JP5690707B2 - Antenna and communication system - Google Patents

Description

  The present invention relates to an antenna and a communication system using a leaky coaxial cable.

    A leaky coaxial cable (LCX) is one in which a plurality of slots are provided in the outer conductor of a normal coaxial cable. Through such a slot, an electromagnetic wave signal inside the cable can be emitted to the outside, or an electromagnetic wave signal outside the cable can be taken into the cable. That is, LCX is a cable type antenna and can be said to be a special long and narrow transmitting / receiving antenna.

  The radiation modes of the electromagnetic wave from the LCX having the zigzag slots include Eφ polarization and Ez polarization in the circumferential direction and the axial direction of the electric field. The radiation angles of the Eφ polarization and the Ez polarization are determined from the operating frequency, the slot pitch, and the relative dielectric constant of the insulator between the inner conductor and the outer conductor (see Non-Patent Document 1).

  In the conventional LCX, a radiation mode having a single Eφ polarization is adopted in order to ensure the stability of the intensity of the radiated electromagnetic wave. In this case, it is often used as a backfire antenna in which the radiation angle of Eφ polarized wave is negative with respect to the direction toward the end of the LCX, that is, toward the feeding side. Therefore, the vicinity of the end of LCX is a blind spot with respect to the Eφ polarized wave. If the LCX is installed in accordance with the communication target area, an incommunicable area is formed at the LCX terminal portion.

  There has been proposed a method for preventing the occurrence of a non-communicable area within the communication target area by superimposing the power supply side portions of a pair of LCXs (see Patent Document 1). The proposed method is effective for an endfire type antenna in which the radiation angle of the Eφ polarized wave is positive with respect to the direction toward the end of the LCX, that is, toward the end. However, in the backfire type antenna, a communication impossible area occurs at the terminal end.

JP 2011-182139 A

Toshihiko Kishimoto and Shin Sasaki “LCX Communication System” The Institute of Electronics and Communication, published on August 20, 1982

  As described above, in the backfire-type LCX, an incommunicable region occurs at the terminal end. As measures against the incommunicable area occurrence, it is possible to secure the communicable area by extending the LCX in the axial direction beyond the communicable area or bending the extended part of the LCX within the communicable area. It is. However, an extra length of LCX, a step of bending the LCX, and the like are required, resulting in an increase in cost.

  In addition, if the radiation angle of the Eφ polarized wave can be set in the substantially radial direction of the LCX, no communication impossible area will occur. However, when the radiation angle corresponds to the radial direction, the resonance state is reached, and the reflected power in the LCX increases and the voltage standing wave ratio deteriorates.

  In view of the above problems, an object of the present invention is to provide an antenna and a communication system capable of preventing the occurrence of a non-communication area within a communication target area.

  According to one aspect of the present invention, a central conductor extending in the axial direction from one end to the other end to which a signal is supplied, an insulator covering the central conductor, and an outer conductor covering the central conductor with the insulator interposed therebetween, A leaky coaxial cable in which a plurality of first slots and a plurality of second slots are provided at a constant pitch on the outer conductor along the axial direction, and connected to the other end, terminated with the characteristic impedance of the leaky coaxial cable, and the outer conductor And a terminator having an outer conductor connected to the plurality of first and second slots at a radiation angle inclined to one end with respect to the normal line of the leaky coaxial cable in a plane parallel to the axial direction. So that only the first polarization, which is the circumferential component of the leaky coaxial cable, is radiated, and the second polarization, whose electric field is the axial component, is radiated from the exterior conductor in the normal direction. The pitch is the free space wavelength of the signal and Antenna is provided which is defined by the dielectric constant of the rim body.

