Information
-
Patent Grant
-
6323812
-
Patent Number
6,323,812
-
Date Filed
Tuesday, April 4, 200024 years ago
-
Date Issued
Tuesday, November 27, 200122 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 343 702
- 343 700 MS
- 343 829
- 343 841
- 343 846
- 343 851
- 343 848
- 343 849
- 343 906
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International Classifications
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Abstract
An antenna feedpoint assembly includes a printed circuit board (400), a signal conductor feed element (2041) mounted on the printed circuit board (400), and a secondary ground element (106) placed parallel to the signal conductor feed element (2041) wherein an electromagnetic coupling is made between the signal conductor feed element (2041) and the secondary ground element (106) for an improved matching of the antenna (100) without an additional matching circuit. The secondary ground element (106) comprises a mounting portion (1061) connected to a ground plane (1002) and a protruded portion (1062) extended from the mounting portion (1061) such that the protruded portion (1062) is elevated from and substantially parallel to the signal conductor feed element (2041) serving as the antenna feedpoint contact.
Description
TECHNICAL FIELD
This invention is generally related to antennas and more particularly to antennas for portable communication devices.
BACKGROUND
As improved integrated circuit technology allows portable communication devices, such as transceivers and radiophones, or their combination, to be reduced in size, it is also desirable to reduce the overall length of the antenna structure used with such devices. One style of antennas is the half wave dipole antenna which requires no extensive ground plane to operate. Half wave dipole antennas produce highly desirable and predictable electrical performance. However, these antennas are large and therefore are undesirable for portable applications.
One of the smallest antenna structures frequently used with portable transceivers is a quarter wave length whip antenna which requires an extensive ground plane to operate effectively. A quarter wave whip antenna radiates at acceptable levels below the standards of the halfwave dipole, however with the benefit of reduced length. The much reduced size of portable communication devices has also reduced the size of the available ground plane. Consequently, the ground interacts with a high level of sensitivity to its surrounding environment. The smaller the antenna and ground become, the more the Q of the system increases, making the antenna and frequency bandwidth of operation smaller.
An antenna grounding improvement is therefore desired that can be used with small portable communication products.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the present invention, which are believed to be novel, are set forth with particularly in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:
FIG. 1
shows an antenna structure in a communication device, with a secondary ground element
106
hidden underneath the top-side of a back housing
114
, in accordance with the present invention.
FIG. 2
shows the underside of the back housing
114
of the communication device of
FIG. 1
, with the secondary ground element
106
mounted, in accordance with the present invention.
FIG. 3
shows a perspective side view of the secondary ground element
106
of
FIG. 2
in relationship with the antenna feedpoint structure, in accordance with the present invention.
FIG. 4
shows a simplified representation of an alternative form of the secondary element
106
, in accordance with the present invention.
FIG. 5
shows a simplified top view of the antenna feedpoint structure related to the simplified secondary element
106
of
FIG. 4
, in accordance with the present invention.
FIG. 6
shows a simplified top view of the antenna feedpoint structure related to another simplified secondary element
106
having a plane extension
1062
instead of a coil extension
1063
, in accordance with the present invention.
FIG. 7
represents a perspective side view of the secondary ground element
106
of
FIG. 6
in relationship with the antenna feedpoint structure, in accordance with the present invention, but with the substrate
400
removed to show the antenna bushing
412
underneath.
FIG. 8
shows a simplified front cross-sectional view of the secondary ground element
106
of
FIG. 7
with the antenna contact
2041
in a simulated transmission line, in accordance with the present invention.
FIG. 9
shows a simplified side cross-sectional view of the secondary ground element
106
of
FIG. 7
with the antenna contact
2041
in a simulated transmission line, in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The principles of the present invention will be better understood by referring to a series of drawings where like numerals are carried forward but dimensions are not to scale or in their actual proportions. Referring to
FIGS. 1 and 2
, a quarter wave antenna
100
is shown. Basically, in accordance with the teachings of the present invention, an antenna feedpoint assembly includes a printed circuit board
400
, a signal conductor feed element
2041
mounted on the printed circuit board
400
, an antenna bushing
412
, and a secondary ground element
106
, hidden underneath a back housing
114
but which can better be seen in the back housing's underside of FIG.
