U.S. patent application number 13/411670 was filed with the patent office on 2013-09-05 for radio frequency identification reader antenna arrangement with multiple linearly-polarized elements.
This patent application is currently assigned to Symbol Technologies, Inc.. The applicant listed for this patent is David E. Bellows. Invention is credited to David E. Bellows.
Application Number | 20130229262 13/411670 |
Document ID | / |
Family ID | 47891941 |
Filed Date | 2013-09-05 |
United States Patent
Application |
20130229262 |
Kind Code |
A1 |
Bellows; David E. |
September 5, 2013 |
RADIO FREQUENCY IDENTIFICATION READER ANTENNA ARRANGEMENT WITH
MULTIPLE LINEARLY-POLARIZED ELEMENTS
Abstract
An antenna method and apparatus for a Radio Frequency
Identification (RFID) reader includes an RFID reader, a plurality
of radio ports of the RFID reader, and a plurality of linearly
polarized antenna elements coupled to the radio ports, wherein the
RFID reader directs the radio ports to sequentially communicatively
connect only one antenna element at a time to the RFID reader such
that only one antenna element is operable to transmit/receive at
any instant in time. The antenna elements are mounted in an
alternating vertically polarized and horizontally polarized
configuration.
Inventors: |
Bellows; David E.; (Wantagh,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bellows; David E. |
Wantagh |
NY |
US |
|
|
Assignee: |
Symbol Technologies, Inc.
Schaumburg
IL
|
Family ID: |
47891941 |
Appl. No.: |
13/411670 |
Filed: |
March 5, 2012 |
Current U.S.
Class: |
340/10.1 ;
343/853 |
Current CPC
Class: |
G06K 7/10356 20130101;
H01Q 3/24 20130101; H01Q 1/2216 20130101; H01Q 7/00 20130101; H01Q
19/106 20130101; H01Q 21/24 20130101; H01Q 21/205 20130101; H01Q
1/007 20130101 |
Class at
Publication: |
340/10.1 ;
343/853 |
International
Class: |
G06K 7/01 20060101
G06K007/01; H01Q 21/00 20060101 H01Q021/00 |
Claims
1. An antenna apparatus for a Radio Frequency Identification (RFID)
reader, comprising: an RFID reader; a plurality of radio ports
coupled to the RFID reader; and a plurality of linearly polarized
antenna elements coupled to the radio ports, wherein the RFID
reader directs the radio ports to sequentially communicatively
connect only one antenna element at a time to the RFID reader such
that only one antenna element is operable to transmit/receive at
any instant in time.
2. The antenna apparatus of claim 1, wherein there is an even
number of antenna elements arranged in a circle to radiate
outwardly from the circle.
3. The antenna apparatus of claim 2, wherein there are eight
antenna elements evenly disposed at 45 degree intervals of the
circle, each with a gain of 6 dB.
4. The antenna apparatus of claim 2, wherein the antenna elements
are linearly polarized to provide either of a first polarization
and a second polarization ninety degrees to the first polarization,
and wherein the antenna elements alternate polarizations around the
circle.
5. The antenna apparatus of claim 4, wherein each antenna element
provides an antenna gain that is down 3 dB (half power) at about
.+-.46.5 degrees from its bore sight, such that RFID read coverage
areas of neighboring antenna elements do not significantly
overlap.
6. The antenna apparatus of claim 4, wherein the antenna elements
with the first polarization have a first angular tilt with respect
to a ceiling and the antenna elements with the second polarization
have a second angular tilt with respect to the ceiling different
from the first angular tilt.
7. The antenna apparatus of claim 6, wherein the first polarization
is a vertical polarization and the second polarization is a
horizontal polarization, and wherein the first angular tilt is
greater than the second angular tilt such that the vertically
polarized antenna elements are directed more downwardly from the
ceiling than the horizontally polarized antenna elements.
8. The antenna apparatus of claim 1, wherein each antenna element
comprises a linearly polarized, full wavelength loop element
oriented between, and parallel to, a director plate and a reflector
panel.
9. The antenna apparatus of claim 8, wherein the reflector panels
of the antenna elements are joined together to define a common
reflector box, wherein the reflector box defines a housing that
contains the radio ports of the RFID reader and acts as an
electrical ground for electrical components in the box.
