WO2013164433A1 - Rfid reader antenna array structure and rfid reader - Google Patents

Rfid reader antenna array structure and rfid reader Download PDF

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Publication number
WO2013164433A1
WO2013164433A1 PCT/EP2013/059210 EP2013059210W WO2013164433A1 WO 2013164433 A1 WO2013164433 A1 WO 2013164433A1 EP 2013059210 W EP2013059210 W EP 2013059210W WO 2013164433 A1 WO2013164433 A1 WO 2013164433A1
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WO
WIPO (PCT)
Prior art keywords
antenna array
base plate
rfid reader
array structure
feeding device
Prior art date
Application number
PCT/EP2013/059210
Other languages
French (fr)
Inventor
Xiu Ping LI
Zhong Yuan SUN
Dong Zhang
Original Assignee
Siemens Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Publication of WO2013164433A1 publication Critical patent/WO2013164433A1/en

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Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
    • G06K7/10316—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers
    • G06K7/10356—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/12—Supports; Mounting means
    • H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
    • H01Q1/2208—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems
    • H01Q1/2216—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems used in interrogator/reader equipment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00—Antenna arrays or systems
    • H01Q21/06—Arrays of individually energised antenna units similarly polarised and spaced apart
    • H01Q21/061—Two dimensional planar arrays
    • H01Q21/065—Patch antenna array
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
    • H01Q9/0421—Substantially flat resonant element parallel to ground plane, e.g. patch antenna with a shorting wall or a shorting pin at one end of the element

Definitions

  • the present invention relates to the field of wireless communication, in particular to an RFID reader antenna array structure and an RFID reader.
  • the object of the present invention is to provide an RFID reader antenna array structure, for realizing a beam scanning function of the RFID reader antenna while reducing the RFID reader size, so as to increase the reading distance and reduce the probability of reading gaps.
  • an RFID reader antenna array structure comprising a base plate and multiple antenna array elements which together form an antenna array, wherein the base plate is connected to each of the antenna array elements by at least one grounding short circuit device, and a feeding device is further connected between each of the antenna array elements and the base plate.
  • At least one support device for supporting the antenna array element is further connected between each of the antenna array elements and the base plate.
  • the base plate is a rectangular plane
  • the antenna array element is a rectangular plane parallel to the base plate .
  • the base plate is a thin metal plate, the length and breadth thereof both being no more than 300 mm, and the antenna array element is an FR4 flat plate, the surface thereof being coated with metal .
  • the grounding short circuit device is a metal plate simultaneously perpendicular to both the antenna array element and the base plate, one end thereof being disposed at an end portion of the antenna array element, and the other end being connected to the surface of the base plate.
  • the feeding device is simultaneously perpendicular to both the antenna array element and the base plate, one end thereof being connected to a coaxial line and establishing contact between an outer conductor of the feeding device and the base plate by means of a hole in the base plate, and the other end being an inner conductor feeding probe which is in contact with the antenna array element by means of a hole in the antenna array element .
  • the feeding device comprises a fixing mechanism for fixing the feeding device to the base plate, and a mechanism for fixing the feeding device is correspondingly included on the base plate.
  • the feeding device is an SMA connector, one end thereof being an inner conductor feeding probe in contact with the antenna array element, and the other end having a threaded structure connected to a coaxial line used to feed the antenna array structure.
  • equal numbers of the antenna array elements are arranged in the length and width directions of the base plate, in a 2 x 2, 3 x 3 or 4 x 4 configuration .
  • an RFID reader comprising the above RFID reader antenna array structure is provided.
  • the antenna array structure of the present invention can obtain a higher far- field gain while achieving a reduction in size in comparison with traditional antenna structures, realizing a beam scanning function of the RFID reader antenna, increasing reading distance and reducing the probability of reading gaps.
  • Fig. 1 is a three-dimensional drawing of the antenna array structure as a whole in the particular embodiments of the present invention
  • Fig. 2 is a three-dimensional drawing of one antenna array element in the antenna array structure in the particular embodiments of the present invention
  • Fig. 3 is view from above of one antenna array element in the antenna array structure in the particular embodiments of the present invention.
  • Fig. 4 is a view from the front of one antenna array element in the antenna array structure in the particular embodiments of the present invention.
  • Fig. 5 is a view from the left of one antenna array element in the antenna array structure in the particular embodiments of the present invention.
  • Fig. 6 is a structural drawing of the SMA connector used in the particular embodiments of the present invention.
  • the present invention can meet today' s ever increasing demands on RFID reader antenna coverage area and size.
  • the antenna array structure of the present invention generates input signals of the same amplitude but different phases by means of a feeding network, and can attain a scanning beam direction of 60° at most.
  • the technical solution of the present invention has low costs, is easy to process, and can achieve beam scanning at multiple angles: the probability of reading gaps is reduced by superposition of scanning in the four beam directions -60°, -20°, 20° and 60°.
