JPS6249715B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a radio wave seal for a high frequency heater. This is particularly effective when applied to devices such as microwave ovens that have doors that can be opened and closed. Conventional configurations and their problems Many radio wave sealing devices have been proposed, and one that is in practical use is the "chiyoke system." Furthermore, there is a prior art that takes measures against radio wave propagation in the longitudinal direction of the chiyoke groove in this "chiyoke method." However, these devices are characterized in that they have a chiyoke groove, and that the effective depth from the chiyoke groove opening to the chiyoke groove end is a quarter wavelength of the frequency of the radio wave used. In other words, the characteristic impedance of the chiyoke groove is
Zo, groove depth l, and impedance Zin at the chiyoke groove opening when the terminal ends are short-circuited.
becomes Zin=jZo tan(2πl/λo). However, λo is the free space wavelength, and in the Chiyoke method, the depth l of the groove is λ
By choosing o/4, |Zin|=Zo tan(π/2)=
It is based on the principle of achieving ∞. When the inside of the chiyoke groove is filled with dielectric material (relative permittivity ε _r ),
The radio wave wavelength λ' is compressed to λ'=λo/ _√v .
In this case, the groove depth l' becomes short as l'≒l/ _√v . However, there is no difference in setting it to l'l'/4. Therefore, in the Chi-Yoke method, the depth of the Chi-Yoke groove cannot be made substantially smaller than a quarter wavelength, and there is a limit to miniaturization. Figures 1 and 2 show examples of conventional configurations. OBJECTS OF THE INVENTION The present invention is similar to the Chi-Yoke method in that it uses a groove for radio wave sealing, but is called a small groove to distinguish it from the Chi-Yoke groove. The present invention aims at configuring the depth of the miniature grooves to be substantially less than a quarter wavelength. Miniaturization can be achieved by changing the characteristic impedance of the small groove in the depth direction of the groove. The limiting conditions are that the characteristic impedance of the aperture of the small groove is less than the characteristic impedance of the end of the groove, and that both the width and depth of the groove are less than one quarter of the effective radio wavelength. The characteristic impedance will be explained below using FIGS. 3 and 4. FIG. 3 is a perspective view of a parallel line, where the line width is a, the line gap is b, and the dielectric constant of the dielectric medium is ε _v . As is well known, the characteristic impedance Zo in this case is

[Formula] (k: constant of proportionality). Therefore, the characteristic impedance Zo can be reduced to a small value by widening the line width a, narrowing the line gap b, and increasing the dielectric constant ε _v . FIG. 4 shows an example of the structure of the door. In this case, the wall surfaces 2 and 3 extending in the x direction provided on the door 1 and the width a,
A groove 5 having a groove width b is formed by a conductive line group 4 having a pitch p. In this case, the conductor line group 4 acts as a radio wave propagation system against the wall surface corresponding to the ground plane, but the characteristic impedance Zo for each line is

