AUTOMOBILE ANTENNA SYSTEM

Abstract: An automobile antenna system for detecting currents induced in a vehicle body by broadcast waves and transmit­ ting the detected current signals to a receiver located in the vehicle body without externally projected antenna poles. The system comprises high-frequency pickup means longitudi­ nally disposed along and in close proximity with the marginal edge portion of the vehicle body, the pickup means being effective to detect surface high-frequency currents which are induced on the vehicle body and concentrated into the marginal edge of the vehicle body for example a vehicle roof panel, a rearwindow frame or a vehicle fender. The pickup means is spaced away from the marginal edge of the vehicle body within a range represented by the following formula: 12 × 10 ³c/f(m) where c = the velocity of light and f = carrier frequency of broadcast waves.

Description: The present invention relates to automobile antenna systems. Antenna systems are indispensable to modern automobiles which need to receive various broadcast wave signals such as radio, television and telephone signals at various receivers located in the vehicle. Such antenna systems are important also for citizen band transceivers. One of the conventional antenna systems is known as a rod or pole antenna which projects outwardly from the vehicle body. Although such a rod antenna is superior in performance in its own way, it presents obstacles against styling of vehicle bodies. Furthermore, the rod antenna is disadvantageous in that it is subject to damage, vandalism or theft and also in that the antenna becomes a cause of noise when the vehicle is driven at high speed. In recent years, there has been an increase in the number of requency bands used for broadcast or communication waves to be received at automobiles. A plurality of antennas are required according to the increased number of frequency bands. This raises other problems that the plurality of rod antennas adversely affects the aesthetic appearance of the automobile and also that the reception performance deteriorates due to electrical interference between the antennas. Efforts have been made to eliminate the rod antenna system or to conceal the same within the vehicle body. One of the proposals is that a length of antenna wire is applied to the rear window glass of an automobile. Another proposal is to utilize surface currents induced by broadcast waves on the vehicle body. This would appear to provide the most positive and efficient means for receiving broadcast wave signals. However, experiments show that such a proposal does not provide any satisfactory results. One of the reasons why surface currents induced by broadcast wave signals have not been effectively utilized is that their magnitude is not as large as expected. The prior art mainly proposed to use surface currents induced in the roof panel of the vehicle body. In spite of this, surface currents of satisfactory level have not been obtained. Another reason is that surface currents contain electrical noise of very high level. Such noise is mainly generated from the engine ignition system and the battery charging regulator and cannot be eliminated unless the engine is stopped. In such a situation, some proposals have been made to overcome the above problems. Japanese Patent Publication Sho 53-22418 describes a member of electrically insulating material located at a portion of the vehicle body on which currents are concentrated, with the currents being detected directly by a sensor connected between the opposite ends of the member. Although such a construction can detect practicable signals which are superior in S/N ratio, a pick-up used therein requires a particular cut-out in the vehicle body. This cannot be accepted in the mass-production of automobiles. Another proposal is shown by Japanese Utility Model Publication Sho 53-34826 in which an antenna including a pick-up coil for detecting currents in the pillar of a vehicle body is provided. This is advantageous in that the antenna can be completely disposed within the vehicle body. However, it is not practical that the pick-up coil used therein must be located adjacent to the vehicle pillar in a direction perpendicular to the longitudinal axis of the pillar. it also appears that such pick-up arrangement cannot obtain any practicable output signal from the antenna. The prior art antenna systems were mainly intended to receive AM band waves the wavelengths of which are too long to obtain good performance by detecting surface currents induced on the vehicle body. An object of the present invention is to make it possible to provide an automobile antenna system wherein the above described problems are overcome and which can achieve efficient reception of signals from surface currents induced in the vehicle body by broadcast wave signals in a predetermined frequency band. DE-A-1949828 describes an automobile antenna system comprising a pick-up mounted on a portion of an automobile body to detect radio frequency surface currents induced in said body portion by broadcast radio frequency signals. The present invention is characterized in that: said pick-up is adapted to detect said surface currents at a frequency above 50 MHz which have a concentrated flow along marginal edge portions of the automobile body; and said pick-up comprises elongate pick-up means extending along a said marginal edge portion substantially parallel to the edge of the marginal edge portion and is arranged to be mounted to said marginal edge portion at a distance from said edge which is less than the distance given by the formula: 12 x 10⁻³c/f(m) where c= the velocity of light and f = the carrier frequency of a broadcast wave to be picked up. The document Funkschau, vol . 