Information
-
Patent Grant
-
6738026
-
Patent Number
6,738,026
-
Date Filed
Monday, December 9, 200221 years ago
-
Date Issued
Tuesday, May 18, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 343 895
- 343 893
- 343 806
- 343 853
- 343 700 MS
-
International Classifications
-
Abstract
A low-profile, tri-filar, helix antenna with linear polarization or circular polarization (CP) includes a single feed without an internal feed network. The antenna includes three metal, bent, quarter-wave monopoles positioned at 0°, 120°, and 240° on a top surface of the antenna. One of the monopoles is directly fed, and the other two are parasitically coupled to the fed monopole. Metal perturbations on the parasitic monopoles control their coupling phase to the fed monopole, and determine the antenna's polarization. Without metal perturbations, the parasitic monopoles are linear polarized and both monopoles are coupled to the fed monopole at ±120. With metal perturbations, the parasitic monopoles are CP polarized and coupled at +120 degrees to the fed monopole. Various perturbations, capacitive and inductive shunts options are possible. The three monopoles are supported by a dielectric substrate, or they are freestanding.
Description
FIELD OF THE INVENTION
This invention relates to the field of radio communications, and more specifically to spiral or helical antennas for use in wireless communication devices and systems.
BACKGROUND OF THE INVENTION
Small, low profile, circular polarized (CP) antennas are used in the mobile communication industry, usually for satellite communication. As the demand for mobile handsets increases, there is a growing need for antennas of this type, and especially for low cost GPS antennas.
One solution to providing a low profile CP antenna is a patch or microstrip antenna. In order to achieve circular polarization, patch antennas need to be a half wavelength long. A patch antenna's free-space half wavelength is usually too long for the compact space that is provided within a wireless communications device, of which a mobile handset is an example. As a result, the physical size of such a patch antenna must be reduced dramatically, using ceramics having a high dielectric constant. However, the use of ceramics having a high dielectric constant increases antenna cost, and also reduces the efficiency of the patch antenna.
FIG. 1A
shows a standard-technology, dielectric-loaded, ceramic-body, hexagonal patch antenna
10
that is tuned to the global positioning system (GPS) frequency (1575.42 MHz, referred to as L1) wherein a high dielectric constant (er=40) ceramic body portion
11
was used to reduce the physical size of patch antenna
10
to less than one inch, which size is usually desirable for mobile wireless communication applications.
FIG. 1B
shows the frequency/magnitude characteristic of antenna
10
, wherein antenna
10
included a ceramic body portion
11
, a top-located metal radiating/receiving surface
12
that lies in the X-Y plane of
FIG. 1B
, an off-center feed conductor
13
that extends in the Z-direction in FIG.
1
B and was connected to a metal-plated top surface
12
, a vertex-to-vertex dimension
14
of about 0.88 inch, and a flat-to-flat dimension
15
of about 0.72 inch.
For wireless communications systems that can tolerate relatively large antennas, the following CP antennas are standard solutions: (1) single helix antennas which have a single feed and are typically a few wavelengths tall, (2) multi-filar helix antennas that have a 90 degree hybrid and are that are typically a few wavelengths tall, (3) crossed dipole antennas that have a 90-degree hybrid and are typically a quarter wavelength tall over a ground plane, or (4) spiral antennas that have a single balanced feed and are typically a quarter wavelength tall over a ground plane.
SUMMARY OF THE INVENTION
This invention provides a small, low-profile, tri-filar helix antenna, which can have either linear polarization or CP, the antenna being provided with a single feed, and the antenna having no internal feed network.
Antennas in accordance with the invention include three metallic, bent, quarter wave monopoles, wherein only one of the monopoles is fed, and wherein the other two monopoles are parasitically coupled to the fed-monopole.
The three bent monopoles of the invention are physically positioned at 0, 120, and 240 degrees, respectively. The three monopoles are self-supporting, or they are supported on a relatively flat dielectric surface. Only one of the three monopoles is fed, for example using an inductive shunt match. The other two monopoles are strongly coupled to, and parasitically feed from, the directly-fed monopole. The two parasitic monopoles are fed at phases that are controlled by the incorporation of, or by the non-incorporation of metal perturbations within the two parasitic monopoles.
In order to induce linear polarization, no metal perturbations are used within the two parasitic monopoles, and the two parasitic monopoles are coupled at positive 120 degrees to the directly-fed monopole.
In order to induce CP, one of the two parasitic monopoles couples at positive 120 degrees to the directly-fed monopole, and the other parasitic monopole couples at negative 120 degrees to the directly-fed monopole. A metal perturbation on a given parasitic monopole operates to offset the resonant frequency of that parasitic monopole, which in turn affects the phase of coupling of that parasitic monopole to the fed-monopole.
Various metal perturbation options are available in order to generate the phase of this coupling to the directly-fed monopole. One of the parasitic monopoles can have a capacitive shunt, and the other parasitic monopole can have a series inductance, or only one parasitic monopole can have a metal perturbation, either a capacitive perturbation or an inductive perturbation, depending on the sense of the CP that is desired.
