JPH07288401A - Non-contact rotary joint - Google Patents

Abstract

PURPOSE:To reduce the increase of a transmission loss and to reduce the directional dependency of transmission characteristics even when fixed side and rotary side positions are deviated. CONSTITUTION:Printed circuit boards 30a and 30b fixed at a fixed part and a rotary part are provided with coupling lines 34a and 34b for the length of the 1/4 wavelength of a transmitting signal, one terminal P1 is grounded, and another terminal P2 is an opened terminal. Then, a current to flow to the coupling lines 34a and 34b is made maximum at the grounded terminal and made minimum at the opened terminal. However, the coupling lines 34a and 34b is made helical and shaped a little over one circumference. Therefore, the maximum and minimum parts of a current amount are compensated each other, an equal magnetic field can be provided as a whole and even in the case of position deviation, influences are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact rotary joint for transmitting a high frequency signal between a fixed part and a rotary part rotatably supported by the fixed part.

[0002]

2. Description of the Related Art Recent BS (Broadcasting Satellite)
With the spread of satellite communications such as, there is an increasing demand to enjoy high-quality satellite broadcasting even for mobiles such as cars and trains. Here, in order to receive BS with sufficient strength, a highly sensitive antenna with a very narrow beam width must be used. On the other hand, in a moving body such as an automobile, the direction of the satellite changes as the vehicle travels. Therefore, in order to receive the BS in the moving body, it is necessary to control the azimuth angle and the elevation angle of the beam according to the movement of the moving body and always keep the beam in the satellite direction.

Of these, with respect to azimuth, it is necessary to direct the beam in all directions (360 ° or more), so a method of mechanically rotating the antenna element in the azimuth plane is generally used. Therefore, the received signal received by the antenna element (BS-IF signal (1015 to 1350M
Hz)) to the BS tuner in the passenger compartment,
A rotatable rotary joint that transmits a high frequency signal in the frequency band of the BS-IF signal is required.

Rotary joints for transmitting high-frequency signals are roughly classified into those that transmit signals by mechanical contacts (contact type) and those that transmit signals non-contact by electrostatic coupling or electromagnetic coupling (non-contact type). There are two types.

Of these, the contact type has excellent transmission characteristics, but the number of revolutions used is limited due to wear of the contacts. For this reason, it is not suitable for a mobile BS antenna that changes the direction of the starting and ending beams as the mobile body travels. Therefore,
A general non-contact type is used for a mobile BS antenna.

On the other hand, in the non-contact type rotary joint for the mobile BS antenna, 1) there is little transmission loss, 2) there is little direction dependence due to rotation of the transmission characteristic, and 3) frequency of the transmission characteristic within the BS-IF band. It is important that the dependence is low (wide band).

Japanese Unexamined Patent Publication No. 3-41801 discloses an example of such a non-contact rotary joint. In this example, as shown in FIG. 11, the rotating portion 12 is arranged opposite to the fixed portion 10. Further, printed circuit boards 14 and 16 are arranged at the facing portions of the fixed portion 10 and the rotating portion 12, respectively. A spiral inductance element 18 is formed on the surfaces of the printed boards 14 and 16. In addition, the printed circuit board 14,
In the inductance element 18 formed on the surface of 16,
The center conductors 20a and 22a of the coaxial feeders 20 and 22 are connected. Here, the length of the inductance element 18 is set to λ _g / 4 (λ _g : effective wavelength).

According to such a non-contact rotary joint, the rotating portion 12 can be freely rotated, and in this state, a high frequency signal can be transmitted between the pair of inductance elements 18. In particular, by disposing a pair of spirally formed inductance elements 18 so as to face each other and performing distributed capacitance coupling, the distributed capacitance becomes large as compared with the one using an ordinary lumped constant coil. Therefore, the Q of the transmission between the inductance elements 18 is low, and the characteristic is that high transmission characteristics can be obtained in a wide band.

