U.S. patent number 3,689,928 [Application Number 05/102,724] was granted by the patent office on 1972-09-05 for multi-band tunable halfwave whip antenna.
This patent grant is currently assigned to International Telephone and Telegraph Corporation, Nutley. Invention is credited to Robert A. Felsenheld.
United States Patent |
3,689,928 |
|
September 5, 1972 |
MULTI-BAND TUNABLE HALFWAVE WHIP ANTENNA
Abstract
A physically shortened halfwave antenna of the whip type is
disclosed. The antenna includes a main antenna rod, a pair of
helices, one helix coupled to each end of the rod, and a capacitive
top load coupled to the upper one of the helices. An RF terminal is
inductively coupled to the lower one of the helices to supply RF
energy to or remove RF energy from the antenna. A variable
capacitance means is coupled between the lower helix and a
capacitive bottom load, which may be ground, a small ground plane
or an equivalent arrangement, to resonate the antenna. A plurality
of lower helices and an associated variable capacitance means for
each are selectively connected to the rod to enable the antenna to
cover a relatively broadband frequency range. In one embodiment an
inductive coupling to the lower helix is accomplished by a single
tuned arrangement for the lower frequency band of the frequency
range and by a doubled tuned arrangement for the middle and upper
frequency band of the frequency range. Other embodiments may
include all single tuned arrangements, all double tuned
arrangements or a different combination of single and double tuned
arrangements than that used for said one embodiment. A directional
coupler and capacitance control arrangement are provided to adjust
the capacitance of the variable capacitance means for reresonating
the antenna when the resonance of the antenna is changed by an
object coming into the proximity of the antenna.
Inventors: |
Robert A. Felsenheld
(Livingston, NJ) |
Assignee: |
International Telephone and
Telegraph Corporation, Nutley, (N/A)
|
Family
ID: |
22291363 |
Appl.
No.: |
05/102,724 |
Filed: |
December 30, 1970 |
Current U.S.
Class: |
343/703; 343/745;
343/752; 343/749 |
Current CPC
Class: |
H03H
7/40 (20130101); H01Q 9/145 (20130101); H01Q
9/16 (20130101) |
Current International
Class: |
H01Q
9/04 (20060101); H01Q 9/14 (20060101); H03H
7/38 (20060101); H01Q 9/16 (20060101); H03H
7/40 (20060101); H01q 009/00 () |
Field of
Search: |
;343/749,750,752,858,895,703,745 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Eli Lieberman
Attorney, Agent or Firm: C. Cornell Remsen, Jr. Walter J.
Baum Paul W. Hemminger Charles L. Johnson, Jr. Philip M. Bolton
Isidore Togut Edward Goldberg Menotti J. Lombardi, Jr.
Claims
1. A physically shortened halfwave antenna of the whip type
comprising: a main antenna rod having an upper and lower end; a
first helix having one end connected to the upper end of said rod;
a capacitive top load connected to the other end of said first
helix; a second helix having one end connected to the lower of said
rod; first means coupled to the other end of said second helix to
resonate said antenna; and second means inductively coupled to said
second helix to feed radio frequency energy to and remove radio
frequency energy from said antenna.