10. A Radio Frequency Identification (RFID) reader, comprising: a
fixed overhead housing containing the RFID reader; a plurality of
radio ports disposed within the housing; and an antenna apparatus
disposed outside of the housing and coupled to provide
communications to the RFID reader via the radio ports, wherein the
antenna apparatus comprises: a plurality of linearly polarized
antenna elements coupled to the radio ports, wherein the RFID
reader directs the radio ports to sequentially communicatively
connect only one antenna element at a time to the RFID reader such
that only one antenna element is operable to transmit/receive at
any instant in time.
11. A method for reading Radio Frequency Identification (RFID) tags
with a fixed overhead RFID reader, the method comprising the steps
of: providing a plurality of linearly polarized antenna elements;
sequentially communicatively connecting only one antenna element at
a time to the RFID reader such that only one antenna element is
operable to transmit/receive at any instant in time; and reading
RFID tags within an RFID read coverage area of each sequenced
antenna element.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates generally to wireless
antennas and more particularly to a Radio Frequency Identification
(RFID) antenna arrangement.
BACKGROUND
[0002] Radio Frequency Identification (RFID) is utilized in a
variety of applications with RFID readers communicating with RFID
tags for purposes of identification, location, tracking, and the
like. In an exemplary RFID application, an RFID reader may be
mounted overhead (e.g., ceiling mounted) relative to a plurality of
RFID tags, such as in a retail environment, a factory environment,
a warehouse environment, etc. The overhead configuration offers
several advantages such as fewer physical obstructions, ease of
access to wiring in a ceiling, tamper resistance, safety, and the
like. However, conventional overhead antenna configurations have
disadvantages.
[0003] For example, it is desirable for an overhead RFID reader to
be able to passively read all the RFID tags in the environment.
However, it should be recognized that the tags and their antennas
may have all different orientations, depending on how they are
placed or stored in the environment. Optimally, a tag that is
placed horizontally is best read by an RFID reader with horizontal
polarization, and a tag that is placed vertically is best read by
an RFID reader with vertical polarization. Of course, such perfect
alignment is rarely achieved.
[0004] One solution to this random tag orientation is to provide
cross-polarization, which provides a vertically polarized antenna
and a horizontally polarized antenna, with overlapping RF coverage
between antennas, in an RFID reader, where the RFID reader can
switch between the antennas. One example of such an antenna
arrangement is a cross-dipole where two dipole antennas are
arranged at 90 degrees to each other making a "+" shape and are
both fed in the center. Cross-polarization can read tags that are
at either orientation and also tags angled between vertical and
horizontal orientations, but with reduced gain. However, since each
cross-polarized reader uses two antennas, the number of antennas
ports required is doubled and the physical size of the solution is
larger. In addition, such cross-polarized readers are not
omnidirectional and do not have a 360 degree beamwidth, requiring
several RFID readers to be deployed to cover the entire
environment. Another solution to the problem is to provide circular
polarization that can read tags at any orientation. However, such
circular polarized readers need to be larger in size in order to
maintain the same gain as their linearly polarized equivalent (i.e.
6 dB linear=9 dB circular). In addition, circular polarized readers
are not omnidirectional and do not have a 360 degree beamwidth,
requiring several RFID readers to be deployed to cover the entire
environment.
[0005] Regarding coverage area, RFID ceiling reader antennas can be
oriented in one of three ways--parallel, normal, or angular to the
ceiling. As examples, when a slot antenna, a patch antenna, or a
loop antenna is mounted parallel to the ceiling or a dipole
antenna, or a Yagi antenna is mounted normal to the ceiling, the
peak gain is at bore sight, with the main lobe of the antenna
radiation directed perpendicular to the ceiling; much of the RF
energy is therefore directed straight down to the floor/ground. In
the angular mounted configuration, the angle of mount is selected
to direct the main radiation lobe of the radiation pattern to a
target of interest. A problem in these above scenarios is that, as
we move away from the main lobe of the radiation pattern, the gain
of the antenna begins to drop. For RFID applications, this
situation results in a requirement to install multiple RFID readers
with antennas aimed at various angles to get a consistent and a
high percentage of RFID read coverage. However, the use of multiple
readers not only drives the installation cost up but also does not
result in a high percentage of tag reads in areas where the antenna
gain falls from its peak. It is therefore very important to
simplify and minimize the size, weight, and cost of the reader
without compromising RF performance.
[0006] Accordingly, there is a need for an RFID antenna apparatus
and method that overcome the aforementioned limitations. It would
be beneficial to provide this overhead system in a small and
lightweight arrangement while minimizing the number of RFID reader
systems (especially ceiling mounted) installed in a particular
environment, and maintaining/increasing overall read accuracy and
read percentages.
