JP2011182280A - On-board antenna system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an on-board antenna system in which receiving performance of an antenna is improved by reducing influences of electromagnetic noise of a vehicle, the need of adjusting the receiving performance of the antenna different for each car type is eliminated and an antenna in the same shape can be diverted. <P>SOLUTION: The on-board antenna system 20 has a tunable antenna 21, a tuner 22, a control panel 23, a digital audio amplifier 24, and a speaker 25. The tunable antenna 21 has a variable capacitance switch 28 provided to an antenna element 27, the conductor plate of a body 31, a feed point 29 provided between the antenna element 27 and the conductor plate of the body 31, a variable filter 32 connected to the feed point 29, a variable attenuator 33 connected to the variable filter 32, and an antenna control unit 26 which is a circuit for controlling these components. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an in-vehicle antenna system mounted on a vehicle, and more particularly to an in-vehicle antenna system having a tuner integrated antenna.

  Conventionally, antennas such as radios and televisions are arranged in automobiles. Such a vehicle antenna is usually mounted as a pole-like antenna protruding outside the vehicle compartment of the vehicle such as a roof or a tail, and thus has the problem that the appearance of the vehicle deteriorates and the aerodynamic performance deteriorates. Yes.

  FIG. 5 shows a configuration of a conventional in-vehicle antenna system 40 mounted on the vehicle 100. Since the vehicle 100 has a metallic body 11 and the body 11 reflects radio waves coming from the outside, the vehicle-mounted antenna system 40 receives radio or television broadcasts by the antenna 43a protruding on the roof. It is. A signal received by the antenna 43 a is input to the tuner 22 in the vehicle interior via the coaxial cable 42, and the tuner 22 extracts a desired signal set from the control panel 23, and the extracted signal is amplified by the digital audio amplifier 24. Output to the speaker. Here, the metal surface of the roof is a conductor plate sufficiently wide with respect to the wavelength of radio broadcasting or an object having a sufficiently large capacitance. The electromagnetic noise radiated from the noise sources 19a and 19b of the electronic device is shielded to prevent the electromagnetic noise from entering the antenna 43a.

  In addition, in addition to antennas such as radios and televisions, a car navigation GPS antenna, a VICS antenna, an ETC antenna, and the like are installed in the vehicle interior close to the body skin. These antennas must be placed as close to the outside of the cabin as possible, such as the upper part of the instrument panel or the top of the dashboard, and in a position where it is easy to receive the radio waves that have passed through the glass. Only antennas can be installed. In particular, since the ETC antenna needs to perform two-way communication with a roadside device, it needs to be disposed in the vicinity of the windshield.

  Currently, the number of media that must be sent and received by vehicles is increasing year by year, and installing all of the corresponding antennas on the glass surface or in the instrument panel means that the antenna transmission and reception performance and installation space, This is impossible due to cost constraints. Therefore, in some cases, it was necessary to employ a protruding antenna.

  In recent years, for the purpose of reducing the weight of a vehicle, attempts have been made to resinize a body outer plate such as a roof. FIG. 6 shows a configuration of an in-vehicle antenna system 40 which is a reference for understanding the present invention, and shows an antenna 43b in which the roof 16 is made of resin and a protruding antenna is disposed inside the roof as a planar antenna. The antenna 43b is connected to the tuner 22 by the coaxial cable 42 as in the conventional case. Since radio waves pass through the roof 16, it is possible to mount all antennas in the roof, which solves the aerodynamic performance deterioration that has been the cause of damage to the design of the vehicle and contributes to improved fuel efficiency. It has become possible.

  However, there are various noise sources 19 in the vehicle. The electromagnetic noise generated from the noise source 19 includes ignition noise generated from the engine, clock noise generated from an in-vehicle computer such as an ECU, noise caused by switching such as lighting of a brake lamp and switch ON / OFF, a wiper and a power window. There is noise of the motor to be operated. Furthermore, these noises increase in hybrid vehicles and electric vehicles. These electromagnetic noises are mixed by the antenna 43b disposed on the resinized roof 16, and the transmission / reception performance of the antenna 43b is deteriorated. This is because, conventionally, the metal surface of the roof has a function of shielding electromagnetic noise, but it is eliminated.

  As a technique for preventing mixing of electromagnetic noise and sneak noise, there is a technique as described in Patent Document 1. In Patent Document 1, a signal having a higher band than the reception band of the tuner is prevented from being mixed as noise into the other system via the other antenna from the tuner side. The filter prevents the noise component to be converted from being mixed.

