JP5619555B2 - Antenna device - Google Patents

Description

  The present invention relates to an antenna device such as a reader / writer for a passive ID tag.

  For example, an antenna device such as a passive ID tag reader / writer transmits a radio wave to a responder such as an RF tag that exchanges information (transmits a main radio wave to an antenna different from the reception antenna), and a responder A receiving antenna for receiving radio waves transmitted from the receiver is provided adjacent to the receiving antenna, and the receiving antenna receives the received radio waves transmitted from the responding device while transmitting the radio wave (main radio wave) to the responding device with the transmitting antenna. The receiving antenna is configured to simultaneously transmit and receive radio waves.

  On the other hand, in this type of antenna device, if a part of the leaked radio wave leaking from the transmitting antenna is received by the receiving antenna directly or wrapping around, this leaked radio wave becomes a high level interference wave. As a result, the antenna pattern is distorted, and the receiving characteristics of the receiving antenna are deteriorated, so that the necessary gain and phase characteristics (isolation) cannot be secured. If a sufficient distance is provided between the transmission antenna and the reception antenna, it is possible to ensure isolation, but it is practically difficult to greatly separate the transmission antenna and the reception antenna as described above.

  For this reason, it has been proposed and put to practical use that a radio wave shield is provided between the transmission antenna and the reception antenna, and that this radio wave shield shields leaked radio waves between the transmission antenna and the reception antenna to ensure isolation ( For example, see Patent Document 1 and Patent Document 2).

JP 2008-283391 A JP 2008-199562 A

  However, in the conventional antenna device in which the radio wave shield is provided between the transmission antenna and the reception antenna, there is a possibility that the leaked radio wave leaking from the transmission antenna goes around the radio wave shield and is received by the reception antenna. . Also, since the size of the radio wave shield is set according to the frequency of the radio wave (leakage radio wave) transmitted from the transmission antenna and the distance between the transmission antenna and the reception antenna, the frequency of the radio wave transmitted from the transmission antenna and the transmission antenna and reception A radio wave shield having a different size is required for each antenna device having a different antenna distance.

  In view of the above circumstances, the present invention can easily and reliably reach the receiving antenna from the transmitting antenna even when the frequency of the radio wave (leakage radio wave) transmitted from the transmitting antenna and the distance between the transmitting antenna and the receiving antenna are different. An object of the present invention is to provide an antenna device capable of securing isolation by attenuating leaked radio waves (interference waves).

  In order to achieve the above object, the present invention provides the following means.

  An antenna device of the present invention includes a receiving antenna that receives radio waves, a transmitting antenna that is provided adjacent to the receiving antenna and transmits main radio waves to an antenna different from the receiving antenna, and leakage that leaks from the transmitting antenna. A reflecting member that reflects a part of the radio wave toward the receiving antenna, and the reflecting member reflects a part of the leaking radio wave with respect to the direct wave of the leaking radio wave that directly reaches the receiving antenna. The reflected wave reaching the receiving antenna is arranged so as to reach the receiving antenna with a phase shift, causing interference due to a phase shift between the direct wave and the reflected wave, and reaching the receiving antenna from the transmitting antenna. It is configured to attenuate a direct wave.

  In the present invention, a direct wave and a reflected wave are reflected by reflecting a part of the leaked radio wave with a reflecting member so as to reach the reception antenna with a phase shifted from the direct wave of the leaked radio wave that reaches the receiving antenna directly from the transmitting antenna. Can be made to interfere with each other. As a result, without providing a radio wave shield between the transmitting antenna and the receiving antenna as in the conventional antenna device, the reflecting member is disposed so that the phase of the reflected wave is shifted from the direct wave. It is possible to obtain an attenuation effect of interference waves (leakage radio waves and direct wave) that reach the receiving antenna from the antenna and deteriorate the reception characteristics of the receiving antenna.

  In the antenna device of the present invention, it is desirable that the transmission antenna is an antenna having directivity for transmitting radio waves toward a predetermined range and generating leaked radio waves outside the predetermined range.

  In the present invention, when the transmission antenna is an antenna that transmits a radio wave (main radio wave) toward a predetermined range and a leaked radio wave is generated outside the predetermined range, the reflection antenna is provided to the reception antenna. The direct wave of the leaked radio wave that reaches directly and the reflected wave of the leaked radio wave reflected by the reflecting member can interfere with each other, and the interference wave that reliably reaches the reception antenna from the transmission antenna and degrades the reception characteristics of the reception antenna can be attenuated.