2. An antenna according to claim 1, wherein said top load
includes
3. An antenna according to claim 1, wherein said first means
includes a capacitive bottom load, and a capacitance means coupled
in series between the other end of said second
4. An antenna according to claim 1, wherein said second means
includes a capacitive bottom load, a radio frequency terminal, an
inductor having one end coupled to said bottom load and the other
end
5. An antenna according to claim 1, wherein said second means
includes a capacitive bottom load, an inductor having one end
coupled to said bottom load, a capacitance means coupled in
parallel with said inductor, and a radio frequency terminal
connected to a selected impedance point along
6. An antenna according to claim 1, wherein said first means
includes a capacitive bottom load, and a variable capacitance means
coupled in series between the other end of said second helix and
said bottom load; and said second means includes a radio frequency
terminal, an inductor having one end coupled to said bottom load
and the other end coupled to said radio frequency terminal; said
variable capacitance means, said second helix and said inductor
providing a single tuned circuit to resonate said antenna and to
provide a narrow band impedance match to said antenna; the
adjustment of said variable capacitance means enabling an
impedance
7. An antenna according to claim 1, wherein said first means
includes a capacitive bottom load,and a first variable capacitance
means coupled in series between the other end of said second helix
and said bottom load; and said second means includes an inductor
having one end coupled to said bottom load; a second variable
capacitance means coupled in parallel with said inductor, and a
radio frequency terminal connected to a selected impedance point
along said inductor; said first and second variable capacitance
means, said second helix and said inductor providing a double tuned
circuit to resonate said antenna
8. An antenna according to claim 1, further including third means
coupled between said second means and said first means, said third
means responding to reflected power, due to an object altering the
resonance of said antenna, to automatically control said first
means and
9. An antenna according to claim 8, wherein said first means
includes a capacitive bottom load, and a first variable capacitance
means coupled in series between the other end of said second helix
and said bottom load; and said third means includes a directional
coupler coupled to said second means, and a capacitance control
means coupled to said directional coupler and said first variable
capacitance means, said control means responding to said reflected
power to alter the capacitance of said first variable
10. An antenna according to claim 9, wherein said second means
includes an inductor having one end coupled to said bottom load and
the other end coupled to said directional coupler; said first
variable capacitance means, said second helix and said inductor
providing a single tuned circuit to resonate said antenna and to
provide a narrow band impedance match to said antenna; the control
of said first variable capacitance means enabling an impedance
11. An antenna according to claim 9, wherein said second means
includes an inductor having one end coupled to said bottom load, a
second variable capacitance means coupled in parallel to said
inductor; and means to couple said directional coupler to a
selected impedance point along said inductor; said first and second
variable capacitance means, said second helix and said inductor
providing a double tuned circuit to resonate said antenna
12. An antenna according to claim 1, further including a capacitive
bottom load; three of said second helix; three of said first means
each coupled between an end of a different one of said three of
said second helix and said bottom load; first switch means to
selectively couple the other end of each of said three of said
second helix to the lower end of said rod; three of said second
means each inductively coupled to an associated one of said three
second helix; a radio frequency terminal; and second switch means
ganged to said first switch means to selectively couple each of
said three of said second means to said terminal; said three of
said second helix, said three of said first means and three of said
second means cooperating to resonate said antenna over a given
broad frequency range, each of said three of said second helix,
said first means and said second means covering a different given
adjacent frequency
13. An antenna according to claim 12, wherein each of said three of
said first means includes a first variable capacitance means; one
of said three of said second means includes a first inductor having
one end coupled to said bottom load and the other end coupled to
said second switch means; said first inductor, the associated one
of said first variable capacitance means and the associated one of
said second helix providing a single tuned circuit, an adjustment
of said associated one of said first variable capacitance means
enabling the resonance of said antenna and an impedance match to
said antenna over the lower one of said frequency bands; and each
of the other two of said three of said second means includes a
second inductor having one end coupled to said bottom load, a
second variable capacitance means coupled in parallel to said
second inductor; and means to couple said second switch means to a
selected impedance point along said second inductor; each of the
associated one of said first variable capacitance means, each of
said second variable capacitance means, the associated one of said
second helix and each of said second inductor providing a double
tuned circuit to resonate said antenna and to provide a broadband
