WO2003044892A1 - Modified loop antenna with omnidirectional radiation pattern and optimized properties for use in an rfid device - Google Patents

Modified loop antenna with omnidirectional radiation pattern and optimized properties for use in an rfid device Download PDF

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Publication number
WO2003044892A1
WO2003044892A1 PCT/FI2002/000934 FI0200934W WO03044892A1 WO 2003044892 A1 WO2003044892 A1 WO 2003044892A1 FI 0200934 W FI0200934 W FI 0200934W WO 03044892 A1 WO03044892 A1 WO 03044892A1
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WIPO (PCT)
Prior art keywords
antenna
rfid device
impedance
foregoing
remote sensor
Prior art date
Application number
PCT/FI2002/000934
Other languages
French (fr)
Inventor
Timo Varpula
Olli Jaakkola
Kaarle Jaakkola
Original Assignee
Valtion Teknillinen Tutkimuskeskus
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 Valtion Teknillinen Tutkimuskeskus filed Critical Valtion Teknillinen Tutkimuskeskus
Priority to AU2002366123A priority Critical patent/AU2002366123A1/en
Publication of WO2003044892A1 publication Critical patent/WO2003044892A1/en

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Classifications

    • 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
    • H01Q1/2225—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 active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
    • 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
    • H01Q9/16—Resonant antennas with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole
    • 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
    • H01Q9/16—Resonant antennas with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole
    • H01Q9/20—Two collinear substantially straight active elements; Substantially straight single active elements
    • H01Q9/24—Shunt feed arrangements to single active elements, e.g. for delta matching
    • 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
    • H01Q9/16—Resonant antennas with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole
    • H01Q9/26—Resonant antennas with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole with folded element or elements, the folded parts being spaced apart a small fraction of operating wavelength
    • H01Q9/265—Open ring dipoles; Circular dipoles

