U.S. patent number 3,623,108 [Application Number 04/824,041] was granted by the patent office on 1971-11-23 for very high frequency antenna for motor vehicles.
This patent grant is currently assigned to The Boeing Company. Invention is credited to Wilbur F. DuBois, Conrad O. Gardner.
United States Patent |
3,623,108 |
DuBois , et al. |
November 23, 1971 |
VERY HIGH FREQUENCY ANTENNA FOR MOTOR VEHICLES
Abstract
An omnidirectional type antenna for very high frequency
receivers in motor vehicles. The antenna utilizes a single
conductive element coupled between a very high frequency receiver
located below the front windshield and a conductive connection with
the body of the motor vehicle at a point immediately above the
front windshield and at the center thereof. A series coupling
capacitor provides coupling of the conductive element to the very
high frequency receiver. The ground connection for the very high
frequency receiver is provided by a conductive connection from the
receiver to a point on the body of the motor vehicle below the
front windshield. The conductive element extends from the point at
the center of and above the front windshield vertically downward
through or adjacent to the windshield to the very high frequency
receiver or extends vertically downward through the corner post
between the front windshield and the adjacent side door.
Inventors: |
DuBois; Wilbur F. (Seattle,
WA), Gardner; Conrad O. (Seattle, WA) |
Assignee: |
The Boeing Company (Seattle,
WA)
|
Family
ID: |
25240457 |
Appl.
No.: |
04/824,041 |
Filed: |
May 13, 1969 |
Current U.S.
Class: |
343/702 |
Current CPC
Class: |
H01Q
1/3291 (20130101) |
Current International
Class: |
H01Q
1/32 (20060101); H01q 001/32 () |
Field of
Search: |
;343/705,708,711,712,713,720,767 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
576,856 |
|
Mar 1958 |
|
IT |
|
1,237,187 |
|
Jun 1960 |
|
FR |
|
Primary Examiner: Lieberman; Eli
Claims
We claim:
1. In a motor vehicle having a metallic conductive roof of
generally rectangular dimension disposed above the front windshield
thereof and separated from a metallic body portion disposed below
said front windshield by window discontinuities distributed around
the vehicle between said roof portion and said metallic body
portion, a very high frequency receiving system comprising in
combination:
a very high frequency receiver for said system, said very high
frequency receiver being electrically grounded to said metallic
body portion;
a very high frequency antenna arrangement for coupling very high
frequency signals to said receiver, said high-frequency antenna
arrangement comprising,
an electroconductive element extending from said conductive roof
portion to said receiver, said electroconductive element being
coupled to said conductive roof portion at substantially the
geometric center of said rectangular dimension for achieving
omnidirectionality characteristics, and means for electrically
insulating said electroconductive element from said metallic body
portion.
Description
This invention relates to very high frequency (V.H.F.) antennas for
motor vehicles, and more particularly to a V.H.F. antenna system
having omnidirectional characteristics.
While present state of the art V.H.F. receiver design has been able
to provide the mobile receiver industry with receivers having
excellent noise, sensitivity, and selectivity characteristics,
V.H.F. receivers for F.M. and F.M. stereo reception have not been
able to displace the A.M. radio as an entertainment device in motor
vehicles. While integrated circuits and other recent technological
developments in the fabrication of electronic components and
devices and mass fabrication techniques have added to continually
lower the cost to the consumer of V.H.F. receivers and make them
competitive with A.M. receivers, the consumer has been generally
unsatisfied with the performance of V.H.F. receivers and has been
leaning toward the purchase of stereo tapes and cartridges which
provide him with the high quality reproduction he desires when
listening to music in his motor vehicle. The same high quality
reproduction in music is available through the V.H.F. stereo radio
receivers only if an antenna having the proper characteristics can
be coupled to provide the necessary signal levels and maintain them
in fringe areas and during changes of direction of the vehicle with
respect to the transmitting antenna. Various prior art V.H.F.
antennas have been developed for mobile installations, but each of
the various types represented by the patent literature and those in
current use have not provided the several qualities required by the
consumer and consequently have been rejected by him as
unsatisfactory.