2
.
Referring now to the simplified drawings of
FIGS. 8-9
, the secondary ground element
106
is placed parallel to the signal conductor feed element
2041
, and antenna bushing
412
. With this arrangement, an electromagnetic coupling is made between the signal conductor feed element
2041
, antenna bushing
412
, and the secondary ground element
106
for an improved matching of the antenna
100
without an additional matching circuit. Better seen in
FIG. 7
, the secondary ground element
106
comprises a mounting portion
1061
connected to a ground plane
1002
and a protruded portion
1062
extended from the mounting portion
1061
such that the protruded portion
1062
is elevated from and substantially parallel to the signal conductor feed element
2041
serving as the antenna feedpoint contact.
Referring back to
FIGS. 1
,
8
, and
9
, the signal conductor feed element
2041
and antenna bushing
412
are used to couple the antenna
100
to a communication device, such as a radio, a phone, a pager, or their combination. The antenna
100
includes a center conductor
410
connected to another optional connector (not shown) which provides internal screwable contact to the antenna bushing
412
. In the preferred embodiment, the center conductor has a range of operating frequencies between 800 MHz and 1.8/1.9 GHz. The close proximity of the center conductor
410
, the antenna bushing
412
, and the center conductor feed element
2041
, to the ground
1002
, extended by the secondary ground element
106
, at the feedpoint end of the antenna
100
shown by the distance
89
, increases bandwidth and radiation efficiency without the additional components or the complexity of matching circuits. In this preferred embodiment, the distance
89
is approximately 0.7 mm. However, in general, a distance between 0.5 mm and 2.0 mm is envisioned by the teachings of the present invention.
The feedpoint structure of the antenna
100
solves the problems of the prior art by almost confining the fields generated through the conductor feed element
2041
to ground and providing a better feedpoint. The almost shorted transmission line that is thus produced acts as a low Q matching element and feeds the transmitted power to the antenna. If the secondary ground element
106
is implemented with a coil extension
1063
, as in
FIGS. 3 and 4
, the element
106
behaves as an additional high Q inductance. Alternatively, the protruded portion
1062
serves as extra capacitance, as provided by an optional plate, as the protruded portion
1062
in
FIGS. 6-9
or an additional planar extension
1064
to the coil
1063
of the embodiment in
FIGS. 2 and 3
. Thus, the input impedance of the quarterwave monopole can be matched to 50 ohms without any discrete matching components and with minimum losses.
Referring back to
FIG. 1
, the length of the center conductor
410
is substantially a quarter wave length at the operating frequency of the transmit signal. The quasi transmission line feed includes the antenna contact
2041
connected to bushing
412
and the ground plane
1002
extended by the secondary ground element
106
of
FIG. 2 and a
dielectric within the distance
89
in
FIGS. 8-9
of air between the antenna contact or feed element
2041
and the secondary ground element
106
. The dielectric between the ground plane
1002
and the antenna contact
2041
on one side and their through holes on the opposed side may be any well known dielectric used in transmission line applications such as TEFLON® or any suitable printed circuit board material. The center conductor
410
is connected to the radio communication device via the antenna bushing
412
of the feedpoint end
2041
of the antenna. This antenna feedpoint structure provides for the efficient radiation of the transmit radio frequency signal without the historical potentially lossy discrete matching components required to improve and enlarge the bandwidth of the quarter wave antenna.
