JPH05211402A - Distributed constant type circuit - Google Patents

Abstract

PURPOSE:To reduce a change in a characteristic due to variance in a line width by forming part of a dielectric board with a dielectric body whose dielectric constant differs from a prescribed dielectric constant of the board. CONSTITUTION:A filter circuit 13 is formed on a dielectric ceramic board 10. The filter circuit 13 consists of main lines 14a, 14b, 14c and stubs 15-18 whose end is open are formed to the lines 14a, 14b, 14c. Moreover, the ceramic board 10a is a board whose dielectric constant is lower than that of the dielectric ceramic board 10 and a transformer 12 is formed on the base 10a. Through the constitution above, the line width is made thick without changing the characteristic impedance of the transformer 12 by using a dielectric material whose dielectric constant is lower than that of a filter for the transformer whose line width is thin and the characteristic is made stable against the dispersion in the line width in the manufacture of strip lines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed constant type circuit used for high frequency transmission, and more particularly to a distributed constant type circuit formed of dielectric substrates having different permittivities.

[0002]

2. Description of the Related Art Conventionally, a distributed constant type circuit used for high frequency transmission includes a band elimination filter for blocking a specific frequency by providing an open-ended quarter-wave stub on a main line, and is composed of a strip line. It is often done. The dielectric substrate used in the filter circuit is made of ceramics having a predetermined dielectric constant. For example, the ceramics is put in a predetermined mold and sintered to form a substrate having a uniform dielectric constant. I was getting. Further, a strip line is formed by forming a conductor line on the substrate by printing copper, silver palladium, or the like, and providing a ground plane on the symmetric surface forming the conductor line.

In the design of the above filter, it is necessary to match it with another circuit whose characteristic impedance is generally designed with Z _out = 50 [Ω]. Here, using a ceramic substrate having a relative permittivity ε _r = 90 and a thickness h = 0.5 [mm], the characteristic impedance Z _in is the same as that of other circuits.
_If we try to design with _out = 50 [Ω], the line width W of the main line will be calculated from Eqs. (1) to (6) below, regardless of the frequency.
_{Since in} is W _in = 0.012 [mm], it is difficult to manufacture strip lines because the line width is too thin. Further, even if the strip line having the above line width can be realized, if the line width W _in deviates from the design value by a little, the characteristic impedance Z _in changes greatly,
The desired characteristics cannot be obtained.

[0004]

[Equation 1]

Where ε _{re is} the equivalent dielectric constant of the substrate ε _{r is} the relative permittivity of the substrate W is the line width of the strip line [mm] h is the thickness of the substrate [mm] λg is the guide wavelength on the substrate [mm] λ ₀ : Free-space wavelength of radio wave [mm] Z: Characteristic impedance [Ω] Therefore, the present applicant uses an actual filter using a λg / 4-length transformer as shown in Japanese Patent Application No. 3-326042. We proposed a filter whose circuit configuration is easy by reducing the impedance and widening the line width by conventional printing and etching. In the filter proposed above, the line width becomes thicker, so that it is possible to suppress the change in the characteristic impedance due to the variation in the line width to be small compared to the conventional design with the characteristic impedance Z _in = 50 [Ω], and the stable characteristic can be obtained. I was able to get

The characteristic impedance Z _{t of the} transformer is

[0007]

[Equation 2]

However, Z _{out is} an external characteristic impedance [Ω] Z _{in is} a characteristic impedance [Ω] of the main line of the filter.

[0009]

However, when the transformer and the filter circuit are formed on a substrate having a uniform dielectric constant, in order to achieve the above proposal, the line width of the transformer is smaller than that of the main line of the filter. Will inevitably become thinner. For example, relative permittivity ε _r = 90, thickness
If the characteristic impedance of the main line of the filter is Z _in = 10 [Ω] using a ceramic substrate of h = 0.5 [mm], the characteristic impedance of the transformer Z _t = 2
It becomes 2.4 [Ω]. At this time, the line widths of the main line of the filter and the transformer are W _in = 1.45 [mm], respectively.
W _t = 0.25 [mm].

Here, when the above-mentioned transformer and filter are formed by printing or etching a conductor, there is a problem that the manufacturing tolerance must be made strict in consideration of the transformer in which the characteristic impedance changes largely due to the variation of the line width. there were. The present invention has been made in view of the above problems, and can suppress changes in characteristics due to variations in line width in manufacturing as compared with conventional ones, thereby giving a margin to manufacturing tolerance and a distributed constant type circuit with stable characteristics. The purpose is to provide.