  • the present invention can design a reader antenna array structure based on the UHF frequency band within a relatively small space (for example 300 mm x 300 mm) .
  • Such an array is formed by two- shorting-pin planar inverted-F antennas (TPIFAs) as basic antenna units, and achieves structural miniaturization of the RFID reader antenna.
  • TPIFAs planar inverted-F antennas
  • the present invention achieves high efficiency and high gain in the reader antenna, and realizes a beam scanning function by way of combination with a feeding network, thereby increasing the reading distance of the reader and reducing the probability of reading gaps.
  • TPIFA indicates that metal grounded shorting pins are added on the antenna unit; viewed from the side, the grounded shorting pins, feeding device and antenna unit together form an inverted F- shape.
  • This TPIFA structure can guarantee reduced antenna size when the antenna resonant frequency remains unchanged, and is an important embodiment of the innovative miniaturization of the antenna in the present invention.
  • the RFID reader antenna array structure in the particular embodiments of the present invention comprises a base plate and multiple antenna array elements which together form an antenna array, wherein the base plate is connected to each of the antenna array elements by at least one grounding short circuit device, and a feeding device is further connected between each of the antenna array elements and the base plate.
  • the antenna array structure comprises a base plate, which can be provided as a thin metal plate with a flat rectangular surface, and can be made of a material such as copper.
  • both the length and breadth of the base plate may be set at a relatively small size, for example about 300 mm.
  • Each part of the base plate facing the array antenna is provided with a hole, the purpose thereof being to enable the passage therethrough of the feeding device while allowing contact to be maintained between the base plate and an outer conductor of the feeding device.
  • each part of the base plate facing the array antenna may also be provided with a mechanism, such as a hole, for fixing the feeding device.
  • each part of the base plate facing the array antenna may also be provided with a mechanism, such as a hole, for fixing a support device used to support the corresponding antenna array element.
  • the support device used to support the corresponding antenna array element may also be fixed in other well-known ways.
  • Each of the antenna array elements used to form the antenna array structure may be constructed as a flat rectangular plate. All of these are disposed parallel to the base plate, and each antenna array element is connected to the base plate by at least one grounding short circuit device, which is disposed at an end portion of the antenna array element and is simultaneously perpendicular to both the antenna array element and the base plate.
  • a hole is provided in each antenna array element, for maintaining contact between the antenna array element and an internal conductor of the feeding device. The position of this hole is opposite that of the hole in the base plate through which the feeding device passes.
  • holes for fixing a support device are provided in the base plate, a corresponding number of holes are correspondingly provided in each of the antenna array elements, and these are also used to fix the support device.
  • the support device used to support the corresponding antenna array element may also be fixed in other well-known ways.
  • Each of the at least one grounding short circuit devices is connected to the base plate and the corresponding antenna array element.
  • the grounding short circuit device is simultaneously perpendicular to both the antenna array element and the base plate; one end thereof may be disposed at an end portion of the antenna array element, the other end being connected to the base plate surface.
  • the grounding short circuit device may be made of a metal material such as copper, and forms the inverted F- shape together with the antenna array element and the feeding device .
  • the feeding device connecting the based plate to the antenna array element is used as a microwave high-frequency connector.
  • One end thereof is a feeding probe (inner conductor) connected to the antenna array element; the other end passes through the base plate in such a way that the outer conductor thereof is in contact with the base plate, and has a threaded structure connected to a coaxial line used to feed the array antenna.
  • a corresponding fixing device for fixing the outer conductor of the feeding device to the base plate may also be provided on the feeding device.
  • At least one support device for example a plastic support post, for supporting the antenna array element is further connected between each antenna array element and the base plate.
  • the two ends of these support devices may be fixed to the antenna array elements and the base plate, respectively, by means of threaded holes, etc., so as to support the antenna array elements.
  • a feeding network which acts in cooperation with the antenna array structure of the present invention by providing a feeding function for the antenna array structure is introduced below.
  • the feeding network employs the Butler matrix, which is well- known in the art.
  • the essential constituent units thereof comprise a 3 dB directional coupler, a cross coupler and a phase shifter.
  • N x M where N and M are both positive integers
  • the principle function served thereby is to allow the energy received by each output port to be of the same am- plitude with equal differences in phase for a given input port.
  • the feeding network is connected to each feeding device in the antenna array structure of the present invention by coaxial line, thereby providing the feeding function.
  • the antenna array structure in this particular embodiment has a base plate 1, the base plate 1 being provided as a thin copper plate with a flat rectangular surface.
  • both the length and breadth of the base plate 1 are set as 300 mm.
  • Each part of the base plate 1 facing the array antenna 2 is provided with five holes of different sizes. One of these five holes is used to pass an inner conductor 41 of an SMA (Small A Type) connector 4 from beneath the base plate 1, such that contact is maintained between an outer conductor 42 of the SMA connector and the base plate 1.
  • SMA Small A Type
  • the diameter of this hole is determined by the outer diameter of the outer conductor, and may be 4.1 mm.
