JPS6347120B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a microstrip line used in a thin microwave heating device.

Conventionally, microstrip lines in which a plurality of long slits are opened in the center conductor at right angles to the microwave propagation direction to form a ladder pattern have already been proposed (for example, in a special (Gan-Sho 55-108644). For a moment, a microwave heating device using this microstrip line will be explained with reference to FIG.

Reference numeral 1 denotes a microstrip line, and a coaxial cable 2 connected to a microwave oscillator (not shown) is connected to the input end of the line. A dummy load 3 is attached to the output end of the dummy load 3, which absorbs and consumes microwaves that have not been consumed by the microstrip line 1 . The microstrip line 1 is composed of a substrate 4 made of a dielectric material such as alumina ceramic, a center conductor 5 attached to the upper surface of the substrate 4, and a grounding plate 6 attached to the lower surface. be done. Both the center conductor 5 and the ground plate 6 are made of a conductive material such as silver or copper, and the center conductor 5
A ladder pattern 8 consisting of a plurality of slits 7 is formed along the propagation direction of the microwave. 9 is a copy paper as a heated object, on the surface of which unfixed toner is selectively adhered;
The ladder pattern 8 is scanned in the direction shown in FIG.

When the copy paper 9 is scanned over the ladder pattern 8 while applying microwaves from the direction of arrow A, the copy paper 9 is heated and fixed by the microwaves leaking from the slits 7.

In this conventional example, the characteristic impedance Z ₀ of the coaxial cable 2 and the characteristic impedance of the wide ladder pattern 8 of the microstrip line 1 are
There was a big difference between Z1 and _Z1 . Specifically, Z ₀ =
50Ω, Z ₁ = about 3Ω. Therefore, in order to achieve impedance matching between the microstrip line 1 and the coaxial cable 2 , the end of the center conductor 5 is tapered as shown in FIG. Therefore, the distance L from the end of the microstrip line 1 to the first slit 7 becomes large.
The entire heating device was unnecessarily long. Furthermore, in order to solve this difficulty, a method can be considered in which a heat-resistant dielectric material having an appropriate dielectric constant is filled between the outer conductor 9 and the center conductor 10 near the end of the coaxial cable 2 . However, heat-resistant dielectric materials are generally difficult to machine, resulting in increased costs. Furthermore, instead of filling the center dielectric material 10 of the coaxial cable 2 with a dielectric material,
It is also conceivable to increase the diameter near the connection part. However, even in this case, there is a risk that sparks may occur between the outer conductor 9 and the center conductor 10, as well as increasing costs.

The present invention has been made in view of the drawbacks of the conventional example, and is intended to miniaturize the coaxial cable without applying any special processing to the coaxial cable. The embodiment will be described below with reference to FIGS. 3 and 4.
Note that parts that are the same as conventional parts are given the same figure numbers.

In Figure 3, 5a is a wide center conductor, 7
... is a slit made in this wide center conductor 5a. 2 is a coaxial cable, 9 is its outer conductor, and 10 is its center conductor. Then, the outer conductor 9 of the coaxial cable 2 and the microstrip line 1
The grounding plate 6 is connected, and the center conductors 5b and 10 are connected to each other. In addition, at this time, the wide center conductor 5a
The distance between the microwave input side end of the substrate 4 and the microwave input side end of the substrate 4 is set to 1/4 of the wavelength λ of the microwave propagating within the substrate 4. Further, a narrow center conductor 5b is provided between the substrate 4 and the wide center conductor 5a. By doing so, the reflected wave at the end of the wide center conductor 5a is canceled by the transmitted wave. In this case, if the characteristic impedance of the coaxial cable 2 is Z ₀ , that of the wide center conductor 5a is Z ₁ , and that of the narrow center conductor 5b is Z ₂ , then the relationship Z ₂ ² =Z ₀・Z ₁ is established. The center conductors 5a and 5b of the microstrip line 1 are formed so as to satisfy the following.

Therefore, the microwave applied from the direction of arrow A is transmitted to the coaxial cable 2 and the microstrip line 1.
The beam propagates efficiently without being reflected at the junction with the beam. Now, when microwaves with a frequency of 2.45 GHz (wavelength in air is approximately 12 cm) are applied to the microstrip line 1 formed of an alumina ceramic substrate 4 with a dielectric constant of 9, the wavelength within the substrate 4 is λ
is 12/√9=4 (cm). Therefore λ/4=1
(cm), and the distance L from the end to the first slit 7 is a little over 1 cm. This is about 1/4 the length of the conventional example.

If the impedance matching cannot be achieved completely, a third central conductor 5c having an intermediate width may be provided between the wide central conductor 5a and the narrow central conductor 5b, as shown in FIG. Good too. By doing this, the length of each of the narrow center conductor 5b and the intermediate width center conductor 5c becomes λ/4, and although the L dimension is longer than that of the previous embodiment, impedance matching can be achieved sufficiently. , microwaves propagate efficiently.

Note that when a coaxial cable (not shown) is connected to the output side of the microstrip line 1 and a dummy load 3 is attached to the end of the coaxial cable, a narrow center conductor 5b similar to that described above is also installed on the output side. What is necessary is to provide the center conductor 5c with a middle width or an intermediate width.

As described above, according to the present invention, by simply providing a wide portion and a narrow portion in the center conductor of a microstrip line, the overall length can be shortened and impedance matching can be easily achieved. Therefore, a small and inexpensive microstrip line for microwave heating can be realized.

[Brief explanation of drawings]

1 and 2 are perspective views and partial plan views showing a conventional example, and FIGS. 3 and 4 are partial plan views showing different embodiments of the present invention. 1 ...Microstrip line, 4...Substrate, 5a
...Wide center conductor, 5b...Narrow center conductor, 5c
...Center conductor of medium width, 8...Ladder pattern.

Claims (1)

[Claims] 1. The distance from the input end of the microwave to the input end of the substrate of the wide center conductor in which a ladder pattern is formed along the microwave propagation direction is equal to the distance within the substrate. A microstrip line whose width is equal to 1/4 of the wavelength of the propagating microwave, and which is connected by a narrow center conductor. 2 The distance from the microwave output side end of the wide center conductor to the output side end of the board is also equal to 1/4 wavelength of the microwave propagating within the board, and the distance between them is connected by the narrow center conductor. A microstrip line according to claim 1, characterized in that: 3. The central conductor according to claim 1 or 2, which is provided with a central conductor whose width becomes stepwise at every 1/4 wavelength of the microwave from the end of the substrate to the end of the wide central conductor. microstrip line.