JPH11112220A - Glass antenna device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the leakage of reception current to single ground through floating capacity against ground by specifying the floating capacity against ground of a defogger. SOLUTION: An antenna conductor 3 and a defogger are closely arranged each other and are capacity-connected. A distance between the antenna conductor 3 and the defogger for capacity-connecting them is usually about 0.1-50 mm. DC current is not transmitted/received between the antenna conductor 3 and the defogger, which are capacity-connected, but the high frequency current of a broadcasting frequency signal is transmitted/received. A choke coil 9 insulates the defogger from car body ground in terms of high frequency. The reception current of the high frequency band such as a broadcasting frequency band, which is induced to a heater line 2 and a bus bar, is prevented from flowing to car body ground. Reception current is sent to a receiver 7 without leakage. The floating capacity against ground of the defogger is set to be not more than 90 pF. Then, reception current leaks to car body ground through floating capacity against ground and sensitivity is prevented from deteriorating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass antenna device for a vehicle, which is suitable for a receiving device for a vehicle and is used for receiving a radio, a television, a telephone and the like.

[0002]

2. Description of the Related Art Conventionally, as a glass antenna apparatus for an automobile for receiving an AM broadcast band and an FM broadcast band, as shown in FIG. 4, a heater wire 2 and a heater wire 2 are supplied to a glass plate 31 at a rear window of the automobile. A defogger 33 of an electric heating type having a bus bar to be connected and an antenna conductor 36 of a predetermined pattern capacitively coupled in close proximity to transmit and receive a high-frequency current between the defogger 33 and the defogger 33 are provided. A glass antenna device in which a choke coil 9 is inserted and connected between DC power supplies 10 is known.

In this prior art, a choke coil 9 is inserted between a bus bar and a DC power supply 10 for a defogger 33 to increase the impedance of the choke coil 9 in a high frequency band such as a broadcast frequency band. To the defogger 33, but cut off the current in the broadcast frequency band.

In this manner, the choke coil 9 can insulate the heater wire 2 of the defogger 33 and the bus bar from the vehicle body ground (ground) at a high frequency, and a high frequency band such as a broadcast frequency band induced on the heater wire 2 and the bus bar. Can be prevented from flowing to the vehicle body ground, and the received current can be sent to the receiver 7 without leakage.

[0005]

However, defogger 3
3 has a stray capacitance with respect to ground of 100 pF or more, so that the reception current leaks to the vehicle body ground via the stray capacitance with respect to ground of the defogger 33, causing a problem that the sensitivity is lowered.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and comprises an electric heating type defogger having a heater wire and a bus bar for supplying power to the heater wire. And a choke coil connected between the bus bar and the DC power supply for the defogger to transmit a reception signal excited by the defogger to the receiver.
Provided is a glass antenna device for an automobile, which is set to 0 pF or less.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a configuration diagram of a typical example of a glass antenna device for a vehicle according to the present invention. In FIG.
1 is a rear window glass of an automobile, 2 is a heater wire, 3 is an antenna conductor, 4a is a feeding point of the antenna conductor 3, 4b is a feeding point connected to a defogger, 5a and 5b are bus bars, 6 is a resonance circuit, and 7 is a resonance circuit. The receiver, 9 is a choke coil, and 10 is a DC power supply. When the antenna conductor 3 has a high frequency band (for example, F
The following description is based on the premise that it is possible to receive an M broadcast band and a low frequency band (for example, an AM broadcast band).

In FIG. 1, the antenna conductor 3 and the defogger are close to each other and are capacitively coupled. The distance between the antenna conductor 3 and the defogger for capacitive coupling is usually about 0.1 to 50 mm. Although a DC current is not transmitted and received between the capacitively coupled antenna conductor 3 and the defogger, a high-frequency current such as a broadcast frequency signal is transmitted and received.

The choke coil 9 can insulate the defogger from the vehicle body ground at a high frequency, and can prevent a reception current in a high frequency band such as a broadcast frequency band induced in the heater wire 2 and the bus bar from flowing to the vehicle body ground. The current can be sent to the receiver 7 without leakage.

In the present invention, the stray capacitance to ground of the defogger is set to 90 pF or less. This is to prevent the receiving current from leaking to the vehicle body ground via the stray capacitance of the defogger with respect to the ground and lowering the sensitivity.

When the defogger has a stray capacitance to ground of 90 pF or less, the defogger has a stray capacitance to ground of 90 pF.
The sensitivity is improved by several dB as compared with the case where the value exceeds pF.
Means for reducing the stray capacitance to ground of the defogger to 90 pF or less include means for reducing the vertical length of the bus bars 5a and 5b to approximately の or less of the vertical length of the vehicle body opening at the rear of the vehicle. Is mentioned.

