Information
-
Patent Grant
-
6445906
-
Patent Number
6,445,906
-
Date Filed
Thursday, September 30, 199924 years ago
-
Date Issued
Tuesday, September 3, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Urban; Edward F.
- Smith; Sheila
Agents
- Breeden; R. Louis
- Loppnow; Matthew C.
-
CPC
-
US Classifications
Field of Search
US
- 455 550
- 455 575
- 455 90
- 455 281
- 455 1932
- 455 1931
- 455 171
- 455 500
- 455 129
- 455 280
- 455 269
- 343 702
- 343 701
- 343 889
-
International Classifications
- H04B104
- H04B106
- H04B118
- H01Q126
-
Abstract
An antenna (100) includes a rectangular dielectric substrate (102); and a U-shaped conductive strip attached to a first surface of the substrate, the U-shaped conductive strip having two side members (202, 203), each about one-eighth a predetermined wavelength in length, and an end member (204) forming a substantially rectangular slot (206) extending parallel to the long edges of the substrate, the slot closed at a first end (212) by the end member, and open at a second end (208). The antenna further includes a microstrip feed line (104) attached to a second surface of the substrate opposite and parallel to the first surface for coupling an RF signal between the antenna and an RF device (502), the microstrip feed line extending across and perpendicular to the slot proximate the second end of the slot, and further extending across a portion of the two side members; and a ground point (210) electrically coupled to a first one of the two side members of the U-shaped conductive strip and positioned proximate the second end of the slot.
Description
FIELD OF THE INVENTION
This invention relates in general to wireless communications, and more specifically to a micro-slot antenna.
BACKGROUND OF THE INVENTION
Prior-art antennas used in portable wireless devices have included loop, ceramic chip, and microstrip patch antennas. The loop antenna is inexpensive, but does not perform well in free-field conditions. The ceramic chip antenna is relatively expensive and has moderate performance both in free-field and on-body environments. The microstrip patch antenna is very expensive and does not perform as well on body as in free-field.
The loop and chip antennas are predominantly vertically polarized, and their performance degrades when incoming signals have a non-vertical polarization. The microstrip patch antenna has both vertical and horizontal polarization, but it is not favorable in terms of size, weight, cost, and bandwidth.
Thus, what is needed is an antenna that has a small size, light weight, low cost, wider bandwidth, and both vertical and horizontal polarization. The antenna preferably will have excellent gain in both free-field and on-body environments.
SUMMARY OF THE INVENTION
An aspect of the present invention is a micro-slot antenna for use at a predetermined wavelength. The antenna comprises a rectangular dielectric substrate having two long edges and two short edges; and a U-shaped conductive strip attached to a first surface of the substrate, the U-shaped conductive strip having two side members, each about one-eighth the predetermined wavelength in length, and an end member forming a substantially rectangular slot extending parallel to the long edges, the slot closed at a first end by the end member, and open at a second end. The antenna further comprises a microstrip feed line attached to a second surface of the substrate opposite and parallel to the first surface for coupling an RF signal between the antenna and an RF device, the microstrip feed line extending across and perpendicular to the slot proximate the second end of the slot, and further extending across a portion of the two side members; and a ground point electrically coupled to a first one of the two side members of the U-shaped conductive strip and positioned proximate the second end of the slot.
Another aspect of the present invention is a radio device comprising a radio element including at least one of a transmitter and a receiver, a user interface coupled to the radio element for interfacing with a user; and a micro-slot antenna coupled to the radio element for use at a predetermined wavelength. The antenna comprises a rectangular dielectric substrate having two long edges and two short edges; and a U-shaped conductive strip attached to a first surface of the substrate, the U-shaped conductive strip having two side members, each about one-eighth the predetermined wavelength in length, and an end member forming a substantially rectangular slot extending parallel to the long edges, the slot closed at a first end by the end member, and open at a second end. The antenna further comprises a microstrip feed line attached to a second surface of the substrate opposite and parallel to the first surface for coupling an RF signal between the antenna and the radio element, the microstrip feed line extending across and perpendicular to the slot proximate the second end of the slot, and further extending across a portion of the two side members; and a ground point electrically coupled to a first one of the two side members of the U-shaped conductive strip and positioned proximate the second end of the slot.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a top plan view of a micro-slot antenna in accordance with the present invention.
FIG. 2
is a bottom plan view of the micro-slot antenna in accordance with the present invention.
FIG. 3
is a top orthogonal view of the micro-slot antenna in accordance with the present invention.
FIG. 4
is a front orthogonal view of the micro-slot antenna in accordance with the present invention.
