Vehicle antenna system

The present invention provides a vehicle antenna system including high frequency pickup type antennas concealed within the vehicle body for receiving broadcast waves. The high frequency pickups are arranged on the vehicle body at locations spaced apart from one another, that is, at least one adjacent to the vehicle roof and the other on a trunk hinge. The antenna system also includes a diversity circuit for automatically selecting one of the high frequency pickups which is in its optimum state of reception. Each of the high frequency pickups is disposed near the marginal portion of the vehicle body such that surface high frequency currents concentratedly induced on the marginal portion of the vehicle body can be detected by the high frequency pickup. Each of the high frequency pickups includes a loop antenna or electrostatic electrode disposed near the marginal portion of the vehicle body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a vehicle antenna system and particularly 
to an improved vehicle antenna system which can efficiently detect 
broadcast waves received by the vehicle body and deliver the detected 
signals to various receivers on board the vehicle. 
2. Description of the Prior Art 
Antenna systems are essential in vehicles for positively receiving various 
broadcast waves such as radio and TV waves, and communication waves such 
as car-telephone waves. A vehicle antenna system also is very important 
for a citizen band transceiver which effects communication between a 
vehicle and another stationary or moving station. Such vehicle antenna 
systems are anticipated to perform very important functions with 
communication instruments to be standardly mounted in future vehicles. 
In the prior art, a generally used and known antenna system is the pole 
type antenna system which extends outwardly from the vehicle body and 
which provides favorable reception performance in its own way. However, 
the pole type antenna is nothing less than an obstacle vehicle design. 
Furthermore, the pole type antenna is frequently bent or damaged 
intentionally or carelessly. In addition, the pole antenna tends to 
produce unpleasant noises when a vehicle on which the pole antenna is 
mounted runs at high speeds. For these reasons, it has been largely 
desired to omit the pole type antenna from the vehicle. 
Recently, there have been allocated additional frequency bands for 
broadcast or communication waves which are to be received by vehicle 
receivers. A plurality of antenna systems are required to receive waves in 
the respective frequency bands. This further damages the aesthetic 
appearance of the vehicle. Moreover, the plurality of antenna systems 
produces an electric interference between antennas thereby degrading 
reception. 
Some efforts have been made to remove or conceal the pole type antenna. For 
example, an antenna wire is applied to the rear window glass of a vehicle. 
Another proposal has been made to detect surface currents induced by 
receiving broadcast waves at the body of a vehicle. This apparently should 
provide the most positive end efficient means for receiving broadcast 
waves. However, experiments have indicated that such a proposal was not as 
superior as was expected. 
A first problem produced when the surface currents are to be used to 
receive broadcast waves at vehicle receivers is that the surface currents 
are not as strong as expected. In the prior art, the surface currents are 
mainly utilized at the front roof of the vehicle body. In spite of this, 
no sufficient signal level could be obtained to utilize the surface 
currents. 
A second problem is that the surface currents include noises at a very 
large rate. Such noises are mainly produced by the ignition system and 
charging regulator system of a vehicle engine and thus cannot be removed 
as long as the engine runs. Therefore, the clear reception of broadcast 
waves could not be realized at all. 
Under such disadvantageous conditions, some other proposals have been made. 
For example, Japanese Patent Publication 53-22418 discloses an antenna 
system utilizing currents which are induced on the body of a vehicle. The 
antenna system comprises an electric insulation provided at a portion of 
the vehicle body in which currents are concentrated. The antenna system 
also comprises a sensor for directly detecting the currents between the 
opposite ends of the electric insulation. In such an arrangement, it is 
sure that the antenna system can detect practicable signals which are 
superior in S/N ratio. However, the antenna system requires a pickup 
structure which must be disposed in a notch intentionally formed on a 
portion of the vehicle body. This proposal cannot be applied to 
mass-production vehicles. 
Japanese Utility Model Publication 53-34826 discloses another antenna 
system comprising pickup coil means for detecting currents on the pillar 
of a vehicle. This antenna system is disadvantageous in that it can 
completely be contained within the vehicle body. However, the antenna 
system requires an undesirable arrangement wherein the pickup coil must be 
disposed near the pillar in a direction perpendicular to the longitudinal 
extent thereof. Moreover, such an arrangement cannot obtain any 
practicable antenna output and is therefore at best a poorly conceived 
idea. 
As can be seen from the foregoing, the prior art does not provide any 
proper construction and arrangement of a pickup device which are required 
to effect the efficient detection of currents flowing on the vehicle body 
and to obtain a practicable S/N ratio. Rather, experiments show that the 
antenna system utilizing currents on the vehicle body is probably 
ineffective in principle. 
Recently, TV sets are increasingly being mounted on vehicles not only to 
receive TV waves but also to display various data relating to the 
vehicles. In such vehicle TV sets, TV wave signals are separated into 
image signals and voice signals. When the vehicle is at zero speed, both 
the image and voice signals are used in the TV set. When the vehicle runs 
at speeds above a predetermined level, only the voice signals are 
outputted from the TV set. 
Such vehicle TV sets have a problem in that the quality of the image can be 
reduced since the state of reception is changed depending on the condition 
of the vehicle. 