[0009]

However, since the length of the inductance element of FIG. 11 is λ _g / 4, the current distribution on the inductance element 18 is as shown in FIG. 12 at the center (coaxial line 20 or 22). It becomes maximum at the connection part) and becomes 0 at the tip of the outer peripheral part. Therefore, the strength of the magnetic field induced by the current on the inductance element 18 is large in the central portion and becomes smaller toward the outer periphery. Therefore, the transmission characteristics of this non-contact rotary joint are considered to be similar to those of a rotary transformer using a coil whose diameter is relatively smaller than the outer diameter of the inductance element 18, as shown in FIG.

For this reason, when mounting on the fixed portion and the rotating portion, a displacement occurs between the inductance elements 18,
As shown in FIG. 14, when the center of the element deviates from the center of rotation, the transmission loss becomes large, and the area where the coils face each other changes due to the rotation, so that the direction dependence of the transmission characteristic becomes strong. There was a problem.

The present invention has been made to solve the above-mentioned problems, and it is possible to reduce the increase in transmission loss even when a position shift occurs and to reduce the direction dependency of transmission characteristics. The purpose is to provide a non-contact rotary joint.

[0012]

According to the present invention, a fixed portion and a rotating portion are arranged to face each other, and a signal transmission element is provided in each of the opposed portions, and a high frequency signal is transmitted between these signal transmission elements in a non-contact manner. The signal transmission element comprises a ground conductor plate made of a conductor and a line length of about ¼ of the wavelength of the transmission signal formed on the ground conductor plate via a dielectric layer. A spiral line having a circumference of one end, one end of which is grounded to a ground conductor plate and the other end of which is open. Each of the signal transmission elements has a coupling line that circulates around, and an outer conductor of a coaxial power feed line that transmits a signal is connected to the ground conductor plate of each signal transmission element, and a central conductor of the coaxial power feed line is connected to the coupling line. Is characterized by.

As described above, the non-contact type rotary joint according to the present invention transmits a high frequency signal in a non-contact manner between the signal transmission elements arranged opposite to each other. Therefore, there is no limit to the number of rotations that can be used, and there is no problem even if the beam direction is changed from start to finish in response to traveling of the moving body.

The coupled line has a spiral shape in which the line length is a quarter of the propagation wavelength, and one end is a ground end.
The other end is open. Therefore, the current flowing in this coupled line is maximum at the ground end and minimum at the open end,
The amount of current is complemented by the fact that the grounded end and the open end are located close to each other. Therefore, the transmission efficiency between the coupled lines is good, the transmission loss is small, and the direction dependence of the transmission characteristics is small. Therefore, it is possible to reduce the transmission loss / direction dependency due to the positional deviation during mounting.

Further, a feed line having one end connected to the spiral coupling line and the other end extending to the center of the rotation axis is provided.
It is characterized in that the central conductor of the coaxial feed line is connected near the center of the rotation axis of the feed line to feed power to the coupling line.

Therefore, the coupling line of the rotating portion can be rotated around the feeding point, and suitable signal transmission can be performed.

Further, it is characterized in that the spiral coupling lines of the two signal transmission elements have different line lengths. As a result, multiple resonances can be achieved in the signal transmission element, and the transmission frequency bandwidth can be widened.

Further, an attenuator is connected to the power feeding line portion. As a result, reflection of signals in bands other than the frequency to be transmitted can be sufficiently reduced, parasitic oscillation or the like does not occur, and the circuit can operate stably.

[0019]

Embodiments of the non-contact rotary joint according to the present invention will be described below with reference to the drawings.

[First Embodiment] FIGS. 1 to 3 show the construction of the essential parts of the first embodiment. The rotary joint of this embodiment is
As shown in FIG. 2, it is composed of a pair of printed circuit boards (signal transmission elements) 30 arranged to face each other. This example
A rotary joint used for a vehicle-mounted antenna, a printed circuit board 30a is provided on the side of a fixed part fixed to the vehicle body, and a printed circuit board 30b is a rotary part rotatably supported by a bearing or the like with respect to the fixed part. It is provided on the side.