The three monopoles in accordance with the invention can be physically supported by a dielectric substrate member, or the three monopoles can be constructed of a material that renders the monopoles free-standing. A metallic ground plane is desirable directly under the three monopoles.
Antennas in accordance with the invention find utility as replacements for a dielectrically-loaded, single feed, CP patch antenna.
Antennas in accordance with the invention do not require dielectric loading. Hence, antennas in accordance with the invention are a less expensive choice for narrow band CP applications.
Antennas in accordance with an embodiment of the invention include three bent quarter wave monopoles, wherein only one of the bent monopoles is fed, and wherein the other two bent monopoles are parasitically coupled to the fed-monopole.
The bent monopoles were, for example, physically positioned at 0, 120, and 240 degrees, respectively. Only one of the bent monopoles was fed, for example with an inductive shunt match. The other two bent monopoles were excited parasitically from the fed-monopole with phases that were controlled by the incorporation of, or by the non-incorporation of, perturbations on or within the two parasitically-fed monopoles.
In antennas constructed and arranged in accordance with the invention the magnitude of the above-described parasitic coupling was relatively large (for example about −6 dB), and this relatively large parasitic coupling between the directly excited monopole and the two parasitic monopoles provided that the antenna generated a symmetric radiation pattern. This relatively large parasitic coupling also effectively acts as a feed network to the two parasitically coupled monopoles, and allows the antenna to have just one of the monopoles directly excited. This relatively large parasitic coupling is, to a large extent, controlled by the width of a capacitive gap that existed between the two parasitic monopoles and the fed-monopole.
In summary, the present invention provides a small, low-profile, single feed, linear polarized or CP, tri-filar, helix antenna having three bent quarter wave monopoles that are physically positioned at about 0, 120, and 240 degrees, respectively. The outer perimeter of the antenna can be a hexagon, or it can be circular, it can approach a circular shape, or it can have a number of sides equal to 6×N where N is an integer that is greater then zero.
Linear antenna polarization is produced when no perturbations are provided for either of the two parasitic monopoles, in which case both of the parasitic monopoles are excited parasitically in-phase at positive 120 degrees.
In order to produce CP, metal perturbations are applied to the two parasitic monopoles in order to generate a positive 120 degree parasitic coupling in one of the parasitic monopoles, and to in order to generate a negative 120 degree parasitic coupling in the other of the two parasitic monopoles.
Various perturbation options can be used to generate the above phasing. For example, one of the two parasitic monopoles can include a capacitive shunt, and the other parasitic monopole can include an inductive shunt. Or, only one of the two parasitic monopoles can be provided with a perturbation, either a capacitive perturbation or an inductive perturbation, depending on the sense of the CP that is desired.
The reactive-capacitance or reactive-inductance perturbations can be provided either by shaping the metal legs of the parasitic monopoles, or by connecting discrete capacitive or inductive electrical components to the parasitic monopoles.
With only one monopole directly fed, the large coupling between this directly-fed monopole and the two parasitic monopoles acts as a feed network to the two parasitic monopoles. It is desirable that all three monopoles be fed with equal RF energy levels in their resonant condition, such that the three monopole antenna will generate three symmetric radiation patterns.
In practice it is desirable that one half of the RF energy that is provided as an input to the directly-fed monopole be coupled to the two parasitic monopoles, and that the other half of this RF energy be radiated into free space.
If coupling from the directly-fed monopole to the two parasitic monopoles is significantly larger than this one-half amount, each of the three monopoles may act as a poor radiator, and the efficiency of the three monopole antenna may be reduced. If the coupling from the directly-fed monopole to the two parasitic monopoles is significantly smaller than this one-half amount it may be difficult to parasitically excite the two parasitic monopoles in order to generate CP.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1A
shows a standard-technology, dielectric-loaded, ceramic-body, hexagon-shaped patch antenna that is tuned to the GPS frequency, wherein a high dielectric constant ceramic body member is used to reduce the physical size of the antenna.
FIG. 1B
shows the frequency/magnitude characteristic of the antenna of FIG.
1
A.
FIG. 2
is a top perspective view of a three-monopole, single-feed, antenna in accordance with the invention, the antenna having no metal perturbations associated with the antenna's three generally identically shaped quarter wave metal monopoles, this figure showing a precursor geometry that pertains to other embodiment of the invention.
FIG. 3
is a top view of three-monopole antenna of
FIG. 2
showing that the antenna's top surface includes three coplanar and quarter wave metal monopole patterns that are physically located at 0-degrees, 120-degrees and 270-degress, respectively, about the top surface of the antenna.
FIG. 4
is an exploded view that shows the physical positioning and the three-dimensional shape of the three metal patterns that form the three monopoles of the
FIG. 2
antenna.
FIG. 5
shows the magnitude of the parasitic coupling (i.e. about −6 dB) between FIG.
2
's directly-fed monopole and FIG.
2
's two parasitically-fed monopoles, wherein about one half of the power that is feed to the directly-fed monopole is coupled to the two parasitically-fed monopoles.
FIG. 6
shows the phase of the coupling (i.e. about plus 120 degrees) that exists between the three monopoles of FIG.