Definitions

  • the invention relates to an antenna structure according to the preamble of claim 1.
  • a remote identification device is a miniature tag device comprising an antenna connected to a microcircuit with a memory that can respond by sending the contents of its memory by backscatter communications responsive to an interrogation signal received from an interrogating reader device that emits an RF signal in the direction of the tag device (FIG. 1).
  • a passive RFID transponder has no battery, but instead captures its operating power from the radio- frequency field of the interrogation signal sent toward the transponder by the reader device. Energy and information transfer between the remote identification device and the reader device may take place using a magnetic field, an electric field or an emitted radio-frequency signal.
  • Remote identification devices will in many cases replace such identification techniques as optically scanned barcode labels, for instance. This is because remote identification devices offer many benefits such as easy rewrite of their memory content, no need for a visual contact to the remote identification device being interrogated by means of an RF signal, a read distance of several meters and more.
  • the present invention concerns remote identification devices that communicate using RF signals.
  • the use of RFID devices is permitted, e.g. in most European countries over frequency bands covering 868 - 870 MHz and 2400 - 2483.5 MHz. In the USA, the corresponding bands are 902 - 928 MHz and 2400 - 2483.5 MHz. The wavelengths at these frequency bands are slightly above 30 cm and about 12 cm, respectively.
  • the dimensions of RFID device antennas can be made relatively small.
  • an antenna according to the present invention for the 868 - 870 MHz band can be readily adapted on a substrate having the size of a credit card or even smaller. In fact, the small size of an RFID device is a benefit in plural applications.
  • the RFID device functions only when receiving an RF signal emitted by a reader device.
  • Such applications can be found, e.g., in the marking of products and raw materials in the logistics systems of trade and industry, production automation, identification of product origin, recycling and access control and the like.
  • its orientation-free function is a substantial benefit as to its usability.
  • a wireless remote sensor device generates its electrical operating power by rectifying the RF voltage delivered by the antenna of the device.
  • rectification is carried out with the help of a circuit comprising one or more diodes, such as a voltage doubler circuit.
  • the highest possible efficiency today is offered by Schottky diodes that can also be manufactured using a CMOS process.
  • the antenna impedance In order to facilitate the transfer of the RF energy from the device antenna to the rectifier, the antenna impedance must be matched with the rectifier input impedance at the operating frequency of the device.
  • the equivalent circuit of the rectifier circuit on a radio frequency comprises the series connection of a capacitor and a resistor.
  • the characteristic impedance of a conventional dipole antenna at its resonant half- wave length is purely resistive at about 73 ohm.
  • One conventional matching technique comprises using a coil as a matching element between the dipole antenna and the rectifier.
  • a separate matching element is problematic. It increases production costs inasmuch as its fabrication presumes tight dimensional control.
  • a separate matching element causes extra losses that reduce the system efficiency.
  • the antenna impedance should preferably match directly with the rectifier impedance.
  • the resistive part R of the antenna impedance should be equal to the resistive part of the rectifier impedance.
  • the imaginary component of the antenna impedance, or the reactance X should also be equal as to its magnitude but with an opposite sign meaning that the reactive part of antenna impedance must be inductive.
  • the resistive part of the impedance comprises the radiation resistance of the antenna and a resistance component related to the ohmic losses of the antenna.
  • the frequency band allocated for operating a wireless remote sensor is very narrow.
  • an antenna representing an inductive reactance is connected to a rectifier representing a capacitive reactance, the system later called a rectenna becomes resonant. Its resonant frequency is centered at the system operating frequency (e.g., 869 MHz).
  • the characteristic impedance of the antenna can be approximated by a resistive and inductive parts only at a discrete frequency.
  • the imaginary component of impedance in a conventional dipole antenna changes much steeper with frequency than imaginary component of impedance for a simple inductance.
  • the system bandwidth tends to become narrow.
  • the bandwidth is not unnecessarily wide.
  • wireless remote sensors are desired to be inexpensive meaning that the manufacturing technology of sensor antennas must be uncomplicated.
  • the bandwidth is made narrow, even a slightest deviation from manufacturing tolerances can shift the maximum of the rectenna frequency-response curve outside the limits of the allocated operating frequency band.
  • the band allocated for remote devices operating just below 1 GHz are centered differently in Europe and the USA (869 MHz and 915 MHz).
  • the frequency-response curve of the rectenna system of a wireless remote sensor should advantageously cover the frequency bands allocated in both Europe and the USA.
  • the goal of the invention is achieved by virtue of a novel antenna construction for an RFID device.
  • One embodiment of the invention is illustrated in FIG. 3.
  • An essential feature of the invention is that the antenna of an RFID device can be made to function simultaneously as an electrical and magnetic dipole radiator.
  • the antenna according to the invention is characterized by what is stated in the characterizing part of claim 1.
  • the invention offers significant benefits.
  • the invention provides all the desirable properties listed above for the antenna of an RFID device: omnidirectional radiation pattern of the antenna with an inductive impedance that permits direct matching of the antenna with the rectifier impedance without the need for separate matching elements; small size; high efficiency; and sufficiently wide bandwidth of the rectenna system. Moreover, the antenna impedance is easy to tailor for different voltage rectifier circuits.
  • the electrical/magnetic radiation pattern mode of the antenna according to the invention can be understood with the help of FIG. 4.
  • the magnitude of current is highest close to the feed point of the antenna, whereby the vector sum of the current vectors forms a radiating electrical dipole.
  • the distribution of the current vectors forms a loop allowing the antenna to perform a double function as a magnetic dipole radiator, too.
  • a dipole antenna does not radiate in its axial direction.
  • the radiation pattern of the antenna is omnidirectional.