BRIEF DESCRIPTION OF THE FIGURES
[0007] The accompanying figures, where like reference numerals
refer to identical or functionally similar elements throughout the
separate views, together with the detailed description below, are
incorporated in and form part of the specification, and serve to
further illustrate embodiments of concepts that include the claimed
invention, and explain various principles and advantages of those
embodiments.
[0008] FIG. 1 is a simplified block diagram of an RFID reader and
antenna arrangement, in accordance with some embodiments of the
present invention.
[0009] FIG. 2 is a perspective view of linearly polarized antenna
elements, in accordance with some embodiments of the present
invention.
[0010] FIG. 3 is a perspective view of an embodiment of an actual
antenna arrangement of FIG. 1.
[0011] FIG. 4 is a cross-sectional top view of radiation patterns
for vertically and horizontally polarized antenna elements in
accordance with some embodiments of the present invention.
[0012] FIG. 5 is a perspective view of the three dimensional
radiation pattern for the antenna arrangement of FIG. 3.
[0013] FIG. 6 is a perspective view of an example environment
utilizing the antenna arrangement and RFID reader of FIG. 1.
[0014] FIG. 7 shows a flowchart of a method in accordance with some
embodiments of the present invention.
[0015] Skilled artisans will appreciate that elements in the
figures are illustrated for simplicity and clarity and have not
necessarily been drawn to scale. For example, the dimensions of
some of the elements in the figures may be exaggerated relative to
other elements to help to improve understanding of embodiments of
the present invention.
[0016] The apparatus and method components have been represented
where appropriate by conventional symbols in the drawings, showing
only those specific details that are pertinent to understanding the
embodiments of the present invention so as not to obscure the
disclosure with details that will be readily apparent to those of
ordinary skill in the art having the benefit of the description
herein.
DETAILED DESCRIPTION
[0017] In various exemplary embodiments, the present invention
provides a Radio Frequency Identification (RFID) antenna apparatus
and method that minimize the number of RFID reader systems
(especially ceiling mounted) installed in a particular environment,
while maintaining/increasing overall read accuracy and read
percentages. The present invention also provides an overhead system
in a small and lightweight arrangement.
[0018] Typically, RFID is a passive technology where a human
operator can read tags affixed to objects presented to the operator
using a hand-held reader. Alternatively, objects can be passed in
proximity to a fixed RFID reader such that the object tags can be
read. However, ceiling-mounted RFID readers that passively read
RFID tags is a logical next step of this technology's evolution.
Overhead RFID readers do not require human operation. However, the
configuration of such readers requires an antenna with high gain,
which can read tags at various locations and distances within the
read environment. High gain (e.g., .about.6 dB) is needed to
maximize read range while keeping required power relatively low.
Furthermore, greater antenna beamwidth is desired in order to
optimize the RF coverage area. Reductions to practice have proven
that in an overhead reader environment, when RF energy is launched
into a wider area, the read performance (overall read accuracy and
read percentages) is improved. As the antenna gain is increased
however, the antenna beamwidth decreases while the required antenna
size increases. Therefore, a proper balance must be achieved that
optimizes the system for a high enough gain, a large enough
beamwidth, a low enough power, and a small enough physical size.
The example embodiment utilizes 6 dB gain antennas operated at 30
dBm transmit power, which meets the acceptable limits imposed by
the FCC. Emitted isotropic radiated power (EIRP) is maximized at 36
dB (or 4 W) and the 3 dB (half power) beamwidth is maximized at 93
degrees. Increasing the gain beyond 6 dB would allow the system to
be operated at a lower power, but the beamwidth would decrease,
hurting RF performance, and the physical size would grow, becoming
too impractical. Physical size of the reader needs to be kept to a
minimum so that the system is unobtrusive, easy to install,
integrate, and maintain, and can allow for other features, such as
a security camera, access point electronics, etc.
[0019] FIG. 1 illustrates a block diagram of an antenna arrangement
of one embodiment of the present invention. An RFID reader 12 can
be connected to a plurality of antenna elements 10 via an antenna
switch or different radio ports of the RFID reader. Also, the RFID
reader can be integrated with an access point (not shown) and can
direct the different radio ports to sequentially communicatively
connect only one antenna element at a time to the RFID reader such
that only one antenna element is operable to transmit/receive at
any instant in time. The RFID reader can provide any tag
information it obtains to an access point (not shown) that can be
wired or wirelessly connected to a local area network (not shown)
for inventory purposes, for example. Although eight antenna
elements are shown, there could be any number of elements.