2
.
FIG. 7
shows the linear polarization pattern of the
FIG. 2
antenna, this figure also showing the antenna's Directivity Pattern (dB) versus Theta at 1580 MHz, and the central axis of the antenna.
FIG. 8
shows the three metal monopoles of a dielectric-supported, single-feed CP antenna in accordance with the invention wherein a metal capacitive perturbation or stub is provided on one of the parasitic monopoles, and wherein a single-feed to the antenna is provided by way of the inductive shunt that forms a portion of a directly-fed monopole.
FIG. 9
shows the three metal monopoles of an antenna in accordance with the invention wherein one of the antenna's two parasitic monopoles includes an inductive metal perturbation that is provided by widening the inductive shunt that is provided at the base of this parasitic monopole.
FIG. 10
shows the Antenna Directivity Pattern (dB) versus Theta at about 1587.5 MHz for an antenna in accordance with the invention, this figure showing the right-hand and the left-hand radiation patterns at the center frequency of about 1587 MHz for a CP antenna wherein the axial ratio is nearly perfect at 0 dB.
FIG. 11
shows a Smith chart for an antenna in accordance with the invention.
FIG. 12
shows the VSWR bandwidth for an antenna in accordance with the invention.
FIG. 13
shows a two-shot-molded tri-arm, single feed, helix antenna in accordance with the invention that is tuned to about 1.575 GHz.
FIG. 14
shows an embodiment of the invention wherein a single-fed, three monopole helix antenna includes three stamped-metal monopole elements that are mounted onto the outer surface of an injection molded plastic and non-conductive support member.
FIG. 15
shows a single-feed, three-monopole helix antenna in accordance with the invention that is made from a printed circuit board that includes three etched areas, each of the three etched areas including a metal monopole element tuned for about 1.575 GHz, wherein the antenna is tuned for CP by using a series inductance (i.e. a wider inductive shunt) in one of the parasitically-fed monopoles.
FIG. 16
shows an antenna in accordance with the invention wherein the antenna's dielectric support is provided by a printed circuit board whose top surface is etched to provide three metal monopole elements, and wherein the printed circuit board includes a through-hole or a via through which a feed conductor is threaded and then connected to the directly-fed monopole.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 2
is a top perspective view of a single feed, three-monopole antenna
20
in accordance with the invention.
Antenna
20
includes a plastic or ceramic, electrically non-conductive, rigid, dielectric, and hexagon-shaped support member
21
having a planar top surface
22
, a planar bottom surface that is generally parallel to top surface
22
, and six side walls
23
-
28
that extend downward and generally perpendicular to top surface
22
. As mentioned above, shapes other than hexagonal can be provided within the spirit and scope of the invention.
FIG. 3
is a top view of three-monopole antenna
20
. As seen in
FIGS. 2 and 3
, the top surface
22
of non-conductive support member
21
carries three coplanar, bent, quarter wave and metal monopole patterns
29
-
31
that are physically located at 0-degrees, 120-degrees and 270-degress, respectively about top surface
22
, as is perhaps best shown in FIG.
3
.
FIG. 4
is an exploded view that shows the three-dimensional shape of the three metal patterns that form the three bent and quarter wave monopole patterns
29
-
31
. In this embodiment of the invention, but without limitation thereto, the three quarter wave monopoles
29
-
31
have a generally identical three-dimensional geometric shape.
As seen in
FIGS. 2 and 4
, the base of each of the three quarter wave monopole metal patterns
29
-
31
includes a metal inductive-shunt portion
3234
, respectively, that respectively lie on the three side walls
24
,
26
and
28
of non-conductive support member
21
. The inductance-value of a shunt portion
32
-
34
is determined by the distance between the antenna's feed and the point of grounding the shunt portion, and by the vertical height of the metal loop that forms the shunt portion
A capacitive shunt portion is formed by adding metal at a location that is close to the ground, in parallel with the shunt inductance portion, so that RF currents flow across the capacitive portion and the inductance portion.
In this embodiment of the invention, none of the three metal quarter wave monopole patterns
29
-
31
shown in
FIGS. 2-4
includes a metal perturbation, and as shown in
FIGS. 2-4
, a single feed is provided for three-monopole antenna
20
by way of an electrical conductor
35
that electrically connects to the inductive shunt
34
that is a portion of the base of monopole metal pattern
31
. Thus, antenna
20
provides linear polarization, monopole
31
is a fed-monopole and monopoles
29
and
33
are parasitic monopoles that are parasitically fed by fed-monopole
31
.
The physical location at which conductor
35
connects to inductive shunt
34
operates to control the inductance value of the inductive shunt.
With reference to monopole
29
as shown in
FIG. 3
, note that each of the three bent monopoles
29
-
31
includes two linear metal sections
17
and
18
that are connected by a bending metal section
19
.
The angle
16
of inclination of one linear section
17
to the other linear section
18
is not critical, and in this embodiment of the invention angle
16
was about 60 degrees.
