Information
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Patent Grant
-
6307516
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Patent Number
6,307,516
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Date Filed
Monday, May 1, 200024 years ago
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Date Issued
Tuesday, October 23, 200122 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 343 713
- 343 704
- 343 711
- 343 712
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International Classifications
-
Abstract
An antenna system for a vehicle radio integrated with the defogger heating elements in a window that provides enhanced impedance matching without requiring lumped matching components. The antenna system includes a vehicle window, a conductive grid embedded in the vehicle window and having a plurality of horizontal and generally parallel conductive elements, and first and second bus bars connecting the grid at opposite ends. The antenna system has first and second vertical conductive elements embedded in the vehicle window and arranged substantially orthogonal to the horizontal conductive elements. Tuning elements are coupled to each of the first and second vertical conductive elements and are substantially orthogonal thereto. The tuning elements have a length selected so as to substantially match characteristic impedance of an RF signal path. The horizontal heating elements are engaged for heating the vehicle window during a heating operation, and also serves to receive radio signals for the radio.
Description
TECHNICAL FIELD
The present invention generally relates to an antenna system for a vehicle radio and, more particularly, to an antenna system for a vehicle radio in which the antenna elements are embedded in a vehicle window and employ the window defogger heating elements.
BACKGROUND OF THE INVENTION
Automotive vehicles are commonly equipped with a radio and a corresponding antenna system to receive amplitude modulation (AM) and frequency modulation (FM) broadcast radio signals. One conventional vehicle antenna system includes a mast antenna vertically extending from the body of the vehicle. Mast antennas are generally limited in signal performance, add wind noise and drag to the vehicle, and are susceptible to corrosion and damage.
Another conventional vehicle radio antenna includes a backlite antenna system in which antenna elements are embedded in a rear window of the vehicle. Examples of backlite antenna systems are disclosed in U.S. Pat. Nos. 5,610,619, 5,790,079, and 5,099,250. The vehicle antenna set forth in U.S. Pat. No. 5,099,250 utilizes the defogger elements encapsulated in the back window of the vehicle as antenna elements to receive broadcast radio signals. Conventional antenna systems that integrate the antenna with the defogger heating elements in the rear window of a vehicle typically require bifilar or toroidal chokes coupled between the conductive window elements and the vehicle DC power supply to separate the received antenna signal from the high current signals that heat the defogger elements. These chokes provide low impedance paths for the propagation of large current flow necessary to power the defogger heating elements, and high impedance paths against the propagation of the radio signals. The chokes are generally incorporated in an antenna impedance matching network in order to match the output of the antenna elements to the input of the amplifier associated with the vehicle radio to reduce the attenuation of power transfer from the antenna elements to the radio.
Typical impedance matching networks are specially designed and vary from one type of vehicle to other types of vehicles to realize the greatest efficiency in impedance matching. This is generally because the capacitance created between the conductive elements in the vehicle body varies from vehicle to vehicle. Further, prior art antenna grid patterns are often directional at FM frequencies, and have relatively low gain at AM frequencies.
It is therefore desirable to provide for an antenna system that employs the defogger heating elements in a vehicle window, such as the rear window, and includes an antenna impedance matching network that can be incorporated into a variety of vehicles. It is further desirable to provide for such an antenna system that does not require lumped matching components.
SUMMARY OF THE INVENTION
The present invention provides for an antenna system integrated with the defogger heating elements in a window to achieve enhanced impedance matching without requiring lumped matching components. To achieve this and other advantages and in accordance with the purpose of the present invention as embodied and described herein, the present invention provides for an antenna system for a radio of a vehicle comprising a vehicle window, a conductive grid formed in the vehicle window and having a plurality of horizontal and generally parallel conductive elements, first and second bus bars connecting the horizontal conductive elements at opposite ends. The antenna system has first and second vertical conductive elements embedded in the vehicle window and arranged substantially orthogonal to the horizontal conductive elements. A tuning element is coupled to each of the first and second vertical conductive elements and is substantially orthogonal thereto. The tuning element has a length selected so as to substantially match impedance of an RF signal path. The horizontal elements are energized to heat the vehicle window during a defogger heating operation, and also serve to receive radio signals for the radio.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1
is a front elevational view of a rear window of a vehicle incorporating an antenna system integrated with a defogger heating grid according to the present invention;
FIG. 2
is a block and diagrammatic view of the antenna system for use with the vehicle radio; and
FIG. 3
is a circuit and block diagram of the antenna module shown in FIG.