  • the radiation intensity of the magnetic dipole is strong in the direction of the radiation minimum of the electrical dipole and vice versa.
  • the amount of conductive material needed in the antennas according to the invention is small in contrast to constructions based on, e.g., a slot antenna. This is a significant benefit as allows low-cost manufacture of the antennas according to the invention. The value of such a feature is crucial in the price-critical market of RFID devices.
  • the antenna according to the invention offers an essential benefit in the use of RFID devices: remote read is always possible irrespective of the mutual orientation between the reader and the RFID device. Since the radiation pattern emitted by the antenna of an RFID device now has the combined polarization of both an electrical and a magnetic dipole radiator, the reader antenna must also be designed for correct polarization. The simplest technique for meeting this requirement is accomplished by using circular polarization in the reader antenna. However, herein half of the radiated power is lost. Linear polarization is most optimal for the reader antenna, but then there must be means for rotating the reader polarization so that becomes the same as the antenna polarization of the RFID device. This can be arranged by way of using, e.g., two antennas of which both have linear polarization and are fed in the same phase but are controlled to operate at different power levels.
  • FIG. 1 shows a schematic diagram of a system suitable for the implementation of the invention
  • FIGS. 2a-2d show prior-art antennas used in RFID devices;
  • FIG. 3 shows an embodiment of the antenna according to the invention for an RFID device;
  • FIG. 4 shows the current distribution of an antenna according to the invention, particularly such as shown in FIG. 3, at the peak of the current waveform;
  • FIG. 5 shows some alternative embodiments of RFID device antennas according to the invention.
  • FIG. 6 shows a graphical plot of the radiation pattern of an antenna according to the invention in two projections.
  • FIG. 7 shows some other alternative embodiments of RFID device antennas according to the invention.
  • a typical remote read system comprises a reader device 10 and an RFID device 20, both of them communicating with each other wirelessly.
  • reader device 10 includes a processor 11, a demodulator 12 and RF electronics 13 with an antenna 14 for producing and receiving an RF signal.
  • RFID device 20 includes an antenna 21, a matching circuit 22, a rectifier 23 with detector and a logic circuit 24. Modulation is implemented with the cooperation of the logic circuit 24 and the matching circuit 22.
  • the RFID device 20 is packaged by lamination on a thin substrate, generally in the credit card size.
  • FIG. 2 shows prior-art antennas used in RFID devices.
  • FIG. 2a is illustrated a half- wave dipole antenna. Its impedance is matched with the rectifier impedance by lowering the radiation resistance of the antenna with the help of a parallel conductor and increasing the reactance with the help of small loops.
  • FIG. 2b shows another half-wave dipole antenna. Its impedance is matched with the rectifier impedance with the help of a parallel capacitance and discrete coils in series with the antenna.
  • FIG. 2c shows a folded half-wave dipole antenna. Its impedance is matched with the rectifier impedance with the help of a parallel coil.
  • FIG. 2d shows a dipole antenna of substantially half- wave long. Its impedance is matched with the rectifier impedance with the help of a parallel coil.
  • FIG. 3 shows an RFID device antenna 1 according to the invention.
  • the antenna is formed by two conductors running noncontactingly close to each other in the shape of two almost complete circles.
  • the antenna feed point 2 is situated essentially centrally at the starting point of the curved conductors.
  • the antenna is typically fabricated on a printed circuit board 3 having a 35 ⁇ m thick copper layer laminated on a 1.6 mm thick dielectric substrate (grade FR4).
  • the embodiment of FIG. 3 may be called a truncated spiral antenna having its feed point 2 located at the cut point of the spiral.
  • FIG. 4 shows the current distribution of an antenna according to the invention, typically such as shown in FIG. 3, at the peak of the current waveform
  • the diagrams of FIG. 5 show some variants of the RFID device antenna according to the invention.
  • These antennas are planar structures suitable for being fabricated by etching or deposition of the conductor pattern on a polymer laminate material or some other like substrate. Typically, the entire antenna is fabricated on a single side of the substrate but, alternatively, the two conductors of the antenna may also be located on opposite sides of the substrate. Accordingly, the antenna is formed by two conductors running noncontactingly close to each other so as to enclose each other as pseudocircular patterns formed by 3 to 5 straight portions.
  • the antennas are designed for 869 MHz frequency and to be made on a PCB material (grade FR4) with a 35 ⁇ m thick copper cladding on a 1.6 mm thick dielectric substrate.
  • the antenna impedances are given beside the diagrams.
  • FIG. 6 shows a graphical plot of the radiation pattern of an antenna according to the invention in two projections.
  • the radiation pattern is substantially omnidirectional.
  • FIG. 7 shows four other alternative embodiments of antenna structures according to the invention, each one of them characteristically representing a combination of a loop antenna with a dipole antenna such that the feed point of the antenna is situated in loop portion of the antenna.
  • the loop portion may also be implemented using rectangular structures in the antenna.
  • the above-described design techniques may also be applied to other remotely readable components such as wireless remote read sensors.
  • RFID device and “wireless remote sensor” must be understood to refer to any device capable of wireless communication with a remote reader.
  • the category of remote readers includes bus pass readers, tracking readers of supply chains, road tolling readers or, e.g., personal ID card readers.
  • the loop shape of the antenna must be understood to refer to such a shape that at the operating frequency renders an antenna impedance that desiredly complements the rectifier/detector impedance of a microcircuit.
  • this goal is achieved at a frequency of about 869 MHz by an antenna structure having an average diameter of about 15 - 35 mm with about 1.5 - 2 turns of antenna conductor.
  • the feed point 2 is located substantially centrally in the loop structure. In other word, the distance from the feed point 2 is approximately equal along either one of the conductors to both ends of the loop structure.
  • planar antenna structures have been discussed above, the invention may equally well be implemented using three-dimensional antenna designs that can form simultaneously both an electrical and a magnetic dipole. In its simplest form, this kind of structure may be realized by stacking planar antenna structures above one another and then connecting the same in series.