As perhaps best seen in
FIG. 3
, the three monopoles
29
-
31
form a helix about the central axis
36
of antenna
20
, wherein axis
36
extends generally perpendicular to the top surface
22
and the bottom surface of support member
21
.
In an embodiment of the invention non-conductive support member
21
had a low dielectric constant of about 3.1. the vertex-to-vertex dimension
37
of antenna
20
was about 0.88 inch, the flat-to-flat dimension
38
was about 0.72 inch, the height
30
was about 0.28 inch, and the coupling between fed-monopole
31
and the two parasitic monopoles
29
and
30
was about −6 dB.
The invention's parasitic coupling between monopole elements is to a relatively large extent controlled by the width of a capacitive-gap that exists between the top of the three monopole elements
29
-
31
, that is by the two generally parallel edges that are formed by the end of one monopole element and the generally middle section of an adjacent monopole element.
The bottom surface of non-conductive support member
21
carries a hexagon-shaped metal ground plane member
40
that cooperates with the metal monopoles
29
-
31
in a well known manner.
As described above relative to
FIGS. 2-4
, the present invention provides a small, low-profile, single feed, tri-filar helix antenna
20
that can be constructed and arranged to provide either linear polarization or CP.
It is now useful to consider a precursor-antenna-geometry that can be used to determine the construction and arrangement of antenna
20
as shown in
FIGS. 2-4
.
As used herein, the term “precursor-antenna-geometry” means an antenna like antenna
20
of
FIGS. 2-4
wherein the precursor-antenna has not as vet been converted to the single feed antenna
20
that is above-described, and wherein the precursor-antenna has not as yet been converted to either linear polarization or CP.
Conversion of the precursor-antenna to a single feed antenna
20
as above-described is accomplished by providing a relatively strong coupling between the three monopoles
29
-
31
of the precursor-antenna, to thereby allow the monopoles of the precursor-antenna to be parasitically excited.
The behavior of the precursor-antenna is determined by feeding each of its three monopoles by way of an individual inductive shunt, i.e. in the precursor-antenna each of the three monopoles is provided with its own individual feed and feed port.
The existence of these three feed ports for the precursor-antenna, and the use of computer simulation, provides a prediction of the coupling that exists in the precursor-antenna between its three monopoles. The final design of a
FIGS. 2-4
single-feed antenna
20
depends upon the magnitude of this coupling.
An input match that is achieved in this manner is shown in
FIG. 5
wherein the magnitude of the coupling between one directly-fed monopole and two parasitically-fed monopoles is about −6 dB at the center frequency of about 1.575 GHz. This input match is controlled by the physical shape of the inductive shunt
32
-
34
that is provided at the base of the three monopoles of the precursor-antenna.
Each monopole of the precursor antenna is a single bent quarter wave monopole, and each monopole has an input impedance that is much lower than the typical 50 ohm signal that is sent to the precursor-antenna. Hence a matching component is necessary.
Energy that is fed to any one of the three monopoles must get past that monopole's feed point before the feed energy can couple to the other two monopoles, or before this feed energy can radiate from that monopole into space. Hence this matching impedance structure of the precursor-antenna is an important portion of the final design of an antenna in accordance with the invention.
The magnitude of this coupling, approximately −6 dB from a given monopole to each of the other two monopoles, is shown in
FIG. 5
wherein about one half of the power that is feed to any given monopole is coupled to the other two monopoles. The magnitude of this coupling is to a large extent controlled by the width of a capacitive gap that exists between the adjacent edges of the three monopoles that reside on the top surface of the non-conductive support member.
In the final design of the single-feed antenna
20
of
FIGS. 2-4
, wherein only monopole
31
is directly fed or excited, it is necessary to induce a relatively large coupling between this directly excited monopole
31
and the two parasitic monopoles
29
and
30
. This relatively large coupling effectively acts as a feed network to the two parasitic monopoles
29
and
30
, thereby allowing the single-feed antenna
20
to have just one of its three monopoles
29
-
31
directly excited. When all three of the monopoles
29
-
31
receive equal amounts of feed energy in the resonance condition, single-feed antenna
20
generates symmetric radiation patterns.
It has been found that a desirable design of a three-feed precursor-antenna provides that about one half of the feed energy that is provided to each of its three monopoles couples to the other two monopoles, whereas and the other half of the feed energy that is provided to each of the three monopoles radiates into free space.
When the coupling that is provided by the design of the three-feed precursor-antenna is larger than this, each monopole tends to be a poor radiator into free space, and the efficiency of the antenna suffers.
When the coupling that is provided by the design of the three-feed precursor-antenna is less than this, it is difficult for a given monopole to parasitically excite the other two monopoles, and it is difficult for the antenna to generate CP.
In the final design of the single-feed antenna
20
of
FIGS. 2-4
, when no metal perturbations are provided on one or more of the two parasitic monopoles
29
and
30
, the phase of the coupling between the three monopoles
29
-
31
is about +120 degrees, as is shown in FIG.
6
. The value of this coupling phase is important in order to induce either linear polarization or CP. Metal perturbations on one or more of the two parasitic monopoles
29
and
30
offsets the resonance frequency of the one or more parasitic monopole
29
/
30
, and also affects the phase of the coupling between the three monopoles.
