AUTOMOBILE ANTENNA SYSTEM

Abstract: An automobile antenna system mounted on a vehicle body electromagnetically detects surface currents induced on the vehicle body by broadcast waves. The antenna system includes a casing, a loop antenna and a circuitry housed in the casing. A part of the loop antenna which is exposed from an opening provided in the casing is mounted on the vehicle body in proximity to a marginal edge portion thereof. The casing has a metallic electrostatically shielded portion for housing the circuitry.

Description: The present invention relates to an automobile antenna system and, more particularly, to an improved automobile antenna system for effectively detecting broadcast radio waves received by the vehicle body and then transferring detected signals to various receivers located in the vehicle. Antenna systems are indispensable to modern automobiles which must positively receive various broadcast waves such as those for radio, television and telephone at the receivers located within the vehicle. Such antenna systems are also very important for citizen band transceivers. One of the conventional antenna systems is known as a pole-type antenna which projects outwardly from the vehicle body of an automobile. Although such a pole antenna is superior in performance in its own way, it always remains a nuisance from the viewpoint of vehicle body design. Furthermore, the pole antenna is disadvantageous in that it is subject to damage, tampering or theft and also in that the antenna acts to generate noises during high-speed driving. For these reasons, there has heretofore been a strong desire to eliminate the need for such pole antennas. With the enlargement of the frequency bands for broadcast or communication waves received at automobiles in recent years, a plurality of pole antennas have been required in accordance with each frequency band. This brings about other problems; a plurality of pole antennas damages the aesthetic appearance of the automobile and the receiving performance is greatly deteriorated by electrical interference between the antennas. Efforts have been made to eliminate the pole antenna system or to conceal the antenna from the exterior. One of such proposals has been to apply a length of antenna wire to the rearwindow glass of an automobile, and this proposal has been put into practical use. Another proposal has been to detect surface currents which are induced by broadcast waves on the vehicle body of an automobile. This means seems to be the most positive and efficient for receiving broadcast waves, but the experiments carried out to date have not provided any satisfactory results. One of the reasons why surface currents induced on the vehicle body by broadcast waves have not been utilized well is that their induced value is not as large as expected. Although the prior art mainly uses surface currents induced on the roof panel of the vehicle body, no surface currents of a satisfactory level have been obtained. Another reason is that surface currents contain noises of a very high level. Such noises are mainly generated by the engine ignition system and the battery charging regulator and cannot be eliminated unless the engine is stopped. Noises transmitted to the interior of the vehicle make it impossible to effect any practicably clear reception of broadcast waves. In such a situation, some proposals have been made to overcome the above problems. One of such proposals is disclosed in Japanese Patent Publication No. 22418/1978 in which an electrical insulation is formed at a portion of the vehicle body on which currents are concentrated, with the currents being detected directly by a sensor between the opposite ends of the insulation. Although such structure can detect utilizable signals which are superior in S/N ratio, a pickup used therein requires a particular cutout in the vehicle body. This cannot be accepted in the mass-production of automobiles. Another proposal is disclosed in Japanese Utility Model Publication 34826/1978 in which an antenna including a pickup coil for detecting currents in the pillar of a vehicle body is provided. This is advantageous in that the antenna can be disposed completely within the vehicle body. However, it is not practical for the pickup coil used therein to be located adjacent to the vehicle pillar in a direction perpendicular to the longitudinal axis of the pillar. Thus, it also appears that this arrangement cannot pick up any utilizable output from the antenna. As has been described above, the conventional antenna systems have not been successful in efficiently detecting currents induced on the vehicle body by broadcast waves. No effective measure has heretofore been proposed for overcoming the above-described principal problems of the conventional art in providing, in particular, a pickup structure for effectively detecting currents induced on the vehicle body by broadcast waves and a pickup