impedance match to said antenna over the associated one of the
middle one and higher
14. An antenna according to claim 1, further including a capacitive
bottom load; a plurality of said second helix; a plurality of said
first means each coupled between and end of a different one of said
plurality of said second helix and said bottom load; first switch
means to selectively couple the other end of each of said plurality
of said second helix to the lower end of said rod; a plurality of
said second means each inductively coupled to an associated one of
said plurality of second helix; a radio frequency terminal; and
second switch means ganged to said first switch means to
selectively couple each of said plurality of said second means to
said terminal; said plurality of said second helix, said plurality
of said first means and plurality of said second means cooperating
to resonate said antenna over a given broad frequency range, each
of said plurality of said second helix, said first means and said
second means covering a different given adjacent
15. An antenna according to claim 14, wherein each of said
plurality of said first means includes a first variable capacitance
means; certain ones of said plurality of said second means includes
a first inductor having one end coupled to said bottom load and the
other end coupled to said second switch means; said first inductor,
the associated one of said first variable capacitance means and the
associated one of said second helix providing a single tuned
circuit, an adjustment of said associated one of said first
variable capacitance means enabling the resonance of said antenna
and an impedance match to said antenna over certain ones of said
frequency bands; and others of said plurality of said second means
includes a second inductor having one end coupled to said bottom
load, a second variable capacitance means coupled in parallel to
said second inductor; and means to couple said second switch means
to a selected impedance point along said second inductor; each of
the associated one of said first variable capacitance means, each
of said second variable capacitance means, the associated one of
said second helix and each of said second inductor providing a
double tuned circuit to resonate said antenna and to provide a
broadband impedance
16. An antenna according to claim 14, wherein each of said
plurality of said first means includes a first variable capacitance
means; each of said plurality of said second means includes a first
inductor having one end coupled to said bottom load and the other
end coupled to said second switch means; said first inductor, the
associated one of said first variable capacitance means and the
associated one of said second helix providing a single tuned
circuit, an adjustment of said associated one of said first
variable capacitance means enabling the resonance of said antenna
and an impedance
17. An antenna according to claim 14, wherein each of said
plurality of said first means includes a first variable capacitance
means; each of said plurality of said second means includes an
inductor having one end coupled to said bottom load, a second
variable capacitance means coupled in parallel to said inductor;
and means to couple said second switch means to a selected
impedance point along said inductor; each of the associated one of
said first variable capacitance means, each of said second variable
capacitance means, the associated one of said second helix and each
of said inductors providing a double tuned circuit to resonate said
antenna and to provide a broadband impedance match to said antenna
over the associated one of said frequency bands.
Description
This invention relates to antennas and more particularly to
antennas of the whip type for mounting on motor vehicles, ships,
tanks, humans and the like.
Whip type antennas for motor vehicles and humans are known in the
prior art that will cover a relatively broadband of frequencies,
for instance, 30 to 80 megahertz (MHz). One such antenna is termed
a center fed antenna. The center feed arrangement is provided by
coupling radio frequency (RF) energy to a coaxial line which has
the center conductor thereof broken in the middle of vertical
length of the antenna. A physically shortened version of this type
of antenna is also known wherein the coaxial line has helical
configuration before reaching the middle of the vertical length of
the antenna and having the center conductor in a helical
configuration above the middle point of the antenna. In both of
these versions of the center fed type antenna, the minimum current
occurrs at the ends of the antenna and a high impedance transformer
section is provided including the input coaxial formed into a helix
about a ferrite core.
These prior art antennas have been employed in the past to cover
the approximate frequency range of 30 to 80 (MHz) by employing in
conjunction therewith loading elements to cover 10 bands within
this frequency ranged. These loading elements are coupled to the RF
choke that is necessarily provided with the antenna in an attempt
to reduce the radio frequency currents flowing on the motor vehicle
carrying the transceiver with the antenna attached thereto.
An object of the present invention is to provide an improved
shortened halfwave antenna of the whip type which is ground
insensitive.
Another object of the present invention is to provide in
conjunction with the antenna of this invention an arrangement to
reresonate the antenna when the capacity of the system is increased
by objects coming into close proximity to the antenna.
Still another object of the present invention is to provide an
energy coupling arrangement as part of the antenna which may be
made broadband and thereby cover relatively broadband of
frequencies.
