JPH11308018A - Transmission line conversion structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the input/output reflection at a connecting part of a coaxial cable and to perform no aerial wiring of a central conductor by arranging a circular punched pattern which is larger than outside diameter of the central conductor and smaller than the outside diameter of an external conductor on a rear conductor of a dielectric substrate on a concentric circle with a coaxial cable. SOLUTION: A coaxial cable 101 is formed by processing an edge surface of the cable, except for the central conductor 104 with the length equivalent to the thickness of the dielectric substrate 102 or more. The coaxial cable 101 is inserted from the rear surface in the direction of the normal line vector of a plane of the dielectric substrate 102 toward the front surface, and a hole which is equal to or larger than the outside diameter of the central conductor 104 is provided on the dielectric substrate 102 on the concentric circle with the coaxial cable 101. Then the central conductor 104 passes the hole, is connected with a front conductor 105 and the external conductor 106 is connected with the rear conductor 107. A punched hole is provided on the rear conductor 107 on the concentric circular with the coaxial cable 101 and its size is set in a range larger than the outside diameter of the central conductor 104 and smaller than the outside diameter of the external conductor 106.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RF circuit using millimeter waves for signal transmission, and more particularly to a transmission line conversion structure for connecting a dielectric substrate and a coaxial cable.

[0002]

2. Description of the Related Art FIG. 11 shows a conventional example of a transmission line conversion structure. In FIG. 11, reference numeral 102 denotes a dielectric substrate, and 101 denotes a coaxial cable. 103 is a pedestal, which is a dielectric substrate 1
02 is adhered to the surface, and a hole having an outer diameter width of the coaxial cable is provided through the dielectric substrate 102 and the pedestal 103. The coaxial cable 101 is inserted into the through hole, and the center conductor 104 of the coaxial cable is connected to the surface conductor 1 of the dielectric substrate.
05 and the outer conductor 106 of the coaxial cable
03 is connected to the back conductor 107 of the dielectric substrate. The diameter of the coaxial cable 101 is at least about 1 mm,
The distance from the surface conductor 105 to the end face of the through hole is 0.05 mm or more in terms of the processing accuracy of the substrate.

[0003] Due to the conventional structure, the aerial wiring of the center conductor 104 requires a length of 0.55 mm or more. Therefore, the impedance of the aerial wiring part in the millimeter wave band is
1 and the characteristic impedance of the dielectric substrate 102, the value appears to be so large that it cannot be ignored on the transmission line.
Reflection or loss of the signal component due to the characteristic impedance discontinuity occurs.

[0004]

SUMMARY OF THE INVENTION RF applying millimeter wave
The device has a short wavelength of several mm and has high straightness, and is therefore used for radar devices, wireless devices, and the like. In mounting a millimeter wave RF circuit, a connection is generally made using a waveguide in order to reduce loss on a transmission line.

[0005] However, since the waveguide itself is made of a metal and is large, processing and installation are complicated. Therefore, a coaxial cable is used as a substitute for the waveguide. Has a diameter of about 1 mm. When connecting the coaxial cable from the back side of the dielectric substrate in parallel with the normal vector of the dielectric substrate plane when connecting only with the coaxial cable and the dielectric substrate, to connect the dielectric substrate and the center conductor of the coaxial cable It is necessary to bend the center conductor to the surface of the dielectric substrate, and the length thereof is a finite value of 0.5 mm or more depending on the radius of the coaxial cable and the processing conditions of the dielectric substrate. Since the center conductor is made of metal, it does not bend at a right angle, and is connected to the dielectric substrate with a certain radius of curvature. Therefore, the center conductor becomes an aerial wiring and becomes longer.

[0006] The center conductor wired in the air is about 1 nH /
Since there is an inductance component of mm, the impedance becomes about 400 ohm at a frequency of 70 GHz. If the characteristic impedance in the high-frequency circuit system is 50 ohms, the value of the impedance of the center conductor is large, and the characteristic impedance becomes discontinuous in the center conductor portion wired in the air, and signal input / output reflection occurs, and the signal is attenuated.

If the structure of the conventional example is maintained, the length of the aerial wiring portion cannot be significantly reduced unless the diameter of the coaxial cable is changed. In addition, a new electronic component must be used because it is necessary to add a capacitance component in parallel to reduce the inductance component.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention suppresses input / output reflection at a connection portion of a coaxial cable and does not perform aerial wiring of a center conductor when the coaxial cable is mounted on an RF circuit. It is intended to provide a conversion structure.