  • the plastic support post 5 is used as the support device in the present invention.
  • Each of the antennas 2 used to form the antenna array is formed as a flat rectangular plate.
  • each antenna 2 is connected to the base plate 1 by two grounded shorting pins 3, which are disposed at an end portion of the antenna 2 and are simultaneously perpendicular to both the antenna 2 and the base plate 1.
  • the antenna 2 is made from a laminate of epoxy resin and glass cloth (FR4) , the top surface thereof being covered with a metal such as copper to satisfy the requirements for antenna characteristics.
  • FR4 epoxy resin and glass cloth
  • Each flat-plate antenna 2 forms an antenna array element 2 in the antenna array.
  • Each antenna array element 2 is provided with three holes of different sizes, one of which is opposite the hole in the base plate 1 that is used for passing the SMA connector
  • this hole is used for inserting and welding the feeding probe 41 (inner conductor) of the SMA connector 4.
  • the diameter of this hole is determined by the outer diameter of the inner conductor 41, and may be 1.3 mm.
  • the other two holes are opposite the holes in the base plate 1 that are used to fix the plastic support post 5, respectively, and are for fixing the plastic support post 5 at the antenna array element 2 end; thus these two holes also have a diameter of 3 mm.
  • the two grounded shorting pins 3 serve as the grounding short circuit devices of the present invention, and are made of a metal material such as copper in the form of a rectangular 16.6 mm x 17 mm plate of thin metal.
  • the SMA connector 4 is a microwave high-frequency connector. The specific structure thereof is shown in Fig. 6. One end thereof is an inner conductor 41, i.e. a feeding probe, partially enclosed in a white dielectric 43; this section of dielectric 43 may be peeled off once the SMA connector 4 has been installed in the antenna array structure.
  • the other end of the SMA connector 4 has a thread 44 for connecting a coaxial line used to feed the array antenna; the outer layer of this end is a metal outer conductor 42, and maintains contact with the base plate 1 after installation.
  • the middle portion of the SMA connector 4 is a seat portion 46 with two fixing holes 45.
  • an SMA-KFD142 -type connector may be used as the SMA connector 4; the inner conductor 41 thereof has a diameter of 1.3 mm, the outer conductor 42 has a diameter of 4.1 mm, and the intermediate dielectric 43 may be made from PTFE with a dielectric constant of 2.02.
  • one end of the inner conductor feeding probe 41 is inserted in the hole left in the base plate 1 from beneath the base plate 1; the inner conductor 41 is then inserted in the hole left in the antenna 2 from beneath the antenna 2 and brought into contact with the antenna 2, until the seat portion 46 comes into contact with the bottom of the base plate 1, at which point the outer conductor 42 of the SMA connector 4 is also in contact with the base plate 1.
  • the lengths of the inner conductor 41 and the outer conductor 42 may be flexibly determined according to such parameters as the thickness of the base plate 1 and the perpendicular distance between the base plate 1 and the antenna 2.
  • That end of the SMA connector 4 which has the thread 44 is used for connecting a coaxial line.
  • This coaxial line and the SMA connector 4 are together used for feeding the array antenna.
  • coaxial line with an impedance of 50 ohms may be used as the coaxial line; the inner conductor thereof has an outer diameter of 0.92 mm, while the outer conductor has an inner diameter of 2.98 mm.
  • plastic support posts 5 for supporting the antenna array element 2 are further connected between each antenna array element 2 and the base plate 1.
  • the two ends of these plastic support posts 5 may be fixed to the antenna array element 2 and - li the base plate 1, respectively, by threaded holes, etc.
  • the plastic support posts 5 may be threaded plastic support posts with an outer diameter of 3 mm (the same as the diameter of the holes in the base plate
  • the antenna array reader formed shall provide energy of the same amplitude but different phases via the multiple antenna units, with the beam scanning performed thereby being possible in the four scanning beam directions -60°, -20°, 20° and 60° in each of two 2 -dimensional planes, namely the horizontal plane and the vertical plane. Therefore the antenna array structure is provided with 9 antenna array elements, equal numbers of antenna array elements 2 being arranged in the length and width directions of the base plate 1; these 9 antenna array elements 2 form a 3 x 3 antenna array.
  • Each antenna array element 2 is disposed parallel to the base plate 1, and these are connected by two grounded shorting pins 3, which are disposed at an end portion of the antenna array element 2 and simultaneously perpendicular to the antenna array element 2 and the base plate 1.
  • the length and breadth of each antenna array element 2 will be less than 100 mm x 100 mm, so as to enable these antenna array elements 2 to be configured in a plane above the base plate 1.
  • the length and breadth of each antenna array element 2 is 85 mm x 65 mm, with a thickness of 1.6 mm .
  • the above beam scanning in a total of 8 directions in two planes corresponds to 8 feed inputs, while the 9 antenna array elements 2 correspond to 9 feed outputs. Therefore the feeding network acting in cooperation with the antenna array structure in the above embodiment may be realized using an 8 x 9 Butler matrix.