Even in such a case, it is preferable not to reduce the area of the defogger in order not to reduce the function of the defogger to prevent fogging. The vehicle body opening means an opening of the vehicle body into which the window glass plate is to be fitted and which should serve as a vehicle body ground, and is made of, for example, a conductive material such as metal.

In the present invention, two resonances may be caused to improve the reception sensitivity. FIG. 2 is a circuit diagram of an example of the resonance circuit 6 in the case where two resonances are caused. 2, 31 is a first coil, 32 is a second coil, 50,
51 is a DC cut capacitor, 42 is a bypass capacitor, 48 and 49 are damping resistors, 47 is a resistor for reducing vehicle noise such as engine noise, and 52 is a high frequency choke coil.

The first resonance is generated by the first coil 31 and the impedance of the antenna conductor 3. The impedance of the antenna conductor 3 mainly consists of stray capacitance, and the impedance of the antenna conductor 3 refers to the impedance when the antenna conductor 3 is viewed from the feeding point 4a. As the first coil 31, a coil of about 10 μH to 1 mH is usually used.

The second resonance is caused by the second coil 32 and the defogger impedance. The impedance of the defogger mainly consists of the stray capacitance with respect to the ground, and the impedance of the defogger means the impedance when the defogger is viewed from the feeding point 4b. Further, the resonance frequency of the second resonance may be adjusted by connecting a capacitance component in parallel between the stray capacitance with respect to the ground of the defogger and the vehicle body ground. As the second coil 32, a coil of about 10 μH to 1 mH is usually used.

When the second coil 32 loses inductance in the high frequency band, the reception signal in the high frequency band leaks to the vehicle body ground, and the reception sensitivity in the high frequency band decreases. In order to prevent this, a high-frequency choke coil 52 may be connected to the second coil 32 in series. For the high frequency choke coil 52, about 0.5 to 2.9 μH is usually used. A preferable range of the value of the high-frequency choke coil 52 is 1.5 to 2.7 μH.

The bypass capacitor 42 is provided as necessary, and has a function of transmitting a high frequency band to the receiver. For example, when the low frequency band is the AM broadcast band and the FM broadcast reception is also performed, the FM broadcast band is passed by the bypass capacitor 42. Note that an impedance matching circuit may be used instead of the resonance circuit 6.

[0018]

【Example】

"Example 1 (Example)" using a rear window glass plate of an automobile,
An automotive glass antenna device as shown in FIG. 1 was manufactured. The constants of each part are shown below.

Coil 31 = 120 μH, Coil 32 = 680 μH, Coil 52 = 2.7 μH, Resistance 47 = 270 Ω, Resistance 48 = 220 Ω, Resistance 49 = 10 kΩ, Capacitor 42 = 22 pF, Capacitor 50 = 1000 pF, Capacitor 51 = 1000pF, vertical length of opening of vehicle body = 750mm, busbar length = 200mm, defogger stray capacitance to ground = 80pF.

FIG. 3 shows frequency-sensitivity characteristics.

"Example 2 (comparative example)"
mm, and the specifications were exactly the same as those in Example 1 except that the stray capacitance with respect to the ground of the defogger was changed to 120 pF, and a glass antenna device for an automobile was manufactured without changing the area of the defogger. FIG. 3 shows the frequency-sensitivity characteristics.

[0022]

According to the present invention, since the stray capacitance to ground of the defogger is set to 90 pF or less, the received current hardly leaks to the vehicle body ground via the stray capacitance to ground of the defogger, and the sensitivity is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a typical example of a glass antenna device for an automobile.

FIG. 2 is a circuit diagram of an example of a resonance circuit 6.

FIG. 3 is a diagram showing frequency-sensitivity characteristics of Examples 1 and 2;

FIG. 4 is a configuration diagram of a conventional example.

[Explanation of symbols]

 1: rear window glass of automobile 2: heater wire 3: antenna conductor 4a: feeding point of antenna conductor 3 4b: feeding point connected to defogger 5a, 5b: bus bar 6: resonance circuit 7: receiver 9: choke coil 10 : DC power supply

Claims (1)

[Claims] An electric heating type defogger having a heater wire and a bus bar for supplying power to the heater wire is provided on a glass plate of a rear window of an automobile, and a choke coil is connected between the bus bar and a DC power supply for the defogger. An automotive glass antenna device for transmitting a reception signal excited by a defogger to a receiver, wherein the defogger has a stray capacitance to ground of 90 pF or less.