JP2005354139A - On-vehicle glass antenna system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an on-vehicle glass antenna system employing antennas for a digital television receiver installed on rear glass capable of controlling the directivity without being affected by heat wires. <P>SOLUTION: Two antenna elements 16A, 16B with a length of (λ/2)k, (where λ<SB>1</SB>≤λ≤λ<SB>2</SB>) are located on the rear glass 10 at an interval of (λ/4)k, (where λ<SB>1</SB>/4λ≤λ≤λ<SB>2</SB>/4). The antenna elements are connected to a phase synthesizer 22 via amplifiers 20A, 20B respectively. The phase synthesizer 22 composes a signal received by the antenna element 16A with a signal received by the antenna element 16B in a state that the phase of the signal received by the antenna element 16A is delayed from the phase of the signal received by the antenna element 16B by 190 to 220°, preferably 200°. The composed signal is fed to a TV tuner 24. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a glass antenna device for a vehicle, and more particularly to a glass antenna device for a vehicle for a digital TV (television).

  The performance required for a glass antenna device for a digital TV (frequency 473 to 701 MHz) provided on a window glass of a vehicle is controlled by directivity so as to be directed to a desired wave direction, and unnecessary waves coming from directions other than the desired wave direction. Is to improve the image quality of the TV. Particularly when traveling at high speed, it is considered that a sensitivity difference (FB ratio; front-back ratio) between the desired wave and the unnecessary wave is required to be 10 dB or more (theoretical value).

As an antenna system that meets such requirements, an “in-vehicle TV diversity system” described in Patent Document 1 is known. According to this system, the output of one of the two TV antennas is phase-shifted by a phase shifter and combined with the output of the other TV antenna, so that the third antenna having a changed antenna directivity is obtained. It is configured to realize diversity in which the best received signal is selected from the signals of the original TV antenna and the third antenna. However, nothing is disclosed about the structure of the antenna.
JP-A-12-252895

  When an antenna for digital TV is provided on a rear glass where heat rays exist, it is difficult to control directivity in a desired wave direction due to the influence of heat rays. This is because the directivity of the rear glass antenna changes in a direction perpendicular to the rear glass surface due to the influence of heat rays, as shown by a dotted line in FIG. 1, and the sensitivity in the horizontal direction decreases.

  In addition, due to the influence of such heat rays, it is difficult to control directivity in the desired wave direction even if a reflector and a director, which are parasitic elements, are used.

  An object of the present invention is to provide a glass antenna device for a vehicle that can control directivity without being affected by heat rays, using a digital TV antenna installed on a rear glass.

  Another object of the present invention is to provide a receiver using such a glass antenna device for a vehicle.

The present invention is a glass antenna device for a vehicle that receives a digital television signal (maximum frequency f ₁ , corresponding frequency λ ₁ , minimum frequency f ₂ , corresponding frequency λ ₂ ), and is provided on a window glass of a vehicle. The phase of one of the received signals from the two upper and lower antenna elements in the vertical relationship and extending in the horizontal direction from the respective feed terminals of the two antenna elements is 190 °. And a phase synthesizer for synthesizing these two received signals with a delay of ˜220 °, preferably 200 °.

The lengths of the upper antenna element and the lower antenna element are each (λ / 2) k (where λ is the wavelength of the received signal, λ ₁ ≦ λ ≦ λ ₂ , and k is the shortening rate), The distance between the antenna element and the lower antenna element is preferably (λ / 4) k (where λ ₁ ≦ λ ≦ λ ₂ ). Here, the shortening rate is related to the propagation speed of the radio wave propagating through the dielectric substrate (in this case, the glass plate), and the dimension of the antenna formed on the dielectric substrate is such that the antenna resonates. The ratio is smaller than the antenna size assumed when there is no dielectric substrate. In the case of vehicle glass, k is about 0.6.

  The vehicle glass antenna device of the present invention can control directivity without being affected by heat rays, particularly when installed on a rear glass. In addition, the vehicle glass antenna device of the present invention can be installed on the windshield and rear glass, and a receiving device with high reception quality can be realized by diversity reception or the like.