  Furthermore, in the antenna device of the present invention, the transmitting antenna may be an antenna that is formed in a rod shape, transmits a radio wave from the end in the axial direction to the predetermined range, and radiates a leaked radio wave at the center of the axis.

  In the present invention, when the transmitting antenna is an antenna that is formed in a rod shape such as a helical antenna and radiates leaked radio waves at the center of the axis, a reflecting member is provided, so that the direct wave and the reflected wave of the leaked radio waves are generated. Interfering waves can be attenuated more reliably by causing interference.

  In the antenna device according to the present invention, the reflecting member may be configured so that the reflected wave that is the shortest propagation path among the reflected waves that reach the reception antenna is the direct current wave that is the shortest propagation path among the direct waves. It is more desirable that they are arranged so as to be shifted by a half wavelength at the position.

  In the present invention, since the reflection member is disposed so that the reflected wave of the leaked radio wave is shifted by a half wavelength at the position of the receiving antenna with respect to the direct wave, the direct wave and the reflected wave can be caused to interfere with each other so as to cancel each other. It is possible to eliminate interference waves that reach the receiving antenna from the transmitting antenna and degrade the receiving characteristics of the receiving antenna. At this time, when the transmitting antenna is an antenna such as a helical antenna, a leaked radio wave is radiated at the center of the axis, but the reflected wave that is the shortest propagation path is half of the direct wave that is the shortest propagation path. By disposing the reflecting member so as to shift the wavelength, it is possible to eliminate interference waves that effectively reach the receiving antenna from the transmitting antenna and degrade the receiving characteristics of the receiving antenna.

  Furthermore, in the antenna device of the present invention, the reflection member, the transmission antenna, and / or the reception antenna according to the distance between the transmission antenna and the reception antenna and / or the frequency of the radio wave transmitted from the transmission antenna. It is desirable that and be configured to move relative to each other.

  In the present invention, even when the frequency of the radio wave transmitted from the transmission antenna and the distance between the transmission antenna and the reception antenna are different, the distance between the transmission antenna and the reception antenna and / or the frequency of the radio wave transmitted from the transmission antenna is set. Accordingly, the relative position of the reflecting member with respect to the transmitting antenna and / or the receiving antenna can be easily set so that the phases of the reflected wave and the direct wave are shifted.

  In the antenna device of the present invention, the reflection member is arranged so that the phase of the reflected wave is shifted with respect to the direct wave of the leaked radio wave without providing a radio wave shield between the transmitting antenna and the receiving antenna unlike the conventional antenna device. By providing it, it is possible to obtain an interference wave attenuation effect that reaches the reception antenna from the transmission antenna and degrades the reception characteristics of the reception antenna.

  Thus, even if the frequency of the radio wave transmitted from the transmission antenna and the distance between the transmission antenna and the reception antenna are different, depending on the distance between the transmission antenna and the reception antenna and / or the frequency of the radio wave transmitted from the transmission antenna. By simply setting the relative position of the reflecting member with respect to the transmitting antenna and / or the receiving antenna so that the phases of the direct wave and the reflected wave are shifted, it is possible to ensure isolation easily and reliably.

It is a figure which shows the antenna apparatus which concerns on one Embodiment of this invention. It is a figure which shows the antenna apparatus which concerns on one Embodiment of this invention. It is a figure which shows the experimental result of the isolation characteristic of the antenna device which concerns on one Embodiment of this invention. It is a figure which shows the experimental result of the isolation characteristic of the antenna device which concerns on one Embodiment of this invention.

  Hereinafter, an antenna device according to an embodiment of the present invention will be described with reference to FIGS. The present embodiment relates to an antenna device such as a reader / writer for a passive ID tag.