arrangement capable of obtaining a utilizable S/N ratio. The results of various kinds of experiments show that it might in fact be basically impracticable to use an antenna system which utilizes currents flowing on the vehicle body. In view of the above-described problems of the prior art, it is an object of the present invention to provide a small-sized improved antenna system for automobiles which is capable of effectively detecting currents induced on the vehicle body by broadcast waves and then transferring detected signals to various receivers located in the vehicle and which is also capable of improving sensitivity and freedom from noise interference. It is a particular object of this invention to make it possible to provide an automobile antenna system wherein the antenna is firmly secured and held so that it does not resonate and so that its output does not suffer attenuation when the antenna is vibrated by vibration of the vehicle body, wherein contact between the antenna and a circuit base board is maintained, and wherein condensation cannot occur on the antenna even in winter. According to the present invention there is provided an automobile antenna system comprising a pick-up mounted by a bracket adjacent a sheet metal member forming a portion of the automobile body to detect radio frequency surface currents, at a frequency above 50 MHz, induced in said sheet metal member by broadcast radio frequency signals and concentrated on a marginal edge portion of the sheet metal member; said pick-up comprising casing means, an elongate loop antenna and a signal processing circuit; said casing means having an elongate opening and at least part of the casing means being formed of metal to serve as a shield against external electromagnetic fields; said elongate loop antenna being received within said casing means with one longer side of the loop antenna extending along said opening; said signal processing circuit being received within said metal shield and connected to said loop antenna to process signals picked up by said antenna; and a filling material filling the space within said casing means around said loop antenna to fix and hold the loop antenna in position. The documents EP-A-181782; EP-A-180462; EP-A-181120; EP-A-181765; EP-A-182497; and EP-A-183521 are not prior publications but may be documents of the type mentioned in Article 54(3) of the European Patent Convention. EP-A-181782 discloses and claims an automobile antenna system comprising a pick-up mounted adjacent a sheet metal member forming a portion of the automobile body to detect radio frequency surface currents, at a frequency above 50 MHz, induced in said sheet metal member by broadcast radio frequency signals and concentrated on a marginal edge portion of the sheet metal member; said pick-up comprising a casing having an elongate opening and an elongate loop antenna received within said casing with one longer side of the loop antenna extending along said opening; and said marginal edge portion of said sheet metal member also extending along said opening; said opening being in the form of a slit having depth to provide an inner portion and an outer portion, said inner portion serving to locate said one longer side of the loop antenna in position, and said outer portion serving as guide groove means to receive said marginal edge portion to locate said pick-up relative to said sheet metal member and so also to locate said longer side of the loop antenna in a predetermined position closely adjacent and parallel to said marginal edge portion. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates surface currents I induced on the vehicle body B by external waves W; Figure 2 illustrates a probe for detecting the distribution of surface currents on the vehicle body and having the same construction as that of a high-frequency pick-up used in the present invention, and a circuit for processing signals from the probe; Figure 3 illustrates the electromagnetic coupling between the surface currents I and the pickup loop antenna; Figure 4 illustrates the directional pattern of the loop antenna shown in Figure 3; Figure 5 illustrates the intensity distribution of the surface currents; Figure 6 illustrates the directions of flow of the surface currents; Figures 7, 8 and 9 are graphs showing the distribution of surface currents at various locations of the vehicle body shown in Figure 5 along the longitudinal axis. Figure 10 is a perspective view of a high-frequency pick-up including a first plastic casing for housing a loop antenna and a second metallic case housing the circuitry; Figure 11 is a fragmentary vertical sectional view of the pick-up shown in Figure 10; Figure 12 is a circuit diagram of an embodiment of the present invention in which a variable capacitor is connected to the loop antenna; Figure 13 is a fragmentary sectional view of an embodiment of the present invention in which the loop antenna is held