Note: Descriptions are shown in the official language in which they were submitted.
r~ACI;~I~oc~rrD or ~I~~ IrmErr~x~zorr
Field of the Invention
~rhe present invention relates to a glass window
antenna for a motor vehicle, wherein antenna conductors are
arranged on a surface of a caindow glass used as an insula-
tor.
Description of the Prior Art
In an antenna system of a motor vehicle, a diver-
sity reception using a plurality of antennas is employed for
reducing changes in reception gain according to traveling
direction of the vehicle. An ~'HI broadcast diversity recep-
tion, for example, a pole antenna attached on the body of
the motor vehicle and an antenna comprising an antenna
conductor attached on a rear glass window are used in a
prior art. ~: space diversity reception is so performed that
the highest level one in reception signals is selected (cf.
Japanese laid open patent application No.140301/1988).
It is known to perform diversity reception with
two or more antenna conductors and feed terminals on a reax
window surface of the motor vehicle (Japanese utility model
registration application laid open Nos. 13808/1983 and
29307/1988 arid a patent application laid open: No.
269625/1988))
As to the pole antenna, tuning adjustment is
possible only with regard to its length. It is less flexible
in arrangements of conductor than that of a glass window
antenna. ft is therefore difficult to tune conductor =or
providing complementary directivity for diversity reception
- 2 -
.1 ~ al ".~ ,,'J
l a ~ f,> > ,~ ",,, ;.~
system. An element of the pole antenna is arranged vertical-
ly so that it shocus a low reception sensibility to receive
horizontally polarized suave.
It is possible to tune directivity of respective
antennas in diversity reception system in which, spaced
conductors arranged on a surface of a glass window. Spaces
on the window, however, are little for the antenna conduc-
tOrS SO that they shocu lo~u average reception sensibility.
Preamplifiers ruith fired gains must be inserted immediately
after feed terminals of the antenna conductors, nhese fixed
gain.amplifiers often saturate at strong radio wave field so
that reception radio voice is remarkably degraded.
OBJECT AND SUt~INIARY OF THE INVENTION
Accordingly it is an object of this invention to
provide window glass antennas which have good complimentary
directivities and high reception sensibilities without using
preamplifiers.
In accordance with an aspect of the present inven-
tion, there is provided a window glass antenna of a motor
vehicle comprising heater cuires formed in a heating area on
a window glass of the motor vehicle; a first antenna conduc-
tor formed in a lower blank area outside the heating area; a
second antenna conductor formed in a lower blank area out-
side the heating area and RF-coupled to the heater wires;
and first and second feed terminals arranged oppositely at
both lateral sides of the window glass for deriving recep-
tion signals from the first and second antenna conductors.
According to opposite wiring courses tacuard the
3
feed terminals, Location of the first and secoFlc'cN~t~ri~i~
conductors is asymmetrical with respect to a center line of
glass window. Directivities of the antenna conductors com-
element with each other. Non-directional reception charac-
teristic is thus achieved by diversity reception)
The above, and other, objects, features and advan-
tages of the present invention, will become readily apparent
from the following detailed description thereof which is to
be read in connection with the accompanying drawings.
BRIEF DESCRIE~TIOrI OF THE DRAVINGS
Fig. 1 is a front view of a rear glass window on
which a glass window antenna for a motor vehicle according
to this invention is provided;
Fig. 2 is a graph showing directivities of upper
and lower antenna conductors;
Fig) 3 is a graph showing variation of reception
sensibility with respect to coupling capacity between heater
wires and the second antenna conductor;
Fig. 4 is a graph showing a gain of the first
antenna conductor for various conductor width of feeder
conductor connected thereto;
Fig. s is a graph showing gain of the second
antenna conductor in a case in which a hori~,ontal element is
added to a bus bar of heater caires and a case in which the
horizontal element is not provided;
Fig. 6 is a graph showing gain of antenna in a
case in which short-circuit conductor and horizontal ele-
ments are added and another case in which these are not
g
rJ ~~ L,~
provided; and
Fig. 7 is a graph showing gain of antenna in a
case in cahich horizontal element is provided to capacitively
couple to the first antenna conductor and another case in
cahich the horizontal element is not provided.
DETAT_Lc,D DESCRIPTIOD1 OF A PREFERRED EL~1BODTP~ZE~'JT
Fig. 1 is shows a rear glass window of a motor
vehicle according to this invention. In the middle zone of
the glass window, a plurality of defogging heater wires 2 is
formed in parallel to each other through a printing and a
baking processes. The heater wires 2 are divided into upper
and lower groups. Power is fed through bus bars 3 and
through a return path via a common bus bar S. Another power
feed system may be arranged in cahich heater ~~rires 2 are not
divided into two groups so that a current flows from a side
bus bar to another side bus bar.
The heater caires 2 are used as an AM radio wave
reception antenna. Magnetically coupled choke coils 8a and
8b are inserted iwto power supply lines 7a and '7b. The choke
coils provides the heater wires 2 with large impedance to
ground in radio frequencies. The power supply line 7a is
coupled to a main power supply through a scvitch 6 and the
power supply line 7b is caupled to ground.