  As shown in FIGS. 1 and 2, the antenna device A of the present embodiment transmits radio waves to a responder such as an RF tag that exchanges information (transmits main radio waves to an antenna different from the receiving antenna 2). A transmission antenna 1 and a reception antenna 2 that receives radio waves transmitted from the responding device are provided adjacent to each other, and the transmission antenna 1 transmits radio waves (main radio waves and transmission radio waves) to the responding device. A radio wave is received by the receiving antenna 2, and the transmission antenna 1 and the receiving antenna 2 are configured to simultaneously transmit and receive the radio wave. The antenna device A of the present embodiment includes a reflection member 3 that transmits radio waves from the transmission antenna 1 and reflects part of the leaked radio waves leaking from the transmission antenna 1 toward the reception antenna 2. Has been.

  In this embodiment, the transmitting antenna 1 and the receiving antenna 2 are, for example, helical antennas, and the transmitting antenna 1 and the receiving antenna 2 have their axes O1 and O2 oriented in the same direction and at a predetermined interval T1. Side by side. That is, the transmission antenna 1 of the present embodiment is an antenna having directivity for transmitting radio waves toward a predetermined range and generating leaked radio waves outside the predetermined range. Further, it is an antenna that is formed in a rod shape and is generated by transmitting radio waves within a predetermined range from the end in the direction of the axis O1 and radiating leaked radio waves at the center of the axis O1.

  The reflecting member 3 is, for example, a reflecting mirror, a metal plate, a metal sheet, and the like, with the reflecting surface 3a facing the transmitting antenna 1 and the receiving antenna 2 and a predetermined interval with respect to both the transmitting antenna 1 and the receiving antenna 2. It is arranged with a gap T2. Further, at this time, the reflecting member 3 reflects the phase of the reflected wave S2 reflected from the reflecting member 3 and reaching the receiving antenna 2 with respect to the direct wave S1 radiated from the transmitting antenna 1 and reaching the receiving antenna 2 directly. It is disposed so as to reach the receiving antenna 2 with a shift.

  In the present embodiment, the reflecting member 3 is disposed so that the reflected wave S2 reaching the receiving antenna 2 is shifted by a half wavelength at the position of the receiving antenna with respect to the direct wave S1. Note that the reflecting member 3 is not limited to being formed in a plate shape, and may be configured with, for example, a mesh structure or a grid structure as long as it can reflect radio waves.

  The antenna device A of the present embodiment configured as described above is used as a response device such as an RF tag for transmitting and receiving information, in which the transmitting antenna 1 and the receiving antenna 2 have directivity in the directions of the axes O1 and O2, respectively. Radio waves are transmitted from the transmission antenna 1. At this time, the transmitting antenna 1 generates leaked radio waves in the radiation direction centered on the axis O1. For this reason, a leaked radio wave (direct wave S1, interference wave) radiated from the transmission antenna 1 is received by the reception antenna 2 adjacent to the transmission antenna 1 with a predetermined interval T1. There is a possibility that the antenna pattern becomes distorted due to a large level of interference wave, and the reception characteristics of the reception antenna 2 are deteriorated, so that the necessary gain and phase characteristics (isolation) cannot be secured.

  On the other hand, since the antenna device A of the present embodiment includes the reflecting member 3, a part of the leaked radio wave radiated from the transmitting antenna 1 is reflected by the reflecting member 3 and reflected by the reflecting member 3. The reflected wave S2 reaches the receiving antenna 2. Further, at this time, the reflecting member 3 has a half-wavelength at the position of the receiving antenna with respect to the direct wave S1 so that the reflected wave S2 reaches the receiving antenna 2 with a phase shifted from the direct wave S1. It arrange | positions so that it may slip | deviate. That is, the difference (path difference) between the path T1 of the direct wave S1 directly reaching the receiving antenna 2 from the transmitting antenna 1 and the path (T3 + T4) of the reflected wave S2 reaching the receiving antenna 2 from the reflecting member 3 and the reflecting member 3 from the transmitting antenna 1. ) Is set so that the phases of the direct wave S1 and the reflected wave S2 reaching the receiving antenna 2 are shifted by a half wavelength.

  For this reason, the direct wave S1 and the reflected wave S2 interfere with each other due to the phase difference between the direct wave S1 and the reflected wave S2 reaching the receiving antenna 2 (the direct wave S1 and the reflected wave S2 cancel each other), and the direct wave S1 is It is attenuated by the reflected wave S2. Thus, the interference wave is attenuated without providing a radio wave shield between the transmitting antenna 1 and the receiving antenna 2 as in the conventional antenna device.

