WO2003077364A2 - Antenna system for a transponder radio-frequency reading device - Google Patents

Antenna system for a transponder radio-frequency reading device Download PDF

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Publication number
WO2003077364A2
WO2003077364A2 PCT/EP2003/002553 EP0302553W WO03077364A2 WO 2003077364 A2 WO2003077364 A2 WO 2003077364A2 EP 0302553 W EP0302553 W EP 0302553W WO 03077364 A2 WO03077364 A2 WO 03077364A2
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WO
WIPO (PCT)
Prior art keywords
antenna
antenna system
tuning circuit
recognition station
wall
Prior art date
Application number
PCT/EP2003/002553
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French (fr)
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WO2003077364A3 (en
Inventor
Richard John Benn
Original Assignee
Gantle Trading & Services Lda
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Publication date
Application filed by Gantle Trading & Services Lda filed Critical Gantle Trading & Services Lda
Priority to AU2003218742A priority Critical patent/AU2003218742A1/en
Publication of WO2003077364A2 publication Critical patent/WO2003077364A2/en
Publication of WO2003077364A3 publication Critical patent/WO2003077364A3/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
    • G06K7/10346—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 the antenna being of the far field type, e.g. HF types or dipoles
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Definitions

  • the present invention relates to an antenna system for a transponder radio-frequency reading device.
  • a passive-transponder radio-frequency reading device normally comprises an activating unit and an antenna system.
  • the antenna system controlled by the activating unit, generates a radio-frequency signal capable of activating any transponders within its operating range; and each transponder, when activated, transmits a radio-frequency return signal which is received and identified by the activating unit.
  • Transponder reading devices of the above type normally employ a 13.56 MHz operating frequency, which is recognized and can be used all over the world with no limitations; and an antenna system comprising a flat, annular, circular or polygonal antenna connected to a tuning circuit set to 13.56 MHz frequency, and an emitting/receiving system for generating alternating electric current in the tuning circuit .
  • the best diameter for a circular antenna is around 340 mm, which gives an antenna impedance of close to 50 Ohms that can be matched almost perfectly with the 50 Ohm impedance of the transmission line.
  • a flat, annular antenna of 340 mm diameter has a limited maximum operating range, and is normally unable to activate transponders at a distance of over 400-500 mm.
  • the strength of the magnetic field produced at a given point by a circular antenna is directly proportional to the square of the antenna radius, and inversely proportional to the cube of the distance between the center of the antenna and the point considered.
  • a field of at least 152 dB ⁇ A/m is required, so that, in laboratory conditions, transponders at a maximum distance of 400 mm could be read using a 200 mm diameter antenna, and at a maximum distance of 800 mm using a 500 mm diameter antenna, providing the transponders are within the radiation cone of the antenna.
  • antenna systems have been proposed comprising noncircular, nonflat antennas. Such systems, however, have proved expensive and difficult to regulate, and fail to provide for the optimum current distribution typical of flat, circular antennas .
  • an object of the present invention to provide an antenna system for a transponder radio-frequency reading device, designed to eliminate the aforementioned drawbacks, and which at the same time is cheap and easy to implement .
  • an antenna system for a transponder radio- frequency reading device as claimed in Claim 1.
  • Figure 1 shows a schematic view in perspective of a transponder reading device antenna system in accordance with the present invention
  • Figure 2 shows a front view of the Figure 1 antenna system
  • Figure 3 shows a front view of an alternative embodiment of some of the Figure 1 antenna system components
  • Figures 4, 5 and 6 show alternative embodiments of stations for recognizing articles fitted with respective transponders, and incorporating a transponder read/write device using the Figure 1 antenna system.
  • FIG. 1 indicates as a whole a radio- frequency reading device for passive-transponder comprising an activating unit 2 (with an emitter/receiver or simply an emitter) having an antenna system 3 and operating at 13.56 MHz frequency.
  • antenna system 3 controlled by activating unit 2 generates a 13.56 MHz radio-frequency signal capable of activating corresponding known transponders (not shown) within the operating range of antenna system 3; and, when activated, each transponder transmits a radio-frequency return signal, which is received and identified by activating unit 2, and which typically contains the identification code of the transponder, and a number of information items stored in a programmable electronic memory of the transponder.
  • transponder reading device 1 is suitable for reading "Smart Label” passive transponders, which are in the form of a thin film for integration in labels, and have a printable surface and a programmable electronic memory.
