Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
GLASS ANTENNA DEVICE FOR VEHICLE AND
RADIO RECEIVER APPARATUS USING THE SAME
Technical Field
The present invention relates to glass antenna devices
for use on motor vehicles and radio receiver apparatus using
such glass antenna devices.
Background Art
Today, glass antenna devices, which comprise antenna
conductor elements formed on a window glass of a motor vehicle,
are being used more popularly than the traditional rod antennas
primarily due to the facts that the glass antenna devices are
esthetically superior because they not protrude outside the
motor vehicle, they are very unlikely to be damaged, and they
do not produce air-cutting sounds.
In many cases, the glass antenna device is installed on
a vehicle's rear window glass where a defogging heater unit is
provided; thus, the antenna conductor elements must be provided
on a limited area of the rear window glass, so as not to
overlap the defogging heater unit. Particularly, where the
glass antenna device is to be provided for radio communications
using the AM, FM, TV, cellular telephone frequency bands, etc. ,
designing and adjusting the glass antenna device tend to be
cumbersome and time-consuming work.
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For example, if a same pattern of antenna conductor
elements is to be used as a dual-purpose antenna for reception
of both AM signals and FM signals, then the antennal pattern
would become very complicated in structure (see, for example,
Japanese Utility Model Publication No. HEI-1-59309). It has
been conventional to adjust such a complicated antenna pattern
on a trial-and-error basis, which also tends to be time-
consuming work. Especially, because the receiving sensitivity
in the AM band is generally proportional to the area occupied
by the AM antenna pattern on the vehicle window glass, it is
important to reserve a large area for the antenna pattern on
the window glass if high receiving sensitivity is to be
obtained.
Therefore, it has been proposed to arrange the defogging
heater unit to also function as an AM antenna on the vehicle
rear window; however, using the defogging heater unit directly
as the AM antenna would produce a problem of unwanted noise and
thus can not suit practical use.
For that purpose, some of the known vehicle glass
antenna devices employ, in between a power source and the
defogging heater unit, a choke coil capable of bearing great
electric currents so that the heater unit can be used also as
an AM antenna, as typically disclosed in Japanese Patent Laid-
Open Publication No. SHO-56-42401. In addition, there has been
used a dual-purpose glass antenna device capable of receiving
both AM signals and FM signals using the above-mentioned
arrangements (e.g., Japanese Patent Laid-Open Publication No.
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SHO-57-188102).
However, the provision of the choke coil would require
an extra cost and mounting space, so that there has been a
demand for a more sophisticated glass antenna device that can
work appropriately with no choke coil.
For example, Japanese Utility Model Publication No. SHO-
59-3604 discloses such a sophisticated vehicle glass antenna
device. As shown in Fig. 11, the disclosed vehicle glass
antenna device 101 is installed on a vehicle rear window glass
102 and includes an AM antenna 104 provided above a defogging
heater unit or defogger 103. In this glass antenna device, the
defogger 103 is arranged to also function as an FM antenna 105,
and the AM antenna 104 and FM antenna 105 are connected to a
radio receiver apparatus (not shown) via respective amplifiers
108 and 109. The defogger 103 and a power feeding point 105b
are connected in series with each other via a lead 120.
The No. SHO-59-3604 publication has a description which
reads "the above-mentioned defogger is connected to a lead of
a suitable length such that an impedance matching is effected
to allow the defogger to work as an FM antenna section". No
subsidiary FM antenna is provided in the vehicle glass antenna
device according to the No. SHO-59-3604 publication.
Importantly, no choke coil is provided between the
defogger 103 and a power source 106 in the vehicle glass
antenna device of the No. SHO-59-3604 publication. However, in
this disclosed vehicle glass antenna device, a large space can
not be allocated to the AM antenna; thus, an amplifier is used
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here to enhance the receiving sensitivity of the AM antenna
installed in the limited space.
Further, U.S. Patent No. 4,791,426 discloses an antenna
device provided on a rear window glass of a motor vehicle. As
shown in Fig. 12, the disclosed antenna device 201 includes an
antenna 204 for reception of long-wave, medium-wave and short-
wave signals, and a plurality of defogging heater elements 203
capable of also functioning as an antenna 205 for reception of
ultra-short-wave signals. The signals received via the
antennas 204 and 205 are coupled via respective amplifiers 208
and 209 to a radio receiver apparatus (not shown) . In Fig. 12,
reference numeral 210 represents a frequency separator.
Further, as regards an amplifier circuit for use in a
glass antenna, Japanese Patent Laid-open Publication No. SHO-
53-97353 teaches an antenna device where a field effect
transistor is connected to a glass antenna and used as a
preamplifier to minimize spurious reception.
The above-discussed vehicle window glass antenna devices
of Japanese Patent Laid-Open Publication Nos. SHO-56-42401 and
SHO-57-188102 and U.S. Patent No. 4,791,426 all employ a choke
coil between a bus bar and a D.C. power source. The provision
of the choke coil, however, would present the problems that the
antenna device can not be readily installed in a limited space
of a vehicle window glass and the overall costs of the antenna
device increase due to the extra cost of the choke coil.
Furthermore, in U.S. Patent No. 4,791,426, the defogger
is used also as the FM antenna, which, however, is not
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practical because power is supplied to the defogger directly
from the power feeding point 205b and thus a sufficient FM
receiving sensitivity can not be attained.
In the antenna device of Japanese Utility Model
Publication No. SHO-59-3604, the defogger is used as the FM
antenna 105 without such a choke coil provided between the
defogger and the power source. Unlike in the AM frequency
band, the defogger may be allowed to operate properly in the FM
frequency band without the provision of the choke coil.