In order to overcome such a problem, the prior art vehicle TV set comprises 
a plurality of TV antennas controlled by a diversity receiving system 
which can select optimum TV antennas depending on the state of reception. 
In such a case, a plurality of TV antennas are disposed on the body of a 
vehicle at various preselected locations. The diversity receiving system 
is electrically connected with the TV antennas such that they can 
selectively be used depending on the state of reception for image signals 
separated from received signals. The diversity receiving system is adapted 
to compare the image signal level with a reference level in synchronism 
with the vertical blanking interval of the image signals to select optimum 
TV antennas. 
The diversity receiving system also has a problem in that the construction 
and arrangement of a pickup device required to efficiently detect currents 
induced by TV waves at the vehicle body and also to obtain a practicable 
S/N ratio cannot properly be established. Particularly, a high frequency 
pickup used as a TV antenna does not have a good high frequency 
directional pattern. And yet, multi-path noises tend to be produced during 
reception of FM waves having a high frequency belonging to the VHF band. 
SUMMARY OF THE INVENTION 
In view of the above problems, it is an object of the present invention to 
provide an antenna system for small-size vehicles, which can efficiently 
detect currents induced on the body of a vehicle by receiving broadcast 
waves for use in vehicle receivers. 
Another object of the present invention is to provide a vehicle antenna 
system comprising a diversity receiving system which can efficiently 
detect currents induced on the body of a vehicle by broadcast waves for 
use in vehicle deliver vehicle-laden TV set means. 
The prior art antenna systems were intended mainly to receive AM waves. 
This resulted in a reduced characteristic of reception since the 
wavelength of broadcast waves to be received is too long. The inventors 
aimed at this dependency of frequency and normally utilized broadcast 
waves having a frequency equal to or higher than 50 MHz as waves to be 
received according to the present invention, such a frequency being higher 
than AM frequency. As a result, reception of signals can very efficiently 
be made from currents on the vehicle body. 
The inventors also aimed at the fact that such currents are distributed on 
a vehicle body in various locations at different rates. The present 
invention is thus characterized in that at least one high frequency pickup 
is provided on the vehicle body at a location wherein currents are 
concentratedly induced by broadcast waves with less noises. In preferred 
embodiments of the present invention, such a location is determined on a 
trunk hinge or roof of the vehicle body. 
In a preferred embodiment, an antenna system of the present invention 
comprises a first high frequency pickup disposed on a trunk hinge of the 
vehicle body along the length thereof, a second high frequency pickup 
arranged on a portion of the marginal edge of the vehicle roof on the same 
side of the vehicle body as the first pickup, and a space diversity 
receiving system for selectively delivering received signals from one of 
the first and second high frequency pickups. 
Where body the first and second high frequency pickups are disposed on the 
vehicle body at the right-hand side thereof, the first high frequency 
pickup will have an FM band directional pattern having a rightward and 
forward dip and a lateral dip while the second high frequency pickup will 
have a directional pattern having a high sensitivity relative to the dips 
in the first pickup. 
On the contrary, where both the first and second pickups are located on the 
left-hand side of the vehicle body, the first pickup will have a leftward 
and forward dip and a lateral dip while the second pickup will have a 
directional pattern having a high sensitivity relative to the dips in the 
first pickup. 
In such a manner, the FM band directional patterns of the first and second 
high frequency pickups complement one another with respect to the dips. 
Furthermore, signals to be received are selectively delivered to one of 
the high frequency pickups to provide a good space diversity effect since 
the pickups are spaced away from each other along the length of the 
vehicle body. 
In order to provide an efficient detection, each of the high frequency 
pickups may be in the form of a loop antenna which electromagnetically 
detects magnetic flux induced by currents on the vehicle body or an 
electrode type antenna which can electrostatically detect high frequency 
signals through an electrostatic capacity formed between the loop antenna 
and the vehicle body. 
In another preferred embodiment, an antenna system of the present invention 
comprises a high frequency roof pickup applied to a vehicle of such a type 
that it includes an edge molding mounting retainer separated from a 
marginal roof plate, for example, a rear window frame or an inner header 
panel. The retainer has a length which easily causes surface currents 
flowing on the marginal portions of the vehicle body to resonate with a 
frequency equal to or higher than 50 MHz. Namely, the length of the 
retainer is designed to be substantially equal to the wavelength of TV 
bands. 
In order to increase the concentration of currents, it is preferred that 
the retainer is spaced apart from the marginal roof plate, that is, the 
rear window frame or inner header panel by a distance equal to about 
2.times.10.sup.-3 .times.wavelength. The high frequency roof pickup 
includes a loop antenna which is disposed near said edge molding mounting 
retainer along the length thereof. 
The antenna system of the present invention also comprises a high frequency 
pickup disposed near a trunk hinge of the vehicle body along the length 
thereof. 
In such an arrangement, the roof and trunk-hinge pickups can complement 
each other with respect to their sensitivities in the characteristic or 
directional pattern of the antenna system which picks up surface high 
frequency currents induced on the vehicle body by broadcast waves. The 
entire sensitivity of the antenna system can further be improved by 
increasing the number of the roof and trunk-hinge high frequency pickups.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Location of High Frequency Pickup 
Referring first to FIGS. 18-23, there is illustrated a process of measuring 
the distribution of high frequency currents and determining the most 
efficient location at which an antenna system according to the present 
invention can preferably be mounted on the body of a vehicle. 