Preferably, there is an even number of antenna elements arranged in
a circle to radiate outwardly from the circle. As shown in this
embodiment, there are eight antenna elements evenly disposed at 45
degree intervals of the circle and connected to an eight-port
radio.
[0020] Referring to FIG. 2, in one embodiment, the antenna element
10 includes a linearly polarized, full wavelength loop as the
driven element 20 that is oriented between, and parallel to, a
conductive circular director plate 22 and a conductive reflector
panel 24, wherein the loop element is fed by an RF signal at a
specific point. It should be recognized that there can be
embodiments without the director plate, reflector panel, or both.
Those skilled in the art will recognize that in addition, the loop
geometry can be different than what is shown in the exemplary
embodiment--as examples, the size can be larger or smaller, the
shape does not have to be a circle, the width of the loop does not
need to be constant, etc. Variations of the director plate geometry
are also acceptable, including but not limited to changes in shape,
size, etc. Also, the director plate and/or the reflector panel may
have holes cut out. Furthermore, the geometric details of the loop,
director plate, and reflector do not necessarily have to be the
same for both antenna polarizations. Ultimately, the physical
shape, size, and configuration of the antenna geometry should be
resonant at 915 MHz, which is a standard frequency for RFID
applications. In accordance with the present invention, the antenna
elements are linearly polarized to provide either of a first
polarization and a second polarization that is ninety degrees to
the first polarization. In particular, half of the antenna elements
have the first polarization and half have the second polarization.
The feed point of the first polarization could be anywhere along
the loop element as long as the feed point of the second
polarization is located ninety degrees from the feed point of the
first polarization. In one embodiment, the feed point of the first
polarization is at point 23 (or opposite point 23) which provides a
vertical polarization. Then the feed point of the second
polarization is at point 21 (or opposite point 21) which provides a
horizontal polarization, i.e. ninety degrees from the first
polarization. In accordance with the present invention, the first
and second polarized antenna elements are positioned around a
circle (as shown in FIG. 1) wherein the antenna elements alternate
polarizations around the circle, e.g. a vertically polarized
antenna element has two neighboring horizontally polarized antenna
elements, and vice versa.
[0021] In the example shown in FIG. 2, the director plate 22 has a
spacing 26 of about 11/4 inches from the loop element 20, and the
loop element 20 has a spacing 27 of about 2 inches from the
reflector panel 24, for a 915 MHz system, which is a standard
frequency for RFID applications. It should be noted that spacing 26
and spacing 27 each do not necessarily have to be the same for both
antenna polarizations. The reflector panel is approximately 7
inches square, while the loop antenna is approximately 4 inches in
diameter, with the director plate being slightly less. It should be
noted that these values are approximate, and they could all be
varied to affect a different antenna gain or radiation pattern. It
should also be noted that the reflector panel(s) are illustrated
herein in a substantially square shape, but those of ordinary skill
in the art will recognize other shapes are also contemplated. The
use of a reflector panel placed behind the loop antenna and having
a parallel spacing thereto helps to reflect back most of the RF
energy, making the antenna element a high gain antenna system. The
reflector panel takes energy that is directed backwards towards it
from the loop element and redirects it, combining it with the
directly radiated pattern that was already directed forward. The
result is a high gain, directional antenna.
[0022] The configuration shown in FIG. 2 provides 6 dB antenna gain
along its bore sight (perpendicular to the plane of the loop),
which equates to 4 watts of radiated power from a 1 watt
transmitter in the RFID reader. The loop element and director plate
can be spaced from each other using insulating spacers or standoffs
(not shown) as are known in the art. The loop element and reflector
panel can be spaced from each other in a similar fashion. It should
also be recognized that completely different antenna element
configurations can be used successfully in the present invention,
other than the embodiment shown, to provide a substantially linear
polarization, including, but not limited to, a partial loop
antenna, a Yagi antenna, a slot antenna, a dipole antenna, a
monopole antenna, and the like. It should be recognized that a Yagi
antenna, a slot antenna, a dipole antenna, a monopole antenna, and
the like can be modified in size and shape while still electrically
behaving as a respective Yagi antenna, slot antenna, dipole
antenna, a monopole antenna, and the like tuned to the proper RFID
frequency band.
[0023] The present invention utilizes a plurality of the linearly
polarized antenna elements of FIG. 2, arranged in a circle (FIG. 1
showing eight elements arranged in a circle) and alternating the
polarization of each antenna to achieve 360 degrees of coverage.