Since the direct wave S1 and the reflected wave S2 are thus shifted in phase due to the phase difference between the direct wave S1 and the reflected wave S2, the interference wave is attenuated. Even when the distance T 1 between the receiving antennas 2 is different, the transmitting antenna 1 and / or the receiving antenna is selected according to the distance T 1 between the transmitting antenna 1 and the receiving antenna 2 and / or the frequency of the radio wave radiated from the transmitting antenna 1. Isolation is ensured only by setting the relative position of the reflecting member 3 to 2 so that the reflected wave S2 interferes with the direct wave S1 and cancels each other.

  The reflecting member 3 and the transmitting antenna 1 and / or the receiving antenna 2 can be relatively moved in advance according to the distance T1 between the transmitting antenna 1 and the receiving antenna 2 and / or the frequency of the radio wave transmitted from the transmitting antenna 1. If the antenna device A is configured as described above, the path T1 of the direct wave S1 and the path (T3 + T4) of the reflected wave S2 even when the frequency of the radio wave and the distance T1 between the transmission antenna 1 and the reception antenna 2 are different. The relative positions of the transmitting antenna 1, the receiving antenna 2 and the reflecting member 3 can be easily and reliably set so that the difference is shifted by half a wavelength between the direct wave S1 and the reflected wave S2. That is, even if the frequency of the transmission radio wave and the distance T1 between the transmission antenna 1 and the reception antenna 2 are different, it is easy and reliable if the relative positions of the transmission antenna 1, the reception antenna 2 and the reflection member 3 are made variable. Therefore, it is possible to secure isolation.

Here, a demonstration experiment in which the superiority of the antenna device A of the present embodiment including the reflecting member 3 is confirmed will be described. FIG. 3 is a diagram showing the results of the demonstration experiment. When the distance T2 between the transmitting antenna 1 and the receiving antenna 2 and the reflecting member 3 is changed stepwise by 20 mm, 40 mm, 60 mm, 80 mm, and 100 mm, FIG. Is shown. In FIG. 3, the horizontal axis is the interval T 1 between the transmitting antenna 1 and the receiving antenna 2, and the vertical axis is the isolation characteristic.

  From FIG. 3, the distance T1 between the two antennas 1 and 2 and the distance T2 between the transmitting antenna 1, the receiving antenna 2, and the reflecting member 3 are in a positional relationship in which interference between the direct wave S1 and the reflected wave S2 occurs. Thus, it was confirmed that a gain of about 8 to 10 and several dB can be gained. That is, the distance T1 between the antennas 1 and 2 and the distance T2 between the transmitting antenna 1 and the receiving antenna 2 and the reflecting member 3 are different from each other in the difference between the path T1 of the direct wave S1 and the path (T3 + T4) of the reflected wave S2. It has been proved that isolation can be ensured when the positional relationship of shifting the phase of the direct wave S1 and the reflected wave S2 reached (shifting the wavelength by half wavelength) is achieved.

  On the other hand, in FIG. 4A to FIG. 4F, the interval T2 between the transmitting antenna 1 and the receiving antenna 2 and the reflecting member 3 is changed stepwise to 6 cm, 10 cm, 20 cm, 30 cm, 40 cm, and 50 cm, The result of having confirmed the isolation characteristic by changing distance T1 of the transmitting antenna 1 and the receiving antenna 2 in each case is shown. In addition, these FIG. 4A to FIG. 4F show calculated values together with actual measured values.

Here, the calculation method of the calculated value will be described with reference to FIG. 2 showing the positional relationship between the transmitting antenna 1 and the receiving antenna 2 and the reflecting member 3. First, when the propagation distance of the direct wave S1 is X, the distance between the antennas is T1, and the radius of the transmission antenna 1 and the reception antenna 2 is R, the propagation distance X of the direct wave S1 is X = T1-2R. Further, if the propagation distance of the reflected wave S2 is Z and the distance between the transmitting antenna 1 and the receiving antenna 2 and the reflecting member 3 is T2, the transmission distance Z of the reflected wave is Z = 2 × (((T1 / 2) ² + (T2 + R) ² ) ^-1/2 ) -R.

  Further, the path difference M between the direct wave S1 and the reflected wave S2 is M = Z−X, and when the wavelength of the transmission radio wave transmitted from the transmission antenna 1 is F and the relative phase difference C is obtained from the path difference M, C = 2. × π × M / F.