[Formula] (k': constant of proportionality) holds almost the same relationship as in the case of parallel lines. Structure of the Invention The principle of the present invention will be explained using FIGS. 5 to 8. FIG. 5 shows an example in which impedances of the small grooves are changed by 2, 3, and n at a, b, and c. The section of the characteristic impedance Zio has a length li, the impedance seen from the impedance change point to the groove end side is Zi, and the impedance seen from the groove opening part to the groove end side is Zin _o . i is a subscript, specifically the groove is 2
In the case of divided (a), Z ₂ = jZ ₂₀ tanβl ₂ ≡jx ₂ or less β is β = 2π/λo Zin ₂ = Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ
₂ tanβl ₁ However, in the case of (Z ₁₀ <Z ₂₀ ) (b), Z ₃ =jZ ₃₀ tanβl ₃ Z ₂ =Z ₂₀ Z ₃ +jZ ₂₀ tanβl ₂ /Z ₂₀ +jZ ₃
tanβl ₂ ≡jx ₃ Zin ₃ =Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ
₂ tanβl ₁ However, in the case of (Z ₁₀ <Z ₂₀ <Z ₃₀ ) (c), Zn=jZno tanβln Zn−1=Z(n−1)oZn+jZ(n−1)o tanβl(n−1)/Z(n -1) o+jZn
tanβl(n-1)〓〓 However, (Z ₁₀ <Z ₂₀ ...<Z ₃₀ ) Z ₂ =Z ₂₀ Z ₃ +jZ ₂₀ tanβl ₂ /Z ₂₀ +jZ ₂
tanβl ₂ ≡jx _o Zin _o =Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ
₂ tanβl ₁ . Therefore, the impedance seen from the small groove hole is n
For discontinuous characteristic impedances Zin _o =Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ ₂ tanβl ₁ =jZ ₁₀ x _o +Z ₁₀ tanβ
l ₁ /Z ₁₀ −x _o tanβl ₁ . The above formula is valid if Z ₁₀ and x _o tanβl ₁ are equal |
Zin _o ｜ means that it can be made into ∞. i.e. Z ₁₀
It can be seen that = x _o tan βl ₁ is a requirement for increasing the impedance at the groove opening. In the example of λo=12.4 mm (=2450 MHz) λo/4=30.8 mm, the condition of Z ₁₀ ≒ x _o tanβl ₁ is satisfied for the case of one discontinuity in figure a and three discontinuities in figure b.
The combination of l ₁ , l ₂ , (l ₃ ), and l total has the opening characteristic impedance Z ₁₀ and the termination characteristic impedance Z ₂₀
Or, if the ratio of Z ₃₀ is calculated as 1:2, it will be as follows.