The system turns each antenna on and off individually, switching
from one antenna to the next, so only one antenna is
transmitting/receiving at any instant in time. In one embodiment,
there are eight antennas spaced at 45 degree intervals, with their
linear polarizations alternating from horizontal to vertical to
horizontal, etc. The antennas have a gain of 6 dB, which
corresponds to a 3 dB (half power) beamwidth of about .+-.46.5
degrees. In other words, each antenna element provides an antenna
gain that is down 3 dB from its 6 dB peak at about .+-.46.5 degrees
from its bore sight, such that RFID read coverage areas of
neighboring antenna elements do not significantly overlap. The
actual radiation patterns can be affected by the configuration of
the loop, director, and reflector plate for each element, and by
the nature of mounting each antenna element together in a circle,
as will be detailed below.
[0024] FIG. 3 shows a perspective view of an eight element antenna
arrangement of the present invention from FIG. 1. All the reflector
panels 24 are joined together to create a central metal box or
housing 16 that is a trapezoidal pyramidal section with planar
surfaces, and that acts as one common reflector for all the antenna
elements 10 as well as an electrical ground for the other system
contents located inside the box. The central housing 16 can
alternatively be a continuous conical surface, as opposed to the
faceted embodiment shown in FIG. 3. The antenna arrangement
includes alternating horizontally polarized antenna elements 30
(fed at a first point 21) and vertically polarized antenna elements
32 fed at a second point 23 that is rotated ninety degrees from the
first point 21. The configuration shown results in an overall
maximum dimension of about 19 inches wide and about 6 inches tall
with the housing portion having a maximum dimension of about 12
inches wide.
[0025] The present invention provides certain advantages over the
known art. In particular, for a fixed overhead RFID reader, it is
not necessary to use circularly polarized antennas or linearly
cross-polarized antennas to cover the full 360 degrees of the read
zone. In fact, when properly arranged, a linearly polarized antenna
solution can be provided where the antenna covering the first 45
degrees of the read zone can be horizontally polarized, and the
adjacent 45 degree read zone can be covered by a vertically
polarized antenna. Conventional thinking would lead one to believe
that alternating linear polarizations does not provide adequate RF
coverage, especially when the patterns of adjacent antennas do not
significantly overlap. In other words, it might be assumed that a
vertically polarized antenna element could not read a horizontally
oriented tag in its read zone, and vice versa. However, multiple
reductions to practice have proven that this is not the case; the
performance of the alternating linear polarization system is indeed
on par or better than its circularly polarized counterpart. Because
of the natural reflections and multipath created by the overhead
reading environment, horizontal antennas can read vertically
oriented tags and vertical antennas can read horizontally oriented
tags. This is because signals can change polarization when they are
reflected. In effect, a reflection from a horizontal tag can have a
vertical component, and vice versa. Therefore, tags will not be
missed using simpler alternating linear antenna polarizations. In
addition, the overhead RFID reader of the present invention has
advantages over a handheld RFID reader in that the overhead reader
environment provides more opportunity for reflections and multipath
since tags are being read over larger distances. As a result, there
are more walls, floor space, store merchandise, people, etc. to
create multipath and reflection signals.
[0026] In practice, the vertically polarized and horizontally
polarized antenna elements provide somewhat different ovoid
radiation patterns due to the configuration of the loop, director
plate, and reflector plate for each element, and by the nature of
mounting each antenna element together in a circle. Furthermore, as
the feed location is rotated to change from one polarization to the
next, the resulting antenna pattern also rotates. FIG. 4 shows a
top view of the radiation patterns of the alternating vertically
and horizontally polarized antenna elements of FIG. 1. As can be
seen, the patterns are not identical, with the vertically polarized
antenna elements having a wider beamwidth in azimuth than the
horizontally polarized antenna elements. In elevation (not shown,
but perpendicular to the drawing sheet), the vertically polarized
antenna elements have a narrower beamwidth than the horizontally
polarized antenna elements. In particular, the horizontally
polarized antenna element provides an azimuth 3 dB (half power)
beamwidth of about 72 degrees and the vertically polarized antenna
element provides an azimuth 3 dB (half power) beamwidth of about 93
degrees as shown. Whereas the horizontally polarized antenna
element provides an elevation 3 dB (half power) beamwidth of about
93 degrees and the vertically polarized antenna element provides an
elevation 3 dB (half power) beamwidth of about 72 degrees (not
shown). To accommodate these radiation pattern differences, the
present invention provides a specialized mounting angle for each
antenna element.