  • Antenna system 3 comprises a circular, flat, annular antenna 4 with a central axis 5 of symmetry; a tuning circuit 6 (set to 13.56 MHz frequency) connected to antenna 4; an emitting/receiving system 7 controlled by activating unit 2 and for generating alternating electric current in tuning circuit 6; a flat, annular antenna 8 parallel to, close to, and therefore coupled magnetically to antenna 4; and a nonpowered tuning circuit 9 (set to 13.56 MHz frequency) connected to antenna 8.
  • Tuning circuit 6 is preferably in the form of a series and parallel capacitance configuration to regulate antenna 4 as accurately as possible; a damping resistor is provided parallel to antenna 4 to adapt the quality Q- factor (normally very high in this type of antenna) to a level compatible with that of the transponders; the value of the damping resistor can be adjusted manually or automatically to adapt the Q-factor of antenna 4 to the type of transponder employed; and, if necessary, a stub can be inserted to improve tuning of antenna 4 and the relative transmission line.
  • Tuning circuit 9 of antenna 8 may comprise one or more known capacitors (not shown) connected in series/parallel to antenna 8, and is short-circuited by a capacitor, as opposed to being connected to the transmission line.
  • Antenna 4 is therefore a radiating antenna, by receiving energy directly from relative tuning circuit 6 powered by emitting/receiving system 7, whereas antenna 8 is a reflecting/directing antenna, i.e. does not receive energy directly from an electric energy source, by relative tuning circuit 9 being nonpowered, i.e. having short-circuited supply terminals.
  • Antenna system 3 is a hybrid system comprising a radiating antenna 4 (small, electrically driven loop) ; and a reflecting/directing antenna 8 (nondriven loop) larger than, and located in a given spatial position close to, radiating antenna 4.
  • antenna 4 when powered, antenna 4 generates an electromagnetic field which is coupled partly with antenna 8, in which a respective current is induced and, in turn, generates a further electromagnetic field, so that antennas 4 and 8 act in the same way as the primary and secondary of a transformer. Tests have shown the interaction between antennas 4 and 8 and the composition of the respective electromagnetic fields provide for an extremely high degree of efficiency of antenna 3.
  • Antennas 4 and 8 are parallel but not coplanar, and are separated by a distance D ranging between 3 mm and 30mm, and which, in the Figure 1 and 2 embodiment, is a distance of 10 mm.
  • Distance D between the antenna planes is necessary to avoid bunching antennas 4 and 8 in the field close to radiating antenna 4, but must not be so great as to impair the overall efficiency of antenna system 3 by increasing flux leakage, i.e. magnetic flux generated by antenna 4 and not linked to antenna 8.
  • Radiating antenna 4 must be an electrically small loop type, i.e. with a radius of less than 660 mm (for 13.56 MHz frequency), and must be a "Top-Loaded” type at antenna-transmission line connection level, so that the current distribution within the loop of radiating antenna 4 can be assumed constant, and antenna 4 considered tantamount to a radiating coil.
  • antenna 4 is most efficient when round, roundish, or of a shape comparable to a full loop, such as a regular polygon or a solenoid with a small number of turns.
  • the preferred shape is round.
  • the perimeter of the loop can be increased, while maintaining the same radius, using a fractal- derived form of antenna (e.g. Koch or Minkowski figures) .
  • the dimensions and characteristics of antenna 4 must be such that the input impedance of antenna 4 ranges between 40 and 80 Ohms, and is preferably 50 Ohms.
  • a 1.6 VSWR factor (expressed as a percentage of the rated power sent by the transponder reader) corresponds to 95% power transmitted by antenna 4, and 5% reflected power.
  • Antenna 8 is preferably larger than antenna 4, so as to cover a much larger surface area (the ratio between the two surface areas may even be greater than 10 to 1) .
  • Antenna 8 is most efficient when in the form of a regular polygon with a length to width ratio of close to 3.5, and preferably must have sharp, not overly beveled corners close to the top and bottom sides.
  • antenna 8 may be such that the inductance, and therefore impedance, values of antenna 8 differ widely from those of radiating antenna 4, which is designed for minimum mismatching with respect to the transmission line.
  • antenna 4 is circular with a diameter of 340 mm to give an impedance value of 78 Ohms
  • antenna 8 is rectangular with a minor-side dimension LI of 500 mm, and a major- side dimension L2 of 1600 mm; and the distance D between the planes of antennas 4 and 8 equals 10 mm.