The printed circuit boards 30a, 30b (30) are
As shown in FIG. 3, the substrate body 31 is made of a dielectric plate such as ceramic or plastic.
The back surface of 1 is a ground plane made of a thin copper layer (ground plane)
32 is formed, and a coupling line 34 formed of a microstrip line is formed on the surface.

As shown in FIG. 1, the coupling line 34 is in the shape of a helix that makes one revolution around the rotation axis of the rotating portion, and its length is approximately 1 / the effective wavelength λ _g of the transmission signal.
It is set to 4. One end (ground end) P1 of the coupled line 34 is connected to the back surface through a through hole and is grounded, and the other end (open end) P2 is open. Further, in the coupling line 34, the ground end P1 and the open end P2 are located close to each other. In this embodiment, the open end P2 side is outside the ground end P1 side, and both are slightly over. It is formed to wrap. The open end P
The two sides may be located inside. In addition, this coupled line 34
The power supply line 36 is formed of a microstrip line from a predetermined portion (in this example, a point distant from the ground end by about 90 °) toward the center.

On the other hand, in the center of the printed circuit board 30,
The coaxial line 38 is connected from the back side. That is,
As shown in FIG. 3, the outer conductor 38B of the coaxial line 38 is
The center conductor 38A is connected to the ground plane 32 of the printed circuit board 30, is guided to the surface, and is connected to the center side end (feed point) P3 of the feed line 36. The center conductor 38A is connected to the coupling line via the feed line 36. 34 (see FIGS. 1 and 2). The connection point P4 of the feed line 36 to the coupling line 34 is a substantial feed point in operation.

Here, the line length of the coupled line 34 is λ _g / 4.
Is. Therefore, the voltage is maximum and the current is 0 at the open end.
And the impedance here is infinite.
On the contrary, at the ground end, the maximum current is 0, and the impedance is 0. Therefore, the impedance at the connection point P4 can be set to an arbitrary value by appropriately selecting the connection point at which the feed line 36 in the coupling line 34 is connected. Therefore, by setting the point P4 connecting the power feeding line 36 to the coupling line 34 according to the impedance of the coaxial line 38, the power feeding line 36 and the coaxial line 38 can be connected with good matching.

Then, the printed circuit boards 30a and 30b configured as described above are held at a predetermined interval so that their surfaces (the coupled lines 34) face each other. At this time, the center of the spiral coupling line 34 on the printed circuit boards 30a and 30b is made to coincide with the center of rotation of the rotating portion. That is, the printed circuit board 30a is fixed to a fixed part such as the roof of the vehicle body, and the printed circuit board 30b is fixed to the rotating part side rotatably supported by bearings or the like,
Both are arranged to face each other. As a result, even when the rotating portion is rotated with respect to the fixed portion, the two printed circuit boards 30a, 3
A high frequency signal is transmitted by electromagnetic coupling between the coupling lines 34 of 0b.

As described above, the line length of the coupled line 34 is λ.
_{Since g} / 4, the current distribution on the coupled line 34 is shown in FIG.
As shown in, the maximum is on the grounded end side and the minimum is on the open end side. In this embodiment, since the coupling line 34 has a spiral shape of about one round and the ground end P1 side and the open end P2 side are overlapped with each other, the maximum current portion and the minimum current portion overlap each other and the current on the circumference is increased. The distribution is almost constant. Therefore, the strength of the magnetic field induced by the current of the coupled line 34 is also substantially constant on the circumference. Therefore, as shown in FIG. 5, the transmission characteristics of the non-contact rotary joint of the present embodiment are similar to those of a rotary transformer using a coil whose size is substantially equal to the diameter of the coupling line 34, and the rotation characteristics are higher than those of the conventional technology. The diameter of the transformer increases. Therefore, the printed circuit boards 30a, 30
When b is arranged to face each other, even if some positional deviation occurs, the transmission loss and the direction dependency of the transmission amount are reduced, and good characteristics can be obtained.

