JPH0626282B2 - Car antenna device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention effectively detects a broadcast wave received by an automobile antenna device, particularly an automobile body, and supplies a detection signal to various receivers mounted on the automobile. The present invention relates to an improved vehicle antenna device.

[Prior Art] In order to reliably receive various broadcast waves, for example, broadcast communication waves of radio, television, telephone, etc., with a receiver provided in the vehicle, an antenna device is indispensable in the vehicle, and This kind of antenna device is also extremely important for transmitting and receiving, for example, civic band radio waves for communication between a vehicle and other stations, and plays a major role for a communication function equipped as standard equipment in the future vehicle.

The conventional general antenna device is known as a pole antenna, and the antenna protruding from the vehicle body shows preferable performance in terms of its reception characteristics, but it has the fate that it is always treated as an obstacle in terms of vehicle body design. Was.

In addition, such a pole antenna is susceptible to damage such as bending and bending even in actual use, is subject to mischief or theft, and causes various problems such as unpleasant wind noise when traveling at high speed. Have,
In the past, there have been many requests to somehow remove this.

In particular, as the frequency band of broadcast waves or communication waves received inside a car expands, as in recent years, it is necessary to install multiple antennas according to each frequency band, and the aesthetic concept of the car's appearance is neglected. I destroyed it. Further, there is a problem that their reception performance is significantly deteriorated by electrical mutual interference between these various antennas.

In the past, some efforts have been made to remove the above-mentioned pole antenna or conceal it so that it cannot be seen from the outside. For example, attaching an antenna thin wire to a rear windshield has been put into practical use.

As another conventional solution, it has been proposed to detect the surface current induced in the vehicle body itself by broadcast waves. The use of such a current flowing through the vehicle body is considered to be the most reliable and efficient method at first glance, but conventional experiments have continued to show results that completely violate such expectations.

The first reason that the surface current induced by a general broadcast wave on the vehicle body cannot be used is that the surface current value is not as large as expected, and conventional surface current is mainly applied to the ceiling plate of the vehicle body. Although it was the target, even with this, it was not possible to obtain a detection output of a level sufficient for sufficient use.

The second conventional problem is that noise is mixed into the surface current at an extremely large rate. Such noise is mainly generated from the ignition system of the engine and the regulator system for charging the battery, and the engine is operating. As long as these noises leaked to the car body, it was impossible to perform a clear broadcast wave reception action that could be practically used.

Even under such disadvantageous conditions, some proposals have been made in the past. As a conventional antenna device that utilizes the current induced in the vehicle body by broadcast waves, Japanese Patent Publication No. 53-22
418 is known, and an electrical insulating portion is formed in a current concentrating portion of a vehicle body, and a current between both ends of the insulating portion is directly detected by a sensor. Although it has been suggested that this conventional device can obtain a practical detection signal having an excellent SN ratio, its pickup structure requires a notch in a part of the vehicle body, which is quite normal. It was impossible to apply it to mass-produced automobiles.

Japanese Utility Model Publication No. 53-34826 is known as another conventional device, and an antenna has been proposed in which a pickup coil detects a current flowing through a pillar of a vehicle. This conventional device was useful for indicating the development direction of incorporating the antenna in the vehicle body, but in practice, it is not practical to provide a pickup coil orthogonal to the longitudinal direction in the vicinity of the pillar, In addition, such a pickup arrangement could not obtain a practical antenna output, and was considered to be a mere idea.

[Problems to be Solved by the Invention] Problems of Prior Art As described above, conventionally, an antenna device for detecting a current induced in a vehicle body by a broadcast wave has not always been successful. In particular, conventionally, the pickup structure for effectively detecting the current induced by the broadcast wave flowing in the vehicle body and the pickup arrangement for obtaining a practical S / N ratio have not been properly solved.

Further, in the conventional device, the receiving sensitivity of the pickup is poor, and the receiving sensitivity varies depending on the frequency band.

SUMMARY OF THE INVENTION The present invention has been made in view of the above conventional problems, and effectively detects a current induced in a vehicle body with respect to a broadcast wave having a desired frequency and transmits the detected current to a vehicle-mounted receiver. An object of the present invention is to provide an antenna device for an automobile that can be manufactured.