  • implementation is achieved by changing this 8 x 9 Butler matrix into two 4 x 3 Butler matrices in this embodiment.
  • the core function of the feeding network lies in converting beamforming in 8 directions to
  • the feeding network includes two 4 x 3 Butler matrices, six 3 -way power dividers and nine 2 -way power combiners. Three 3 -way power dividers are connected after each 4 x 3 Butler matrix, thereby achieving beam scanning in four directions in one plane. Then, using the nine 2 -way power combiners, the 9 output ports of each of the two parts are connected to the 9 feeding devices 4 of the antenna array structure by coaxial lines, and in turn connected to the 9 antenna array elements 2 of the antenna array structure, and feed these 9 antenna array elements 2 selectively.
  • the antenna array structure can realize beam scanning in a total of 8 directions: 4 directions in each of two 2 -dimensional planes, namely the horizontal and the vertical planes.
  • equal numbers of antenna array elements are provided in the length and breadth directions of the base plate (3 in the above embodiment, although in fact this number could also be 2 or 4 , etc.) ; therefore the antenna array reader formed therefrom provides energy of the same amplitude but different phases via multiple antenna elements, while the beam scanning performed thereby is possible in the four scanning beam directions -60°, -20°, 20° and 60° in each of two 2- dimensional planes, namely the horizontal plane and the vertical plane.
  • different numbers of antenna array elements 2 may be provided in the length and breadth directions of the antenna, such as 3 x 2 or 4 x 3, in coordination with a correspondingly designed feeding network.
  • the array is formed from two- shorting-pin planar inverted-F antennas as basic antenna units, and operates in the European RFID frequency band of 865 - 868 MHz.
  • Such a two- shorting-pin planar inverted-F antenna structure gives a reduced antenna size in comparison with traditional antenna structures.
  • the omnidirectional far-field characteristics of each basic antenna unit all cover the range of -60° to 60°, and so the antenna array reader formed therefrom provides energy of the same amplitude but different phases via multiple antenna elements, the beam scanning performed thereby being possible in the four scanning beam directions -60°, -20°, 20° and 60°.

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Abstract

Disclosed in the present invention is an RFID reader antenna array structure, the RFID reader antenna array structure comprising a base plate and multiple antenna array elements which together form an antenna array, wherein the base plate is connected to each of the antenna array elements by at least one grounding short circuit device, and a feeding device is further connected between each of the antenna array elements and the base plate. By way of the technical solution of the present invention, the antenna array structure can obtain a higher far-field gain while achieving a reduction in size in comparison with traditional antenna structures, realizing a beam scanning function of the RFID reader antenna, increasing reading distance and reducing the probability of reading gaps.

Description

Description
RFID reader antenna array structure and RFID reader
Technical field
The present invention relates to the field of wireless communication, in particular to an RFID reader antenna array structure and an RFID reader.
Background art
In general, labels in RFID systems are quite small in size, and this restricts the radiation aperture size of RFID reader antennas. Therefore in this field, the question of how to increase the coverage of a reader antenna so as to reduce the probability of reading gaps is crucial in RFID reader antenna design, and makes the latter difficult.
Existing RFID reader antennas operating within the UHF band satisfying the European RFID frequency band 865 - 868 MHz are generally all quite large in size, and so are unable to meet the design requirements of RFID reader miniaturization. On the other hand, if the antenna size is reduced, it becomes very difficult to satisfy the reading demands for RFID labels.
Content of the invention
In view of this, the object of the present invention is to provide an RFID reader antenna array structure, for realizing a beam scanning function of the RFID reader antenna while reducing the RFID reader size, so as to increase the reading distance and reduce the probability of reading gaps.
According to one aspect of the present invention, an RFID reader antenna array structure is provided, the RFID reader antenna array structure comprising a base plate and multiple antenna array elements which together form an antenna array, wherein the base plate is connected to each of the antenna array elements by at least one grounding short circuit device, and a feeding device is further connected between each of the antenna array elements and the base plate.
Preferably, at least one support device for supporting the antenna array element is further connected between each of the antenna array elements and the base plate.
Preferably, the base plate is a rectangular plane, and the antenna array element is a rectangular plane parallel to the base plate .
Preferably, the base plate is a thin metal plate, the length and breadth thereof both being no more than 300 mm, and the antenna array element is an FR4 flat plate, the surface thereof being coated with metal .
Preferably, the grounding short circuit device is a metal plate simultaneously perpendicular to both the antenna array element and the base plate, one end thereof being disposed at an end portion of the antenna array element, and the other end being connected to the surface of the base plate.
Preferably, the feeding device is simultaneously perpendicular to both the antenna array element and the base plate, one end thereof being connected to a coaxial line and establishing contact between an outer conductor of the feeding device and the base plate by means of a hole in the base plate, and the other end being an inner conductor feeding probe which is in contact with the antenna array element by means of a hole in the antenna array element .
