WO2012121015A1

WO2012121015A1 - Antenna

Info

Publication number: WO2012121015A1
Application number: PCT/JP2012/054278
Authority: WO
Inventors: 功高吉野; 覚坪井
Original assignee: ソニー株式会社
Priority date: 2011-03-07
Filing date: 2012-02-22
Publication date: 2012-09-13
Also published as: JP2012186737A

Abstract

[Problem] To implement high antenna gain with a miniaturized simple configuration, as a UHF wide frequency band antenna, for example, which is usable in a vehicle-mounted device, etc. [Solution] An inner conductor (7) of one end of adjacent coaxial cables (CL1-CL3) connects with another outer conductor (5), an outer conductor (5) of one end connects with another end of the inner conductor (7), and one inner conductor (7) of the coaxial cable (CL3) which is second from the end stage connects with another outer conductor (5) of a coaxial cable (CL4) of the end stage. A plurality of coaxial cables (CL1-CL4) is thus positioned in a column. The length (L2) of each of the coaxial cables (CL1-Cl4) is effectively 1/4 the used wavelength λ.

Description

antenna

The present disclosure relates to an antenna, and more particularly, to an antenna that can be used for in-vehicle devices and the like, for example, a wide frequency band of the UHF band.

In receiving UHF band digital broadcasting, an antenna having a simple configuration with good sensitivity that can be used in a vehicle or indoors is required. In particular, in the field of automobiles, in order to differentiate from mobile phones and to increase the size of displays, HDTV (High Definition Television) has been changed from the so-called one-segment broadcasting (terrestrial digital television broadcasting mainly for portable devices). )
The transition to Full Seg (digital terrestrial television broadcasting including One Seg) is progressing.

In the case of one seg, the receiver sensitivity for the required channel is supposed to be about 7 to 8 dB. On the other hand, in the case of full segment, reception sensitivity of 19 dB or more is required, and it is the mainstream to use a synthesis diversity technique. For this reason, in-vehicle devices currently receive digital terrestrial television broadcasts using two film antennas with amplifiers. But,
It is difficult for ordinary people to mount film antennas on automobile windows. Furthermore, it is necessary to apply a power source to the amplifier, and it is necessary to use an expensive connector for a power source having a polarity separated into a hot side and a ground side. As described above, the film antenna has a large number of parts, is inconvenient to mount, requires assembly, and is more expensive.

By the way, as an example of a high-gain antenna, a collinear antenna configured by connecting coaxial cables in cascade is known. The length of each coaxial cable is ½ of the wavelength used. The collinear antenna is used in a base station for wireless communication such as a cellular phone network, but since it is fixed, it can sharpen directivity and gain.

However, when it is used as an antenna for an in-vehicle device, it cannot be put into practical use if the directivity is sharp like a conventional collinear antenna. In the case of a conventional collinear antenna, the length of each coaxial cable is ½ of the wavelength used, and the entire antenna is large.

The present disclosure has been made in view of the above situation, and is used for in-vehicle devices, for example, U.
As an antenna of a wide frequency band of the HF band, a high antenna gain is realized with a small and simple configuration.

In the antenna of one aspect of the present disclosure, the inner conductor at one end of an adjacent coaxial line is alternately connected to the other outer conductor, the outer conductor at one end is alternately connected to the inner conductor at the other end, and one antenna before the final stage is connected. One inner conductor of the coaxial line is connected to the other outer conductor of the final stage coaxial line. Thereby, a plurality of coaxial lines are arranged in a column. The length of each coaxial line is substantially ¼ of the wavelength used.
It is preferable that three or more coaxial wires are connected.

According to one aspect of the present disclosure, one antenna is formed with a simple structure in which coaxial lines having a length of ¼ wavelength are connected in cascade. The antenna has a plurality of feeding points in the connection portion of adjacent coaxial lines, including the connection portion of the final coaxial line and the coaxial line immediately before. And
Phase feeding is performed from a coaxial line having a length of ¼ wavelength adjacent to the feeding point.

According to the present disclosure, a small antenna can be configured with a simple structure in which coaxial lines having a length of ¼ wavelength are connected in cascade. In addition, a wide band and a high gain can be realized by feeding a phase to a feeding point existing at a connection portion between coaxial lines of the antenna.