JP 2009-253491 A

  The tuner of Patent Document 1 prevents the introduction of wraparound noise by blocking signals in a band higher and lower than the desired wave with a filter, but the circuit configuration is complicated. Further, the metal surface of the roof described above plays a role of radiating radio waves as a uniform conductor plate with respect to the antenna, and it is unnecessary to adjust the antenna resonance frequency for each vehicle type, which is a vehicle type. However, if there is no uniform conductor plate, the body part, which has a different shape for each car-shaped design such as pillars, side members, and phosphorus hoses, which are the remaining metal surfaces, becomes a conductor plate, so the resonance frequency of the antenna varies. In addition to the filter as in Patent Document 1, it is necessary to change the physical antenna shape for adjusting the resonance frequency for each vehicle type.

  Therefore, in order to solve such problems, the effect of electromagnetic noise of the vehicle is reduced to improve the reception performance of the antenna, and it is not necessary to adjust the reception performance of the antenna which is different for each vehicle type. An object of the present invention is to provide a vehicle-mounted antenna system that can be used for the above.

  In order to achieve the above object, an in-vehicle antenna system according to the present invention is an in-vehicle antenna system mounted on a vehicle, and is connected to an antenna element whose resonance frequency can be adjusted by a variable capacitance switch. A variable filter, an adjustment circuit that corrects a shift in resonance frequency that varies depending on the vehicle type using a variable capacitance switch and a variable filter, a tuner that demodulates a signal received by an antenna element, and a controller that controls the tuner The control unit provided inside the tuner controls the adjustment circuit, and the tuner is arranged in the vicinity of the antenna element. By adopting such a configuration, it is possible to prevent the reception performance from being deteriorated even when the uniform conductor plate in the vicinity of the antenna element differs for each vehicle type due to the resinization of the vehicle body.

  According to another aspect of the present invention, an in-vehicle antenna system is characterized in that a variable attenuator is provided at the output of the antenna element in order to suppress distortion of a signal output from the antenna element, and the control unit controls the variable attenuator. With such a configuration, it is possible to reduce the occurrence of distortion due to a strong electric field signal.

  By using the in-vehicle antenna system according to the present invention, it is possible to reduce the influence of electromagnetic noise of the vehicle and improve the reception performance of the antenna. There is an effect that an in-vehicle antenna system for diverting the antenna can be realized.

1 is a configuration diagram illustrating an overall configuration of a vehicle-mounted antenna system according to an embodiment of the present invention. It is a circuit block diagram which shows the circuit structure of the vehicle-mounted antenna system of FIG. It is explanatory drawing explaining the operating state of the antenna element of FIG. It is a circuit block diagram which shows the circuit structure of the vehicle-mounted antenna system used as a reference in understanding this invention. It is a block diagram which shows the structure of the conventional vehicle-mounted antenna system. It is a block diagram which shows the structure of the vehicle-mounted antenna system used as a reference in understanding this invention.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings.

  FIG. 1 shows an overall configuration of a vehicle-mounted antenna system 20 mounted on a vehicle 10 and outlines the vehicle-mounted antenna system 20. The roof 16 of the vehicle 10 is made of resin, and the roof 16 includes a tunable antenna 21 that can change the frequency of the antenna, and a signal that controls the tunable antenna 21 and is received by the tunable antenna 21. A tuner 22 for demodulating a desired signal is disposed. A signal cable 41 connected from the tuner 22 to the control panel 23 and the digital audio amplifier 24 is wired from the roof via the vehicle interior. A tuner 22 arranged in the roof takes out a desired signal set from the control panel 23, and the taken out signal is amplified by a digital audio amplifier 24 and then outputted from a speaker.

  2 shows a circuit configuration of the vehicle-mounted antenna system 20 shown in FIG. 1, and FIG. 3 shows an operating state of the antenna element shown in FIG. The in-vehicle antenna system 20 in FIG. 2 includes a tunable antenna 21, a tuner 22, a control panel 23, a digital audio amplifier 24, and a speaker 25. The tunable antenna 21 includes a variable capacitance switch 28 provided in the antenna element 27, a conductor plate of the body 31, a feeding point 29 provided between the antenna element 27 and the conductor plate of the body 31, and a feeding point 29. , A variable attenuator 33 connected to the variable filter 32, and an antenna control unit 26 which is a circuit for controlling these. Note that the variable filter 32 and the variable attenuator 33 are arranged directly below or in the vicinity of the antenna element in order to reduce mixing of electromagnetic noise.