The several characteristics which are required in a satisfactory
mobile V.H.F. antenna include the following:
A. Omnidirectional characteristics. Unless the V.H.F. antenna is
omnidirectional, a change of vehicle direction with respect to the
transmitting antenna will cause a change in amplitude of the signal
voltage delivered by the mobile receiving antenna at the input of
the receiver. Where the field strength pattern of the antenna is
other than omnidirectional, a change in direction may cause abrupt
loss of signal and consequent reception or other undesirable
effects.
B. Satisfactory gain. If an antenna is made omnidirectional at very
high frequencies, there is in many instances a consequent loss of
gain. While omnidirectional characteristics can be achieved to some
degree, for example, by a monopole type antenna, its gain is not
appreciable over a reference dipole. While techniques are known in
V.H.F. antenna design for increasing the gain of an omnidirectional
antenna by vertical stacking of dipoles, such as in the well-known
collinear type antenna arrangements, such structures become
undesirable for mobile installations because of size, necessity for
supporting structure, increased wind resistance, etc., and
consequently such techniques for increasing the gain of
omnidirectional V.H.F. antennas are generally limited to
installations of a fixed nature.
The several characteristics which are desirable in a satisfactory
mobile V.H.F. antenna include the following:
a. The antenna should be aesthetically pleasing to the eye. The
ultimate in this regard would be a V.H.F. antenna which is
completely concealed or hidden from view.
b. The V.H.F. antenna should be inexpensive. Known types of V.H.F.
antennas sometimes materially increase the cost of the entire radio
receiver system installation, particularly where there is a labor
cost of cutting through the vehicle body and installation outside
the factory.
c. The antenna installation should be resistant to shock and
vibration damage and not susceptible to damage by vandalism.
It is therefore an object of this invention to provide a V.H.F.
antenna which provides the above delineated characteristics both
those specified as desirable and those which are required.
It is yet a further object of this invention to provide for
improved performance in a mobile V.H.F. receiving system by
providing an antenna in the system which is omnidirectional and
responsive to both horizontally and vertically polarized waves and
waves having the polarization of the type presently utilized by
frequency modulation (F.M.) stations in the broadcast service.
It is still another object of this invention to provide an
omnidirectional type antenna arrangement of minimal cost for
reception of V.H.F. frequency modulation broadcast signals in the
88-108 megacycles band.
Other objects of this invention will become apparent from the
following description when taken in conjunction with the
accompanying drawings in which:
FIG. 1 is a perspective view of the interior of a motor vehicle
illustrative of one embodiment of a V.H.F. antenna system
arrangement coupled to a receiver in accordance with the teachings
of the invention.
FIG. 2 is a perspective view of the interior of a motor vehicle
showing a further embodiment of a V.H.F. antenna system arrangement
coupled to a receiver in accordance with the teachings of this
invention.
FIG. 3 illustrates in block schematic form details of the receiving
system including transmission line coupling to the antenna system
arrangements of FIGS. 1 and 2.
In accordance with the invention, a V.H.F. receiver is coupled to
different points on the conductive body portion of a motor vehicle
to provide both the antenna arrangement and ground connections for
the V.H.F. receiver. The location of the antenna arrangement
connection to the conductive body portion is in the region above
the front windshield of the motor vehicle. The ground connection
from the receiver occurs on that portion of the conductive body
below the windshield. The particular configurations of antenna
arrangements, transmission line arrangements, manner of coupling to
the V.H.F. receiver and ground for the V.H.F. receiver illustrated
provide the desired omnidirectionality and gain
characteristics.