[0009]

FIG. 1 is a diagram showing the principle of the present invention. In this figure, 101 is a coaxial cable, and 102 is a dielectric substrate. Reference numeral 103 denotes a pedestal, on which a dielectric substrate 102 is adhered, a hole having an outer diameter of the coaxial cable 101 is provided through the pedestal 103, and the coaxial cable 101 is inserted. 104 is a center conductor of the coaxial cable, 105 is a front conductor of the dielectric substrate, 106 is an outer conductor of the coaxial cable, and 107 is a back conductor of the dielectric substrate. It passes through the dielectric substrate 102 provided with a hole having an outer diameter width of the center conductor 104 and is connected to the surface conductor 105. The outer conductor 106 is directly connected to the back conductor 107. The discontinuous portion of the characteristic impedance of the center conductor 104 has a transmission path conversion structure in which only the thickness of the dielectric substrate 102 is limited.

[0010]

FIG. 2 shows a first embodiment of the present invention. FIG. 2 (a) shows the upper side of the transmission line conversion structure, and FIG. 2 (b) is a cross section of the coaxial cable insertion portion. Is shown. 101
Is a coaxial cable, 102 is a dielectric substrate, and 1
A pedestal 03 supports the coaxial cable 101 and the dielectric substrate 102. The coaxial cable 101 has a structure in which a periphery of a center conductor 104 is covered with a dielectric 120 and an outer conductor 106. The dielectric substrate 102 has a structure in which a dielectric is sandwiched between a front conductor 105 on the front surface and a back conductor 107 on the rear surface.

The dielectric substrate 102 is disposed on the surface of the pedestal 103, and the pedestal 103 has a hole facing the dielectric substrate 102 so that the coaxial cable 101 can pass therethrough. The end face of the coaxial cable 101 is processed except for a central conductor 104 having a length equal to or longer than the thickness of the dielectric substrate 102. The coaxial cable 101 is inserted from the back surface to the front surface in the direction of the normal vector of the plane of the dielectric substrate 102, and a hole larger than the outer diameter of the center conductor 104 is provided on the dielectric substrate 102 concentric with the coaxial cable, and The conductor 104 passes through the hole and the surface conductor 1
05, and the outer conductor 106 is connected to the back conductor 107. The back conductor 107 is provided with a hollow hole concentrically with the coaxial cable 101, and the size thereof is
4 and smaller than the outer diameter of the outer conductor 106.

FIG. 3 is a top view of the dielectric substrate 102.
The front conductor 105 and the back conductor 107 are formed in a microstrip line structure, adjust the characteristic impedance, and match with the coaxial cable. By providing a donut-shaped land pattern 108 at the connection portion with the center conductor 104, the capacitance component with the back surface conductor 107 can be improved and the inductance component of the center conductor 104 can be reduced, thereby improving the wetting of the connection material. As a result, the impedance characteristics at the connection portion can be suppressed to be small.

FIG. 4 is a rear view when the dielectric substrate 102 is turned upside down. The dielectric substrate 102 is provided with a hole for passing the center conductor 104 to the front surface conductor 105, and the back surface conductor 107 is provided with a circular nucleation pattern 109 concentrically with the hole. This Nuki pattern 109
Inner diameter of the outer conductor 106 is larger than the outer diameter of the center conductor 104.
Of the center conductor 104
In order to suppress the inductance value and maintain the continuity of the characteristics of the microstrip line of the surface conductor, it is desired that the wavelength is sufficiently smaller than the wavelength of the electromagnetic wave.

FIG. 5 shows a second embodiment of the present invention. FIG. 5A shows the upper surface of the transmission line conversion structure, and FIG. 5B shows a cross section of the coaxial cable insertion portion. 101 is a coaxial cable, 102 is a dielectric substrate, and 103 is a pedestal supporting the coaxial cable 101 and the dielectric substrate 102. The coaxial cable 101 has a structure in which a periphery of a center conductor 104 is covered with a dielectric 120 and an outer conductor 106. The dielectric substrate 102 has 105 surface conductors on the front surface and 10
7 is a structure in which a dielectric is sandwiched between the back conductors in a sandwich shape.

The dielectric substrate 102 is disposed on the surface of the pedestal 103, and the pedestal 103 is formed with a hole facing the dielectric substrate 102 such that the coaxial cable 101 can pass therethrough. The end face of the coaxial cable 101 is processed except for a central conductor 104 having a length equal to or longer than the thickness of the dielectric substrate 102. The coaxial cable 101 is inserted from the back surface to the front surface in the direction of the normal vector of the plane of the dielectric substrate 102, and a hole larger than the outer diameter of the center conductor is provided on the dielectric substrate 102 concentric with the coaxial cable. 104 passes through the hole and passes through the surface conductor 105
And the outer conductor 106 is connected to the back conductor 107.
The back conductor 107 is provided with a hollow hole on the concentric circle with the coaxial cable 101, and its size is set to be larger than the outer diameter of the center conductor 104 and smaller than the outer diameter of the outer conductor 106.