49, no. 16, July 1977 at pages 714-718 describes certain results such as reception patterns when prior art antenna systems are positioned in various locations on an automobile body. Our co-pending European Patent Application under publication No. EP-A-182497 is a document of the type mentioned in Article 54(3) of the European Patents Convention, and describes a pick-up adapted to detect high frequency surface currents which have a concentrated flow along a roof pillar of the automobile body, the pick-up comprising elongate pick-up means extending along the pillar substantially parallel to the length thereof. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a schematic perspective view showing a first embodiment of an automobile antenna system according to the present invention, with an electromagnetic coupling type pick-up mounted on the rear window frame of the vehicle roof panel. Figure 2 is a plan view showing the details of the mounting of the pick-up shown in Figure 1. Figure 3 is a section through the mounted pick-up of Figure 1. Figure 4 is a section from another direction of the mounting of the pick-up of Figure 1. Figure 5 is a schematic perspective view of a second embodiment of an automobile antenna system constructed according to the present invention, with a pick-up mounted on an inner header panel in the vehicle roof. Figure 6 is a section through the mounted pick-up of Figure 5. Figure 7 is a perspective view of a third embodiment of an automobile antenna system constructed according to the present invention, with a pick-up mounted on a wheel arch of the vehicle body. Figures 8 and 9 are sectional views showing the mounting of the pick-up of Figure 7 as viewed from different directions. Figure 10 illustrates surface currents I induced on the vehicle body B by external waves W. Figure 11 illustrates a probe for determining the distribution of surface currents on the vehicle body and having the same construction as that of a pick-up used in the present invention, and a circuit for processing signals from the probe. Figure 12 illustrates the electromagnetic coupling between the surface currents and the pick-up loop antenna. Figure 13 illustrates the directional pattern of the loop antenna shown in Figure 12. Figure 14 illustrates the intensity distribution of the surface currents. Figure 15 illustrates the directions of flow of the surface currents. Figures 16, 17 and 18 are graphs showing the distribution of surface currents at various locations on the vehicle body shown in Figure 14, along the longitudinal axis of the body. Reference will now be made to Figures 10 to 18 which illustrate a process of determining the distribution of high-frequency currents so as to permit determination of locations at which an antenna system can operate most efficiently on the vehicle body of an automobile. Figure 10 shows that as external electromagnetic waves W, such as broadcast waves, are incident on the vehicle body B of conductive metal, surface currents I are induced at various locations on the vehicle at levels corresponding to the intensities of electromagnetic waves incident thereon. The present invention is concerned only with electromagnetic waves which belong to relatively high frequency bands in excess of 50 MHz, such as FM broadcast waves, television waves and others. The distribution of surface currents induced on the vehicle body by electromagnetic waves at a frequency above 50 MHz is measured to permit determination of locations on the vehicle body which are higher in surface current density and lower in noise and at which a pick-up used in the present invention is to be located. The distribution of surface currents is determined by simulation using a computer and also by measuring actual intensities of surface currents at various locations on the vehicle. The measurement is carried out by the use of a probe which can operate in accordance with the same principle as that of a pick-up actually located on the vehicle body at the desired location as will be described hereinafter. Such a probe is moved on the vehicle body over the entire surface thereof to measure the level of surface currents at various locations on the vehicle body. Figure 11 shows an example of such a probe which is constructed in accordance with substantially the same principle as that of the pick-up described hereinafter. The probe P comprises a casing of electrically conductive material 10 for preventing any external electromagnetic waves from migrating into the interior thereof and a loop coil 12 rigidly located within the casing 10. The casing 10 includes an opening 10a formed therein through which a portion of the loop coil 12 is externally exposed. The exposed portion of the loop coil 12 is positioned in close proximity with the surface of the vehicle body B to serve as pick-up means to detect a magnetic flux induced by surface currents on the vehicle body. bother portion of the loop coil 12 is connected to the casing 10 through a short-circuiting line 14. The loop coil 12 further includes an output end 16 connected to a core 20 of a coaxial cable 18. Still another portion of the loop coil 12 includes a capacitor 22 for causing the frequency in the loop coil 12 to resonate relative to the desired frequency to be measured to increase the efficiency of the pick-up. Thus, when the probe P is moved along the surface of the vehicle