Antenna conductors 10 and 11 are arranged on upper
and lower blank areas of the heater wires 2. The upper
antenna conductor 1(? is e:~clusively used for FM .broadcast
reception. The lower antenna conductor 11 is used both for
AM and Fb~ broadcast receptions. A diversity reception is per-
- 5 -
Yd ~~ (J ~ 4s c.I
formed for Fc~9 ;~roadcast reception with using the upper and
lower antenna conductors 10 and 11.
Asymmetrical arrangement of conductors is employed
faith respect to the center line or the glass window for
satisfactory Fr7 diversity reception. For securing asymmetri-
cal arrangement of the conductors, a feed terminal 10a of
the upper antenna conductor 10 is located at the right side
(viewed from inside of a car) of the glass raindow 1 and a
feed terminal 11a of the lower antenna conductor 11 is
located at left side.
The antenna conductor 10 comprises horizontal ele-
ments 10b - 10g. A main element 10b is a single element
antenna of about 800 mm in length and is symmetrically
arranged with respect to the center line of the glass caindow
1. At the center o= the conductor 10b, a vertical coupling
conductor 10h is connected to form an antenna of generally
inverse letter -T configuration. The coupling conductor 10h
is connected to a feeder conductor 10i arranged along an
upper edge of the glass window 1. An end of the feeder
conductor 10i is connected to the feed terminal 10a located
at the side end of the glass window 1.
The feeder conductor 10i is 3 mm in width and made
wider than other conductors so that impedance matching is
satisfied between a feeder cable of 5052 to be connected to
the feed terminal 10a and the inverse T-antenna comprising
the main element 10b and the coupling conductor 10h. The
feeder conductor 10i has a desired capacitance to ground
which is produced by capacitive coupling to a window frame
c~~ra~,~~~~.~~
(ground potential) near the upper edge of the glass cnindow.
A desired impedance measured at the feed terminal 10a is ob-
twined.
Horizontal elements 10d and 10f are extended from
the bus bar 3 of the heater wires 2 in parallel with the
main element 10b. These horizontal elements are capacitively
coupled with the main element 10b so as to tune the antenna
in directivity. Respective ends of the horizontal elemer_ts
10d and 10f are located at 300 mm and 400 mm away from the
center line of the windoca 1.
A short-circuiting conductor 10j of 4 mm in width
is provided along the center line of the glass caindow 1 to
short-circuit all of upper half of the heater caires 2. A
horizontal element 10g is e:aended from an end of the
short-circuit conductor 10j toward the bus bar 3 so as to
couple capacitively, with the element 10h for improving
directivity. An end of the horizontal element 10g is located
at 500 mm away from the center line of the glass window 1.
The short-circuit conductor 10j connects equipotential
points of the heater wires 2 so that na short-.circuiting
current actually flows through the short-circuit conductor
10j.
Tn.this embodiment, line intervals 10d - 10b, 10b
- 10f, 10f - 10g and 10g - heater crires 2 are respectively
10, 15, 7.S and 7,5 mm.
A horizontal auxiliary element 10e of 165 mm in
length is extended from the feed terminal 10a so as to tune
the antenna in directivit~r as well as high frequency charac--
-
~~l~~r,;~ra~
teristic.
The above-.mentioned elements 10d, 10h, i0g and 10e
improve reception directivity of the main element 10b on the
left side thereof. These elements are arranged generally on
the right side of the center line of the glass caindow 1, The
antenna conductor 10 is thus arranged asymmetrically in
general with respect to the center line of the glass window
1.
The lower antenna conductor 11 has a horizontal
main element 11b extended from the feed terminal 11a in
parallel with the heater wires 2 at an interval of 2 mm. The
main element 10b is capacitively coupled to the heater wires
2 to serve as an antenna used both in receptions of ADT and
~PZ waves induced on the heater wires 2. The lower half of
the heater wires 2 serves as ground circuitry e.g, a return
path of a heater current so that noises in a heater power
supply do not propagate directly from the heater wires 2 to
the main element 11b. No remarkable noises are recognized in
a reception signal. An end of the main element 11b is locat-
ed at 210 mm away from the center line of the glass window
1.
Auxiliary horizontal elements 11c, 11d and 11e are
extended from bus bars 3 and 5 of the heater wires 2 for
improving directivity and frequency characteristics of the
main element 11b. The heater wires 2 are thus tuned as an
antenna. The element 11c is extended horizontally from the
locaer end of the common bus bar 5 by 150 mm awav from the
center line of the glass window with an interval of 30 mm to
~3 _
mw 4 ~
7.,
!a ~ ~ ~ ~J ~~ rJ
the heater wires 2.
The element 11d is extended from the lower end of
the bus bar 3 along the right side oT the glass window 1 and
then extended horizontally to a position X10 mm a~nay from
the center line of the glass window 1 with an interval of 15
mm to the heater wires 2.
The element 11e is extended from the upper end of
the common bllS bar 5 along a corner portion and upper side
of the glass windoc~r 1 to a position 1 SO mm acaay from the
center line.