Abstract

The present invention relates to an antenna for use in an RFID device or remote sensor. The radiation emitted by the RFID device antenna is a combination of an electrical and a magnetic dipole radiation. The antenna is formed by two conductors that run curvedly enclosing close to each other and may be formed by circular arcs and/or straight portion. The antenna according to the invention has a simple structure, yet offering ideal properties for most remote identification applications: an omnidirectional antenna allowing the read operation of an RFID device from any direction; small size; sufficiently wide bandwidth; matching of the antenna with the rectifier of the RFID device microchip without any discrete circuit elements; high efficiency; easy-to-modify construction; and freedom from critical dimensional manufacturing tolerances.

Description

Modified loop antenna with omnidirectional radiation pattern and optimized properties for use in an RFID device
The invention relates to an antenna structure according to the preamble of claim 1.
Generally, a remote identification device (an RFID transponder) is a miniature tag device comprising an antenna connected to a microcircuit with a memory that can respond by sending the contents of its memory by backscatter communications responsive to an interrogation signal received from an interrogating reader device that emits an RF signal in the direction of the tag device (FIG. 1). A passive RFID transponder has no battery, but instead captures its operating power from the radio- frequency field of the interrogation signal sent toward the transponder by the reader device. Energy and information transfer between the remote identification device and the reader device may take place using a magnetic field, an electric field or an emitted radio-frequency signal.
Remote identification devices will in many cases replace such identification techniques as optically scanned barcode labels, for instance. This is because remote identification devices offer many benefits such as easy rewrite of their memory content, no need for a visual contact to the remote identification device being interrogated by means of an RF signal, a read distance of several meters and more.
The present invention concerns remote identification devices that communicate using RF signals. The use of RFID devices is permitted, e.g. in most European countries over frequency bands covering 868 - 870 MHz and 2400 - 2483.5 MHz. In the USA, the corresponding bands are 902 - 928 MHz and 2400 - 2483.5 MHz. The wavelengths at these frequency bands are slightly above 30 cm and about 12 cm, respectively. Hence, the dimensions of RFID device antennas can be made relatively small. For instance, an antenna according to the present invention for the 868 - 870 MHz band can be readily adapted on a substrate having the size of a credit card or even smaller. In fact, the small size of an RFID device is a benefit in plural applications. Inasmuch as an RFID transponder typically generates its operating voltages and power from the radio-frequency field of the incident interrogation signal, the RFID device functions only when receiving an RF signal emitted by a reader device. In most applications of RFID technology, it is essential that the reader device can communicate with an RFID device irrespective of their mutual physical orientation. Such applications can be found, e.g., in the marking of products and raw materials in the logistics systems of trade and industry, production automation, identification of product origin, recycling and access control and the like. In addition to the small size of a wireless remote sensor device, its orientation-free function is a substantial benefit as to its usability.
A wireless remote sensor device generates its electrical operating power by rectifying the RF voltage delivered by the antenna of the device. Conventionally, rectification is carried out with the help of a circuit comprising one or more diodes, such as a voltage doubler circuit. The highest possible efficiency today is offered by Schottky diodes that can also be manufactured using a CMOS process. In order to facilitate the transfer of the RF energy from the device antenna to the rectifier, the antenna impedance must be matched with the rectifier input impedance at the operating frequency of the device. The equivalent circuit of the rectifier circuit on a radio frequency comprises the series connection of a capacitor and a resistor. The characteristic impedance of a conventional dipole antenna at its resonant half- wave length is purely resistive at about 73 ohm. One conventional matching technique comprises using a coil as a matching element between the dipole antenna and the rectifier. However, such a separate matching element is problematic. It increases production costs inasmuch as its fabrication presumes tight dimensional control. Moreover, a separate matching element causes extra losses that reduce the system efficiency. Hence, the antenna impedance should preferably match directly with the rectifier impedance. Hereby the resistive part R of the antenna impedance should be equal to the resistive part of the rectifier impedance. Respectively, the imaginary component of the antenna impedance, or the reactance X, should also be equal as to its magnitude but with an opposite sign meaning that the reactive part of antenna impedance must be inductive. The resistive part of the impedance comprises the radiation resistance of the antenna and a resistance component related to the ohmic losses of the antenna.
The frequency band allocated for operating a wireless remote sensor is very narrow. When an antenna representing an inductive reactance is connected to a rectifier representing a capacitive reactance, the system later called a rectenna becomes resonant. Its resonant frequency is centered at the system operating frequency (e.g., 869 MHz). The frequency-response curve of the rectenna has a maximum at the resonant frequency with a half-value bandwidth substantially equal to B =βJX. For practicable purposes, the characteristic impedance of the antenna can be approximated by a resistive and inductive parts only at a discrete frequency. E.g., the imaginary component of impedance in a conventional dipole antenna changes much steeper with frequency than imaginary component of impedance for a simple inductance. As a result, the system bandwidth tends to become narrow. In order to reject external spurious signals, it is advantageous that the system bandwidth is not unnecessarily wide. On the other hand, however, there are two reasons why the bandwidth should advantageously be substantially wider than the information transmission bandwidth permitted by authorities. First, wireless remote sensors are desired to be inexpensive meaning that the manufacturing technology of sensor antennas must be uncomplicated. However, if the bandwidth is made narrow, even a slightest deviation from manufacturing tolerances can shift the maximum of the rectenna frequency-response curve outside the limits of the allocated operating frequency band. Secondly, the band allocated for remote devices operating just below 1 GHz are centered differently in Europe and the USA (869 MHz and 915 MHz). As to world-wide compatibility of wireless remote sensors on different continents, the frequency-response curve of the rectenna system of a wireless remote sensor should advantageously cover the frequency bands allocated in both Europe and the USA.
Commercially available wireless remote sensors operating in the UHF range (300 - 3000 MHz) generally use electrical dipole antennas similar to those illustrated in FIG. 2. Frequently, dipole antennas have been complemented with elements (FIGS. 2b - 2d) serving to match the antennas with the rectifier. Such embodiments based on a simple dipole antenna suffer from many of the above-mentioned drawbacks. Emitting no radiation in its axial direction, a dipole is not omnidirectional. A solution to this problem has been sought by using two dipole antennas oriented orthogonally to each other. This arrangement increases the size of the RFED device and the second antenna requires an extra pin on the integrated circuit of the device. The matching elements of the antenna system are lossy and difficult to fabricate.
It is an object of the invention to provide an entirely novel type of antenna for an RFID device or wireless remote sensor such that the above-described problems of the prior art can be overcome.
The goal of the invention is achieved by virtue of a novel antenna construction for an RFID device. One embodiment of the invention is illustrated in FIG. 3. An essential feature of the invention is that the antenna of an RFID device can be made to function simultaneously as an electrical and magnetic dipole radiator.
More specifically, the antenna according to the invention is characterized by what is stated in the characterizing part of claim 1.