[0027] Inasmuch as a vertically polarized antenna element provides
a different radiation pattern than a horizontally polarized antenna
element, the present invention seeks to provide a more uniform
elevation beamwidth strength for all antenna elements. In other
words, tags at a specific distance from the antenna arrangement and
at a specific height from the floor should receive the same minimum
signal strength from an antenna element no matter which (vertical
or horizontal) read zone it is located in. Therefore, the present
invention provides the vertically polarized antenna elements with a
first angular tilt with respect to a ceiling and the horizontally
polarized antenna elements with a second angular tilt with respect
to the ceiling different from the first angular tilt, such that the
radiation patterns from each antenna element are similar. To
achieve this, the first angular tilt is greater than the second
angular tilt such that the vertically polarized antenna elements
are directed more downwardly from the ceiling than the horizontally
polarized antenna elements. In the configuration shown in FIG. 3,
the vertically polarized antenna elements are 30 degrees off
vertical and the horizontally polarized antenna elements are 15
degrees off vertical. Numerous RF simulations were run and physical
RF mockups of the system of FIG. 3 were built, and the testing
validates the concepts associated with the antenna apparatus of the
present invention. Antenna gain and radiation pattern were all
confirmed, and this configuration provides the ability to read all
tags in the environment.
[0028] The present invention also provides advantages over prior
art antenna arrangements. For example, although multiple circularly
polarized antennas could be used to provide a 360 degree read
field, circularly polarized antennas need an additional 3 dB of
circular gain to match the gain of their linear equivalent (e.g. 9
dB circular=6 dB linear). This need for higher gain would result in
a significantly larger circularly polarized antenna over that of
the linearly polarized antennas of the present invention, and when
multiplying by the number of antennas in the overhead reader needed
for 360 degrees of coverage (e.g. eight antenna elements spread out
in 45 degree intervals), a resulting product using circularly
polarized antennas would be significantly larger. Therefore, the
solution of providing the physically smaller alternating linearly
polarized antenna elements of the present invention results in a
truly integrated solution that is simpler, smaller, and lighter
than is available in the prior art.
[0029] FIG. 5 is a perspective view of the composite radiation
patterns of the antenna arrangement of FIG. 3. As previously
described, the separate tilt of the vertically and horizontally
polarized antenna elements results in radiation patterns that
provide a more uniform elevation beamwidth strength for all antenna
elements. In particular, the vertical elements have a weaker
elevation beamwidth and are therefore aimed lower than the stronger
horizontal elements.
[0030] FIG. 6 is a perspective diagram of an exemplary retail
environment with an RFID reader 60 using the RFID antenna
arrangement of the present invention in a ceiling-mounted overhead
configuration. The RFID reader 60 is configured to wirelessly
interrogate a plurality of RFID tags located on or affixed to a
plurality of items 62. The RFID reader 60 may be mounted to a
ceiling or other overhead fixture in the retail environment. The
retail environment is shown solely for illustration purposes, and
the RFID antenna may be used in any environment including
warehouse, manufacturing facility, file room, storage area, and the
like.
[0031] The RFID reader 60 of the present invention includes a
housing enclosing the wireless radios of the RFID reader disposed
therein and communicatively coupled to the antenna arrangement by
providing an RF feed thereto via the radio ports. The housing can
also include associated electronics for providing RFID reader
functionality. The housing may further include a camera and an
access point coupled to or integrated with the RFID reader. The
RFID reader including the antenna apparatus is configured to
operate in an overhead configuration with respect to a plurality of
RFID tags. The multiple antenna elements are configured to provide
a far field radiation pattern covering the floor of the
environment.
[0032] In general, the RFID reader is configured to provide
communication between the RFID reader and RFID tags. For example,
the RFID reader "interrogates" RFID tags, and receives signals back
from the tags in response to the interrogation. The reader is
sometimes termed as "reader interrogator" or simply "interrogator".
In an exemplary embodiment, the RFID reader may include, without
limitation one or more of: a processor, a communication module,
memory, a camera, and the antenna arrangement (10 of FIG. 1). The
elements of the RFID reader may be interconnected together using a
communication bus or another suitable interconnection arrangement
that facilitates communication between the various elements of RFID
reader. It should be appreciated that the above description depicts
the RFID reader in an oversimplified manner and a practical
embodiment can include additional components and suitably
configured processing logic to support known or conventional
operating features that are not described in detail herein for the
sake of brevity.
