Title: Glass antenna system for vehicles
Abstract: A glass antenna system for vehicles to receive AM and FM bands is provided. An electrically conductive transparent film is formed on a side glass. A silver printed line have a wide width is formed around the electrically conductive transparent film. A loop-shaped silver printed line is provide surrounding the film, which is capacitively coupled to the body. In this manner, an opening is formed in a space between the silver printed line and the electrically conductive film. An electrically shorted portion is provided between the silver printed line and the electrically conductive film. A coaxial feeder for AM/FM is provided. A central conductor of the feeder is connected to the silver printed line and the outer conductor to the body.
Patent Number: 6,937,198 Issued on 08/30/2005 to Iijima, et al.
| Inventors:
|
Iijima; Hiroshi (Osaka, JP);
Kakizawa; Hitoshi (Osaka, JP);
Doi; Ryokichi (Osaka, JP)
|
| Assignee:
|
Nippon Sheet Glass Company, Limited (Tokyo, JP)
|
| Appl. No.:
|
872622 |
| Filed:
|
June 21, 2004 |
Foreign Application Priority Data
| Jun 20, 2003[JP] | 2003-175721 |
| Current U.S. Class: |
343/713; 343/704 |
| Intern'l Class: |
H01Q 001/32 |
| Field of Search: |
343/713,704,711,712
|
References Cited [Referenced By]
U.S. Patent Documents
| 5831580 | Nov., 1998 | Taniguchi et al.
| |
| 6147654 | Nov., 2000 | Nagy.
| |
| 2004/0080460 | Apr., 2004 | Davies.
| |
| 2005/0035913 | Feb., 2005 | Baranski.
| |
| Foreign Patent Documents |
| 38 08 401 | Sep., 1989 | DE.
| |
| 101 46 439 | Nov., 2002 | DE.
| |
Primary Examiner: Le; Hoanganh
Attorney, Agent or Firm: RatnerPrestia
Claims
1. A glass antenna system for vehicles comprising:
an electrically conductive portion formed on a window glass of a vehicle except
for a region adjacent to a metal portion of a vehicle surrounding the window glass;
a loop-shaped electrically conductive printed line formed in the region so that
an opening is formed surrounding the electrically conductive portion and so as
to be capacitively connected to the metal portion;
an electrically shorted portion to short between the electrically conductive
portion and the loop-shaped electrically conductive printed line; and
a coaxial feeder, the central conductor thereof being connected to the electrically
conductive portion and the outer conductor thereof being connected to the metal
portion;
wherein the electrically conductive portion and the loop-shaped electrically
conductive printed line function as AM antenna, and the opening functions as FM
antenna.
2. An antenna system for vehicles according to claim 1, wherein the electrically
shorted portion is provided at a position where the impedance of a slot antenna
formed by the opening is matched to that of the coaxial feeder.
3. An antenna system for vehicles according to claim 1, wherein the electrically
conductive portion is formed by an electrically conductive transparent film.
4. An antenna system for vehicles according to claim 3, wherein an electrically
conductive printed line is formed on the peripheral portion of the electrically
conductive transparent film.
5. An antenna system for vehicles according to claim 1, wherein the electrically
conductive portion is composed of a ladder-shaped electrically conductive pattern.
6. An antenna system for vehicles according to any one of claims
1-
5,
wherein the window glass is a side glass.
7. An antenna system for vehicles according to any one of claims
1-
5,
wherein the window glass is a windshield.
8. An antenna system for vehicles according to claim 1, wherein the electrically
conductive portion is composed of a heating line and an electrically conductive
printed line formed at the circumference of the heating line.
9. An antenna system for vehicles according to claim 8, wherein the window glass
is a rear glass.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a glass antenna system for vehicles,
particularly to a glass antenna system for receiving AM and FM broadcasts.
2. Description of the Prior Art
A rod antenna has been provided as an antenna system for receiving AM and FM
broadcasts.
An antenna element of the rod antenna is protruded from the body of a vehicle,
so that the antenna element has a tendency to be injured. As an alternative to
the rod antenna, a glass antenna system has been provided in which the pattern
of electrically conductive lines of the paste including silver powders (referred
to as silver printed lines) are printed on a window glass of a vehicle.
In the glass antenna system using silver printed lines, an antenna pattern becomes
complicated in order to realize a good sensitivity for FM band (76-90 MHz) in the
case that the antenna pattern is formed on a small window such as a side window,
resulting in a bad appearance of the side window.
A slot antenna has also provided which is formed in a space between an electrically
conductive transparent film for reflecting sunlight provided on a glass window
of a vehicle and a body of the vehicle. This kind of a slot antenna has been disclosed
in Japanese Patent Publication Nos. 6-45817, 9-175166 and 2002-290145.