As described above,
FIGS. 2-4
show a single-feed, tri-filar, linear polarized helix antenna
20
in accordance with the invention wherein antenna
20
exploits a strong monopole-coupling that was determined by way of the above-described investigation of a precursor-antenna wherein each of the three monopoles of the precursor-antenna were fed.
In order to generate linearly polarization, only one of the three monopoles of the
FIGS. 2-4
antenna
20
needs to be directly-fed (i.e. monopole
31
in FIGS.
2
-
4
), the two other +120 degree coupled monopoles (i.e. monopoles
29
and
30
having no perturbations in
FIGS. 2-4
) are coupled to the directly-fed monopole in order to generate linear polarization, and the directly-fed monopole is fed by way of an inductive shunt match (i.e. inductive shunt
34
in
FIGS. 2-4
.
The linear polarization radiation pattern of such a tri-arm, single-feed, no-perturbation, helix antenna
20
is shown in
FIG. 7
, wherein this figure shows the antenna's Directivity Pattern (dB) versus Theta at 1580 MHz, and wherein this figure also shows the central axis
36
of the
FIGS. 2-4
single-feed antenna
20
. The
FIG. 7
radiation patterns are “patch-like”, following the Ludwig 3rd definition, and the antenna's polarization is parallel to axis
36
through the antenna's feed point
34
and the geometric center of antenna
20
.
In order to induce CP, one of the two parasitic monopoles
29
or
30
needs to couple to fed-monopole
31
at positive 120 degrees, and the other parasitic monopole
29
or
30
needs to couple to fed-monopole
31
at negative 120 degrees.
This construction and arrangement in accordance with the invention generates an electric field that rotates uniformly with time around the outer perimeter of antenna
20
. Various metal perturbation options can be used within the spirit and scope of this invention in order to generate this +120-degree/−120-degree phasing of the two parasitic monopoles.
FIG. 8
provides a non-limiting example of a dielectric-supported, single-feed CP helix antenna
20
in accordance with the invention wherein a metal capacitive perturbation or stub
50
is provided on FIG.
4
's parasitic monopole
31
, and wherein the single-feed
35
to antenna
20
is provided by way of the inductive shunt
33
that forms a portion of directly-fed monopole
30
.
In this embodiment of the invention monopole
30
is the directly-fed monopole, whereas the two monopoles
29
and
31
are the two parasitically-fed monopoles.
Capacitive stub
50
lies on the bottom surface of FIG.
4
's non-conductive support member
21
in a manner so as to be electrically insulated from FIG.
4
's ground plane
40
.
Capacitive stub
50
forms a bottom metal portion of monopole
31
that extends inward and parallel to the top metal portion of monopole
31
that lies on the top surface
22
of non-conductive support member
21
.
FIG. 9
shows another embodiment of the invention wherein one of the parasitic monopoles
30
of a dielectric-supported CP antenna
20
of the type shown in
FIGS. 2-4
includes an inductive metal perturbation that is provided by lowering the series inductance of the inductive shunt
33
that is provided at the base of that one parasitic monopole
30
.
This lower of the inductance of the inductive perturbation occurs by virtue of the fact that a wider metal conductor that is positioned where electrical current is a maximum provides less inductance than does a thinner metal conductor.
More specifically, and with reference to
FIG. 9
, monopole
31
is the directly-fed monopole, monopole
29
is a parasitically-fed monopole, and monopole
30
is a parasitically-fed monopole that includes an inductive metal perturbation that is provided by a relatively wide (see dimension
60
) metal inductive shunt
33
.
In other embodiments of the invention, both of the parasitic monopoles may include metal perturbations. For example, one parasitic monopole may include a capacitive stub such as shown in
FIG. 8
, and the other parasitic monopole may include a series inductance as shown in FIG.
9
.
In addition, a relatively small change in the shape of a parasitic monopole, at its base and/or at its top portion, will create a metal perturbation that changes the phase of the coupling to the directly-fed monopole.
In addition, the sense of the CP can be reversed by switching a perturbation from one parasitic monopole to the other parasitic monopole.
FIG. 10
shows an Antenna Directivity Pattern (dB) versus Theta at about 1587.5 MHz for an antenna
20
in accordance with the invention, this figure showing the right-hand and the left-hand radiation patterns at the center frequency of about 1587 MHz for the CP antenna
20
, wherein the axial ratio is nearly perfect at 0 dB.
FIG. 11
shows a Smith chart, and
FIG. 12
shows the voltage-standing-wave-ratio (VSWR) bandwidth for such an antenna
20
in accordance with the invention.
Antennas
20
in accordance with the invention provide better efficiency, as is typical with most antennas, when antenna
20
is wider (see dimensions
37
and
38
of
FIG. 2
) or taller (see dimension
39
of FIG.
