JP4944719B2 - Vehicle antenna device - Google Patents

Description

  The present invention relates to the structure of a vehicle antenna device.

  An automobile is equipped with various devices that are required to transmit and receive radio waves in communication with the outside of the automobile. These devices include, for example, a non-stop automatic payment system (ETC, Electronic Toll Collection System), which is one of intelligent transport systems (ITS), and road traffic information systems used in car navigation systems. (VICS, Vehicle Information and Communication System), communication devices used in satellite positioning systems (GPS, Global Positioning System), etc., in-vehicle telephones, AM, FM radio, and the like. Further, in recent years, for the safety of automobiles, an inter-vehicle communication system that mutually communicates the position or running state of automobiles has been installed.

  Since such various communication systems have different frequency bands and modulation schemes, it is desirable to provide a dedicated antenna for each communication system. However, the space for mounting an automobile is limited, and an antenna is installed outside the vehicle. Installation is often limited by aesthetics and design.

  Accordingly, it has been proposed to share a plurality of antennas or install a plurality of antennas in a smaller space. For example, Patent Document 1 proposes a stacked patch antenna in which patches, which are two radiating elements that operate at a plurality of frequencies, are arranged to overlap to operate in two frequency bands and the antenna height is kept low. Has been.

  In addition, various communication systems mounted on automobiles often have different corresponding polarizations. For example, the ETC system uses a circularly polarized wave with high directivity in the direction of high elevation, and the inter-vehicle communication system uses a vertically polarized wave with directionality in the low elevation direction. Since the patch antenna described in Patent Document 1 has high directivity in the vertical direction, the patch antenna can be applied to a system such as ETC that uses radio waves with circular polarization and directivity in the high elevation direction. Therefore, it cannot be used for a vehicle-to-vehicle communication system using directivity radio waves in a low elevation angle direction, and a plurality of antennas are required. For this reason, in Patent Document 2, a circularly polarized radio wave and a vertically polarized wave are connected by connecting a circularly polarized patch antenna and a vertically polarized antenna composed of a radiating element standing vertically to the ground conductor. A dual-polarized antenna that can deal with two polarized radio waves has been proposed.

JP 2002-158535 A JP 2005-20301 A

  However, the dual-polarized antenna according to the prior art described in Patent Document 2 rises vertically from the ground conductor to correspond to a flat patch and a vertically polarized radio wave corresponding to a circularly polarized radio wave. Since the radiating element is provided, there is a problem that the entire antenna becomes large and cannot be mounted in a narrow antenna installation space of the automobile.

  Therefore, an object of the present invention is to provide a low-profile antenna device that can cope with vertically polarized radio waves.

The vehicle antenna device of the present invention includes a flat ground conductor provided with first and second holes, and a square first flat radiation conductor provided with a third hole in the center and installed substantially parallel to the flat ground conductor. A cylindrical conductor that short-circuits the peripheral edge of the second hole of the flat plate conductor and the peripheral edge of the third hole of the first flat plate radiation conductor; and spaced apart from the flat plate conductor and passed through the first hole of the flat plate conductor. And a first feed line connected to a first feed point of a single flat plate radiation conductor, the center of the cylindrical conductor connecting each center of one opposite side of the first flat plate radiation conductor is disposed at the center position in the X direction center line, the first feeding point is arranged at a distance from the center of the cylindrical conductor on the X-direction center line, the first flat radiation conductor has a length in the direction X, the first the length of the radiating conductor for vertically polarized flat radiation conductor resonates at higher mode in the X direction and the center as a node of the voltage There, the X-direction of the first flat radiation conductor is mounted on a vehicle such that the longitudinal direction of the vehicle, characterized by.