by a filling material in the first casing; Figure 14 is a fragmentary sectional view of a still further embodiment of the present invention in which the loop antenna is located obliquely and held by a filling material in a metal casing; Figure 15 is a perspective view of a high-frequency pick-up mounted on the roof panel of a vehicle body; Figure 16 is an explanatory view of an experiment undertaken for the purpose of examining a relative angle between the metallic vehicle panel and the loop surface of the loop antenna, and how it affects the efficiency of detecting the surface currents on the vehicle body; Figure 17 is an explanatory diagram of the results of the measurements taken in the experiment shown in Figure 19; Figure 18 is an explanatory view of an automobile antenna according to the present invention in the state wherein it is attached to the roof of the vehicle body. Preferred embodiments of the automobile antenna system according to the present invention will be described hereinunder with reference to the accompanying drawings. Figures 1 to 9 illustrate a process of examining the distribution characteristics of high-frequency currents to determine a location at which an antenna system can operate most efficiently on the vehicle body of an automobile. Figure 1 shows that when external electromagnetic waves W, such as broadcast waves, pass through the vehicle body B of conductive metal, surface currents I are induced at various vehicle locations at levels corresponding to the intensities of electromagnetic waves passing therethrough. The present invention aims at only 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 the surface currents induced on the vehicle body by electromagnetic waves within the above-described particular wave bands is measured so as to seek a location on the vehicle body which is 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 a simulation using a computer and also by measuring actual intensities of surface currents at various locations on a 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 high-frequency pick-up actually located on the vehicle body at the desired location, as will be described later. Such a probe is moved on the vehicle body throughout the entire surface thereof to measure the level of surface currents at various locations on the vehicle body. Figure 2 shows an example of such a probe P which is constructed in accordance with substantially the same principle as that of the high-frequency pick-up described hereinafter. The probe P is composed of a casing of electrically conductive material 10 for preventing any external electromagnetic wave from transmitting to the interior thereof and a loop coil 12 rigidly located within the casing 10. The casing 10 includes an opening 1Oa 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 to the surface of the vehicle body B to detect magnetic flux induced by surface currents on the vehicle body B. Another 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 with a core 20 in an 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 vehicle locations. In Figure 2, the output of the probe P is amplified by a high-frequency voltage amplifier 24 and the resulting output voltage is measured by a high-frequency voltmeter 26. This coil output voltage is read at the indicated value of the high-frequency voltmeter 26 and also is recorded by an XY recorder 28 to provide the distribution of surface currents at various vehicle locations. The input of the XY recorder 28 receives signals indicative of various vehicle locations from a potentiometer 30 to recognize the value of high-frequency surface currents at the corresponding vehicle location. Figure 3 illustrates an angle ϑ of deflection between the high-frequency surface currents I and the loop coil 12 of the pick-up. As is clear from the drawing, magnetic flux  intersects the loop coil 12 to generate a detection voltage V in the loop coil 12. As shown in Figure 4, when the angle ϑ of deflection is equal to zero, that is, the surface currents I are parallel to the loop coil 12 of the pick-up, the maximum voltage can be obtained. The direction of the surface currents I when the probe P is rotated to obtain the maximum voltage can also be determined. Figures 5 and 6 respectively show the magnitude and direction of high-frequency surface currents induced at various different locations on the vehicle body at the frequency of 80 MHz, the values of which are obtained from the measurements of the probe P and the simulation effected by the computer. As can be seen from Figure 5, the distribution of surface currents has higher densities at the marginal edge of the vehicle body and lower densities at the central portions of the flat vehicle panels. It will also be apparent from Figure 6 that the surface currents are concentrated in the direction parallel to the marginal edge of the vehicle body or in the direction along the connections