The invention offers significant benefits.
The invention provides all the desirable properties listed above for the antenna of an RFID device: omnidirectional radiation pattern of the antenna with an inductive impedance that permits direct matching of the antenna with the rectifier impedance without the need for separate matching elements; small size; high efficiency; and sufficiently wide bandwidth of the rectenna system. Moreover, the antenna impedance is easy to tailor for different voltage rectifier circuits.
The electrical/magnetic radiation pattern mode of the antenna according to the invention can be understood with the help of FIG. 4. The magnitude of current is highest close to the feed point of the antenna, whereby the vector sum of the current vectors forms a radiating electrical dipole. Simultaneously, the distribution of the current vectors forms a loop allowing the antenna to perform a double function as a magnetic dipole radiator, too. Normally, a dipole antenna does not radiate in its axial direction. Inasmuch as the magnetic and electrical dipole in the antenna according to the invention are oriented orthogonal to each other, the radiation pattern of the antenna is omnidirectional. The radiation intensity of the magnetic dipole is strong in the direction of the radiation minimum of the electrical dipole and vice versa.
The amount of conductive material needed in the antennas according to the invention is small in contrast to constructions based on, e.g., a slot antenna. This is a significant benefit as allows low-cost manufacture of the antennas according to the invention. The value of such a feature is crucial in the price-critical market of RFID devices.
The antenna according to the invention offers an essential benefit in the use of RFID devices: remote read is always possible irrespective of the mutual orientation between the reader and the RFID device. Since the radiation pattern emitted by the antenna of an RFID device now has the combined polarization of both an electrical and a magnetic dipole radiator, the reader antenna must also be designed for correct polarization. The simplest technique for meeting this requirement is accomplished by using circular polarization in the reader antenna. However, herein half of the radiated power is lost. Linear polarization is most optimal for the reader antenna, but then there must be means for rotating the reader polarization so that becomes the same as the antenna polarization of the RFID device. This can be arranged by way of using, e.g., two antennas of which both have linear polarization and are fed in the same phase but are controlled to operate at different power levels.
Next, the invention will be examined by making reference to the appended drawings in which
FIG. 1 shows a schematic diagram of a system suitable for the implementation of the invention;
FIGS. 2a-2d show prior-art antennas used in RFID devices; FIG. 3 shows an embodiment of the antenna according to the invention for an RFID device;
FIG. 4 shows the current distribution of an antenna according to the invention, particularly such as shown in FIG. 3, at the peak of the current waveform;
FIG. 5 shows some alternative embodiments of RFID device antennas according to the invention;
FIG. 6 shows a graphical plot of the radiation pattern of an antenna according to the invention in two projections; and
FIG. 7 shows some other alternative embodiments of RFID device antennas according to the invention.
Referring to FIG. 1, a typical remote read system comprises a reader device 10 and an RFID device 20, both of them communicating with each other wirelessly. Typically, reader device 10 includes a processor 11, a demodulator 12 and RF electronics 13 with an antenna 14 for producing and receiving an RF signal. Respectively, RFID device 20 includes an antenna 21, a matching circuit 22, a rectifier 23 with detector and a logic circuit 24. Modulation is implemented with the cooperation of the logic circuit 24 and the matching circuit 22. Typically, the RFID device 20 is packaged by lamination on a thin substrate, generally in the credit card size.
The diagrams of FIG. 2 show prior-art antennas used in RFID devices. In FIG. 2a is illustrated a half- wave dipole antenna. Its impedance is matched with the rectifier impedance by lowering the radiation resistance of the antenna with the help of a parallel conductor and increasing the reactance with the help of small loops. FIG. 2b shows another half-wave dipole antenna. Its impedance is matched with the rectifier impedance with the help of a parallel capacitance and discrete coils in series with the antenna.
FIG. 2c shows a folded half-wave dipole antenna. Its impedance is matched with the rectifier impedance with the help of a parallel coil.
FIG. 2d shows a dipole antenna of substantially half- wave long. Its impedance is matched with the rectifier impedance with the help of a parallel coil.
FIG. 3 shows an RFID device antenna 1 according to the invention. The antenna is formed by two conductors running noncontactingly close to each other in the shape of two almost complete circles. The antenna feed point 2 is situated essentially centrally at the starting point of the curved conductors. The antenna is typically fabricated on a printed circuit board 3 having a 35 μm thick copper layer laminated on a 1.6 mm thick dielectric substrate (grade FR4). The size of the antenna is determined by the operating frequency and its precise shape by the impedance of the rectifier circuit on the microchip. For instance, the antenna diameter D = 35 mm in a practicable embodiment operating at 869 MHz. In short, the embodiment of FIG. 3 may be called a truncated spiral antenna having its feed point 2 located at the cut point of the spiral.
FIG. 4 shows the current distribution of an antenna according to the invention, typically such as shown in FIG. 3, at the peak of the current waveform
The diagrams of FIG. 5 show some variants of the RFID device antenna according to the invention. These antennas are planar structures suitable for being fabricated by etching or deposition of the conductor pattern on a polymer laminate material or some other like substrate. Typically, the entire antenna is fabricated on a single side of the substrate but, alternatively, the two conductors of the antenna may also be located on opposite sides of the substrate. Accordingly, the antenna is formed by two conductors running noncontactingly close to each other so as to enclose each other as pseudocircular patterns formed by 3 to 5 straight portions. The antennas are designed for 869 MHz frequency and to be made on a PCB material (grade FR4) with a 35 μm thick copper cladding on a 1.6 mm thick dielectric substrate. The antenna impedances are given beside the diagrams.
FIG. 6 shows a graphical plot of the radiation pattern of an antenna according to the invention in two projections. The radiation pattern is substantially omnidirectional.
FIG. 7 shows four other alternative embodiments of antenna structures according to the invention, each one of them characteristically representing a combination of a loop antenna with a dipole antenna such that the feed point of the antenna is situated in loop portion of the antenna. As is evident from two lower embodiments, the loop portion may also be implemented using rectangular structures in the antenna.
Besides RFID devices, the above-described design techniques may also be applied to other remotely readable components such as wireless remote read sensors.
In the context of this invention, terms "RFID device" and "wireless remote sensor" must be understood to refer to any device capable of wireless communication with a remote reader. Hence, the category of remote readers includes bus pass readers, tracking readers of supply chains, road tolling readers or, e.g., personal ID card readers.
The loop shape of the antenna must be understood to refer to such a shape that at the operating frequency renders an antenna impedance that desiredly complements the rectifier/detector impedance of a microcircuit. Advantageously, this goal is achieved at a frequency of about 869 MHz by an antenna structure having an average diameter of about 15 - 35 mm with about 1.5 - 2 turns of antenna conductor. Typically, the feed point 2 is located substantially centrally in the loop structure. In other word, the distance from the feed point 2 is approximately equal along either one of the conductors to both ends of the loop structure. While only planar antenna structures have been discussed above, the invention may equally well be implemented using three-dimensional antenna designs that can form simultaneously both an electrical and a magnetic dipole. In its simplest form, this kind of structure may be realized by stacking planar antenna structures above one another and then connecting the same in series.