Te vehicular antenna apparatus odor of the present invention, a second flat radiating conductor for circularly polarized wave which is installed in parallel schematically the opposite side of the flat ground conductor of the first flat radiation conductor, flat ground conductor and the first flat plate radiation A second space that is spaced apart from the conductor and the cylindrical conductor and is connected to the second feed point of the second flat plate radiation conductor through the second hole of the flat ground conductor, the third hole of the first flat plate radiation conductor, and the cylindrical conductor. And the second flat plate radiation conductor is smaller than the first flat plate radiation conductor and is installed so as not to protrude from the first flat plate radiation conductor. The length of the first flat plate radiation conductor along the first feed point from the second feed point and the length of the first flat plate radiation conductor in the direction perpendicular thereto are also suitable as the length at which the second flat plate radiation conductor resonates in the primary mode. And the first flat plate radiation conductor and the second flat plate radiation conductor have a common resonance frequency. Rukoto, also to be suitable as the first flat radiation conductor it is for inter-vehicle communication, it is also preferable.

  The present invention has an effect that it is possible to provide a low-profile antenna device that can deal with vertically polarized radio waves.

  Preferred embodiments of the present invention will be described below with reference to the drawings. The vehicle antenna device 10 shown in FIGS. 1 and 2 (a) is mounted on a vehicle (not shown). In FIGS. 1 and 2 (a), X indicates the longitudinal direction of the vehicle, and Y is the width of the vehicle. Indicates the direction, and Z indicates the height direction of the vehicle. The direction of the arrow in the Z direction is the upward direction of the vehicle. As shown in FIG. 1, the vehicle antenna device 10 of the present embodiment is installed on a ground conductor 11 that is a flat ground conductor, a dielectric 41 disposed on the ground conductor 11, and the dielectric 41. Vehicle-to-vehicle communication radiation conductor 21, which is a first flat plate radiation conductor, dielectric 43 provided on vehicle-to-vehicle communication radiation conductor 21, and second radiation conductor provided on dielectric 43. ETC communication radiating conductor 31, cylindrical conductor 25 that short-circuits the center of inter-vehicle communication radiating conductor 21 and the center of ground conductor 11, and an inner conductor of a coaxial cable, which feeds radiating conductor 21 for inter-vehicle communication A power supply line 29 that supplies power to the point 27, a power supply line 35 that supplies power to the power supply point 33 of the radiation conductor 31 for ETC communication, and outer conductors 45 and 47 of the power supply lines 29 and 35 connected to the lower surface side of the ground conductor 11. And. The dielectric 41 has a uniform thickness so that the ground conductor 11 and the inter-vehicle communication radiating conductor 21 are held substantially in parallel, and the dielectric 43 is also similar to the dielectric 41 in the inter-vehicle communication radiating conductor 21. And the ETC communication radiation conductor 31 and the ground conductor 11 are substantially parallel to each other, and the thickness between the inter-vehicle communication radiation conductor 21 and the ETC communication radiation conductor 31 is uniform.

  The ground conductor 11 includes a first hole 12 through which the power supply line 29 to the inter-vehicle communication radiation conductor 21 passes, and the dielectric 41 includes a hole 42 of the same size at the same position as the first hole 12. The ground conductor 11 and the inter-vehicle communication radiating conductor 21 include a second hole 13 and a third hole 23 through which the power supply line 35 to the ETC communication radiating conductor 31 passes. The second hole 13 and the third hole 23 are provided at the same position on the XY plane. The peripheral edge of the third hole 23 of the inter-vehicle communication radiation conductor 21 and the peripheral edge of the second hole 13 of the ground conductor 11 are short-circuited by the cylindrical conductor 25. The dielectric 41 is provided on the outer peripheral side of the cylindrical conductor 25. The dielectric 43 has a hole 46 of the same size at the same position as the third hole 23 of the radiation conductor 21 for inter-vehicle communication. A feed line 29 that passes through the first hole 12 so as not to touch the inter-vehicle communication radiation conductor 21 is connected to a feed point 27 of the inter-vehicle communication radiation conductor 21 through the hole 42 of the dielectric 41. The vehicle-to-vehicle communication radiation conductor 21 is configured to supply power. Further, the feed line 35 that passes through the second hole 13, the cylindrical conductor 25, and the third hole 23 so as not to touch the conductors 11, 25, 21 passes through the hole 46 of the dielectric 43 and is used for ETC communication. It is connected to the feeding point 33 of the radiation conductor 31 and configured to feed power to the radiation conductor 31 for ETC communication.

