JP2007194903A - Antenna structure for in-pipe wireless communications device and wireless lan system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure capable of adjusting the degrees of coupling between an electromagnetic wave propagation mode of propagation in a pipe and electromagnetic waves transmitted from and received, by an antenna element, regardless of the size and shape of the pipe, and to provide an antenna structure capable of economically extracting electromagnetic waves from many parts of the one pipe, by transmitting and receiving electromagnetic waves in the pipe, without affecting electromagnetic waves propagated in the pipe. <P>SOLUTION: In the antenna structure for an in-pipe wireless communications device for performing wireless communication between antennas installed in the pipe, the antennas are each in a coaxial rod shape and are provided with a coaxial connector at an end and can be inserted into the pipe side along a pipe internal surface, and an antenna fitting part is formed which can adjust quantities of insertion of the antennas into the pipe. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wireless communication system for placing information to be transmitted wirelessly and propagating it in pipes in factories and other buildings and various facilities so that communication can be made between distant places.

Transmitters and receivers are placed at both ends of hollow metal pipes installed in ventilation ducts and construction tunnels in underground space facilities, and metal pipes are used as electromagnetic wave waveguides. Patent Document 1 discloses a wireless communication system configured to perform wireless communication with a unit.
Patent Document 2 is known as a related art relating to an antenna device attached to a wall surface of a duct duct in order to perform wireless communication using such a pipe.
JP-A-8-223095 JP 2004-228691 A

By the way, as a frequency used as a wireless LAN, a 2.4 GHz band system is currently widely used. The waveguide shape is determined by the JIS standard and EIAJ standard as efficient standards for propagating 2.4 GHz band radio. For example, JIS has a standard called WRJ-2, which results in a rectangular waveguide having an inner diameter of 109.2 mm x 54.6 mm.
However, piping shapes in general buildings and factories are not designed mainly for the purpose of propagating high frequencies, and thus differ from the standard shapes of rectangular waveguides as described above. In addition, the cross-sectional shape of the pipe is not constant, and there is a change in shape (step, branching, etc.) in the middle.

The same applies to cylindrical pipes. The cylindrical waveguide shape is determined by the standard, but is different from the standard of the rectangular waveguide. For example, Kazuo Fujisawa “Revised Microwave Circuit” (edited by the Institute of Electronics and Communication Engineers, Corona) shows on page 79 the attenuation characteristics of main propagation modes propagating in a 100 mmφ cylindrical waveguide (cylindrical pipe). Has been. According to this, for a given pipe shape, it can be seen that a radio having a communication frequency has various propagation modes and propagates in the pipe.
Therefore, it is important to construct a system that can be flexibly applied to a wide variety of pipes installed in ordinary factories as described above and can be efficiently propagated.

  However, in the case of wireless communication within a pipe, the antenna device described in Patent Document 2 merely shows the basic concept of performing wireless communication by inserting an antenna into the pipe. For example, it could not be flexibly applied to a wide variety of pipes with different pipe sizes and shapes, and it did not meet the concrete problem of whether it could be propagated efficiently.

  As described above, in order to propagate radio of a given communication frequency in a given piping route, it is necessary to convert radio characteristics, but it is economical to perform such conversion at the antenna unit. .

Further, in order to propagate radio of a given communication frequency in a given pipe path, it is necessary to convert the mode to propagate in the pipe with a small attenuation coefficient. In the antenna device, since the antenna is inserted into the center of the pipe so as to block the electromagnetic wave guide path, the antenna itself is structured to absorb the electromagnetic wave. For this reason, the antenna disclosed in Patent Document 2 has a structure in which electromagnetic waves do not reach far.
That is, such an antenna structure has a problem that it cannot be applied to a system in which electromagnetic waves are extracted from many parts on the piping system.

  The wireless LAN system according to the present invention aims at solving such problems, and the degree of coupling between the electromagnetic wave propagation mode propagating in the pipe and the electromagnetic wave transmitted and received from the antenna element regardless of the size and shape of the pipe. It is economical to provide electromagnetic wave from many parts of one pipe by providing a structure capable of adjusting the frequency and transmitting and receiving radio in the pipe without affecting the radio (electromagnetic wave) propagating in the pipe. The antenna structure that can be taken out is based on the basic concept and consists of the following solutions.

The present invention in accordance with the above concept is an antenna structure for a wireless communication device in a pipe for performing wireless communication between antennas installed in the pipe. The antenna structure has a coaxial rod shape and is coaxial with the end. The antenna is provided with a connector. Further, as a structure for mounting the antenna, an antenna mounting portion is formed on the pipe side so that the antenna can be inserted along the inner surface of the pipe and the amount of insertion of the antenna into the pipe can be adjusted.
The antenna as described above has flexibility so that an external coaxial cable can be freely connected, or when the inner surface is a situation like a cylindrical pipe, it can be arranged along the curved surface. It is desirable to do.