Preferably, the feeding device comprises a fixing mechanism for fixing the feeding device to the base plate, and a mechanism for fixing the feeding device is correspondingly included on the base plate.
Preferably, the feeding device is an SMA connector, one end thereof being an inner conductor feeding probe in contact with the antenna array element, and the other end having a threaded structure connected to a coaxial line used to feed the antenna array structure.
Preferably, in the antenna array structure, equal numbers of the antenna array elements are arranged in the length and width directions of the base plate, in a 2 x 2, 3 x 3 or 4 x 4 configuration .
According to another aspect of the present invention, an RFID reader comprising the above RFID reader antenna array structure is provided.
It can be seen from the above solution that the antenna array structure of the present invention can obtain a higher far- field gain while achieving a reduction in size in comparison with traditional antenna structures, realizing a beam scanning function of the RFID reader antenna, increasing reading distance and reducing the probability of reading gaps.
Description of the accompanying drawings
Preferred embodiments of the present invention shall be described in detail below with reference to the accompanying drawings, so that those skilled in the art may have a clearer understanding of the above and other features and advantages of the present invention. In the drawings:
Fig. 1 is a three-dimensional drawing of the antenna array structure as a whole in the particular embodiments of the present invention; Fig. 2 is a three-dimensional drawing of one antenna array element in the antenna array structure in the particular embodiments of the present invention;
Fig. 3 is view from above of one antenna array element in the antenna array structure in the particular embodiments of the present invention;
Fig. 4 is a view from the front of one antenna array element in the antenna array structure in the particular embodiments of the present invention;
Fig. 5 is a view from the left of one antenna array element in the antenna array structure in the particular embodiments of the present invention;
Fig. 6 is a structural drawing of the SMA connector used in the particular embodiments of the present invention.
Particular embodiments
In order to clarify the object, technical solution and advantages of the present invention, it is described below in further detail by way of embodiments.
In combination with high-gain beam scanning array antenna technology, the present invention can meet today' s ever increasing demands on RFID reader antenna coverage area and size. The antenna array structure of the present invention generates input signals of the same amplitude but different phases by means of a feeding network, and can attain a scanning beam direction of 60° at most. The technical solution of the present invention has low costs, is easy to process, and can achieve beam scanning at multiple angles: the probability of reading gaps is reduced by superposition of scanning in the four beam directions -60°, -20°, 20° and 60°. The present invention can design a reader antenna array structure based on the UHF frequency band within a relatively small space (for example 300 mm x 300 mm) . Such an array is formed by two- shorting-pin planar inverted-F antennas (TPIFAs) as basic antenna units, and achieves structural miniaturization of the RFID reader antenna. In combination with phased array antenna technology, the present invention achieves high efficiency and high gain in the reader antenna, and realizes a beam scanning function by way of combination with a feeding network, thereby increasing the reading distance of the reader and reducing the probability of reading gaps.
Here, the term TPIFA indicates that metal grounded shorting pins are added on the antenna unit; viewed from the side, the grounded shorting pins, feeding device and antenna unit together form an inverted F- shape. This TPIFA structure can guarantee reduced antenna size when the antenna resonant frequency remains unchanged, and is an important embodiment of the innovative miniaturization of the antenna in the present invention.
Specifically, the RFID reader antenna array structure in the particular embodiments of the present invention comprises a base plate and multiple antenna array elements which together form an antenna array, wherein the base plate is connected to each of the antenna array elements by at least one grounding short circuit device, and a feeding device is further connected between each of the antenna array elements and the base plate.
The antenna array structure comprises a base plate, which can be provided as a thin metal plate with a flat rectangular surface, and can be made of a material such as copper. In order to reduce the size of the RFID reader while satisfying the requirements of the antenna array in terms of operational performance, both the length and breadth of the base plate may be set at a relatively small size, for example about 300 mm. Each part of the base plate facing the array antenna is provided with a hole, the purpose thereof being to enable the passage therethrough of the feeding device while allowing contact to be maintained between the base plate and an outer conductor of the feeding device. In a preferred embodiment, each part of the base plate facing the array antenna may also be provided with a mechanism, such as a hole, for fixing the feeding device. Of course, the feeding device may also be fixed to the base plate in other ways, such as by welding, so as to establish contact between the outer conductor thereof and the base plate. In a preferred embodiment, each part of the base plate facing the array antenna may also be provided with a mechanism, such as a hole, for fixing a support device used to support the corresponding antenna array element. Of course, the support device used to support the corresponding antenna array element may also be fixed in other well-known ways.