As shown in FIG. 2A, the ground conductor 11 is a square flat plate having a side length L ₀ , and the inter-vehicle communication radiation conductor 21 has a side length L ₁ shorter than that of the ground conductor 11. It is a square flat plate, and the ETC communication radiating conductor has a shape in which two opposing corners of the L ₂ square flat plate whose one side is shorter than the inter-vehicle communication radiating conductor 21 are chamfered. The ground conductor 11 and the inter-vehicle communication radiation conductor 21 are arranged so that the X-direction center line 51 and the Y-direction center line 52 coincide with each other, and the ETC communication radiation conductor 31 has the center in the X direction. Arranged so as to coincide with the center of the ground conductor 11 and the radiation conductor 21 for inter-vehicle communication, and in the Y direction, the center line 53 is shifted from the X direction center line 51 by a distance D in order to achieve impedance matching. . The ETC communication radiation conductor 31 is arranged so as not to protrude from the inter-vehicle communication radiation conductor 21. The sides of the square ground conductor 11 and the inter-vehicle communication radiation conductor 21 are arranged in parallel to each other, and the sides of the ETC communication radiation conductor 31 other than the chamfered portion are arranged for the square ground conductor 11 and the inter-vehicle communication. The radiating conductor 21 is arranged so as to be parallel to each side. The dielectrics 41 and 43 are squares having the same size as the ground conductor 11, and are arranged so that the four circumferences overlap the four circumferences of the ground conductor 11.

  As shown in FIG. 2 (a), in the vehicle antenna device 10, the direction from the first feeding point 27 of the vehicle-to-vehicle communication radiation conductor 21 to the tube conductor 25 is the X direction, that is, the vehicle longitudinal direction (not shown). It is mounted on the vehicle. Therefore, the Y direction in FIG. 2 is the vehicle width direction.

  Hereinafter, the operation of the embodiment of the present invention will be described. As shown in FIG. 1 and FIG. 2A, the vehicle-to-vehicle communication radiation conductor 21 of this embodiment is short-circuited to the ground conductor 11 at the center of the radiation conductor by the cylindrical conductor 25, so the voltage at the center is always constant. It becomes zero. For this reason, when power is supplied to the vehicle-to-vehicle communication radiation conductor 21 from the feeding point 27, the vehicle-to-vehicle communication radiation conductor 21 is used as a radiation conductor that resonates in a higher-order resonance mode in which the central voltage is zero. it can. As shown in FIG. 2B, in this embodiment, the length of each side of the square-to-vehicle communication radiation conductor 21 resonates in the third-order mode when the relative permittivity of the dielectrics 41 and 43 is taken into consideration. It is as long as you want. For this reason, as shown by the solid line in FIG. 2B, the inter-vehicle communication radiation conductor 21 has a node of zero voltage in the center and a third mode in which both ends are antinodes, that is, 3 / Resonates in a two-wavelength mode or a mode with an electrical length of 3π. Further, as shown by the dotted line in FIG. 2B, the current has a maximum antinode at the node where the voltage is zero, and both ends where the voltage is the maximum are nodes where the current flow is zero.

  In this way, when the tubular conductor 25 that short-circuits the center of the vehicle-to-vehicle communication radiation conductor 21 to the ground conductor 11 is used and the vehicle-to-vehicle communication radiation conductor is used in the tertiary mode, the feed point 27 goes to the tube conductor 25. Directionality in the horizontal direction can be obtained in the direction. Then, it is possible to transmit and receive vertically polarized radio waves by this horizontal directivity.

  Further, the ETC communication radiating conductor 31 of the present embodiment is approximately one third of the length of the inter-vehicle communication radiating conductor 21, and as shown by the solid line in FIG. Resonance occurs in a primary mode in which the voltage at both ends is the maximum and the voltage at the center is zero, that is, a mode of ½ wavelength or electrical length π. Further, as shown by the dotted line in FIG. 2C, the current has a maximum antinode at a node where the voltage is zero, and both ends where the voltage is the maximum are nodes where the current flow is zero. The ETC communication radiation conductor 31 has directivity in the direction perpendicular to the surface thereof, that is, the Z direction that is the vertical direction of the vehicle, and can transmit and receive circularly polarized radio waves by the directivity in the vertical direction. . Since the ETC communication radiating conductor 31 is provided on the inter-vehicle communication radiating conductor 21 so as not to protrude from the inter-vehicle communication radiating conductor 21, it radiates radio waves with the ground conductor 11. There is no resonance, and resonance occurs independently of the vehicle-to-vehicle communication radiation conductor 21.