of various flat panels. Carefully studying the distribution of surface currents induced at various metallic vehicle portions along the longitudinal axis of the vehicle body as shown in Figure 5, distribution characteristics such as those shown in Figures 7 to 9 can be obtained. Figure 7 shows a distribution of surface currents along a trunk lid between two points A and B on the longitudinal axis. As can be seen from this drawing, the surface currents attain 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 high-frequency pick-up is disposed near the marginal edge of the trunk lid, the currents concentrating thereon can be detected. Similarly, Figure 8 shows the distribution of surface currents along the roof panel of the vehicle body while Figure 9 shows the distribution of surface currents along the engine hood of the vehicle body. As is apparent from these drawings, surface currents of a very high level flow at the marginal edges of the roof panel and the engine hood, respectively. The value of the surface currents decreases toward the central portion of each panel area of the vehicle body. It is thus understood that the pick-up should be disposed at or near the marginal edge of each of the vehicle panel areas in order to catch broadcast waves with high sensitivity. It goes without saying that the high-frequency pick-up can similarly be located on one of pillars and fenders as well as on the trunk lid, the engine hood and the roof panel. Although the loop antenna of the high-frequency pick-up is arranged longitudinally adjacent to and along the marginal edge of each vehicle panel area, this loop antenna is preferably positioned within a range determined depending upon the carrier frequency of broadcast waves in order to obtain sensitivity very suitable for practical use. The distribution of currents shown in Figures 7 to 9 relates to the currents induced on the vehicle body by FM broadcast waves having the frequency of 80 MHz. The value of surface currents decreases in accordance with the distance between the position of the surface currents and the marginal portions of the vehicle. Considering that good sensitivity can actually be obtained in the range of decreased currents below 6 dB, it is understood that such sensitivity may be realized if the pick-up is located within a distance of 4.5 cm from each marginal edge of the vehicle. Thus, a satisfactory antenna system can be provided if a high-frequency pick-up is arranged within a distance of 4.5 cm away from a marginal vehicle portion for the carrier frequency of 80 MHz. It is found from the computer's simulation and experimental measurements that the above distance which is suitable for practical use depends upon the carrier frequency used therein. It is also recognized that the distance is decreased as the value of the carrier frequency is increased. From the fact that the suitable distance of 4.5 cm from the corresponding marginal vehicle 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 high-frequency pick-up is spaced away from the marginal edge of a metallic vehicle panel within a distance represented by the following formula: 12 × 10⁻³ c/f(m) where c = the velocity of light and f = carrier frequency. In this manner, the high-frequency pick-up is located adjacent to the marginal edge of each panel area of the metallic vehicle body and is preferably disposed within said range from that marginal edge. For example, where a carrier frequency equal to 100 MHz is to be caught, a high-frequency pick-up may be disposed at a vehicle location spaced away from a desired marginal edge 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 high-frequency pick-up and the corresponding marginal edge of the vehicle body will be decreased. Figure 10 shows the external appearance of a high-frequency pick-up suitable for an automobile antenna system, and Figure 11 is a schematic vertical sectional view thereof. The pick-up shown in Figs 10 and 11 is outside the scope of the present invention. A high-frequency pick-up 32 includes therewithin a loop antenna 34 for detecting high-frequency surface currents therewithin and a circuitry 36 which is connected to the loop antenna in order to match and amplify detected signals. The high frequency pick-up 32 constituting an electromagnetic coupling type pick-up in this way is disposed in proximity to a marginal edge of the vehicle body. The high-frequency detection signal which is processed by the circuitry 36 is fed outward by a coaxial cable 38, and is processed by a circuit similar to that used for measurement of the distribution of the surface currents. A power source and a signal for controlling the circuit is supplied to the circuitry 36 from a cable 40. The high-frequency pick-up 32 is composed of a first casing 42 and a second casing 44, which protect the loop antenna 34, and the circuitry 36, and is provided with brackets 46, 48 for fastening the high-frequency pick-up 