[Means for Solving the Problems] In order to achieve the above object, the present invention arranges a high-frequency pickup in the vicinity of a peripheral portion of a vehicle body.
An antenna device for detecting a high-frequency surface current having a predetermined frequency or higher is provided, and the high-frequency pickup includes a loop antenna on the side facing the peripheral portion of the vehicle body.

That is, in the present invention, there is a case in which the circuit portion side that processes the signal detected by the loop antenna is formed of a metal member, and the loop antenna side is formed of a non-magnetic member, and the loop antenna includes a coil. It has a spiral coil part that is wound in a coil shape and is closely attached to the peripheral part of the vehicle body so as to bend and detects high-frequency surface current, and causes self-inductance and parasitic capacitance of the coil to cause resonance in a wide range of frequencies. , To get a high sensitivity reception.

The conventional antenna device was mainly intended to receive the AM wave from the background of the times, but for this reason, the wavelength of the broadcast wave intended for the antenna for detecting the vehicle body current is too large, so that the good reception is achieved. The result is that the characteristics cannot be obtained, and paying attention to this frequency dependency, in the present invention, the broadcast wave to be received is set to 50 MHz or more in the normal case of the FM frequency band or more,
It has made it possible to receive from the vehicle body current, which was previously impossible, very effectively.

[Embodiment] A preferred embodiment of an automobile antenna device according to the present invention will be described below with reference to the drawings.

FIG. 9 shows that when an external radio wave W such as a broadcast wave passes through a vehicle body B made of a metal conductor, a surface current I corresponding to the intensity of the electromagnetic wave is induced in each part of the vehicle body. In the above, only the frequency band used for FM waves of 50 MHz or more, television waves, etc. belonging to a relatively high frequency band among these radio waves is targeted.

The present invention is characterized in that the induced current distribution of the vehicle body is measured in such a specific high frequency band, and the pickup is installed in a portion where the surface current density is high and noise is small.

In order to know the surface current distribution, computer simulations and actual current intensity measurements are performed at each point.In the present invention, a probe based on the same principle as a high-frequency pickup provided in a desired vehicle body part described later is used. This probe was used, and the surface current was measured by moving the probe over the entire surface of the vehicle body while changing the direction at each point.

FIG. 10 shows a schematic structure of a probe P made on the basis of a principle similar to that of a high-frequency pickup to be described later, and a case 10 made of a conductor is provided in order to avoid mixing of electric waves from the outside. Loop coil 1 inside
2 is fixed, an opening 10a is provided in a part of the case 10, a part of the loop coil 12 is exposed to the outside through the opening 10a, and an exposed portion of the loop coil 12 is brought close to the surface of the vehicle body B. The loop coil 12 detects the magnetic flux generated by the vehicle body surface current. A part of the loop coil 12 is connected to the case 10 by a short-circuit wire 14, and the output end 16 is a core wire 2 of a coaxial cable 18.
It is connected to 0. Further, a capacitor 22 is provided in a part of the loop coil 12, so that the frequency of the loop coil 12 can resonate to a desired measured frequency and the pickup efficiency can be increased.

As described above, by moving the probe P along the surface of the vehicle body B and rotating the angle at each measurement point, it becomes possible to accurately obtain the surface current distribution on the vehicle body surface and its direction. In FIG. 10, the output of the probe P is amplified by the high frequency voltage amplifier 24, and the output voltage is measured by the high frequency voltage measuring device 26. The coil output voltage is read by the meter indication value of the measuring device 26, and the voltage corresponding to the meter indication value is recorded by the XY recorder 28 as the surface current distribution in each part of the vehicle body. The XY recorder 28 has a potentiometer 30.
A signal indicating each position of the vehicle body is input from, and it becomes possible to know the high-frequency surface current at each position.

1 and 2 show an embodiment of the present invention in which a high-frequency pickup is arranged close to the rear peripheral edge of the ceiling plate.

In FIG. 2, the ceiling plate 32 is shown in a bare or painted state, and the metallic ceiling plate 32 is connected to the rear glass 36 with the rear window frame 34 as its peripheral terminal.