Since the phase is inverted by 180 degrees when reflected by the reflecting member 3, the relative phase difference C _Z on the receiving side is C _Z = C + π (rad). Further, when the amplitude value of the combined wave in which the reflected wave S2 interferes with the direct wave S1 is A, the amplitude value A is A = 1 + cos (C _Z ). If the logarithmic value of the amplitude value is B, B = 10 × log (A), and further, if the propagation loss of the direct wave S1 is V, the propagation loss V is V = 20 × log ((4 × π × (L−2R)) / F).

  From the propagation loss V thus obtained and the directivity P in the horizontal direction of the receiving antenna 2, the calculated value I of the isolation on the receiving side is obtained by I = B + VP.

  4 (a) to 4 (f) showing the calculated value and the actual measurement value obtained in this way, the interval T1 between the two antennas 1 and 2, the transmitting antenna 1, the receiving antenna 2, and the reflecting member 3 are also shown. Is a positional relationship in which the difference between the path T1 of the direct wave S1 and the path (T3 + T4) of the reflected wave S2 shifts the phase of the direct wave S1 and the reflected wave S2 reaching the receiving antenna 2 (shifts the wavelength by a half wavelength). As a result, it was confirmed that isolation could be secured.

  Therefore, in the antenna device A of the present embodiment, a part of the leaked radio wave is reflected by the reflecting member so as to reach the reception antenna 2 with a phase shifted from the direct wave S1 of the leaky radio wave that reaches the reception antenna 2 directly from the transmission antenna 1. The direct wave S1 and the reflected wave S2 can be made to interfere with each other. Thus, the reflection member 3 is disposed so that the phase of the reflected wave S2 is shifted from the direct wave S1 without providing a radio wave shield between the transmitting antenna 1 and the receiving antenna 2 as in the conventional antenna device. Thus, it is possible to obtain an attenuation effect of interference waves (leakage radio waves) that reach the reception antenna 2 from the transmission antenna 1 and degrade the reception characteristics of the reception antenna 2.

  Therefore, according to the antenna device A of the present embodiment, even if the frequency of the radio wave transmitted from the transmission antenna 1 and the distance T1 between the transmission antenna 1 and the reception antenna 2 are different, the transmission antenna 1 and the reception antenna 2 In accordance with the distance T1 and / or the frequency of the radio wave transmitted from the transmission antenna 1, the relative position of the reflection member 3 with respect to the transmission antenna 1 and / or the reception antenna 2 is set so that the phases of the direct wave S1 and the reflected wave S2 are shifted. This makes it possible to ensure isolation easily and reliably.

  Further, as in the present embodiment, when the transmission antenna 1 has directivity for transmitting radio waves toward a predetermined range and leaks radio waves outside the predetermined range, the transmission antenna 1 When 1 is an antenna such as a helical antenna that is formed in a rod shape, transmits radio waves within a predetermined range from the end in the direction of the axis O1, and radiates leaked radio waves at the center of the axis O1, the reflective member 3 is provided. The direct wave S1 and the reflected wave S2 of the leaked radio wave are caused to interfere with each other so that the interference wave can be surely attenuated.

  Further, since the reflecting member 3 is disposed so that the reflected wave S2 of the leaked radio wave is shifted by a half wavelength at the receiving antenna position with respect to the direct wave S1, the direct wave S1 and the reflected wave S2 are caused to interfere with each other so as to cancel each other. It is possible to eliminate an interference wave that reaches the reception antenna 2 from the transmission antenna 1 and degrades the reception characteristics of the reception antenna 2.

  Further, when the reflecting member 3 and the transmitting antenna 1 and / or the receiving antenna 2 are configured to move relative to each other, the frequency of the radio wave transmitted from the transmitting antenna 1 and the distance T1 between the transmitting antenna 1 and the receiving antenna 2 are different. Even so, depending on the distance T1 between the transmitting antenna 1 and the receiving antenna 2 and / or the frequency of the radio wave transmitted from the transmitting antenna 1, the relative position of the reflecting member 3 with respect to the transmitting antenna 1 and / or the receiving antenna 2 is It is possible to easily set the reflected wave S2 and the direct wave S1 to be out of phase.

