Window Glass Antenna for Vehicle

This invention relates generally to a windshield antenna, for a vehicle and, more particularly, to an antenna which is mounted on a rear windshield of a vehicle on which a rear window defogger (defroster) comprising heating wires is mounted.

FIG. 1 shows one conventional antenna of the type described. More specifically, a plurality of heating wires 2 which together constitute a window defogger are mounted on a rear windshield 1 of a vehicle in parallel, closely spaced relation to one another, and extend longitudinally of the rear windshield 1. A pair of first and second antenna elements 3 and 4 are mounted on the rear windshield 1 parallel to and above and below the defogger heating wires 2. Electric power is supplied from a battery 6 of the vehicle to the defogger heating wires 2 via a power supply wire 8a, which is wound on a ferrite core 7. A grounding wire 8b also is wound on the ferrite core 7 so that the power supply wire 8a, and hence the defogger heating wires 2 are grounded to the body of the vehicle. Thus, this arrangement is set so that the inductance produced by the wires wound around the ferrite core 7 has a high impedance at a receiving frequency, so that the defogger heating wires 2 are isolated from the earth of the vehicle body, thereby reducing the influence of the defogger wires 2 in the directivity of the antenna elements. Moreover, the power supply wire 8a and the grounding wire 8b are connected together electrically through the ferrite core 7, and this prevents noise from developing in the defogger heating wires 2. Reference numeral 5 denotes rear pillars on the vehicle.

The first antenna element 3 serves as an antenna for receiving both FM (frequency-modulated) waves and AM (amplitude-modulated) waves, while the second antenna element 4 serves as a sub-antenna for FM waves. The outputs of the two antenna elements 3 and 4 are connected respectively to amplifiers 9 and 10 contained in the rear pillar 5. Particularly when receiving FM broadcasting, one of the first and second antenna elements 3 and 4 having a better signal reception condition is selectively used; such is known as "diversity reception" in the trade.

In the above conventional windshield antenna, since the upper side and lower side of the rear window glass 1 are different in length from each other, it is difficult to design the two antenna elements 3 and 4 to have the same reception characteristics. The two antenna elements 3 and 4 themselves differ in gain because of the differences in size and shape. Therefore, when the diversity reception is performed by the antenna elements 3 and 4, a satisfactory diversity effect cannot be obtained, since the two antenna elements 3 and 4 have different gains in the first place.

Further, it is difficult to design the FM antenna elements 3 and 4, disposed respectively on the upper and lower sides of the defogger heating wires 2, to have the same reception characteristics because of the difference in their spatial positions from the surface of the ground, the difference between the upper and lower their antenna patterns 3 and 4 in antenna pattern such as the shape and size in view of the receiving band, and so on. Therefore, a difference in gain occurs between the two antenna elements. As a result, when diversity reception is performed by the antenna elements 3 and 4, the rate of selecting one of the two antennas which has a higher gain is high because of the presence of such gain difference. This prevents a good diversity reception from being performed.

Still, further, since the first antenna element 3 is designed to receive both FM and AM waves, it is quite difficult to obtain good reception characteristics with respect to both. Further, the amplifiers 9 and 10 have to be mounted within one of the rear pillars 5 because of the position of mounting of the antenna elements 3 and 4. This considerably limits the size and shape of these amplifiers.

In view of the foregoing, it is an object of this invention to provide a windshield antenna for a vehicle which has good diversity reception, has good reception characteristics with respect to both AM and FM waves, and does not limit the size and shape of the amplifiers which are connected to the antenna elements.

According to the present invention, there is provided a windshield antenna for a vehicle having a rear windshield, the antenna including:

(a) a heating wire mounted on a central portion of the rear window glass, the heating wire serving as a window defogger element, and also as an antenna for receiving amplitude-modulated (AM) waves; and

(b) a pair of first and second antenna elements disposed on right and left sides of the heating wire, each of the first and second antenna elements serving as an antenna for receiving frequency-modulated (FM) waves.

The first and second FM antenna elements are disposed on the right and left sides of the heating wire, and therefore the two antenna elements can be of the same configuration because the rear window glass is symmetrical with respect to its generally vertical central axis. Therefore, there is no difference in gain between the two antenna elements, which is suitable for a diversity reception. Further, the spacing between the first and second antenna elements can be greater than that between the upper and lower antenna elements 3 and 4 of the conventional antenna (FIG. 1), and therefore good space diversity reception characteristics can be obtained. Still further, since the AM antenna elements are mounted on the central portion of the rear glass of the vehicle in a multi-line fashion, AM waves can be received by the antenna having a wide receiving area. Yet another advantage is that, since the FM antenna elements are disposed on the right and left sides of the heating wire, amplifiers to be connected respectively to these antenna elements can be mounted below a rear tray of the vehicle. Therefore, the shape and size of these amplifiers are much less limited.

FIG. 1 is a view showing a conventional antenna;

FIG. 2 is a schematic plan view of a rear window glass of a vehicle incorporating a windshield antenna provided in accordance with the present invention; and

FIG. 3 is a cross-sectional view of a partly-modified version of the vehicle glass antenna of FIG. 2.

