JPH10163710A - Transmission line for high frequency - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In a conventional microstrip line, an electric field is applied to both ends of a lower surface of a conductor line formed on a surface of a dielectric substrate.
Since the current is concentrated, there is a problem that transmission loss of a high-frequency signal increases in a high-frequency region. SOLUTION: The lower surface is embedded in the dielectric substrate 1 on the surface of the dielectric substrate 1 having the ground conductor layer 2 on the rear surface,
This is a high-frequency transmission line provided with a conductor line 3 whose upper surface is exposed. A change in the dielectric constant distribution on the lower surface of the conductor line 3 can be eliminated, and the concentration of electric field and current on both ends of the lower surface of the conductor line 3 can be reduced.
Even in a high-frequency region, transmission loss of a high-frequency signal can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency signal transmission line, and more particularly to a high-frequency transmission line suitable for signal transmission on a high-frequency signal circuit board in a microwave / millimeter-wave band.

[0002]

2. Description of the Related Art Conventionally, in a high-frequency circuit using high-frequency signals in a microwave band or a millimeter-wave band, for example, a microstrip line is used as a transmission line for transmitting those high-frequency signals.

A conventional microstrip line as a high-frequency transmission line is, as shown in a perspective view in FIG. 4, a dielectric substrate 1 functioning as an insulating layer and a support layer for a conductor line.
And a ground conductor layer 2 formed on substantially the entire lower surface (back surface) of the dielectric substrate 1, and a ground conductor layer 2 formed on the upper surface (front surface) of the dielectric substrate 1 so as to face the ground conductor layer 2. And a conductor line (strip conductor) 3.

As the material of the dielectric substrate 1, various insulating ceramics, insulating resin-based materials, or other dielectric materials are used, and the materials of the ground conductor layer 2 and the conductor line 3 are dielectric materials. Depending on the material of the substrate 1, a conductive material that can be formed thereon is used. Normally, a ground conductor layer 2 is formed on the back surface of the dielectric substrate 1 and a conductor line 3 having a desired pattern is formed on the front surface, and an electric circuit or an electronic circuit using a high-frequency signal is formed on the dielectric substrate 1 in a planar manner. Has been realized.

Since such a microstrip line is excellent in productivity and integration, compared with a three-dimensional high-frequency circuit using a waveguide or the like for transmitting a high-frequency signal,
This is a transmission line for a high-frequency circuit board suitable for miniaturization and mass production.

[0006]

However, in the microstrip line having the above-mentioned structure, the structure itself in which the conductor line 3 is formed as a conductor pattern on the surface of the flat dielectric substrate 1 has an electric characteristic. Had the problem of That is, the high-frequency signal transmitted by the microstrip line is an electromagnetic wave propagating through the line, and its propagation mode is a quasi-TEM (Transverse Electro-M
In this mode, an electric field (lines of electric force) is distributed from the conductor line 3 toward the surface of the ground conductor layer 2. As shown in FIG. 4, the distribution of the electric flux lines is indicated by 4 in FIG. 4, but some of the electric flux lines exit from the upper surface of the conductor line 3. 1 and particularly at the end of the conductor line 3 in contact with the dielectric substrate 1. This is because the electric field (lines of electric force 4) is distributed such that the electric path to the ground conductor layer 2 formed on the back surface of the dielectric substrate 1 is the shortest, and as a result, the electric field is large. The part is a conductor line 3 in the dielectric substrate 1.
And the ground conductor layer 2. Further, when the current density in the conductor line 3 is taken into consideration, the cross-sectional shape of the conductor line 3 is usually a horizontally long rectangular shape as shown in FIG. Because the density has increased significantly,
The energy distribution of the electromagnetic field is concentrated on both ends of the conductor line 3 on the side in contact with the dielectric substrate 1, and the conductor line 3
However, there is a problem in that a current flowing intensively at the end of the conductor is converted into thermal energy by the resistance of the conductor, causing an electrical loss, thereby causing a transmission loss. Because of this, especially
There is also a problem that transmission loss in the conductor line 3 increases in a high frequency band such as 10 GHz.

