JPH10145136A - Leakage coaxial cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a broad-band leakage coaxial cable with less directivity and having a wide radiation frequency band width, even when a high frequency is used. SOLUTION: An outer conductor 14 is formed with other zigzag slot 15, in parallel with a zigzag slot 13 and having a larger period P2 than a period P1 of the zigzag slot 13 to extend the radiation frequency band. Since the zigzag slots 13, 15 are formed in parallel and a radio wave is emitted from the zigzag slots 13, 15 even when a high radiation frequency is set and a direction is produced, a radio wave is emitted effectively over a wide radiation angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leaky coaxial cable used for communication with a moving object and detecting an obstacle.

[0002]

2. Description of the Related Art Communication with a mobile object and detection of an obstacle on the path of the mobile object have been spotlighted with the recent increase in speed of the mobile object.

[0003] Transmission lines used in this system include a leaky coaxial cable, a leaky waveguide, and a surface wave line.

FIG. 3 shows a conventional example of a leaky coaxial cable.

[0005] A leaky coaxial cable 1 shown in FIG. 1 includes a center conductor 2, an insulator 3 provided on the outer periphery of the center conductor 2, and an outer conductor provided coaxially with the center conductor 2 on the outer periphery of the insulator 3. And 4. The outer conductor 4 is formed with zigzag slots 5 having a C shape at regular intervals in the longitudinal direction. Such a leaky coaxial cable 1 has only twice the effective radiation band (for example, if the lower limit frequency of the radiated radio wave is 100 MHz, the upper limit frequency is 200 MHz), and is called a narrow band leaky coaxial cable.

FIG. 4 is a diagram showing another conventional example of a leaky coaxial cable.

[0007] The leaky coaxial cable 6 shown in FIG. 1 has an Eφ component of the mutual wave source strength (a circumferential component of the leaky coaxial cable 6 of the electric field strength E) at equal intervals Pb within one cycle Pa.
Is a leaky coaxial cable having a wide frequency bandwidth realized by a double-period slot arrangement in which slots 7 having a sinusoidal distribution are arranged (broadband leaky coaxial cable).

[0008] By using such a leaky coaxial cable, for example, the lower limit is 120 MHz and the upper limit is 500 MHz.
z.

[0009]

However, the conventional leaky coaxial cable described above has a frequency that cannot be used effectively in the radiation frequency band due to voltage reflection due to uneven impedance in the cable due to the slot period. .

FIG. 5 shows a conventional leaky coaxial cable (150M).
FIG. 4 is a diagram showing a relationship between a radiation frequency f in the Hz band / 400 MHz band) and the transmission loss α, wherein the horizontal axis represents the radiation frequency and the vertical axis represents the transmission loss α. FIG. 6 shows the radiation frequency f of the conventional leaky coaxial cable and the voltage standing wave ratio V.V. S.
W. It is a figure which shows the relationship with R (Voltage Standing Wave Ratio), a horizontal axis shows a radiation frequency and a vertical axis | shaft shows a standing wave ratio. 5 and 6, the emission frequency is 235 MHz
The voltage standing wave ratio V.V. S. W. R has increased, and the voltage standing wave ratio V.R. S. W. It can be seen that R has increased. Voltage standing wave ratio S. W. R
Is large, the reflected component becomes large when used as a transmitting antenna, and radio waves are not effectively emitted.

On the other hand, the transmission loss α depends on the voltage standing wave ratio V.V.
S. W. It can be seen that R increases at increasing frequencies. That is, the voltage standing wave ratio V.V. S. W. If R is large, the leaky coaxial cable cannot be used.

Further, as described below, when a leaky coaxial cable having a row of zigzag slots is used at a high frequency, directivity is generated in a cable cross-sectional direction due to a shielding effect of the leaky coaxial cable (radiation occurs in the cable cross-sectional direction). Some places are restricted).

FIGS. 7A and 7B show the directivity of a conventional leaky coaxial cable in the cross-sectional direction of the cable. FIG. 7A shows a case where the radiation frequency is 450 MHz, and FIG. 7B shows a case where the radiation frequency is 2.6 GHz. Is the case.

The effective diameter of the leaky coaxial cable is about 42 mm
, And the center direction of the slot is on the right side.

The radiation frequency is 450 MHz (wavelength 667 m
In the case of m) (FIG. 7A), the front / rear ratio to the slot position is about 2 dB, and the directivity is substantially circular. This indicates that the cross-sectional dimension of the leaky coaxial cable is sufficiently smaller than the wavelength, the diffraction phenomenon is large, and the shielding effect of the cable itself can be almost ignored.

On the other hand, when the radiation frequency is 2.6 GHz (FIG. 7B), the wavelength is 115 mm, and the cross-sectional dimension of the leaky coaxial cable is so large that it cannot be ignored compared to the wavelength. It can be seen that the effect appears and directivity occurs.

Accordingly, an object of the present invention is to solve the above-mentioned problems, to minimize voltage reflection in a used frequency band, to have a wide radiation frequency band, and to have a low directivity even when a high frequency is used. Is to provide.

[0018]

In order to achieve the above object, the present invention provides a center conductor, an insulator provided on the outer periphery of the center conductor, and an insulator provided coaxially with the center conductor on the outer periphery of the insulator. In a leaky coaxial cable provided with an outer conductor in which a zigzag slot having a U-shape is formed at a constant period in the direction, another zigzag having a period larger than the period of the zigzag slot and parallel to the zigzag slot in the outer conductor. A slot is formed. The C-shaped zigzag slots may be a double-period slot arrangement.