32 to the vehicle body. The first casing 42 and the second casing 44 are secured to each other, and they are disposed such that the first casing 42 protects the loop antenna 34 and the second casing 44 protects the circuitry 36. The first casing 42 is formed of a synthetic resin, and an opening 42a is formed on the side facing the marginal edge portion of the vehicle body so that a longer side of the loop antenna 34 is exposed. Therefore, the magnetic flux induced by the high-frequency current flowing at the marginal edge portion of the vehicle body is positively caught by the loop antenna 34. In addition, since the first casing 42 is made of a synthetic resin, the loop surface is not magnetically shielded and thus the magnetic flux produced at the marginal edge portion of the vehicle body can be detected over a wide range. On the other hand, the second casing 44 is made of a metal and is connected to the shield layer of the coaxial cable 38, thereby functioning as a shield and removing the influence of any noise on the circuitry 32. The brackets 46, 48 are made of a synthetic resin, and locate and firmly fix the high-frequency pick-up 32 to the marginal edge portion of the vehicle body. When the high-frequency pick-up 32 is mounted, it assumes an electrically insulated state, so that the output is increased by about 5 dB in comparison with a case where metal brackets are used. This is because they prevent the currents in the opposite direction of the high-frequency surface currents flowing at the marginal edge portion of the vehicle body from flowing into the metal casing 44 and decreasing the degree of magnetic flux which passes the loop surface. The loop antenna 34 is in the form of a single wound coil which is covered with an insulation such that the coil can be arranged in an electrically insulated relationship with and in close contact with the marginal edge portion of the vehicle body. Thus the magnetic flux induced by the surface currents can intersect the loop antenna 42 with increased intensity. In this embodiment, the side of the loop antenna 34 which is exposed from the casing 42 is disposed within a distance of 4.5 cm from the marginal edge portion of the vehicle body, whereby the FM broadcast waves of the frequency of 80 MHz can be positively detected from the surface currents flowing at the marginal edge portion of the vehicle body. Since the surface currents on the vehicle body flow along its marginal portions, as is clear from Figure 6, the loop antenna 34 in this embodiment is disposed longitudinally along the marginal edge portion of the vehicle body. As described above, in this embodiment, the surface currents flowing along the marginal edge of the vehicle body are electromagnetically detected with high sensitivity by the high-frequency pick-up, and reception in a high-frequency range is ensured without any external exposure of the antenna system. In addition, the use of synthetic resin for various components reduces the weight of the antenna as a whole. Thus this embodiment is very useful as an automobile antenna system. Fig 12 shows a variable capacitor 50 connected in series to a loop antenna 134 in a first casing 142. The frequency of the loop antenna 134 can be caused to resonate relative to a desired frequency to be measured in order to increase the efficiency of the pick-up by adjusting the variable capacitor 50 through an adjust hole formed in the first synthetic resin case 142. The signal from the loop antenna 134 is connected to a matching circuit 54, the latter matching the impedance of the signal in relation to an amplifying circuit 56 which is to be employed in a later step. The amplifying circuit 56 is connected to a battery power source through a filter 58 by a cable 140 and the output of the amplifying circuit 56 is connected with a receiver by a coaxial cable 138. Figure 13 shows an embodiment similar to that shown in Figure 11. The loop antenna in this embodiment is fixed and held by a filling material in the first case. Elements similar to those shown in Figure 11 are indicated by the correspondent reference numerals prefixed by the numeral 2. This embodiment is characterized in that a loop antenna 234 is fixed and held by a filling material 60 in a first casing 242. As is indicated by the hatched portion in Figure 13, a dielectric material having a low dielectric constant such as polyester, epoxy resin, silicone resin is formed by pouring, molding, or the like, in the gap between the casing 242 and the loop antenna 234 and integrally fixes and holds the loop antenna 234. The filling material 60 preferably has a dielectric constant of 2 to 4 in the frequency bands ranging from 70 to 1,000 MHz, and a small dielectric loss tangent. In the embodiment, ribs 64 are provided around a printed circuit base board 62 which electrically connects the loop antenna 234 and a circuitry 236, so that inclination or deformation of the printed circuit