  According to another aspect of the present invention, a power feeding unit that generates a high-frequency signal, a center conductor that extends in the axial direction from one end to the other end connected to the power feeding unit, an insulator that covers the center conductor, and an outer periphery of the insulator A leaky coaxial cable having a plurality of first slots and a plurality of second slots provided at a constant pitch in the outer conductor along the axial direction, and connected to the other end of the leaky coaxial cable. And a terminator having an outer conductor connected to the outer conductor and having a radiation angle inclined to one end side with respect to the normal line of the leaky coaxial cable in a plane parallel to the axial direction. From the first and second slots, only the first polarization whose electric field is the circumferential component of the leaky coaxial cable is radiated, and the second polarization whose electric field is the axial component from the outer conductor in the normal direction. Pitch so that the waves are radiated A transmitting antenna which is defined by the dielectric constant of the free space wavelength and the insulator of the signal, the communication system comprising a receiving antenna for receiving the first and second polarization is provided.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the antenna and communication system which can prevent generation | occurrence | production of the communication impossible area | region within a communication object area | region.

It is the schematic which shows an example of the antenna which concerns on embodiment of this invention. It is the schematic which shows an example of LCX used for the antenna which concerns on embodiment of this invention. FIG. 3 is a diagram for explaining a slot arrangement of the LCX shown in FIG. 2. It is the schematic which shows an example of the measurement system of the radiation intensity distribution of the antenna which concerns on embodiment of this invention. It is a figure explaining the radiation angle of Ephi polarization by the measurement system shown in FIG. It is a figure which shows an example of the radiation intensity distribution of Ephi polarized wave and Ez polarized wave obtained by the measurement system shown in FIG. It is the schematic which shows an example of the communication system which concerns on embodiment of this invention. It is the schematic which shows another example of the antenna which concerns on embodiment of this invention. It is a figure which shows an example of the radiation intensity distribution of Ephi polarized wave and Ez polarized wave obtained by the antenna shown in FIG. It is the schematic which shows the other example of the terminator used for the antenna which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  The following embodiments of the present invention exemplify apparatuses and methods for embodying the technical idea of the present invention. The technical idea of the present invention is based on the material and shape of component parts. The structure, arrangement, etc. are not specified below. The technical idea of the present invention can be variously modified within the technical scope described in the claims.

  The antenna 1 according to the embodiment of the present invention includes an LCX 3 and a terminator 5 as shown in FIG. When the antenna 1 is used as a transmission antenna, the feeding unit 7 is connected to one end of the LCX 3 via an approach cable 9 such as a coaxial cable. A terminator 5 is connected to the other end of the LCX 3. The terminator 5 is a termination resistor having the same resistance value as the characteristic impedance of the LCX 3 so that unnecessary reflection does not occur. The outer conductor of the terminator 5 is connected to the outer conductor 14. On the plane parallel to the axial direction of LCX3, the radiation angle of the radiation wave R from LCX3 is θ. When the radiation angle θ is positive, the radiation wave R is radiated toward the terminator 5 with respect to the normal line of the LCX 3. When the radiation angle θ is negative, the radiated wave R is radiated to the opposite side of the terminator 5 with respect to the normal line of LCX3.

  As shown in FIG. 2, the LCX 3 includes a center conductor 10, an insulator 12, an outer conductor 14, and a sheath 16. The center conductor 10 extends in the axial direction from one end to the other end where the high-frequency signal is supplied from the power supply unit 7. The insulator 12 is provided so as to cover the central conductor 10. The outer conductor 14 is provided so as to cover the central conductor 10 with the insulator 12 interposed therebetween. The sheath 16 is provided so as to cover the outer periphery of the outer conductor 14.

  As illustrated in FIGS. 2 and 3, the outer conductor 14 is provided with a plurality of first slots 18 a and a plurality of second slots 18 b in a zigzag shape along the axis (z-axis) direction of the LCX 3. The first and second slots 18a and 18b are provided at a constant pitch P, respectively. The second slots 18b are provided at an interval of 1/2 of the pitch P with respect to the first slots 18a. The first slot 18a is disposed at a first angle α with respect to the z-axis direction. The second slot 18b is disposed to be inclined at the second angle β with respect to the z-axis direction. The first and second angles α and β are complementary to each other.