~ig. 2 shows directivity of antenna conductors 10
and 11 with respect to FM broadcast caave of 95 MHz. The
directivity of dotted line B11 corresponds to the antenna
conductor 10 and the directivity of a solid line D10 corre-
sponds to the antenna conductor 11. As is apparent from the
directivity chart, a dip in gain of the lower antenna 11
appearing on the right side of a traveling course of a car
is complemented by a gain of the upper antenna conductor 10.
In the directivity of the antenna conductor 10, a dip ap-
peering on the left side of a traveling course of a car is
complemented by a gain of the lower antenna conductor 11. A
diversity reception is achieved by selecting a higher level
one of reception signals from the complementary antenna
conductors 10 and 11 in response to comparison of these
signals. A stable reception signal is obtained regardless of
changes of traveling direction of the car.
The lower antenna conductor 11 functions as an t'1b1
reception antenna. In this radio band, the heater wires 2. is
_ g _
:~ ~..3 ,.C~ ,,..a r, cl
~,i '" ~.~ G.i -.% r,) 2.~
operable as an ant enna conductor since conductors of the
wires are relatively long.
Fig. 3 is a graph showing a relation between AM
reception sensibility and coupling capacitance of the main
antenna element 11 to the heater wires 2. Differences in
sensibility are plotted with reference to that (OdB) of a
rear pole antenna of 1200 mm long. The difference reaches
the reference cahen the coupling capacitance exceeds 60 pF,
and saturates at 70 pF or more) In the embodiment, the main
element 11b and the heater wires 2 are set at an interval of
2 mm to give capacitive coupling not less than 70 pF so that
an AM reception signal is obtained by the antenna conductor
11 with a sufficient gain.
Fig. 4 shows reception gains of the upper antenna
conductor 10 in FM broadcast wave ranging 80 - 90 MHz in
cases cahere width of the feeder conductor 1Oi in Fig. 1 is 1
mm and 8 mm as respectively shown by a dotted line and a
solid line. As is apparent from the graph, reception gains
in lower side and upper side of FM broadcast band are re-
spectively improved when the width of the feeder conductor
10i is set mare than 3 mm. Frequency characteristics are
improved over a wide range. The feeder conductar 10i is
extended from the center line of the window glass 1 toward
right side to the feed terminal 10a and operates as an
antenna element which serves to improve reception gain on
the right side of traveling course.
Fig. 5 shows reception gains of the lower antenna
conductor 11 in a range 80 - 90 MHz in cases where the
- 10 -
horizontal elements 11c and 11e are eetended from the common
bus 5 of the heater wires 2 and these elements 11c and 11e
are removed, respectively as shown by a solid line A and a
dotted line B. A condition of FM radio wave current induced
on the heater ~oires 2 is changed by extending the elements
11c and 11e from the common bus bar 5 of the heater wires 2,
frequencj bands each in which a good sensibility is obtained
are shifted to each other as shown by the graph. These
elements 11c and 11e are arranged on the left side of the
glass window 1 so that it operates to improve reception gain
of the lower antenna conductor 11 on the left side of the
traveling course.
rFig. 6 shows gain characteristics in a band of 80
- 110 i~9Hz for a case (solid line A) where the short-
circuiting conductor 10j is provided to the heater wires 2
in Fig. 1 and the horizontal element 10g is extended from an
end of the conductor 10j in parallel to the heater wires 2,
and another case (dotted line B) where these conductors 10j
and 10g are not used, State of FM radio frequency current
induced on the heater wires 2 is changed by attaching these
conductors 10j and 10g. Frequency band having good sensibil-
ity can be shifted as shown by the graph. The horizontal
elements 10g is extended on the left side of the glass
caindow 1 so that it operates to improve reception gain of
the upper antenna conductor 10 on the left side of the
traveling course.
Fig. 7 shows reception gains in a band of 80 - 110
MHz in a ease (solid line A) cahere the horizontal elements
- 11 -
10d and 10f are e:ctended from the bus bar 3 of the heater
cvires 2 as shown in Fig. 1 to capacitively couple with the
main element 10b on both sides (upper and lower sides)
thereof and another case (dotted line B) where the elements
10d and 10f are not used. Influence to the main element 10b
by the heater wires 2 can be changed by capacitive coupling
of horizontal elements 10d and 10f with the main element 10b
at a distance within 15 mm. Frequency band having good
sensibility can be shifted as shown by the graph. These
horizontal elements 10d and 10f operate to improve a gain of
the upper antenna conductor 10 on the right side of a trav-
eling course.
According to this invention, due to asymmetrical
arrangement of the first and second antenna conductors with
respect to the center of the glass window, directivities
complementing to each other are obtained. Good reception
characteristics are obtained with diversity reception re-
gardless of traveling direction of car. especially, a recep-
tion system in which any preamplifier is riot employed can be
arranged so that a reception signal of high quality is
received without distortion even in a strong radio wave
field.
According to other features of this invention,
reception gains of the first and second antenna conductors
are improved. Complementary characteristics of the first and
second antenna elements are ensured to operate a diversity
reception system with high performance.
- 12 -