[0033] The RFID reader is controlled by one or more processors to
interrogate the RFID tags of the items. The housing can further
include electronics and RF components for operation of the antenna
arrangement. For example, the electronics and components may
include electrical connectivity to the antenna feeds for
transmission and reception of radio frequency signals. The housing
may further include electronics and the like for operation of the
RFID reader as well as other components as described herein. The
housing is defined by the joined reflector panels of all the
antenna elements. The electronics, components, etc. may be disposed
or located behind the reflector panels within the housing.
[0034] The processor may be any microprocessor, application
specific integrated circuit (ASIC), field programmable gate array
(FPGA), digital signal processor (DSP), any suitable programmable
logic device, discrete gate or transistor logic, discrete hardware
components, or combinations thereof that has the computing power
capable of managing the RFID reader 10. The processor generally
provides the software, firmware, processing logic, and/or other
components of the RFID reader 10 that enable functionality of the
RFID reader.
[0035] The RFID reader can also include a communication module
including components enabling the RFID reader to communicate on a
wired or wireless network. For example, the communication module
may include an Ethernet interface to communicate on a local area
network. The communication module can be compliant to IEEE 802.11
and variants thereof). Additionally, the RFID reader may include
other wireless technologies such as, but are not limited to: RF;
IrDA (infrared); Bluetooth; ZigBee (and other variants of the IEEE
802.15 protocol); IEEE 802.11 (any variation); IEEE 802.16 (WiMAX
or any other variation); Universal Mobile Telecommunications System
(UMTS); Code Division Multiple Access (CDMA) including all
variants; Global System for Mobile Communications (GSM) and all
variants; Time division multiple access (TDMA) and all variants;
Direct Sequence Spread Spectrum; Frequency Hopping Spread Spectrum;
wireless/cordless telecommunication protocols; wireless home
network communication protocols; paging network protocols; magnetic
induction; satellite data communication protocols; wireless
hospital or health care facility network protocols such as those
operating in the WMTS bands; GPRS; and proprietary wireless data
communication protocols such as variants of Wireless USB.
[0036] The RFID reader can also include a memory including any of
volatile memory elements (e.g., random access memory (RAM, such as
DRAM, SRAM, SDRAM, etc.)), nonvolatile memory elements (e.g., ROM,
hard drive, tape, CDROM, etc.), and combinations thereof. Moreover,
the memory can incorporate electronic, magnetic, optical, and/or
other types of storage media. Note that the memory can have a
distributed architecture, where various components are situated
remotely from one another, but can be accessed by the processor.
The memory may be utilized to store data associated with RFID
interrogations, the camera, etc. The camera may include any device
for capturing video, audio, photographs, etc.
[0037] Referring to FIG. 7, the present invention describes a
method for reading Radio Frequency Identification (RFID) tags with
a fixed overhead RFID reader. A first step 70 includes providing a
plurality of linearly polarized antenna elements. In one
embodiment, each antenna element comprises a linearly polarized,
full wavelength loop element oriented between, and parallel to, a
director plate and a reflector panel. In another embodiment, there
is an even number of antenna elements arranged in a circle to
radiate outwardly from the circle. In another embodiment, there are
eight antenna elements evenly disposed at 45 degree intervals of
the circle, each with a gain of 6 dB. Preferably, the antenna
elements are linearly polarized to provide either of a first (e.g.
vertical) polarization and a second (e.g. horizontal) polarization
ninety degrees to the first polarization, and wherein the antenna
elements alternate polarizations around the circle. In this
configuration, each antenna element provides an antenna gain that
is down 3 dB (half power) at about .+-.46.5 degrees from its bore
sight, such that RFID read coverage areas of neighboring antenna
elements do not significantly overlap. It can be that the reflector
panels of the antenna elements are joined together to define a
common reflector box, wherein the reflector box defines a housing
that contains the radio and RFID reader and acts as an electrical
ground for electrical components in the box. In another embodiment,
the antenna elements with the first (e.g. vertical) polarization
have a first angular tilt with respect to a ceiling and the antenna
elements with the second (e.g. horizontal) polarization have a
second angular tilt with respect to the ceiling different from the
first angular tilt, where the first angular tilt is greater than
the second angular tilt such that vertically polarized antenna
elements are directed more downwardly from the ceiling than
horizontally polarized antenna elements.