FIG. 5
is an electrical block diagram of an exemplary radio device in accordance with the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1
is a top plan view of a micro-slot antenna
100
in accordance with the present invention. This view depicts a rectangular dielectric substrate
102
and a microstrip feed line
104
. The substrate
102
is preferably formed from a conventional thin, low-loss, soft, dielectric material having a thickness of 0.51 to 0.76 mm and a dielectric constant of 3.0. The microstrip feed line
104
is preferably formed from copper having a thickness of 0.036 mm. The length
106
of the short edges is preferably about 1/24 of a predetermined wavelength of an RF signal which the antenna
100
is intended to intercept (e.g., 1.25 cm at 1 GHz). It will be appreciated that, alternatively, other similar materials, thicknesses, and dimensions can be substituted in accordance with the present invention.
FIG. 2
is a bottom plan view of the antenna
100
in accordance with the present invention. This view depicts a U-shaped conductive strip attached to a first surface of the substrate
102
, the U-shaped conductive strip comprising two side members
202
,
203
, each having an effective length
216
of about one-eighth the predetermined wavelength (e.g., 3.75 cm at 1 GHz). The U-shaped conductive strip also includes an end member
204
. The U-shaped conductive strip forms a substantially rectangular slot
206
extending parallel to the long edges of the substrate
102
, the slot
206
closed at a first end
212
by the end member
204
, and open at a second end
208
. The width
214
of the slot
206
is preferably 2.5 mm, except at the second end
208
, where the slot
206
widens linearly to about 5 mm at the edge of the substrate. A ground point
210
on the side member
202
and positioned proximate the second end
208
of the slot
206
is utilized for grounding the antenna
100
. The U-shaped conductive strip
202
,
203
,
204
preferably is formed from copper having a thickness of 0.36 mm. It will be appreciated that, alternatively, other similar materials, thicknesses, and dimensions can be substituted in accordance with the present invention.
FIG. 3
is a top orthogonal view of the antenna
100
in accordance with the present invention. Here the position and orientation of the microstrip feed line
104
with respect to the slot
206
and the U-shaped conductive strip
202
,
203
,
204
can be observed. Note that the microstrip feed line
104
extends across and perpendicular to the slot
206
proximate the second end
208
of the slot
206
, and further extends across a portion of the two side members
202
,
203
. The microstrip feed line preferably also extends (extended portion
302
) a distance parallel to the slot
206
and proximate a central portion of the side member
203
and towards the end member
204
. Note that the side member
203
does not include the ground point
210
, but is opposite the side member
202
, which includes the ground point
210
. The resonant frequency of the antenna
100
is tuned primarily by adjusting the effective length
216
of the two side members
202
,
203
. The resonant frequency is also affected by the length of the extended portion
302
of the microstrip feed line
104
. The input impedance of the antenna
100
is adjusted by changing the width of the microstrip feed line and the width of the slot
206
.
FIG. 4
is a front orthogonal view of the antenna
100
in accordance with the present invention. This view is not drawn to scale. The view shows that the U-shaped conductive strip
202
,
203
,
204
and the microstrip feed line
104
are on opposite parallel surfaces of the substrate
102
.
Due to size limitations in a portable communication device for which the antenna
100
is intended, the slot
206
cannot be made one-half-wavelength long for efficient radiation. For this reason, one end of the slot is left open. The micro-slot antenna
100
in accordance with the present invention functions through the theory of microstrip-to-slot transition. The microstrip feed line
104
and the U-shaped conductive strip
202
,
203
,
204
interact as follows to produce advantageous results. First, the U-shaped conductive strip
202
,
203
,
204
forms the slot
206
, as described above. Second, the U-shaped conductive strip
202
,
203
,
204
is a narrow strip of conductor, one-quarter wave long, with one end grounded and the other end open, to form a standing wave along the strip. Energy propagates down the microstrip feed line
104
, couples to the slot
206
, and creates an electric field along the slot. A differential potential formed across the slot causes a current to flow around the U-shaped conductive strip. In effect, the open slot and the U-shaped conductive strip form two radiators in a single configuration. When the antenna
100
is oriented such that the electromagnetic wave propagated from the open slot is vertically polarized, then the U-shaped conductive strip produces a horizontally-polarized electric field, and vice versa. As a result, the micro-slot antenna
100
is linearly polarized with about 45 degrees of tilt.
FIG. 5
is an electrical block diagram of an exemplary radio device
500
in accordance with the present invention. The radio device
500
comprises a conventional radio element
502
including at least one of a conventional receiver
506
and a conventional transmitter
508
. The radio device
500
further comprises a conventional user interface
504
(e.g., control buttons and display) coupled to the radio element
502
for interfacing with a user. The radio device
500
also includes the micro-slot antenna
100
coupled to the radio element
502
for intercepting a radio signal to be received.