An antenna disclosed in Japanese Patent Publication No. 6-45817 is a slot antenna
formed on a windshield of a vehicle. The technical word "slot antenna" means an
antenna comprising a rectangular opening having a fixed length and width in an
electrically conductive plate. The slot antenna, therefore, has both ends in a
rectangular opening independently of the shape of the opening. The slot antenna
disclosed in the Japanese Patent Publication is structured by a complete loop-shaped
opening, so that the slot antenna does not have both ends thereof. In this meaning,
this slot antenna is a slot antenna in a broad sense. This slot antenna is also
has a complicated structure because an interface region is required to match the
impedance of the slot antenna to that of a coaxial feeder.
The antenna disclosed in Japanese Patent Publication No. 9-175166 has a composite
structure consisting of a slot antenna and an antenna element provided in the slot
antenna in order to receive a wide frequency band.
A slot antenna for receiving FM and TV bands is disclosed in Japanese Patent
Publication
No. 2002-290145. This slot antenna is formed between an electrically conductive
film and a body of a vehicle, and comprises two electrically conductive portion
each for electrically connecting the electrically conductive film and the body
of a vehicle to each other. In this slot antenna, the bands capable of receiving
are limited to only FM and TV bands, and then AM band may not be received.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a glass antenna system for
vehicles having a simple structure and capable of receiving both AM and FM bands.
A glass antenna system according to the present invention is structured in such
a manner that the system functions both as a planar antenna for receiving AM band
and as a slot antenna for receiving FM band. The term "slot antenna" herein means
an antenna comprising an opening having a fixed length and width in an electrically
conductive plate.
Also, the word "opening" is used herein to mean an opening which is formed
in an electrically conductive plate by removing a part thereof. The slot antenna,
therefore, has both ends in an opening independently of the shape of the opening.
According to the present invention, a loop-shaped opening is formed between
an electrically conductive portion and an electrically conductive printed line
surrounding the electrically conductive portion. By providing an electrically shorted
portion at one position in the opening, the opening may function as a slot antenna
for receiving FM band. In this case, the electrically conductive printed line is
to be connected in an alternating current (AC) manner to a metal part of a vehicle
according to the definition of the word "slot antenna". As the electrically conductive
printed line is provided along the circumference of a window glass, the electrically
conductive printed line is capacitively coupled to the metal part of a vehicle,
and then is connected to the metal part of a vehicle in AC manner.
On the other hand, the electrically conductive portion and electrically conductive
printed line are connected to each other by an electrically shorted portion to
function as a planar antenna for receiving AM band. In this case, both the electrically
conductive portion and the printed line should not be connected to the metal part
of a vehicle in AC manner. As the printed line is selected so that the impedance
thereof is high in AC band, the printed line is not connected to the metal part
of a vehicle in AC manner.
In this manner, a glass antenna system according to the present invention may
function as a planar antenna and slot antenna to allow the reception of AM and
FM bands.
A glass antenna system for vehicles according to the present invention comprises:
an electrically conductive portion formed on a window glass of a vehicle except
for a region adjacent to a metal portion of a vehicle surrounding the window glass;
a loop-shaped electrically conductive printed line formed in the region so that
an opening is formed surrounding the electrically conductive portion and so as
to be capacitively connected to the metal portion; an electrically shorted portion
to short between the electrically conductive portion and the loop-shaped electrically
conductive printed line; and a coaxial feeder, the central conductor thereof being
connected to the electrically conductive portion and the outer conductor thereof
being connected to the metal portion; respectively; wherein the electrically conductive
portion and the loop-shaped electrically conductive printed line function as AM
antenna, and the opening functions as FM antenna.
The electrically shorted portion is provided at a position where the impedance
of a slot antenna formed by the opening is matched to that of the coaxial feeder.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an embodiment of a glass antenna system for vehicles according
to the present invention.
FIG. 2 shows an example of an electrically conductive pattern which is formed
by means of silver printed lines on the surface of a window glass.
FIG. 3 shows a glass antenna system formed on a windshield.
FIG. 4 shows a glass antenna system using a heating line.
DESCRIPTION OF THE EXEMPLARY EMBODIMENT
Referring to FIG. 1, there is shown an embodiment of a glass antenna system
for vehicles according to the present invention. The antenna system is provided
on a side window of a vehicle.
A side glass
10 forming a side window is surrounded by a body
12
made of metal. An electrically conductive transparent film
14 for reflecting
sunlight is provided on the side glass
10, and a silver printed line
16
having a wide width is formed on the peripheral portion of the electrically conductive
transparent film
14. A loop-shaped silver printed line
18 is provide
surrounding the film
14, which is capacitively coupled to the body
12.