In general, the pipe itself is made of metal. In the present invention, since the antenna is mounted along the inner surface of the pipe, the antenna itself hardly absorbs electromagnetic waves propagating in the pipe. The antenna itself does not hinder the electromagnetic wave from reaching. Moreover, since it does not absorb electromagnetic waves as described above, it is economical for the side supplying electromagnetic waves.
In this case, since the antenna is constituted by a coaxial cable, an effect of reducing electromagnetic wave absorption by the antenna is also expected.
Furthermore, since the insertion length of the antenna into the piping is adjustable as described above, it can be flexibly adapted to piping of various shapes and materials, and the coupling degree (the power of electromagnetic waves propagating in the piping and Therefore, it is possible to create an economical system in which electromagnetic waves can be effectively used.
Moreover, the adjustment can be performed with a very simple operation because it merely changes the amount of insertion of the antenna.

  The antenna structure as described above does not reduce the degree of electromagnetic wave coupling in each antenna even if a plurality of wireless antennas are attached to one pipe as described above. In addition, when multiple antennas are arranged along a long pipe and electromagnetic waves are transmitted to multiple areas, the propagation power in the pipe varies depending on the location of the antenna (difference in propagation length in the pipe). Therefore, when drawing the same power from inside the pipe, it is necessary to adjust the degree of coupling between the antenna and the pipe.

  Also in this respect, the antenna structure according to the present invention has a low degree of electromagnetic wave absorption by the antenna itself, so that the electromagnetic wave can be propagated to many antennas installed in one pipe, and the insertion amount of the antenna is changed. Therefore, the electromagnetic wave power can be easily adjusted. For example, it is applied to a wireless LAN system in which a plurality of pipes are arranged in the longitudinal direction of a pipe as disclosed in JP-A-2002-204240. It is extremely effective.

Next, an embodiment of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
FIG. 1 shows an embodiment when the present invention is applied to a rectangular pipe, and FIG. 2 shows an embodiment when the present invention is applied to a cylindrical pipe.
First, the case of the antenna structure for a wireless communication device in a pipe for performing wireless communication between the antennas 2 installed in the rectangular pipe 1 will be described.

Of the propagation modes, in order to couple with the most efficient propagation mode, that is, the attenuation mode having a small attenuation characteristic, as shown in FIG. 1, the inserted antenna 2 on the side surface of the target pipe 1 is along the inner surface of the pipe. Antenna mounting holes 3 are provided at various positions.
The antenna 2 is inserted into the antenna mounting hole 3 and fixed with a screw (not shown) or an appropriate clip. The insertion length of the antenna 2 into the pipe 1 can be freely adjusted by loosening a screw or the like. The antenna mounting hole 3 is provided with an appropriate antenna mounting bracket and adapter as a matter of course, but the illustration is omitted.

The antenna 2 shown by a broken line is an electric field coupling type rod antenna. Specifically, it is composed of a coaxial structure (consisting of a central conductor and a metal cylinder surrounding the center conductor), and a rod (metal rod-like portion) protruding from the metal cylinder at the tip is coupled to the electric field in the propagation mode.
Since such an antenna 2 has a coaxial structure as described above, the absorbability of electromagnetic waves propagating in the piping can be minimized. Further, in order to minimize the influence on the propagation mode by inserting the antenna 2, the antenna mounting hole 3 is formed at the corner of the pipe 1 so that the antenna 2 can be inserted along the inner wall surface of the pipe 1. Has been.
In such an antenna 2, the coaxial structure of the antenna is made of metal, and the pipe is usually made of metal. Therefore, if the outer shape of the antenna is sufficiently smaller than the inner diameter of the pipe 1, the propagation mode of electromagnetic waves The effect on the environment is almost negligible.

A coaxial connector 4 is attached to the end opposite to the insertion portion of the antenna 2, and various antennas such as a radio modem, a high-frequency power meter 5a, a coaxial waveguide converter 5b, a horn antenna 5c, and a planar antenna 5d. Can be connected.
Since various antennas and converters are usually fixedly attached to the pipe 1 side, the rod antenna 2 is flexible and flexible so that the coaxial cable can be connected even if the amount of insertion of the antenna 2 into the pipe 1 is changed. It is desirable to make it of the nature.