FIG. 18 shows the fact that when external waves W such as broadcast waves 
pass through the vehicle body of conductive metal material, surface 
currents I are induced on the vehicle body at various locations depending 
on the intensity of the external waves W. The present invention intends to 
utilize only waves having a frequency equal to and higher than 50 MHz and 
belonging to relatively high frequency bands such as FM bands, TV bands 
and others. 
In accordance with the present invention, an antenna system is 
characterized by pickup means for such particular high frequency bands, 
which is disposed on the vehicle body at a location which is determined by 
measuring the distribution of surface currents induced on the vehicle body 
and in which the surface currents are concentratedly induced with less 
noise. 
The distribution of surface currents is determined by actually measuring 
intensities of current on the vehicle body at various locations and by 
using a computer simulation. The present invention utilizes a probe 
constructed in accordance with the same principle as that of a high 
frequency pickup means which is to be disposed on the vehicle body, as 
will be described. The probe is moved through the entire surface area of 
the vehicle body while changing its orientation at each location. Thus, 
the surface currents can exactly be measured on the vehicle body 
throughout the surface area thereof. 
Referring to FIG. 19, there is shown a probe P comprising a casing 10 of a 
conductive material for preventing the influence of external waves and a 
loop coil 12 located within the casing 10. The casing 10 is provided with 
an opening 10a through which a portion of the loop coil 12 is exposed 
externally. The exposed portion of the loop coil 12 is positioned close to 
the surface of the vehicle body B such that a magnetic flux induced by the 
surface currents on the vehicle body can be detected by the loop coil 12. 
The loop coil 12 is electrically connected with the casing 10 through a 
short-circuiting line 14. The loop coil 12 includes a capacitor 22 which 
functions to resonate the frequency of the loop coil 12 with a frequency 
to be measured for an improved pick-up efficiency. 
When the probe P is moved along the surface of the vehicle body B and 
angularly rotated at each point of measurement, the distribution and 
orientation of the surface currents can be exactly determined on the 
vehicle body. Referring again to FIG. 19, the output of the probe P is 
amplified by a high frequency voltage amplifier 24 the output voltage of 
which in turn is displayed by a high frequency voltage meter 26 and at the 
same time recorded by an XY recorder 28 as a surface current value on the 
vehicle body at the respective one of various locations. The XY recorder 
28 also receives a signal indicative of the corresponding location on the 
vehicle body from a potentiometer 30. Thus, the distribution of surface 
currents on the vehicle body can be determined at the XY recorder 28. 
FIG. 20 shows a declination angle .theta. between the surface high 
frequency currents I and the loop coil 12 of the probe P. As shown, a 
magnetic flux .phi. induced by the surface currents I intersects the loop 
coil 12 to provide a voltage V to be detected at the loop coil 12. As can 
be seen from FIG. 21, the maximum voltage is provided when the declination 
angle .theta. is equal to zero, that is, when the surface currents I are 
parallel to the loop coil 12 of the probe. When the maximum voltage is 
obtained by rotating the probe P at each point of measurement, the 
orientation of the surface currents I can be known at that point of 
measurement. 
FIGS. 22 and 23 show the magnitude and orientation of the surface high 
frequency currents produced on the vehicle body at the respective 
locations by external waves having a frequency equal to 80 MHz, the 
magnitude and orientation of the surface currents being determined from 
the actual operation of the probe P and by the use of a computer 
simulation. A seen from FIG. 22, the magnitude of the surface currents 
becomes maximum at the marginal portions of the flat panels of the vehicle 
body and minimum at the central portions of these flat panels. 
As seen from FIG. 23, it is further understood that the surface currents 
are concentratedly induced in the direction parallel to each of the 
marginal edges of the vehicle body or along the connection between each 
adjacent flat panels. 
Further, by studying the distribution of the surface currents induced on 
the vehicle body along the longitudinal axis shown by the dotted line in 
FIG. 22, there are found such sectional distributions as shown in FIGS. 
24-26. 
FIG. 24 shows a sectional distribution of surface currents along a 
longitudinal section A-B on the trunk lid. As seen from this graph, the 
surface currents are maximum at the opposite ends. It is therefore 
understood that if a high frequency pickup is disposed at a portion of the 
margin of the trunk lid, for example, along one of the trunk hinges, the 
concentrated currents can effectively be detected. 
FIG. 25 shows a sectional distribution of surface currents along the front 
roof of the vehicle body and also FIG. 26 shows a sectional distribution 
of surface currents along the engine hood of the vehicle body. It is 
similarly understood that the magnitude of the surface currents becomes 
maximum at the opposite ends of the front roof or engine hood. 
It is thus apparent that good sensitivity can be provided if the high 
frequency pickup according to the present invention is disposed on the 
vehicle body near one of the respective margins thereof. 
Of course the high frequency pickup of the present invention may similarly 
be applied to a pillar or fender in place of the trunk hinge and front 
roof. 
When the high frequency pickup of the present invention is located near the 
marginal edge of the vehicle body, for example, such that the length of 
the loop antenna extends parallel to the length of the marginal edge, it 
is preferred that the pickup is spaced apart from the marginal edge within 
a range depending on the carrier frequency of broadcast waves to be 
provided to provided a very good practicable sensitivity. 