2
). Better efficiency is achieved using taller antennas
20
, under the constraint that the above-described strong coupling between the three monopoles is maintained. Providing a taller antenna
20
in accordance with the invention may become impractical after a certain height
39
has been achieved due to the fact that the directly-fed monopole becomes so efficient that it, in itself, radiates most of its energy into space before a portion of this energy can be coupled to the two parasitically-fed monopoles. In this limiting height case, antennas
20
in accordance with the invention may function as a single bent monopole antenna.
Spacing the three bent quarter wave monopoles of an antenna
20
in accordance with this invention farther away from each other may increase the efficiency of the antenna. However, again the above-described monopole coupling must be maintained. That is, the three monopoles must be physically close enough so that significant coupling occurs.
Note that antennas in accordance with this invention, using very little dielectric loading, have the same small physical size as the highly dielectrically loaded patch antenna
10
that is shown in FIG.
1
A. Hence antennas in accordance with this invention can replace dielectrically-loaded, single-feed CP patch antennas of the same physical size, and antennas in accordance with the invention do not require dielectric loading. Thus antennas in accordance with the invention are a less expensive choice, especially for narrow band CP applications.
Various manufacturing methods can be used to produce single-fed, tri-filar helix antennas in accordance with this invention.
For example, and with reference to
FIGS. 2-4
, antenna
20
can be made using a two-shot molding process wherein a first-shot of a polymer material is used to form the major portion of non-conductive support
21
, and wherein a second-shot of a different polymer material is used to form those portions of antenna
20
that correspond to the metal portions of antenna
20
. These portions of the second polymer material are then treated in a well known manner to facilitate the deposition or plating of metal onto these second polymer portions.
Other manufacturing techniques include a two-shot molding process wherein metal monopole elements are placed on the top and on the bottom of a molded polymer member in order to create a low-dielectrically loaded antenna; insert molding of an antenna having the above described metal portions; a hybrid antenna that includes an etched printed circuit board (PCB) and stamped metal portions; a completely PCB antenna; and an antenna that includes free-standing metal portions.
FIG. 13
shows a two-shot-molded tri-arm helix antenna
65
in accordance with the invention that is tuned to about 1.575 GHz.
In a non-limiting embodiment of the invention antenna
65
had a flat-to-flat dimension
73
of about 0.88 inch, a vertex-to-vertex dimension
74
of about 1.01 inch, and a height dimension
75
of about 0.30 inch.
Antenna
65
includes three not-plated plastic portions
69
-
72
and three metal-plated plastic portions
66
-
68
. Not-plated plastic portions
69
-
72
provide the mechanical support for antenna
65
. Metal plated portions
66
-
68
comprise three metal antenna monopoles as above described, one monopole of which is directly-fed, and the other two of which are parasitically-fed monopoles. Plated metal portions
66
-
68
are nearly fully covered by a metal in order to reduce dielectric loss and in order to reduce dielectric loading, which would reduce the bandwidth of antenna
65
.
One advantage of the
FIG. 13
embodiment of the invention is that “lossy” plastics can be used without reducing the efficiency of antenna
65
. Another advantage is that two-shot molding achieves tight mechanical tolerances for the construction and arrangement of antenna
65
.
FIG. 14
shows an embodiment of the invention wherein a single-feed, three monopole helix antenna
80
includes three stamped-metal monopole elements
81
-
83
that are mounted onto an injection-molded plastic and non-conductive support member
84
. Tri-monopole helix antenna
80
is tuned to about 1.575 GHz. In accordance with the above description, one of the three metal monopoles is directly-fed, and the other two of the metal monopoles are parasitically-fed from the directly-fed monopole.
An advantage of antenna
80
is low cost in that after plastic molding, metal-stamping and metal-bending tools are made, antenna
80
can be manufactured from a sheet metal and a plastic material that are relatively inexpensive.
FIG. 15
shows a single-feed, three-monopole helix antenna
88
that is made from a PCB
86
that includes three etch dielectric areas
87
-
89
areas. Each of the three etched dielectric areas
87
-
89
includes a stamped-metal monopole element
90
-
92
that is tuned for about 1.575 GHz. As before, one of the three monopoles
90
-
92
is directly-fed, and the other two monopoles are parasitically-fed from the directly-fed monopole. Antenna
88
is tuned for CP by using a series inductance (i.e. a wider inductive shunt) at the base of the directly-fed monopole.
In a non-limiting embodiment of antenna
85
, the flat-to-flat dimension
93
was about 0.76 inch, the vertex-to-vertex dimension
94
was about 0.27 inch, and the height dimension
95
was about 0.27 inch.
An advantage of FIG.
15
's antenna
88
is that mechanical support is provided by thin PCB
86
, and as a result the material-cost of antenna
88
is minimized. Another advantage to the
FIG. 15
antenna is that etching provides tight tolerances on the top surface of the antenna.
FIG. 16
shows an antenna
96
in accordance with the invention wherein the antenna's dielectric support function is provided by a PCB
97
whose top surface
98
is etched to provide three metal quarter wave monopole elements
99
-
101
. PCB
97
includes a through-hole or via
102
through which a feed conductor
103
is threaded and then connected to monopole
101
at location
104
. Thus, monopole
101
is the directly-fed monopole, and monopoles
99
and
101
are parasitically-fed from directly-fed monopole
101
.