  The reason why the amount of phase change of the received signal of one antenna is set to 190 ° to 220 ° according to the present invention will be described. A model shown in FIG. 2 was created as an antenna analysis model.

  On the glass, a roof of the vehicle body and a grounding plate 8 simulating a heat ray (shown by oblique lines) and two antenna elements 16A and 16B were formed. The length of the antenna element was (λ / 2) k, the distance between the antenna elements was (λ / 4) k, and the distance between each antenna element and the ground plate was (λ / 8) k. λ is the center frequency of the band of 600 MHz, k = 0.6, the length of the antenna elements is 15 cm, and the distance between the antenna elements is 7.5 cm.

  The antenna element and the ground plate are connected to a phase synthesizer (not shown) via a coaxial cable (not shown). At that time, the feeding terminals of the antenna elements 16A and 16B are connected to the center conductor of a coaxial cable (not shown), and the ground plate 8 is connected to the outer conductor of the coaxial cable.

  The high-frequency signal obtained by the antenna element 16A is transmitted through the coaxial cable, delayed in phase in the phase synthesizer, and then synthesized with the high-frequency signal obtained by the antenna element 16B.

  Such an antenna analysis model is placed in an anechoic chamber with an installation angle of 30 ° (angle with respect to the horizontal direction), irradiated with radio waves of 470 to 700 MHz, and the phase of the received signal from the antenna element 16A is in the range of 90 ° to 270 °. The phase was synthesized with the received signal from the antenna element 16B, and the F / B ratio was measured. Here, the F / B ratio is the difference between the directivity gain to the front and the directivity gain to the back (Back) when the beam exit direction is the front. (Beam intensity) is evaluated. If this value is small, the directivity gain difference between the front and back is small (round), and if it is large, the directivity gain difference is large (has strong directivity in the front direction). ) Indicates an antenna.

  The measurement results are shown in Table 1. The unit of the numerical value is dB.

  From this measurement result, it can be seen that a good F / B ratio is obtained when the phase change amount is 190 ° to 220 °. In particular, the F / B ratio is maximized at a phase change amount of 200 °.

  From the above, it will be understood that the amount of change in the phase of one antenna is preferably 190 ° to 220 °.

  FIG. 3 shows an embodiment in which the glass antenna device for a vehicle of the present invention is provided on the rear glass. The periphery of the rear glass 10 is surrounded by a vehicle body edge 12. The rear glass 10 is provided with a hot wire 14 for anti-fogging.

  An antenna element is provided in a space between the hot wire 14 and the upper vehicle body. The antenna element is composed of two parallel antenna elements 16A and 16B extending in the horizontal direction. It is assumed that the antenna element 16A is on the antenna element 16B.

  The antenna element may be either a printed wire formed by printing a silver paste on the glass surface or a conductive wire provided inside the laminated glass. One end of the antenna element is connected to the power supply terminals 18A and 18B.

  Each antenna element has a length of (λ / 2) k. The distance between the antenna elements 16A and 16B is (λ / 4) k. λ is the center frequency of the band 600 MHz, k = 0.6, the length of the antenna elements is 15 cm, and the distance between the antenna elements is 7.5 cm.

  The power supply terminals 18A and 18B are connected to the amplifiers 20A and 20B by coaxial cables 19A and 19B, respectively. These amplifiers amplify the digital TV signal received by the antenna element. The central conductor of the coaxial cable is connected to the amplifier, and the outer conductor is connected to the vehicle body.

  In addition, since the antenna comprised by antenna element 16A, 16B has high impedance, it is necessary to use a cable with high impedance. Since the impedance of a realistic coaxial cable is as low as about 75Ω, when the antenna element and the coaxial cable are connected as they are, impedance mismatch occurs, and the performance may be deteriorated particularly at a low frequency.

  Regarding the relationship between the characteristic impedance of the coaxial cable and the frequency characteristic of the reception performance of the antenna, the result of simulation with an electromagnetic simulator using the analysis model shown in FIG. 2 shows that a 300Ω coaxial cable has a frequency band of 470 to 700 MHz. The result that the characteristic can be made flat was obtained.