SUMMARY OF THE INVENTION The present invention has been devised to solve the above problems, and an object of the invention is to reduce the concentration of an electric field or current at both ends of a conductor line in a microstrip line as a high-frequency transmission line. Accordingly, it is an object of the present invention to provide a high-frequency transmission line having good transmission characteristics in which transmission loss of a high-frequency signal is suppressed.

[0008]

A high-frequency transmission line according to the present invention is a conductor having a lower surface buried in a dielectric substrate having a ground conductor layer on the back surface, the lower surface being embedded in the dielectric substrate, and an upper surface being exposed. It is characterized by providing a line.

According to the high-frequency transmission line of the present invention, since the lower surface of the conductor line is embedded in the dielectric substrate, the permittivity at both ends of the conductor line in contact with the dielectric substrate is reduced. The lower surface of the conductor line on which the electric field (line of electric force) and current are concentrated without largely changing can be present in the same dielectric constant distribution, and the concentration of the electromagnetic field distribution on both ends of the lower surface of the conductor line can be reduced. As a result, the transmission loss of the high-frequency signal propagating through the conductor line can be suppressed.

Further, since the lower surface of the conductor line is embedded in the dielectric substrate, the distribution of the dielectric constant on the lower surface of the conductor line can be made uniform. It is also possible to reduce concentration. Since the density distribution of the magnetic flux density is directly related to the current density distribution, it is also possible to reduce the concentration of current at both ends of the lower surface of the conductor line, thereby suppressing the occurrence of transmission loss. Become.

According to the high-frequency transmission line of the present invention, since the lower surface exposes the upper surface of the conductor line embedded in the dielectric substrate, the pattern can be easily designed.
In the case where adjustment is necessary after manufacturing by firing or the like as in the case of the conventional microstrip line, adjustment by trimming is easy, mounting of element parts is easy, integration is good, and electronic It is possible to provide a circuit board having high mountability of components.

As described above, according to the present invention, there is provided a high-frequency transmission line having excellent transmission characteristics in which transmission loss of a high-frequency signal propagating in a conductor line is suppressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A high-frequency transmission line according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view similar to FIG. 4, showing an example of a high-frequency transmission line according to an embodiment of the present invention. In FIG. 1, the same parts as those in FIG. 4 are denoted by the same reference numerals, 1 is a dielectric substrate, 2 is a ground conductor layer, 3 is a conductor line, and 4 is a line of electric force.

The dielectric substrate 1 includes an insulating layer and a conductor line 3.
The material used is a dielectric material such as various insulating ceramics such as an alumina-based material or an aluminum nitride-based material, or an insulating resin-based material such as PTFE or glass epoxy. ing. The dielectric constant, thickness, dimensions, etc., of the desired impedance, e.g.
Are set in relation to other components.

The ground conductor layer 2 is a conductor layer made of tungsten, chromium, molybdenum, copper, silver, gold, or the like which is formed on substantially the entire back surface (lower surface) of the dielectric substrate 1. Grounded. As this material, a conductor material that can be formed on the dielectric substrate 1 according to the material of the dielectric substrate 1 is used. For a high frequency signal in a microwave band or a millimeter band, for example, the dielectric substrate 1 of an alumina material is used. And a ground conductor layer 2 made of chromium-copper-nickel-gold may be used.

In the high-frequency transmission line of the present invention, the conductor line 3 provided on the surface of the dielectric substrate 1
The lower surface is embedded in the dielectric substrate, and the upper surface is exposed. In the example shown in FIG. 1, the upper surface of the conductor line 3 is substantially flush with the surface of the dielectric substrate 1. The conductor line 3 is embedded in the dielectric substrate 1 such that Thereby, the distribution of the dielectric constant on the lower surface of the conductor line 3 becomes uniform, so that the concentration of the electric flux lines 4 at both ends of the lower surface of the conductor line 3 is reduced as shown in FIG. The transmission loss of the high-frequency signal propagating in the inside is suppressed.