【table】

【table】

[Table] This result means the following. Characteristic impedance Z ₁₀ < Z ₂₀ or Z ₁₀ < Z ₂₀
By setting <Z ₃₀ , the groove depth l (total) can be made smaller than a quarter wavelength. The dimensional compression ratio of the depth of the groove is almost determined by the opening characteristic impedance _Z10 and the end characteristic impedance Zno, and is hardly influenced by the number n of changes in the characteristic impedance. The above explanation is for the case where Z ₂₀ /Z ₁₀ = Z ₃₀ /Z ₁₀ = 2, but Fig. 6 shows the case where the ratio of dimensions l ₁ and l ₂ is changed from 1 to 5 in the case of two divisions. The graph shows the relationship between the characteristic impedance ratio and the compression ratio at which the depth of the small groove is reduced in size relative to the depth of the chiyoke groove. This graph shows that by carefully selecting the characteristic impedance, it is possible to reduce the characteristic impedance to less than one tenth of that of the chiyoke groove. Figure 7 is a blot of the absolute value of the characteristic impedance of the opening using dimension l ₂ as a parameter when dimension l ₁ is 12 mm, and shows that the maximum value is taken at dimension l ₂ of 24 mm and 25 mm. There is. Figure 8 shows the measured values of radio wave leakage. This result also
The _l2 dimension shows a minimum value between 23.5 mm and 24.5 mm, which means that: Increasing the absolute value of the aperture impedance of the small groove reduces the amount of radio wave leakage. Regarding the groove depth dimensions (l ₁ , l ₂ ) that increase the aperture impedance of the small groove, the calculated value and the actual measured value must match accurately. It is possible to reliably reduce the size compared to the depth of the chiyoke groove. The present invention performs impedance inversion using a less than λ/4 line instead of the λ/4 line that has been historically used in the field of radio wave seals. In order to make this principle easier to understand, part of the analysis results are shown in FIG. In FIG. 9, a groove having an opening B whose tip C is short-circuited is provided in a part of a transmission line in which the A end is an excitation source and the D end is open. The width of the groove on the short circuit side is twice that on the open hole side. When point A is excited under the same conditions and the depth of the groove l _T is changed, the electric field in the transmission line changes as shown in a, b, and c, and in case b the radio wave does not reach end D. , that is, when the groove depth l _T is approximately 80% of a quarter wavelength (λ/4
Even if the line is longer or shorter (cases a and c), radio waves leak more than line b. In actual application, the groove cover space (TOP1) and the bending reinforcement space (L _X1 )
is often provided. In these cases, compared to the case where the principle is explained, the radio waves are disturbed and the calculated dimensions are slightly deviated. The details of the deviation are shown below. When the dimension of TOP1 is 2mm and l _X1 is 5~
An example is shown when the width is set to 6 mm. Figure 10 is an example of a 915MHz sealing device.
This shows the relationship in which the groove depth l _T changes with the dimensions of TOP1. If the dimension of TOP1 is set to 1 to 3 mm, l _T becomes deeper by 1 to 6 mm. Figure 11 is an example of a 2450MHz sealing device, with the reinforcement space (l _X1 ) fixed at TOP1 = 2mm.
shows the relationship in which the groove depth l _T changes. By setting the space l _X1 to 2 to 6 mm, the groove depth l _T becomes deeper by 1 to 3 mm. DESCRIPTION OF EMBODIMENTS The present invention is characterized in that at least one of the wall groups constituting a small groove is made up of a line group with a conductor width smaller than the pitch, and that the characteristic impedance is increased stepwise in the depth direction of the groove. It is characterized by its composition. In FIG. 12, wall group 6,
A small groove 9 is constituted by 7 and 8, and a wall surface 8 is constituted by a group of lines. The small groove 9 has an aperture region of the groove and a region following it in the depth direction of the groove, and the boundary with the region is indicated by 10. When the characteristic impedance of the region Z ₁₀ (length l ₁ , propagation constant β ₁ =2π/λ ₁ ) and the characteristic impedance of the region are Z ₂₀ and reactance jX when looking from the boundary 10 to the groove end side, Z ₁₀ < Z ₂₀ It is characterized by the fact that it is set so that Z ₁₀ =Xtanβ ₁ l ₁ . By adopting such a configuration, the depth of the small groove can be made substantially smaller than one quarter of the wavelength used. Effects of the invention (1) The depth of the small groove can essentially be made smaller than a quarter wavelength. (2) Since at least one of the walls constituting the small groove is composed of a group of lines, the amount of radio wave propagation in the x direction can be reduced, and the radio wave sealing performance can be improved. (3) The characteristic impedance of each region is given by the conductor width a, the groove width b, and the dielectric constant ε _v .

Design is easy because the correlation with the amount of leakage can be determined by a simple calculation that it is proportional to [Formula].

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing conventional examples of chiyoke grooves;
FIG. 3 is a diagram showing a parallel line, FIG. 4 is a perspective view showing an example of the structure of a groove by a modified parallel line, FIGS. 5 to 8 are diagrams for explaining the principle of the present invention, and FIGS.
b, c are electric field analysis diagrams of the groove portion in the present invention, 1st
Figure 0 a, b, and c are cross-sectional views, side views, and characteristic diagrams of the device at 915MHz. Figure 11 a, b, and c are
FIG. 12 is a perspective view of the device of the present invention. 6, 7, 8...Groove wall group, 9...Small groove, 10...
...boundary, a... conductor width, p... pitch.

Claims (1)

[Scope of Claims] 1. At least one of the door or the main body of a high-frequency heater having a door that can be opened and closed has one or more small grooves having a groove opening surrounded by a group of groove walls and a short-circuit end. However, at least one of the wall groups is composed of a line group in which the conductor width in the x direction is smaller than the pitch, and the characteristic impedance is gradually increased from the opening in the depth direction of the small groove. At the same time, the aperture area parameters are set to characteristic impedance Z ₁₀ and propagation constant β ₁ (=2π/λ ₁
), and when the reactance seen from the boundary between the above opening area and the next area to the end of the groove is jX, Z ₁₀ =X
A radio wave sealing device in which the width and depth of the groove are set within a range that is substantially smaller than a quarter of the wavelength used so that tanβ ₁ l ₁ .