  The tuner 22 in FIG. 2 controls an AGC 34 having an auto gain control function, a preamplifier 35, a mixer 36, an oscillator 37, an A / D converter 38, a tuner 22 and a digitized signal as an audio signal. DSP 39 for converting to A signal received by the tunable antenna 21 is output to the mixer 36 through the AGC 34 and the preamplifier 35. The mixer 36 converts the radio wave amplified by the AGC 34 and the preamplifier 35 into an IF signal, and the converted IF signal is converted into a digital signal by an A / D converter 38. The IF signal converted into the digital signal is demodulated into an audio signal by the DSP 39. The demodulated audio signal is amplified by the digital audio amplifier 24 and output from the speaker 25.

  The DSP 39 acquires setting information such as the broadcasting station and volume set by the user from the control panel, and transmits the pre-stored vehicle type, resonance frequency of the tunable antenna, reception status of the tunable antenna, etc. to the antenna control unit 26. To do. The antenna control unit 26 controls the antenna characteristics by changing the resonance frequency and the antenna gain of the tunable antenna 21 based on information from the DSP.

  The variable capacitance switch 28 provided in the antenna element 27 of FIG. 2 can electrically adjust the resonance frequency of the antenna under the control of the antenna control unit 26. The variable filter 32 connected to the feeding point 29 is configured by a band-pass filter, and can pass / block a signal having a characteristic frequency under the control of the antenna control unit 26. The variable attenuator 33 at the subsequent stage of the variable filter 32 can adjust the magnitude of the signal passing therethrough by changing the attenuation amount under the control of the antenna control unit 26.

  A characteristic matter in this embodiment is that there is no uniform conductor plate due to the resinized roof, and the remaining metal surfaces such as pillars, side members, phosphorus hoses, etc. The tuner 22 adjusts the resonance frequency of the tunable antenna 21. Therefore, this embodiment will be described in detail in comparison with a reference configuration.

  FIG. 4 shows a circuit configuration of a vehicle-mounted antenna system 40 which is a reference for understanding the present invention. The vehicle-mounted antenna system 40 is mounted on the vehicle 110 of FIG. 6 having a resin roof. The antenna 43 includes an antenna element 27, a feeding point 29, an AGC 44, and a preamplifier 45, and is connected to a tuner 22 disposed in the instrument panel by a coaxial cable 42. Here, the AGC 44 and the preamplifier 45 amplify the radio wave received by the antenna directly under the antenna in order to compensate for the attenuation of the radio wave by the coaxial cable 42. However, since the roof is made of resin, various electromagnetic noises generated from the noise source 19 are directly input to the antenna 43 built in the resin roof. The electromagnetic noise input from the antenna 43 is superimposed by the AGC 34 and the preamplifier 35 of the tuner 22 through the coaxial cable 42.

  For this reason, a large amount of electromagnetic noise is input to the tuner 22 together with the received radio wave, which causes the reception performance of the antenna system to deteriorate. In addition, in the in-vehicle antenna system 40 of FIG. 4, the AGC and the preamplifier are doubled directly below the antenna and in the tuner, so that it is strong enough to reach the saturation region beyond the linear region of transistors and FETs in the preamplifier. When an electric field signal or electromagnetic noise is input, the signal is double-distorted by the preamplifier, which is another cause of a decrease in reception performance. Furthermore, since the metallic roof surface which is a uniform conductor plate is eliminated, the resonance frequency varies, and it is necessary to change the shape of the antenna element for each vehicle type and adjust the resonance frequency.

  On the other hand, in the vehicle-mounted antenna system 20 of FIG. 2 in the present embodiment, the electromagnetic noise directly input to the antenna can be removed (blocked) by blocking the frequency of the electromagnetic noise by the variable filter 32. . Further, by integrating the tunable antenna 21 and the tuner 22, the coaxial cable can be eliminated, and electromagnetic noise superimposed on the coaxial cable can be prevented.