  Such an antenna device A can be suitably employed in an automatic toll collection system such as ERP (Electronic Road Pricing) installed in a toll gate such as a highway. Further, for example, the antenna device A of the present embodiment is provided on the roof portion of a police vehicle so that information can be exchanged with a responder mounted on another vehicle, and the contents of the license plate of the other vehicle are identified. The present invention can also be suitably employed for acquiring data while traveling. In this case, the roof portion of the vehicle may be used as the reflecting member 3.

  As mentioned above, although one Embodiment of the antenna device which concerns on this invention was described, this invention is not limited to said one Embodiment, In the range which does not deviate from the meaning, it can change suitably. For example, although the present embodiment has been described assuming that the transmission antenna 1 and the reception antenna 2 are helical antennas, the transmission antenna and the reception antenna according to the present invention are not necessarily limited to helical antennas.

  In the present embodiment, the path T1 of the direct wave S1 that directly reaches the receiving antenna 2 from the transmitting antenna 1, and the path (T3 + T4) of the reflected wave S2 that reaches the receiving antenna 2 from the reflecting member 3 and the reflecting member 3 from the transmitting antenna 1. In the above description, the difference (path difference) is set so that the phases of the direct wave S1 and the reflected wave S2 are shifted by a half wavelength. On the other hand, in the present invention, the path difference is appropriately adjusted to shift the phases of the direct wave S1 and the reflected wave S2, so that the interference effect between the direct wave S1 and the reflected wave S2 can be sufficiently obtained. However, it is not necessarily limited to setting the path difference so that the phases of the direct wave S1 and the reflected wave S2 are shifted by a half wavelength. In particular, as shown in FIGS. 4C and 4E, depending on the distance T2 between the reflecting member 3 and the antennas 1 and 2, and the types and shapes of the antennas 1 and 2, the path difference may be determined as the direct wave S1 and the reflected wave. If the phase of S2 is set to be shifted by a half wavelength, the interference effect between the direct wave S1 and the reflected wave S2 may be reduced. Even in such a case, by adjusting the path difference as appropriate, It is possible to enhance the interference effect of the reflected wave S2 and effectively eliminate the interference wave that degrades the reception characteristics of the reception antenna 2.

DESCRIPTION OF SYMBOLS 1 Transmission antenna 2 Reception antenna 3 Reflective member 3a Reflecting surface A Antenna apparatus O1 Transmission antenna axis O2 Reception antenna axis R Antenna radius S1 Direct wave S2 Reflected wave

Claims (5)

A receiving antenna that receives radio waves; a transmitting antenna that is provided adjacent to the receiving antenna and that transmits a main radio wave to an antenna different from the receiving antenna; and a part of the leaked radio waves leaking from the transmitting antenna A reflective member that reflects toward the antenna;
The reflecting member is arranged so that the reflected wave reaching the receiving antenna is reflected from a part of the leaked radio wave and reaches the receiving antenna with a phase shift with respect to the direct wave of the leaking radio wave that reaches the receiving antenna. Established,
An antenna device configured to attenuate the direct wave reaching the receiving antenna from the transmitting antenna by causing interference due to a phase shift between the direct wave and the reflected wave. The antenna device according to claim 1, wherein
An antenna apparatus, wherein the transmitting antenna is an antenna having directivity for transmitting radio waves toward a predetermined range, and leaking radio waves are generated outside the predetermined range. The antenna device according to claim 2, wherein
The antenna apparatus according to claim 1, wherein the transmission antenna is an antenna that is formed in a rod shape, transmits a radio wave from an end in an axial direction to the predetermined range, and radiates a leaked radio wave at the center of the axis. The antenna device according to any one of claims 1 to 3,
The reflecting member is arranged such that a reflected wave that becomes a shortest propagation path among the reflected waves that reach the receiving antenna is shifted by a half wavelength at a position of the receiving antenna with respect to a direct wave that becomes the shortest propagation path among the direct waves. An antenna device characterized by being made. The antenna device according to any one of claims 1 to 4,
The reflection member and the transmission antenna and / or the reception antenna are configured to move relative to each other according to a distance between the transmission antenna and the reception antenna and / or a frequency of a radio wave transmitted from the transmission antenna. An antenna device comprising:

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