Further, in this embodiment, the high frequency pickup 38 is provided in a region within l = 12 × 10 ⁻³ λ (where λ is the wavelength of the broadcast wave) from the outer peripheral edge of the body of the rear window frame 34.

As shown in detail in FIG. 1, the high frequency pickup 38 includes a loop antenna 42 inside a case 40 to form an electromagnetically coupled pickup, which was used to know the surface current distribution of the vehicle body. It has a structure similar to that of a probe including a loop coil.

Here, a characteristic of the present invention is that the high frequency pickup 38 includes a loop antenna 42 wound in a coil shape.

That is, as shown in FIGS. 3 and 4, the loop antenna 42 is provided so as to project from the circuit portion 44 and includes the spiral coil portion 42a and the lead-out portion 42b.
The signals detected by the impedance matching circuit and the amplifier circuit provided at 4 are processed. Then, the high frequency detection signal thus obtained is supplied to the BNC connector 5
It is taken out from the coaxial cable 48 via 0 and transmitted to various receivers such as a radio and a television provided in the automobile.

The outside of the circuit portion 44 is covered with a metal case 40a that shields electromagnetic waves from the outside, and the outside of the lead-out portion 42b of the loop antenna 42 passes through the magnetic flux in order to effectively detect the external magnetic flux. It is covered with a resin case 40b. The resin case 40b is provided with a holding arch 46 that holds the spiral coil portion 42a.

The loop antenna 42 includes a rear wind frame 34.
An insulating coating is applied to the coil so that the coil is placed in an electrically insulated state and in close contact with the coil, and the spiral coil portion 42a is slightly bent as shown in FIG. The magnetic flux generated by the surface current can be more strongly interlinked with the loop antenna 42.

Further, the present invention is characterized in that resonance can be generated in a desired frequency band by self-inductance and parasitic capacitance (capacitor generated between loops) of the coil, and high-sensitivity reception can be performed. The diameter is about 1 cm in the embodiment, and the number of turns can be adjusted according to the desired frequency.

For example, as shown in FIG. 6 showing the frequency band-reception level, if the first resonance is desired to be around 100 MHz, it is about 20.
It can be achieved in ~ 30 turns.

In this case, the length of the loop antenna 42 in the longitudinal direction is about 10 cm.
Further, in this embodiment, the resonance point appears at an integer multiple of the frequency of the first resonance, and for example, the first resonance is F
70-11, which corresponds to the M band or the VHF (Lo) band of television
If the center of 0MHz and 90MHz is taken, the second resonance is V of the TV.
High-sensitivity characteristics can be obtained at 180 MHz corresponding to the HF (Hi) band.

The curve shown by the broken line in FIG. 6 shows the parallel resonance type sensitivity characteristic of the single loop antenna, and as is clear from this graph, the sensitivity characteristic of this embodiment is higher than that of the single loop antenna. It can be seen that the sensitivity is improved by about 5-10 dB.

Further, in FIG. 7, as described above, the impedance matching circuit 5 is provided in the case 40 of the high frequency pickup 38.
4 and the amplifier circuit 56 are integrally housed as the circuit section 44, and the output impedance of the amplifier circuit 56 and the characteristic impedance of the coaxial cable 48 are matched to each other, whereby extremely efficient signal processing is performed. .

In the figure, a capacitor 52 is provided in the loop antenna 42.
Are connected in series, the signal detected by the loop antenna 42 is impedance-matched by an impedance matching circuit 54, further high-frequency amplified by an amplifier circuit 54 in the subsequent stage, and taken out from a coaxial cable 48 to a receiver mounted on a vehicle. Be done. The resonance frequency of the capacitor 52 can be finely adjusted by using a variable capacitor.

FIG. 8 shows the specific circuit configuration of FIG.
The circuit connection and operation will be described below at the same time.

The impedance matching circuit 54 includes a bandpass filter 58 and a discharge tube 60, the detection voltage of the capacitor 52 obtained from the loop antenna 42 is supplied to the input of the bandpass filter 58, and the output of the bandpass filter 58 has the discharge tube 60 and the capacitor. It is output to the parallel circuit path with C ₃ .