  Since the signal received by the tunable antenna 21 is converted into an audio signal digitized by the tuner 22, even if electromagnetic noise is superimposed on the wiring to the digital audio amplifier, it is hardly affected. The reception performance as an antenna system is maintained. Further, the integration of the tuner makes it possible to reduce the number of AGCs and preamplifiers, suppress double generation of signal distortion at the time of a strong electric field, and attenuate the power by the variable attenuator 33, thereby reducing the strong electric field signals to the AGC and the preamplifier. Can be suppressed.

  As described above, in the vehicle-mounted antenna system 20 of FIG. 2, the resonance frequency can be adjusted by the variable capacitance switch 28 and the variable filter 32, so that it is not necessary to tune each vehicle type. In addition, in order to reduce the size of the circuit and reduce the cost, a circuit necessary for adjustment is provided in the vicinity of the antenna, and the tuner is integrated. Next, a method for adjusting the resonance frequency using the variable capacitance switch will be described.

  3 shows the operating state of the antenna element, FIG. 3A shows the antenna element of FIG. 4, and FIGS. 3B and 3C show the antenna element of FIG. In the case of a monopole antenna as shown in FIG. 3, resonance occurs at a frequency at which the antenna length is a quarter of the wavelength. Therefore, as shown in FIGS. 3B and 3C, the variable capacitance switch 28 is provided to change the electrical length of the antenna element, and the electrical conduction / insulation state is switched, whereby an apparent antenna is obtained. The length can be changed to adjust the resonance frequency of the antenna. In the present embodiment, for the sake of explanation, a configuration in which two types of resonance frequencies are adjusted is shown, but it goes without saying that a plurality of variable capacitance switches can be provided for finer control. With such a configuration, it is not necessary to change the physical shape of the antenna element for each vehicle type, and the antenna having the same shape can be used in various vehicle types.

  In addition, the antenna control unit not only controls the variable capacitance switch to adjust the resonance frequency for each vehicle type, but also dares to input signals and electromagnetic noises in a strong electric field based on instructions from the DSP at the rear stage. By shifting the resonance frequency of the antenna from that frequency, it is possible to reduce the apparent antenna gain and suppress the input of a strong electric field signal to the AGC and the preamplifier. Furthermore, in the case of a weak electric field, the antenna control unit may positively adjust the resonance frequency to the frequency desired to be received, thereby increasing the Q value of the antenna and controlling so as to obtain higher reception sensitivity.

  As described above, by using the vehicle-mounted antenna system according to the present embodiment, the influence of electromagnetic noise is reduced, the antenna reception performance is improved, and the antenna reception performance that is different for each vehicle type is adjusted. It becomes unnecessary, and it becomes possible to divert the antenna having the same shape. The antenna element in the present embodiment is a monopole antenna, but is not limited to this. If the resonance frequency can be adjusted, the antenna element is a modified antenna specialized for mounting on a vehicle including a dipole antenna. Also good. In this embodiment, an AGC, preamplifier, mixer, oscillator, variable filter, and variable attenuator are used. However, if the DSP has high processing capability, the signal received by the antenna can be converted directly into an IF signal by the DSP. In this case, it is possible to further reduce the size of the tunable antenna.

10, 100, 110 Vehicle, 11 Body, 16 Roof, 19 Noise source, 20, 40 In-vehicle antenna system, 21 Tunable antenna, 22 Tuner, 23 Control panel, 24 Digital audio amplifier, 25 Speaker, 26 Antenna control unit, 27 antenna element, 28 variable capacity switch, 29 feed point, 31 body, 32 variable filter, 33 variable attenuator, 34, 44 AGC, 35, 45 preamplifier, 36 mixer, 37 oscillator, 38 A / D converter, 39 DSP, 41 Signal cable, 42 Coaxial cable, 43 Antenna.

Claims (2)

In an in-vehicle antenna system mounted on a vehicle,
An antenna element whose resonance frequency can be adjusted by a variable capacitance switch;
A variable filter connected to the antenna element;
An adjustment circuit that corrects a shift in resonance frequency that varies depending on the vehicle type using a variable capacitance switch and a variable filter;
A tuner for demodulating the signal received by the antenna element;
A control unit for controlling the tuner;
Have
Furthermore, a vehicle-mounted antenna system characterized in that a control unit provided inside the tuner controls the adjustment circuit, and the tuner is disposed in the vicinity of the antenna element. The in-vehicle antenna system according to claim 1,
An in-vehicle antenna system, wherein a variable attenuator is provided at an output of an antenna element in order to suppress distortion of a signal output from the antenna element, and a control unit controls the variable attenuator.

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