However, because the defogger and power feeding point 105b are
connected directly by the lead 120, there would arise the
problem that a sufficient FM receiving sensitivity can not be
attained. Thus, currently, the antenna device as disclosed in
Japanese Utility Model Publication No. SHO-59-3604 has not yet
been put to actual use. In addition, as shown in Fig. 11, the
lead 120 has a length greater than one half of the width of the
window glass.
Moreover, with the above-discussed vehicle window glass
antenna devices provided with amplifiers, the amplifiers may
produce an unwanted distortion in their output FM signals due
to an excessive gain when the input or received FM signals are
of high level (great electric field intensity). In addition,
when received FM signals having similar or close frequencies
are amplified, the glass antenna devices with amplifiers would
present the problem that, these FM signals may be mutually
modulated with each other and a resultant mutually-modulated
signal, corresponding to a difference between the close
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frequencies, may assume a frequency belong to the AM frequency
band and thereby exert undesired influences on the reception of
FM signals.
Further, with the vehicle window glass antenna device
disclosed in U.S. Patent No. 4,791,426, there is a need to use
a low-capacity, thick and heavy coaxial cable. Such a thick
and heavy coaxial cable provides a very poor handling
flexibility and thus is difficult to lay in place, thereby
presenting a significant obstacle to assemblage of the antenna
device.
Further, due to the fact that a combination of required
signal receiving performance and signal receiving band, as well
as a vehicle body shape, differs for each type of motor
vehicle, it has been necessary to design a different glass
antenna for each motor vehicle type, which would take much time
and labor.
In addition, in the case where a combination AM and FM
antenna pattern is to be employed, a great amount of time would
generally have to be spent in adjusting the antenna pattern
before and after actual use thereof.
Besides, even with motor vehicles of a same type, it is
normally necessary to modify the antenna pattern in case
available frequency bands differ among places to which the
vehicles are shipped (i.e., destinations) and adjust the
antenna pattern depending on presence/absence of a rear
windscreen wiper, which would take even greater time and
labor.
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Furthermore, in view of the fact that the time period
allocated for developing motor vehicles has been made shorter
and shorter these days, there is a demand that the time period
for adjusting the design of the glass antenna using an actual
vehicle body be shortened at the development stage of the glass
antenna.
Therefore, there is currently a demand for an improved
vehicle window glass antenna device which can be applied to
various different types of motor vehicles without the basic
design of its antenna pattern having to be changed and is thus
readily adjustable in accordance with the various different
types of motor vehicles.
Disclosure of the Invention
In view of the foregoing, it is a first object of the
present invention to provide a vehicle window glass antenna
device which is cable of receiving AM and FM waves with high
sensitivity without using a choke coil.
It is a second object of the present invention to
provide a vehicle window glass antenna device which can be used
appropriately in various places or destinations by just
modifying its frequency setting. It is yet another object of
the present invention to provide a vehicle window glass antenna
device which can be applied appropriately to various types of
motor vehicles, without a need to change the basic design of
its antenna pattern, as long as the size and mounting areas of
the window glass are similar between the vehicle types.
'15-0~-2001 oy : y I U f1 i ' C ; I v' ~ ~ U ~ ~ d,..-
_I= ,~0,~,~n?g~;
CA 02373258 2001-11-06
It is a third object of the present invention to provide
a vehicle window glass antenna device which does not produce an
unwanted signal distortion in response to an input signal of a
strong electric field and which can avoid a mutual modulation
between received FM signals of close frequencies.
It is a fourth object of the present invention to
provide a vehicle window glass antenna device in which there
can be employed a thin .coaxial cable that is easy to handle and
lay in position.
~0 According to one aspect of the present invention, there
is provided a vehicle window glass antenna device comprising:
a defogging heater unit provided on a window glass of a
vehicle, the defogging heater unit being of the type having no
choke coil; an AM antenna provided above the defogging heater
unit for receiving a signal of an AM frequency band, the AM
antenna comprising a plurality of horizontal antenna conductor
elements each having a length in a range of 800 mm to 1300
mm; an FM antenna provided between the defogging heater unit
and the AM antenna for receiving a signal of an FM frequency
band, the FM antenna comprising a single horizontal antenna
conductor element having a length in a range of 300 mm to 500
mm; AM amplifier means for amplifying the signal received via
the AM antenna; and FM amplifier means for amplifying the
signal received via the FM antenna.
In the vehicle window glass antenna device of the
present invention, the defogging heater unit is capacitively
coupled with the FM antenna to function as a subsidiary FM
AMENDED SHEET
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,~'= 000''Jv282_
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antenna.
The vehicle window glass antenna device of the present
invention may further comprise a separate subsidiary FM antenna
provided below the defogging heater unit. In this case, the
subsidiary FM antenna constitutes a diversity antenna with the
above-mentioned FM antenna provided between the defogging
heater unit and the AM antenna functioning as a main antenna.
The AM antenna may also include a short-circuiting line
interconnecting the plurality of horizontal antenna conductor
3.D elements .
Further, the defogging heater unit may comprise a
plurality of heater lines and a short-circuiting line
interconnecting these heater lines.