body B and also angularly rotated at various locations of measurement, the distribution and direction of surface currents can accurately be determined at each of the locations. In Figure 11, the output of the probe P is amplified by a high-frequency voltage amplifier 24 with the resulting output voltages being able to be read at a high-frequency voltmeter 26 and also being recorded by an XY recorder 28 to provide the distribution of surface currents at various locations on the vehicle. The input of the XY recorder 28 receives signals indicative of various locations from a potentiometer 30 to associate the value of the surface high-frequency current with the corresponding location on the vehicle. Figure 12 illustrates an angle of deflection ϑ between a surface high-frequency current I and the loop coil 12 of said pick-up. As shown, a magnetic flux  intersects the loop coil 12 to generate a detection voltage V in the loop coil 12. When the angle ϑ is equal to zero, that is, the surface current I is parallel to the loop coil 12 of the pick-up, the maximum voltage can be obtained. In addition, the direction of flow of the surface current I can be determined when the probe P is rotated to obtain the maximum voltage. Figures 14 and 15 respectively show the magnitude and direction of surface high-frequency currents induced at various different locations on the vehicle body at the frequency of 80 MHz, the values of which are obtained from measurements by the probe P and simulation by the computer. As can be seen from Figure 14, the surface currents have higher densities at the marginal edge portions of the vehicle body and lower densities at the central portions of the flat vehicle panels. It will also be apparent from Figure 15 that the surface currents have a concentrated flow along the marginal edge portions of the vehicle body including along the connections of various flat panels. A careful study of the distribution of surface currents induced at various metallic vehicle portions along the longitudinal axis of the vehicle body as shown in Figure 14, enables distribution characteristics to be obtained as shown in Figures 16 to 18. Figure 16 shows a distribution of surface currents along a trunk lid between two points A and B on said longitudinal axis. As can be seen from this figure, the surface currents have very high levels at these points A and B and decrease toward the central portion of the trunk lid from the opposite points thereof. Thus, if a pick-up is disposed near the marginal edge of the trunk lid, the concentrated current flow along that marginal edge portion can be detected. Similarly, Figure 17 shows the distribution of surface currents along the roof panel of the vehicle body, while Figure 18 shows the distribution of surface currents along the engine hood of the vehicle body. As will be apparent from these figures, very high levels of surface currents flow respectively along the marginal edge portions of the roof panel and engine hood. The value of the surface currents decreases toward the central portion of each of the vehicle sections. It is thus understood that the pick-up should be disposed at or near the marginal edge of each of the vehicle sections to catch broadcast waves with a good sensitivity. The marginal edge portions of the vehicle body include the marginal edge portions of the pillars and wheel arches as well as of the engine hood, trunk lid and roof panel. Although the loop antenna of the pick-up has to extend longitudinally of the marginal edge portion substantially parallel to the marginal edge thereof, the loop antenna has also to be positioned within a distance from the edge determined depending upon the carrier frequency of the broadcast waves to be received to obtain very practicable sensitivity. The distributions of currents shown in Figures 16 to 18 relate to vehicle currents induced by signals in the FM broadcast wave band at a frequency of 80 MHz. The value of surface currents decreases in the direction away from each of the marginal edge portions toward the corresponding central portions. Considering the range of decreased currents below 6 dB in which a good sensitivity can actually be obtained, it is understood that it becomes possible if the pick-up means is positioned within a distance of 4.5 cm from the actual edge of the marginal edge portion. Thus, a satisfactory antenna system can be provided in accordance with the present invention if a pick-up means is arranged within a distance of 4.5 cm away from the actual edge of a marginal edge portion for the carrier frequency of 80 MHz. It is found from the computer's simulation and experimental measurements that the above practicable distance depends upon the carrier frequency used. It is also recognized that the distance decreases, as the value of the carrier frequency is increased. From the fact that the practicable distance of 4.5 cm from the corresponding actual edge of the marginal edge portion is inversely proportional to the value of the carrier frequency, good results can be obtained relative to the respective values of the carrier frequency if the pick-up means is spaced away from the edge of a metallic vehicle panel within a distance represented by the following formula: 12 x 10⁻³c/f(m) where c = the velocity of light and f = carrier frequency. For example, where a carrier frequency equal to 100 MHz is to be received, a pick-up means may be disposed at a vehicle location spaced away from an actual edge of a desired marginal edge portion of the vehicle body within a distance of 3.6 cm. It will be apparent that