Antenna
96
can be tuned for CP by providing a discrete reactive electrical element in series with feed conductor
103
.
Antenna
96
provides an advantage in that little or no capital cost or specialized tooling is required. As a result, the tuning, of antenna
96
can be integrated into each individual antenna platform.
In summary, it can be seen that the present invention provides a small, low-profile, tri-filar, single-feed, helix antenna that includes three bent quarter wave metal monopoles. The three bent-monopoles are positioned at about 0 degrees, 120 degrees, and 240 degrees about the top surface of the antenna. The perimeter of the antenna that supports the three bent-monopoles can be a hexagon, or it can be another shape such as a circle or a shape that approaches a circle. Only one of the three quarter wave monopoles is fed, for example, with an inductive shunt match, and the other two monopoles are excited parasitically from the fed-monopole. Linear polarization is produced when no metal perturbation is applied to the two parasitic monopoles, such that both parasitic monopoles are parasitically excited in phase at positive 120 degrees. In order to produce CP, metal perturbations are applied to at least one of the two parasitic monopoles in order to generate positive 120 degrees coupling in one of the two parasitic monopoles and negative 120 degrees in the other of the two parasitic monopole. Various metal perturbation options are available in order to generate this phasing: For example, one of the parasitic monopoles can have a capacitive shunt, and the other parasitic monopole can have an inductive shunt. Or, only one parasitic monopole need be provided with a metal perturbation, either capacitive or inductive, depending on the sense of the CP that is desired. These electrically reactive metal perturbations can be provided by either shaping the metal legs or metal base of the parasitic monopoles, or by the electrical connection of discrete electrically reactive components in series with the parasitic monopoles.
While the present invention has been described with respect to certain preferred embodiments of the invention, modifications and variations may be employed without departing from the spirit and scope of the present invention as set forth in the following claims.
Claims
- 1. A helix antenna, comprising:a generally flat and electrically non-conductive antenna top-surface; said top-surface having an outer perimeter and a central axis; first, second and third metal monopole antenna elements generally equally spaced on said top surface at generally 120-degree intervals; said first, second and third monopole antenna elements each having relatively closely spaced and parasitically-coupled first end portions that relatively closely surrounding said central axis; said first, second and third monopole elements each having second end portions relatively closely adjacent to said outer perimeter; and antenna feed means connected only to said second end portion of said first monopole element.
- 2. The helix antenna of claim 1 wherein about one-half of feed-energy presented to said antenna feed means is transmitted into space from said first monopole element, and about one-half of said feed-energy is parasitically coupled to said second and third monopole elements.
- 3. The helix antenna of claim 1 wherein said first, second and third monopole antenna elements are quarter wave monopole elements.
- 4. The helix antenna of claim 1 wherein a parasitic-coupling is about −6 dB.
- 5. The helix antenna of claim 1 wherein a parasitic coupling acts as a feed network to said second and third monopole elements, and including:inductive shunt means connected intermediate said antenna feed means and said second end portion of said first monopole element.
- 6. The helix antenna of claim 1 wherein said perimeter of said top-surface is selected from a group consisting of a hexagon perimeter, a circle perimeter, a circle-like perimeter, and a perimeter having 6×N surfaces, where N is an integer that is larger than 1.
- 7. The helix antenna of claim 1 wherein said top-surface has a dielectric constant of about 3.1.
- 8. The helix antenna of claim 1 wherein said second end portion of each of said first, second and third monopole elements includes a shaped metal portion constructed and arranged to provide an electrical function selected from a group consisting of capacitive reactance and/or inductive reactance.
- 9. The helix antenna of claim 1 wherein said perimeter of said top-surface has a major dimension that is less than about 0.2 wavelengths in free space of an operating frequency of the antenna, and wherein said top-surface is selected from a group consisting of a multi-sided perimeter, a circle perimeter and circle-like perimeter.
- 10. The helix antenna of claim 1, including:a single metal ground plane member cooperating with each of said first, second and third monopole elements.
- 11. The helix antenna of claim 1 wherein said second and third monopole elements are parasitically coupled to said first monopole element at plus 120-degrees, to thereby provide a linear polarized helix antenna.
- 12. The helix antenna of claim 1 wherein said second monopole element is parasitically coupled to said first monopole element at plus 120-degrees and said third monopole element is parasitically coupled to said first monopole element at minus 120-degrees, to thereby provide a circular polarized helix antenna.
- 13. The helix antenna of claim 1 wherein at least one of said second and third monopole elements includes a metal perturbation, such that one of said second and third monopole elements is coupled to said first monopole element at plus 120-degrees and such that another of said second and third monopole elements is coupled to said first monopole element at minus 120-degrees, to thereby provide a circular polarized helix antenna.
- 14. The helix antenna of claim 1 wherein each of said first, second and third monopole elements includes a bent portion located intermediate said first and second end portions.
- 15. The helix antenna of claim 1 wherein said first, second and third monopole elements define generally identical metal patterns on said top-surface.
