JP2010045740A - Vehicle antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle antenna which does not require any balun, is in conformity to a maintenance reference of road transportation vehicles and can be disposed at an upper edge of front glass of a vehicle. <P>SOLUTION: A first element 12 is disposed rectangularly downward to an upper edge 10a of front glass 10, and a second element 14 is disposed along with the upper edge 10a so as to be approximately inversely L-shaped with respect to the first element. A length of the first element 12 is defined as an effective length of a 1/4 wavelength of a transmission/reception frequency band. A length of the second element 14 is defined as an effective length of a 1/4 wavelength of the transmission/reception frequency band, and its width is set to 13 times or more the width of the first element 12 and 25, and not more than 25 mm. A central conductor 16a and an external conductor 16b of a coaxial line 16 are electrically connected to the first element 12 and the second element 14, respectively. Even when a vehicle antenna is operated practically as an unbalanced antenna or electrically connected with an unbalanced coaxial line 16, any balun is not required. The width of the second element 14 is set at 25 mm or less and the vehicle antenna is in conformity to a maintenance standard of road transportation vehicles. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle antenna disposed on an upper edge portion of a windshield of a vehicle.

  When the vehicle antenna is disposed on the windshield of the vehicle, it is desirable that the antenna has a small installation area and is disposed on the periphery of the windshield in order to ensure the driver's field of view. Therefore, in order to ensure the visibility of the driver, it is obliged to install the antenna within 25 mm from the periphery of the windshield according to Article 29, Paragraph 4, Item 7 of the safety standard for road transport vehicles. According to the safety standard, it is allowed to protrude from a width of 25 mm at the peripheral edge in a fine line of 1.0 mm or less.

  Therefore, a V-shaped dipole antenna has been studied as an example of such a vehicle antenna. The structure of this V-shaped dipole antenna will be briefly described with reference to FIG. In FIG. 10, a first element 12 serving as a radiation pattern is disposed on the upper edge of the windshield 10 of the vehicle and directed downward substantially perpendicularly to the upper edge 10a of the windshield 10. A second element 14 serving as a grounding pattern is disposed along the upper edge 10a so as to be substantially inverted L-shaped together with the element 12 of FIG. The first and second elements 12 and 14 are formed of a conductive thin film or the like, and the width thereof is 0.8 mm as an example. For example, the length c of the first element 12 is set to be an effective length of a quarter wavelength of the transmission / reception frequency in the 800 MHz band for mobile phones, and the physical length is set to 46 mm. . Similarly, the length d of the second element 14 is set to be an effective length of a quarter wavelength of the transmission / reception frequency, but the physical length is set to 80 mm. Here, since the second element 14 is disposed along the upper edge 10a, a capacitive coupling is generated between the second element 14 and the vehicle body that is made of a conductive metal and acts as a ground electrode, so that the same quarter wavelength is obtained. Even if the effective length is, the physical length d is required to be longer than that of the first element 12. Note that the physical length that is the effective length of the quarter wavelength is greatly affected by electrical characteristics such as the dielectric constant of the windshield 10 on which these elements are disposed, and is between the ground electrode and the ground electrode. Those skilled in the art will readily understand that this is greatly influenced by the degree of capacitive coupling. The central conductor 16 a of the coaxial line 16 is electrically connected to the first element 12, and the outer conductor 16 b of the coaxial line 16 is electrically connected to the second element 14.