as the value of the carrier frequency f is increased, the distance between the pick-up means and the corresponding actual edge will be decreased. Figures 1 to 4 illustrate a first embodiment of pick-up used in the present invention in which it is disposed on the marginal edge portion of the rearward area of the vehicle roof panel. Referring to Figure 1, a roof panel 32 of metals is shown to be exposed. This roof panel 32 includes a rear window frame 34 in which a rear window glass 36 is mounted and which forms a desired marginal edge portion of the vehicle body. In the illustrated embodiment, a pick-up 38 is positioned inwardly spaced away from the actual edge of the rear window frame 34 within a distance of 4.5 cm. As shown in Figure 2, the pick-up 38 includes a metallic casing 40 and a loop antenna 42 located therein and shielded from external electromagnetic fields by the casing. Therefore, this pick-up is of an electromagnetic coupling type similar to the aforementioned probe including its loop coil for measuring the distribution of surface currents on the vehicle body. Figure 3 shows the pick-up 38 rigidly mounted on the roof panel 32 which includes a roof panel portion 44. The rear window frame 34 is connected to one edge of this roof panel portion 44. The rear window glass 36 also is rigidly mounted on the roof panel portion 44 by means of a fastener 46 and seal 48 which are sealingly adhered to each other by a mass of adhesive 50. Furthermore, a molding 52 is rigidly mounted between the roof panel portion 44 and the rear window glass 36. In the illustrated embodiment, the rear window frame 34 is provided with an opening 34a into which the casing 40 of the pick-up 38 is inserted. Thus, the loop antenna 42 of the pick-up 38 can be positioned at a desired location on the marginal edge portion of the rear window frame 34. As seen from Figure 3, the casing 40 is provided with an opening 40a through which one longitudinal side of the loop antenna 42 is externally exposed. Thus, the exposed portion of the loop antenna 42 serves as pick-up means located in close proximity to the actual edge of the rear window frame 34 adjacent the window glass. Therefore, any magnetic flux induced by surface currents flowing concentratedly along the marginal edge portion of the rear window frame 34 can be picked up by the loop antenna 42. Moreover, since any external magnetic flux is shielded by the casing 40, the induced currents can more sensitively be detected by the pick-up 38. The casing 40 of the pick-up 38 can be fixed to the rear window frame 34 in position by the use of L-shaped brackets 54 and 56 which are respectively secured to opposite ends of the casing 40 and also secured to the rear window frame 34 by any suitable screws. The casing 40 of the pick-up 38 includes a circuitry 58 contained therein which is connected to the loop antenna 42. The circuitry 58 includes components such as a pre-amplifier for processing detected signals. The resulting high-frequency detected signals are fed out through a coaxial cable 60 and then processed by the same circuit as that used in measuring the distribution of surface currents. The circuitry 58 receives power and control signals through the coaxial cable 62. The loop antenna 42 is in the form of a single wound coil which is covered with electrical insulation such that the coil can be arranged in an electrically insulated relationship with and in contact with the rear window frame 34. Thus, the magnetic flux induced by the surface currents can intersect the loop antenna 42 with an increased intensity. After the pick-up has been incorporated into the exposed portion of the roof panel 32 and particularly the rear window frame 32, a roof trim 63 is rigidly mounted on the roof panel 32 while an edge molding 66 is secured to the ends of the roof trim and rear window frame 63, 34. In the present embodiment, the exposed side of the loop antenna 42 serves as pick-up means and is spaced from the actual edge of the rear window frame 34 within a distance of 4.5 cm so that the broadcast waves in the FM broadcast frequency band of 80 MHz can be detected by acquiring the surface currents having a concentrated flow along the marginal edge portion of the rear window frame 34. Since such surface currents flow in the direction along the marginal edge portion of the vehicle body as can be seen from Figure 15, the length of the loop antenna 46 is arranged in the direction along the marginal edge portion of the rear window frame 34. The first embodiment of the present invention has thus provided a very efficient antenna system for automobiles which has no visibly exposed portion and which can receive electromagnetic waves belonging to frequency bands above 50 MHz by electromagnetically detecting the surface currents flowing along the marginal edge portion of the vehicle body and particularly along the marginal edge portion of the roof panel by the use of the pick-up as described. Figures 5 and 6 show a second embodiment of the present invention in which a pick-up 138 is disposed in a service hole 64a of an inner header panel 64 on the forward end of the roof panel 32. As can be seen from Figure 6, a windshield 68 is rigidly mounted on the roof panel portion 44 of the roof panel 32 by means of a seal 66. As is well-known, a molding 72 is secured between the roof panel portion 44 and the windshield 68 by means of a stopper 70. The pick-up 138 of the second embodiment is similar to that in the first embodiment and therefore similar parts are denoted by similar reference numerals respectively