When the pipe 1 has a cylindrical shape, an antenna mounting hole 3a is formed in the circumferential direction on the wall surface of the cylindrical pipe 1a as shown in FIG. 2, and the antenna 2a is attached to an antenna mounting bracket or the like provided along the hole. It is desirable to fix. By forming the antenna mounting hole 3a in this way, the antenna 2a can be arranged in an arc along the inner surface of the cylindrical pipe 1a, and the absorbability of electromagnetic waves propagating in the pipe can be set small.
In either case, the coupling degree of the antenna can be adjusted by adjusting the insertion length of the antenna 2 or 2a. An example of the operation is as follows.

  That is, for example, when setting the coupling degree to the maximum, two antennas 2 (or 2a) are inserted into the pipes 1 and 1a, a radio transmission modem is connected to one, and a high-frequency power meter is connected to the other. By changing the amount of insertion of the two antennas, the antenna is fixed at a position that maximizes the power propagating between the two. At this time, the two antennas are electric field coupled to the mode with the least attenuation among the propagation modes transmitted through the pipe.

In this state, the high frequency wattmeter is removed and, for example, a high frequency antenna such as a horn antenna 5d or a dipole antenna is connected. It is possible to transmit from the inside to the room.
Fig. 4 shows the results of experiments using actual piping. A rectangular duct with an external dimension of 40cm x 30cm was used as the piping. Along the bottom surface (40 cm surface), the coaxial cable type antenna of the present invention (coaxial outer diameter: about 10 mm, rod protrusion: 30 mm) is inserted into the pipe perpendicular to the longitudinal direction of the pipe. The result of obtaining the degree of coupling with the high-frequency signal propagating through the rectangular duct is shown in FIG. The horizontal axis shows the amount of antenna insertion, and the vertical axis shows the degree of coupling. It can be seen that high-frequency signals of various modes are propagated in the pipe, and the degree of coupling does not show a simple increase / decrease trend, but the degree of coupling varies depending on the amount of insertion. For example, to obtain a strong degree of coupling, the insertion amount is 6 cm. In this case, the coupling degree is 10 dB. On the other hand, to make it weaker, the insertion amount is, for example, 16 cm. As a result, the degree of coupling is 23 dB. Thus, the required degree of coupling can be easily obtained by changing the amount of antenna insertion.

FIG. 3 shows an application example to such a wireless system. This example is also applicable to the case described in Japanese Patent Laid-Open No. 2002-204240.
The pipe 1 is an air conditioning pipe located behind the ceiling of an office or the like, or an air conditioning pipe located under a roof in a factory. The signal of the wireless access point 5 is input into the pipe 1 via the rod antenna 2 from one place of the pipe 1. Electromagnetic waves propagating in the pipe 1 are received by the rod antennas 2 provided at a plurality of locations of the pipe, and radiated toward the floor surface by the antenna 5c (horn antenna, flat antenna, etc.) provided outside the pipe.

As a result, it is possible to radiate radio waves to the office or factory without being affected by walls or partitions. The radiated radio is received by a radio terminal modem (not shown), and data is demodulated.
The radio transmitted from the radio terminal modem propagates in the reverse direction. First, it is received by an antenna 5 c provided outside the pipe 1, guided to the antenna 2 in the pipe 1, propagated in the pipe 1, received by the wireless LAN access point 5, and demodulated. As a result, bidirectional communication is possible, and it is possible to construct an intranet in a space relatively easily using existing pipes in an office or factory without using wired wiring work.

The conceptual diagram which shows an example which applied this invention to rectangular piping. The conceptual diagram which shows an example which applied invention to cylindrical piping. The conceptual diagram which shows the radio | wireless communications system which applied the antenna structure concerning this invention to piping laid in the ceiling part of the room. The graph which shows the relationship between the antenna insertion length and coupling degree in the antenna structure concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a ... Piping 2, 2a ... Antenna 3, 3a ... Antenna mounting hole 4 ... Coaxial connector 5 ... Wireless LAN access point

Claims (3)

In an antenna structure for a wireless communication device in a pipe for performing wireless communication between antennas installed in the pipe,
The antenna is a coaxial rod-shaped antenna with a coaxial connector at the end,
An antenna structure for an in-pipe wireless communication apparatus, wherein an antenna attachment portion is formed on the pipe side so that the antenna can be inserted along the inner surface of the pipe and the amount of the antenna inserted into the pipe can be adjusted.   2. The antenna structure for a wireless communication device in a pipe according to claim 1, wherein the antenna itself has flexibility.   A wireless LAN system in which a plurality of antenna structures for in-pipe wireless communication devices are arranged in the longitudinal direction of a pipe.

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