  • antenna 4 is circular with a diameter of 340 mm to give an impedance value of 78 Ohms;
  • antenna 8 is in the form of an octagon inscribable in a 500 mm by 800 mm rectangle; and the distance D between the planes of antennas 4 and 8 equals 10 mm.
  • antenna 8 and the distance D between antenna 4 and antenna 8 depend on the diameter of antenna 4 and the shape of antenna 8, and can be determined easily by calculation and testing.
  • Antennas 4 and 8 are preferably made of copper, which can be used in various forms, e.g. as a coaxial cable (mainly RG58, RG213 or RG214) ; as a strip (single or with multiple parallel gap-insulated tracks) ; or as a hollow pipe of a diameter compatible with the size of the antenna to achieve the required inductance level . It should be pointed out that a given relationship must be maintained between the dimensions of the conductors used for radiating antenna 4 and reflecting/directing antenna 8. Laboratory tests have shown that a ratio of 1 to almost 3 must exist between the diameter of the radiating antenna 4 pipe and the diameter of the reflecting/directing antenna 8 pipe.
  • antenna 4 may also have portions of ferrite, which, as is known, provides for strengthening the field lines.
  • antenna system 3 The efficiency of antenna system 3 is directly proportional to the extent to which antennas 4 and 8 are coupled.
  • the position giving the highest coupling value is best determined experimentally, e.g. using a field probe located at antenna 8 to determine the position in which the magnetic field is strongest. Such tests clearly show the position giving the highest coupling value of antennas 4 and 8 to be the one shown in the accompanying drawings, in which antenna 4 is located close to the periphery of antenna 8.
  • an element of dielectric material is interposed between antennas 4 and 8 to increase the capacitance between antennas 4 and 8 and, therefore, performance of antenna system 3 as a whole.
  • Antenna system 3 may therefore also be of considerable size (physically and electrically) , thus providing an extensive operating surface area and a considerable transponder reading/programming range distributed over a wide surface area.
  • Antenna system 3 also has a minimum input impedance change level (however prescribed in transponder reading device design specifications) even at high power levels (over 5 W) , and comprises tuning circuits 6 and 9 which are straightforward and cheap, and which can be adapted easily and automatically to Q-factor levels of different types of transponders.
  • antenna system 3 is capable of reading and/or programming a large number of transponders at relatively long distances (over 1000 mm) with a very low electric power level, and therefore with a low level of induced electromagnetic noise.
  • reading device 1 can be used in a wide range of recognition stations 10 for recognizing articles, people, or animals provided with respective transponders.
  • recognition station 10 comprises at least one wall 11 defining an article read space 12, and antenna system 3 is housed and integrated inside wall 11.
  • wall 11 of recognition station 10 is incorporated in the horizontal element of a table made predominantly of dielectric material, so as to form a "desk" system for automatically recognizing the objects placed on the table.
  • a recognition station 10 of this sort may perform the functions required of a check-out counter.
  • recognition station 10 comprises a first vertical wall 11 housing antenna system 3; and a second vertical wall 11 facing and opposite first wall 11, and housing a nonpowered further antenna 13 identical with antenna 8 of antenna system 3, and which tests have shown improves the overall efficiency of antenna system 3.
  • Recognition station 10 in Figure 5 may be used to form a compulsory exit gate forming part of a shop security system to prevent shoplifting.
  • recognition station 10 comprises a horizontal wall 11 housing antenna system 3; and a vertical wall 11 housing a nonpowered further antenna 13 identical with antenna 8 of system 3.
  • Recognition station 10 in Figure 6 is preferably used in logistic applications requiring simultaneous identification of various objects with respective transponders, and the orientation of which with respect to the planes of antenna system 3 is not known beforehand.
  • antenna system 3 can read both transponders placed on the wall 11 containing antenna system 3 , and transponders simply passing through read space 12, without being placed on the wall 11 containing antenna system 3.
  • Walls 11 and all the structural components of recognition station 10 are preferably made of dielectric material, with as few metal elements as possible, to avoid interfering with the electromagnetic field generated by antenna system 3.
  • a number of antenna systems 3 may be used and connected to activating unit 2 by a MUX (antenna multiplexer) device.
  • MUX antenna multiplexer
  • Recognition station 10 is normally connected to a communication device for displaying an information sheet relative to each article identified, and for also sounding an alarm in the event of unlawful displacement of the article (e.g. as in museums) .