  For example, the LCX 3 includes a copper center conductor 10 having a diameter of 2 mm, a foamed polyethylene insulator 12 having a diameter of 5 mm and a relative dielectric constant εr of about 1.5, a copper outer conductor 14, and a flame retardant polyethylene sheath 16. Is used. The characteristic impedance of LCX3 is 50Ω. An antenna 1 is formed by connecting a 50Ω terminator 5 to the other end of the LCX 3. The length of the antenna 1 is about 1 m.

  The pitch P of the first and second slots 18a, 18b is 80 mm. When a high frequency signal having a frequency of 2.4 GHz is supplied from the power feeding unit 7 shown in FIG. 1, the radiation angle θ is −20 degrees from the first and second slots 18a and 18b provided in the LCX 3, and the electric field is in the circumferential direction. The Eφ polarized wave is radiated as a radiated wave R. That is, the antenna 1 operates as a backfire antenna. The LCX3 does not radiate Ez polarized waves whose electric field is in the z-axis direction. Further, the length and width of the first and second slots 18a and 18b, and the first and second angles α so that the radiation intensity of the radiated wave R at a position about 1.5 m away from the antenna 1 is about 60 dB. , Β are set.

  As shown in FIG. 4, the antenna 1 having a length of about 1 m was installed on the floor surface of the anechoic chamber 30, and the radiation intensity distribution was measured. In the anechoic chamber 30, the axial direction of LCX3 is z, the circumferential direction of LCX3 is φ, and the height direction is x. The antenna 1 is arranged so that one end to the other end of the antenna 1 are located at z = 1 m to 2 m. A power feeding unit 7 provided outside the anechoic chamber 30 is connected to one end of the antenna 1 via an approach cable 9. As the receiving antenna 20, for example, a half-wavelength standard dipole antenna is disposed immediately above the antenna 1. The receiving antenna 20 is connected via an approach cable 22 to a receiving unit 24 provided outside the anechoic chamber 30.

  A signal having a frequency of 2.4 GHz and an input power Pt is supplied from the power feeding unit 7 to one end of the antenna 1, and a radiated wave from the antenna 1 is received by the receiving antenna 20. The reception unit 24 detects the reception power Pr of the radiated wave. The radiation intensity Lc is calculated by the following equation.

Lc = 10 log (Pt / Pr) (dB) (1)

As described above, the antenna 1 shown in FIG. 4 is a backfire antenna having a radiation angle θ of −20 degrees. Therefore, as shown in FIG. 5, the communicable region Ca in which the Eφ-polarized radiated wave Rφ propagates is shifted toward one end of the antenna 1 with respect to the communication target region CT directly above the antenna 1. As a result, an incommunicable region Nc in which the radiated wave Rφ does not propagate is generated in the vicinity immediately above the terminator 5.

  FIG. 6 shows the result of measuring the distribution of the radiation intensity Lc while changing the height (x) of the receiving antenna 20 in the range of 0.25 m to 1.5 m and the position (z) in the range of 0 to 5 m. . As shown in FIG. 6, the radiation intensity Lcφ measured with respect to the Eφ polarization has a distribution inclined toward the LCX 3 by the radiation angle θ of the radiation wave Rφ, and the radiation of the Eφ polarization is weak above the terminator 5. On the other hand, the radiation intensity Lcz measured with respect to the Ez polarized wave is distributed unevenly above the terminator 5 as shown in FIG. That is, Eφ polarization is dominant on the LCX 3 side, and Ez polarization is dominant on the terminator 5 side. The radiation intensities Lcφ and Lcz are approximately the same intensity.