Highlighted parts of a communication device
10
will be described in more detail to show the relationship between the antenna feedpoint assembly and the rest of the communication device
10
, in accordance with the teachings of the present invention. The communication device
10
includes the front housing
314
on which the antenna bushing
412
is located. The center conductor
410
of the antenna is preferably attached to the radio communication device
10
via the bushing. By connecting the center conductor
410
to the antenna bushing
412
and subsequently to the antenna contact, a quarter wave resonant antenna operates much more efficiently, without the need for additional matching elements. If the protruded portion
1062
of the secondary ground element
106
in
FIG. 8
takes on the form of a coil
1063
, the secondary ground element
106
acts like a large inductance at the frequency of operation. This action moves the non-ideal quarterwave antenna closer to the center of the well known impedance matching Smith chart (50 ohm point). The key is the almost shorting of the center conductor
412
to the ground plane
1002
, via the parallel and close transmission line or other type of electromagnetic coupling between the secondary ground element
106
and the combination antenna bushing
412
/feed element
2041
. With such a scheme, quarter wave antenna operates more efficiently without additional matching circuits. In fact, the matching is automatically provided by almost shorting the combination antenna bushing
412
/antenna contact
2041
to the secondary ground element
106
to simulate a transmission line.
The antenna feedpoint assembly is both constrained and supported by the housing of the communication device
10
. The antenna contact
2041
and the secondary ground element
106
, in sheet metal and single wire forms, are ideal for applications having tight space and high deflection requirements. For example, a phone using the teachings of the present invention could measure just 4.5×2.2×1.2 inches (115×56×30 mm) and weighs as little as five ounces (142 grams) with a Lithium Ion battery (not shown). The battery is piggy-backed or mounted to a back cover
114
which is mated to the front housing or cover
314
of the radio or communication device. The back housing or cover has a raised back housing portion to recess a battery compartment cavity
116
formed therein between first
118
and second
120
side wall s for receiving the battery. This raised back housing portion is bored through to form at least one internal boss
220
more clearly seen in FIG.
2
.
The substrate, preferably in the form of a printed circuit board (PCB)
400
, has a notch
402
cut-away, in the corner nearest the first sidewall
118
, closest to the radio antenna
410
. The PCB substrate
400
contains radio frequency (RF) circuitry and other circuitry including the ground plane
1002
and other ground accessible points such as
2042
. Near the top edge of the substrate, at least one aperture
320
has a solder pad formed around its periphery. This substrate
400
seen in
FIG. 2
is inserted underneath the secondary ground element
106
for resting within the top of the screw support
420
of FIG.
1
.
To show further detail, the radio front cover
314
has the antenna bushing
412
, preferably ultrasonically inserted at the top of the front cover
314
, for receiving the radio antenna
410
. The front cover
314
mates with the back cover
114
, containing the battery compartment
116
, for encapsulating the substrate board
400
in- in-between. Optionally, the front cover
314
has support members or screw support
420
with a wider base for elevating the substrate
400
to the height needed for forming the back support for and resting the back cover
114
. The top of the screw support
420
protrudes through the solder surrounded aperture
320
of the substrate
400
for allowing a screw (not shown) to be inserted and tighten through the boss
220
of the back housing
114
of
FIG. 2
when the boss
220
mates with the screw support
420
over the substrate's aperture
320
.
Referring to
FIG. 2
, the secondary ground element is designed to fit around the boss
220
and underneath the raised back housing portion between the two different levels of the substrate
400
and the underside of the raised portion. To optimize this fit, the secondary ground element
106
is preferably S-shaped (better seen in
FIG. 8
) to form a metal retainer boss covering. The mounting portion of the boss covering is provided by a grommet-shaped ring retainer having an eyelet
2061
surrounded by at least one retaining leg
2062
and a sidewall
2063
. The protruded portion, at the top of the “S” comprises a planar
1062
(in
FIG. 7
) or an optional coil
1063
extension to the sidewall (body or vertical member of the “S”)
2063
such that the planar extension/coil
1062
, the sidewall
2063
, and the eyelet (bottom of the “S” for mating with the substrate
400
below)
2061
together provide an S-shaped retainer. Hence, the mounting portion formed by the sidewall
2063
and the eyelet
2061
provides a sheet metal portion having sufficient retaining elements to be captured between the underside of the internal boss
220
and the printed circuit board
400
. The protruded portion
1063
then extends from the sheet metal mounting portion
2063
and resides underneath the raised back housing portion such that the protruded portion is elevated from and substantially parallel to a cantilevered hook or beam portion
30
(seen in
FIG. 1
) of the signal conductor feed element
2041
and the antenna bushing
412
.