Here, in the coplanar line with ground shown in FIG. 5, it is an absolute condition that the ground of the coplanar line of the surface conductor 105 has the same potential as the back surface conductor 107. Therefore, the via hole 130 is a hole for electrically connecting the front surface conductor 105 and the rear surface conductor 107,
The potential on the front and back surfaces of the dielectric substrate 102 is kept equal. When processing the via hole 130, if the period of the via hole is designed to be larger than 1/4 wavelength of the millimeter wave signal, or if the via hole position from the gap between the main line of the surface conductor coplanar line and the ground is discontinuous, the A potential difference occurs between the ground of the conductor and the back conductor, so that the electrical characteristics of the coplanar transmission line become discontinuous, resulting in insertion loss of the transmission line. Therefore, the cycle of the via hole 130 is designed to be smaller than １ ／ wavelength, and is arranged with a certain distance from the gap between the main line of the coplanar line and the ground.

FIG. 6 shows the upper surface of the dielectric substrate. The front surface conductor 105 is formed in a coplanar line structure, and the back surface conductor 107 functions as a back surface ground of the coplanar line. The ground of the coplanar line of the front surface conductor 105 and the back surface conductor 107 are connected by a via hole 109.
The coplanar line of the dielectric substrate also adjusts the characteristic impedance to match the coaxial cable. Also in the coplanar line, by providing a donut-shaped land pattern 108 at the connection portion with the center conductor 104, the capacitance component with the back conductor can be improved, and the inductance component of the center conductor can be suppressed to be small. It is possible to improve the wetting and to reduce the impedance characteristics at the connection portion.

FIG. 7 is a rear view when the dielectric substrate 102 is turned upside down. The dielectric substrate 102 is provided with a hole for passing the center conductor 104 to the front surface conductor 105, and the back surface conductor 107 is provided with a circular nucleation pattern 109 concentrically with the hole. This Nuki pattern 109
Is set within a range larger than the outer diameter of the center conductor and smaller than the outer diameter of the outer conductor. To suppress the inductance value of the center conductor 104 and maintain the continuity of the characteristics of the surface conductor, It is desired to be much smaller.

FIG. 8 shows a third embodiment of the present invention, and is a configuration diagram of a moving body on which an RF circuit having a transmission line conversion structure is mounted. In FIG. 8, reference numeral 201 denotes an RF circuit;
Reference numeral 2 denotes a moving body, and the RF circuit 201 is mounted on the moving body 202.

FIG. 9 shows the internal configuration of the RF circuit 201.
The RF circuit 201 includes a dielectric substrate 10 on the surface of the base 103.
2 are adhered, and the transmission line conversion structure 301 of the present invention is formed on a part of the conductor pattern.

FIG. 10 shows a cross-sectional configuration of the RF circuit. Dielectric substrates 1021 and 1022 are adhered to the front and back surfaces of the pedestal 103, and the dielectric substrate 1021 is used as an antenna substrate, and the dielectric substrate 1022 is used as an RF substrate. Dielectric substrate 10
21 and the dielectric substrate 1022 are connected via the coaxial cable 101, and the connection portion uses the transmission line conversion structure of the present invention.

When an electromagnetic wave is coming from the front, RF
The circuit is arranged in the front part of the moving body 202 and the dielectric substrate 1
By supporting the antenna directivity of the antenna No. 021 forward, an electromagnetic wave from the front is induced into an electric signal by the antenna, transmitted through the coaxial cable 101 to the RF substrate of the dielectric substrate 1022, and the signal is processed by a certain algorithm. It is processed.
The signal from the RF board passes through the coaxial cable 101 and is radiated as an electromagnetic wave from the antenna of the dielectric board 1021. By using the transmission line conversion structure of the present invention when passing through the coaxial cable 101, the discontinuity of the characteristic impedance at the conversion portion is reduced, and the transmission from the dielectric substrate to the coaxial cable and from the coaxial cable to the dielectric substrate is reduced. Propagation has improved characteristics with reduced reflection and loss.