  FIG. 3 is a diagram showing the directivity in the horizontal plane of the vehicle antenna device 10 of the present embodiment. In FIG. 3, the circumferential direction indicates a horizontal angle, the angles 0 and 180 indicate the longitudinal direction of the vehicle, and the angles 90 and 270 indicate the width direction of the vehicle. Further, the radial direction of FIG. 3 indicates the gain (dB) of the signal, the outermost circumference is 5 (dB), and the center is −5 (dB). As shown in FIG. 3, in the present embodiment, a gain of 1 (dB) or more necessary for communication is ensured when the circumferential angle is in the range of 0 ° to 21 °, 161 to 198 °, and 338 to 360 °. It can be seen that communication is possible within an angle range of about 40 ° in the front-rear direction.

  FIG. 4 shows the directivity in the vertical plane of the vehicle antenna device 10 of the present embodiment. In FIG. 4, the circumferential direction indicates a look-up angle in the vertical plane, angle 0 indicates the upward direction of the vehicle, angle 180 indicates the downward direction of the vehicle, and angles 90 and 270 indicate the width direction of the vehicle. Also, the radial direction in FIG. 4 indicates the gain (dB) of the signal, the outermost periphery is 10 (dB), and the center is −20 (dB). As can be seen from FIG. 4, the vehicle antenna device 10 of the present embodiment has a gain of 1 (dB) or more required for communication in a wide range centering on the angle zero that is the upward direction of the vehicle, and the angle 23 It can be seen that a gain of 4.4 (dB) is obtained on the ETC road side, and that the antenna has sufficient characteristics as an ETC communication antenna.

  FIG. 5 is a graph showing the degree of coupling between the return loss of the inter-vehicle communication radiation conductor 21 and the ETC communication radiation conductor 31 of the present embodiment. In FIG. 5, the curve a indicates the return loss of the inter-vehicle communication radiation conductor 21, and the curve b indicates the degree of coupling with the ETC communication radiation conductor 31. The vehicle antenna device 10 of the present embodiment is a vehicle-to-vehicle communication radio wave having a low elevation angle directionality with 5.8 GHz vertical polarization, and an ETC communication having a high elevation angle directionality with a circular polarization of 5.8 GHz. The dimensions of the radiation conductors 21 and 31 are determined so as to correspond to the radio waves for use. As shown by a curve a in FIG. 5, the vehicle-to-vehicle communication radiation conductor 21 of the vehicle antenna device 10 of the present embodiment has a return loss of about −20 (dB) at 5.8 GHz. In addition to showing good characteristics, the degree of coupling with the ETC communication radiation conductor 31 that receives circularly polarized radio waves of the same frequency is -18 (dB) or less at the corresponding frequency of 5.8 GHz, which is good. It can be seen that it has excellent separation characteristics. Thus, the vehicular antenna device 10 of this embodiment functions as a dual-polarized antenna that can satisfactorily transmit and receive radio waves of the two polarization methods of vertical polarization and circular polarization of the same frequency.

  As described above, the vehicular antenna apparatus 10 of the present embodiment is provided with the cylindrical conductor 25 that short-circuits the ground conductor 11 and the inter-vehicle communication radiating conductor 21 at the center, and the size of the inter-vehicle communication radiating conductor 21. Can be used in the third-order higher-order mode to obtain the directivity in the horizontal direction, keep the overall height of the antenna low, and obtain a gain necessary for communication as a vehicle-to-vehicle communication antenna using vertical polarization. There is an effect. In the present embodiment, the ETC communication radiation conductor 31 having a length resonating in the primary mode and smaller than the inter-vehicle communication radiation conductor 21 is stacked on the inter-vehicle communication radiation conductor 21. As a result, there is an effect that a dual-polarized antenna having a low height that can deal with vertically polarized waves and circularly polarized waves without mutual interference can be obtained.