Electrically, the ground element
106
thus acts as a ground plane which retains the electromagnetic energy between it, the feed element
2041
, and the antenna bushing
412
, to mimic a transmission line as simplified in
FIGS. 8-9
. This transmission line configuration limits the radiation energy that would normally escape from this feedpoint area and allows the antenna to radiate more efficiently.
Referring back to
FIG. 1
, the feed element or RF circuitry contact
2041
includes a resilient metal form or tab for making a connection inside
1
the radio. Preferably, the resilient metal is in the form of a “J”-shaped sheet metal hook
2041
having a base portion
20
, a “J”-shaped tip portion
40
, and the cantilever beam portion
30
integrally connecting the tip
40
to the base
20
(details in FIG.
7
). The base portion
20
is surface mounted on top of the substrate
400
. The cantilever beam portion
30
extends from the base portion
20
, over the notch
402
, such that the “J”-shaped tip portion
40
, terminating the cantilever beam portion
30
, can protrude through the notch
402
for resiliently biasing the antenna bushing
412
underneath. At the same time, this RF or positive terminal antenna contact
2041
, serves as the hot contact, or RF connection for the antenna
410
, via the antenna bushing
412
, to connect the antenna
410
to the radio frequency circuitry of the rest of the radio through the electrical conductive path of the substrate
400
. Optionally, the base
20
of the “hot” RF contact
2041
has a pair of legs
25
that are inserted and soldered through a pair of through holes to provide better support.
This cantilever design allows an easier blind assembly of the substrate
400
to the antenna
410
, in a small package, without the risk of damaging the hot contact. Adjacent to the hot contact
2041
on the substrate
400
, a ground contact
2042
is also surface mounted on top of the substrate
400
to provide a ground terminal for the radio frequency circuitry.
In
FIGS. 5-6
, certain like numbers and items of
FIG. 1
are carried forward to show the RF contacts in more detail and in context with other components but without further reference to them. In this top view of the hot RF contact
2041
, the secondary ground element
106
is shown overlaid on top in a very simplified representation. The shapes of the “hot” or positive RF contact
2041
and the secondary ground element
106
are shown different than in
FIG. 1
to show the allowable geometrical variations in the contact and element configurations. Optimizing the antenna feedpoint structure is quite a difficult task, as many physical laws need to be followed. For example, the circular or squarish end of the base
20
of the hot point contact and the ground point or negative contact
2042
can not be located too far apart in order to avoid ground loop currents. It is recommended with this invention that a distance
1003
, no greater than 4 mm, be used between the termination points of these two adjacent contacts
2041
and
2042
. Preferably, the area around the “hot” RF contact
2041
is not covered with the resist layer covering the ground plane
1002
in order to provide the desired ground relief for the “hot” contact
2041
. The resist is a light thin film deposited on the ground
1002
of the PC board
400
and functioning to isolate the circuit from any potential shorts. In the actual radio example, the “hot” contact base termination comes within 0.03 inches or 0.75 mm of the ground resist area to prevent the ground from becoming an antenna.