2
.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to
FIG. 1
, the rear transparent window
10
of a vehicle, such as an automobile, is illustrated having an AM antenna
12
and a combination FM antenna and defogger grid
20
embedded within the transparent window
10
. The AM antenna
12
is a stand-alone antenna for receiving amplitude modulation (AM) radio frequency (RF) signals. The FM antenna and defogger grid
20
is electrically energizeable to heat the window
10
to eliminate condensation and ice from the window, as is well understood in the art, and further is utilized as part of the FM antenna for receiving frequency modulation (FM) radio wave signals. It should be appreciated that the window
10
may have an outward curvature as is conventionally known in the vehicle window art.
The AM antenna
12
is shown generally made up of three horizontal and generally parallel conductive elements
14
, each coupled at one end to a signal bus
16
. The horizontal conductive elements
14
may be configured in different lengths and numbers. Signal bus
16
is coupled to a terminal output pad
18
which, in turn, is coupled to an insulated signal conductor
36
that provides a signal path for transmitting the received AM signals to a radio.
The FM antenna and defogger grid
20
is formed below AM antenna
12
and extends across a substantial area of window
10
. The antenna and defogger grid
20
includes an array of horizontal and generally parallel conductive elements
22
, each extending between a negative defogger bus bar
24
on the left side and a positive defogger bus bar
26
on the right side. Bus bars
24
and
26
are located near the left and right edges, respectively, of window
10
. Negative defogger bus bar
24
contacts a terminal pad
28
which, in turn, is connected to an insulated wire
32
for providing a grounded signal connection to form the negative side of the defogger circuit. Positive defogger bus bar
26
likewise has a terminal pad
30
connected to an insulated wire
34
which receives DC power to form the positive side of the defogger circuit. Insulated wire
34
serves as an antenna feed pigtail and is kept as short in length as possible, preferably less than 250 mm. During the window defogging operation, bus bar
26
is energized with a positive DC voltage which generates current through each of the horizontal and generally parallel conductive elements
22
to heat window
10
to an elevated temperature for the purpose of eliminating condensation and ice from the window
10
.
According to the present invention, the FM antenna
20
further includes first and second vertical conductive elements
40
and
50
coupled to each of horizontal conductive elements
22
and further extending vertically above the uppermost conductive element by a height H
2
. Accordingly, the vertical elements
40
and
50
are arranged substantially orthogonal to horizontal elements
22
and cross each other to form crossing nodes. The first vertical conductive element
40
is connected to a substantially horizontal first tuning element
44
having a length L
1
. Tuning element
44
is preferably arranged substantially orthogonal to vertical element
40
. It should be appreciated that the length L
1
of tuning element
44
is selected so as to match the effective characteristic impedance on the output signal path
34
leading to a vehicle radio. The selection of length L
1
will generally vary from vehicle to vehicle, depending on the vehicle body construction.
The second vertical conductive element
50
is horizontally spaced apart from the first vertical conductive element
40
. Connected to the second vertical conductive element
50
is a substantially horizontal second tuning element
54
having a length L
2
. Tuning element
54
is preferably substantially orthogonal to vertical conductive element
50
. The length L
2
of tuning element
54
is likewise selected so as to substantially match the effective characteristic impedance of the RF signal exiting on output signal path
34
leading to the radio.