Each of the antenna array elements used to form the antenna array structure may be constructed as a flat rectangular plate. All of these are disposed parallel to the base plate, and each antenna array element is connected to the base plate by at least one grounding short circuit device, which is disposed at an end portion of the antenna array element and is simultaneously perpendicular to both the antenna array element and the base plate. A hole is provided in each antenna array element, for maintaining contact between the antenna array element and an internal conductor of the feeding device. The position of this hole is opposite that of the hole in the base plate through which the feeding device passes. In a preferred embodiment, when holes for fixing a support device are provided in the base plate, a corresponding number of holes are correspondingly provided in each of the antenna array elements, and these are also used to fix the support device. Of course, the support device used to support the corresponding antenna array element may also be fixed in other well-known ways.
Each of the at least one grounding short circuit devices is connected to the base plate and the corresponding antenna array element. The grounding short circuit device is simultaneously perpendicular to both the antenna array element and the base plate; one end thereof may be disposed at an end portion of the antenna array element, the other end being connected to the base plate surface. The grounding short circuit device may be made of a metal material such as copper, and forms the inverted F- shape together with the antenna array element and the feeding device .
The feeding device connecting the based plate to the antenna array element is used as a microwave high-frequency connector. One end thereof is a feeding probe (inner conductor) connected to the antenna array element; the other end passes through the base plate in such a way that the outer conductor thereof is in contact with the base plate, and has a threaded structure connected to a coaxial line used to feed the array antenna. In addition, a corresponding fixing device for fixing the outer conductor of the feeding device to the base plate may also be provided on the feeding device.
As stated above, in a preferred embodiment, at least one support device, for example a plastic support post, for supporting the antenna array element is further connected between each antenna array element and the base plate. The two ends of these support devices may be fixed to the antenna array elements and the base plate, respectively, by means of threaded holes, etc., so as to support the antenna array elements.
A feeding network which acts in cooperation with the antenna array structure of the present invention by providing a feeding function for the antenna array structure is introduced below. The feeding network employs the Butler matrix, which is well- known in the art. The essential constituent units thereof comprise a 3 dB directional coupler, a cross coupler and a phase shifter. Generally, the number of input ports and output ports thereof is expressed as N x M (where N and M are both positive integers) . The principle function served thereby is to allow the energy received by each output port to be of the same am- plitude with equal differences in phase for a given input port. In the process of using the RFID antenna, the feeding network is connected to each feeding device in the antenna array structure of the present invention by coaxial line, thereby providing the feeding function.
Embodiment
The specific structure of the RFID reader antenna array in a particular embodiment of the present invention is described below with reference to Figs. 1 - 6.
The antenna array structure in this particular embodiment has a base plate 1, the base plate 1 being provided as a thin copper plate with a flat rectangular surface. In order to reduce the size of the RFID reader while satisfying the requirements of the antenna array in terms of operational performance, both the length and breadth of the base plate 1 are set as 300 mm. Each part of the base plate 1 facing the array antenna 2 is provided with five holes of different sizes. One of these five holes is used to pass an inner conductor 41 of an SMA (Small A Type) connector 4 from beneath the base plate 1, such that contact is maintained between an outer conductor 42 of the SMA connector and the base plate 1. Here, the SMA connector 4 is used as the feeding device in the present invention. In this particular embodiment, the diameter of this hole is determined by the outer diameter of the outer conductor, and may be 4.1 mm. There are another two holes used to fix the SMA connector 4, the diameter thereof being determined according to the thread used for fixing; when an M3-type thread is used, the diameter thereof is 3 mm. There are another two holes used to fix a plastic support post 5, which is used to support the antenna plane. The diameter thereof may also be 3 mm for the M3-type thread. Here, the plastic support post 5 is used as the support device in the present invention. Each of the antennas 2 used to form the antenna array is formed as a flat rectangular plate. All of these are disposed parallel to the base plate 1, and each antenna 2 is connected to the base plate 1 by two grounded shorting pins 3, which are disposed at an end portion of the antenna 2 and are simultaneously perpendicular to both the antenna 2 and the base plate 1. In this particular embodiment, the antenna 2 is made from a laminate of epoxy resin and glass cloth (FR4) , the top surface thereof being covered with a metal such as copper to satisfy the requirements for antenna characteristics. Each flat-plate antenna 2 forms an antenna array element 2 in the antenna array. Each antenna array element 2 is provided with three holes of different sizes, one of which is opposite the hole in the base plate 1 that is used for passing the SMA connector
through; this hole is used for inserting and welding the feeding probe 41 (inner conductor) of the SMA connector 4. In this particular embodiment, the diameter of this hole is determined by the outer diameter of the inner conductor 41, and may be 1.3 mm. The other two holes are opposite the holes in the base plate 1 that are used to fix the plastic support post 5, respectively, and are for fixing the plastic support post 5 at the antenna array element 2 end; thus these two holes also have a diameter of 3 mm.
In this particular embodiment, the two grounded shorting pins 3 serve as the grounding short circuit devices of the present invention, and are made of a metal material such as copper in the form of a rectangular 16.6 mm x 17 mm plate of thin metal.