It is preferred that the .AM amplifier comprise an
electric circuit including a common.-source FET (Field Effect
Transistor) and have an input impedance of at least 1 MQ. The
AM amplifier may include a choke coil provided at its output
stage and have an output impedance of 100 c or less.
in a preferred implementation, the FM amplifier
comprises an electric circuit including a grounded-base
transistor or grounded-gate FET. Preferably, the FM amplifier
has an input impedance of 50 9 or less. Further, the FM
amplifier preferably has a gain of 3 d8 or less. In addition,
the FM amplifier may include, at its output stage, a filter in
the form of a tank circuit Which acts to prevent generation of
a mutually-modulated signal of the AM frequency band through a
mutual modulation between a plurality of output FM signals from
AMENDED SHEET
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the FM amplifier.
According to another aspect: of the present invention,
there is provided a r~ac~io receiver apparatus for a vehicle
which comprises : a defogging heater unit provided on a window
glass of a vehicle, to.e: defogging heater unit. being of the
type having no choke coil; an AM antenna provided above the
defogging heater unit for receiving a signal of an AM
frequency band; an FM antenna provided between the defogging
heater unit and the AM antenna for receiving a signal of an FM
frequency band, the FM antenna comprising a single horizontal
antenna conductor element; an AM amplifier for amplifying the
signal received via the AM antenna ; an FM amplifier for
amplifying the signal xece.ived via the FM antenna; and a radio
receiver connected. witr:~ re:~pective output terminals of the AM
amplifier and FM ampl:if_ier via a signal-transmitting cable
having a diameter of 3 mrn o:r less .
In the radio rece~.v~~r apparatus of the present invention,
it is preferrE~d that the signal-transmitting cable have an
impedance of 75 S2 or less .
The present invention is based on the following basic
designing policies.
First of ,~11, eaclu of the AM and FM antennas is designed
as a dedicated simple antenna pattern so that basic designing
and adjustment of the _:~hl and FM antennas can be substantially
facilitated.
Second, the defogging heater unit is equipped with no
choke coil and therefore can not be used as an AM antenna in
the present invention. Th,,.~s, a separate AM antenna pattern
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having as large an area as possible is provided in a space
above the defogging heater unit in such a manner that the AM
antenna pattern is not capacitively coupled with the defogging
heater unit.
Lowering the impedance of the AM antenna is very
effective in enhancing the receiving sensitivity of the AM
antenna. To lower the impedance of the AM antenna, it is
preferred that the area and length of the AM antenna conductor
pattern be maximized so as to provide a greatest possible
antenna capacity. This is why the AM antenna pattern having as
large an area as possible is provided in a space above the
defogging heater unit in such a manner that the AM antenna
pattern is not capacitively coupled with the defogging heater
unit.
Because there is not a very great available space above
the defogging heater unit on the vehicle window glass, it is
preferred that the AM antenna comprise a plurality of
horizontal antenna conductor elements connected together to
constitute a fork-shaped AM antenna pattern. Alternatively,
the AM antenna may comprise a plurality of antenna conductor
elements connected to form a loop-shaped AM antenna pattern.
It is also preferred that the fork-shaped or loop-shaped AM
antenna pattern include a short-circuiting line extending
centrally across the antenna pattern.
Further, to improve the receiving sensitivity of the AM
antenna provided in the limited space above the heater unit, it
is necessary to minimize the reception loss of the antenna; to
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this end, there is a need to feed power separately to the AM
and FM antennas.
In this case, it is preferable that the AM antenna
pattern have as large an area as possible, as noted earlier.
Flexibility in choosing a vertical dimension of the AM antenna
pattern is limited inevitably by factors such as the size of
the vehicle window glass, region where the defogging heater
unit is installed and necessary spacings between the AM
antenna, FM antenna and defogging heater unit. Thus, to
maximize the area of the AM antenna pattern as desired, the
horizontal dimension or length of the antenna pattern has to be
increased.
But, it is also important to make arrangements for
preventing the AM antenna from adversely influencing the
receiving sensitivity of the FM antenna. Experiments have
shown that a desirable horizontal dimension of the AM antenna
pattern that will not adversely influence the receiving
sensitivity of the FM antenna is in the range of 800 mm - 1,300
mm and more preferably 900 mm - 1,200 mm.
In the present invention, the FM antenna is constructed
as follows.
Namely, the inventive glass antenna device includes a
single horizontal FM antenna conductor element disposed between
the defogging heater unit and the AM antenna. The reasons why
the FM antenna comprises only one horizontal antenna conductor
element are to make the shape of the FM antenna as simple as
possible in order to facilitate necessary adjustment of the FM
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antenna, and to make the area of the FM antenna as small as
possible in order to allow the area of the AM antenna to be
maximized.
In a preferred implementation of the invention, the
length of the above-mentioned FM antenna is determined in
accordance with the following mathematical expression:
LFM = A / 4 x contraction ratio Expression (1)
where ?~ represents a designed wavelength. As may be known,
the FM frequency band is 76 - 90 MHZ in Japan and 88 - 108 MHZ
in North America, and the designed wavelength is selected from
among such FM frequency bands. Here, the "contraction ratio"
can generally be defined by the following mathematical
expression:
contraction ratio - (electrical wavelength reflecting
a dielectric effect / free-space wavelength) x 100 0)
Expression (2)
Generally, in the glass antennas, an antenna pattern is
provided on a dielectric substance in the form of a glass
sheet. Thus, the dielectric effect produced by the glass sheet
allows the antenna pattern to work effectively even when the
pattern length is shorter than a given length calculated on the
basis of the wavelength 1~.