[0011]

In order to solve the above-mentioned problems, the present invention provides a distributed constant type circuit in which a conductor line is arranged on a dielectric substrate having a predetermined dielectric constant to form a strip line. Provided is a distributed constant circuit in which at least a part of a substrate is formed of a dielectric having a dielectric constant different from a predetermined dielectric constant of the dielectric substrate.

[0012]

With this structure, the transformer having a narrow line width is made of a dielectric material having a lower permittivity ε _r than the filter, so that the line width W _t can be increased without changing the characteristic impedance Z _in of the transformer. However, the characteristics can be stabilized against variations in the line width due to the manufacturing of the strip line.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawing of FIG. FIG. 1 is a perspective view showing a configuration in which the distributed constant circuit according to the present invention is used as a band elimination filter. In the figure, 10 and 10a are dielectric ceramic substrates having the same thickness h and different relative permittivity ε _r , 12
Is a transformer for matching the filter circuit with other circuits, 13 is a filter circuit formed between the transformers 12, and 11 is a ground plane. The filter circuit 13 includes a main line 14a, 14b, 14c and a main line 1
It is composed of 5, 16, 17, and 18 open-end stubs.

The dielectric ceramic substrates 10 and 10a are
Before sinter-molding, each is die-cut into a predetermined size, combined, and then sinter-molded. Alternatively, they may be separately sintered and then adhered. Furthermore, on the dielectric ceramic substrate integrated by the above method,
The transformer 12, the filter circuit 13, and the ground plane 11 are formed by printing copper or silver-palladium or etching after copper plating.

For example, the dielectric ceramic substrate 10 is
Similar to the conventional example, relative permittivity ε _r = 90, thickness h = 0.5 [m
m] of ceramics, and the filter circuit 13 is formed on the substrate. The filter circuit 13 has characteristic impedances Z _in = 10 [Ω] for the main lines 14a, 14b, 14c, a line width W _in = 1.45 [mm], and a length.
l _in is λg / 4 of the passing frequency f ₀ , and the open-end stubs 15 to 18 have blocking frequencies f ₁ to
The length of f ₄ is λg / 4, and the line width is designed so that the characteristic impedance Z _in seen from the input end of the filter circuit 13 is 10 [Ω]. Furthermore, the dielectric ceramic substrate 10
a is made of ceramics having a relative permittivity ε _r = 35 and a thickness h = 0.5 [mm], and the transformer 12 is formed on the substrate. Since the characteristic impedance Z _t of the transformer 12 matches the characteristic impedance Z _out = 50 [Ω] of the other external circuit and the characteristic impedance Z _in = 10 [Ω] of the above filter circuit, Z from Equation (7).
_{With t} = 22.4 [Ω], the line width W _t can be calculated from equations (1) to (6).
W _t = 0.79 [mm], length l _t is λg / 4 with pass frequency f ₀
Has become. In FIG. 1, the relative dielectric constant of the dielectric ceramics substrate 10a forming the transformer 12 is lower than that of the dielectric ceramics substrate 10 forming the filter circuit, so that the guide wavelength λg becomes longer and the transformer length l _t becomes longer. Therefore, the transformer 12 is arranged in a bent state for downsizing.

In this embodiment, the relative permittivity ε in the conventional example is
The line width W _t of the transformer 12 becomes thicker than when a uniform dielectric ceramic substrate with _r = 90 is used.
It is possible to suppress changes in characteristics due to variations in the line width W _{t during} manufacturing, and obtain a more stable distributed constant type circuit.

[0017]

As described above, according to the present invention, in a distributed constant type circuit in which conductor lines are arranged on a dielectric substrate having a predetermined dielectric constant to form strip lines, at least a part of the dielectric substrate is provided. Is formed of a dielectric material having a dielectric constant different from the predetermined dielectric constant of the dielectric substrate, it is possible to suppress changes in characteristics due to variations in line width, and to provide a stable distributed constant type circuit.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration when a distributed constant circuit according to the present invention is used as a band elimination filter.

[Explanation of symbols]

 10 Dielectric Ceramic Substrate 10a Dielectric Ceramic Substrate with Different Permittivity 11 Ground Plane 12 Transformer 13 Filter Circuit 14a, 14b, 14c Main Line 15, 16, 17, 18 Open-end Stub

Claims (1)

[Claims] 1. A distributed constant circuit in which conductor lines are arranged on a dielectric substrate having a predetermined dielectric constant to form a strip line, wherein at least a part of the dielectric substrate has a predetermined dielectric constant of the dielectric substrate. A distributed constant circuit characterized by being formed of a dielectric material having a dielectric constant different from that of.