The SMA connector 4 is a microwave high-frequency connector. The specific structure thereof is shown in Fig. 6. One end thereof is an inner conductor 41, i.e. a feeding probe, partially enclosed in a white dielectric 43; this section of dielectric 43 may be peeled off once the SMA connector 4 has been installed in the antenna array structure. The other end of the SMA connector 4 has a thread 44 for connecting a coaxial line used to feed the array antenna; the outer layer of this end is a metal outer conductor 42, and maintains contact with the base plate 1 after installation. The middle portion of the SMA connector 4 is a seat portion 46 with two fixing holes 45. Specifically, an SMA-KFD142 -type connector may be used as the SMA connector 4; the inner conductor 41 thereof has a diameter of 1.3 mm, the outer conductor 42 has a diameter of 4.1 mm, and the intermediate dielectric 43 may be made from PTFE with a dielectric constant of 2.02. During installation, one end of the inner conductor feeding probe 41 is inserted in the hole left in the base plate 1 from beneath the base plate 1; the inner conductor 41 is then inserted in the hole left in the antenna 2 from beneath the antenna 2 and brought into contact with the antenna 2, until the seat portion 46 comes into contact with the bottom of the base plate 1, at which point the outer conductor 42 of the SMA connector 4 is also in contact with the base plate 1. At this point, two screws are passed through the base plate 1 and the two holes 45 in the seat 46 to fix the SMA connector 4 to the base plate 1, the inner conductor 41 then being welded to the antenna 2. It can be seen from the above installation process that the lengths of the inner conductor 41 and the outer conductor 42 may be flexibly determined according to such parameters as the thickness of the base plate 1 and the perpendicular distance between the base plate 1 and the antenna 2.
That end of the SMA connector 4 which has the thread 44 is used for connecting a coaxial line. This coaxial line and the SMA connector 4 are together used for feeding the array antenna. In this particular embodiment, coaxial line with an impedance of 50 ohms may be used as the coaxial line; the inner conductor thereof has an outer diameter of 0.92 mm, while the outer conductor has an inner diameter of 2.98 mm.
Two plastic support posts 5 for supporting the antenna array element 2 are further connected between each antenna array element 2 and the base plate 1. The two ends of these plastic support posts 5 may be fixed to the antenna array element 2 and - li the base plate 1, respectively, by threaded holes, etc. In this particular embodiment, the plastic support posts 5 may be threaded plastic support posts with an outer diameter of 3 mm (the same as the diameter of the holes in the base plate
1/antenna array element 2 that are used to fix the plastic support posts) .
In this particular embodiment, shown in Fig. 1, it is desired that the antenna array reader formed shall provide energy of the same amplitude but different phases via the multiple antenna units, with the beam scanning performed thereby being possible in the four scanning beam directions -60°, -20°, 20° and 60° in each of two 2 -dimensional planes, namely the horizontal plane and the vertical plane. Therefore the antenna array structure is provided with 9 antenna array elements, equal numbers of antenna array elements 2 being arranged in the length and width directions of the base plate 1; these 9 antenna array elements 2 form a 3 x 3 antenna array. Each antenna array element 2 is disposed parallel to the base plate 1, and these are connected by two grounded shorting pins 3, which are disposed at an end portion of the antenna array element 2 and simultaneously perpendicular to the antenna array element 2 and the base plate 1. When the number of antenna array elements 2 is 9, the length and breadth of each antenna array element 2 will be less than 100 mm x 100 mm, so as to enable these antenna array elements 2 to be configured in a plane above the base plate 1. In this particular embodiment, the length and breadth of each antenna array element 2 is 85 mm x 65 mm, with a thickness of 1.6 mm .
The above beam scanning in a total of 8 directions in two planes corresponds to 8 feed inputs, while the 9 antenna array elements 2 correspond to 9 feed outputs. Therefore the feeding network acting in cooperation with the antenna array structure in the above embodiment may be realized using an 8 x 9 Butler matrix. However, owing to the complexity of the process of implementing an 8 x 9 Butler matrix and the high level of diffi- culty involved in designing one, implementation is achieved by changing this 8 x 9 Butler matrix into two 4 x 3 Butler matrices in this embodiment. The core function of the feeding network lies in converting beamforming in 8 directions to
beamforming in 4 directions in two planes, and realizing the function of an 8 x 9 Butler matrix on this basis.
Specifically, the feeding network includes two 4 x 3 Butler matrices, six 3 -way power dividers and nine 2 -way power combiners. Three 3 -way power dividers are connected after each 4 x 3 Butler matrix, thereby achieving beam scanning in four directions in one plane. Then, using the nine 2 -way power combiners, the 9 output ports of each of the two parts are connected to the 9 feeding devices 4 of the antenna array structure by coaxial lines, and in turn connected to the 9 antenna array elements 2 of the antenna array structure, and feed these 9 antenna array elements 2 selectively. Thus the antenna array structure can realize beam scanning in a total of 8 directions: 4 directions in each of two 2 -dimensional planes, namely the horizontal and the vertical planes.
