AUTOMOBILE ANTENNA DEVICE

Abstract: An automobile antenna device in which broadcast waves received by the automobile body are effeciently detected so that the various kinds of receivers equipped with the automobile can be supplied the detected signal. This device comprises an electrostatic shield case which is formed an opening thereat to face to a metal plate of the automobile body and a loop antenna being internally arranged in the electrostatic shield case so that the loop antenna can be facingly provided to the opening in its close vicinity. The loop antenna is equipped with a plurality of loops which are respectively formed by wound antenna wires, and the respective loops are sectorially arranged with the side of the electrostatic shield opening side as their centers. Therefore, the surface current being induced by the broadcast waves and flowing in the metal plate of the automobile body can be efficiently detected, and there is no need of pole antenna and others externally exposed, and further, the automobile antenna device can be easily obtained with small sizes and high accuracy.

Description: The present invention relates to automobile antenna devices. In order to receive the various kinds of broadcast wave signals, for example broadcast communications by radio, television and telephone, with high accuracy, an automobile needs to be equipped with an antenna device. It is also necessary to install an antenna device for transmission and reception of citizen's band communications between the automobile and other stations. It is understood that antenna devices have an important role in the communicating functions which will be standard equipment in automobiles in the future. A rod or pole antenna is well known in the art as an automobile antenna device. It projects from the automobile body and is preferred for the quality of its reception characteristics. In practical use, however, the pole antenna has problems in that it is easily damaged by being snapped or bent by accident or vandals, is easily stolen, and causes wind noise, and it has been a long felt want to solve these problems. In recent years, the frequency bands of broadcast wave signals and communication wave signals to be received in the automobile have increased in number and width, thereby necessitating a corresponding increase in the number of antennas to be installed in accordance with the respective frequency bands. The appearance of the automobile is ruined by so many antennas, and mutual electric interference among the antenna lowers their reception capability. Accordingly, it is an object of the present invention to make it possible to provide an automobile antenna device of high efficiency in a small size and without using a pole antenna which must be externally exposed out of the automobile body. DE-A-1949828 describes an automobile antenna device comprising a pick-up mounted on a metal portion of an automobile body to detect radio frequency surface currents induced in said body portion by broadcast radio frequency signals; said pick-up comprising an elongate loop antenna. The present invention is characterized in that: said pick-up includes a casing of electrically conductive material having an elongate opening; said loop antenna is disposed within said casing with a portion exposed through said opening and the remainder of said loop antenna is shielded from external electro-magnetic fields by said casing; said loop antenna comprises a plurality of serially connected generally rectangular loops extending in a corresponding plurality of planes, said planes disposed in a sectorial array so that they intersect one another along a common line along said opening and lie at substantially uniform angles to one another about said common line; and said exposed portion of said loop antenna comprises one longer side of each said loop which is exposed through said opening to extend lengthwise of and closely adjacent to a marginal edge portion of said automobile body. The loop antenna intersects the magnetic field created by the radio frequency surface currents induced in the marginal edge portion of the metallic portion of the automobile body. Because the loop antenna is formed with a plurality of loops, the output voltage from the loop antenna is equal to the voltage generated across each loop multiplied by the number of serially connected loops. Tuning resonance can thereby be strengthened so that disturbance from adjacent broadcasting stations can be more easily eliminated to increase the ability to separate adjacent stations and increase reception sensitivity. Because the loops are sectorially arranged with one longer side of each loop lying concentrated together in the vicinity of the opening of the casing and the other longer sides spaced widely apart at substantially uniform distances, the stray capacitance generated between the respective loops is extremely low. Furthermore, in view of the range of angular orientation of the loops in the sectorial array, at least one of the individual loops is likely to be at an angle at which the surface current can be detected most efficiently from the metal portion of the automobile body. This mitigates the problem of low sensitivity which might result from incorrect angular installation of the automobile antenna device and reception of broadcast wave signals is thereby improved. