JP5684764B2 - antenna - Google Patents

Description

  The present invention relates to an antenna 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, the electromagnetic wave signal inside the cable can be emitted to the outside, and the 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. Since LCX emits electromagnetic waves from each of a plurality of slots, a stable communication area can be realized along LCX. Moreover, if the input power to the LCX is appropriately weakened, a stable communication area can be obtained only in the vicinity of the LCX. Therefore, the communication target area can be limited only to the periphery of the LCX main body, and it is used as an antenna for preventing information leakage and ensuring communication security.

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

  However, when the vicinity of the end portion of the LCX was investigated in detail, it was found that there was actually Ez-polarized radiation. Such unintentional emission of Ez polarized waves in the vicinity of the LCX termination is unnecessary, and it is necessary to suppress it in order to ensure communication security.

  In view of the above-described problems, an object of the present invention is to provide an antenna capable of ensuring communication security at a terminal portion.

  According to one aspect of the present invention, a linear center conductor, an insulator covering the center conductor, the center conductor is covered with the insulator interposed therebetween, and a plurality of slots are provided at a predetermined pitch along the axial direction of the center conductor. Leakage coaxial that has an outer conductor and a sheath covering the outer circumference of the outer conductor with a thickness in the range of 0.01 mm or more and less than 1.5 mm and extending in the axial direction from one end to the other end where signals are supplied An antenna is provided that includes a cable and a termination member connected to the other end and including a terminator that terminates at the characteristic impedance of the leaky coaxial cable and having an outer conductor connected to an external conductor.

  According to another aspect of the present invention, a linear center conductor, an insulator covering the center conductor, and the center conductor is covered with the insulator interposed therebetween, and a plurality of slots are formed at a predetermined pitch along the axial direction of the center conductor. Leakage coaxial cable that has an outer conductor provided and that exposes the outer circumference of the outer conductor and extends in the axial direction from one end to the other end where the signal is supplied, and the characteristics of the leaky coaxial cable connected to the other end An antenna is provided that includes a terminator having an outer conductor connected to an outer conductor, including a terminator that terminates at an impedance.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the antenna and communication system which can ensure the communication security in a termination | terminus part.

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. It is the schematic which shows an example of the termination | terminus member of LCX shown in FIG. It is the schematic which shows an example of the measurement system of the coupling loss distribution of the antenna which concerns on embodiment of this invention. FIG. 5 is a schematic diagram illustrating an example of an arrangement of receiving antennas in the measurement system illustrated in FIG. 4. It is a figure which shows an example of the coupling loss distribution of the Ephi polarization obtained from the antenna which concerns on embodiment of this invention, and Ez polarization. It is a figure which shows an example of the relationship of the coupling loss of Ephi polarization and Ez polarization with respect to sheath thickness. It is a figure which shows the other example of the coupling loss distribution of Ephi polarization obtained from the antenna which concerns on embodiment of this invention, and Ez polarization.

  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 according to the embodiment of the present invention includes an LCX 1 and a termination member 3 as shown in FIG. When the antenna is used as a transmission antenna, the feeding unit 7 is connected to one end of the LCX 1 via an approach cable 9 such as a coaxial cable. The termination member 3 is connected to the other end of the LCX 1.

  In a plane parallel to the axial direction of LCX1, the radiation angle of the radiation wave R from LCX1 is defined as θ with respect to the normal line NL of LCX1. When the radiation angle θ is positive, the radiation wave R is radiated toward the termination member 3 with respect to the normal line NL of the LCX1. When the radiation angle θ is negative, the radiation wave R is radiated to the opposite side of the termination member 3 with respect to the normal line NL of LCX1.

  As shown in FIG. 2, the LCX 1 includes a center conductor 10, an insulator 12, an outer conductor 14, and a sheath 16. The center conductor 10 extends linearly 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 shown in FIG. 2, the outer conductor 14 is provided with a plurality of first slots 18a and a plurality of second slots 18b in a zigzag shape along the axis (z-axis) direction of the LCX1. The first and second slots 18a and 18b are each provided at a predetermined pitch. The second slots 18b are provided at an interval of 1/2 the pitch with respect to the first slots 18a. The first and second slots 18a and 18b are disposed at different inclination angles with respect to the z-axis direction. The inclination angles of the first and second slots 18a and 18b with respect to the z-axis direction are complementary to each other.

  As shown in FIG. 3, the terminating member 3 includes a connector 44 attached to the other end of the LCX 1 and a terminator 40 connected to the connector 44. The terminator 40 is a termination resistor having the same resistance value as the characteristic impedance of the LCX 1 so that unnecessary reflection does not occur. The outer conductor 42 of the terminator 40 is connected to the outer conductor 14 shown in FIG. 2 through the outer conductor 46 of the connector 44.

  For example, the LCX 1 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 sheath made of resin such as polyethylene. 16 is used. The characteristic impedance of LCX1 is 50Ω. A termination member 3 having a termination resistance of 50Ω is connected to the other end of the LCX 1 to form an antenna. The length of the antenna is about 2 m.