1 is a schematic diagram illustrating a configuration example of an antenna according to an embodiment of the present disclosure. It is explanatory drawing of the principle of operation of the antenna shown in FIG. It is an external view which shows the example of 1 aspect of the antenna shown in FIG. It is the schematic which shows the structural example of the multistage antenna used for verification of an antenna characteristic. It is the schematic which shows the structural example of the antenna of 1 step | paragraph structure. It is a graph and a table | surface which show the measurement result of the peak gain in the UHF band by the antenna of 1 step | paragraph structure. It is the schematic which shows the structural example of the antenna of a 2 step | paragraph structure. It is a graph and a table | surface which show the measurement result of the peak gain in the UHF band by the antenna of 2 steps | paragraph structure. It is the schematic which shows the structural example of the antenna of 3 steps | paragraphs structure. It is a graph and table | surface which show the measurement result of the peak gain in the UHF band by the antenna of 3 steps | paragraphs structure. It is the schematic which shows the structural example of the antenna of 4 steps | paragraphs structure. It is the graph and table | surface which show the measurement result of the peak gain in the UHF band by the antenna of 4 steps | paragraphs structure. It is the schematic which shows the structural example of the antenna of a 5-stage structure. It is a graph and a table | surface which show the measurement result of the peak gain in the UHF band by the antenna of a 5-stage structure. It is the schematic which shows the structural example of the antenna of 6 steps | paragraphs structure. It is a graph and a table | surface which show the measurement result of the peak gain in the UHF band by the antenna of 6 steps | paragraphs structure. It is a directivity pattern figure in the UHF band of an antenna having a four-stage configuration. It is a graph and a table | surface which show the measurement result of the peak gain and average gain in the UHF band by the antenna of 4 steps | paragraphs structure. It is a graph and a table | surface which show the measurement result of the peak gain of a UHF band by the antenna of coaxial line impedance 50ohm. It is a graph and a table | surface which show the measurement result of the peak gain of a UHF band by the antenna of coaxial line impedance 75ohm. It is a graph and a table | surface which show the measurement result of the peak gain of a UHF band by the antenna of coaxial line impedance 97ohm. It is explanatory drawing which shows the example of attachment of the antenna which concerns on one embodiment of this indication.

Hereinafter, exemplary embodiments for carrying out the present disclosure will be described with reference to the accompanying drawings.
In addition, in each figure, the same code | symbol is attached | subjected to the common component and the overlapping description is abbreviate | omitted.

[Configuration example of multi-stage antenna]
FIG. 1 illustrates a configuration example of an antenna according to an embodiment of the present disclosure.
The antenna (cable antenna) according to the present disclosure includes only a plurality of coaxial wires (coaxial structure conductors such as coaxial cables) connected to the connector 2 connected to the communication device 9. As the connector 2, it is desirable to select a connector with a small loss of high-frequency signals. The cable antenna 1 shown in FIG. 1 is an example in which four coaxial lines CL1 to CL4 are connected in a column. In the following, a cable antenna in which a plurality of coaxial lines are connected in cascade is referred to as a multistage antenna, and when four coaxial lines are used, it is referred to as a four-stage antenna.

In the cable antenna 1, one end of the coaxial line CL1 connected to the connector 2 is connected to the other end of the coaxial line CL2 via the relay portion R1. Similarly, one end of the coaxial line CL2 is connected to the other end of the coaxial line CL3 via the relay portion R2, and one end of the coaxial line CL3 is connected to the coaxial line C via the relay portion R3.
It is connected to the other side of L4. The substantial length L1 of each coaxial line that is an antenna element is:
It is 1/4 of the wavelength λ of the used radio wave.

The first-stage coaxial line CL1 includes a ferrite core 1 made of a high magnetic material as a high-frequency blocking member.
0 is provided. This ferrite core 10 is arranged at a position having a length of ¼ of the wavelength λ of the radio wave to be received from the relay portion R1 (feed point Fp2) toward the connector 2. As a result, the conductor portion from the ferrite core 10 to the connector 2 has high impedance in terms of high frequency, and is separated from the antenna portion in the high frequency band. That is, ferrite core 1
Since the coaxial line CL1 between 0 and the connector 2 is separated in high frequency from the previous antenna portion, even if a high frequency current flows through that portion, the influence on the antenna portion is reduced. Thereby, the distance from the ferrite core 10 to the relay part R1 with respect to the coaxial line CL1 can be made substantially ¼ of the wavelength λ. Moreover, the length from the ferrite core 10 of the coaxial line CL1 to the connector 2 can be arbitrarily determined.