As was described hereinbefore, the sectional distributions of surface 
currents shown in FIGS. 24-26 are for FM broadcast waves having a 
frequency equal to 80 MHz. The magnitude of the surface currents decreases 
as the distance from the marginal edge of the vehicle body increases. 
Considering that a lower limit of 6 dB or less is a good sensitivity which 
can actually be provided, it is understood from FIGS. 24-26 that if the 
distance from the marginal vehicle edge is within 4.5 cm, very good 
sensitivity can be obtained. 
Therefore, the antenna system will have a sufficient performance for a 
carrier frequency of 80 MHz in practice if its high frequency pickup is 
disposed on the vehicle body at a position spaced apart from the marginal 
edge thereof within a range of distance equal to 4.5 cm. 
From results of the computer simulation and experiments, it is recognized 
that such a range of distance depends on the level of the carrier 
frequency in an inverse proportional relation therebetween. 
Thus, the present invention can be defined that a good reception can be 
obtained for each of various carrier frequencies if the distance of a high 
frequency pickup from the marginal portion of a metallic panel on the 
vehicle body is within a range: 
EQU 12.times.10.sup.-3 c/f(m) 
where c is the velocity of light and f is the carrier frequency. 
Briefly, the antenna system of the present invention will exhibit good 
reception if its high frequency pickup is disposed on the vehicle body 
near the marginal portion thereof within the aforementioned range of 
distance. 
For a carrier frequency equal to 100 MHz, the high frequency pickup is 
preferably disposed spaced from the marginal portion of the vehicle body 
within a distance equal to 3.6 cm. As the carrier frequency f increases, 
the high frequency pickup should be disposed on the vehicle body at a 
location closer to the marginal portion thereof. 
Where high frequency pickups are respectively located near the marginal 
portions of the vehicle body to receive broadcast waves as described 
hereinbefore, the high frequency pickups will have directional antenna 
patterns different from one another. 
The present invention is further characterized in that such high frequency 
pickups having different directional patterns are combined with a 
diversity receiving system to effectively receive broadcast waves under 
all traveling conditions. To this end, a diversity type antenna system 
according to the present invention comprises a first high frequency pickup 
disposed on the vehicle body at one trunk hinge along the length thereof 
and a second high frequency pickup disposed on the vehicle body near the 
marginal edge of the roof preferably on the same side as said one trunk 
hinge. 
EMBODIMENT 
Referring now to FIG. 1, there is shown a preferred embodiment of an 
antenna system according to the present invention characterized by a first 
high frequency pickup 32 disposed on the vehicle body at a right-hand 
trunk hinge 34a along the length thereof and a second high frequency 
pickup 138 disposed on the vehicle body near the right-hand marginal edge 
of the front roof 132 along the length thereof. 
FIG. 2 shows the FM directional patterns of the first high frequency pickup 
32 mounted on the right-hand trunk hinge 34a. It is apparent from this 
figure that the first high frequency pickup 32 has dips at the rightward 
and forward position and at the lateral position. 
FIG. 3 shows the FM directional pattern of the second high frequency pickup 
138 disposed near the right-hand marginal edge of the front roof 132. It 
is apparent from this figure that the second high frequency pickup 138 has 
a high sensitivity for the dip directions of the first high frequency 
pickup 32. 
Thus, by combining the first and second high frequency pickups 32 and 138 
with a diversity receiving system, the first and second pickups can 
complement each other with respect to their directional patterns to 
provide good reception of FM waves. 
The first and second high frequency pickups 32 and 138 are spaced apart 
from each other by a distance equal to about 2 meters in the longitudinal 
direction of the vehicle body. This is very effective in a space diversity 
antenna system for FM bands since the wavelength of FM waves is equal to 
about 4 meters. 
Although the embodiment shown in FIG. 1 has been described as to the 
right-hand portion of the vehicle body on which the first and second high 
frequency pickups 32 and 138 are mounted, these pickups may similarly be 
mounted on the left-hand trunk hinge and the left-hand roof portion of the 
vehicle body, respectively. In such a case, the first and second high 
frequency pickups 32 and 138 will have directional patterns completely 
inversed from those of FIGS. 2 and 3 in the right-to-left direction. 
However, the first and second pickups 32 and 138 will similarly complement 
each other with respect to their direction patterns to provide an improved 
space diversity receiving antenna system. 
With reference to FIG. 1, there will now be described a circuit for 
automatically selecting one of the first and second high frequency pickups 
32 and 138 which can more sensitively receive broadcast waves. 
The outputs of the first and second high frequency pickups 32 and 138 are 
connected with a high frequency amplifying circuit 42 through coaxial 
cables via a switch circuit 40. The switch circuit 40 is actuated by the 
output of a T-type flip flop 44 to selectively connect one of the high 
frequency pickups 32 or 138 with the high frequency amplifying circuit 42. 
The output of the amplifying circuit 42 is supplied to a detection circuit 
50 through an intermediate frequency amplifying circuit 48 which is 
connected with a local oscillator 46. At the detection circuit 50, only 
voice signals are taken out from the output signals of the high frequency 
amplifying circuit 42. 