It should be noted that the coupling line 34 having a spiral shape of about one round is provided.
Since the line length (circumferential length) of A must be approximately λ _g / 4 as described above, since the diameter of the coupling line 34 (that is, the diameter of the rotary transformer) is increased, the current distribution on the periphery becomes substantially constant. It is desirable that the angle of revolution from the grounded end P1 to the open end P2 is 315 ° (that is, an angle that does not overlap) to 450 ° (that is, an angle that overlaps), and further 360 ° to 420 ° (the overlapping angle is 0). It is preferable that the angle is about 60 ° to 60 °) because the uniformity of the current distribution is enhanced.

FIG. 6 shows the transmission characteristics. Thus, around the resonance frequency (frequency f _g corresponding to the wavelength lambda _g), it is possible to obtain a high transmission characteristic.

[Second Embodiment] FIG. 7 shows the configuration of a second embodiment of the present invention. In the first embodiment, since the line lengths of the coupling lines 34 of the two printed boards 30a and 30b are equal to each other, the loss is very low near the resonance frequency, but the bandwidth is relatively narrow. In the mobile BS antenna, BS-I
In a wide range of F signal (1015 MHz to 1350 MHz), it is necessary to perform signal transmission between the fixed part and the rotating part. Therefore, it is desirable that the transmission loss in this frequency range be substantially constant.

Therefore, in the second embodiment, the line lengths of the coupling line 34 in the two printed boards 30a and 30b are made different. As a result, the coupled line 34
The resonance points at a and 34b are different from each other.
Therefore, in the rotary joint of the second embodiment, as shown in FIG.
As shown in (1), multiple resonance occurs and the transmission band is widened. For this reason, the transmission loss increases slightly from the minimum point of the first embodiment, but almost constant transmission characteristics can be obtained over a wide frequency range. In addition, in order to make the frequency characteristic in the transmission band substantially flat, it is preferable that the resonance frequency difference between the coupling lines 34a and 34b is approximately 20% or less.

[Third Embodiment] As is apparent from FIGS. 6 and 8, the non-contact rotary joint of the present invention functions as a kind of band-pass filter for transmitting signals in a certain frequency range. Therefore, in a frequency band other than the transmission band, a mismatching state occurs, and in particular, when connected to a wide band amplifier, a problem such as parasitic oscillation may occur. Therefore, in the third embodiment, as shown in FIG. 9, an attenuator 40 using a chip resistor or the like is inserted and arranged in the feed line 36. As a result, although the transmission loss in the pass band is slightly increased, the reflection outside the pass band is reduced and the matching is improved, so that the circuit operates stably and the reliability is improved.

[Example of Transmission Characteristics] FIG. 10 shows the results of measurement of the transmission characteristics of the non-contact rotary joint, which is an embodiment of the present invention prepared for a mobile BS antenna, with a network analyzer. Here, in the rotary joint of this example, multiple resonance for widening the band (second embodiment) and addition of an attenuator 40 for improving matching outside the pass band (third embodiment) are performed, Second embodiment and third
It has the characteristics of the embodiment. The attenuator 40 is inserted by 3 dB in each of the power supply lines 36 on the rotating portion side and the fixed portion side. The wavelength shortening rate of the coupled line in this example is about 0.55, the longer coupled line length is 37.5 mm, and the shorter one is 31.7 mm.
The distance between the two printed circuit boards 30a and 30b is 2 mm.

Further, in the measurement of FIG. 10, the frequency characteristic and the direction dependency of the transmission characteristic are simultaneously measured, and therefore the frequency sweep is slowly performed while rotating the rotating part side at high speed. Therefore, the small fluctuation width in the measurement data shows the direction dependence of the transmission loss. Note that the transmission band required for the mobile BS antenna is shown between the marker Δ1 and the marker ▽ 2 in the figure.

From the measured data in FIG. 10, the transmission loss in the desired band is 12 dB at maximum, the fluctuation width with respect to frequency is within 3 dB, and the direction dependency is within 2 dB, which is sufficient performance as a non-contact rotary joint for a mobile BS antenna. It can be seen that is obtained.