The upper end of vertical conductive elements
40
and
50
and tuning elements
44
and
54
are preferably formed midway between the lower end (i.e., lowest element
14
) of AM antenna
12
and the uppermost horizontal conductive element
22
of FM antenna
20
. Accordingly, height H
1
is substantially equal to height H
2
. It should be appreciated that first and second vertical conductive elements
40
and
50
with tuning elements
44
and
54
advantageously transform the characteristic impedance of the FM antenna and defogger grid
20
to a level where it becomes possible to match the characteristic impedance to the characteristic impedance of a coaxial cable RF signal path, which typically has an impedance in the range of 50 to 150 ohms.
In order to enhance the signal impedance match, and therefore increase the antenna sensitivity over the FM band frequency range, third and fourth vertical conductive elements
42
and
52
are further provided, one on either side of the corresponding vertical conductive elements
40
and
50
. Third vertical conductive element
42
is substantially parallel to first vertical conductive element
40
, but is horizontally offset and slightly out of alignment therewith. Accordingly, first and third vertical elements
40
and
42
have a separation width W
1
at the connection with the uppermost horizontal conductive element
22
and a separation width W
2
at the lowermost end termination with the bottom horizontal conductive element
22
. Width W
2
is slightly larger than width W
1
so as to compensate for the curvature of window
10
and thereby provide a constant effective width therebetween.
The fourth vertical conductive element
52
is likewise horizontally offset and slightly out of alignment with second vertical conductive element
50
. Second and fourth vertical conductive elements
50
and
52
also have a separation width W
1
at the connection with the uppermost horizontal element
22
and a slightly larger width W
2
at the termination on the lowermost horizontal element
22
so as to compensate for curvature of the window
10
and thereby provide a constant effective width therebetween. Accordingly, the addition of third and fourth vertical conductive elements
42
and
52
in proximity with and spaced from first and second vertical conductive elements
40
and
50
, respectively, advantageously increases the antenna sensitivity over the FM frequency band.
Referring to
FIG. 2
, the window
10
with AM antenna
12
and FM antenna
20
is shown coupled to an antenna module
60
, which, in turn, is coupled to a vehicle radio
62
and a defogger circuit
68
. Antenna module
60
receives AM radio wave signals from AM antenna
12
on the insulated wire
36
and FM radio wave signals from the FM antenna
20
on the insulated wire
34
. The antenna module
60
allows the received AM and FM radio wave signals to pass therethrough and onto a coaxial cable
64
to car radio
62
. The coaxial cable
64
, as well as the insulated wire
34
, provide an RF signal transmission path. In order to minimize the length of wire
34
, the antenna module
60
is preferably packaged near the FM antenna
20
, such as in the C-pillar of the vehicle. In addition, antenna module
60
is powered by a power signal on line
66
which may be supplied by radio
62
.
The defogger circuit
68
is shown coupled through antenna module
60
. Defogger circuit
68
controls energization of direct current (DC) power to the conductive defogger grid
20
for purposes of defogging the rear window
10
. When a window defogger operation is requested, the defogger circuit
68
generates a high DC current in the range of approximately sixteen to thirty amps, which is transmitted through antenna module
60
to the positive defogger bus bar
26
via insulated wire
34
. Also shown is a grounded FM trap
70
coupled to the negative defogger bus bar
24
for preventing FM signals from passing therethrough to ground. It should be appreciated that during the defogging operation, current is applied to the positive defogger bus bar
26
and passes to the negative defogger bus bar
24
through the horizontal conductive elements
22
and exits window
10
on wire
32
to FM trap
70
where the DC current passes to ground.
The antenna module
60
is further illustrated in more detail in FIG.
3
. Antenna module
60
includes an amplifier
72
for amplifying the received AM signal, and an FM trap
74
for passing the amplified AM signal to the coaxial cable
64
, while preventing FM signals from interfering with the AM amplification. The amplifier
72
is powered by a power supply
76
which, in turn, receives switched power from radio
62
. Also included in antenna module
60
is an FM trap
78
that passes the defogger DC power received from the defogger circuit
68
. FM trap
78
prevents FM signals received on FM antenna
20
from passing through the trap
78
. It should be appreciated that FM traps
78
,
74
, and
70
advantageously float the conductive grid
20
so as to enable DC current to flow through the grid
20
during the defogging operation, while not interfering with the FM signal reception.
Also included in antenna module
60
is an FM coupling capacitor
80
coupled to FM signal line
34
for receiving the FM signal and passing the FM signal to the coaxial cable
64
for transmission to radio
62
. The FM coupling capacitor
80
blocks the DC defogging current from flowing through the FM signal path and couples the FM signal to the coaxial cable
64
for transmission to the radio
62
. The FM coupling capacitor
80
and FM trap
78
together serve as a filter to isolate received radio frequency signals from the defogger current signal.
The FM antenna
20
advantageously employs vertical conductive elements
40
and
50
with corresponding tuning elements
44
and
54
in a manner that transforms the high characteristic impedance generally found in standard defogger grid elements to a level where it is possible to match the effective characteristic impedance to the coaxial cable
64
. The horizontal tuning elements
44
and
54
are selected in length so as to match the effective characteristic impedance of the coaxial cable
64
. The length of tuning elements
44
and
54
are selected for the particular type of vehicle and may vary depending on the vehicle type. It should be appreciated that the length L
1
and L
2
of corresponding tuning elements
44
and
54
determines the voltage standing wave ratio (VSWR) which affects the effective impedance and radiating power efficiency of the antenna. In order to further enhance the impedance match and therefore increase the antenna sensitivity over the entire FM frequency band (88 to 108 MHz), vertical conductive elements
42
and
52
are further included.
According to one example, the FM antenna and defogger grid
20
employs an even number of horizontal conductive elements
22
, such as
18
grid line elements as shown. However, any number of horizontal conductive elements
22
may be employed. In addition, FM antenna
20
, in one example, may employ tuning elements
44
and
54
having length L
1
equal to 350 millimeters and L
2
equals 207 millimeters. Height H
1
and H
2
may both be equal to 32 millimeters. In addition, W
1
may be set equal to 50 millimeters, while W
2
may be set equal to 60 millimeters. The aforementioned specific dimensions and other physical characteristics relating to the example disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.
Accordingly, the FM antenna grid
20
of the present invention advantageously provides for FM signal reception with an antenna that utilizes the defogger heating grid in a rear window of a vehicle. The horizontal conductive elements
22
operate to receive horizontally polarized FM radio wave signals. The FM antenna grid
20
advantageously employs vertical conductive elements
40
,
42
,
50
and
52
to receive vertically polarized radio wave signals, and further employs the tuning elements
44
and
54
to match the effective characteristic impedance of the RF signal path coaxial cable
64
, and thereby eliminates the need for conventional lumped matching components to provide special impedance matching as is generally required in most conventional rear window radio antennas. While the present invention has been described in connection with an FM antenna combined with a rear window defogger in the rear window of a vehicle, it should be appreciated that other types of signal reception may be employed, and various types of windows may be employed without departing from the teachings of the present invention.
It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.
Claims
- 1. An antenna system for a radio of a vehicle, said antenna system comprising:a vehicle window; a conductive grid formed in the vehicle window and having a plurality of horizontal and generally parallel conductive elements for heating the vehicle window during a heating operation; first and second bus bars connecting the horizontal conductive elements at opposite ends; first and second vertical conductive elements embedded in said vehicle window and arranged substantially orthogonal to said horizontal conductive elements; a first tuning element coupled to said first vertical conductive element and substantially orthogonal thereto, wherein said first tuning element has a length selected so as to substantially match a characteristic impedance of an RF signal transmission path; and a feed line coupled to one of the first and second bus bars, wherein the feed line transmits current to the conductive elements during the heating operation and further transmits RF radio wave signals.
- 2. The antenna system as defined in claim 1 further comprising a second tuning element coupled to said second vertical conductive element and substantially orthogonal thereto, wherein said second tuning element has a length selected so as to substantially match a characteristic impedance of the RF signal transmission path.
- 3. The antenna system as defined in claim 1 further comprising third and fourth vertical conductive elements coupled to said horizontal conductive elements and spaced from said first and second vertical conductive elements.
- 4. The antenna system as defined in claim 3, wherein said third vertical conductive element is substantially parallel to said first conductive element, and said fourth vertical conductive element is substantially parallel to said second vertical conductive element.
- 5. The antenna system as defined in claim 1, wherein said RF signal transmission path comprises a coaxial cable electrically coupled to said antenna system and adapted to be coupled to a radio.
- 6. The antenna system as defined in claim 1 further comprising an antenna module including a filter for isolating received RF signals from a heating current signal.
- 7. The antenna system as defined in claim 1, wherein said first tuning element is disposed substantially midway between one end of said horizontal conductive elements and an end of another antenna.
- 8. The antenna system as defined in claim 1, wherein said antenna system comprises an FM antenna system.
- 9. An antenna provided in a vehicle window and operative with an array of heating elements, said antenna comprising:a vehicle window; a conductive heating grid formed in the vehicle window and having a plurality of horizontal and generally parallel conductive elements for heating the vehicle window during a heating operation; a first vertical conductive element connected to said horizontal heating elements and arranged substantially orthogonal thereto; a second vertical conductive element connected to said horizontal heating elements and arranged substantially orthogonal thereto; a first tuneable conductive element connected to said first vertical conductive element, said tuneable conductive element being located substantially orthogonal to said first vertical conductive element and having a first length selected so as to substantially match a characteristic impedance of an RF signal transmission path; a second tuneable conductive element connected to said second vertical conductive element, said tuneable conductive element being located substantially orthogonal to said second vertical conductive element and having a second length selected so as to substantially match the characteristic impedance of the RF signal transmission path; and a feed line coupled to one of the first and second bus bars, wherein the feed line transmits current to the conductive elements during the heating operation and further transmits RF radio wave signals.
- 10. The antenna system as defined in claim 9 further comprising third and fourth vertical conductive elements coupled to said horizontal heating elements and separate from said first and second vertical conductive elements.
- 11. The antenna system as defined in claim 9, wherein said RF signal transmission path comprises a coaxial cable electrically coupled to said antenna system and adapted to be connected to a radio.
- 12. An antenna system for a radio of a vehicle, said antenna system comprising:a vehicle window; a conductive grid formed in the vehicle window and having a plurality of horizontal and generally parallel conductive elements for heating the vehicle window during a heating operation; first and second bus bars connecting the horizontal conductive elements at opposite ends; a first vertical conductive element formed in the vehicle window and arranged substantially orthogonal to said horizontal conductive elements; a second vertical conductive element formed in said vehicle window and arranged substantially orthogonal to said horizontal conductive elements; a third vertical conductive element formed in said vehicle window and arranged substantially orthogonal to said horizontal conductive elements; a fourth vertical conductive element formed in said vehicle window and arranged substantially orthogonal to said horizontal conductive elements, wherein said first, second, third and fourth vertical conductive elements are spaced apart from one another; and a feed line coupled to one of the first and second bus bars, wherein the feed line transmits current to the conductive elements during the heating operation and further transmits RF radio wave signals.
- 13. The antenna system as defined in claim 12 further comprising a first tuning element coupled to said first vertical conductive element and arranged substantially orthogonal thereto, wherein said first tuning element has a length selected so as to substantially match a characteristic impedance of an RF signal transmission path.
- 14. The antenna system as defined in claim 13 further comprising a second tuning element coupled to said second vertical conductive element and arranged substantially orthogonal thereto, wherein said second tuning element has a length selected so as to substantially match a characteristic impedance of the RF signal transmission path.
- 15. The antenna system as defined in claim 13, where in said RF signal transmission path comprises a coaxial cable electrically coupled to said antenna system and adapted to be connected to a radio.
- 16. The antenna system as defined in claim 12, wherein said first and third vertical conductive elements are substantially parallel to each other and spaced from one another by a first separation distance, and wherein said second and fourth vertical conductive elements are substantially parallel and spaced from one another by a second separation distance, such that first and second separation distances are substantially equal.
US Referenced Citations (9)