It is also preferred that the FM antenna pattern be
capacitively coupled with the defogging heater unit. Note that
the inventive glass antenna device includes no choke coil
between the defogging heater unit and a power source. However,
in the inventive glass antenna device where the FM antenna
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pattern and defogging heater unit are capacitively coupled with
each other, there would not arise the inconveniences as
presented by the device of Japanese Utility Model Publication
No. SHO-59-3604 having been discussed earlier, and the
defogging heater unit can be used appropriately as a subsidiary
FM antenna. As a consequence, the inventive glass antenna
device achieves an enhanced FM-wave receiving sensitivity.
Because the FM antenna pattern and defogging heater unit are
capacitively coupled with each other, the above-mentioned
contraction ratio must be determined taking the antenna's
coupling capacitance into account.
The FM antenna employed in the inventive glass antenna
device comprises only a single horizontal antenna conductor
element that is therefore very simple in construction. Thus,
the vehicle window glass antenna device of the invention can be
used appropriately in various places or destinations of
different frequency bands, by just modifying its frequency
setting and changing the length of the FM antenna. Namely,
with the inventive vehicle window glass antenna device, there
is no need to change or adjust the shape of the FM antenna.
Further, if necessary, there may be provided a
subsidiary FM antenna below the defogging heater unit on the
vehicle window glass. In this case, the subsidiary FM antenna
may be constructed to function as a diversity antenna with the
FM antenna provided between the defogging heater unit and the
AM antenna functioning as a main antenna. Preferably, such a
subsidiary FM antenna comprises a single horizontal antenna
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conductor element, for the same reason as stated above in
relation to the main FM antenna. The subsidiary FM antenna may
also be capacitively linked with the defogging heater unit.
The length of this subsidiary FM antenna may also be determined
in the same manner as set forth above in relation to the main
FM antenna.
To enhance the FM-wave receiving sensitivity, it is
preferred that the defogging heater unit include a short-
circuiting line extending substantially centrally across its
heater elements or lines to interconnect the heater lines at
their substantial central points. The short-circuiting line
acts to control coupling, in a high-frequency operating state,
of distributed capacitance of the main FM antenna, defogging
heater unit and subsidiary FM antenna, to thereby enhance the
overall receiving sensitivity of the FM antennas. Two or more
short-circuiting lines, rather than just one, may be provided
in the defogging heater unit.
The AM amplifier employed in the inventive glass antenna
device is constructed as follows.
In the inventive glass antenna device, the defogging
heater unit occupying a large area on the window glass is not
constructed to also function as an AM antenna, and therefore a
separate AM antenna is provided in the limited space above the
defogging heater unit. Thus, the separate AM antenna can not
have a sufficiently large area, so that the receiving voltage
can not be increased sufficiently. The AM amplifier is
provided to make up for the shortage of the receiving
voltage.
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In the inventive glass antenna device, the AM amplifier
comprises a semiconductor element such as a transistor or FET,
resistor, coil and capacitor, so as to amplify a received
signal of the AM frequency band and match input and output
impedances of the amplifier. It is preferred that the AM
amplifier has a high output impedance and a low output
impedance. For that purpose, a high-frequency transformer may
be provided at the output stage of the AM amplifier, so as to
cause the output impedance to be 1,000 S2 or less.
On the other hand, the FM amplifier employed in the
inventive glass antenna device is constructed as follows.
The FM amplifier comprises a semiconductor element such
as a transistor or FET, resistor, coil and capacitor, so as to
amplify a received signal of the FM frequency band and match
input and output impedances of the amplifier. It is preferred
that the FM amplifier have low noise in order to increase its
S/N ratio. Further, in order to properly receive an input
signal of great electric field intensity, it is also preferred
that the FM amplifier comprise a grounded-gate circuit using a
low-noise FET and be set to a gain of 3 dB (i.e., an
amplification rate of one) or less. Preferably, the FM
amplifier has an input impedance of 50 ~2 or less.
It is also preferred that the FM amplifier include, at
its output stage, a filter in the form of a tank circuit which
can prevent generation of a mutually-modulated signal of the AM
frequency band through a mutual modulation between a plurality
of output FM signals from the FM amplifier. Alternatively, the
FM amplifier may comprise a grounded-base circuit using a low-
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noise transistor.
As set forth above, the inventive glass antenna device
is characterized in that it includes dedicated FM and AM
antennas and dedicated amplifiers are provided respectively for
the FM and AM antennas; thus, the inventive glass antenna
device can receive both FM-wave signals and AM-wave signals
with superior sensitivity.
In addition, in the vehicle radio receiver apparatus
employing the inventive glass antenna device, the AM and FM
amplifiers can be set to sufficiently low output impedances,
which allows the antenna device to be connected to the radio
receiver apparatus using a signal-transmitting cable having a
diameter of just 3 mm or less. Such a signal-transmitting
cable ( typically, a coaxial cable ) having a diameter of 3 mm or
less is very pliable and can be handled with utmost ease, so
that the coaxial cable can be readily laid in place on the
vehicle. Specific examples of the signal-transmitting cable
include ones commonly known as "1.5C2N" (about 2.3 mm in
diameter) or "1.5C2V" or "1.5C2E" (about 2.9 mm in diameter)
(applicable standard: JIS C 3501).
Brief Description of the Drawings
Fig. 1 is a diagram showing a basic structure of a
vehicle window glass antenna device in accordance with an
embodiment of the present invention.
Fig. 2 is a diagram showing a basic structure of a
vehicle window glass antenna device in accordance with another
embodiment of the present invention.
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Fig. 3 is a diagram showing a basic structure of a
vehicle window glass antenna device in accordance with still
another embodiment of the present invention.