base board 62 is prevented. According to this embodiment, the loop antenna 234 is firmly secured and held, and the loop antenna 234 does not resonate at all, furthermore the output does not attenuate even when a pick-up 232 is vibrated by vibration of the vehicle body. This embodiment also prevents any probability of insufficient contact between the printed circuit base board 62 and the loop antenna 234. In addition, since the loop antenna 234 is enveloped by the filling material 60, no condensation is produced on the loop antenna 234 even in winter. Figure 14 shows still another embodiment, in which the loop antenna 234 is provided in such a manner as to be inclined in relation to the printed circuit base board 62. Such arrangement allows the loop antenna 234 to have a large loop surface and, hence, the output is advantageously increased. In the embodiment shown in Figure 14, the loop antenna 234 and a circuitry 236 is housed in a metal casing 43. Figure 15 shows a high-frequency pick-up in accordance with the invention mounted on the rear marginal edge portion of the roof panel. In the drawing, a roof panel 66 is illustrated in the exposed state, and the metallic roof panel 66 is connected to a rearwindow glass 70 with a rearwindow frame 68 as its marginal edge. In this embodiment, the high-frequency pick-up 32 is disposed within a distance of 4.5 cm inward of the rearwindow frame 70. In this case, an opening 68a is provided at a part of the rearwindow frame 68 in order to dispose the loop antenna of the high-frequency pick-up 32 such as to face the marginal edge portion of the rearwindow frame 68, and the casing 43 of the high-frequency pick-up 32 is inserted into the opening 68a. In order to locate and fix the case 43 of the high-frequency pickup 32 in relation to the rearwindow frame 68, L-shaped brackets 72 and 74 are connected to both side surfaces of the casing 43 by bolts or the like. These brackets 54 and 56 are screwed to the rearwindow frame 68. The loop antenna is in the form of a compound wound coil which is covered with an insulation such that the coil can be arranged in an electrically insulated relationship with and in close contact with the rear window frame 68. Thus, the magnetic flux induced by the surface currents can intersect the loop antenna with increased intensity. In this embodiment, the loop antenna is disposed within a distance of 4.5 cm from the edge portion of the rearwindow frame 68, whereby the FM broadcast waves of the frequency of 80 MHz can be positively detected from the surface currents flowing at the marginal edge portion of the rearwindow frame 68. Since the surface currents on the vehicle flow along its marginal portions, as is clear from Figure 6, the loop antenna is disposed longitudinally along the marginal edge portion of the rearwindow frame 68. As described above, in this embodiment, the surface currents flowing along the marginal edge of the vehicle, especially along the marginal edge portion of the roof panel, are electromagnetically detected with high sensitivity by the high-frequency pick-up, and reception in a high-frequency range is ensured without any external exposure of the antenna system. Fig. 16 shows a state in which the loop antenna 334 is located in proximity to a metallic vehicle panel a. The angle of degrees between the loop surface of the loop antenna 334 and the prolongation of the center line of the metallic vehicle panel a was varied successively in this state, to examine how it affects the efficiency of detecting the surface currents flowing on the metallic panel a. The results of the measurements are shown in Figure 20. It will be understood from the graph that the efficiency in detecting the surface currents is very good when the angle ϑ between the loop surface of the loop antenna 334 and the prolongation of the center line of the metallic panel a is within the range of 45 to 90 degrees or -45 to -90 degrees, and that the efficiency is lowered if any other angle is employed. In other words, with reference to Figure 19, the surface currents are detected with high efficiency if the loop antenna 334 of the automobile antenna system is arranged such that the loop surface thereof makes an angle of 45 to 90 degrees or -45 to -90 degrees with respect to the prolongation of the center line of the metallic panel a. It is known that the efficiency of the loop antenna in picking up the magnetic flux induced by the surface currents on the vehicle body is decreased directly in proportion to the square of the distance between the metallic panel and the loop antenna. Therefore it is requested that the loop antenna 334 is arranged in close proximity to the metallic vehicle panel. As described above, it will be understood that the position of the loop antenna and further, the state in which the automobile antenna system is mounted lend great influence on the efficiency with which the surface currents induced on the