Still another object of the present invention is to provide, by
relatively simple components as compared to the impedance
transformer section of the above mentioned prior art, a high
impedance end fed antenna.
A feature of the present invention is the provision of a physically
shortened halfwave antenna of the whip type comprising a main
antenna rod having an upper and lower end; a first helix having one
end connected to the upper end of the rod; a capacitive top load
connected to the other end of the helix; a second helix having one
end connected to the lower end of the rod; first means coupled to
the other end of the second helix to resonate the antenna; and
second means inductively coupled to the second helix to feed radio
frequency to and remove radio frequency energy from the
antenna.
Another feature of the present invention is a physically shortened
halfwave antenna of the whip type as described hereinabove which
further include a third means coupled between the second means and
the first means, the third means responding to reflected power due
to the resonance of the antenna being altered by an object that
comes into the proximity of the antenna to reresonate the
antenna.
Still a further feature of the present invention is the provision
of a physically shortened halfwave antenna of the whip type which
includes a plurality of the second helices; a plurality of the
first means each coupled between an end of a different one of the
plurality of the second helix and a capacitive bottom end load;
first switch means to selectively couple the other end of each of
the plurality of the second helix to the lower end of the rod; a
plurality of the second means each inductively coupled to an
associated one of the plurality second helix; a radio frequency
terminal; and second switch means ganged to the first switch means
to selectively couple each of the plurality of the second means to
the terminal; the plurality of the second helix, the plurality of
the first means and the plurality of the second means cooperating
to resonate the antenna over a given broad frequency range, each of
the plurality of the second helix, the first means and the second
means covering a different given adjacent frequency band within the
given broad frequency range.
BRIEF DESCRIPTION OF THE DRAWING
Above-mentioned and other features and objects of this invention
will become more apparent by reference to the following description
taken in conjunction with the accompanying drawing, in which:
FIG. 1 is a schematic diagram of one form of the prior art antenna
mentioned hereinabove under the heading "Background of the
Invention;"
FIG. 2 is a physically shortened version of the antenna of FIG.
1;
FIG. 3 is a schematic diagram of an antenna system in accordance
with the principles of the present invention capable of covering a
relatively broadband frequency range in three different frequency
bands;
FIGS. 4A and 4B illustrate schematically two alternatives for the
capacitive bottom load that may be employed in the antenna system
of FIG. 3; and
FIG. 5 illustrates the current and voltage distribution on the
antenna of FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is illustrated diagrammatically one of
the center fed prior art antenna mentioned under the heading
"Background of the Invention." This antenna includes a coaxial line
1 coupled to the transceiver which is configured to be helical in
nature about a ferrite core 2 to form the necessary high impedance
transformer to obtain the desired radiation characteristics. An RF
choke sleeve 3 is coupled to the outer conductor of coaxial line 1
with the coaxial line 1 extending a given distance above sleeve 3.
The center conductor 4 of coaxial line 1 is broken in the middle of
its vertical height as shown at 5. This break 5 is the center feed
point for the upper and lower portion of the antenna. The minimum
voltage point is at the break 5 in the center conductor and the
maximum current is at this location while the minimum current is at
the ends of the antenna.
The antenna of FIG. 1 can be resonated over a relatively narrow
frequency band as compared to the antenna of the present invention
by each of a number of different base loading elements 6 which are
coupled between ground and sleeve 3. Selectively coupling ten
appropriately selected elements 6 to shield 3 would enable the
antenna to cover in 10 bands the frequency range of 30 to 80
MHz.
FIG. 2 illustrates diagrammatically the antenna of FIG. 1 in a
physically shortened version. The coaxial line 1 has a helical
configuration about a ferrite choke 2 to provide the high impedance
transformer with an RF choke sleeve 3 being coupled to the outer
conductor of coaxial line 1 substantially as illustrated in FIG. 1.