  The pitch of the first and second slots 18a and 18b is 40 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 and the electric field is in the circumferential direction from the first and second slots 18a and 18b provided in the LCX1. Eφ polarization is emitted as a radiated wave R. That is, the antenna operates as a backfire antenna. LCX1 does not radiate Ez polarized waves whose electric field is in the z-axis direction. Further, the length, width, and inclination angle of the first and second slots 18a and 18b are set so that the coupling loss of the radiation wave R at a position away from the antenna by about 1.5 m is about 60 dB.

  As shown in FIG. 4, an antenna having a length of about 2 m was installed on the floor of the anechoic chamber 30, and the coupling loss distribution was measured. In the anechoic chamber 30, the axial direction of LCX1 is z, and the height direction of LCX1 is x. The antenna is arranged so that one end to the other end of the antenna is located at z = 1 m to 3 m. A power feeding unit 7 provided outside the anechoic chamber 30 is connected to one end of the antenna via an approach cable 9. As the receiving antenna 20, for example, a half-wave standard dipole antenna is disposed directly above the antenna. 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 an input power Pt with a frequency of 2.4 GHz is supplied from the power feeding unit 7 to one end of the antenna, and a radiated wave from the antenna is received by the receiving antenna 20. The reception unit 24 detects the reception power Pr of the radiated wave. The coupling loss Lc is calculated by the following equation.

Lc = −10 log (Pr / Pt) (dB) (1)

As described above, the antenna shown in FIG. 4 is a backfire type antenna in which the radiation angle θ of the Eφ polarization is −20 degrees. For example, as shown in FIG. 5, using a receiving antenna 20a that can receive Eφ polarized waves in accordance with the circumferential direction of LCX1 and a receiving antenna 20b that can receive Ez polarized waves in accordance with the axial direction, The measurement of was carried out.

  In FIG. 6, using the LCX 1 having a thickness of the sheath 16 of 1.5 mm, the height x of the receiving antennas 20 a and 20 b is changed in the range of 0.25 m to 1.5 m, and the position z is changed in the range of 0 to 5 m. The result of measuring the distribution of coupling loss Lc is shown. As shown in FIG. 6, the coupling loss Lcφ measured with respect to the Eφ polarization has a distribution inclined toward the LCX 1 at the radiation angle θ of the radiation wave Rφ, and the radiation of the Eφ polarization is weak above the termination member 3. On the other hand, the coupling loss Lcz measured with respect to the Ez polarized wave has a distribution unevenly distributed above the termination member 3 as shown in FIG. That is, Eφ polarization is dominant in the region Ca on the LCX1 side, and Ez polarization is dominant in the region Cb on the termination member 3 side.

  The coupling losses Lcφ and Lcz have substantially the same strength. For example, when the height x is 1.5 mm, the coupling loss Lcφ is approximately 60 dB in the region Ca, and the coupling loss Lcz is approximately the same strength as approximately 61 dB in the region Cb.

  In the conventional antenna in which the LCX 1 is terminated by the termination member 3, the Ez polarized wave is radiated to the area Cb that is not necessary as the communication area, and information leakage occurs. Therefore, it is difficult to ensure communication security.

  Therefore, the coupling loss Lc was measured in the measurement form shown in FIG. 4 using LCX in which the thickness of the polyethylene sheath was changed by 0.5 mm from 0.5 mm to 3 mm. FIG. 7 shows the relationship between the coupling loss Lcφ of the Eφ polarization in the region Ca and the sheath thickness of the coupling loss Lcz of the Ez polarization in the region Cb, measured at a height x of 1.5 m. The sheath thickness of “0 mm” is a case where LCX having no sheath and exposing the outer periphery of the outer conductor is used. As shown in FIG. 7, the coupling loss Lcφ is about 60 dB regardless of the sheath thickness. On the other hand, it can be seen that the coupling loss Lcz increases as the sheath thickness decreases.

  In FIG. 8, using the LCX1 having a thickness of the sheath 16 of 0.5 mm, the height x of the receiving antennas 20a and 20b shown in FIG. 5 is in the range of 0.25 m to 1.5 m, and the position z is 0 to 5 m. The result of measuring the coupling loss distribution while changing the range is shown. As shown in FIG. 8, the coupling loss Lcφ measured with respect to the Eφ polarized wave has a distribution inclined to the LCX 1 side by the radiation angle θ of the radiated wave Rφ as in FIG. The radiation of is weak. On the other hand, the coupling loss Lcz measured with respect to the Ez polarization has a distribution unevenly distributed above the termination member 3. That is, Eφ polarization is dominant in the region Ca on the LCX1 side, and Ez polarization is dominant in the region Cb on the termination member 3 side.

  However, as shown in FIG. 8, the coupling loss Lcz of the Ez polarization in the region Cb is larger than the coupling loss Lcφ of the Eφ polarization in the region Ca, unlike FIG. Comparing the coupling loss Lc when the height x is 1.5 m, the coupling loss Lcφ in the region Ca is about 60 dB, while the coupling loss Lcz in the region Cb is about 69 dB.

