JPS6314831B2 - - 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 especially 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. That is, the characteristic impedance of the chiyoke groove is Zo,
When the depth of the groove is l and the terminal end is short-circuited, the impedance Zin at the chiyoke groove opening is Zin=jZotan (2πl/λo). However, λo is the free space wavelength, and the Chi-Yoke method is based on the principle that |Zin|=Zotan(π/2)=∞ is achieved by selecting the groove depth l to be λo/4. When the cheese groove is filled with a dielectric material (relative dielectric constant εr), the radio wave wavelength λ' is compressed to λ'=λo/√. In this case, the groove depth l' becomes short as l'≒l/√. but,
There is no difference in setting l'=λ'/4. Therefore, in the chiyoke method, the depth of the chiyoke 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 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 smaller than the characteristic impedance of the end of the groove, and that both the width and depth of the groove are smaller 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 εv. As is well known, the characteristic impedance Zo in this case is

[Formula] (k: constant of proportionality). Therefore, the characteristic impedance Zo is the line width a
To widen the line gap b, to narrow the line gap b,
By increasing the relative dielectric constant εv, it can be reduced to a small value. 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. In FIG. 5, examples in which the impedance of the small grooves is changed by 2, 3, and n are shown in 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, in the case of (a) where the groove is divided into two, 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 _1However , (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 _1However , in the case of (Z ₁₀ <Z ₂₀ <Z ₃₀ ) (c), Zn=jZnotanβln Zn−1=Z(n−1)oZn+jZ(n−1)atanβl (n
−1) /Z(n-1)o+jZntanβl(n-1)…However, (Z ₁₀ <Z ₂₀ …<Z ₃₀ ) Z ₂ =Z ₂₀ Z ₃ +jZ ₂₀ Jtanβl 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 opening is Zin _o =Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +iZ ₂ tanβl ₁ =jZ ₁₀ x _o +Z ₁₀ tanβl 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 tanβl ₁ is a requirement for increasing the impedance at the groove opening. In the example of λo=122.4 mm (=2450 MHz) λo/4=30.8 mm, the condition of Z ₁₀ ≒ x _o tanβl ₁ is satisfied for the case of two discontinuities in figure a and three discontinuities in figure b. l ₁ , l ₂
(l ₃ ), ltotal combination of opening characteristic impedance Z ₁₀ and termination characteristic impedance Z ₂₀ or Z ₃₀
If the ratio is 1 to 2, it will be calculated 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 plots the absolute value of the characteristic impedance of the aperture using dimension l ₂ as a parameter when dimension l ₁ is 12 mm, and shows that the maximum value is obtained when dimension l ₂ is 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. For the groove depth dimensions (l ₁ , l ₂ ) that increase the aperture impedance of small grooves, the calculated values and actual measured values 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, a 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 (line less than λ/4)
, and even if it is longer or shorter than that (a, c
), the radio waves leak more than in case b. In actual applications, it is not uncommon to provide a groove cover space (TOP1) and a bending reinforcement space ( _lX1 ). 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 5~6mm
An example is shown below. 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.
This shows the relationship in which the groove depth l _T changes with the reinforcement space (l _X1 ) fixed as TOP1 = 2 mm. Space l _X1 2
By setting it to ~6 mm, the groove depth l _T becomes 1 to 3 mm deeper. DESCRIPTION OF THE EMBODIMENTS The present invention changes the characteristic impedance by changing the width of the small groove. Examples are shown in FIGS. 12a and 12b. The radio wave sealing device consists of groove walls 6, 7, 8, 9, a small groove 10 and an outer groove 11.
is partitioned by a wall 9, and this wall has a conductor width a,
It is composed of a group of lines with pitch p (p>a).
12 is a main body wall. With this configuration, the groove width of the small groove aperture is smaller than that of the terminal end, which is the bottom of the groove, so that the characteristic impedance of the aperture can be made smaller than that of the terminal end. Therefore, the depth L of the small groove can be made substantially smaller than a quarter wavelength, and the radio wave sealing device can be made smaller. Although it is possible to fill the small grooves with a dielectric material as in the case of the Chi-Yoke method, since the depth of the small grooves can be substantially less than a quarter wavelength, it is possible to use the same dielectric material. If so, the depth can be made smaller than the depth of the chiyoke groove. As described above, in the present invention, the radio wave sealing device is basically configured with approximately parallel microstrip lines. 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 radio wave propagation component in the x direction can be reduced, and the radio wave sealing performance can be improved. (3) Simple processing is sufficient by simply deforming one of the wall surfaces. (4) Since the wall surface is bent, the strength is increased when the wall surface is made of sheet metal. (5) Since the lines are roughly parallel, manufacturing and processing are easy.

[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 part of the device of the present invention, 1st
Figures a, b, and c are cross-sectional views of the device at 915MHz,
Side view, characteristic diagram, Figure 11 a, b, c are 2450MHz
Sectional view, side view, and characteristic diagram of the device in 12th
Figures a and b are cross-sectional views showing embodiments of the present invention. 6, 7, 8... Groove wall group, 6, 9... Wall surface, 10
...Small groove, a...Conductor width, p...Pitch.

Claims (1)

[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, and the wall surface at least one of the group
The conductor width a and the pitch p are p>a in the x direction.
, and at least one of the wall surfaces extending in the depth direction of the small groove has a groove width smaller than a quarter of the wavelength used. A radio wave sealing device in which the short-circuit end portion is larger than the groove opening portion, and the substantial depth of the small groove is smaller than a quarter of the wavelength used.