However, this V-shaped dipole antenna is a balanced antenna, and when electrically connected to an unbalanced coaxial line 16 as a signal path, a balun is required to transmit a signal satisfactorily. . In addition, this V-shaped dipole antenna has a relatively narrow band and is not suitable as an antenna for a wide band such as an 800 MHz band for a cellular phone. Such problems of the V-shaped dipole antenna are described in Japanese Patent Laid-Open No. 2007-96475. Further, an antenna in which the grounding pattern of the V-shaped dipole antenna has a hollow shape is described in Japanese Patent No. 3173904.
JP 2007-96475 A Japanese Patent No. 3173904

  In the technique proposed in the above-mentioned Patent Document 1, in order to make the balun unnecessary, in addition to the linear elements constituting the V-shaped dipole antenna, other linear elements are arranged. In order to add another linear element, the structure as an antenna becomes complicated. Further, in the technique proposed in Patent Document 2 described above, if the grounding pattern has a hollow shape, the width is 40 mm, and the vehicle is disposed on the upper edge of the windshield of the vehicle, the road transport vehicle The safety standard is not met, and at least cannot be disposed on the upper edge of the windshield of the vehicle.

  The present invention has been made in view of the circumstances as described above, does not require a balun, conforms to the safety standards of road transport vehicles, and can be disposed on the upper edge of the windshield of the vehicle. An object is to provide a vehicular antenna.

  In order to achieve the above object, a vehicle antenna according to the present invention is a vehicle antenna disposed on an upper edge portion of a windshield of a vehicle, and is directed downward at a right angle to the upper edge of the windshield. The first element is disposed, the second element is disposed along the upper edge so as to be substantially inverted L-shaped with the first element, and the length of the first element is transmitted and received. The effective length of the quarter wavelength of the frequency band is set, the length of the second element is set to the effective length of the quarter wavelength of the transmission / reception frequency band, and the width is set to 13 of the width of the first element. It is set to be not less than double and not more than 25 mm, and the central conductor of the coaxial line is electrically connected to the first element, and the outer conductor of the coaxial line is electrically connected to the second element.

  In the vehicle antenna according to claim 1, the width of the second element that acts as the grounding pattern is 13 times or more that of the first element that acts as the radiation pattern. The balun is not necessary even if it is operated as an unbalanced antenna and electrically connected to an unbalanced coaxial line. Also, if the width of the second element as the grounding pattern is infinite, it acts as a complete unbalanced antenna, but its width is 25 mm or less, which conforms to the safety standards of road transport vehicles, It was confirmed experimentally that there was no practical defect in the structure.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing the structure of a first embodiment of a vehicle antenna according to the present invention. FIG. 2 is a diagram showing a simulation of the VSWR frequency characteristics of the conventional V-shaped dipole antenna shown in FIG. 10 with the second element widened. FIG. 3 is a diagram showing a simulation of the VSWR frequency characteristics of the conventional V-shaped dipole antenna shown in FIG. 10 and a state in which the center frequency is adjusted by increasing the width of the second element and shortening the length of the first element. It is. FIG. 4 is a diagram of actual measurement data of the VSWR frequency characteristics of the vehicle antenna of the present invention shown in FIG. FIG. 5 is a measured directional characteristic diagram of the vehicle antenna of the present invention of FIG. 1 with respect to a vertically polarized frequency with an elevation angle of 0 degrees, (a) is 815 MHz, (b) is 843 MHz, (c ) Is 875 MHz, and (d) is 925 MHz. In FIG. 1, the same or equivalent members as in FIG.

  In FIG. 1, the difference from the conventional V-shaped dipole antenna shown in FIG. 10 is that the width b ′ of the second element 14 acting as a ground pattern is first widened from 0.8 mm to 12 mm. . Furthermore, the length c ′ of the first element 12 is shortened from 46 mm to 42 mm.