The voice signals are then separated into right-hand output signals and 
left-hand output signals by a multiplexer 52. The right- and left-hand 
output signals are reproduced at right- and left-hand speakers 56R and 56L 
through right- and left-hand amplifiers 54R and 54L, respectively. 
The output signals from the intermediate frequency amplifier 48 are 
compared with its threshold set in a comparator 58. If the output level of 
the amplifier 48 is lower than the threshold to indicate that the 
sensitivity in either of the high frequency pickup 32 or 138 decreases 
beyond a predetermined level, the comparator 58 generates a trigger output 
used to invert the output of the T-type flip flop 44. 
When the output of the flip flop 44 is inverted, the switch circuit 40 is 
shifted to select one of the high frequency pickups 32 or 138 which can 
more sensitively receive broadcast waves. 
In such a manner, a space diversity receiving antenna system will be 
defined by the first high frequency pickup 32 on the trunk hinge 34a of 
the vehicle body and the second high frequency pickup 138 on the marginal 
portion of the front roof, the first and second pickups complementing each 
other with respect to their directional patterns to always provide the 
automatically selected antenna having good sensitivity. 
First High Frequency Pickup 
FIGS. 4-6 illustrate the details of the first high frequency pickup 32 
mounted on the trunk hinge 32a. Generally, surface currents are 
concentratedly induced on the trunk hinges by broadcast waves having a 
frequency belonging to FM bands with a density equal to or higher than 
those of other vehicle parts. This density is increased as the level of 
the frequency increases. Accordingly, surface currents can unexpectedly be 
detected from the trunk hinges which were not recognized to have surface 
currents sufficient to be detected for broadcast waves belonging to AM 
bands. The trunk hinges are advantageous in that since they are remote 
from the engine, they are difficult to be adversely affected by noises 
from the vehicle body. Therefore, the surface currents detected at the 
trunk hinges have a superior S/N ratio. 
The high frequency pickup 32 is in the form of an electromagnetic coupling 
type pickup which has a construction similar to the aforementioned probe 
including the loop coil for determining the distribution of surface 
currents on the vehicle body. 
The trunk hinge 34 is pivotally mounted at one end on the vehicle body with 
the other end thereof rigidly mounted on a trunk lid 60 to provide a pivot 
point for the trunk lid 60. The end of the trunk hinge 34 mounted on the 
vehicle body is provided with a torsion bar 62 which functions to position 
and hold the trunk lid 60 at its open state. As is well-known in the art, 
a water-tight weather strip 64 is located between the trunk lid 60 and the 
vehicle body to prevent external water from entering the interior of the 
trunk through the margin of a rear window glass 66. 
In the illustrated embodiment, the first high frequency pickup 32 is 
mounted on the outer or trunk-room side of the trunk hinge 34 and extends 
along the length of that trunk hinge. The first high frequency pickup 32 
includes a loop antenna 68 mounted therein and which is located with its 
length extending along the length of the trunk hinge 34. As was described 
hereinbefore, the loop antenna 68 can positively and efficiently catch the 
surface currents flowing on the trunk hinge 34. 
The first high frequency pickup 32 further comprises a casing 70 of a 
conductive material within which the loop antenna 68 and circuitry 
including a pre-amplifier and others are mounted. The casing 70 is 
provided with an opening facing the trunk hinge 34. The opening side of 
the casing 70 includes L-shaped fittings 74 and 76 rigidly connected 
therewith at the opposite ends. Each of the fittings 74 and 76 is rigidly 
mounted on the trunk hinge 34 by suitable screws. Thus, only a magnetic 
flux induced by the surface high frequency currents flowing on the trunk 
hinge 34 will be detected by the loop antenna 68 without any interference 
from other external fluxes. 
The loop antenna 68 extends along the length of the trunk hinge 34 and may 
preferably be curved to the curvature of the trunk hinge 34. 
The circuitry 72 is connected with a power supply and receives control 
signals through a cable 78. High frequency signals detected by the loop 
antenna 68 are taken out through a coaxial cable 80 and then processed by 
a circuit similar to that used in the aforementioned probe for determining 
the distribution of surface currents. 
The loop antenna 68 is in the form of a single electrically insulated 
winding which is in contact with the trunk hinge 34. Thus, the loop 
antenna 68 can intersect the magnetic flux induced by the surface currents 
on the trunk hinge 34. 
In such a manner, the present invention provides a very advantageous 
vehicle antenna system which can positively receive broadcast waves 
belonging to high frequency bands without external exposure. 
FIG. 6 shows another way of mounting the first high frequency pickup 32 on 
the trunk hinge 34. This is substantially the same way as that of FIG. 4 
except that the high frequency pickup is mounted on the inner side of the 
trunk hinge 34. The first high frequency pickup 32 is similarly of an 
electromagnetic coupling type and includes a casing 70 within which a loop 
antenna 68 and associated circuitry 72 are mounted. The casing 70 is 
similarly rigidly mounted on the trunk hinge 34 through L-shaped fittings 
74 and 76 by any suitable screw means. 
In such an arrangement, the first high frequency pickup 32 will not contact 
baggage and other items housed in the trunk room since the pickup 32 is 
mounted on the side of the trunk hinge 34 opposite to the trunk room. 