- 16. A helix antenna, comprising:an electrically non-conductive body member having a generally hexagonal generally flat top-surface, and having six generally equal size side walls that extend generally perpendicularly downward from said top-surface; said top-surface having a central axis; a first quarter wave monopole element having a first straight metal portion on said top-surface adjacent to a first of said side walls, having a bent metal portion on said top-surface adjacent to a portion of a second of said side walls, and having a second straight metal portion on said top-surface extending from said portion of said second side wall toward said central axis so as to position an end of said second straight metal portion generally adjacent to said central axis; a second quarter wave monopole element having a first straight metal portion on said top-surface adjacent to a third of said side walls, having a bent metal portion on said top-surface adjacent to a portion of a fourth of said side walls, and having a second straight metal portion on said top-surface extending from said portion of said fourth side wall toward said central axis so as to position an end of said second straight metal portion generally adjacent to said central axis a third quarter wave monopole element having a first straight metal portion on said top-surface adjacent to a fifth of said side walls, having a bent metal portion on said top-surface adjacent to portion of a sixth of said side walls, and having a second straight metal portion on said top-surface extending from said portion of said sixth side wall toward said central axis so as to position an end of said second straight metal portion generally adjacent to said central axis; said ends of said second straight metal portions of said first, second and third monopole elements having relatively closely physical spacing so as to be parasitically-couple said first, second and third monopole elements; a first inductive shunt metal pattern on said sixth side wall connected to said first straight metal portion of said first monopole element; a second inductive shunt metal pattern on said third side wall connected to said first straight metal portion of said second monopole element; a third inductive shunt metal pattern on said forth side wall connected to said first straight metal portion of said third monopole element; and antenna feed means connected only to said first inductive shunt metal pattern.
- 17. The helix antenna of claim 16 wherein about one-half of any feed-energy presented to said antenna feed means is transmitted into space from said first monopole element, and about one-half of said feed-energy is parasitically coupled to said second and third monopole elements.
- 18. The helix antenna of claim 16 wherein said parasitic-coupling is about minus 6 dB.
- 19. The helix antenna of claim 16 wherein said body member has a dielectric constant of about 3.1.
- 20. The helix antenna of claim 16 wherein said hexagonally-shaped top-surface has a vertex-to-vertex dimension of about one inch.
- 21. The helix antenna of claim 16, including:a single metal ground plane member cooperating with said first, second and third quarter wave monopole elements.
- 22. The helix antenna of claim 16 wherein said second and third monopole elements are parasitically coupled to said first monopole element at plus 120-degrees, to thereby provide a linear polarized helix antenna.
- 23. The helix antenna of claim 16 wherein said second monopole element is parasitically coupled to said first monopole element at plus 120-degrees and said third monopole element is parasitically coupled to said first monopole element at minus 120-degrees, to thereby provide a circular polarized helix antenna.
- 24. The helix antenna of claim 16 wherein at least one of said second and third monopole elements includes a metal perturbation, such that one of said second and third monopole elements is parasitically coupled to said first monopole element at plus 120-degrees and said the other of said second and third monopole elements is parasitically coupled to said first monopole element at minus 120-degrees, to thereby provide a circular polarized helix antenna.
- 25. A method of making a single-feed, three-monopole, helix antenna, comprising the steps of:providing three planar, metal and quarter-wave monopole antenna elements; physically positioning said three monopole elements in a common plane at about 0-degrees, 120-degrees, and 240-degrees, respectively, about a central axis; physically positioning said three monopole elements such that first end portions of each of said three monopoles are located physically adjacent to each other and to said central axis, and such that said three monopole elements are relatively strongly coupled; connecting an antenna-feed to a second end of a first of said monopole elements; such that said first monopole element is a directly-fed monopole element, and such that a second and a third monopole element are parasitically-fed from said first monopole element; and providing that said relatively strong coupling between said three monopole elements results in about one-half of any feed energy that is applied to said antenna feed is radiated from said first monopole element into space, as a remaining portion of said feed energy is parasitically coupled to said second and third monopole elements.
- 26. The method of claim 25 including the steps of:providing an inductive shunt; and connecting said inductive shunt intermediate said antenna-feed and said second end of said first monopole element.
- 27. The method of claim 25 wherein said relatively strong coupling is capacitive coupling.
- 28. The method of claim 25 wherein said relatively strong coupling has a magnitude of about −6 dB.
- 29. The method of claim 25 wherein said common plane is provided by an electrically non-conductive member having a relatively low dielectric constant.
- 30. The method of claim 25 wherein said common plane is provided by an electrically non-conductive member having a dielectric constant of about 3.1.
- 31. The method of claim 25 wherein said second and third monopoles are both ed at about positive 120 degrees to said first monopole element.
- 32. The method of claim 25 wherein said second monopole element is coupled to said first monopole element at about positive 120-degrees, and wherein said third monopole element is coupled to said first monopole element at about negative 120-degrees.
- 33. The method of claim 25 including the step of:providing one or more metal perturbations on one or both of said second and third monopole elements in order to control a phase-of-coupling of said second and third monopole elements to said first monopole element.
US Referenced Citations (9)