Each relay part is molded by a resin such as an elastomer. Inside, the protective coating 4 of each coaxial wire and the shielded wire 5 (outer conductor) of the hollow cylinder are removed,
The core material 6 (derivative) and the core wire 7 (internal conductor) are exposed.

In the relay portion R1, the tip of one core wire 7 of the coaxial line CL1 is connected to the other shield wire 5 of the coaxial line CL2 by soldering or the like on the substrate 8. Further, one shielded wire 5 of the coaxial line CL1 is connected to the tip of the other core wire 7 of the coaxial line CL2 by soldering or the like on the substrate 8. Similarly, in the relay part R2, the coaxial line CL2 and the coaxial line CL3 are connected to be relayed. Then, in the relay section R3 that relays the coaxial line CL3 of the last stage from the coaxial line CL4 of the last stage and the coaxial line CL4 of the final stage, the tip part of one core wire 7 of the coaxial line CL3 is connected to the other end of the coaxial line CL4. Connect to shielded wire 5. One shielded wire 5 of the coaxial wire CL3
Is not connected to the tip of the other core wire 7 of the coaxial line CL4.

[Operation principle of multi-stage antenna]
The operation principle of the cable antenna 1 shown in FIG. 1 will be described with reference to FIG.
FIG. 2A shows the voltage distribution of the voltage induced inside each coaxial line by a certain moment of radio wave.
Shows the voltage distribution of the voltage induced by the inverted radio wave as in FIG. 2A at the same moment. At this time, in the cable antenna 1, as shown in FIG. 1, a current distribution of ½λ is formed in the coaxial line CL1 and the coaxial line CL2 around the feeding point Fp1, and coaxial with the coaxial line CL3 around the feeding point Fp2. A current distribution of ½λ is generated on the line CL4.

In the case of the cable antenna 1, the final coaxial line CL4 among the four coaxial lines CL1 to CL4.
And a connection portion (relay portion R3) with the coaxial line CL3 immediately before that is a feeding point Fp1. Further, the first coaxial line CL1 and the next coaxial line C, which are at a distance of ½ wavelength from the feeding point Fp1,
The connection part (relay part R1) of L2 becomes the feed point Fp2. That is, a half-wave dipole antenna composed of the coaxial line CL1 and the coaxial line CL2 is configured, and similarly the coaxial line CL3 and the coaxial line CL.
A four-wavelength half-wave dipole antenna is constructed. The cable antenna 1 functions as an antenna in which the two half-wave dipole antennas are connected in cascade.

In the voltage distribution of FIG. 2A, in the section 11A, the core wire 7 of the coaxial line CL1, in the section 11B, the shield wire 5 of the coaxial line CL2, and in the section 11C, the core wire 7 of the coaxial line CL3, the section 11D.
Then, a voltage is induced in each shield wire 5 of the coaxial line CL4. 2B, in the section 12A, the shield line 5 of the coaxial line CL1, in the section 12B, to the core line 7 of the coaxial line CL2, in the section 12C, to the shield line 5 of the coaxial line CL3, and in the section 12D, the coaxial line. A voltage is induced in each of the core wires 7 of CL4.

When attention is paid to the voltage induced in the shield line 5 as an example, the feeding point Fp2 captures a current corresponding to the voltage (+) induced in the shield line 5 of the coaxial line CL2 in a certain radio wave section 11B (FIG. 2A). On the other hand, for example, a current corresponding to the voltage (+) of the same phase induced in the shield line 5 of the coaxial line CL1 in another radio wave section 11A whose phase is inverted is taken in.
Similarly, at the feeding point Fp1, a current having the same phase corresponding to the voltage (−) induced in the shield line 5 is taken in. In this manner, the power of the high-frequency signal to be taken in is amplified by taking in the current of the same phase due to the voltage induced at each feeding point. Then, the current captured at the feeding point Fp1 is added in the same phase as the current captured at the feeding point Fp2. Therefore, a high frequency signal is amplified in the connector 2 (see FIG. 1) according to the number of feeding points.