metallic vehicle panel by broadcast waves are detected. Brackets having slots for adjusting the retaining position of screws may be secured to the shield casing through these slots, thereby enabling the positional relationship between the automobile antenna system and the metallic vehicle panel to be adjusted as desired, and, hence, the antenna system to be attached such as to efficiently detect the surface currents induced by broadcast waves and flowing through the metallic vehicle panel. Thus this dispenses with the need for an externally exposed pole antenna as employed in the prior art, or the like and provides a small-sized automobile antenna of high performance. Furthermore, since the same antenna is usable for various kinds of automobiles and positions of mounting, mass production and, hence, reduction in costs are enabled. Figure 18 shows an automobile antenna system according to the invention in the state of being attached to the vehicle roof. A rearwindow glass 82 is connected to the rear marginal edge of a roof panel 78 through a water sealing dam 80 and, the external marginal edge of the rearwindow glass 82 is, as is known, enveloped with a molding 86 with one end thereof secured to a stopper 84 which is provided on a roof panel 78. The marginal edge portion of a roof strip 88 on the side of the rearwindow glass is opposed to the inside of the roof panel 78, and is bonded with the roof panel 78 by spot welding or the like. Therefore, the surface currents induced on the roof panel 78 by broadcasting waves flow not only on the roof panel but also on the roof strip 88 after being transmitted directly or diffracted. The automobile antenna system shown in Figure 18 is mounted in such a manner that the surface currents induced on the roof strip 88 by broadcast waves are detected with high efficiency. The marginal edge portion 88a of the roof strip 88 is bent in such a manner that it makes an angle of 45 degrees in relation to the loop surface of the loop antenna 334, in other words, such that ϑ= 45 in Figure 16, and the automobile antenna system is mounted such that the loop antenna 334 is opposed to the marginal edge portion 88a of the roof strip in proximity thereto. The automobile antenna system is supported by a bracket 346 which is attached to the side surface of a shield casing 343, and that portion of the bracket which is attached to the vehicle body is fastened to the marginal edge portion 88a of the roof strip 88 by a screw 90.

Claims: An automobile antenna system comprising a pick-up (232) mounted by a bracket (46) adjacent a sheet metal member (68,88a) forming a portion of the automobile body to detect radio frequency surface currents, at a frequency above 50 MHz, induced in said sheet metal member by broadcast radio frequency signals and concentrated on a marginal edge portion of the sheet metal member; said pick-up (232) comprising casing means (242,244), an elongate loop antenna (234) and a signal processing circuit (236); said casing means (242,244) having an elongate opening (242a) and at least part of the casing means being formed of metal to serve as a shield against external electromagnetic fields; said elongate loop antenna (234) being received within said casing means with one longer side of the loop antenna extending along said opening (242a); said signal processing circuit (236) being received within said metal shield and connected to said loop antenna (234) to process signals picked up by said antenna; and a filling material (60) filling the space within said casing means around said loop antenna to fix and hold the loop antenna in position. An automobile antenna system according to claim 1 characterized in that said casing means (242,244) comprises first and second casings secured to one another, said first casing (242) being formed of a synthetic resin and receiving said loop antenna (234), said second casing (244) being formed of metal to serve as said shield and receiving said signal processing circuit (236). An automobile antenna system according to claim 1 or claim 2 characterized in that said filling material (60) is a dielectric material. An automobile antenna system according to claim 3 characterized in that said dielectric filling material (60) has a dielectric constant in the range of from 2 to 4 in the frequency band of from 70 to 1000 MHz. An automobile antenna system according to any one of claims 1 to 4 characterized in that said bracket (46) is formed of a synthetic resin. An automobile antenna system according to any one of claims 1 to 5 characterized in that said bracket (46) has a slot and a screw extends through said slot to permit adjustment of the mounting position of the pick-up (232) to the vehicle body. An automobile antenna system according to any one of claims 1 to 6 characterized by a variable capacitor (50) connected in series with said loop antenna (234).

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