In addition, the diameter of the circular or sides of the squarish base termination
20
of the hot test point
2041
, serving as the antenna launch feed, must not be larger than 0.020 inches or 0.4 mm in order to avoid the larger base rectangular or squarish area of the hot contact above the termination, providing the launch or actual feedpoint to the RF circuitry below the PC board
400
, to be too large and radiate inside the radio. To provide strength to the soldered joints formed by the legs
25
, this feedpoint area needs to be as large as possible without being too large to interfere with RF propagation. The hot contact basically can be of any shape but it can not exceed 0.09 inches or 2.25 mm in its largest dimension. In other words, the overall length of the antenna launch area, including the antenna bushing
412
, the cantilevered contact portion
30
, the base contact portion
20
(containing the circle and the square or two squares connected by a rectangular path) should be kept below 15 mm.
While the different preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents in the shape of the secondary ground element will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims
Claims
- 1. A communication device, comprising:a transmitter for producing a transmit signal having an operating frequency, the transmitter having a feedpoint and a ground; a center conductor for radiating the transmit signal; a housing; a connector for connecting the center conductor to the top of the housing; a printed circuit board having a notch and located within the housing; a signal conductor feed element having a cantilevered hook mounted on the printed circuit board and the cantilevered hook resiliently engaging the connector over the notch for connecting the center conductor to feedpoint of the transmitter; and a secondary ground element connected to the ground of the transmitter, mounted within the housing and placed parallel to the signal conductor feed element wherein an electromagnetic coupling is made between the signal conductor feed element and the secondary ground element for an improved matching of the antenna without a matching circuit.
- 2. The communication device of claim 1, wherein the center conductor has a length close to a quarter wavelength at the operating frequency.
- 3. The communication device of claim 1, wherein the center conductor has a range of operating frequencies between 800 MHz and 1.8/1.9 GHz.
- 4. The communication device of claim 1, wherein the connector comprises an antenna bushing.
- 5. The communication device of claim 1, wherein the housing includes an internal boss bored from a raised back housing portion.
- 6. The communication device of claim 5, wherein the secondary ground element comprises:a sheet metal portion having retaining elements to be captured between the underside of the internal boss and the printed circuit board; and a protruded portion extended from the sheet metal portion and residing underneath the raised back housing portion such that the protruded portion is elevated from and substantially parallel to the cantilevered hook of the signal conductor feed element.
- 7. The communication device of claim 6, wherein the protruded portion comprises a coil.
- 8. The communication device of claim 6, wherein the protruded portion comprises a coil to provide inductance to the feedpoint.
- 9. The communication device of claim 6, wherein the protruded portion comprises a shield to simulate a transmission line with the cantilevered hook of the signal conductor feed element.
- 10. The communication device of claim 6, wherein the protruded portion comprises a shield to provide capacitance to the feedpoint.
- 11. An antenna assembly, comprising:a quarter wavelength center conductor; a housing; a connector for connecting the quarter wavelength center conductor to the top of the housing; a printed circuit board having a notch; a signal conductor feed element having a hook mounted on the printed circuit board and the hook resiliently engaging the connector over the notch; and a secondary ground element mounted within the housing and placed parallel to the signal conductor feed element wherein an electromagnetic coupling is made between the signal conductor feed element and the secondary ground element for an improved matching of the antenna without a separate matching circuit; wherein the secondary ground element comprises an S-shaped metal retainer.
- 12. A secondary ground element comprises:a mounting portion connected to a ground plane; and a protruded portion extended from the mounting portion such that the protruded portion is elevated from and substantially parallel to an antenna feedpoint contact; wherein the mounting portion comprises a housing boss covering comprising a grommet-shaped ring retainer having an eyelet surrounded by at least one retaining leg and a sidewall.
- 13. The secondary ground element of claim 12, wherein the protruded portion comprises a coil.
- 14. The secondary ground element of claim 12, wherein the protruded portion comprises a shield.
- 15. The secondary ground element of claim 12, wherein the protruded portion comprises a planar extension to the sidewall such that the outline of the planar extension, the sidewall, and the eyelet in combination provides an S-shaped retainer.
- 16. The secondary ground element of claim 12, wherein the protruded portion comprises a coil attached to the sidewall at a level different than the level of the eyelet.
US Referenced Citations (8)