FIG. 3 is an external view showing an aspect of the cable antenna 1 shown in FIG.
In this example, the coaxial lines CL1 to CL4 are connected in cascade via the relay portions R1 to R3. The length L1 of each coaxial line is about 15 cm, which is a quarter of the wavelength of the 500 MHz radio wave. The coaxial line CL1 is not provided with the ferrite core 10 and is 1 / wavelength of the radio wave to be received.
A connector 2 is directly connected to a coaxial line CL1 having a length of 4. The tip 20 on the opposite side of the relay portion R3 of the final coaxial line CL4 is molded by a resin such as an elastomer as in each relay portion.

[Verification of antenna characteristics]
In order to verify the characteristics of the antenna according to the present disclosure, the inventors conducted an experiment of receiving radio waves by changing the number of stages of the multi-stage cable antenna shown in FIG. In the cable antenna used for verification, n coaxial lines CL1 to CLn are connected in series via each of the relay portions R1 to Rn-1, and the number of stages is changed one by one. The length L1 of each coaxial line is 10 cm (frequency 7
(Corresponding to about 1 / 4λ of 50 MHz), the characteristic impedance of each coaxial line is 100Ω. Here, the characteristic impedance is an impedance between the shield wire 5 and the core wire 7. In the case of a cable antenna composed of n coaxial lines CL1 to CLn, the final coaxial line CLn
And a connection portion (relay portion Rn-1) with the coaxial line CLn-1 immediately before that becomes a feeding point. Starting from this feeding point, a plurality of connecting portions (relay portions) corresponding to the number of coaxial lines from the last stage coaxial line CLn to the first stage coaxial line CL1 function as feeding points. The measurement was performed with the antenna installed in a state where it can receive strong horizontal polarization (horizontally placed horizontally) assuming actual use.

(Characteristics of single-stage antenna)
FIG. 5 is a schematic diagram illustrating a configuration example of a one-stage antenna. FIG. 6 is a graph and a table showing measurement results of peak gains of vertically polarized waves and horizontally polarized waves with a single-stage antenna. In the graph of FIG. 6A, the horizontal axis represents frequency (MHz), and the vertical axis represents peak gain (dBd).
Indicates. The frequency band to be measured was the UHF band (470 MHz to 870 MHz). Vertically polarized waves are indicated by broken lines, and horizontally polarized waves are indicated by solid lines. 6B and 6C show values at each measurement point in the graph shown in FIG. 6A. That is, FIG. 6B shows the peak gain value in the vertical polarization, and FIG. 6C shows the peak gain value in the horizontal polarization. 6B and 6C.
6 also shows a measured value at 906 MHz that is not in the graph of FIG. 6A.

The one-stage cable antenna is composed only of the coaxial line CL1 and does not function as an antenna at all because there is no antenna element on one side. As shown in FIGS. 6A to 6C, the peak gain at each frequency is low for both the vertical polarization and the horizontal polarization.

(Characteristics of two-stage antenna)
FIG. 7 is a schematic diagram illustrating a configuration example of a two-stage antenna. FIG. 8 is a graph and table showing measurement results of peak gains of vertically polarized waves and horizontally polarized waves with a two-stage antenna. In the graph of FIG. 8A, the horizontal axis represents frequency (MHz), and the vertical axis represents peak gain (dBd).
Indicates. Vertically polarized waves are indicated by broken lines, and horizontally polarized waves are indicated by solid lines. 8B and 8C show values at each measurement point in the graph shown in FIG. 8A. That is, FIG. 8B shows the peak gain value in the vertically polarized wave, and FIG. 8C shows the peak gain value in the horizontally polarized wave.

The two-stage cable antenna is composed of two antenna elements, a coaxial line CL1 and a coaxial line CL2, and has a configuration close to a half-wave dipole antenna. As shown in FIGS. 8A to 8C, in the vicinity of 720 to 750 MHz, the peak gain value is −10 dB or more for both the vertical polarization and the horizontal polarization, and it can be seen that the antenna gain is obtained. That is, it can be said that both vertical polarization and horizontal polarization can be received in the UHF band.