  As described above, it was confirmed that the Ez-polarized radiated wave is strongly distributed on the side of the terminator 5 which is a communication impossible area in the conventional communication system using the Eφ-polarized radiated wave. Therefore, in the communication system according to the embodiment, as shown in FIG. 7, in the communication target region CT above the antenna 1, the Eφ polarization (first polarization) and the Ez polarization (second polarization) orthogonal to each other. ) Are provided on the LCX 3 side and the terminator 5 side. For example, a half-wavelength standard dipole antenna directed in a direction in which Eφ polarization can be received is used as the reception antenna 20a, and a half-wavelength standard dipole antenna in a direction in which Ez polarization can be received is used as the reception antenna 20b. As a result, it is possible to prevent the occurrence of an incommunicable area in the communication target area CT.

  In the above description, the receiving antennas 20a and 20b corresponding to the first and second polarized waves orthogonal to each other are used. However, when the mobile body receives the radiated wave from the antenna 1, an antenna that can simultaneously receive the Eφ polarization and the Ez polarization is desirable. For example, a cross dipole antenna, a circularly polarized planar antenna, a circularly polarized dual loop antenna, a helical antenna, a spiral antenna, or the like may be used as the receiving antenna 20 mounted on the moving body.

  In order to radiate Ez polarized light from the terminator 5, the pitch P of the first and second slots 18a and 18b needs to satisfy the relationship represented by the following equation.

(Εr) ^1/2 <λ / P <1+ (εr) ^1/2 (2)

Here, λ is the free space wavelength of the high-frequency signal, and εr is the relative dielectric constant of the insulator 12. When λ / P = (εr) ^1/2 , the radiation angle is 0, but the resonance condition is satisfied and the antenna characteristics are deteriorated. Further, when λ / P> 1+ (εr) ^1/2 , a radiated wave from the antenna 1 cannot be obtained.

Note that, under the condition of Expression (2), the radiation angle θ is in the range of 0 to −90 degrees. When the radiation angle θ is close to 0, the slope of the distribution of the radiation intensity Lcφ of the Eφ polarization becomes small. On the other hand, the radiation intensity Lcz of Ez polarized waves becomes stronger as the radiation angle θ is closer to −90 degrees. In order to suppress the occurrence of an incommunicable region in the communication target region CT and to secure the radiation intensity Lcφ and Lcz of Eφ polarization and Ez polarization, the radiation angle θ is −5 degrees to −45 degrees. A range of is desirable. If the radiation angle θ is in the range of −5 degrees to −45 degrees,

0.1+ (εr) ^1/2 ≦ λ / P ≦ 0.7 + (εr) ^1/2 (3)

It becomes. That is, if the radiation angle θ is less than −5 degrees, the radiation intensity Lcz of the Ez polarization is weak, and if the radiation angle θ exceeds −45 degrees, the slope of the radiation intensity Lcφ distribution of the Eφ polarization increases. .

  For example, when there are two communication target areas apart from each other, an LCX can be arranged on one side and a terminator can be arranged on the other side to ensure a communicable area. As shown in FIG. 8, the antenna 1a includes LCX3, another coaxial cable 40 connected to the LCX3 and the connector 42, and a terminator that terminates the general-purpose coaxial cable. As the coaxial cable 40, a general-purpose coaxial cable or the like may be used. Compared to LCX, general-purpose coaxial cables are inexpensive and can be arranged easily.

  FIG. 9 shows the result of measuring the radiation intensity distribution in the anechoic chamber 30 shown in FIG. 4 by connecting the coaxial cable 40 having a length of 1 m. As shown in FIG. 9, it is confirmed that the Eφ polarization is radiated from the LCX 3 of the antenna 1 a and the Ez polarization is radiated from the terminator 5 extended by the coaxial cable 40. The attenuation amount of the signal by the coaxial cable 40 is about 0.5 dB / m, and the reduction of the intensity of the Ez polarization is slight and does not cause a problem.