Second High Frequency Pickup 
Referring next to FIGS. 7-9, there is shown a second high frequency pickup 
138 disposed near the margin of the front vehicle roof. FIG. 7 shows the 
front roof 132 of a metallic material in its naked state, which roof 
includes a front window frame 134 connected with a front window glass 136 
to define a marginal edge portion of the front roof 132. 
FIG. 8 shows the details of the second high frequency pickup 138 which 
includes a metallic casing 140 for shielding any external flux and a loop 
antenna 142 mounted therewithin, with these components defining an 
electromagnetic coupling type pickup similar to the aforementioned probe 
used to determine the distribution of surface currents on the vehicle 
body. 
FIG. 9 is a cross sectional view of the second high frequency pickup 138 
mounted on the front roof 132 which includes a roof panel 144. The front 
window frame 134 is joined to the roof panel 144 at its one edge. The roof 
panel 144 also supports the front window glass 136 through a fastener 146 
and a dam 148. The fastener and dam 146, 148 are air-tightly joined 
together through an adhesive 150. A molding 152 is rigidly mounted between 
the roof panel 144 and the front window glass 136. 
A roof garnish 164 is rigidly mounted on the roof panel 144 inwardly of the 
front window frame 134 of the front roof 132 (passenger room side). The 
roof garnish 164 is connected at one edge with the corresponding edge of 
the front window frame 134 through an edge molding 166. 
An edge molding mounting retainer 168 is disposed between the front window 
frame 134 and the roof garnish 164 to support the edge molding 166. The 
retainer 168 is separated from the front window frame 134 by means of 
spacers 170 and 172. 
The loop antenna 142 of the second high frequency pickup 138 is disposed 
facing the marginal portion of the retainer 168. To this end, the front 
window frame 134 is provided with an opening 134a in which the casing 140 
of the pickup 138 is located. 
In such a manner, the second high frequency pickup 138 will have its loop 
antenna 142 disposed near the marginal portion of the retainer 168 and 
extending along the length thereof. 
The length of the retainer 168 is preselected to be equal to about a 
half-wavelength of the broadcast waves belonging to FM bands. 
As seen from FIG. 9, the casing 140 of the pickup 138 is provided with an 
opening 140a in which one longitudinal side of the loop antenna 142 is 
positioned to face the marginal portion of the retainer 168 through the 
opening 140a. 
Within the interior of the casing 140, the loop antenna 142 can positively 
catch a magnetic flux induced by the surface currents flowing on the 
marginal portion of the retainer 168. Any other external flux can 
positively be blocked by the metallic casing 140. Thus, the second high 
frequency pickup 138 can more sensitively detect the surface currents 
induced on the vehicle body by the broadcast waves. 
The casing 140 includes L-shaped brackets 154 and 156 formed thereon at the 
opposite ends such that the pickup 138 can positively be positioned 
relative to the retainer 168, as shown in FIG. 8. The brackets 154 and 156 
are rigidly secured to the front window frame 134 by any suitable 
fastening means such as screws. 
The casing 146 of the pickup 138 contains circuitry 158 connected with the 
loop antenna 142 and which includes a pre-amplifier and other components 
for processing detected signals. High frequency signals detected by the 
loop antenna 142 are taken out through a coaxial cable 160 and then 
processed by a circuit similar to that used in the aforementioned probe 
for measuring the distribution of surface currents. The circuitry 158 is 
connected with a power supply and receives control signals through a cable 
162. 
The loop antenna 142 is in the form of a single electrically insulated 
winding which is arranged in contact with the retainer 168. As a result, 
the loop antenna 142 can more sensitively detect a magnetic flux induced 
by the surface currents on the retainer 168. 
In the present embodiment, the exposed side of the loop antenna 142 through 
the opening of the casing 140 is located apart from the margin of the 
retainer 168 within a range of 4.5 cm. Thus, the loop antenna 142 can 
positively detect broadcast waves belonging radio frequency bands 
(particularly, 50 MHz-300 MHz) from the surface currents flowing on the 
marginal portion of the retainer 168. As seen from FIG. 23, the 
orientation of the flowing surface currents is along the marginal portions 
of the vehicle body. Therefore, the loop antenna 146 is located so that 
the length thereof extends along the marginal edge of the retainer 168. 
Although the embodiments of the present invention have been described as to 
the electromagnetic coupling type pickup, the present invention may 
similarly be applied to an electrostatic coupling type pickup as long as 
it can detect external waves through the detection of surface currents on 
the trunk hinges and the marginal portion of the roof, which locations 
were expected to receive broadcast waves efficiently in the prior art. 
When electrostatic coupling type pickups are used according to the present 
invention, detecting electrodes are disposed on and along the 
corresponding trunk hinge and front roof margin through air gaps or 
insulating sheets to form electrostatic capacities therebetween, 
respectively. Surface currents will be taken out by the detecting 
electrodes and then converted into audible signals in any suitable manner. 
Roof High Frequency Pickup 
Referring to FIG. 10, there is shown the entire arrangement of a diversity 
antenna comprising two high frequency pickups 232-1 and 232-2 mounted on 
the rearward edge of the roof of the vehicle body and two high frequency 
pickups 234-1 and 234-2 mounted on the trunk hinges of the vehicle body. 