(Characteristics of three-stage antenna)
FIG. 9 is a schematic diagram illustrating a configuration example of a three-stage antenna. FIG. 10 is a graph and table showing measurement results of peak gains of vertical polarization and horizontal polarization using a three-stage antenna.
In the graph of FIG. 10A, the horizontal axis represents frequency (MHz), and the vertical axis represents peak gain (dB).
d). Vertically polarized waves are indicated by broken lines, and horizontally polarized waves are indicated by solid lines. 10B and 10C show values at each measurement point in the graph shown in FIG. 10A. That is, FIG. 10B
Indicates the value of peak gain in vertical polarization, and FIG. 10C shows the value of peak gain in horizontal polarization.

The cable antenna having a three-stage configuration has a relay part R1 and a relay part R2, and it is considered that there are a plurality of power feeding points including a feeding point Fp1 (relay part R2) by radio waves. FIG.
As shown in FIG. 10A to FIG. 10C, in the vicinity of 720 to 750 MHz, the peak gain value is −10 dB or more for both the vertical polarization and the horizontal polarization, and it can be seen that the antenna gain is obtained. However, it is considered that the antenna characteristics are not stable because a reverse-phase voltage is induced inside the coaxial line.

(Characteristics of 4-stage antenna)
FIG. 11 is a schematic diagram illustrating a configuration example of a four-stage antenna. FIG. 12 is a graph and a table showing measurement results of peak gains of vertically polarized waves and horizontally polarized waves using a four-stage antenna. In the graph of FIG. 12A, the horizontal axis represents frequency (MHz), and the vertical axis represents peak gain (d
Bd). Vertically polarized waves are indicated by broken lines, and horizontally polarized waves are indicated by solid lines. 12B and 12C show values at each measurement point in the graph shown in FIG. 12A. That is, FIG.
B shows the value of the peak gain in the vertical polarization, and FIG. 12C shows the value of the peak gain in the horizontal polarization.

The cable antenna having a four-stage configuration has relay portions R1 to R3, and has a feed point Fp1 (relay portion R3) and a feed point Fp2 (relay portion R1). Compared with the two-stage cable antenna (half-wavelength dipole antenna configuration) shown in FIG. 7, the in-phase current is taken in and the antenna gain is improved. In addition, the peak gain at a frequency of 500 MHz or less is improved as compared with the cable antenna having a three-stage configuration. As shown in FIGS. 12A to 12C, it can be seen that the peak gain value is −10 dB or more in the entire frequency band particularly in the horizontally polarized wave, and the antenna gain is obtained. In other words, it can be said that the four-stage cable antenna can receive the horizontally polarized wave well in the UHF band.

(Characteristics of 5-stage antenna)
Furthermore, the measurement of the reception state was also performed for a cable antenna having a four-stage configuration or more, and will be described for reference.
FIG. 13 is a schematic diagram illustrating a configuration example of a five-stage antenna. FIG. 14 is a graph and a table showing the measurement results of the peak gains of vertically polarized waves and horizontally polarized waves with a 5-stage antenna. In the graph of FIG. 14A, the horizontal axis indicates the frequency (MHz), and the vertical axis indicates the peak gain (d
Bd). Vertically polarized waves are indicated by broken lines, and horizontally polarized waves are indicated by solid lines. 14B and 14C show values at each measurement point in the graph shown in FIG. 14A. That is, FIG.
B shows the peak gain value in the vertical polarization, and FIG. 14C shows the peak gain value in the horizontal polarization.

In a five-stage cable antenna, as shown in FIGS. 14A to 14C, the horizontal polarization has a peak gain value of −10 dB or more in all frequency bands to be measured, and the horizontal polarization is generally high gain in the UHF band. Is receiving well. However, for frequencies of 500 MHz or less, the peak gain value is about −10 dB or less for both vertical polarization and horizontal polarization,
Antenna gain is not set. Similar to the measurement result of the three-stage configuration, there is a portion where the antenna characteristics are not stable, and there is a possibility that a reverse-phase voltage is induced inside the coaxial line.