Claims

What is claimed is:
1. A substantially omnidirectional antenna (1) for an RFID device or wireless remote sensor,
characterized in that said antenna (1) is shaped in such a fashion that
- the radiation emitted from the antenna is substantially a combination of the radiation patterns of a magnetic dipole and an electrical dipole.
2. The antenna (1) of claim 1, characterized in that said antenna (1) has an essentially loop-like shape such that at the operating frequency of the remote sensor the antenna impedance can be matched with the impedance of the RFID device or remote sensor without separate matching elements.
3. The antenna (1) of any one of foregoing claims, characterized in that said antenna (1) is substantially planar.
4. The antenna (1) of any one of foregoing claims, characterized in that said antenna is formed by two branches running noncontactingly close to each other so as to enclose each other as two almost complete circles.
5. The antenna (1) of any one of foregoing claims, characterized in that said antenna (1) has a substantially spiral shape such that the antenna feed point (2) forms a cut point of the spiral.
6. The antenna (1) of any one of foregoing claims, characterized in that said antenna is formed by two branches running noncontactingly close to each other in a circular shape of multiple straight sections thus resembling a pseudocircular or pseudospiraling pattern.
7. The antenna (1) of any one of foregoing claims, characterized in that the galvanically separated conductor parts of the antenna are located on opposite sides of the insulating substrate material (3) of the antenna.
PCT/FI2002/000934 2001-11-22 2002-11-20 Modified loop antenna with omnidirectional radiation pattern and optimized properties for use in an rfid device WO2003044892A1 (en)