In this manner, an opening
20 is formed in a space between the silver printed
line
18 and the electrically conductive film
14. An electrically
shorted portion (i.e., a short stub)
24 is provided between the silver printed
line
18 and the electrically conductive film
14. As a result, the
silver printed line
18 and the electrically conductive film
14 are
connected in a direct current (DC) manner. The purpose for providing the silver
printed line
16 around the electrically conductive film
14 is to
make the connection of a central conductor of a coaxial feeder thereto easy and
to increase the sensitivity of a slot antenna by improving the flow of a current.
Also, the purpose for providing the loop-shaped silver printed line
18
is such that the line
18 functions together with the film
14 as a
planner antenna for AM band, and the line
18 capacitively coupled to the
body
12 to function the opening
20 between the film
14 and
the line
18 as a slot antenna.
The electrically conductive transparent film
14 may be formed directly
on the surface of the side glass
10 or may be adhered to the side glass.
In the case of a laminated glass, an electrically conductive film may be stacked
in the laminated glass. It is preferable that a sheet resistance of the electrically
conductive transparent film
14 is low (for example, lower than 4Ω/□).
The glass antenna system shown in FIG. 1 further comprises a coaxial feeder
22
for AM/FM. A central conductor of the feeder is soldered to the silver printed
line
16 and the outer conductor to the body
12.
The connections of the central and outer conductors of the coaxial feeder
22
for AM/FM may be implemented by using terminals and connectors other than soldering.
In the case of a laminated glass, a film-shaped connector that is embedded in the
laminated glass may be used for connecting the conductors to an electrically conductive
transparent film provided in the laminated glass.
The position of a terminal of the coaxial feeder
22 for AM/FM may be determined
considering a design and a fabrication thereof.
In the glass antenna system shown in FIG. 1, the electrically conductive film
14 and loop-shaped silver printed line
18 are used for AM antenna
as a planar antenna, and the opening
20 electrically shorted by means of
the short stub
24 is used for FM antenna as a slot antenna. As stated above,
the body
12 and film
14 must be electrically shorted in order to
cause the opening
20 to function as a slot antenna, and then the short stub
24 is provided for this purpose.
The position of the short stub
24 is selected in a following manner. That
is, where the opening
20 forms a slot antenna for FM, the impedance of the
slot antenna should be matched to that of the coaxial feeder
22 for AM/FM.
The impedance of the slot antenna is determined by the length L thereof (i.e.,
the length of the opening
20), the width thereof (i.e., the width of the
opening
20), the resistance of the silver printed line
18, and the
position of the short stub
24 with respect to the feeding point of the coaxial
feeder. While the position of short stub may be expected by simulation, it would
be also determined by measuring the impedance of the slot antenna.
The antenna system having a structure described above, the length L of the slot
antenna is determined by following equation;
herein, λ
0 is the wavelength of the central frequency of
a band to be received, n is 1, 2, 4 . . . , and k is a shortening factor of antenna
size due to glass, the range thereof being 0.55-1.0. The shortening factor relates
to a propagation rate of a wave propagated through a dielectric substrate (a glass
plate in this case), and is a ratio of the size of an antenna formed on the dielectric
substrate with respect to the size of an antenna provided in a space rather than
on the dielectric substrate. Therefore, it is preferable that the length of a slot
antenna is determined so that the equation denoted above is satisfied.
In the case that the glass antenna system according to the present invention
is
provided on a window glass having small area, the length of an opening is determined
such that n=2 in the equation, i.e. the antenna resonates at ½ wavelength.
As FM band (76-90 MHz) is received by means of the slot antenna, the maximum
½
wavelength is approximately 1.95 m. Therefore, it is preferable that the length
L of the slot antenna is approximately 1.5 m or less assuming k=0.65. Also, the
width of the opening is determined so as to be in the range of (0.0004λ
0-0.02λ
0)×k.
The distance between the loop-shaped silver printed line
18 and the body
12 is regulated such that the impedance is high for AM band and low for
FM band. The capacitance between the line
18 and the body
12 is regulated
in a range of 20-30 pF for AM band.
It is also desirable that each of the silver printed lines
16 and
18
has preferably the width of 5 mm or more from the point of view for the connection
of a central conductor of the coaxing feeder
22 and the antenna efficiency.
In designing a slot antenna having the length and width of the opening described
above, the electrically conductive transparent film
14 and the loop-shaped
silver printed line
18 work as a planner antenna for receiving AM band,
so that the area surrounded by the line
18 is determined in view of AM sensitivity.
AM sensitivity is therefore determined by the area of a window glass. The area
of a window glass of 0.14 m
2 or more is preferable in view of AM sensitivity.