Referring now to FIG. 1 of the drawings, reference numeral 10
refers to the lower body portion of an automobile body, and
including the frame portion at or below the level of the decorative
finish moulding 22 which runs along the bottom edge of the
conventional automobile front windshield 14 and all portions of the
automobile in conductive contact therewith which do not extend
above the level of the decorative finish moulding 22. A decorative
strip extends around the window opening of "wraparound" windshields
in modern automobiles and having an upper portion 20 running along
the upper edge of the front windshield 14 and a lower portion 22
running along the lower edge of the front windshield 14. The side
portions 61 of the decorative strip are coextensive with and cover
a portion of the sideposts 18 of the motor vehicle. The sideposts
18 separate the lower body portion 10 from the upper body portion
or roof portion 16 of the motor vehicle. A conventional automobile
includes a rear view mirror 26 mounted on a mounting bracket 24
suspended from the upper body portion or roof portion 16 of the
automobile directly behind the center of the upper portion 20 of
the decorative strip and also behind the midpoint of the upper edge
of the windshield 14. The upper portion 20 of the decorative strip
extends along and closely adjacent to the upper edge of the front
windshield 20. The upper body or roof portion 16 of the motor
vehicle includes all the metallic roof portion forming the top
exterior surface of the automobile and all conductive material in
conductive contact therewith above the corner posts and top level
of the front windshield 14 covered by upper portion 20 of the
decorative moulding strip. The screws 29 which hold the mounting
bracket 24 suspended from the upper body portion or roof portion 16
make conductive contact with and therefore form part of the roof
portion 16. The antenna arrangement installed in accordance with
the principles of the present invention in the manner illustrated
in FIG. 1 is coupled to a receiver 30 capable of V.H.F. reception
in the manner shown in more detail in FIG. 3.
While attempts have been made to derive radio frequency signal
energy at broadcast band frequencies of 550 to 1600 kilocycles from
metallic bodies of automobiles as exemplified, for example, in U.S.
Pat. No. 2,353,111, such efforts have been largely unsuccessful for
several reasons including the pick up of undesirable signal
impulses representing high frequency interference originating in
the ignition system of the automobile itself and other surrounding
automobiles. Indeed, in the above-referred-to patent and in U.S.
Pat. No. 1,943,394, attempts were made to overcome this problem by
utilizing particular types of circuit arrangements or modifying the
antenna arrangement itself. The trend has been away from the
earlier attempted use of antenna arrangements utilizing direct
coupling to the metallic body of the automobile at A.M. broadcast
band frequencies because of the various deficiencies including
noise developed by such antennas. Presently a monopole antenna has
been used extensively for reception of signals in the A.M.
broadcast band and efforts have also been made to avoid coupling to
the automobile metal in the design of new antennas as, for example,
in U.S. Pat. No. 3,414,902.
Coupling across discontinuities in the conductive bodies of motor
vehicles to derive radio frequency signals has been effected at
broadcast band frequencies as shown in U.S. Pat. No. 2,923,813
where the window openings constitute the discontinuities and also
at F.M. band frequencies as typified by U.S. Pat. No. 2,575,471
where coupling was made to a long narrow air gap or slot in the
body surface such as the trunk slot. Such coupling, however, has
resulted in non-omnidirectional types of radiation patterns, and in
the former reference U.S. Pat. No. 2,923,813 such deficiency is
sought to be overcome by coupling also to a second window on an
opposite side of the vehicle (see col. 8, line 62), whereas in the
latter U.S. Pat. No. 2,575,471 the cardioid pattern which results
in less signal strength from the direction in which the vehicle is
facing is accepted (see col. 3, line 11). While signal voltages
have been developed across different discontinuities such as the
trunk slot or windows as mentioned above, directional
characteristics of such antennas are accentuated which are
dependent on their location at the back or side of the vehicle. The
antenna arrangements of FIGS. 1 and 2, however, rely upon
development of the V.H.F. signal voltage between points on the roof
portion 16 and the lower body portion 10. The hereinafter described
V.H.F. receiving apparatus derives its input signal voltage between
a point on each of these separated surfaces which are in fact
separated by the window discontinuities distributed around the
vehicle between these two surfaces. The signal voltage is not
developed from the perimeter of or directly across the single
discontinuity such as a window or trunk slot. Excellent
omnidirectionality characteristics are achieved where the signals
are derived between the points shown in FIGS. 1 or 2. In practicing
this invention it was found that the gain of the antenna
arrangement illustrated in FIG. 1 exceeded the gain of the
installation shown in FIG. 2. While the theoretical explanation of
the manner in which the new antenna system functions is quite
complex due to the complex nature of the surface area over which
the signal voltages are developed, since the gain increased when
the contact to the roof portion was located at the center where the
dome light is located, it would appear that if the windows are
acting as discontinuities and developing signal voltages as has
been indicated in prior art theoretical explanations, then better
coupling to more discontinuities is being achieved in the
arrangement of FIG. 1 than in the arrangement of FIG. 2.