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Application Number Priority Date Filing Date Title
AU2002366123A AU2002366123A1 (en) 2001-11-22 2002-11-20 Modified loop antenna with omnidirectional radiation pattern and optimized properties for use in an rfid device

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Cited By (29)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1341257A1 (en) * 2000-12-08 2003-09-03 Matsushita Electric Industrial Co., Ltd. Antenna apparatus and communication system
WO2005081018A1 (en) * 2004-02-24 2005-09-01 Tagmaster Ab Transponder for an rfid-system
EP1628360A1 (en) 2004-08-21 2006-02-22 Samsung Electronics Co., Ltd Small planar antenna with enhanced bandwidth and small rectenna for RFID and wireless sensor transponder
WO2006020529A1 (en) * 2004-08-13 2006-02-23 Sensormatic Electronics Corporation Tunable spiral antenna for security tag
US7098794B2 (en) 2004-04-30 2006-08-29 Kimberly-Clark Worldwide, Inc. Deactivating a data tag for user privacy or tamper-evident packaging
US7151455B2 (en) 2004-04-30 2006-12-19 Kimberly-Clark Worldwide, Inc. Activating a data tag by load or orientation or user control
WO2007015205A1 (en) 2005-08-02 2007-02-08 Nxp B.V. Antenna structure, transponder and method of manufacturing an antenna structure
WO2007054900A2 (en) 2005-11-10 2007-05-18 Nxp B.V. Broadband antenna for a transponder of a radio frequency identification system
EP1826866A1 (en) * 2004-12-14 2007-08-29 Fujitsu Limited Antenna and noncontact tag
DE102006009043A1 (en) * 2006-02-27 2007-09-06 Siemens Ag High frequency antenna device for receiving magnetic resonance signal, has high frequency antenna tuned with resonant frequency by tuning device and with two electrodes which are connected by discrete tuning device
EP1850275A2 (en) * 2006-04-26 2007-10-31 Fujitsu Ltd. Tag-use antenna and tag using the same
EP1895620A1 (en) * 2005-06-16 2008-03-05 Fujitsu Limited Rfid tag antenna and rfid tag
WO2008073218A1 (en) * 2006-12-11 2008-06-19 Massachusetts Institute Of Technology Rf power extracting circuit and related techniques
WO2009025700A1 (en) * 2007-08-22 2009-02-26 Sensormatic Electronics Corporation Rfid antenna for use adjacent to conductive elements
WO2009077312A1 (en) * 2007-12-19 2009-06-25 Continental Automotive Gmbh Multi-part antenna having a circular polarization
EP2212969A1 (en) * 2007-10-11 2010-08-04 3M Innovative Properties Company Rfid tag with a modified dipole antenna
US7948381B2 (en) 2004-04-30 2011-05-24 Binforma Group Limited Liability Company Reversibly deactivating a radio frequency identification data tag
WO2012002998A1 (en) * 2010-07-01 2012-01-05 Sensormatic Electronics, LLC Wide bandwidth hybrid antenna for combination eas and rfid label or tag
US8284111B2 (en) 2007-08-09 2012-10-09 Continental Automotive Gmbh Multipart antenna with circular polarization
US8289163B2 (en) 2007-09-27 2012-10-16 3M Innovative Properties Company Signal line structure for a radio-frequency identification system
EP2845264A1 (en) * 2012-05-01 2015-03-11 Corning Incorporated Discontinuous loop antennas suitable for radio-frequency identification (rfid) tags, and related components, systems, and methods
JP2015092802A (en) * 2013-11-08 2015-05-14 三菱電機株式会社 Rectenna device
AU2013248243B2 (en) * 2007-08-22 2016-04-14 Sensormatic Electronics Llc RFID antenna for use adjacent to conductive elements
JP2016105647A (en) * 2009-04-14 2016-06-09 株式会社村田製作所 Wireless IC device
GB2537345A (en) * 2014-10-03 2016-10-19 Cambridge Consultants Inc Antenna for implant and associated apparatus and methods
US9543654B2 (en) 2014-05-14 2017-01-10 Universal Scientific Industrial (Shanghai) Co., Ltd. NFC antenna
US10062025B2 (en) 2012-03-09 2018-08-28 Neology, Inc. Switchable RFID tag
WO2018197832A1 (en) * 2017-04-28 2018-11-01 Drayson Technologies (Europe) Limited Loop rectenna
CN110768000A (en) * 2019-09-27 2020-02-07 宁波大学 Ultrahigh frequency RFID (radio frequency identification) tag antenna for wirelessly measuring dielectric constant