  As described above, in the antenna 1 according to the embodiment, Ez polarized waves are radiated from the exterior conductor of the terminator 5 connected to the outer conductor 14 of the LCX 3. The radiation direction of the Ez polarization varies depending on the shape of the outer conductor. For example, when an elongated conductor extending in the axial direction is provided on the end face side of the terminator 5, it is strongly distributed in the radial direction of the Ez polarized wave. When it is desired to distribute Ez-polarized radiation in the radial direction of the terminator 5, it is desirable to use an outer conductor of the terminator 5 having a cross section perpendicular to the axial direction. Further, FIG. 10 shows the distribution of the radiation intensity Lcz = 60 dB of Ez polarized wave when the terminator 5 having substantially the same diameter from the LCX3 side to the end surface side and the terminator 5a having a larger end surface side diameter than the LCX3 side are used. It is the result of having measured. As shown in FIG. 10, the distribution F of the terminators 5 is isotropic in the radial direction. On the other hand, the distribution Fa of the terminator 5a is shifted from the radial direction to the LCX3 side. Therefore, the overlap of the radiation intensity distributions of the Eφ polarization and the Ez polarization on the terminal end side of the antenna 1 becomes strong, and stable communication within the communication target area becomes possible.

(Other embodiments)
Although the embodiments of the present invention have been described as described above, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. Accordingly, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

1 ... Antenna 3 ... Leaky coaxial cable (LCX)
DESCRIPTION OF SYMBOLS 5 ... Terminator 7 ... Feeding part 10 ... Center conductor 12 ... Insulator 14 ... Outer conductor 16 ... Sheath 18a ... 1st slot 18b ... 2nd slot 20 ... Reception antenna 24 ... Reception part 40 ... Coaxial cable 42 ... Connector

Claims (12)