Thus, it should be clear from the preceding disclosure that the present invention advantageously provides an antenna that has a small size, light weight, low cost, and both vertical and horizontal polarization. Tests have determined that the antenna in accordance with the present invention also has a wider bandwidth than prior-art antennas and has an excellent gain in both free-field and on body environments, matching the performance of a conventional slot antenna in a fraction of the size.
Claims
- 1. A micro-slot antenna for use at a predetermined wavelength, the antenna comprising:a rectangular dielectric substrate having two long edges and two short edges; a U-shaped conductive strip attached to a first surface of the substrate, the U-shaped conductive strip having two side members, each about one, eighth the predetermined wavelength in length, and an end member forming a substantially rectangular slot extending parallel to the long edges, the slot closed at a first end by the end member, and open at a second end; a microstrip feed line attached to a second surface of the substrate opposite and parallel to the first surface for coupling an RF signal between the antenna and an RF device, the microstrip feed line extending across and perpendicular to the slot proximate the second end of the slot, and further extending across a portion of the two side members; and a ground point electrically coupled to a first one of the two side members of the U-shaped conductive strip and positioned proximate the second end of the slot.
- 2. The antenna of claim 1, wherein the two short edges each are about one twenty-fourth the predetermined wavelength in length.
- 3. The antenna of claim 1, wherein the microstrip feed line further extends a distance parallel to the slot and proximate a central portion of a second one of the two side members and towards the end member, the second one of the two side members not including the ground point.
- 4. The antenna of claim 1, wherein the substrate is a thin, low-loss, soft, dielectric material.
- 5. The antenna of claim 1, wherein the microstrip feed line and the U-shaped conductive strip are formed of copper.
- 6. The antenna of claim 1, wherein the two short edges each are about one-twenty-fourth the predetermined wavelength in length.
- 7. The antenna of claim 1, wherein the microstrip feed line further extends a distance parallel to the slot and proximate a central portion of a second one of the two side members and towards the end member, the second one of the two side members not including the ground point.
- 8. The antenna of claim 1, wherein the substrate is a thin, low-loss, soft, dielectric material.
- 9. The antenna of claim 1, wherein the microstrip feed line and the U-shaped conductive strip are formed of copper.
- 10. A radio device, comprising:a radio element including at least one of a transmitter and a receiver; a user interface coupled to the radio element for interfacing with a user; and a micro-slot antenna coupled to the radio element for intercepting a radio signal to be received at a predetermined wavelength, the antenna comprising a rectangular dielectric substrate having two long edges and two short edges; a U-shaped conductive strip attached to a first surface of the substrate, the U-shaped conductive strip having two side members, each about one-eighth the predetermined wavelength in length, and an end member forming a substantially rectangular slot extending parallel to the long edges, the slot closed at a first end by the end member, and open at a second end; a microstrip feed line attached to a second surface of the substrate opposite and parallel to the first surface for coupling an RF signal between the antenna and the radio element, the microstrip feed line extending across and perpendicular to the slot proximate the second end of the slot, and further extending across a portion of the two side members; and a ground point electrically coupled to a first one of the two side members of the U-shaped conductive strip and positioned proximate the second end of the slot.
- 11. The radio device of claim 10, wherein the two short edges each are about one-twenty-fourth the predetermined wavelength in length.
- 12. The radio device of claim 10, wherein the microstrip feed line further extends a distance parallel to the slot and proximate a central portion of a second one of the two side members and towards the end member, the second one of the two side members not including the ground point.
- 13. The radio device of claim 10, wherein the substrate is a thin, low-loss, soft, dielectric material.
- 14. The radio device of claim 10, wherein the microstrip feed line and the U-shaped conductive strip are formed of copper.
- 15. A micro-slot antenna for use at a predetermined wavelength, the antenna comprising:a rectangular dielectric substrate having two long edges and two short edges; a U-shaped conductive strip attached and parallel to a first surface of the substrate, the U-shaped conductive strip having two side members, each about one-eighth the predetermined wavelength in length, and an end member forming a substantially rectangular slot extending parallel to the long edges, the slot closed at a first end by the end member, and open at a second end; a microstrip feed line attached and parallel to a second surface of the substrate opposite and parallel to the first surface for coupling an RF signal between the antenna an RF device, the microstrip feed line extending across and perpendicular to the slot proximate the second end of the slot, and further extending across a portion of the two side members; and a ground point electrically coupled to a first one of the two side members of the U-shaped conductive strip and positioned proximate the second end of the slot.
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A |
5943020 |
Liebendoerfer |
Aug 1999 |
A |
6133879 |
Grangeat et al. |
Oct 2000 |
A |
6184833 |
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Feb 2001 |
B1 |