  • reading device 1 is not activated continuously, to avoid generating an electromagnetic field which may constitute a health hazard to anyone in the vicinity of recognition station 10. More specifically, recognition station 10 comprises an enabling device 14, which activates reading device 1 when necessary, and which may receive an enabling command from an operator, or may detect the passage of an article through read space 12 by means of a sensor (proximity, motion, barrier, etc.).

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Abstract

An antenna system (3) for a transponder radio­frequency reading device (1) ; the antenna system (3) having a flat, annular, circular first antenna (4) connected to a first tuning circuit (6) set to 13.56 MHz frequency; an emitting/receiving system (7) for generating an alternating electric current in the first tuning circuit (6); and a flat, annular, polygonal second antenna (8), which is connected to a nonpowered second tuning circuit (9) set to 13.56 MHz frequency, is parallel to the first antenna (4), and is separated from the first antenna (4) by a distance ranging from 3 to 30 mm, so as to be coupled magnetically to the first antenna (4).

Description

ANTENNA SYSTEM FOR A TRANSPONDER RADIO-FREQUENCY READING DEVICE
TECHNICAL FIELD
The present invention relates to an antenna system for a transponder radio-frequency reading device. BACKGROUND ART
A passive-transponder radio-frequency reading device normally comprises an activating unit and an antenna system. In actual use, the antenna system, controlled by the activating unit, generates a radio-frequency signal capable of activating any transponders within its operating range; and each transponder, when activated, transmits a radio-frequency return signal which is received and identified by the activating unit.
Transponder reading devices of the above type normally employ a 13.56 MHz operating frequency, which is recognized and can be used all over the world with no limitations; and an antenna system comprising a flat, annular, circular or polygonal antenna connected to a tuning circuit set to 13.56 MHz frequency, and an emitting/receiving system for generating alternating electric current in the tuning circuit . The best diameter for a circular antenna is around 340 mm, which gives an antenna impedance of close to 50 Ohms that can be matched almost perfectly with the 50 Ohm impedance of the transmission line. On the other hand, a flat, annular antenna of 340 mm diameter has a limited maximum operating range, and is normally unable to activate transponders at a distance of over 400-500 mm.
More specifically, the strength of the magnetic field produced at a given point by a circular antenna is directly proportional to the square of the antenna radius, and inversely proportional to the cube of the distance between the center of the antenna and the point considered. For example, to read a transponder, a field of at least 152 dBμA/m is required, so that, in laboratory conditions, transponders at a maximum distance of 400 mm could be read using a 200 mm diameter antenna, and at a maximum distance of 800 mm using a 500 mm diameter antenna, providing the transponders are within the radiation cone of the antenna.
To eliminate the above drawback, antenna systems have been proposed comprising noncircular, nonflat antennas. Such systems, however, have proved expensive and difficult to regulate, and fail to provide for the optimum current distribution typical of flat, circular antennas .
On the other hand, using a flat, circular antenna of well over 340 mm in diameter (the greater the diameter, the greater the maximum operating range) results, as the size of the antenna increases, in increased electromagnetic noise, thus impairing the overall efficiency of the system. To eliminate this drawback, greater RF power is normally applied to increase the operating range and/or the number of controllable transponders. Increasing the RF power to the antenna, however, affects the input impedance level of the antenna, thus resulting in gradual mismatching of the impedance of the transmission line (not normally balanced, by being defined by a coaxial cable) and the input impedance of the antenna, and therefore in gradual impairment in the overall operating conditions of the system. These drawbacks can be eliminated using sophisticated so-called electronic tuning circuits (for tuning transmission line impedance and the input impedance of the antenna) . Such circuits, however, have numerous components that are difficult to produce and install; furthermore such circuits should operate at a given mismatch, i.e. power, level and thus they require the replacing of some physical parts of the circuit for having an automatic modulation of the radiating power.
Finally, it should be pointed out that a high RF power level, as required by large-size antennas, may not conform with regulations governing RF emissions of this type of device .
DISCLOSURE OF INVENTION
It is an object of the present invention to provide an antenna system for a transponder radio-frequency reading device, designed to eliminate the aforementioned drawbacks, and which at the same time is cheap and easy to implement . According to the present invention, there is provided an antenna system for a transponder radio- frequency reading device, as claimed in Claim 1.