According to the above configuration, since the other conductor has another zigzag slot formed in parallel with the zigzag slot and having a period longer than the period of the zigzag slot, the radiation frequency band is widened. In addition, since the zigzag slots are formed in parallel, even if directivity occurs when the radiation frequency is increased, radio waves are radiated from each zigzag slot, and as a result, radio waves are radiated at a wide radiation angle.

[0020]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a side view showing an embodiment of a leaky coaxial cable according to the present invention.

The leaky coaxial cable 10 shown in FIG. 1 includes a center conductor (for example, an aluminum tube) 11 and an insulator (for example, a polyethylene tube) 12 provided on the outer periphery of the center conductor 11.
And an outer conductor (for example, an aluminum tube) 14 provided coaxially with the center conductor 11 on the outer periphery of the insulator 12 and having a zigzag slot 13 formed in a U shape at a constant period P1 in the longitudinal direction. .

The outer conductor 14 has three zigzag slots 15 formed in parallel with the zigzag slots 13 and having a period P2 longer than the period P1 of the zigzag slots 13.

The lower limit frequency fl of the radiation frequency band of the leaky coaxial cable 10 having only the zigzag slot 13 is given by the following equation (1).

[0025]

(Equation 1)

Where c is the speed of light, ν is 1 / √ (ε) when the equivalent dielectric constant of the cable is ε, and P1 is the period of the slot.

In the leaky coaxial cable 10 having only the zigzag slot 13, the leaky coaxial cable 10
The transmission loss increases due to the non-uniformity of the impedance in the above, and the frequency fu that cannot be used effectively is given by a multiple of the frequency expressed by the equation (2).

However, the influence of the transmission loss due to the uneven impedance is smaller in the transmission loss at a frequency that is a multiple of the frequency fu on the higher frequency side than the transmission loss at the frequency fu.

[0029]

(Equation 2)

The leaky coaxial cable having only the zigzag slot 13 corresponds to the conventional leaky coaxial cable 1 shown in FIG. On the other hand, according to the present invention, as shown in FIG. 1, the zigzag slot 13 (corresponding to the zigzag slot 5 in FIG. 1) of the leaky coaxial cable 10 further has a zigzag slot 15.
Is added, whereby transmission loss due to uneven impedance can be reduced. Further, by making the period P2 of the zigzag slot 15 longer than the period P1, the voltage reflection (transmission loss due to the unevenness of impedance in Expression 2) can be shifted to the lower frequency side outside the used frequency band. A new radiation frequency band with the lower limit is obtained.

[0031]

(Equation 3)

However, P2 is a new zigzag slot 15
Is the cycle of

In the above, the period P2 longer than the period P1
, The voltage reflection can be shifted to the lower frequency side, the transmission loss due to the uneven impedance can be suppressed, and the radiation frequency band of the zigzag slot 13 and the radiation frequency band of the zigzag slot 15 overlap. Therefore, it is possible to provide a wideband leaky coaxial cable having a wide operating frequency band.

Even in the case of a high radiation frequency as shown in FIG. 7B, by forming the zigzag slots 13 and 15 in parallel like the leaky coaxial cable of the present invention, the respective zigzag slots 13 and 15 are formed. As a result, radio waves are radiated from the leaky coaxial cable 10, and as a result, the directivity in the cross-sectional direction of the leaky coaxial cable 10 is increased accordingly.

FIG. 2 is a side view showing another embodiment of the leaky coaxial cable of the present invention.

The difference from the embodiment shown in FIG. 1 is that the zigzag slots 16 are arranged in a double period slot arrangement.

According to such a leaky coaxial cable 17, as in the embodiment shown in FIG. 1, voltage reflection in the operating frequency band can be minimized and the directivity can be reduced even at a high frequency. In addition to the above, a wider band can be achieved.

The center conductor 11 is not limited to an aluminum tube, but may be a copper tube or another metal tube. The outer conductor 18 is not limited to an aluminum tube, but may be a resin pipe made of polyethylene or the like wound with a metal tape such as aluminum. The insulator 12 is not limited to polyethylene but may be another resin.

[0039]

In summary, according to the present invention, the following excellent effects are exhibited.

Since another zig-zag slot is formed in the outer conductor in parallel with the zig-zag slot and having a period longer than that of the zig-zag slot, the radiation frequency band is wide, and the directivity is low even when a high frequency is used. Provision of a leaky coaxial cable of a wide band can be realized.

[Brief description of the drawings]

FIG. 1 is a side view showing an embodiment of a leaky coaxial cable according to the present invention.

FIG. 2 is a side view showing another embodiment of the leaky coaxial cable of the present invention.

FIG. 3 is a diagram showing a conventional example of a leaky coaxial cable.

FIG. 4 is a diagram showing another conventional example of a leaky coaxial cable.

FIG. 5 is a diagram illustrating a relationship between a radiation frequency f and a transmission loss α of a conventional leaky coaxial cable.

FIG. 6 shows the radiation frequency f of a conventional leaky coaxial cable and the voltage standing wave ratio V.V. S. W. It is a figure showing the relation with R.

FIG. 7 is a diagram showing directivity of a conventional leaky coaxial cable in a cable cross-sectional direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Center conductor 12 Insulator 13, 15 Zigzag slot 14 Outer conductor

Claims (2)

[Claims] 1. A center conductor, an insulator provided on the outer periphery of the center conductor, and a zigzag zigzag provided on the outer periphery of the insulator coaxially with the center conductor at a constant period in a longitudinal direction. In a leaky coaxial cable having an outer conductor having a slot formed therein, another zigzag slot having a period longer than the period of the zigzag slot is formed in the outer conductor in parallel with the zigzag slot. And leaky coaxial cable. 2. A leaky coaxial cable characterized in that the zigzag slots in a U-shape according to claim 1 are arranged in a double-period slot arrangement.