Other embodiments
In the above embodiment, equal numbers of antenna array elements are provided in the length and breadth directions of the base plate (3 in the above embodiment, although in fact this number could also be 2 or 4 , etc.) ; therefore the antenna array reader formed therefrom provides energy of the same amplitude but different phases via multiple antenna elements, while the beam scanning performed thereby is possible in the four scanning beam directions -60°, -20°, 20° and 60° in each of two 2- dimensional planes, namely the horizontal plane and the vertical plane. Of course, if parameter requirements are set in only one 2 -dimensional plane, different numbers of antenna array elements 2 may be provided in the length and breadth directions of the antenna, such as 3 x 2 or 4 x 3, in coordination with a correspondingly designed feeding network. These numbers can be set flexibly on the basis of the requirements for RFID reader size and performance parameters.
It can be seen from the above technical solution that in the antenna array structure in the particular embodiments of the present invention, the array is formed from two- shorting-pin planar inverted-F antennas as basic antenna units, and operates in the European RFID frequency band of 865 - 868 MHz. Such a two- shorting-pin planar inverted-F antenna structure gives a reduced antenna size in comparison with traditional antenna structures. The omnidirectional far-field characteristics of each basic antenna unit all cover the range of -60° to 60°, and so the antenna array reader formed therefrom provides energy of the same amplitude but different phases via multiple antenna elements, the beam scanning performed thereby being possible in the four scanning beam directions -60°, -20°, 20° and 60°.
The above are merely preferred embodiments of the present invention, and are not intended to limit it. Any amendments, equivalent substitutions or improvements, etc. made without departing from the spirit and principles of the present invention should be included within the scope of protection thereof.

Claims

Claims
1. An RFID reader antenna array structure, characterized in that the RFID reader antenna array structure comprises a base plate (1) and multiple antenna array elements (2) which together form an antenna array;
the base plate (1) is connected to each of the antenna array elements (2) by at least one grounding short circuit device (3), and a feeding device (4) is further connected between each of the antenna array elements (2) and the base plate (1) .
2. The RFID reader antenna array structure as claimed in claim 1, characterized in that
at least one support device (5) for supporting the antenna array element (2) is further connected between each of the antenna array elements (2) and the base plate (1) .
3. The RFID reader antenna array structure as claimed in any of claims 1 or 2 , characterized in that
the base plate (1) is a rectangular plane, and the antenna array element (2) is a rectangular plane parallel to the base plate (1) .
4. The RFID reader antenna array structure as claimed in claim 3, characterized in that
the base plate (1) is a thin metal plate, the length and breadth thereof both being no more than 300 mm, and the antenna array element (2) is an FR4 flat plate, the surface thereof being coated with metal .
5. The RFID reader antenna array structure as claimed in any of claims 1 - 4, characterized in that
the grounding short circuit device (3) is a metal plate simultaneously perpendicular to both the antenna array element (2) and the base plate (1) , one end thereof being disposed at an end portion of the antenna array element (2), and the other end being connected to the surface of the base plate (1) .
6. The RFID reader antenna array structure as claimed in any of claims 1 - 5, characterized in that
the feeding device (4) is simultaneously perpendicular to both the antenna array element (2) and the base plate (1), one end thereof being used to connect a coaxial line and establishing contact between an outer conductor (42) of the feeding device (4) and the base plate (1) by means of a hole in the base plate (1) , and the other end being an inner conductor feeding probe (41) which is in contact with the antenna array element (2) by means of a hole in the antenna array element (2) .
7. The RFID reader antenna array structure as claimed in any of claims 1 - 6, characterized in that the feeding device (4) comprises a fixing mechanism (46) for fixing the feeding device to the base plate (1) , and a mechanism for fixing the feeding device (4) is correspondingly included on the base plate (1) .
8. The RFID reader antenna array structure as claimed in any of claims 1 - 7, characterized in that the feeding device (4) is an SMA connector (4), one end thereof being an inner conductor feeding probe (41) in contact with the antenna array element (2), and the other end having a threaded structure (44) connected to a coaxial line used to feed the antenna array structure .
9. The RFID reader antenna array structure as claimed in any one of claims 1 - 8, characterized in that in the antenna array structure, equal numbers of the antenna array elements (2) are arranged in the length and width directions of the base plate (1) , in a 2 x 2, 3 x 3 or 4 x 4 configuration.
10. An RFID reader comprising the RFID reader antenna array structure as claimed in any one of claims 1 - 9.
11. The RFID reader as claimed in claim 10, characterized in that the RFID reader employs a Butler matrix, comprising at least one directional coupler, at least one cross coupler and at least one phase shifter, the Butler matrix having output ports, each output port having an output signal of the same amplitude with equal differences in phase for related input ports, the output ports being connected to each feeding device in the antenna array structure.
PCT/EP2013/059210 2012-05-03 2013-05-03 Rfid reader antenna array structure and rfid reader WO2013164433A1 (en)

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