(Characteristics of 6-stage antenna)
FIG. 15 is a schematic diagram illustrating a configuration example of a six-stage antenna. FIG. 16 is a graph and table showing measurement results of peak gains of vertical polarization and horizontal polarization using an antenna having a six-stage configuration. In the graph of FIG. 16A, the horizontal axis represents frequency (MHz), and the vertical axis represents peak gain (d
Bd). Vertically polarized waves are indicated by broken lines, and horizontally polarized waves are indicated by solid lines. 16B and 16C show values at each measurement point in the graph shown in FIG. 16A. That is, FIG.
B shows the value of peak gain in vertical polarization, and FIG. 16C shows the value of peak gain in horizontal polarization.

The six-stage antenna has a large total antenna length and exceeds the measurement size that can be handled in the measurement environment in which the experiment was performed. As shown in FIG. 16A to FIG. 16C, data with higher gain is obtained for the horizontal polarization compared to the case of the five-stage configuration. Although there are some places where the peak gain value is not stable in some frequency bands of vertical polarization and horizontal polarization, the entire frequency band to be measured can be received almost satisfactorily.

According to the present embodiment, a single linear antenna is configured with a simple structure using a plurality of coaxially-connected antenna elements connected in cascade, and the single linear antenna is obtained by performing phase feeding. Can achieve wide bandwidth and high gain. In addition, since the components and the structure are simple, the cost is low, and the ease of mounting improves, so the convenience is improved.

In addition, according to the measurement results of the plurality of types of cable antennas, the antenna gain tends to be improved as the number of stages of the multistage antenna increases, that is, as the number of coaxial lines (antenna elements) connected in the column increases. Theoretically, the multi-stage antenna can be a two-stage configuration, but in a narrow sense, it has a configuration of three or more stages in terms of differentiation from the prior art. In addition, odd-numbered cable antennas are presumed that a reverse-phase voltage is induced inside the coaxial line and the antenna characteristics may not be stable. Therefore, the number of coaxial lines is desirably an even number. .

(Directivity pattern of 4-stage antenna)
In addition, the directivity pattern was measured about the 4-stage antenna shown in FIG. The length L1 of each coaxial line used for measurement is 10 cm (corresponding to about 1 / 4λ of a frequency of 500 MHz), and the characteristic impedance of each coaxial line is 97Ω. FIG. 17 shows an example of the directivity pattern of a four-stage antenna. In FIGS. 17A to 17H, the frequency of the received radio wave is 470 MHz and 520 M, respectively.
Hz, 570 MHz, 620 MHz, 670 MHz, 720 MHz, 770 MHz, 90
The directivity characteristic in the case of 6 MHz is shown. Vertically polarized waves are indicated by broken lines, and horizontally polarized waves are indicated by solid lines. FIG. 18 is a graph and a table showing the measurement results of the peak gains of vertical polarization and horizontal polarization when the radiation pattern is measured. In the graph of FIG. 18A, the horizontal axis represents the frequency (M
Hz), and the vertical axis represents the peak gain (dBd). Also, FIG. 18B shows FIGS.
The values of peak gain (dBd) and average gain (dBd) in the vertical polarization shown in 7H are shown. FIG. 18C shows the values of peak gain (dBd) and average gain (dBd) at the same horizontal polarization. Furthermore, FIG. 18D shows values of peak gain (dBd) and average gain (dBd) calculated from measured values of vertical polarization and horizontal polarization.

As shown in FIGS. 17A to 17H, it can be seen that the directivity pattern of the four-stage antenna draws a curve that is approximately close to a circle in the vertical plane and approximately 8 in the horizontal plane. In particular, the horizontal plane at 570 Hz and 620 Hz has directivity close to the figure 8 that is the directivity of the dipole antenna. In FIGS. 17A to 17H, the gain of the vertical polarization is high at an angle where the gain of the horizontal polarization is small. Thereby, it is possible to pick up the vertically polarized wave at an angle where the horizontally polarized wave cannot be picked up. Note that the measurement is carried out in an installation situation (horizontal horizontal) that can receive strong horizontal polarization assuming actual use, but this tendency increases depending on the installation situation of the antenna. For example, if the antenna is installed such that horizontal polarization and vertical polarization can be received evenly, the directivity pattern in which horizontal polarization and vertical polarization complement each other is obtained.