The roof pickups may be disposed on the forward edge of the vehicle roof 
as shown by 232'-1 and 232'-2 in FIG. 10. 
FIG. 11 shows the roof pickup 232-1 mounted on the vehicle roof along the 
edge of the rear window. The roof panel 236 is shown in its naked state 
and as being connected with a rear window glass 240 through a rear window 
frame 238. 
The roof high frequency pickups 232-1 and 232-2 are disposed on the vehicle 
roof at the opposite ends of an edge molding mounting retainer 242, 
respectively. These pickups 232 are mounted on the vehicle roof in the 
same manner as shown in FIG. 9. 
As in the previously described embodiments, the retainer 242 is disposed 
between the rear window frame 238 and a roof garnish (not shown) to 
support an edge molding (not shown). The retainer 242 is separated from 
the rear window frame 238 by spacers (not shown) such that the surface 
currents can more concentratedly be induced on the retainer 242. 
A variable antenna sensitivity depending on the spacing between the rear 
window frame 238 and the retainer 242 is shown as a variable density of 
surface current in FIG. 12. Fron this graph, it will be apparent that the 
antenna sensitivity becomes maximum at a spacing equal to about 
2.times.10.sup.-3 .times.wavelength. Thus, the surface currents can more 
concentratedly be induced on the marginal portion of the vehicle body if 
the retainer 242 is disposed spaced apart from the rear window frame 238 
by such a spacing. 
In such a manner, the roof high frequency pickup 232 can efficiently detect 
the surface currents induced on the vehicle body. Since the retainer is 
spaced apart from the rear window frame by the spacing of about 
2.times.10.sup.-3 .times.wavelength and the length of the retainer is 
preselected to be about a half-wavelength for TV waves belonging to bands 
of 90 MHz-108 MHz, to be about one wavelength for waves belonging to bands 
of 170 MHz-222 MHz and to be about two to four wavelengths for UHF bands, 
the surface currents will much more concentratedly be induced so that the 
broadcast waves belonging to the above bands can more sensitively be 
received. 
The roof high frequency pickups 232 may be disposed on the vehicle roof 
near the front window. FIG. 13 shows high frequency pickups 232'-1 and 
232'-2 mounted on the front roof panel 248 near the front window. These 
roof high frequency pickups 232' are located within a service hole 266a 
formed in an inner header panel 266 adjacent to the marginal edge of the 
front window. 
The roof panel 248 includes a roof panel section 250 on which a front 
window glass 340 is rigidly mounted through a dam 354. A molding 358 is 
connected between the roof panel section 250 and the front window glass 
340. As in the roof high frequency pickups 232 adjacent to the rear 
window, an edge molding mounting retainer 342 is arranged between the 
inner header panel 266 and a roof garnish 260 to support an edge molding 
362. 
The retainer 342 is separated from the inner header panel 266 by spacers 
364-1 and 364-2 such that the surface currents will more concentratedly be 
induced on the retainer 342. 
A magnetic flux induced by the surface high frequency currents flowing on 
the marginal portion of the inner header panel 266 can positively be 
detected by a loop antenna 264 of the high frequency pickup 232' including 
a casing 244 within which the loop antenna 246 is mounted as described 
hereinbefore and which can positively shield any external flux of 
electromagnetic waves. 
In the embodiment of FIG. 13, the loop antenna 246 of each of the high 
frequency pickups 232' is partially exposed through the casing 244 with 
the exposed antenna part being spaced apart from the marginal portion of 
the retainer 342 within a range of 4.5 cm. The loop antenna 246 can 
efficiently detect the surface currents induced on the marginal portion of 
the retainer 342 by broadcast waves having a frequency belonging to FM or 
TV bands. As seen from FIG. 23, the orientation of the induced surface 
currents is along the marginal portion of the retainer. Therefore, the 
loop antenna 246 is arranged with the length thereof extending along the 
marginal edge of the retainer 342. 
Trunk Hinge High Frequency Pickup 
In order to complement the directional pattern of the roof high frequency 
pickups 232, other high frequency pickups are arranged on the trunk 
hinges. Surface currents having a density equal to or higher than those of 
the other vehicle parts are induced on the trunk hinges. Such a tendency 
is increased for broadcast waves having higher frequencies. Thus, the 
surface currents can be detected from the trunk hinges which was not 
expected for AM bands. 
Since the trunk hinges are remote from the engine, surface currents 
detected therefrom have less noise and thus have a superior S/N ratio. 
FIG. 14 shows the above high frequency pickups mounted on the trunk hinges 
of the vehicle body with the details thereof already shown in FIG. 4. Each 
of the trunk hinge high frequency pickups 234 is shown as being of an 
electromagnetic coupling type which includes a loop antenna for detecting 
the surface currents induced on the corresponding trunk hinge as in the 
roof high frequency pickups 232. The construction of these trunk hinges is 
similar to those of the trunk hinge previously described. Similarly, each 
trunk hinge high frequency pickup may be mounted on the corresponding 
trunk hinge at the inner side thereof rather than the outer side. As a 
result, the high frequency pickup will not contact baggage or other items 
housed in the trunk room. 