In the antenna arrangement illustrated in FIG. 1, electroconductive
element 12 is coupled from a point 34 on the upper body portion or
roof portion 16 to the input terminal 50 (shown in FIG. 3) of the
receiver 30 which is capable of receiving and processing very high
frequency modulated broadcast signals in the 88-108 megacycles band
and providing audio output to the speaker system 53 (shown in FIG.
3). The signals are developed between point 34 on the upper body
portion 16 and another point 37 termed ground connection for the
receiving system. This point 37 is in conductive relationship with
the lower body portion and establishes the reference point above
which the received signal from the antenna arrangement is
developed. Point 37 in the arrangement shown in FIG. 1 is the
grounded or outer braided portion 36 of shielded cable 38 at the
receiver end of electroconductive element 12. The shielded outer
braid 36 is brought to the ground connection 37 at the receiver 30
chassis by means of a male type coaxial connector, the center
conductor of the coaxial connector being soldered to the
electroconductive element 12 and the male connector being
positioned in the female connector which is mounted on the receiver
chassis, thereby providing a direct electrical connection between
the electroconductive element 12 and receiver input terminal 51.
The V.H.F. receiver 30 is fastened to the lower body portion 10 to
provide the ground connection for this receiving system. Point 34
is the screw or fastening point for attaching the dome light 32 to
the roof portion 14 of the motor vehicle. While electroconductive
element 12 is shown as comprising the inner conductor of shielded
cable 38 (which may comprise a low impedance 50-ohm coaxial
transmission line) having an outer sheath 36 grounded to the
receiver chassis, tests have shown that electroconductive element
12 can comprise an insulated wire. When an insulated wire is
utilized, it may be positioned behind the ceiling and corner post
interior upholstery of the vehicle. While previously mentioned
V.H.F. antennas have developed signal voltages directly across a
single discontinuity, such as window or trunk lid, the present
arrangement can be seen to develop a signal voltage between two
large metallic surface areas isolated by discontinuities in the
form of windows between them. The contacts made to these large
surface areas provide an antenna arrangement having the desired
degree of omnidirectionality. The lower or ground side of the
antenna arrangement is not adjacent the window frame or
discontinuity as heretofore but is positioned well down in the
lower body portion at the receiver mounting connection point which
is at least 2 or more inches below the front windshield periphery.
The upper body contact point 34 was made in the central region of
the roof portion 16, specifically to the dome light 32 mounting
screw 34 where maximum gain was realized. The signal voltages
developed between these two contact points so remotely located in
the upper and lower body portions were highly satisfactory. When
this particular antenna arrangement was utilized with an F.M.
receiver having a ratio detector but without limiters, the noise
level did not appear as high as might have been expected due to the
utilization of large spaced apart metallic surfaces. The gain of
this arrangement utilizing insulated wire appeared to exceed the
gain of the previously utilized exteriorly mounted monopole antenna
while requiring only a single electroconductive element 12
connected and located in the above-described manner.
Referring now to FIG. 2, it can be seen that while the ground
return for the V.H.F. receiving system remains the receiver 30
chassis coupled to the lower body portion 60 by its mounting
arrangement beneath the cowl 60, the signal voltages are developed
between a mounting screw 29 for the mirror mounting bracket 24 and
the above defined ground return to the lower body portion. The
mounting screw 29 provides conductive contact to the upper body
portion 16 at its edge adjacent and above the center of the front
windshield 14. While this arrangement provides somewhat less gain
than the arrangement shown in FIG. 1, such location minimizes the
need for shielding of the electroconductive element 12 extending
from a point on the upper roof portion 16 to the receiver input
terminal 51 and also permits a minimum length of electroconductive
element 12. Since electroconductive element 12 in this arrangement
is comprised of a first section comprising the wire element 40
passing in a generally vertical direction downward, inside or on
the surface of the windshield 14, it is not required to be
insulated here nor shielded since not running along a low impedance
metallic body surface, and the lower section 48 of
electroconductive element 12 which is coupled to the end of element
40 is very short in length and not required to be shielded since
the distance on to the receiver input terminal is less than 2 feet
in most cases, depending upon exact receiver mounting position in
the particular type and style motor vehicle. Techniques for placing
the wire elements within the windshield 14 which may be of the
laminated type are shown in the previously referred to U.S. Pat.
