveguide. A high-frequency heating device provided symmetrically with respect to a point, and provided between the end face of the other end of the waveguide and a position approximately ½ of the high-frequency transmission wavelength . The high-frequency heating device according to claim 1, comprising a configuration in which a capacitive component is provided in the vicinity of a point-symmetrical point. The two radiating port high frequency heating apparatus according to claim 1 where the structure does not cross the tube axis of the waveguide.

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