  In the present embodiment described above, the vehicle-to-vehicle communication radiating conductor 21 has been described as having a size that resonates in the third-order mode. However, the vehicle-to-vehicle communication radiating conductor 21 has a high resonance frequency with the center as a voltage node. As long as it is used by the next mode, the dimension is not limited to the dimension that resonates in the third mode, and may correspond to a higher mode such as the fifth mode. The cylindrical conductor that short-circuits the center of the ground conductor 11 and the center of the inter-vehicle communication radiating conductor 21 is an outer conductor of the feeder line 35 to the ETC communication radiating conductor 31 connected to the lower side of the ground conductor 11. 47 may be extended.

It is sectional drawing of the antenna apparatus for vehicles in embodiment of this invention. It is a top view of the antenna apparatus for vehicles in the embodiment of the present invention. It is a graph which shows the directivity in the horizontal surface of the antenna apparatus for vehicles in embodiment of this invention. It is a graph which shows the directivity in the vertical surface of the antenna apparatus for vehicles in embodiment of this invention. It is a characteristic view which shows the return loss of the radiation conductor for vehicle-to-vehicle communication in the antenna apparatus for vehicles in embodiment of this invention, and a coupling characteristic with the radiation conductor for ETC communication.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Vehicle antenna device, 11 Ground conductor, 12 1st hole, 13 2nd hole, 21 Radiation conductor for inter-vehicle communication, 23 3rd hole, 25 Tube conductor, 27, 33 Feed point, 29, 35 Feed line, 31 Radiation conductor for ETC communication, 41, 43 Dielectric, 42, 46 hole, 45, 47 Outer conductor, 51 X direction center line, 52 Y direction center line, a, b curve, D distance.

Claims (5)

A flat ground conductor provided with first and second holes;
A square first flat plate radiation conductor provided with a third hole in the center and installed substantially parallel to the flat plate conductor;
A cylindrical conductor that short-circuits the periphery of the second hole of the flat plate conductor and the periphery of the third hole of the first flat plate radiation conductor;
A vehicular antenna apparatus comprising: a first feed line that is spaced apart from the flat plate conductor and passes through the first hole of the flat plate conductor and is connected to the first feed point of the first flat plate radiation conductor;
The center of the cylindrical conductor is arranged at the center position on the X-direction center line connecting the centers of one opposite side of the first flat plate radiation conductor,
The first feeding point is disposed on the center line in the X direction so as to be separated from the center of the cylindrical conductor,
The first flat radiation conductor has a length in the direction X, a radiating conductor for the length vertically polarized waves of the first flat plate radiating conductor resonates at a higher order mode in the X direction to the center as a node voltage,
Being mounted on the vehicle so that the X direction of the first flat plate radiation conductor is the longitudinal direction of the vehicle;
A vehicle antenna apparatus characterized by the above. The vehicle antenna device according to claim 1 ,
A second flat plate radiating conductor for circularly polarized waves installed substantially parallel to the opposite side of the flat plate ground conductor of the first flat plate radiating conductor;
The second flat plate radiation conductor second is spaced apart from the flat plate ground conductor, the first flat plate radiation conductor, and the cylindrical conductor, passes through the second hole of the flat plate ground conductor, the third hole of the first flat plate radiation conductor, and the cylindrical conductor. A second feed line connected to the feed point,
The second flat plate radiation conductor is smaller than the first flat plate radiation conductor and is installed so as not to protrude from the first flat plate radiation conductor;
A vehicle antenna apparatus characterized by the above. The vehicle antenna device according to claim 2,
The direction along the first feed point of the first flat plate radiation conductor from the second feed point of the second flat plate radiation conductor and the length in the direction perpendicular thereto are the lengths at which the second flat plate radiation conductor resonates in the primary mode. thing,
A vehicle antenna apparatus characterized by the above. The vehicle antenna device according to claim 2 or 3,
The first flat plate radiation conductor and the second flat plate radiation conductor have a common resonance frequency;
A vehicle antenna apparatus characterized by the above. The vehicle antenna device according to any one of claims 1 to 4,
The first flat plate radiation conductor is for inter-vehicle communication;
A vehicle antenna apparatus characterized by the above.

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