  First, since the monopole antenna on a finite ground plane is an unbalanced antenna, the inventors have established a balanced V-shaped dipole antenna close to the monopole antenna on a finite ground plane so that the structure is unbalanced. Predicted to work as. Therefore, in order to change the balanced type conventional V-shaped dipole antenna to an unbalanced type, the width b 'of the second element 14 acting as a ground pattern serving as a finite ground plane is increased from 0.8 mm to 12 mm. Here, the length c of the first element 12 remains 46 mm, which is the same as the conventional length. Then, as shown in FIG. 2, in the simulation of the VSWR frequency characteristic, the center frequency decreased as the bandwidth was increased. Therefore, the inventors shortened the length c ′ of the first element 12 to 42 mm in order to adjust the center frequency. Then, as shown in FIG. 3, in the simulation of the VSWR frequency characteristics, the bandwidth was widened and the center frequency could be matched with the conventional one. Then, the inventors manufactured the vehicle antenna of the present invention and measured the VSWR frequency characteristics. As shown in FIG. 4, the VSWR characteristics were confirmed in the range of 815 MHz to 925 MHz in the 800 MHz band for mobile phones. It was done. Further, when the directivity characteristics were measured at 815 MHz, 843 MHz, 875 MHz, and 925 MHz with respect to the vertically polarized frequency at an elevation angle of 0 degrees, as shown in FIG. Directionality was obtained. Moreover, the average gain was excellent at 0.27 dBi at 815 MHz, -0.77 dBi at 843 MHz, -1.01 dBi at 875 MHz, and -1.02 dBi at 925 MHz. The second element 14 has a width b ′ of 12 mm, and the antenna required by the road transport vehicle safety standard Article 29, Paragraph 4, Item 7 is within 25 mm from the edge 10a of the windshield 10. Can be installed. Therefore, the vehicle antenna according to the first embodiment of the present invention is practically excellent. Note that the width a of the first element 12 is 0.8 mm, which contributes to expanding the bandwidth of VSWR of 3 or less, and enables the wide band required for the 800 MHz band for mobile phones. . Therefore, the width a of the first element 12 is desirably 0.8 mm or more. However, the thin line protruding from the 25 mm width of the peripheral portion of the windshield 10 is regulated to 1.0 mm or less according to the safety standard of the road transport vehicle. Therefore, the width a of the first element 12 is limited to 0.8 mm or more and 1.0 mm or less.

  In the vehicle antenna according to the first embodiment of the present invention, the width b ′ of the second element 14 is 12 mm, and a: b ′ = 1: 15 with respect to the width a of the first element 12. Are in a relationship. Therefore, the inventors set the width b ′ of the second element 14 acting as a grounding pattern to 10 mm, and the gain of the relationship a: b ′ = 1: 13 with respect to the width a of the first element 12. I tried to measure the directivity. Then, as shown in FIG. 6, almost no directivity was obtained at any of 815 MHz, 843 MHz, 875 MHz, and 925 MHz. Moreover, the average gain was -3.06 dBi at 815 MHz, -4.65 dBi at 843 MHz, -5.39 dBi at 875 MHz, and -4.60 dBi at 925 MHz. The difference between the maximum and minimum gains at 925 MHz was 8.00 dB. The vehicular antenna of the present invention having such characteristics can be sufficiently used practically. However, the vehicle antenna of the present invention in which the width b ′ of the second element 14 is 10 mm is different from the vehicle antenna of the present invention of the first embodiment in which the width b ′ of the second element 14 is 12 mm. The characteristics are poor in terms of gain and omnidirectionality, suggesting a minimum width b ′ of the second element 14. The maximum width of the width b ′ of the second element 14 is closer to the monopole antenna on the finite ground plane that operates as an unbalanced antenna and becomes more unbalanced. It must be limited to 25 mm or less as required by Article 29, Paragraph 4, Item 7. In order to set the width b 'of the second element 14 to 10 mm, the length c' of the first element 12 is of course adjusted to match the center frequency.

  Further, the inventors insert a matching circuit 18 formed by connecting a coil L and a capacitor C in series between the first element 12 and the central conductor 16a of the coaxial line 16 as shown in FIG. , VSRW characteristics were measured. As an example, the coil L constituting the matching circuit 18 is 5.6 nH, and the capacitor C is 10 pF. Then, as shown in FIG. 8, characteristics with a VSWR of 3 or less were obtained in the range of 815 MHz to 1.575 GHz. As a result, by interposing the matching circuit 18, it can be sufficiently used as a dual-band antenna for two frequency bands of 800 MHz band and GPS 1.5 GHz band for mobile phones. If the constants of the coil L and the capacitor C constituting the matching circuit 18 are set appropriately, it is used as a dual-band antenna for two frequency bands of 800 MHz band and 1.8 GHz to 2.0 GHz band for mobile phones. It is also possible.