  Thus, by reducing the thickness of the sheath 16 to 0.5 mm, the coupling loss Lcz of the Ez polarization increases by about 9 dB compared to the coupling loss Lcφ of the Eφ polarization, that is, the received power is about 1/8. It was confirmed that it decreased. When the sheath thickness is 1.5 mm, Lcz is about 61 dB, which is about the same as Lcφ. When the sheath thickness is thicker than 1.5 mm, Lcz becomes 60 dB or less, and the loss becomes smaller than Lcφ.

  The coupling loss Lcz in the region Cb on the terminal member 3 side of the LCX 1 depends on the thickness of the sheath 16. In order to increase the Ez polarization coupling loss in the region Cb and prevent information leakage, the thickness of the sheath 16 is less than 1.5 mm, preferably less than 1 mm, more preferably less than 0.7 mm. You can do it. If the thickness of the sheath 16 is less than 1.5 mm, the coupling loss of Ez polarization increases as compared to Eφ polarization. If the thickness of the sheath 16 is 1 mm or less, the coupling loss of the Ez polarization increases by about 3 dB as compared to the Eφ polarization, that is, the received power decreases to about ½ or less. Further, if the thickness of the sheath 16 is 0.7 mm or less, the coupling loss of Ez polarization increases by about 6 dB as compared with the Eφ polarization, that is, the received power decreases to about ¼ or less. As shown in FIG. 7, when an LCX having a sheath thickness of 0 mm, that is, without a sheath, is used, the coupling loss of Ez polarization increases by about 10 dB compared to Eφ polarization, that is, the received power is about 1/10. To decrease. Further, the sheath is often extruded by an extruder, and in the case of extrusion molding, the thickness of the sheath is limited to 0.1 mm to 0.3 mm. However, when the sheath is formed by wrapping tape or covering the shrinkable tube, the thickness of the sheath can be 0.01 mm. Therefore, the sheath thickness is desirably 0.01 mm or more.

  As described above, in the antenna according to the embodiment, the thickness of the sheath 16 is less than 1.5 mm. As a result, as shown in FIGS. 7 and 8, the coupling loss Lcz of Ez polarization near the termination member 3 can be increased. It has been confirmed that the thickness of the sheath 16 has no effect on the coupling loss Lcφ of Eφ polarization. Thus, in the antenna according to the embodiment, it is possible to prevent information leakage at the terminal portion of the LCX 1 and ensure communication security.

  In the above description, polyethylene is used as the sheath 16. However, the resin used for the sheath 16 is not limited to polyethylene. For example, polyvinyl chloride (PVC) may be used as the sheath 16. Polyethylene has a relative dielectric constant of about 2.3, whereas PVC has a relative dielectric constant of about 6. Although there is a slight decrease in the coupling loss Lcz of Ez polarization due to the difference in relative permittivity, it has been confirmed that the coupling loss is almost the same. Therefore, if a resin having a relative dielectric constant in the range of 6 or less is used as the sheath 16, it is possible to suppress the emission of Ez polarized waves at the terminal portion of the LCX 1 and to ensure communication security.

(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 ... Leaky coaxial cable (LCX)
DESCRIPTION OF SYMBOLS 3 ... Termination member 10 ... Center conductor 12 ... Insulator 14 ... External conductor 16 ... Sheath 18a ... 1st slot 18b ... 2nd slot 40 ... Terminator 42, 46 ... Exterior conductor 44 ... Connector

Claims (3)

A linear center conductor, an insulator that covers the center conductor, an outer conductor that covers the center conductor across the insulator and is provided with a plurality of slots along the axial direction of the center conductor, and A leaky coaxial cable having a sheath covering the outer periphery of the outer conductor and extending in the axial direction from one end to which the signal is supplied toward the other end;
Connected to said other end, comprises a terminator that terminates in the characteristic impedance of the leakage coaxial cable, an antenna having a, and the end member having connected to said outer conductor outer conductor,
In order to make the coupling loss of Ez polarized wave larger than the coupling loss of Eφ polarized wave in the range of 0.25 m to 1.5 m in the direction perpendicular to the axial direction from the antenna , the thickness of the sheath is set to 0. An antenna having a range of 0.01 mm or more and less than 1.5 mm.   The antenna according to claim 1, wherein the sheath has a relative dielectric constant of 6 or less. A linear center conductor, an insulator covering the center conductor, and an outer conductor provided with a plurality of slots at a predetermined pitch along the axial direction of the center conductor, covering the center conductor with the insulator interposed therebetween. A leaky coaxial cable extending in the axial direction from one end to the other end to which a signal is supplied;
Connected to said other end, comprises a terminator that terminates in the characteristic impedance of the leakage coaxial cable, an antenna having a, and the end member having connected to said outer conductor outer conductor,
In order to make the coupling loss of Ez polarized wave larger than the coupling loss of Eφ polarized wave in the range of 0.25 m to 1.5 m in the direction perpendicular to the axial direction from the antenna , the outer periphery of the outer conductor is exposed. An antenna characterized by having been made.

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