Fig. 4 is a circuit diagram illustrating an embodiment
of an AM amplifier employed in the present invention.
Fig. 5 is a graph showing variations in noise that occur
as the value of a gate resistance is varied.
Fig. 6 is a circuit diagram illustrating an embodiment
of an FM amplifier employed in the present invention.
Fig. 7 is a block diagram showing a basic construction
of a synthesizer section employed in the present invention.
Fig. 8 is a diagram illustrating an exemplary circuit
organization of the synthesizer section.
Fig. 9 is a view showing a specific example of antenna
patterns employed in the vehicle window glass antenna device of
the present invention.
Figs. 10A and lOB are diagrams explanatory of two
different FM antenna constructions selectively usable depending
on presence/absence of a connecting lead.
Fig. 11 is a diagram explanatory of a prior art glass
antenna device (Japanese Utility Model Laid-open Publication
No. 59-3604).
Fig. 12 is a diagram explanatory of another prior art
glass antenna device (U. S. Patent No. 4,791,426).
Best Mode for Carrying Out the Invention
Several preferred embodiments of the present invention
will be described hereinafter with reference to the
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accompanying drawings.
Referring first to Fig. 1, a vehicle window glass
antenna device 1 includes the following components provided on
a window glass (e. g., rear window glass) 2 of a motor vehicle.
Namely, the glass antenna device 1 includes a dedicated AM
antenna 4, a dedicated FM antenna 5 and a defogging heater unit
3 in the form of a printed conductor pattern.
The vehicle window glass antenna device 1 also includes
an amplification section 7 for amplifying input AM and FM
signals VA and VF received via the AM and FM antennas 4 and 5
(hereinafter called "received AM and FM signals"),
respectively, and a radio receiver apparatus 10 that reproduces
amplified AM and FM signals VAO and VFO output from the
amplification section 7 (hereinafter called "output AM and FM
signals").
The motor vehicle is also provided with a heater power
source 6 for heating the defogging heater unit 3.
The defogging heater unit 3 includes a pair of opposed
bus bars 3a and 3b disposed and extending along left and right
side edges of the vehicle window glass, power feeding patterns
3c and 3d for coupling the heater power source 6 to the
respective bus bars 3a and 3b, and a plurality of horizontal
heater elements 3e extending between the opposed bus bars 3a
and 3b.
As D.C. power VH is fed from the heater power source 6,
such as a battery, via the feeding patterns 3c and 3d to the
defogging heater unit 3, a heater current, whose value is
determined by a voltage VH between the bus bars 3a and 3b and
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respective resistance values of the heater elements 3e, flows
through the defogging heater unit 3 to thereby resistively heat
the heater elements 3e. Thus, the defogging heater unit 3 is
heated and causes condensation on the window glass 2 to
evaporate, so as to defog the window glass surface.
Note that the defogging heater unit 3 in this embodiment
is connected directly to the heater power source 6 via the
feeding patterns 3c and 3d. In this way, the defogging heater
unit 3 can present a low impedance to an AM wave and is
prevented from functioning as an AM antenna.
The following paragraphs describe the AM antenna 4
employed in the antenna device.
The AM antenna 4 in this embodiment comprises a
plurality of AM antenna conductor elements extending
horizontally in a region between the uppermost heater element
3e of the defogging heater unit 3 and the top edge of the
window glass 2; these AM antenna conductor elements 4a together
constitute a fork-shaped AM antenna pattern. The AM antenna
receives an AM wave by means of the antenna conductor elements
4a and supplies a received AM signal VA to an AM amplifier 8 of
the amplification section 7 via the AM feeding pattern 4b.
The reason why the AM antenna 4 is constructed of the
plurality of horizontal AM antenna conductor elements is that
the receiving sensitivity to the incoming AM wave depends on a
total area of the AM antenna pattern 4a and it is preferable
that the total area of the AM antenna pattern 4a be as large as
possible and the AM antenna conductor elements 4a be formed
into a simple antenna pattern.
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In the specific illustrated example, the AM antenna 4
is constructed of five horizontal AM antenna conductor elements
each having a length L~,, of 1,000 mm and spaced from each other
by about 20 mm.
The 1,000 mm length L~", is a value determined such that
the AM antenna 4 does not exert adverse influences on the
receiving sensitivity of the FM antenna 5.
As one of the essential designing features of the
present invention, each of the AM and FM antennas 4 and 5 is
designed as a dedicated simple antenna pattern, so as to
minimize interferences between the AM antenna and the FM
antenna. However, a certain degree of such interferences may
be unavoidable due to the fact that the AM and FM antennas and
defogging heater unit are all provided on the rear window glass
having a limited area.
To verify the advantageous effects achieved by the
foregoing arrangements of the present invention, TABLE 1 is
given below which shows measurements of the receiving
sensitivity of the FM antenna in relation to EXAMPLE 1 where
each of the AM antenna conductor elements is set to the 1,000
mm length L~,, and EXAMPLE 2 where each of the AM antenna
conductor elements is set to a maximum length.
TABLE 1
EXAMPLE L~,I,~ (mm) FM-siqnal Receiving Sensitivity
1 1, 000 48 dB~uV
2 1,400 45 dBuV
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From TABLE 1 above, it can be seen that less influences
are exerted on the FM antenna in Example 1 than in EXAMPLE 2.
Note that the influences exerted on the FM antenna in EXAMPLE
2 are not of such a level that would lead to inconveniences in
actual use.