The coaxial line 1 is then configured in a tight helix 7 and will
extend to the middle of the vertical height of the antenna. The
center conductor of coaxial line 1 would then be extended by itself
and formed into a helix 8, the top of which has coupled thereto a
capacitive load 9.
Referring to FIG. 3, there is illustrated diagrammatically an
antenna in accordance with the principles of the present invention.
The antenna of the present invention includes a main rod 10 having
one end thereof coupled to a helix 11 and a capacitive top load in
the form of one or more conductive elements 12, such as wires or
rods. The other end of rod 10 is coupled to one of the second
helices 13, 14 and 15 through switch means 10'. Helix 13 is coupled
to a variable capacitance means 16 which may be in the form of a
physical capacitor, a varactor or a PIN diodes and capacitor
arrangement. Capacitance means 16 has its other terminal connected
to a capacitive bottom load, one form of which is ground 16a as
illustrated. Other illustrative forms of the capacitive bottom end
load are illustrated in FIGS. 4A and 4B. FIG. 4A illustrates a
capacitive bottom end load formed by a small ground plane 16b
spaced from the lower terminal of capacitance means 16. FIG. 4B
illustrates a capacitive bottom end load formed by a conductive
element 16c, such as a wire or rod, directly connected to the lower
terminal of capacitance means 16. Secondhelix 14 has one end
thereof connected to one terminal of variable capacitance means 17
which also may be in the form of a physical capacitor, a varactor
or a PIN diodes and capacitor arrangement. The other terminal of
capacitance means 17 is coupled to a capacitive bottom load as
illustrated by 17a, FIG. 3, 17b, FIG. 4A and 17c, FIG. 4B. Second
helix 15 has one end coupled to one terminal of variable
capacitance means 18. The other terminal of means 18 is coupled to
a capacitive bottom load as illustrated by 18a, FIG. 3, 18b, FIG.
4A and 18c, FIG. 4B. Capacitance means 18 also may be in the form
of a physical capacitor, a varactor or a PIN diodes and capacitor
arrangement.
The purpose of capacitors 16, 17 and 18 is to resonate the antenna
in its particular band of frequencies. In one embodiment of the
present antenna system, capacitance means 16 resonates the antenna
system for the frequency band 51-60 MHz, capacitance means 18
resonates the antenna system for the frequency band 60-80 MHz, a
capacitance means 17, by varying the value thereof, can resonate
the antenna of the present invention through the frequency band
30-51 MHz.
In accordance with one version of the antenna, the antenna system
may be energized with radio frequency energy from the transceiver
or radio frequency energy can be removed from the antenna for
application to the transceiver by a parallel tuned circuit
including an inductor 19 and a variable capacitor 20. The
combination of inductor 19, helix 13, capacitor 20 and capacitance
means 16 forms a doubled tuned circuit which will provide both
resonance and impedance matching over the frequency range 51-60
MHz. A similar arrangement is provided in conjunction with the
second helix 15 wherein the inductor 21 and the variable capacitor
22 form a parallel tuned circuit which in combination with the
helix 15 and the variable capacitance means 18 provides a double
tuned circuit for resonating and providing an impedance match for
the antenna system over the frequency range 60-80 MHz. Energy is
coupled to and removed from the second helix 14 by means of a
winding or inductor 23 having one end thereof connected to ground
and the other end thereof connected to a terminal 24 associated
with switch 25 which is ganged with switch 10' so that the
appropriate components will be provided for the frequency band
being considered in the broadband frequency range. An appropriate
impedance point 26 along inductor 19 has coupled thereto the inner
conductor of a coaxial line 27 coupled to switch means 25.
Similarly the center conductor of coaxial line 28 is coupled to an
impedance point 29 along inductor 21. The impedance points 26 and
29 are selected to have an impedance to match the impedance of the
associated coaxial line, such as 50 ohms if the coaxial line is a
50 ohm coaxial line.