  Therefore, power can be supplied by connecting a 4: 1 balun (balanced-unbalanced conversion circuit) that converts a 75Ω coaxial cable to 300Ω between the antenna element and the cable. FIG. 4 shows an example in which 4: 1 baluns 17A and 17B are provided in the configuration of FIG.

  The outputs of the amplifiers 20A and 20B are connected to the phase synthesizer 22. The phase synthesizer 22 synthesizes the signal received by the upper antenna element 16A with the signal received by the lower antenna element 16B by delaying the phase by 190 ° to 220 °, preferably 200 °. The synthesized signal is sent to the TV tuner 24.

  FIG. 5 shows an example of the configuration of the phase synthesizer 22. The phase synthesizer 22 includes a two-signal synthesis type phase shifter 32 and a synthesizer 34 that synthesizes two signals. The synthesized signal from the synthesizer 34 is sent to the TV tuner 24.

  The TV tuner 24 sends a phase control signal to the phase shifter 32 so that the reception sensitivity is maximized. The phase shifter 32 can set the optimum phase difference with the output signal of the amplifier 20B by delaying the phase of the input signal from the amplifier 20A by the phase adjustment signal from the TV tuner 24.

  FIG. 6 shows an example of the configuration of the phase shifter 32. The amplifier 50, the 90 ° hybrid 52, variable attenuators 54 and 56 that can be controlled by a phase control signal from a TV tuner, and a coupler 58, respectively. Two signals having a phase difference of 90 ° are formed by the 90 ° hybrid 52, and the two signals thus formed are multiplied by cos θ and sin θ in attenuators 54 and 56, respectively, and the outputs of the attenuators 54 and 56 are combined. Thus, a signal whose phase is delayed by θ from the signal input to the amplifier 50 can be formed.

  In the case of a glass antenna, θ is 190 ° to 220 ° as described above because the antenna is fixed on the glass surface, surrounded by ground, and the inclination of the glass is about 30 °. ° and 200 ° is optimal.

  The output signal from the phase shifter 32 and the signal from the amplifier 20B are combined by a combiner 34. The synthesized signal is sent to the TV tuner 24.

  The synthesizer 34 is preferably composed of a 3 dB hybrid type distributor or a distributor using ferrite beads. This is because these distributors have little loss and a wide band.

  In this manner, the directivity is determined by combining the signals from the two antenna elements with a predetermined phase difference. The directivity can reduce the influence of the heat ray 14 and can be directed in the rear direction. Therefore, since the sensitivity in the rear direction can be increased and the sensitivity in the front direction can be decreased, the F / B ratio (Front / Back ratio) can be improved.

  In order to further improve the F / B ratio, a reflector element that is a parasitic element or a parasitic element such as a waveguide element may be added. FIG. 7 shows an example in which a waveguide element 30 is added to the antenna elements 16A and 16B shown in FIG. The director element 30 extends below the antenna element 16B in parallel with the antenna element 16B. The antenna elements 16A and 16B are each connected to a phase synthesizer via an antenna, as described in FIG. 3 or FIG.

  In the antenna element described above, the impedance of the antenna element may not be in an optimum state due to the shape of the vehicle or other antenna elements. Therefore, the shape of the antenna element may be changed for the reason of performing impedance matching.

  If the glass antenna device described in FIG. 3, FIG. 4 or FIG. 7 is installed on the windshield side and rear glass side and diversity switching is performed, only the desired wave is received in all directions of the vehicle and unnecessary waves are cut. Therefore, high reception quality can be obtained.

  FIG. 8 is a schematic diagram showing this embodiment. The antenna elements of the antenna devices 42-1 and 42-2 are installed on both sides of the upper portion of the windshield of the vehicle 40, and the antenna elements of the antenna devices 42-3 and 42-4 are installed on both sides of the upper portion of the rear glass. Each antenna device includes two amplifiers 20A and 20B and a phase synthesizer 22 in addition to the antenna element provided on the glass. In the figure, the directional characteristics of each antenna device are indicated by dotted lines.

  FIG. 9 shows a diversity receiver. The received signals from the antenna devices 42-1, 42-2, 42-3, and 42-4 are selected by the switch 44 and sent to the TV tuner 46 as a desired wave.