It is preferred that the AM antenna 4 be spaced from the
uppermost heater element 3e by more than a predetermined
distance (e. g., 30 mm) so that it can be reliably prevented
from being capacitively linked with the defogging heater unit
3. Further, the AM antenna's receiving sensitivity to the AM
wave can be set to a desired value by coupling the heater power
source 6 directly to the power feeding patterns 3c and 3d to
thereby set the impedance of the heater pattern 3e to a value
low enough to significantly reduce electrical coupling from the
defogging heater unit 3.
Now, the following paragraphs describe the FM antenna
5.
The FM antenna 5 comprises a single horizontal antenna
conductor element positioned between the uppermost heater
element of the defogging heater unit 3 and the AM antenna 4.
The FM antenna 5 supplies a received FM signal to an FM
amplifier 9 of the amplification section 7 via the FM feeding
pattern 5a.
In the present invention, the FM antenna 5 is not
directly connected with the defogging heater unit 3, but it is
preferred that the FM antenna 5 be capacitively linked with the
defogging heater unit 3. For example, it is preferable that a
distance from the FM antenna 5 to the uppermost heater element
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of the defogging heater unit 3 be set to a predetermined value
(e.g., in the range of 5 mm - 10 mm) so that the FM antenna 5
is capacitively linked with the heater unit 3 (see Fig. 2).
In the specific illustrated example, the FM antenna 5
is set to a length LFM ranging from 300 mm to 500 mm. However,
the length LFM is varied depending on a particular way of power
feeding to the FM antenna, i.e., whether (a) the FM feeding
pattern 5a on the window glass is used as the power feeding
point or (b) the FM feeding pattern 5a is connected via a
connecting lead to the FM amplifier 9 and the connection point
therebetween is used as the power feeding point. In the latter
case, the connecting lead functions also as an FM antenna
conductor element and the FM feeding pattern functions only as
a mere connecting pattern.
In the ( a ) case above, it is preferable that the length
LFM of the FM antenna be set, on the basis of a designed
wavelength, in accordance with mathematical expression (1)
above.
In the (b) case, on the other hand, it is necessary that
the FM antenna be set to a length calculated by subtracting the
length of the connecting lead from the designed length LFM.
Namely, the length of the FM antenna 5 formed on the window
glass has to be made smaller as the length of the connecting
lead increases.
Further, it is preferred that the FM antenna 5 be spaced
from the AM antenna 4 by more than a predetermined distance
(e.g., 25 mm) so as to minimize interferences between the FM
and AM antennas 5 and 4.
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By properly positioning the defogging heater unit 3, AM
antenna 4 and FM antenna 5 as mentioned above, the inventive
glass antenna device can minimize mutual interferences between
the AM antenna 4 and the FM antenna 5, between the AM antenna
4 and the defogging heater unit 3 and between the FM antenna 5
and the defogging heater unit 3.
Further, in the inventive glass antenna device, a
separate subsidiary FM antenna may be provided as necessary
(see Fig. 3); for example, such a subsidiary FM antenna 5s may
be provided in a marginal region below the defogging heater
unit 3. In this case, the FM antenna 5 may be constructed as
a main antenna and the subsidiary FM antenna 5s may be
constructed as a diversity antenna.
Preferably, the subsidiary FM antenna 5s also comprises
a single horizontal antenna conductor element, for the same
reason as set forth above in relation to the main FM antenna.
It is further preferred that the subsidiary FM antenna 5s be
also capacitively linked with the defogging heater unit 3. The
length of this subsidiary FM antenna 5s may also be determined
in the same manner as set forth above in relation to the main
FM antenna. Specifically, the subsidiary FM antenna 5s may be
set to a length LFMS ranging from 300 mm to 500 mm.
As mentioned above, the inventive glass antenna device
includes the dedicated FM antenna and AM antenna, each of which
is operable independently of the other and designed basically
as a straight-shaped antenna pattern. Thus, these antennas can
be designed and adjusted with utmost ease.
Now, a description will be made about the amplification
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section 7.
The amplification section 7 includes the AM and FM
amplifiers 8 and 9 which amplify received AM and FM signals VA
and VF supplied via the AM and FM feeding patterns 4b and 5a of
the AM and FM antennas 4 and 5, respectively. Thus, the
amplification section 7 supplies the radio receiver apparatus
with amplified output FM and AM s ignals VAO and VFO
More specifically, the AM amplifier 8 has a high input
impedance and low output impedance and amplifies the received
10 AM signal VA to supply the amplified output AM signal VAO to the
radio receiver apparatus 10.
Fig. 4 is a circuit diagram illustrating an embodiment
of the AM amplifier employed in the present invention.
In Fig. 4, the AM amplifier 8 comprises a common-source
amplifier circuit, which includes an input capacitor C1, an
input resistor R1, an FET (Field Effect Transistor) Q1, a load
resistor R2, a choke transformer L1, a source resistor R3, and
an output capacitor C2.
Because the FET Q1 has a very high input impedance, the
input impedance of the AM amplifier 8 is determined by a
resistance value (e.g., 1 MS2) of the input resistor R1
connected between the gate G and the ground GND.
Fig. 5 shows variations in noise occurring as the input
resistance Rl, acting as a gate resistance, is varied from 500
2 5 kS2 to 2 MS2 .
As clearly seen from Fig. 5, the noise can be reduced
by setting the input resistance R1 to a small value. For
instance, setting the input resistance R1 to a value of 1 MS2 or
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more will attain better results in actual use. Therefore, if
the input impedance is set to a high level, the AM amplifier
can effectively prevent unwanted noise from being introduced
into the amplifier via the resistor R1.