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a perspective view of an automobile antenna device in accordance with the present invention; Fig. 2 is a vertical section through the device of Fig. 1; Fig. 3 is an illustration of surface currents I generated in an automobile body B by an external radio frequency electromagnetic field W; Fig. 4 is an illustration of the principle of automobile antenna devices in accordance with the present invention; Fig. 5 is an illustration of means for ascertaining the relation between the angle of the plane of a loop of the antenna with respect to a metal plate of the automobile body and the detection efficiency of the surface current in the body; Fig. 6 is a graph showing the measured relation ascertained from the experiments in Fig. 5; and Fig. 7 is an illustration for explaining the relation between the number of loops of the loop antenna and the detection efficiency of the surface electric current. Fig. 3 shows that surface currents I are induced in various parts of an automobile body, specifically in their marginal edge portions, in accordance with the strength of an electromagnetic wave, such as a broadcast wave signal W, when the signal intersects the automobile body B consisting of metal conductor. The inventors made experiments to pick up the surface currents induced in the body by such broadcast waves by means of automobile antenna device as illustrated in Fig. 4. In the automobile antenna device shown in Fig. 4, a generally rectangular loop antenna 12 is internally fixed in a casing 10 made of electrically conductive material to shield the loop antenna from unwanted external electromagnetic fields. A portion of this loop antenna 12 is exposed to the outside through an opening 10a which is provided in the casing 10 and this exposed portion is placed closely adjacent to the surface of the body B so that the magnetic flux produced by the surface current can be easily picked up by the loop antenna 12. Another part of the loop antenna 12 is connected to the casing 10 by a lead 14, and the output end 16 is connected to a center lead 20 of a coaxial cable 18. A capacitor 22 is connected to another part of the loop antenna 12 in order to increase the pick-up efficiency of the antenna by resonance of the frequency of the loop antenna 12 to the desired reception frequency. According to the embodiment shown in Fig. 4, therefore, the magnetic flux created by the high frequency surface current which is induced by the broadcast waves is acquired by the loop antenna 12, and the casing 10 shields the antenna from unwanted external electromagnetic fields thereby enabling sensitive detection of the surface current induced in the automobile body by the broadcast waves. The detected signal obtained in this way is fed out through the coaxial cable 18 and supplied to the various receivers by way of voltage amplifiers, not illustrated. It has been found that the detection efficiency varies in dependance on the angle between the plane of the loop antenna 12 and a metal plate surface of the automobile body B adjacent to the loop antenna 12. The experiment shown in Fig. 5 was carried out in order to ascertain the best angle of the loop antenna 12 to the body B. In Fig. 5 the loop antenna of the automobile antenna device is installed with one longer side 24a of a pick-up 24, similar to the loop antenna 12 shown in Fig. 4, closely adjacent to the marginal edge of a metal plate 26. In this state, the angle made between the plane of the loop of the pick-up probe 24 and the extended center line of the metal plate 26 is changed gradually to investigate the relation between the angle ϑ and the detection efficiency of the surface current flowing through the metal plate 26 by the pick-up probe 24. The measured result of this investigation is shown in Fig. 6. As is evident from this figure, the detection efficiency of the surface current is greatest in the ranges 45 to 90 degrees and -45 to -90 degrees in the angle ϑ made between the plane of the loop of the pick-up probe 24 and the extended center line of the metal plate 26, and the detection efficiency is lower at any other angle. Accordingly, as shown in Fig. 6, the loop antenna 12 can detect the surface current of the automobile body with high efficiency by arranging the plane of its loop at an angle in the range of 45 to 90 degrees or -45 to -90 degrees to the extended center line of the metal plate of the body. The surface currents induced in the automobile body by broadcast waves are comparatively weak. In order to increase the output voltage from the loop antenna, the number of serially connected winding turns or loops of the antenna wire is increased in most cases. In other words, as shown in Fig. 7, it is evident that, when the loops A-B and the loop C-D are closely arranged with one longer side adjacent an electric conductor through which an electric current I flows, connection of C and B provides an output voltage between A and D which is twice that between either A-B or C-D, separately. However, when the antenna wire is simply wound around densely, incidental capacitance arises between the respective loops to cause an unwanted shift in the resonant frequency of the antenna, and the acuteness (Q) and sensitivity of the antenna decrease. An automobile antenna device in accordance with the present invention is based on the above described principles and findings, and an embodiment will be hereinafter described with reference to Figs. 1 and 2. Fig. 1 is a perspective illustration of an automobile antenna device in accordance with the present invention, and Fig. 2 is a sectional view taken on line II-II of Fig. 1. The automobile antenna device in Fig. 1 includes a loop antenna 102 which is internally fixed in a casing 100 of electrically conductive material to shield the loop antenna