[Measurement results when changing the characteristic impedance of the coaxial cable]
Next, the measurement result when changing the characteristic impedance of the coaxial line constituting the multistage antenna will be described.
FIG. 19 shows a graph and a table showing the measurement results of the peak gain in the UHF band by a four-stage antenna using a coaxial line having a characteristic impedance of 50Ω. FIG. 20 shows a graph and a table showing the measurement result of the peak gain in the UHF band by a four-stage antenna using a coaxial line having a characteristic impedance of 75Ω. Further, FIG. 21 shows that a coaxial line having a characteristic impedance of 97Ω is used.
The graph and table | surface which show the measurement result of the peak gain of the UHF band by a stage antenna are shown. Each coaxial line has a length of 15 cm (about 1 / 4λ of a frequency of 500 MHz).

As shown in FIGS. 19 to 21, the characteristic impedance of the coaxial line is 50Ω, 75Ω, and 97Ω.
As the value increases, a high gain is obtained, and the gain value has little variation in the target frequency band and is stable. From the above, in a multistage antenna, it is better that the characteristic impedance at the desired frequency of the coaxial line connected to the feeder is higher, at least 50Ω.
It is desirable that there be more.

[Example of mounting a multistage antenna]
Next, an example of mounting a multistage antenna will be described.
FIG. 22 illustrates an example in which the multistage antenna according to the present disclosure is mounted on an automobile. In this example, the four-stage cable antenna 1 shown in FIG. 1 is used. Coaxial lines CL1 to CL4 extending from the connector 2 connected to the communication device 9 such as a navigation device are turned toward the left window on the dashboard, and are further turned upward on the frame at the left end of the dashboard. Then, the upper part of the windshield is attached from the upper part of the frame so as to lie almost horizontally toward the rearview mirror. Thus, the cable antenna 1 is configured as a V-shaped antenna with the relay portion R2 as a base point.

As described above, the cable antenna 1 does not need to be carefully attached to a window like a film antenna, and does not require components such as an amplifier built in the film antenna. That is, the cable antenna 1 is convenient because it can be easily installed in the automobile by drawing the linear antenna.

As described above, the present disclosure is not limited to the above-described embodiments, and various other modifications and application examples can be taken without departing from the gist of the present disclosure described in the claims. Of course.

In the above-described embodiment, the ferrite core 10 made of a high magnetic material is used as the high-frequency cutoff portion provided in the first-stage coaxial line CL1 of the multistage antenna. However, the present invention is not limited to this example as long as the high-frequency signal can be electrically disconnected. For example, a stub structure in which a coaxial shield wire is bent at a length of about λ / 4 of a desired frequency may be employed. It is also conceivable to form a balun called a super top by processing the shield wire.

In the above-described embodiment, a multi-stage cable antenna is configured using a plurality of coaxial wires. However, for example, another wire material in which two conductors (conductors) such as feeder wires are arranged substantially in parallel is used. However, it is possible to create a multistage antenna.

DESCRIPTION OF SYMBOLS 1 ... Antenna, 2 ... Connector, 3A-3E ... Relay part, 4 ... Protective clothing, 5 ... Shield wire (outer conductor), 6 ... Core material (dielectric material), 7 ... Core wire (internal conductor), 8 ... Substrate,
10 ... Ferrite core, 11A to 11D, 12A to 12C ... Voltage distribution, 20 ... Tip, CL1 to CLn ... Coaxial line, Fp1, Fp2 ... Feed point, R1 to Rn-1 ... Relay

Claims

Having a plurality of coaxial lines connected in cascade;
In the plurality of coaxial lines, an inner conductor at one end of an adjacent coaxial line is alternately connected to the other outer conductor, an outer conductor at one end is alternately connected to an inner conductor at the other end, and the coaxial line one before the last stage is connected. An antenna in which one inner conductor of the wire is connected to the other outer conductor of the final coaxial line, and the length of each coaxial line is substantially ¼ of the wavelength used.
The antenna according to claim 1, wherein three or more coaxial wires are connected.
The antenna according to claim 2, wherein the number of the coaxial lines is an even number.