  Further, as shown in FIG. 9, the vehicle antennas 20 and 20 of the present invention are arranged on the upper edge of the vehicle windshield 10 so as to be separated from each other by two so as to function as a diversity antenna. Is possible. When two vehicle antennas according to the present invention are arranged to act as a diversity antenna, the arrangement positions of the two vehicle antennas are not limited to the structure shown in FIG. Further, the wiring routed around the coaxial line 16 is not limited to the structure shown in FIG.

It is a figure which shows the structure of 1st Example of the vehicle antenna of this invention. FIG. 11 is a diagram illustrating a simulation of a VSWR frequency characteristic of the conventional V-shaped dipole antenna shown in FIG. 10 in a state where the width of the second element is widened. FIG. 11 is a diagram illustrating a simulation of a VSWR frequency characteristic of the conventional V-shaped dipole antenna shown in FIG. 10 and a state in which the center frequency is adjusted by increasing the width of the second element and shortening the length of the first element. It is a figure of the measurement data of the VSWR frequency characteristic of the vehicle antenna of this invention of FIG. FIG. 2 is an actually measured directional characteristic diagram with respect to a vertically polarized frequency at an elevation angle of 0 degrees of the vehicle antenna of the present invention in FIG. Yes, (d) is 925 MHz. The width b ′ of the second element is 10 mm, and the relationship of a: b ′ = 1: 13 with respect to the width a of the first element is as follows. It is a directional characteristic diagram of actual measurement with respect to frequency, (a) is 815 MHz, (b) is 843 MHz, (c) is 875 MHz, (d) is 925 MHz. It is a circuit diagram which shows the matching circuit 18 interposed between the 1st element and the center conductor of a coaxial line. It is a figure of the measurement data of the VSRW frequency characteristic at the time of interposing the matching circuit of FIG. FIG. 2 is a view in which two vehicle antennas of the present invention are arranged apart from each other on the upper edge of a vehicle windshield so as to act as a diversity antenna. It is a figure which shows the structure of the conventional V-shaped dipole antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Windshield 10a Upper edge 12 1st element 14 2nd element 16 Coaxial line 16a Center conductor 16b Outer conductor 18 Matching circuit L Coil C Capacitor 20 Vehicle antenna of this invention

Claims (4)

A vehicle antenna disposed on an upper edge of a windshield of a vehicle, wherein the first element is disposed at a right angle with respect to the upper edge of the windshield, and together with the first element A second element is disposed along the upper edge so as to have a substantially inverted L shape, the length of the first element is set to an effective length of a quarter wavelength of the transmission / reception frequency band, The length of the element 2 is set to an effective length of a quarter wavelength of the transmission / reception frequency band, and the width is set to be not less than 13 times the width of the first element and not more than 25 mm, and is coaxial with the first element. A vehicular antenna, wherein a central conductor of a line is electrically connected, and an outer conductor of the coaxial line is electrically connected to the second element. 2. The vehicle antenna according to claim 1, wherein an effective length of the first element and the second element is set to a quarter wavelength of the 800 MHz band so that the transmission / reception frequency band is an 800 MHz band for a mobile phone. A vehicular antenna characterized by being configured. The antenna for a vehicle according to claim 1, wherein a matching circuit comprising a series connection of a coil and a capacitor is interposed between the first element and the central conductor of the coaxial line to provide an 800 MHz band for a mobile phone. And a vehicular antenna, which is configured to transmit and receive two frequency bands of 1.5 GHz for GPS. A vehicular antenna comprising a diversity antenna by disposing two vehicular antennas according to claim 1 on the upper edge of a vehicle windshield.