The above described double tuned arrangements provides antenna
impedance match and antenna resonance over a relatively wide
frequency band as compared to the above mentioned prior art
arrangements and the single tuned arrangement of the present
invention. Also the single tuned arrangement provides antenna
impedance match and antenna resonance over a frequency band that is
wider than the above mentioned prior art arrangements.
As is apparent from FIG. 5 the voltage is maximum at the ends of
the antenna of FIG. 3, while the current is maximum in the center
of the antenna of FIG. 3 and the current is minimum at the ends of
this antenna. Thus, there is an elimination or at least a
substantial reduction in RF currents that may flow on the surface
of the motor vehicle or in the body of the human carrying the
transceiver and associated antenna. Thus, the feeding arrangement
as illustrated and described with respect to FIG. 3 renders the
antenna ground insensitive and, therefore, changes in configuration
of the ground over which the motor vehicle travels, or the
dielectric constant of the human body will not upset the desired
characteristics of the antenna.
As is customary in all mobile and portable antennas, an object 30
such as a building, a tree, a mountain, a bridge or underpass
coming into close proximity to the antenna will cause an increase
capacitance in the antenna system and, hence, a detuning or a
change of the resonance of the antenna. This is undesirable since
the antenna characteristics are changed by the proximity of the
object 30. It is proposed in accordance with the present invention
to couple the coaxial line 31 extending from switch means 25 to a
directional coupler 32 such that when the resonance of the antenna
is changed by object 30 a reflected standing wave is produced on
coaxial line 31 which will be recovered by coupler 32 for
application to amplifier 33. The capacitance control arrangement 34
will respond to the magnitude of the reflected power, as
represented by the reflected standing wave on coaxial 31, to
produce that amount of control voltage that is necessary to
decrease the capacitance of capacitors 16, 17 or 18, depending upon
the frequency band in operation, so as to reresonate the antenna
system and thereby compensate for the resonance changing effect of
object 30. Arrangement 34 may be strictly mechanical to control a
variable capacitor, it may be electro-mechanical to also control a
variable capacitor or it may be completely electrical to control
the capacitance of a varactor or a PIN diodes and capacitor
arrangement.
For purposes of illustration switch 35 is provided which is ganged
with switch means 10' and 25 so that the control signal is coupled
only to the one of the capacitive means 16, 17 and 18 which have
been selected by switch means 10' and 25. Better reliability,
however, would be obtained if switch 35 were eliminated and the
control output of arrangement 34 was coupled to all capacitance
means 16, 17 and 18 simultaneously. Reresonance would only be
accomplished by that one of the capacitance means 16, 17 and 18
coupled to the antenna by switches 10' and 25.
The antenna system of FIG. 3 has been reduced to practice in three
forms, a five foot version for vehicle use and a four foot and one
foot version for portable use by a human. These reductions to
practice have a performance that exceeds the performance of the
above-mentioned prior art arrangement.
The antenna system of the present invention will enable the
achievement of a high impedance end coupled antenna by substituting
the simple double tuned or single tuned arrangements of the present
invention for the high impedance transformer of the above mentioned
prior art of FIGS. 1 and 2 formed by coaxial line 1 having a
helical configuration about ferrite core 2.
In addition, the antenna system of the present invention covers the
same frequency range as the above mentioned prior art antenna
system using a fewer number of switched elements, or a greater
frequency range can be covered by the antenna system of the present
invention with the same number of switched elements as the above
mentioned prior art antenna system.
The antenna system of FIG. 3 should not be considered as the only
arrangement capable of covering a given frequency range in steps of
a number of adjacent frequency bands. The given frequency range can
be covered by a plurality of adjacent frequency bands greater or
less in number than three and the energy coupling arrangements may
be either all double tuned arrangements, all single tuned
arrangements or a different combination of single and double tuned
arrangements than that shown in FIG. 3.
While I have described above the principles of my invention in
connection with specific apparatus it is to be more clearly
understood that this description is made only by way of example and
not as a limitation to the scope of my invention as set forth in
the objects thereof and in the accompanying claims.
* * * * *