FIG. 2 is a perspective view showing another embodiment of the high-frequency transmission line according to the present invention. In FIG. 2, the same parts as those in FIGS. 1 and 4 are denoted by the same reference numerals. . FIG.
1 shows an example in which substantially the lower half of the conductor line 3 is embedded in the dielectric substrate 1 so that the lower surface is embedded in the dielectric substrate and the upper surface is exposed. This also makes the distribution of the dielectric constant on the lower surface of the conductor line 3 uniform, so that the concentration of the electric flux lines 4 at both ends of the lower surface of the conductor line 3 is reduced as shown in FIG. The transmission loss of the high-frequency signal propagating in the inside is suppressed.

The cross-sectional shape of the conductor line 3 in the high-frequency transmission line of the present invention is such that its base (lower surface) is flat.
In addition to the horizontally long rectangular shape as shown in FIGS. 1 and 2, an upwardly convex arc shape or a trapezoidal shape may be used. In addition, conductor line 3
As in the case of the ground conductor layer 2, a conductor material that can be formed on the dielectric substrate 1 according to the material of the dielectric substrate 1 may be used.

The dimensions such as the cross-sectional shape, width, thickness, etc. of the conductor line 3 and the depth to be embedded in the dielectric substrate 1 are determined according to the specifications of the high-frequency circuit in which the high-frequency transmission line is used. For example, it is set in relation to other components so as to realize 50Ω.

If the lower surface of the conductor line 3 is embedded in the dielectric substrate 1 and the upper surface is exposed, the conductor line 3 can be further deepened into the dielectric substrate 1 in addition to the above example. It may be embedded so that the upper surface of the conductor line 3 is lower than the surface of the dielectric substrate 1. In this case as well, the above-described functions and effects are exhibited, and since the upper surface of the conductor line 3 is exposed, a lumped electronic component can be mounted. As a result, a high-frequency transmission line having good transmission characteristics is obtained.

According to the high-frequency transmission line of the present invention, since the transmission line has good transmission characteristics with a small transmission loss with respect to a high-frequency signal, the transmission line is suitable for a high-frequency circuit. When used as a transmission line in a circuit board of a circuit portion, power consumption can be reduced.

[0022]

Next, a specific example of the high-frequency transmission line of the present invention will be described.

First, as the dielectric substrate 1, a thickness h = 0.2
mm, material constant εr (relative permittivity) = 9.6, tan δ _eff
A substrate made of an alumina-based material having a value of (effective dielectric loss) = 45 × 10 ⁻⁴ is used, and a ground conductor layer 2 is provided on the back surface as a thickness t = 10 μm and a material constant σ _eff (effective conductivity).
A conductor layer made of chromium-copper-nickel-gold having a value of 1.67 × 10 ⁷ (S / m) was deposited. Further, the conductor line 3 is formed on the surface as a conductor line 3 having a thickness t = 10 μm and a line width w = 0.
2 mm, material constant σ _eff (effective conductivity) = 1.67 × 10
^A conductor line layer made of chromium-copper-nickel-gold having a value of ⁷ (S / m) embedded in the dielectric substrate 1 so that its upper surface is flush with the surface of the dielectric substrate 1;
A high-frequency transmission line A of the present invention having the configuration shown in FIG. 1 was manufactured.

As a comparative example, the same ground conductor layer 2 is formed on the back surface of the same dielectric substrate 1 as above, and the conductor line 3 of the same material, shape and dimensions as above is formed on the lower surface thereof. Was formed without being embedded in the dielectric substrate 1 to produce a conventional high-frequency transmission line B having the configuration shown in FIG.