[0023]

As described above, according to the present invention, in the millimeter wave RF circuit, the length of the center conductor at the end face of the coaxial cable is processed so as to be equal to or greater than the thickness of the dielectric substrate to be connected. The surface conductor of the dielectric substrate to which is connected is a donut-shaped land pattern arranged concentrically with the coaxial cable, and the back conductor of the dielectric substrate to which the outer conductor of the coaxial cable is connected is the center conductor concentric with the coaxial cable A circular nucleus pattern that is larger than the outer diameter of the outer conductor and smaller than the outer diameter of the outer conductor is arranged.

Further, a coaxial cable is introduced from the back side to the front side in the direction of the normal vector to the plane of the dielectric substrate, and a hole through which the center conductor can pass is provided in the dielectric substrate to connect the center conductor and the surface conductor to each other. Connect the conductor and the back conductor.

The discontinuous portion of the characteristic impedance at the connection between the dielectric substrate and the transmission line of the coaxial cable is only the central conductor having the length of the dielectric substrate. Its thickness is well below one millimeter, approximately one millimeter in length. Therefore, the inductance of the center conductor can be reduced to a small value. Further, the provision of the land pattern of the front conductor and the null pattern of the rear conductor makes it possible to further suppress the impedance value at the central conductor. Therefore, the impedance discontinuity of the center conductor can be suppressed to an almost negligible level. By adjusting the characteristic impedance of the microstrip line or coplanar line fabricated on the dielectric substrate and the coaxial cable, the transmission line can be reduced. Thus, it is possible to provide a transmission line conversion structure capable of suppressing reflection and loss to a small level.

Further, if a millimeter wave RF circuit using this transmission line conversion structure is used for a mobile body, it is expected that reflection and loss at the conversion part will be reduced.
The dynamic range of the signal can be expanded and the power consumption can be reduced. Since the transmission line conversion structure itself is composed only of the coaxial cable and the dielectric substrate, the cost of the moving body can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining the principle of a transmission line conversion structure according to the present invention.

FIG. 2 is a perspective view showing a configuration of a transmission line conversion structure according to one embodiment of the present invention.

FIG. 3 is a perspective view of a microstrip line dielectric substrate used in the transmission line conversion structure of the present invention.

FIG. 4 is a perspective view showing the back surface of the microstrip line dielectric substrate.

FIG. 5 is a perspective view showing a transmission line conversion structure according to another embodiment of the present invention.

FIG. 6 is a perspective view of a coplanar line dielectric substrate used in the transmission line conversion structure of FIG. 5;

FIG. 7 is a perspective view showing the back surface of the coplanar line dielectric substrate.

FIG. 8 is a perspective view of a moving object having a transmission line conversion structure according to an embodiment of the present invention.

FIG. 9 is a perspective view showing an internal configuration of an RF circuit mounted on a moving object.

FIG. 10 is a partial cross-sectional perspective view illustrating a cross-sectional configuration of an RF circuit mounted on a moving object.

FIG. 11 is a cross-sectional view showing a configuration of a conventional transmission line conversion structure.

[Explanation of symbols]

101: coaxial cable, 102: dielectric substrate, 103 ...
Pedestal, 104: center conductor of coaxial cable, 105: surface conductor of dielectric substrate, 106: outer conductor of coaxial cable, 1
07: a back conductor of the dielectric substrate, 108: a dielectric between the center conductor and the outer conductor of the coaxial cable, 109: a via hole on the dielectric substrate, 201: an RF circuit, 202: a moving body,
Reference numeral 301 denotes a transmission path conversion structure; 1021, a dielectric substrate for an antenna; and 1022, a dielectric substrate for an RF substrate.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroshi Kondo 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] In an electronic circuit including a coaxial cable, the coaxial cable is guided from a back surface side of a dielectric substrate in a direction of a normal vector to a plane of the dielectric substrate included in the electronic circuit, and is connected to a center of the coaxial cable. The conductor passes through the back surface of the dielectric substrate and connects to the front surface conductor, and the outer conductor of the coaxial cable has a circular hollow hole smaller than the outer diameter of the outer conductor formed concentrically with the center conductor. A transmission path conversion structure characterized by connecting to a transmission line. 2. The doughnut-shaped land formed on the surface conductor of the dielectric substrate according to claim 1, which is formed concentrically with the center conductor of said coaxial cable and larger than the outer diameter of said center conductor. A transmission line conversion structure characterized by having a pattern conductor attached. 3. The transmission line conversion structure according to claim 1, wherein the structure of the front and rear conductors of the dielectric substrate is continuously adjusted so as to match the characteristic impedance of the coaxial cable. Therefore, a transmission line conversion structure characterized by being defined by a microstrip line or a coplanar line. 4. The transmission path conversion structure according to claim 1, wherein said transmission path conversion structure is mounted on at least a part of a moving body or an object. Road conversion structure.