  The above is an example of diversity reception, but means for synthesizing received signals from four antenna devices in the same phase may be added before the TV tuner. FIG. 10 shows this receiving apparatus. The synthesizer 48 synthesizes the received signals from the four glass antenna devices 42-1, 42-2, 42-3, 42-4 and sends them to the TV tuner 46.

  With this method, it is possible to obtain a directivity with good sensitivity in the front-rear direction. In a situation where unnecessary waves do not exist in a weak electric field such as a weak electric field, reception can be performed from all directions of the vehicle, so that reception quality can be improved.

  In the above embodiment, the digital TV signal is described as the received signal. However, the present invention can also be applied as an antenna for existing media other than the digital TV.

It is a figure which shows a mode that the directivity of the antenna of a rear glass changes to the direction perpendicular | vertical to a rear glass by the influence of a heat ray. It is a figure which shows an antenna analysis model. It is a figure which shows the Example which provided the glass-mounted antenna apparatus for vehicles of this invention in the rear glass. FIG. 4 is a diagram showing an embodiment in which a 4: 1 balun is provided in the configuration of FIG. 3. It is a figure which shows an example of a structure of a phase synthesizer. It is a figure which shows an example of a structure of a phase shifter. It is a figure which shows the antenna element which provided the parasitic element. It is a figure for demonstrating diversity reception. It is a figure which shows the structure of a diversity receiver. It is a figure which shows the structure of the receiver which synthesize | combines the received signal from a several antenna apparatus with the same phase.

Explanation of symbols

8 Ground plate 10 Rear glass 12 Body edge 14 Heating wire 16A, 16B Antenna element 18A, 18B Feeding terminal 17A, 17B 4: 1 Balun 20A, 20B, 50 Amplifier 22 Phase combiner 24, 46 TV tuner 30 Parasitic element 32 Phase shifter 34 Synthesizer 42 Antenna Device 44 Switcher 52 90 ° Hybrid 54, 56 Variable Attenuator 58 Coupler

Claims (9)

A glass antenna device for a vehicle that receives a digital television signal (maximum frequency f ₁ , corresponding wavelength λ ₁ , minimum frequency f ₂ , corresponding wavelength λ ₂ ),
Two upper antenna elements and a lower antenna element which are provided on a window glass of a vehicle and extend in the horizontal direction in a vertical relationship;
A phase synthesizer that synthesizes the two received signals by delaying the phase of one of the received signals from the power supply terminals of the two antenna elements by 190 ° to 220 °;
A glass antenna device for a vehicle comprising:   The glass antenna device for a vehicle according to claim 1, wherein the reception signal is synthesized by delaying a phase by 200 °.   The glass antenna device for vehicles according to claim 1 or 2 which synthesizes by delaying the phase of the received signal of said upper antenna element. The lengths of the upper antenna element and the lower antenna element are each (λ / 2) k (where λ is the wavelength of the received signal, λ ₁ ≦ λ ≦ λ ₂ , and k is the shortening rate), The glass antenna device for a vehicle according to claim 1, wherein an interval between the upper antenna element and the lower antenna element is (λ / 4) k (where λ ₁ ≦ λ ≦ λ ₂ ).   The glass antenna device for a vehicle according to any one of claims 1 to 4, further comprising one parasitic element extending horizontally below the lower antenna element.   The glass antenna device for a vehicle according to any one of claims 1 to 5, wherein an amplifier is provided between each of the power supply terminals and the phase synthesizer.   The glass antenna device for a vehicle according to claim 6, wherein a coaxial cable is connected between each of the power supply terminals and a corresponding amplifier.   The glass for vehicles according to claim 7, wherein when the coaxial cable has an impedance of 75Ω, a 4: 1 balun that converts the impedance to 300Ω is connected between each antenna and the corresponding coaxial cable. Antenna device. The vehicle glass antenna device according to any one of claims 1 to 8, which is installed on a windshield and a rear glass,
A switch for switching a reception signal from the glass antenna device for a vehicle;
A diversity receiver comprising:

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