This invention will now be described with reference to FIG. 2, in which a window glass antenna comprises a plurality of linear heating wires 20 mounted on a rear windshield 11 of a vehicle (e.g., an automobile) in parallel, closely spaced relation to one another and extending along the width direction of the rear windshield 11 (i.e., upwardly and downwardly with respect to the rear windshield 1), the heating wires 20 disposed at the central portion of the rear windshield 1 constituting a window defogger (defroster). A pair of first and second antenna elements 21a and 21b for receiving FM waves are mounted on the rear window glass 1 parallel to the defogger heating wires 20 (i.e, generally vertically), and are disposed to the left and right of the defogger heating wires 20, respectively. The first and second linear antenna elements 21a and 21b are arranged symmetrically with respect to the defogger heating wires 20. The first and second antenna elements 21a and 21b are connected respectively at their lower ends to amplifiers 22a and 22b contained in a rear trunk of the vehicle disposed immediately below these antenna elements. The amplifiers 22a and 22b amplify the FM signal received by the antenna elements 21a and 21b and feed it to an FM receiver (not shown).

Electric power is supplied from a battery 6 of the vehicle to the defogger heating wires 20 via a power supply wire 8a which is wound on a ferrite core 7. A grounding wire 8b also is wound on a ferrite core 7, so that the power supply wire and hence the defogger heating wires 20, are grounded to a body of the vehicle. Thus, the power supply wire 8a and the grounding wire 8b are connected together electrically through the ferrite core 7, to prevent noise from developing in the defogger heating wires 20. Also, a signal feed wire 24 is wound on the ferrite core 7, one end of the signal feed wire 24 being grounded while the other end is connected to an amplifier 23. With the above construction, an electric current to be supplied to the defogger heating wires 20 is supplied to the primary side of the ferrite core 7 in the opposite phase as indicated by arrows X in the drawings, thereby preventing the magnetic saturation of the ferrite core 7 which would be caused by the flow of a direct current, and the signal of an AM band present in the defogger heating wires 20 flows in the same phase in a direction indicated by arrows Y and can be taken out from the secondary side of the ferrite core 7.

The AM receiving signal, received by the defogger heating wires 20 serving as the AM antenna having a wide receiving area, is taken out through the ferrite core 7 as described above, and then is amplified by the amplifier 23 and is fed to an AM receiver (not shown).

The FM receiver, to which the FM signal is fed from the first and second antenna elements 21a and 21b via the respective amplifiers 22a and 22b, selects the one of the two antenna elements 21a and 21b which has a better reception condition to conduct diversity reception.

In the above embodiment, the defogger heating wires 20 are used as the AM antenna element. However, in the case where the rear glass comprised a laminated glass as shown in FIG. 3, the defogger heating wires 20 may be mounted on one of the surface 1c of contact between two mated glass panes 1a and 1b of the laminated glass and the surface 1d of the glass pane 1a facing the interior of the vehicle, and in this case separate AM antenna elements independent of the defogger heating wires 20 are mounted on the other of the surface 1c and the surface 1d. Such AM antenna elements are superimposed on the defogger heating wires 20 mounted on the different surface, and occupy generally the entire central area of the rear glass, and are arranged in a multi-line fashion.

Because the right and left sides of the rear windshield 1 are the same length, the first and second antenna elements 21a and 21b may be designed with relative ease to have the same reception characteristics, and the two antenna elements 21a and 21b can be designed to have the same gain. Therefore good diversity reception can be

Further, the defogger heating wires 20 also serve as the AM antenna elements, or alternatively the AM antenna elements are superimposed on the defogger heating wires 20 to constitute the antenna having a wide receiving area. Therefore, good reception characteristics with respect to the AM wave can be obtained.

Still, further, since the first and second antenna elements 21a and 21b connected respectively to the amplifiers 22a and 22b are positioned on the left and right sides of the defogger heating wires 20, the two amplifiers 22a and 22b do not need to be contained in a rear pillar of the vehicle, as was the case with a conventional system. Therefore, the shape and size of the amplifiers 22a and 22b need not be so limited. Furthermore, the distance between each of the first and second antenna elements 21a and 21b and the input terminal of a respective one of the amplifiers can be reduced, and therefore an influence of the impedance of signal wires connecting them can be reduced.

As described above, the symmetrical arrangement of the left and right FM antenna elements 21a and 21b enables these antenna elements to have the same gain. Further since the spacing between the left and right antenna elements 21a and 21b is greater than that between the upper and lower antenna elements 3 and 4 of the prior antenna (FIG. 1), good space diversity reception characteristics can be obtained.

Further, because the AM waves are received by the wide receiving area defined by the defogger heating wires 20, this arrangement can achieve much higher gain as compared with the conventional AM antenna composed of a single wire.

Still, further, because of the position of mounting of the FM antenna elements 21a and 21b on the rear window glass 1, the mounting position of the amplifiers 22a and 22b connected respectively to these antenna elements is not restricted, and therefore no limitation is imposed on the shape and size of these amplifiers.

Various changes within the spirit of the invention will be apparent to those of working skill in this field. Accordingly, the scope of the invention is to be considered as limited only by the scope of the appended claims.