[0038] A next step 72 includes sequentially communicatively
connecting only one antenna element at a time to the RFID reader
via radio ports such that only one antenna element is operable to
transmit/receive at any instant in time. This can be done under the
direction of an RFID reader or other processor.
[0039] A next step 74 includes reading RFID tags within an RFID
read coverage area of each sequenced antenna element.
[0040] In the foregoing specification, specific embodiments have
been described. However, one of ordinary skill in the art
appreciates that various modifications and changes can be made
without departing from the scope of the invention as set forth in
the claims below. Accordingly, the specification and figures are to
be regarded in an illustrative rather than a restrictive sense, and
all such modifications are intended to be included within the scope
of present teachings.
[0041] The benefits, advantages, solutions to problems, and any
element(s) that may cause any benefit, advantage, or solution to
occur or become more pronounced are not to be construed as a
critical, required, or essential features or elements of any or all
the claims. The invention is defined solely by the appended claims
including any amendments made during the pendency of this
application and all equivalents of those claims as issued.
[0042] Moreover in this document, relational terms such as first
and second, top and bottom, and the like may be used solely to
distinguish one entity or action from another entity or action
without necessarily requiring or implying any actual such
relationship or order between such entities or actions. The terms
"comprises," "comprising," "has", "having," "includes",
"including," "contains", "containing" or any other variation
thereof, are intended to cover a non-exclusive inclusion, such that
a process, method, article, or apparatus that comprises, has,
includes, contains a list of elements does not include only those
elements but may include other elements not expressly listed or
inherent to such process, method, article, or apparatus. An element
proceeded by "comprises . . . a", "has . . . a", "includes . . .
a", "contains . . . a" does not, without more constraints, preclude
the existence of additional identical elements in the process,
method, article, or apparatus that comprises, has, includes,
contains the element. The terms "a" and "an" are defined as one or
more unless explicitly stated otherwise herein. The terms
"substantially", "essentially", "approximately", "about" or any
other version thereof, are defined as being close to as understood
by one of ordinary skill in the art, and in one non-limiting
embodiment the term is defined to be within 10%, in another
embodiment within 5%, in another embodiment within 1% and in
another embodiment within 0.5%. The term "coupled" as used herein
is defined as connected, although not necessarily directly and not
necessarily mechanically. A device or structure that is
"configured" in a certain way is configured in at least that way,
but may also be configured in ways that are not listed.
[0043] It will be appreciated that some embodiments may be
comprised of one or more generic or specialized processors (or
"processing devices") such as microprocessors, digital signal
processors, customized processors and field programmable gate
arrays (FPGAs) and unique stored program instructions (including
both software and firmware) that control the one or more processors
to implement, in conjunction with certain non-processor circuits,
some, most, or all of the functions of the method and/or apparatus
described herein. Alternatively, some or all functions could be
implemented by a state machine that has no stored program
instructions, or in one or more application specific integrated
circuits (ASICs), in which each function or some combinations of
certain of the functions are implemented as custom logic. Of
course, a combination of the two approaches could be used.
[0044] Moreover, an embodiment can be implemented as a
computer-readable storage medium having computer readable code
stored thereon for programming a computer (e.g., comprising a
processor) to perform a method as described and claimed herein.
Examples of such computer-readable storage mediums include, but are
not limited to, a hard disk, a CD-ROM, an optical storage device, a
magnetic storage device, a ROM (Read Only Memory), a PROM
(Programmable Read Only Memory), an EPROM (Erasable Programmable
Read Only Memory), an EEPROM (Electrically Erasable Programmable
Read Only Memory) and a Flash memory. Further, it is expected that
one of ordinary skill, notwithstanding possibly significant effort
and many design choices motivated by, for example, available time,
current technology, and economic considerations, when guided by the
concepts and principles disclosed herein will be readily capable of
generating such software instructions and programs and ICs with
minimal experimentation.
[0045] The Abstract is provided to allow the reader to quickly
ascertain the nature of the technical disclosure. It is submitted
with the understanding that it will not be used to interpret or
limit the scope or meaning of the claims. In addition, in the
foregoing Detailed Description, it can be seen that various
features are grouped together in various embodiments for the
purpose of streamlining the disclosure. This method of disclosure
is not to be interpreted as reflecting an intention that the
claimed embodiments require more features than are expressly
recited in each claim. Rather, as the following claims reflect,
inventive subject matter lies in less than all features of a single
disclosed embodiment. Thus the following claims are hereby
incorporated into the Detailed Description, with each claim
standing on its own as a separately claimed subject matter.
* * * * *