It is also preferred that the AM amplifier be set to a
low output impedance. The output impedance of the AM amplifier
8 is determined by a composite impedance of the load resistor
R2 connected to the drain D and the choke transformer L1
connected in parallel with the load resistor R2.
Here, the choke transformer L1 includes a tap positioned
at a point thereof corresponding to a 2:1 turns ratio and an
output from the amplifier is extracted via this tap, so that
the extracted output assumes one quarter of the composite
impedance. Thus, a high-frequency transformer is preferably
provided at the output stage of the AM amplifier 8, so as to
cause the output impedance to be 1,000 S2 or less.
It is preferred that the ground (GND) terminal of the
AM amplifier 8 be connected to the body earth of the motor
vehicle.
The following paragraphs describe behavior of the AM
amplifier 8.
The received AM signal VA input to the gate G is
multiplied by a voltage amplification coefficient (gm) of the
FET Q1 and load impedance ( i. e. , the composite impedance of the
load resistor R2 and the choke transformer L1 connected in
parallel with the resistor R2), and the output from the drain
D of the FET Q1 corresponds in value to a product of "gm x VA
load impedance". Consequently, the output AM signal vAo
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corresponds in value to one half of the product of "gm x VA x
load impedance".
By setting the input impedance to a high level in the
above-mentioned manner, the AM amplifier 8 can effectively
prevent unwanted noise from being introduced into the amplifier
via the resistor R1.
Further, because the load impedance is implemented by
the choke transformer, the output impedance can be set to a low
value even when the amplification gain is increased. Thus, the
output AM signal VAO can be taken out at a high level, and also
an impedance matching can be made between a coaxial cable
connecting to the radio receiver apparatus 10 and the output
impedance.
Note that the AM amplifier 8 may be constructed as a
grounded-emitter amplifier using an ordinary transistor (and,
if necessary, a darlington connection) in place of the FET.
Fig. 6 is a circuit diagram illustrating an embodiment
of the FM amplifier 9 employed in the present invention.
In Fig. 6, the FM amplifier 9 is constructed as a
grounded-gate amplifier circuit, which includes resistors R11,
R13, an inductor L12, an FET Q2, a resistor R12, a capacitor
C11 and a choke transformer L11.
Because the FET Q2 has a very low input impedance, the
input impedance of the FM amplifier 9 is determined by the
resistor R11. The resistor R13 and inductor L12 connected in
series with each other constitute a bias circuit for the FET
Q2.
The output impedance of the FM amplifier 9 is determined
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by an impedance ZFO of a parallel circuit that consists of the
load resistor R12 connected to the drain D, capacitor C11 and
choke transformer L11. Here, the output FM signal VFO is taken
out via a center tap positioned on the choke transformer L11,
so that the output impedance of the FM amplifier 9 equals one
quarter of the impedance ZFO of the parallel circuit. It is
preferred that the ground (GND) terminal of the FM amplifier 9
be connected to the body earth of the motor vehicle.
Appropriate impedance matching can be made by setting
the output impedance of the FM amplifier 9 (ZFO/4) to be
substantially the same as an impedance of the coaxial cable
connecting to the radio receiver apparatus 10.
Further, it is preferable that the FM amplifier 9 be set
to a gain on the order of 0 - 3 dB so as to prevent a waveform
distortion from occurring in the received FM signal VF when the
signal VF has an excessive level. The output FM signal VFO is
supplied to the radio receiver apparatus 10.
In Fig. 6, a tank circuit, comprising the capacitor C11
and the choke transformer L11 connected in parallel with each
other, constitutes a band-pass filter which permits a signal of
the FM frequency band to pass therethrough.
In a situation where two received FM signals VF1 and VFz
of close frequencies fl and f2 (fl<f2) would result in mutually
modulated signals corresponding to a sum of the two close
frequencies fl and f2 (fl+f2) and a difference between the
frequencies fl and f2 (f2-fl), particularly where the mutually
modulated signal representing the difference (f2-fl) assumes a
frequency of the AM frequency band, the above-mentioned tank
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circuit can eliminate the mutually modulated signal
representing the difference (f2-fl) to thereby effectively
prevent the mutually modulated signal from being output from
the amplifier and thus avoid a waveform distortion resulting
from such a mutual modulation.
Thus, even when the FM signal received by the FM antenna
is of an excessive level, the FM amplifier employed in the
present invention can properly perform impedance conversion and
signal amplification at an appropriate level without producing
a waveform distortion in the output FM signal from the FM
amplif ier.
Further, by the capability to suppress a mutually
modulated signal in the AM frequency band that would result
from a mutual modulation between a plurality of output FM
signals, the FM amplifier employed in the present invention can
reliably prevent the output of the mutually modulated signal
and thus avoid a waveform distortion resulting from such a
mutual modulation.
Note that the FM amplifier 9 may be constructed as a
grounded-base amplifier using an ordinary transistor in place
of the FET.
The inventive glass antenna device may further include
a synthesizer section 71 that synthesizes the output signals
from the above-mentioned AM and FM amplifiers 8 and 9 as shown
in Fig. 7.
Fig. 8 is a circuit diagram illustrating an example of
the synthesizer section 71. The synthesizer section 71
includes passive components such as capacitors and inductance
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elements. The amplified output signal from each of the AM and
FM amplifiers 8 and 9 is filtered so as not to flow back into
the corresponding amplifier, and the thus-filtered signals are
combined together or synthesized so that the synthesized result
is supplied to the radio receiver apparatus 10 via the coaxial
cable.
