JPS6249716B2 - - 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. 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=j Zotan(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|=Zotan(π/2)=
It is based on the principle of achieving ∞. When the inside of the chiyoke groove is filled with dielectric material (relative permittivity εr),
The radio wave wavelength λ' is compressed to λ'=λo/√.
In this case, the groove depth l' becomes short as l'≒l/√. However, 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. FIGS. 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, a wall surface 2.3 provided on the door 1 extending in the x direction and a 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 n small grooves 2, 3, and n are changed are shown in a, b, and c. The section of characteristic impedance Zio has a length li, and the impedance seen from the impedance change point to the groove end side is
Zi, and the impedance when looking from the groove opening to the groove end side is Zin _o . i is a subscript Specifically, in case (a) where the groove is divided into two, Z ₂ = jZ ₂₀ tanβl ₂ ≡jx ₂ or less β is β = 2π/λo Zin = Z ₁₀ Z ₂ +jZ ₁₀ tanβl ₁ /Z ₁₀ +jZ ₂
tanβl ₁ However, (Z ₁₀ <Z ₂₀ ) In the case of (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 tanβl _o Zn−1=Z(n− 1) oZn+jZ(n−1) otanβl(n−1)
/Z(n-1)o+jZntanβl(n-1)〓〓 However, (Z ₁₀ <Z ₂₀ ... < Z ₃₀ ) Z ₂ =Z ₂₀ Z ₃ +iZ ₂₀ tanβl ₂ /Z ₂₀ +jZ ₂
tanβl ₂ ≡jX _o Zin _o =Z ₁₀ Z ₂ +iZ 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 in the case of n discontinuous characteristic impedances.
₂ tanβl ₁ =jZ ₁₀ xn+Z ₁₀ tanβl ₁ /Z ₁₀ −xnta
nβl becomes ₁ . The above formula is valid if Z ₁₀ xntanβl 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=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.
When the combination of l ₁ , l ₂ , (l ₃ ), and ltotal is calculated assuming that the ratio of the opening characteristic impedance Z ₁₀ to the termination characteristic impedance Z ₂₀ or Z ₃₀ is 1:2, the result is as follows.

【table】

【table】

[Table] This result means the following (1) The characteristic impedance is 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. (2) The dimensional compression ratio of the depth of the groove is almost determined by the opening characteristic impedance Z ₁₀ and the end characteristic impedance Z _op , and is hardly influenced by the number of changes n 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: (1) Increasing the absolute value of the impedance of the small groove opening reduces the amount of radio wave leakage. (2) For the groove depth dimensions (l ₁ , l ₂ ) that increase the aperture impedance of small grooves, the calculated values and actual measurements must match accurately. (3) 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. Excite point A under the same conditions,
When the groove depth l _T is changed, the electric field of the transmission line changes as a, b, and c, and the radio wave does not reach the D end in case b, that is, the groove depth l _T
is about 80% of a quarter wavelength (less than λ/4 line), and even if it is longer or shorter than that (cases a and c), radio waves leak more than in case 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 comprises a line group in which at least one of the wall groups constituting a small groove has a conductor width a smaller than the pitch p, and (i) short-circuits the conductor width a ₁ at the groove opening. The conductor width shall be larger than ₂ . (ii) Make the effective permittivity of the groove opening part larger than the effective permittivity of the short-circuit termination part. (iii) The width of the small groove is within a range smaller than a quarter of the wavelength used, and the groove width b ₁ of the opening part is smaller than the groove width b ₂ of the short-circuit termination part. The present invention is characterized in that the depth of the small groove is made smaller than a quarter of the wavelength used by combining two or more of the above structures. An example is illustrated in FIG. A small groove 9 is constituted by the groove wall groups 6, 7, and 8. The inside of the trench consists of two regions: a region filled with dielectric 10 and a space region. The boundaries between regions are 11. The figure shows a combination of the above, the conductor width is a ₁ > a ₂ , the effective permittivity on the opening side is εr, and the permittivity on the end side is 1
, and the dielectric constant on the opening side is large. The groove width is b ₁ < b ₂ . It is becoming. The characteristic impedance Zo is between the conductor width a and the effective dielectric constant εr groove width b.

Because of the relationship of [Formula] (k″: constant of proportionality), the depth of the groove can be synergistically reduced in size. 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 made up 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) Changes in the conductor width and groove width (4) When combining dielectric loading and changing the conductor width or groove width, the dielectric can also be used as a spacer. (5) When dielectric loading is combined with conductor width change or groove width change, the line width or groove width change boundary after inserting the dielectric is Can be used as a prevention part.

[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 of the present invention; Fig. 10 a, b, c are cross-sectional views, side views, and characteristic diagrams of the device at 915 MHz; Fig. 11 a, b, c are cross-sectional views of the device at 2450 MHz. , a side view, a characteristic diagram, and a perspective view of an embodiment of the present invention. 6, 7, 8...Groove wall group, 9...Small groove, 10...
...dielectric material, a ₁ ... line width at opening, a ₂ ... line width at short-circuit termination, p... pitch, b ₁ ... groove width at opening,
b ₂ ...Short-circuit end groove width.

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 at least one small groove having a groove opening surrounded by a group of groove walls and a short-circuit termination. However, at least one of the wall groups is composed of a line group in which the conductor width in the (b) a configuration in which the conductor width at the groove opening portion is larger than the conductor width at the short-circuit termination portion; (c) a configuration in which the effective permittivity of the groove opening portion is greater than the effective permittivity of the short-circuit portion; A radio wave sealing device having a combination configuration of two or more of the above, and in which the width and depth of the small groove are substantially smaller than a quarter of the wavelength used.