BRIEF DESCRIPTION OF THE DRAWINGS
A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:
Figure 1 shows a schematic view in perspective of a transponder reading device antenna system in accordance with the present invention; Figure 2 shows a front view of the Figure 1 antenna system;
Figure 3 shows a front view of an alternative embodiment of some of the Figure 1 antenna system components; Figures 4, 5 and 6 show alternative embodiments of stations for recognizing articles fitted with respective transponders, and incorporating a transponder read/write device using the Figure 1 antenna system.
BEST MODE FOR CARRYING OUT THE INVENTION Number 1 in Figure 1 indicates as a whole a radio- frequency reading device for passive-transponder comprising an activating unit 2 (with an emitter/receiver or simply an emitter) having an antenna system 3 and operating at 13.56 MHz frequency. In actual use, antenna system 3 controlled by activating unit 2 generates a 13.56 MHz radio-frequency signal capable of activating corresponding known transponders (not shown) within the operating range of antenna system 3; and, when activated, each transponder transmits a radio-frequency return signal, which is received and identified by activating unit 2, and which typically contains the identification code of the transponder, and a number of information items stored in a programmable electronic memory of the transponder.
More specifically, transponder reading device 1 is suitable for reading "Smart Label" passive transponders, which are in the form of a thin film for integration in labels, and have a printable surface and a programmable electronic memory.
Antenna system 3 comprises a circular, flat, annular antenna 4 with a central axis 5 of symmetry; a tuning circuit 6 (set to 13.56 MHz frequency) connected to antenna 4; an emitting/receiving system 7 controlled by activating unit 2 and for generating alternating electric current in tuning circuit 6; a flat, annular antenna 8 parallel to, close to, and therefore coupled magnetically to antenna 4; and a nonpowered tuning circuit 9 (set to 13.56 MHz frequency) connected to antenna 8.
Tuning circuit 6 is preferably in the form of a series and parallel capacitance configuration to regulate antenna 4 as accurately as possible; a damping resistor is provided parallel to antenna 4 to adapt the quality Q- factor (normally very high in this type of antenna) to a level compatible with that of the transponders; the value of the damping resistor can be adjusted manually or automatically to adapt the Q-factor of antenna 4 to the type of transponder employed; and, if necessary, a stub can be inserted to improve tuning of antenna 4 and the relative transmission line.
Tuning circuit 9 of antenna 8 may comprise one or more known capacitors (not shown) connected in series/parallel to antenna 8, and is short-circuited by a capacitor, as opposed to being connected to the transmission line.
Antenna 4 is therefore a radiating antenna, by receiving energy directly from relative tuning circuit 6 powered by emitting/receiving system 7, whereas antenna 8 is a reflecting/directing antenna, i.e. does not receive energy directly from an electric energy source, by relative tuning circuit 9 being nonpowered, i.e. having short-circuited supply terminals.
Antenna system 3 is a hybrid system comprising a radiating antenna 4 (small, electrically driven loop) ; and a reflecting/directing antenna 8 (nondriven loop) larger than, and located in a given spatial position close to, radiating antenna 4.
In actual use, when powered, antenna 4 generates an electromagnetic field which is coupled partly with antenna 8, in which a respective current is induced and, in turn, generates a further electromagnetic field, so that antennas 4 and 8 act in the same way as the primary and secondary of a transformer. Tests have shown the interaction between antennas 4 and 8 and the composition of the respective electromagnetic fields provide for an extremely high degree of efficiency of antenna 3.
Antennas 4 and 8 are parallel but not coplanar, and are separated by a distance D ranging between 3 mm and 30mm, and which, in the Figure 1 and 2 embodiment, is a distance of 10 mm. Distance D between the antenna planes is necessary to avoid bunching antennas 4 and 8 in the field close to radiating antenna 4, but must not be so great as to impair the overall efficiency of antenna system 3 by increasing flux leakage, i.e. magnetic flux generated by antenna 4 and not linked to antenna 8.
Radiating antenna 4 must be an electrically small loop type, i.e. with a radius of less than 660 mm (for 13.56 MHz frequency), and must be a "Top-Loaded" type at antenna-transmission line connection level, so that the current distribution within the loop of radiating antenna 4 can be assumed constant, and antenna 4 considered tantamount to a radiating coil.