[0035]

As described above, since the non-contact rotary joint according to the present invention is non-contact, there is no limit to the number of rotations that can be used. Since the coupling line has a spiral shape of about one round, the transmission efficiency between the coupling lines is good, the transmission loss is small, and the direction dependence of the transmission characteristic is small. Therefore, there is little increase in transmission loss and directional dependence due to displacement during mounting. Furthermore, the transmission frequency bandwidth can be widened by making the line lengths of the pair of coupled lines different.

Further, by providing the attenuator, parasitic oscillation or the like does not occur and the circuit operates stably.

Excellent characteristics such as

Therefore, it is suitable for transmitting a high frequency signal between the rotating part and the fixed part in a mobile BS antenna or the like.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a printed circuit board according to a first embodiment.

FIG. 2 is a diagram showing an arrangement of a pair of printed circuit boards according to the first embodiment.

FIG. 3 is a diagram showing a connected state of the coaxial feeder line of the first embodiment.

FIG. 4 is a diagram showing a current state on the coupled line of the first embodiment.

FIG. 5 is a diagram showing a rotary transformer similar to the coupled line of the first embodiment.

FIG. 6 is a diagram showing frequency characteristics of transmission loss according to the first embodiment.

FIG. 7 is a diagram showing a configuration of a printed circuit board according to a second embodiment.

FIG. 8 is a diagram showing frequency characteristics of transmission loss according to the second embodiment.

FIG. 9 is a diagram showing a configuration of a printed circuit board according to a third embodiment.

FIG. 10 is a diagram showing an example of transmission characteristics according to the embodiment.

FIG. 11 is a diagram showing a configuration of a conventional printed circuit board.

FIG. 12 is a diagram showing current characteristics of a conventional example.

FIG. 13 is a diagram showing a rotary transformer similar to the conventional example.

FIG. 14 is a diagram showing transmission loss and direction dependence of a conventional example.

[Explanation of symbols]

 30 Printed Circuit Board (Signal Transmission Element) 32 Ground Plane 34 Coupling Line 36 Feed Line 38 Coaxial Feed Line 38A Center Conductor 38B Outer Conductor P1 Ground End P2 Open End P3 Center End (Feed Point) P4 Connection Point

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Eiji Teramoto, Eiji Teramoto, Nagakute-cho, Aichi-gun, Aichi Prefecture, No. 1 No. 41 Yokomichi, Toyota Central Research Institute Co., Ltd. (72) Inventor, Toshiaki Watanabe, Nagachite-machi, Aichi-gun, Aichi-gun 1 in 41 Chuo-do, Toyota Central Research Institute Co., Ltd. (72) Inventor Masaru Ogawa, Nagakute-cho, Aichi-gun, Aichi-gun, Nagatoji 1-in-1 Toyota Chuo Research Center (72) Inventor, Masa Morita Aichi Toyota city, Toyota city, Toyota city (72) Inventor Atsushi Kozaka, Toyota city, Toyota city, Aichi prefecture Toyota car company

Claims (4)

[Claims] 1. A non-contact rotary joint for arranging a fixed portion and a rotating portion so as to face each other and providing signal transmitting elements at the facing portions, respectively, for transmitting a high frequency signal between these signal transmitting elements in a non-contact manner. The signal transmission element consists of a ground conductor plate made of a conductor and a spiral line that is formed on the ground conductor plate via a dielectric layer and has a line length of about 1/4 of the wavelength of the transmission signal. One end is grounded to the ground conductor plate and the other end is open, and each has a coupling line that circulates around the rotation axis of the rotating unit so that the open end is located near the ground end. A non-contact rotary joint characterized in that an outer conductor of a coaxial feed line for transmitting a signal is connected to a ground conductor plate of each signal transmission element, and a central conductor of the coaxial feed line is connected to a coupling line. 2. The non-contact rotary joint according to claim 1, wherein one end is connected to the spiral coupling line, and the other end has a feed line extending to the center of the rotation axis. A non-contact rotary joint that feeds power to a coupling line by connecting a central conductor of a coaxial power feed line near the center. 3. The non-contact rotary joint according to claim 1, wherein the spiral coupling lines of the two signal transmission elements have different line lengths. 4. The non-contact rotary joint according to claim 1, wherein an attenuator is connected to the power feed line portion.