increased by one hundred. As is apparent from Figure 6, a loop antenna 142 has its exposed pick-up means portion positioned inwardly away from the actual edge of the inner header panel 64 within the range of 4.5 cm. Thus, surface currents having a concentrated flow along the inner header panel 64 can be detected by the pick-up 138. Figures 7, 8 and 9 show a third embodiment of the present invention in which an electromagnetic coupling type pick-up 238 is located on the marginal edge portions defining a wheel arch 74 in a vehicle body panel since the concentrated flow of surface currents runs similarly along that wheel arch portion as will be understood from Figures 14 and 15. The pick-up 238 is positioned inwardly away from the actual edge of the marginal edge portion defining the wheel arch 74 within a predetermined distance (4.5 cm in the illustrated embodiment) such that FM broadcast waves having a frequency of 80 MHz can more efficiently be detected by the pick-up 238. In Figures 7, 8 and 9, similar parts are designated by similar reference numerals respectively increased by two hundred. In the third embodiment, the pick-up 238 includes a loop antenna 242 which is previously adhered to the inside of the wheel arch portion 74 by means of adhesive 76 with the length of the loop antenna 242 extending substantially parallel to the edge of the wheel arch portion 74. Thereafter, a liner 78 is rigidly fastened to the opposite side of the wheel arch portion 74 by any suitable means such as screws. In the third embodiment of the present invention, similarly, the pick-up is longitudinally positioned along the marginal edge portion of the metal sheet defining the wheel arch of the vehicle body. By setting the distance between the pick-up means and the actual edge of the wheel arch 74 within 4.5 cm, surface currents flowing on the vehicle body can efficiently be detected by the pick-up. Although the embodiments have been described as to the electromagnetic coupling type pick-up, the invention can similarly utilize an electrostatic coupling type pick-up which comprises a detecting electrode longitudinally disposed along the marginal edge of a vehicle sheet metal member through an air gap or electrical insulation. Between the detecting electrode and the surface of the vehicle is formed an electrostatic capacitance through which high-frequency surface currents are acquired by the detecting electrode. Furthermore, the present invention may use a pick-up of a coil type having a ferrite core which is arranged so that the core will be parallel to and in close proximity with the marginal edge of a rear window frame, inner header panel or wheel arch. A coil wound about the ferrite core is used to acquire the induced currents. It will be apparent from the foregoing that in accordance with the described embodiments, the antenna system can receive broadcast waves belonging to relatively high frequency bands above 50 MHz, such as FM frequency bands, by detecting the surface currents induced particularly along the marginal edge portions of the vehicle body. Therefore, the antenna system can effect good detection of these higher density currents and with less noise and be miniaturized without any externally visibly exposed portion.

Claims: An automobile antenna system comprising a pick-up (38) mounted on a portion (34) of an automobile body to detect radio frequency surface currents induced in said body portion by broadcast radio frequency signals; characterized in that: said pick-up (38) is adapted to detect said surface currents at a frequency above 50 MHz which have a concentrated flow along marginal edge portions of the automobile body; and said pick-up (38) comprises elongate pick-up means (42) extending along a said marginal edge portion substantially parallel to the edge of the marginal edge portion and is arranged to be mounted to said marginal edge portion (34) at a distance from said edge which is less than the distance given by the formula: 12 x 10⁻³c/f(m) where c = the velocity of light and f = the carrier frequency of a broadcast wave to be picked up. A system according to claim 1 characterized in that said pick-up (38) is mounted to the rear marginal edge portion (34) of a vehicle roof panel (32). A system according to claim 2 characterized in that said pick-up (38) comprises a metal casing (40) having an opening (40a) and a loop antenna (42) disposed within said casing with one side thereof externally exposed through said opening to form the pick-up means (42) and the remainder of said loop antenna is shielded from external electromagnetic fields by said casing. A system according to claim 3 characterized in that said casing (40) is mounted within an opening (34a) provided in a frame (34) of a rear window of the vehicle, said exposed portion of the loop antenna (42) extending along said frame substantially parallel to the edge of the frame adjacent to the rear window. A system according to claim 4 characterized in that said loop antenna (42) is in the form of a single turn loop covered with electrical insulation and the pick-up is mounted so that the insulated loop is in contact with said frame (34). A system according to claim 1 characterized in that said pick-up (138) is mounted in a service opening (64a) in an inner header panel (64) at the forward marginal edge portion of a vehicle roof panel (44). A system according to claim 1 characterized in that said pick-up (238) is mounted to the marginal edge portion (74) defining a wheel arch in a vehicle body panel.

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