In general, antenna 4 is most efficient when round, roundish, or of a shape comparable to a full loop, such as a regular polygon or a solenoid with a small number of turns. The preferred shape, however, is round. If necessary, the perimeter of the loop can be increased, while maintaining the same radius, using a fractal- derived form of antenna (e.g. Koch or Minkowski figures) . The dimensions and characteristics of antenna 4 (diameter or equivalent diameter for noncircular shapes, radius of the connector used to form the loop, type of material, use of ferrite, tuning circuit configuration, etc.) must be such that the input impedance of antenna 4 ranges between 40 and 80 Ohms, and is preferably 50 Ohms. This is vital to obtain a VSWR factor of maximum 1.6, and so control mismatching of the transmission line (50 Ohm nominal impedance) and antenna 4 at the source. A 1.6 VSWR factor (expressed as a percentage of the rated power sent by the transponder reader) corresponds to 95% power transmitted by antenna 4, and 5% reflected power. Antenna 8 is preferably larger than antenna 4, so as to cover a much larger surface area (the ratio between the two surface areas may even be greater than 10 to 1) .
Antenna 8 is most efficient when in the form of a regular polygon with a length to width ratio of close to 3.5, and preferably must have sharp, not overly beveled corners close to the top and bottom sides.
The dimensions and characteristics of antenna 8 (diameter or equivalent diameter for noncircular shapes, radius of the connector used to form the loop, type of material, tuning circuit configuration, etc.) may be such that the inductance, and therefore impedance, values of antenna 8 differ widely from those of radiating antenna 4, which is designed for minimum mismatching with respect to the transmission line.
In the antenna system shown in Figures 1 and 2, antenna 4 is circular with a diameter of 340 mm to give an impedance value of 78 Ohms; antenna 8 is rectangular with a minor-side dimension LI of 500 mm, and a major- side dimension L2 of 1600 mm; and the distance D between the planes of antennas 4 and 8 equals 10 mm.
In the antenna system shown in Figure 3, antenna 4 is circular with a diameter of 340 mm to give an impedance value of 78 Ohms; antenna 8 is in the form of an octagon inscribable in a 500 mm by 800 mm rectangle; and the distance D between the planes of antennas 4 and 8 equals 10 mm.
In general, the dimensions of antenna 8 and the distance D between antenna 4 and antenna 8 depend on the diameter of antenna 4 and the shape of antenna 8, and can be determined easily by calculation and testing.
Antennas 4 and 8 are preferably made of copper, which can be used in various forms, e.g. as a coaxial cable (mainly RG58, RG213 or RG214) ; as a strip (single or with multiple parallel gap-insulated tracks) ; or as a hollow pipe of a diameter compatible with the size of the antenna to achieve the required inductance level . It should be pointed out that a given relationship must be maintained between the dimensions of the conductors used for radiating antenna 4 and reflecting/directing antenna 8. Laboratory tests have shown that a ratio of 1 to almost 3 must exist between the diameter of the radiating antenna 4 pipe and the diameter of the reflecting/directing antenna 8 pipe.
Other materials (e.g. aluminium, gold, or silver) may also be used for particular requirements (lightness, corrosion resistance, etc.); and antenna 4 may also have portions of ferrite, which, as is known, provides for strengthening the field lines.
The efficiency of antenna system 3 is directly proportional to the extent to which antennas 4 and 8 are coupled. The position giving the highest coupling value is best determined experimentally, e.g. using a field probe located at antenna 8 to determine the position in which the magnetic field is strongest. Such tests clearly show the position giving the highest coupling value of antennas 4 and 8 to be the one shown in the accompanying drawings, in which antenna 4 is located close to the periphery of antenna 8.
It is important to note that a high coupling value of antennas 4 and 8 should not be sought at the expense of overly reducing distance D between the two antennas, which is necessary to avoid bunching antennas 4 and 8 in the field close to radiating antenna 4.
In an embodiment not shown, an element of dielectric material is interposed between antennas 4 and 8 to increase the capacitance between antennas 4 and 8 and, therefore, performance of antenna system 3 as a whole.
Antenna system 3 may therefore also be of considerable size (physically and electrically) , thus providing an extensive operating surface area and a considerable transponder reading/programming range distributed over a wide surface area.
Antenna system 3 also has a minimum input impedance change level (however prescribed in transponder reading device design specifications) even at high power levels (over 5 W) , and comprises tuning circuits 6 and 9 which are straightforward and cheap, and which can be adapted easily and automatically to Q-factor levels of different types of transponders.
Finally, antenna system 3 is capable of reading and/or programming a large number of transponders at relatively long distances (over 1000 mm) with a very low electric power level, and therefore with a low level of induced electromagnetic noise.