The transmission characteristics of the high-frequency signals are measured for these high-frequency transmission lines A and B using a vector network analyzer.
Parameter (Scattering Parameter)
, The frequency characteristics of the reflection coefficient S ₁₁ and the transmission coefficient S ₂₁ were obtained. Of these results, showing the frequency characteristics of the transmission coefficient S ₂₁ in FIG. 3.

FIG. 3 is a diagram showing the frequency characteristic of the transmission coefficient S ₂₁ , wherein the horizontal axis represents the frequency f (GHz) and the vertical axis represents the transmission coefficient S ₂₁ (dB), which is shown by a solid line in the figure. A curve A indicates a characteristic curve of the high-frequency transmission line A of the present invention, and a broken line curve B indicates a characteristic curve of the high-frequency transmission line B of the comparative example. As can be seen from these figures, in the low frequency region, the high-frequency transmission line B of the comparative example has a smaller loss and shows better characteristics in the low frequency region at a frequency of about 20 GHz. it is loss less of the high frequency transmission line a of the present invention Te (large transmission coefficient S ₂₁₎ has good transmission characteristics in the region.

As a result, it has been confirmed that the transmission line for high frequency of the present invention suppresses the occurrence of transmission loss especially in a high frequency region, and has a good transmission characteristic for high frequency signals.

It should be noted that the above is only an example of the embodiment of the present invention, and the present invention is not limited to the embodiment. Various changes and improvements may be made without departing from the gist of the present invention. No problem.

[0029]

As described above, according to the high-frequency transmission line of the present invention, the lower surface is embedded in the dielectric substrate and the upper surface is exposed on the surface of the dielectric substrate having the ground conductor layer on the back surface. The conductor line on the side where the dielectric substrate is in contact with the dielectric substrate, the dielectric constant at both ends of the conductor line does not change significantly, and the electric field (line of electric force) and current concentrate on the conductor line. All the lower surfaces can be in the same dielectric constant distribution, so that the concentration of the electromagnetic field distribution at both ends of the conductor line lower surface can be reduced, and the concentration of the magnetic flux density can also be reduced. As a result, the concentration of current at both ends of the lower surface of the conductor line can be reduced, and as a result, transmission loss of a high-frequency signal propagating through the conductor line can be suppressed.

According to the high-frequency transmission line of the present invention, since the lower surface exposes the upper surface of the conductor line embedded in the dielectric substrate, the pattern can be easily designed.
In the case where adjustment is necessary after manufacturing by firing or the like as in the case of the conventional microstrip line, adjustment by trimming is easy, mounting of element parts is easy, integration is good, and electronic A circuit board with high component mountability can be provided.

As described above, according to the present invention, in a microstrip line as a high-frequency transmission line, transmission of a high-frequency signal propagating in the conductor line is reduced by alleviating the concentration of electric field and current at both ends of the conductor line. A high-frequency transmission line with good transmission characteristics, in which loss is suppressed, can be provided.

According to the high-frequency transmission line of the present invention, since the transmission line has good transmission characteristics with a small transmission loss with respect to a high-frequency signal, the transmission line is suitable for a high-frequency circuit. When used as a transmission line in a circuit board of a circuit portion, power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of an embodiment of a high-frequency transmission line according to the present invention.

FIG. 2 is a perspective view showing another example of the embodiment of the high-frequency transmission line of the present invention.

FIG. 3 is a diagram illustrating a frequency characteristic of a transmission coefficient of a high-frequency transmission line.

FIG. 4 is a perspective view showing a conventional high-frequency transmission line.

[Explanation of symbols]

 1 ... Dielectric substrate 2 ... Ground conductor layer 3 ... Conductor line

Claims (1)

[Claims] 1. A high-frequency transmission line characterized in that a conductor line whose lower surface is embedded in the dielectric substrate and whose upper surface is exposed is provided on the surface of a dielectric substrate having a ground conductor layer on the back surface. .