Consequently, the area of a window glass to which a glass antenna system
according to the present invention is formed may be at least 0.14 m
2 in
the case that the antenna is resonated at ½ wavelength. As a result, a glass
antenna system according to the present invention may be applied to a side window
having a small area.
When a vertical dimension of the opening
20 is 400 mm and a horizontal
dimension is 350 mm, as an example, the length L of the opening is 1500 mm. On
the other hand, ½ wavelength is approximately 1.8 m for the central frequency
83 MHz of FM band (76-90 MHz). Considering a shortening factor, the length L of
a slot antenna satisfies the equation (n=2) described above. Also, the area of
a window glass is 0.14 m
2 and therefore satisfies the condition necessary
for AM sensitivity. It will be understood that the glass antenna system having
such dimensions may successfully receive both AM and FM bands. It is also understood
that a glass antenna system according to the present invention may easily be implemented
for a side window having an area of 0.15 m
2 or more, for example.
The operation will now be described in the case that the glass antenna system
as shown in FIG. 1 functions as AM and FM antennas.
(1) AM Antenna
The electrically conductive transparent film
14 and the loop-shaped silver
printed line
18 become a planar antenna and function as AM antenna.
(2) FM Antenna
The loop-shaped silver printed line
18 is equivalent to the body in potential
because the line
18 is capacitively coupled to the body in FM band. A slot
antenna, therefore, is formed between the film
14 and the line
18.
A better sensitivity may be obtained because the short stub
24 is provided
at the position where the impedance of the slot antenna is matched to that of the
coaxial feeder
24.
In the embodiment described above, it is useful that the area of the side glass
is 0.15 m
2 or more. The distance between the film
14 and the
line
18 is regulated in a range of 10-30 mm for an impedance for FM.
In the embodiment described above, the electrically conductive transparent film
has been used. However, a ladder-shaped electrically conductive pattern made of
silver printed lines may also be used instead of the electrically conductive film.
An example of an electrically conductive pattern which is formed on the surface
of a window glass by means of silver printed lines is shown in FIG.
2. The
pattern comprises a rectangular silver printed line
40 at a circumferential
portion and a plurality of horizontal silver printed lines
42 within the
rectangular line
40. The number of the printed lines
42 may be determined
considering an appearance thereof and AM sensitivity. If the number thereof is
three or more, then the sensitivity equivalent to that of the electrically conductive
transparent film may be obtained.
Also, the space between the body
12 and the line
18 work as a
capacitor, which capacitor may be replaced by a capacitor having an equivalent
capacitance as a lumped constant. In that case, one end of the replaced capacitor
is connected to the film
14 and the other end is directly connected to the
body
12, at the position of the short stub
24.
While the antenna system is provided on the side glass of a vehicle with the
resonance wavelength being ½ wavelength in the embodiment described above,
the antenna system may be applied to a windshield or rear glass if the resonant
frequency is one wavelength in the equation described above.
An electrically conductive transparent film
14 may be used as shown in
FIG. 3 in the case that an antenna system is provided on a windshield. The structure
of the antenna system is the same as in the side glass. The same element as in
FIG. 1 is designated by the same reference numeral. When FM band (76-90 MHz) is
received by a slot antenna, a maximum one wavelength is approximately 3.9 m. It
is understood that the antenna system may be provided on a windshield considering
a shortening factor.
A heating line or an electrically conductive transparent film may be used in
the
case that an antenna system is provided on a rear glass. FIG. 4 shows an example
in which a heating line
50 is used. A silver printed line
52 is formed
surrounding the heating line
50 and is connected to the heating line
50.
A loop-shaped silver printed line
18 is formed surrounding the silver printed
line
52, which is capacitively coupled to the body. In this manner, an opening
20 is formed in a space between the printed lines
52 and
18.
A short stub
24 is provided between the printed lines
52 and
18.
A coaxial feeder
22 for AM/FM is connected to the antenna. It is preferable
that a central conductor of the coaxing feeder
22 is connected to a feeding
point
26 via a capacitor to prevent DC current through the heating line
from flowing into the coaxial feeder
22.
This glass antenna system functions in the same manner as the system in FIG.
1.
According to the present invention described above, the following effects
are obtained.
(1) A glass antenna system for vehicles for receiving AM and FM bands may be
implemented in a simple structure.
(2) A better sensitivity for FM band (76-90 MHz) may be realized, because a slot
antenna is formed utilizing the circumference of a window glass to obtain the length
of an antenna enough for FM band.
(3) A better sensitivity of a glass antenna system is realized for a window glass
having a small area using an electrically conductive transparent film, because
the position of a short stub between a silver printed line and a loop-shaped silver
printed line is selected so that the impedance of a slot antenna is matched to
that of a feeder.
*