In such a manner, the present invention can provide a vehicle antenna 
system which comprises a combination of the roof pickups 232 with the 
trunk hinge pickups 234 such that the directional patterns of the roof and 
hinge pickups will be complemented by each other to provide an improved 
directional pattern. 
Reception of Broadcast Waves 
Referring now to FIG. 15, there is shown a switching circuit 288 which is 
adapted to receive the respective signals from the roof high frequency 
pickups 232-1 and 232-2 and from the trunk hinge high frequency pickups 
234-1 and 234-2 through coaxial cables 286-1-286-4, respectively. 
In the embodiment of FIG. 15, each of the high frequency pickups 232 and 
234 is adapted to receive TV waves and selected by the actuation of the 
switching circuit 288. The switching circuit 288 is actuated to select 
signals from one of the pickups and to supply them to a tuner 290. 
The tuner 290 comprises a well-known circuit including a high frequency 
amplifier 292, a local oscillator 294 and a mixer 296. Signals selected by 
the tuner 290 are then amplified by an intermediate frequency image 
amplifier 298 with the amplified signals being supplied to an image 
display circuit 300 and a voice output circuit 302, respectively. The 
output of the voice output circuit 302 is coupled with a speaker 304. 
The image display circuit 300 comprises a drive state discriminating 
circuit 306 for judging whether a vehicle is in its stop or drive state, 
and a switch 310 located between an image detection circuit 308 and an 
image amplifier 312 to selectively block the communication therebetween. 
When the drive state discriminating circuit 306 senses the stop state of 
the vehicle, the switch 310 is turned on. On the drive state of the 
vehicle, the switch 310 is turned off. 
As shown in FIG. 16, the drive state discriminating circuit 306 is adapted 
to judge the stop state of the vehicle when a parking position switch and 
a parking brake are placed on their ON positions and if the velocity of 
the vehicle is lower than a predetermined reference level. The drive state 
discriminating circuit 306 also comprises and AND gate generating 
high-level output signals which in turn are used to actuate the switch 
310. Under conditions other than the above conditions, the discriminating 
circuit 306 judges the vehicle at its running state and then causes the 
AND gate to generate low-level output signals which in turn are used to 
shift the switch 310 to its OFF state. The drive state discriminating 
circuit 306 further comprises a high pass filter and a comparator. Pulses 
indicative of the vehicle velocity are supplied to the comparator through 
the high pass filter wherein the pulses are compared with a reference 
level to judge the velocity of the vehicle. 
When the switch 310 is in its ON state under the stop state of the vehicle, 
images are displayed on a Broun tube 318 and also voices are outputted 
from the speaker 304. When the switch 310 is in its OFF state under the 
vehicle stop state, no image can be displayed on the Broun tube 318 and 
only voices are outputted from the speaker 304. 
In order that excellent images and voices can always be obtained following 
a variable reception of TV waves even when the vehicle is running, the 
present invention provides a diversity receiving system for selecting one 
of the pickups 332 and 334 depending on the variable reception of TV 
waves. 
If the output of the image detection circuit 308 becomes lower than a 
preselected level, an antenna switching circuit 320 then generates a 
switching output signal 320a which in turn is supplied to the switching 
circuit 288 which in turn selects one of the pickups having the most 
sensitivity at that time. Such selection may be carried out by utilizing 
voice detection output signals. 
The timing of the antenna switching may be in synchronism with a vertical 
synchronizing signal such that the pickups will be switched from one to 
another during a flyback term of scanning lines. The circuitry of FIG. 15 
further comprises a chromaticity circuit 314 and a synchronizing and 
deflecting circuit 316. 
In such a manner, the antenna system of the present invention can select a 
high frequency pickup having an optimum sensitivity such that the optimum 
reception of TV waves can always be made by the antenna system. The 
antenna system can further be improved by providing high frequency pickups 
respectively mounted on the roof and trunk hinge of the vehicle body such 
that their directional patterns can be complemented by each other. 
FIG. 17A shows the directional pattern of a roof high frequency pickup 
mounted on the vehicle roof adjacent to the rear window frame while FIG. 
17B shows the directional patterns of a high frequency pickup mounted on 
one of the trunk hinges of the vehicle. 
As will be apparent from FIGS. 17A and 17B, the characteristic curve a of 
the roof pickup 232 indicates the fact that the sensitivity is increased 
in a direction across the vehicle body. On the contrary, the 
characteristic curve b of the trunk hinge pickup shows that the 
sensitivity is increased in a direction along the longitudinal axis of the 
vehicle body. It is thus understood that the high frequency pickups can be 
complemented by each other in sensitivity by effecting the diversity 
reception based on these pickups. As a result, the reception of TV waves 
can be highly improved. 
It is clearly understood from the foregoing that the present invention 
provides a diversity receiving antenna system consisting of high frequency 
pickups which are respectively mounted on the roof and trunk hinges of the 
vehicle and thus have different directional patterns. Such a diversity 
receiving antenna system can receive broadcast wave with largely improved 
directional patterns and with less multi-path noises. In addition, the 
diversity receiving antenna system desirably includes no outwardly 
extending antenna since it is adapted to receive broadcast waves from 
surface currents induced on the vehicle body by the broadcast waves.