The discharge tube 60 is for electrostatic breakdown protection and prevents circuit breakdown due to static electricity, lightning, etc. from the outside. Further, the bandpass filter 58 performs impedance matching of the loop antenna 42.

The detection signal thus impedance-matched is then input to the high-frequency amplifier circuit 56 and is high-frequency amplified.

The amplifier circuit 56 includes transistors Q ₁ and Q ₂ connected in two stages.
, Whose output is fed to the receiver via coaxial cable 48.

In the figure, inductances L ₁ and L ₂ are peaking coils, resistors R ₂ and R ₃ are resistors for stabilizing the operation of the transistor Q ₁ , R ₅ and R ₆ are bias resistors, and C ₃ and C ₉ are bypass capacitors.

The outer conductor of the coaxial cable 48 is grounded, and forms the ground wire of the impedance matching circuit 54 and the high frequency amplifier circuit 56 provided in the case.

The output impedance of the high frequency amplification circuit 56 is matched with the characteristic impedance of the coaxial cable 48 to be substantially the same value.
And the coaxial cable 48 are well matched.

As described above, according to the present invention, the loop antenna 4
The weak signal detected in 2 can be subjected to desired impedance matching and high frequency amplification processing in the case that is the detection site, and these circuits themselves are extremely small and can be easily accommodated in the case 40. Four
The signal taken out from 8 is made extremely stable, and the wide band reception of FM or TV can be efficiently performed with high sensitivity.

[Effects of the Invention] As described above, according to the present invention, the high frequency surface current generated at a specific portion of the vehicle body, particularly at the peripheral portion of the vehicle body is used for the broadcast wave in the relatively high frequency band, for example, the FM frequency band or higher. To form a broadcast wave receiving antenna, and to form a case in the high-frequency pickup with a metal member on the circuit side and an insulating member on the loop antenna side, and in a coil shape, and around the vehicle body peripheral portion so as to bend. By including the loop antenna having the spiral coil portion closely arranged, the self-inductance and the parasitic capacitance of the coil provide the resonance characteristic to the frequency of the wide band and high-sensitivity reception can be performed.

[Brief description of drawings]

FIG. 1 is a plan view showing a mounting state of a high frequency pickup, FIG. 2 is a perspective view showing a state where an electromagnetic coupling type high frequency pickup is mounted on a rear window frame of an automobile ceiling plate, and FIG. 3 is an external perspective view of the high frequency pickup. Fig. 4, Fig. 4 is a sectional view taken along the line A-A in Fig. 3, Fig. 5 is a schematic explanatory view when a high frequency pickup is closely attached to a peripheral portion of a vehicle body, and Fig. 6 is a frequency by an automobile antenna device according to the present invention. FIG. 7 is a circuit diagram schematically showing a high frequency pickup, and FIG. 8 is a circuit diagram specifically showing a circuit configuration of the high frequency pickup shown in FIG. FIG. 9 is an explanatory diagram showing the surface current I generated in the vehicle body B by the external wave W, and FIG. 10 is a diagram showing the surface current I of the vehicle body using a probe similar to the high frequency pickup used in the present invention. It is an explanatory view of the probe and its processing circuit for knowing the fabric. 38 ... High frequency pickup 40 ... Case 42 ... Loop antenna 44 ... Circuit part 46 ... Holding arch 48 ... Coaxial cable 52 ... Capacitor 54 ... Impedance matching circuit 56 ... Amplification circuit

Claims (1)

[Claims] 1. An automobile for detecting a high frequency surface current induced in a vehicle body by a broadcast wave, which is arranged close to a vehicle body peripheral portion along a longitudinal direction thereof, and includes a loop antenna on a side facing the vehicle body peripheral portion. In the antenna device, the circuit part side that processes the signal detected by the loop antenna is a metal member, and the loop antenna side is a non-magnetic member, and each case has a case, and the loop antenna has a coil shape. It has a spiral coil part that detects high-frequency surface current by being wound and flexibly placed close to the peripheral part of the vehicle body, and has resonance characteristics for a wide range of frequencies due to the self-inductance and parasitic capacitance of the coil. An antenna device for an automobile characterized by: