U.S. patent number 3,576,576 [Application Number 04/772,182] was granted by the patent office on 1971-04-27 for concealed windshield broadband antenna.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to William K. Jensen.
United States Patent |
3,576,576 |
Jensen |
April 27, 1971 |
CONCEALED WINDSHIELD BROADBAND ANTENNA
Abstract
An AM-FM antenna for vehicular radio receivers comprising a pair
of L-shaped fine wire conductors disposed between the laminates of
a windshield in reversely symmetrical relation and connected to a
receiver by way of a coaxial lead. Spacings between the conductors
and the vehicle body portion bounding the windshield are chosen to
capacitively load the antenna for AM reception and to resonate the
antenna for FM reception.
Inventors: |
Jensen; William K. (Royal Oak,
MI) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
25094217 |
Appl.
No.: |
04/772,182 |
Filed: |
October 31, 1968 |
Current U.S.
Class: |
343/712; 343/873;
343/830 |
Current CPC
Class: |
H01Q
1/1271 (20130101); B60J 1/02 (20130101); B32B
17/10036 (20130101) |
Current International
Class: |
B60J
1/02 (20060101); H01Q 1/12 (20060101); H01q
001/32 () |
Field of
Search: |
;343/705,708,711,720,712,830,873 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Leberman; Eli
Claims
I claim:
1. An AM-FM broadband radio antenna for a vehicle-mounted receiver
comprising in combination: a metallic vehicle body element defining
a window opening, a window disposed in the opening, first and
second conductors having terminal ends, the conductors being
disposed in the opening in reversely symmetrical relation and
supported by the window, each of the conductors having a portion
relatively closely adjacent but spaced from the metallic body
element and a portion relatively remote from the metallic body
element, the relatively remote portions serving to develop
electrical radio signals in response to intercepted electromagnetic
radio waves, the relatively adjacent portions providing a
capacitance determined as a function of the length of the
relatively adjacent portions and as a function of the spacing of
the relatively adjacent portions from the metallic body element,
the capacitance having such a value that the relatively adjacent
portions serve to tune the relatively remote portions for maximum
performance in both the AM band and the FM band, and means
electrically connecting the terminal ends of the remote conductor
portions and the body element to a receiver in the vehicle.
2. An AM-FM broadband radio antenna for a vehicle-mounted receiver
comprising in combination: a metallic vehicle body element defining
a windshield opening, a windshield disposed in the opening, first
and second conductors having terminal ends, the conductors being
disposed in the opening in reversely symmetrical relation and
supported by the windshield, each of the conductors having a first
portion extending transversely of the windshield and relatively
closely adjacent but spaced from the body element and a second
portion extending longitudinally of the windshield and relatively
remote from the metallic body element, the second conductor
portions serving to develop electrical radio signals in response to
intercepted electromagnetic radio waves, the first conductor
portions providing a distributed inductance and a distributed
capacitance, the distributed inductance determined as a function of
the length of the first conductor portions, the distributed
capacitance determined as a function of the length of the first
conductor portions and as a function of the spacing of the first
conductor portions from the metallic body element, the distributed
inductance and the distributed capacitance having such values that
the first conductor portions serve to tune the second conductor
portions for proper impedance matching in the AM band and for
maximum resonant response in the FM band, contact means
electrically connecting the terminal ends of the second portions,
and means electrically connecting the contact means and the body
element to a receiver in the vehicle.
3. A broadband radio antenna for a vehicle-mounted receiver
comprising in combination: a windshield aperture in the vehicle
defined by a metallic body element, a laminated windshield of known
dielectric constant disposed within the aperture, first and second
conductors disposed between the laminates of the windshield, and
having transverse portions adjacent but spaced from the body
element bounding the upper periphery of the windshield and
longitudinal portions extending in spaced parallel fashion along
the centerline of the windshield, an antenna lead comprising
coaxial center and outer conductors for connecting the first and
second conductors to a radio receiver, means adjacent the bottom
periphery of the windshield for electrically connecting the
longitudinal portions of the first and second conductors to the
center conductor, means connecting the body element to the outer
conductor, the first and second conductors being constructed and
arranged to operate as a capacitively loaded dipole antenna in the
AM band and a resonant antenna in the FM band.
4. A broadband radio antenna as defined in claim 3 wherein the
transverse portions are of effectively dissimilar length to
resonate the antenna at spaced frequencies in the FM band.
5. An AM-FM antenna for vehicular radio receivers comprising in
combination: a windshield aperture defined by a metallic vehicle
body element, a laminated windshield of known dielectric constant
diaposed within the aperture, first and second L-shaped fine wire
conductors disposed between the laminates of the windshield in
reversely symmetrical relation, each of the conductors having a
transverse portion adjacent but spaced from the body element
bounding the top periphery of the windshield, and a longitudinal
portion extending in spaced parallel fashion along the centerline
of the windshield to points adjacent the bottom periphery thereof,
an antenna lead comprising coaxial center and outer conductors for
connecting the first and second conductors to a radio receiver,
means connecting the first and second conductors to the center
conductor at said points, and means connecting the body element to
the outer conductor, the first and second conductors being
constructed and arranged such that in the AM band the transverse
portions operate as capacitors loading the longitudinal portions,
and in the FM band the transverse portions operate as a
transmission line with the adjacent body element to resonate the
conductors.
6. A broadband radio antenna as defined in claim 5 wherein the
transverse portions are of dissimilar length to resonate the first
and second conductors at spaced frequencies in the FM band.
Description
INTRODUCTION AND SUMMARY OF THE INVENTION
This invention relates to antennae for vehicular radio receivers
and more particularly to a broadband antenna which includes
conductors disposed within a vehicle window opening such as the
windshield aperture.
In accordance with the present invention a highly inconspicuous
antenna for vehicle radio receivers is provided. This is
accomplished by placing conductors such as fine wires within a
window opening in the vehicle body. So disposed, the conductors may
be supported by the glass in the window. In a specific and
preferred embodiment, the conductors are placed in the windshield
aperture between the glass laminates so as to be fully supported in
a fixed position relative to the body.
The present invention also provides an antenna of a configuration
which exhibits broadband reception characteristics so as to
accommodate both AM and FM signal reception. In general, this is
accomplished through the use of two separate conductors of
reversely symmetrical disposition each of which includes a portion
which is relatively close to a metallic body element and a portion
which is relatively remote from the metallic body. The conductor
portions which are relatively remote from the body intercept the
incident radio waves and the conductor portions which are
relatively close to the body act to condition the antenna for
broadband reception. In the AM band, the conductor portions
relatively close to the body form capacitor elements which load the
remote portions for proper antenna impedance characteristics. In
the FM band, the relatively close conductor portions act to
resonate the antenna conductors for maximum response in the
standard FM frequency band.
Further features and advantages of the invention will become
apparent upon reading the following specification which is to be
taken with the accompanying drawings of which:
FIG. 1 is a plan view of a vehicle windshield incorporating an
embodiment of the present invention; and
FIG. 2 is a bottom view of the vehicle windshield showing more of
the nature of the connection means.
In FIG. 1, the illustrative embodiment of the antenna comprises a
pair of L-shaped fine wire conductors 10 and 12 having terminal
ends and being disposed in reversely symmetrical fashion within a
vehicle windshield aperture defined by a surrounding metallic body
molding 14. While the molding 14 is shown as one piece, it may also
consist of several connected sections. Conductors 10 and 12 are
supported in the position shown by the windshield glass 16. This
may be accomplished by placing the conductors 10 and 12 in the
thermoplastic layer 18 between laminates 20 and 22 shown in FIG. 2.
Alternatively, the conductors may be disposed on the surface of
glass 16 by means of a transparent plastic tape.
As shown in FIG. 1 with reference to conductor 10, each of the
reversely symmetrical conductors 10 and 12 includes a transverse
portion A which is relatively closely adjacent the body molding 14.
Each conductor also includes a longitudinal portion B which is near
the centerline of windshield glass 16 and thus is relatively remote
from the body molding 14.
The longitudinal portions B of conductors 10 and 12 extend in
parallel fashion to a point in the bottom center of the windshield
glass 16. At this point conductors 10 and 12 are electrically
connected to a copper foil contact 24. As shown in the FIGS.,
contact 24 extends between the laminates 20 and 22 to the bottom
periphery where it wraps around the interior laminate 20.
The antenna comprising conductors 10 and 12 is connected to a radio
receiver 26 by means of a coaxial conductor cable 28. The center
conductor of cable 28 is connected by a short lead 30 to the foil
contact 24. The outer conductor of cable 28 is connected to the
body molding 14 by a conductor represented at 32. The body molding
14 is grounded as indicated at 34.
It will be understood that receiver 26 may be equipped for either
AM or FM broadcast reception or, alternatively, it may be equipped
for both AM and FM reception as is often the case. The antenna
represented by conductors 10 and 12 in the windshield aperture
defined by molding 14 is effective to abstract energy from passing
radio waves in both AM and FM frequency bands. Accordingly, the
antenna is particularly suitable for broadband applications.
In the AM band of 550 to 1,600 kc., the conductors 10 and 12
constitute a capacitively loaded, two-conductor antenna. To
abstract maximum energy from a passing AM frequency radio wave, it
is desirable to match the reactance of the load with a reactive
component of antenna impedance of opposite type or sign. The
transverse conductor portions A of conductors 10 and 12 are
capacitively coupled to the adjacent grounded body molding 14.
Accordingly, the capacitances produced by the transverse portions
are in series with the longitudinal conductor portions B and serve
to at least approximate the desired reactance match. It has been
found that with the antenna conductor disposed within the laminates
20 and 22, a satisfactory capacitance value of more than 40 pf. can
be achieved at 900 kc. Of course, it will be understood that wire
size, length and spacing may affect this value, as well as the
dielectric constant of the material between the conductors 10 and
12 and the body molding 14.
For FM broadcast reception, the transverse portions A adjacent body
molding 14 may be considered to function as an open wire
transmission line having distributed inductive and capacitive
impedance characteristics. The longitudinal portions B again act as
a short vertical antenna. Like all transmission lines, the
conductors 10 and 12 act as a resonant circuit. Antenna resonance
occurs when the open circuit impedance of the top sections formed
by transverse portions A and the reactance of the longitudinal
portions B cause zero total reactance. It has been found that by
proper choice of wire size, length and spacing, this resonant
circuit may be made resistive, that is, resonant, at approximately
the center of the FM band, 100 mc. Thus the antenna presents a
relatively constant impedance to the receiver 26 over the FM
band.
Although not to be understood as limiting the present invention,
the following design parameter numbers have been found to give good
performance in both the AM and FM bands: ##SPC1##
The transverse conductor portions A may be of the same length as
indicated above to produce a purely resistive, or resonant,
condition at a frequency at or approximately at the center of the
FM band. Alternatively, the portions A may be made of dissimilar
length or dissimilar spacing relative to the molding 14. Changes in
the conductor length and spacing result in changes in the
distributed impedance quantities and thus alter the resonant
frequency. Since the conductors 10 and 12 are physically separate,
it is possible to resonate one conductor at a frequency of less
than 100 mc. and the other conductor at a frequency of more than
100 mc. For example, resonant frequencies of 92 mc. and 108 mc. are
obtainable with changes in conductor length of 10 percent or
less.
It has been found that a change in the spacing between conductor
portions A and the body molding 14 produces a less proportional
shift in resonance than does a change in wire length. Accordingly,
it may ordinarily be preferable to vary antenna characteristics by
changing conductor length where such change is desired.
It has also been found that the window opening defined by body
molding 14 exhibits a resonant cavity characteristic which results
in antenna sensitivity to signals of frequencies in bands other
than AM and FM. For example, the combination of the conductors 10
and 12 in a typical windshield opening exhibits a resonance at
approximately 27 mc. which is within the Citizens Band.
Accordingly, the antenna may also serve additional special purpose
receivers.
It is to be understood that the foregoing description refers to an
illustrative embodiment of the invention and is not to be construed
in a limiting sense.
* * * * *