In the illustrated example of Fig. 8, the synthesizer
section 71 includes capacitors C31 and C32 and choke coils L31
and L32. The synthesizer section 71 also has an AM signal
input terminal connected to one end of the choke coil L32,
which is connected at the other end to an output terminal of
the synthesizer section 71. The synthesizer section 71 also
has an FM signal input terminal connected to one end of the
capacitor C31, which is connected at the other end to the
choke coil L31 and capacitor C32. The other end of the choke
coil L31 is grounded, and the other end of the capacitor C32 is
connected to the output terminal of the synthesizer section
71.
Now, a description will be given about exemplary details
of the antenna patterns employed in the inventive glass antenna
device, with reference to Fig. 9.
The AM antenna 4 comprises a plurality of horizontal AM
antenna conductor elements 4a that together constitute a fork-
shaped AM antenna pattern. The AM antenna 4 also includes a
short-cutting line 42 extending centrally across the fork-
shaped AM antenna pattern. Further, a horizontal bypass
element 41 is disposed above the horizontal AM antenna pattern
4a. This horizontal bypass element 41 is additionally provided
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here because there is formed a relatively large marginal gap
between the upper end of the horizontal AM antenna pattern 4a
and an upper window frame portion of the vehicle when the rear
window glass is actually fitted in the window frame, although
such a large gap is not clearly visible in Fig. 9 that is a
plan of the antenna patterns as viewed from the inside of the
vehicle.
Whereas the AM antenna has been described above as
comprising the fork-shaped AM antenna pattern, the present
invention is not so limited; for example, the AM antenna may
comprise a loop-shaped antenna pattern. In the case of such a
loop-shaped antenna pattern, a short-circuiting line may be
provided centrally across the antenna pattern.
The following paragraphs describe specific examples of
the FM antenna, either one of which may be selectively used
depending on the way of power feeding to the FM antenna. More
specifically, Fig. 10 A shows one example of the FM antenna
that is suitable for use in the case where the FM feeding point
5a is used as the power feeding point, and Fig. 10 B shows
another example of the FM antenna that is suitable for use in
the case where the FM feeding pattern 5a is connected via the
connecting lead. Although the designed length of the FM
antenna based on the basic design specifications is the same
for both the Fig. 10A example and the Fig. lOB example, the FM
antenna pattern 5 of Fig. lOB is constructed to be shorter than
that of Fig. 10A by an amount corresponding to the length of
the connecting lead. Note that even in the Fig. 10A example,
the FM antenna 5 does not extend beyond the centerline of the
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window glass.
In the above-described vehicle window glass antenna
device of the present invention, each of the AM and FM antennas
comprises a dedicated simple antenna pattern; thus, basic
designing of these antenna patterns can be made with
facility.
Typically, a region on the read window glass where
defogging is required and other regions where the glass antenna
patterns may be provided are determined depending on the type
of the vehicle body (such as the sedan, wagon or hatch-back
type). More particularly, these regions will be determined
taking into account particular design specifications, such as
the size, mounting angle, etc. of the rear window glass and
presence/absence of a trunk room. Thus, for a given vehicle
type, the size of the window glass and the regions where the
antenna patterns may be provided are determined, and then the
inventive vehicle window glass antenna device is designed for
application to such a window glass.
The inventive vehicle window glass antenna device can
be applied appropriately to various types of motor vehicles,
without changing its basic design, as long as the size and
mounting areas of the window glass are similar between the
vehicle types. Therefore, the necessary time for adjusting the
design of the antenna device can be minimized by the present
invention.
As mentioned above, the inventive glass antenna device
includes the dedicated FM antenna and AM antenna, each of which
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is constructed basically as a straight antenna pattern. Thus,
these antennas can be designed and adjusted with increased
ease.
Further, because the FM and AM antennas are equipped
with respective dedicated amplifiers, the inventive glass
antenna device can receive both of FM and AM waves with high
sensitivity, thereby achieving superior FM- and AM-wave
reception.
Furthermore, because no choke coil has to be connected
to the defogging heater unit, it is possible to reserve a wider
space for mounting the antenna components and achieve reduced
costs.
Moreover, even when an FM signal received by the FM
antenna is of an excessive level, the FM amplifier employed in
the present invention can properly perform impedance conversion
and signal amplification at an appropriate level without
producing an unwanted waveform distortion in the output FM
signal from the FM amplifier, with the result that the FM
signal can be reproduced with high quality.
Besides, by suppressing a mutually modulated signal in
the AM frequency band that would result from a mutual
modulation between a plurality of output FM signals, the
present invention can reliably prevent output of the mutually
modulated signal in the AM frequency band and thus avoid a
waveform distortion resulting from such a mutual modulation.
As a result, the FM signal can be reproduced with high
quality.
In addition, in the vehicle radio receiver apparatus
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employing the inventive glass antenna, the AM and FM amplifiers
are set to sufficiently low output impedances, which allows the
antenna device to be connected to the radio receiver apparatus
using a signal-transmitting cable having a diameter of 3 mm or
less that is quite easy to handle.
Thus, it is possible to lay the signal-transmitting
cable (coaxial cable) in and around the vehicle and thereby
significantly reduce the necessary time and labor for
assemblage.
Industrial Applicability
With the arrangements so far described, the present
invention can be used advantageously as a vehicle window glass
antenna device for receiving AM and FM waves with high
sensitivity.