from unwanted external electromagnetic fields. The casing 100 has an elongate opening 100a to expose one longer side of each of a plurality of generally rectangular loops of the loop antenna 102. The longer sides of the loop antenna 102 exposed through the opening 100a extend lengthwise of and closely adjacent to a marginal edge portion of a metal plate of the automobile body, for example a roof rim member. It is preferable that the automobile antenna device is attached to the automobile body by the attachments 104 fixed to the casing 100 by bolts and nuts, spot welding or the like. The embodiment is characterized in that the loop antenna 102 is composed of five serially connected generally rectangular loops 102a, 102b, 102c, 102d, and 102e extending in a corresponding plurality of planes, the planes being disposed in sectorial array so that they intersect one another along a common line along the opening 100a and lie at uniform angles to one another about the common line. The sectorial array has an included angle at the common line of substantially 45° on each side of the centre line of plate 105. According to the embodiment, therefore, when the automobile antenna device is attached with the opening 100a closely adjacent, or actually receiving, the end portion of the metal plate 105 of the automobile body in order to detect the surface currents induced in the metal plate 105 by broadcast waves, one loop at least among the loops 102a to 102e can be positioned at an efficient detection angle for the surface currents, that is, at 45 to 90 degrees or -45 to -90 degrees, as is shown in Fig. 6, and the surface currents can be detected with high efficiency, despite the casing being attached at any angle. Furthermore, according to the loop antenna 102 consisting of five loops, the output voltage can theoretically be five times higher than that of an antenna with just one loop. As the respective loops are sectorially arranged, the incidental capacitance between the respective loops is extremely small in comparison with that which arises in a simple densely packed winding. The practical problems of a shift of the resonant frequency and a decrease of acuteness (Q) and sensitivity caused by the shift do not occur. In Fig. 2 it is also preferable that the metal plate 105 of the automobile body be inserted and arranged into the opening 100a to have the distance between the exposed longer sides of the loops of the loop antenna 102 and the metal plate 105 as short as possible. Consequently, the detection efficiency of the surface current is increased. The surface currents detected as described above are fed to a circuit 106 housed in the casing 100 by way of output terminals 102f and 102g of the loop antennas to be matched and amplified by circuit 106. Furthermore, the detected signal obtained in such a way is fed out by a coaxial cable not illustrated, by way of a connector 108 to be supplied to the various receivers through voltage amplifiers. Incidentally, the power source and a control signal source are connected and supplied to control the circuit 106 through a control signal wire 110. As described hereinabove, the automobile antenna device permits broadcast waves to be received with high efficiency and reliability without undue restriction of installing angles, and without externally exposing the automobile antenna device. Furthermore the automobile antenna device can be installed closely adjacent the marginal edge portion of any part of the metal plate of the automobile body where the surface currents can be produced by broadcast waves, for example a roof rim member, engine hood, or trunk lid, and preferably where the surface current flows strongly.

Claims: An automobile antenna device comprising a pick-up mounted on a metal portion of an automobile body to detect radio frequency surface currents induced in said body portion by broadcast radio frequency signals; said pick-up comprising an elongate loop antenna (102); characterized in that: said pick-up includes a casing (100) of electrically conductive material having an elongate opening (100a); said loop antenna (102) is disposed within said casing with a portion exposed through said opening and the remainder of said loop antenna is shielded from external electromagnetic fields by said casing; said loop antenna (102) comprises a plurality of serially connected generally rectangular loops (102a-102e) extending in a corresponding plurality of planes, said planes disposed in a sectorial array so that they intersect one another along a common line along said opening (100a) and lie at substantially uniform angles to one another about said common line; and said exposed portion of said loop antenna comprises one longer side of each said loop (102a-102e) which is exposed through said opening (100a) to extend lengthwise of and closely adjacent to a marginal edge portion (105) of said automobile body. A device according to claim 1 characterized in that said sectorial array of said loops (102a-102e) has an included angle at said common line of up to 45° on each side of a centre line extending perpendicularly through said elongate opening (100a). A device according to claim 1 or claim 2 characterized in that said marginal edge portion (105) of said automobile body portion is received in said elongate opening (100a). A device according to any one of claims 1 to 3 characterized in that said loop antenna consists of five said loops (102a-102e).

Inventors: KONDO, HIROSHI, OHE, JUNZO
Applicants: TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1985
Main classification: H01Q1
IPC codes: H01Q1