As shown in Figures 4, 5 and 6, by virtue of its efficiency, reading device 1 can be used in a wide range of recognition stations 10 for recognizing articles, people, or animals provided with respective transponders. As shown in Figures 4, 5 and 6, recognition station 10 comprises at least one wall 11 defining an article read space 12, and antenna system 3 is housed and integrated inside wall 11.
In Figure 4, wall 11 of recognition station 10 is incorporated in the horizontal element of a table made predominantly of dielectric material, so as to form a "desk" system for automatically recognizing the objects placed on the table. A recognition station 10 of this sort may perform the functions required of a check-out counter.
In Figure 5, recognition station 10 comprises a first vertical wall 11 housing antenna system 3; and a second vertical wall 11 facing and opposite first wall 11, and housing a nonpowered further antenna 13 identical with antenna 8 of antenna system 3, and which tests have shown improves the overall efficiency of antenna system 3. Recognition station 10 in Figure 5 may be used to form a compulsory exit gate forming part of a shop security system to prevent shoplifting.
In Figure 6, recognition station 10 comprises a horizontal wall 11 housing antenna system 3; and a vertical wall 11 housing a nonpowered further antenna 13 identical with antenna 8 of system 3. Recognition station 10 in Figure 6 is preferably used in logistic applications requiring simultaneous identification of various objects with respective transponders, and the orientation of which with respect to the planes of antenna system 3 is not known beforehand.
By virtue of its efficiency, antenna system 3 can read both transponders placed on the wall 11 containing antenna system 3 , and transponders simply passing through read space 12, without being placed on the wall 11 containing antenna system 3.
Walls 11 and all the structural components of recognition station 10 are preferably made of dielectric material, with as few metal elements as possible, to avoid interfering with the electromagnetic field generated by antenna system 3.
If necessary, a number of antenna systems 3 may be used and connected to activating unit 2 by a MUX (antenna multiplexer) device.
Recognition station 10 is normally connected to a communication device for displaying an information sheet relative to each article identified, and for also sounding an alarm in the event of unlawful displacement of the article (e.g. as in museums) .
In conformance with current regulations, reading device 1 is not activated continuously, to avoid generating an electromagnetic field which may constitute a health hazard to anyone in the vicinity of recognition station 10. More specifically, recognition station 10 comprises an enabling device 14, which activates reading device 1 when necessary, and which may receive an enabling command from an operator, or may detect the passage of an article through read space 12 by means of a sensor (proximity, motion, barrier, etc.).

Claims

1) An antenna system for a transponder radio- frequency reading device (1) ; the antenna system (3) comprising a flat, annular, radiating first antenna (4) ; a first tuning circuit (6) connected to the first antenna (4) ; and an emitting/receiving system (7) for generating an alternating electric current in the first tuning circuit (6) ; the antenna system (3) being characterized by comprising a flat, annular, reflecting/directing second antenna (8) located close to the first antenna (4) so as to be coupled magnetically to the first antenna (4) ; and a nonpowered second tuning circuit (9) connected to the second antenna (8) .
2) An antenna system as claimed in Claim 1, wherein said first tuning circuit (6) and said second tuning circuit (9) are set to a frequency of 13.56 MHz.
3) An antenna system as claimed in Claim 1 or 2, wherein the first antenna (4) is circular with a radius of no more than 660 mm.
4) An antenna system as claimed in Claim 3, wherein the first antenna (4) has a diameter of 340 mm to impart to the first antenna (4) an impedance of roughly 50 Ohms.
5) An antenna system as claimed in one of Claims 1 to 4, wherein the first antenna (4) and the second antenna (8) are parallel and not coplanar.
6) An antenna system as claimed in Claim 5, wherein the first antenna (4) and the second antenna (8) are parallel and separated by a distance (D) ranging between 5 mm and 30 mm.
7) An antenna system as claimed in Claim 5, wherein the first antenna (4) and the second antenna (8) are parallel and separated by a distance (D) of 10 mm.
8) An antenna system as claimed in one of Claims 1 to 7, wherein the second antenna (8) is in the form of a polygon, and is larger than the first antenna (4) .
9) An antenna system as claimed in Claim 8, wherein the ratio between the surface area of the first antenna
(4) and the surface area of the second antenna (8) ranges between 4 and 15.