No. 3,414,902. The method of coupling lower section 48 through
metal foils 46 and 42 to wire element 40 is the same as that shown
in FIG. 1 of U.S. Pat. No. 3,414,902 wherein braid 32 is coupled
through corresponding foils 48 and 46 to wire element 40z. In FIG.
2 of this application, lower section 48, which is simply an
insulated length of wire, is brought through aperture 59 in the
cowl down to the receiver terminal 51. The overall physical length
of the electroconductive element 12 made up of wire element 40 and
lower insulated wire section 48 is less than 1/2 wavelength in free
space at the lowest frequency of the very high frequency band tuned
by receiver 30, the total physical length of electroconductive
element 12 including sections 40 and 48 being about 48 inches. A
single length of insulated wire about 48 inches long, coupled
between mirror bracket 24 and receiver input terminal 51, in tests
provided excellent reception in weak signal areas when the receiver
30 used was a Sears, Roebuck and Co. model number 833.62830 all
transistor A.M./F.M. 12-volt portable autoradio, and the receiver
was tuned to stations in the F.M. band. The electroconductive
element 12 which may be a single section of wire or length of low
impedance (50 ohm) type coaxial cable as in FIG. 1, or may comprise
two sections which include a wire element 40 and insulated wire 48
as in FIG. 2 is coupled to the receiver input terminal 51 as shown
in FIG. 3. The electroconductive element 12 may be incorporated in
all vehicles during the vehicle assembly process previous to the
insertion of interior decorational material and coupled in
accordance with the teachings of this invention to provide a highly
satisfactory V.H.F. antenna arrangement of minimum cost to the
industry. A series capacitor 52 may then be coupled between
receiver input terminal 51 and the high side terminal 50 of the
antenna input coil, the capacitor 52 having a range of 7 picofarads
to 40 picofarads. This capacitor 52 is peaked to provide maximum
signal in the receiver.
When capacitor 52 was peaked for a midband F.M. station, it was not
found necessary with this antenna arrangement to readjust the
matching capacitor 52 at either end of the F.M. broadcast band to
provide adequate signal strength from stations located near the
band edges which is indicative of the desirable broadband
characteristics of this antenna configuration. Where
electroconductive element 12 was about 48 inches long, the
capacitance setting of capacitor 52 for maximum signal strength of
a midband station in the receiver was found to be about 22
picofarads. The receiver 30 utilized in tests of the type and model
number previously identified did not include limiter circuitry and
therefore the noise characteristics of test antenna arrangements
could be monitored and were found to be much lower than expected.
The noise level was found to be higher in configurations tested
which utilized an unshielded electroconductive element 12 passing
along the corner post 18 as in FIG. 1 instead of down along the
windshield as in FIG. 2, which effect was probably due to increased
coupling to the metallic body in the latter case. The
above-identified receiver is shown as block 30 in FIG. 3, the
receiver circuit beyond F.M. R.F. amplifier stage 70 utilizing
transistor 70 is well known and as illustrated may be typically of
the previously identified type and model number. Speaker leads 80
couple the audio output signals from the receiver to speaker system
53. Capacitor 52 shown serially connected between the receiver
input terminal 51 and antenna input coil terminal 50 may be located
inside the receiver as illustrated or may be serially connected
instead between the receiver input terminal 51 and
electroconductive element 12 and located physically outside the
receiver 30.
While receiver 30 has been shown herein as a V.H.F. receiver
capable of tuning the F.M. broadcast band for entertainment, the
receiver 30 may be a fixed frequency or tunable V.H.F. receiver
capable of operation on a frequency or frequencies assigned to and
utilized by other services such as, for example, police, fire,
marine, television or aeronautical. The antenna structures herein
shown may be utilized in accordance with the techniques described
on motor vehicles of various types having an upper body or roof
portion 16 and lower body portion 10 separated by discontinuities
formed by windows 14 or the like which extend between and separate
the large metallic surfaces 16 and 10.
* * * * *