JPH0159716B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microstrip line and an improvement in a microwave heating device using the same. Hitherto, microstrip lines in which a ladder pattern is formed on the center conductor, and microwave heating devices using this have already been proposed (for example, Japanese Patent Application No. 163751/1986,
178332). For a moment, this conventional example will be explained with reference to FIG. In the figure, 1 is a microstrip line, which is composed of a dielectric substrate 2 made of alumina ceramic or the like, a wide center conductor 3 attached to its upper surface, and a ground conductor 4 attached to its lower surface. . A plurality of slits 5 are opened in the central conductor 3 along the propagation direction of the microwave, and a ladder pattern 6 is formed. 7 is
This is a coaxial line for supplying microwaves to one end of the microstrip line 1 , and is connected to a magnetron (not shown). 8 is a dummy load attached to the other end of the microstrip line 1, which absorbs and consumes the microwaves that have not been completely consumed by the ladder pattern 6. When a heated object 9 that is thinner than the direction of arrow A is scanned on such a microstrip line 1 and microwaves are supplied from the direction of arrow B, a part of the supplied microwaves is transmitted to each of the slits 5. leaks from ... and the object to be heated 9 is heated by microwaves. The characteristic impedance of such a microstrip line 1 is approximately given by the following equation ().
Z ₀ =10 ⁴ /3√εr{7+8.83(a/h)} ...() Here, εr is the relative permittivity of the dielectric substrate 2, h is the thickness of the dielectric substrate 2, and α is the center conductor. 3, that is, the length in the direction intersecting the microwave propagation direction. In the conventional example, εr′=9, α=40mm,
Since h = 2 mm, Z ₀ = 6, and the characteristic impedance of the microstrip line is 6.
It was around Ω. On the other hand, the characteristic impedance of the coaxial line 7 that supplies microwaves to the microstrip line 1 is about 50Ω. Therefore, it is necessary to match the impedance between the microstrip line 1 and the coaxial line 7, and for this purpose, the width of the connecting portion of the center conductor 3 to the coaxial line 7 is gradually narrowed as shown in the figure. Therefore, the microstrip line 1 had to be made longer than necessary, resulting in an increase in the size of the entire device. Furthermore, since the width of the center conductor 3 is wide, the characteristic impedance is low, and therefore the current flowing through the center conductor 3 increases, resulting in a high temperature due to Joule heat. If the microstrip line 1 itself becomes too hot, the dielectric substrate 2 will heat up due to thermal expansion, etc.
There was a risk that it would become distorted or damaged. The present invention has been made in view of the drawbacks of the conventional example, and one embodiment thereof will be described below with reference to the drawings. FIG. 2 is a perspective view of this embodiment as seen from diagonally above, and FIG. 3 is a perspective view of this embodiment as seen diagonally from below. In FIGS. 2 and 3, 10 is the center conductor 1
2 is a standard narrow microstrip line. This microstrip line 10 includes a dielectric substrate 11 made of alumina ceramic or the like.
and a silver ground conductor 1 baked on its top surface.
3 and a central conductor 12, also made of silver, which is pasted by baking on the lower surface. The ground conductor 13
, a plurality of long slits 14 are distributed along the microwave propagation direction in a direction perpendicular to the microwave propagation direction, and a ladder pattern 15 is formed. In this embodiment, the width α of the center conductor 12 is set to approximately 3.5 mm, and other values are set to be the same as in the conventional example. 16 is a coaxial line similar to the conventional example for supplying microwaves from the direction of arrow B, and is connected to a microwave oscillator (not shown). The center conductor 16A of this coaxial line 16 and the center conductor 12 of the microstrip line 10 are connected, and the outer conductor 16B of the coaxial line 16 and the ground conductor 13 of the microstrip line 10 are connected. 17 is also a dummy load similar to the conventional example, which absorbs and consumes the microwaves that have not been consumed by the ladder pattern 15 without reflecting them. 18,1
8 is a transfer roller that transfers the thin object to be heated 19 in the direction of arrow B. The object to be heated 19 is scanned over the ladder pattern 15 by the transfer rollers 18, 18. When the characteristic impedance in this embodiment is calculated using the above equation (), Zo≈50, which matches the characteristic impedance of the coaxial line 16. In the conventional example, a long slit 5 was formed in the center conductor 3 in a direction perpendicular to the microwave propagation direction, so the width α of the center conductor 3 was inevitably wide. An impedance matching means was required. However, according to the present invention, since the slits 14 are formed in the ground conductor 13 as described above, the width α of the center conductor 12 does not need to be wide. Therefore, the microstrip line 1 does not require impedance matching means as in the conventional example.
0 is not made unnecessarily long. Furthermore, since the characteristic impedance of the microstrip line 10 can be made high, the current flowing through the center conductor 12 can be reduced, and heat generation can be suppressed. Although the effects corresponding to the object of the present invention are as described above, the present invention is not limited thereto, and also has the following effects which are more remarkable and noteworthy. That is, the electric field strength of the microwave leaking from the ladder pattern 15 increases dramatically compared to the conventional example. Although the reason for this is not clear, it can be estimated as follows. The characteristic impedance of the microstrip line 10 can also be expressed as in the following equation. Zo=Eo/Ho...() Here, Eo represents electric field strength and Ho represents magnetic field strength. According to this equation (), it can be seen that as the characteristic impedance increases, the electric field strength becomes relatively large. According to the present invention, the characteristic impedance of the microstrip line 10 can be increased as described above. Therefore, it is thought that the electric field strength increases, and the leakage electric field strength from the ladder pattern 15 also inevitably increases. Comparing the experimental results of the conventional example and this example, the time required to heat the same objects to be heated 9 and 19 is about 1/3 of that of the conventional example in the case of this example. I found out.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a conventional example, and FIGS. 2 and 3 are perspective views of an embodiment of the present invention viewed from different directions. DESCRIPTION OF SYMBOLS 10 ... Microstrip line, 12... Center conductor, 13... Ground conductor, 14... Slit, 15... Ladder pattern, 16... Coaxial line, 18, 18... Transfer roller, 19... Heated object.

Claims (1)

[Scope of Claims] 1. A microstrip line characterized in that a plurality of slits are formed in a ground conductor along the propagation direction of microwaves to form a ladder pattern. 2. A microstrip line in which a plurality of slits are formed in a ground conductor along the propagation direction of microwaves to form a ladder pattern, and means for supplying microwaves to the microstrip line; A microwave heating device comprising means for scanning an object to be heated over a ladder pattern.