10) An antenna system as claimed in Claim 8 or 0, wherein the length to width ratio of the second antenna (8) tends towards 3.5 and ranges between 2.5 and 4.5.
11) An antenna system as claimed in Claim 8, 9 or 10, wherein the second antenna (8) has sharp, not overly beveled corners close to the top and bottom sides.
12) An antenna system as claimed in one of Claims 8 to 11, wherein the second antenna (8) is rectangular.
13) An antenna system as claimed in one of Claims 8 to 11, wherein the second antenna (8) is octagonal.
14) An antenna system as claimed in one of Claims 1 to 13, wherein the first antenna (4) is not coaxial with the second antenna (8) , and is located close to the periphery of the second antenna (8) .
15) An antenna system as claimed in one of Claims 1 to 14, wherein said first antenna (4) is a "Top-Loaded" type at antenna-transmission line connection level.
16) An antenna system as claimed in one of Claims 1 to 15, wherein said first tuning circuit (6) is in the form of a series and parallel capacitance configuration. 17) An antenna system as claimed in Claim 16, wherein said first tuning circuit (6) has a damping resistor parallel to the first antenna (4) and adjustable in value .
18) An antenna system as claimed in one of Claims 1 to 17, wherein said second tuning circuit (9) comprises a number of capacitors connected in series with/parallel to the second antenna (8) .
19) An antenna system as claimed in one of Claims 1 to 18, and comprising at least one element of dielectric material located between the first antenna (4) and the second antenna (8) .
20) An antenna system as claimed in one of Claims 1 to 19, wherein said first antenna has a fractal-derived shape to increase the perimeter of the first antenna (4) while maintaining the same diameter.
21) An antenna system as claimed in Claim 20, wherein said fractals are Koch or Minkowski figures.
22) A transponder radio-frequency reading device comprising an activating unit (2) having an antenna system (3) of the type claimed in Claims 1 to 21.
23) A recognition station for recognizing articles having respective radio-frequency transponders; the recognition station (10) comprising at least a first wall (11) defining an article read space (12) ; and a transponder reading device (1) , in turn comprising an activating unit (2) having an antenna system (3) ; the recognition station (10) being characterized in that the antenna system (3) is housed in the first wall (11) so as to be integrated in the first wall (11) .
24) A recognition station as claimed in Claim 23, wherein the antenna system (3) is of the type claimed in Claims 1 to 19. 25) A recognition station as claimed in Claim 23 or 24, and comprising a second wall (11) facing and opposite the first wall (11) and housing a nonpowered further antenna (13) identical with the second antenna (8) of the antenna system (3) . 26) A recognition station as claimed in Claim 23 or 24, wherein said first wall is horizontal; and a second wall (11) , located vertically and laterally with respect to the first wall (11) , houses a nonpowered further antenna (13) identical with the second antenna (8) of the antenna system (3) .
27) A recognition station as claimed in one of Claims 23 to 26, wherein said walls (11) are made of dielectric material.
28) A recognition station as claimed in one of Claims 23 to 27, and comprising an enabling device (14) for enabling the reading device (1) when necessary.
29) A recognition station as claimed in Claim 28, wherein said enabling device (14) receives an' enabling command from an operator.
30) A recognition station as claimed in Claim 28, wherein said enabling device (14) receives an enabling command from a sensor for detecting the passage of an article through the read space (12) .
PCT/EP2003/002553 2002-03-13 2003-03-12 Antenna system for a transponder radio-frequency reading device WO2003077364A2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003218742A AU2003218742A1 (en) 2002-03-13 2003-03-12 Antenna system for a transponder radio-frequency reading device

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
PT102739 2002-03-13
PT10273902A PT102739A (en) 2002-03-13 2002-03-13 ANTENNA SYSTEM FOR A TRANSPONDER RADIOFREQUENCY READING DEVICE

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WO2003077364A3 WO2003077364A3 (en) 2004-03-11

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US8447234B2 (en) 2006-01-18 2013-05-21 Qualcomm Incorporated Method and system for powering an electronic device via a wireless link
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US8378522B2 (en) 2007-03-02 2013-02-19 Qualcomm, Incorporated Maximizing power yield from wireless power magnetic resonators
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US8629576B2 (en) 2008-03-28 2014-01-14 Qualcomm Incorporated Tuning and gain control in electro-magnetic power systems
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WO2003077364A3 (en) 2004-03-11
PT102739A (en) 2003-09-30

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