A central conductor extending in an axial direction from one end to the other end to which a signal is supplied, an insulator covering the central conductor, and an outer conductor covering the central conductor with the insulator interposed therebetween, along the axial direction A leaky coaxial cable provided with a plurality of first slots and a plurality of second slots at a constant pitch in the outer conductor;
A terminator connected to the other end, terminated with a characteristic impedance of the leaky coaxial cable, and having an outer conductor connected to the outer conductor;
In a plane parallel to the axial direction, an electric field is generated in the circumferential direction of the leaky coaxial cable from the plurality of first and second slots at a radiation angle inclined toward the one end side with respect to the normal line of the leaky coaxial cable. Only the first polarization, which is a component, is radiated, and the pitch is the signal of the signal so that the second polarization, which is an axial component, is radiated from the exterior conductor in the normal direction. It is defined by the free space wavelength and the dielectric constant of the insulator ,
The pitch is P, the free space wavelength of the signal is λ, and the dielectric constant of the insulator is εr.
(Εr) 1/2 <λ / P <1+ (εr) 1/2
An antenna characterized by satisfying the above relationship. A central conductor extending in an axial direction from one end to the other end to which a signal is supplied, an insulator covering the central conductor, and an outer conductor covering the central conductor with the insulator interposed therebetween, along the axial direction A leaky coaxial cable provided with a plurality of first slots and a plurality of second slots at a constant pitch in the outer conductor;
A terminator connected to the other end, terminated with a characteristic impedance of the leaky coaxial cable, and having an outer conductor connected to the outer conductor;
In a plane parallel to the axial direction, an electric field is generated in the circumferential direction of the leaky coaxial cable from the plurality of first and second slots at a radiation angle inclined toward the one end side with respect to the normal line of the leaky coaxial cable. Only the first polarization, which is a component, is radiated, and the pitch is the signal of the signal so that the second polarization, which is an axial component, is radiated from the exterior conductor in the normal direction. It is defined by the free space wavelength and the dielectric constant of the insulator ,
The pitch is P, the free space wavelength of the signal is λ, and the dielectric constant of the insulator is εr.
0.1+ (εr) 1/2 <λ / P <0.7+ (εr) 1/2
An antenna characterized by satisfying the above relationship. Each of the plurality of second slots is provided at a pitch that is ½ of the pitch with respect to each of the plurality of first slots,
Each inclination of the plurality of first slots with respect to the axial direction is a first angle, and each inclination of the plurality of second slots with respect to the axial direction is a second angle that is complementary to the first angle. antenna according to claim 1 or 2, characterized in that. The outer conductor, the antenna according to any one of claims 1 to 3, characterized in that it has a perpendicular end face in the axial direction. The antenna according to claim 4 , wherein the outer conductor has a larger diameter on the end face side than on the leaky coaxial cable side. Antenna according to any one of claims 1 to 5, wherein said terminator is characterized in that it is connected to the leakage coaxial cable through the other coaxial cable. A power feeding unit for generating a high-frequency signal;
A central conductor extending in an axial direction from one end to the other end connected to the power supply unit; an insulator covering the central conductor; an outer conductor covering an outer periphery of the insulator; and the external along the axial direction A leaky coaxial cable having a plurality of first slots and a plurality of second slots provided on a conductor at a constant pitch, connected to the other end, terminated with a characteristic impedance of the leaky coaxial cable, and connected to the outer conductor A terminating device having an outer conductor, and in a plane parallel to the axial direction, from the plurality of first and second slots at a radiation angle inclined toward the one end side with respect to a normal line of the leaky coaxial cable, Only the first polarization whose electric field is a component in the circumferential direction of the leaky coaxial cable is radiated, and the second polarization whose electric field is a component in the axial direction is radiated from the outer conductor in the normal direction. To be A transmitting antenna, wherein the pitch is defined by the dielectric constant of the free space wavelength and the insulator of said signal,
A receiving antenna for receiving the first and second polarized waves ;
The pitch is P, the free space wavelength of the signal is λ, and the dielectric constant of the insulator is εr.
(Εr) 1/2 <λ / P <1+ (εr) 1/2
A communication system characterized by satisfying the above relationship. A power feeding unit for generating a high-frequency signal;
A central conductor extending in an axial direction from one end to the other end connected to the power supply unit; an insulator covering the central conductor; an outer conductor covering an outer periphery of the insulator; and the external along the axial direction A leaky coaxial cable having a plurality of first slots and a plurality of second slots provided on a conductor at a constant pitch, connected to the other end, terminated with a characteristic impedance of the leaky coaxial cable, and connected to the outer conductor A terminating device having an outer conductor, and in a plane parallel to the axial direction, from the plurality of first and second slots at a radiation angle inclined toward the one end side with respect to a normal line of the leaky coaxial cable, Only the first polarization whose electric field is a component in the circumferential direction of the leaky coaxial cable is radiated, and the second polarization whose electric field is a component in the axial direction is radiated from the outer conductor in the normal direction. To be A transmitting antenna, wherein the pitch is defined by the dielectric constant of the free space wavelength and the insulator of said signal,
A receiving antenna for receiving the first and second polarized waves ;
The pitch is P, the free space wavelength of the signal is λ, and the dielectric constant of the insulator is εr.
0.1+ (εr) 1/2 <λ / P <0.7+ (εr) 1/2
A communication system characterized by satisfying the above relationship. Each of the plurality of second slots is provided at a pitch that is ½ of the pitch with respect to each of the plurality of first slots,
Each inclination of the plurality of first slots with respect to the axial direction is a first angle, and each inclination of the plurality of second slots with respect to the axial direction is a second angle that is complementary to the first angle. The communication system according to claim 7 or 8 , wherein the communication system is provided. The outer conductor, the communication system according to any one of claims 7-9, characterized in that it has a perpendicular end face in the axial direction. The communication system according to claim 10 , wherein the outer conductor has a larger diameter on the end face side than on the leaky coaxial cable side. The communication system according to any one of claims 7 to 11 , wherein the terminator is connected to the leaky coaxial cable via another coaxial cable.

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