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3474452A (en) * 1967-02-16 1969-10-21 Electronics Research Inc Omnidirectional circularly polarized antenna
DE2312536A1 (en) * 1973-03-14 1974-10-10 Jun Hans Koell WHOLE-WAVE DIPOLE FOR VHF AND DECIDUAL WAVES
DE3247425A1 (en) * 1982-12-22 1987-01-02 Licentia Gmbh Printed dipol antenna using stripline technology
GB2260065A (en) * 1991-09-25 1993-03-31 Tokimec Inc Detectable device and movable item detecting system
EP0711000A2 (en) * 1994-10-27 1996-05-08 SICAN F&E GmbH ( SIBET) Hybrid antenna and broadband hybrid antenna array
US5526007A (en) * 1992-03-26 1996-06-11 Aisin Seiki Kabushiki Kaisha Wire antenna for circularly polarized wave
US6147606A (en) * 1998-03-26 2000-11-14 Intermec Ip Corp. Apparatus and method for radio frequency transponder with improved read distance
EP1134840A2 (en) * 2000-03-06 2001-09-19 Horst Prof. Dr. Ziegler Antenna

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3474452A (en) * 1967-02-16 1969-10-21 Electronics Research Inc Omnidirectional circularly polarized antenna
DE2312536A1 (en) * 1973-03-14 1974-10-10 Jun Hans Koell WHOLE-WAVE DIPOLE FOR VHF AND DECIDUAL WAVES
DE3247425A1 (en) * 1982-12-22 1987-01-02 Licentia Gmbh Printed dipol antenna using stripline technology
GB2260065A (en) * 1991-09-25 1993-03-31 Tokimec Inc Detectable device and movable item detecting system
US5526007A (en) * 1992-03-26 1996-06-11 Aisin Seiki Kabushiki Kaisha Wire antenna for circularly polarized wave
EP0711000A2 (en) * 1994-10-27 1996-05-08 SICAN F&E GmbH ( SIBET) Hybrid antenna and broadband hybrid antenna array
US6147606A (en) * 1998-03-26 2000-11-14 Intermec Ip Corp. Apparatus and method for radio frequency transponder with improved read distance
EP1134840A2 (en) * 2000-03-06 2001-09-19 Horst Prof. Dr. Ziegler Antenna

Cited By (57)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1341257A4 (en) * 2000-12-08 2004-03-24 Matsushita Electric Ind Co Ltd Antenna apparatus and communication system
US6859174B2 (en) 2000-12-08 2005-02-22 Matsushita Electric Industrial Co., Ltd. Antenna device and communications system
EP1341257A1 (en) * 2000-12-08 2003-09-03 Matsushita Electric Industrial Co., Ltd. Antenna apparatus and communication system
WO2005081018A1 (en) * 2004-02-24 2005-09-01 Tagmaster Ab Transponder for an rfid-system
US7948381B2 (en) 2004-04-30 2011-05-24 Binforma Group Limited Liability Company Reversibly deactivating a radio frequency identification data tag
US7701346B2 (en) 2004-04-30 2010-04-20 Jeffrey Dean Lindsay Deactivating a data tag for user privacy or tamper-evident packaging
US8487769B2 (en) 2004-04-30 2013-07-16 Binforma Group Limited Liability Company Reversibly deactivating a radio frequency identification data tag
US7098794B2 (en) 2004-04-30 2006-08-29 Kimberly-Clark Worldwide, Inc. Deactivating a data tag for user privacy or tamper-evident packaging
US7151455B2 (en) 2004-04-30 2006-12-19 Kimberly-Clark Worldwide, Inc. Activating a data tag by load or orientation or user control
WO2006020529A1 (en) * 2004-08-13 2006-02-23 Sensormatic Electronics Corporation Tunable spiral antenna for security tag
US7262740B2 (en) 2004-08-21 2007-08-28 Samsung Electronics Co., Ltd. Small planar antenna with enhanced bandwidth and small rectenna for RFID and wireless sensor transponder
EP1628360A1 (en) 2004-08-21 2006-02-22 Samsung Electronics Co., Ltd Small planar antenna with enhanced bandwidth and small rectenna for RFID and wireless sensor transponder
US8045947B2 (en) 2004-09-17 2011-10-25 Massachusetts Institute Of Technology RF power extracting circuit and related techniques
EP1826866A1 (en) * 2004-12-14 2007-08-29 Fujitsu Limited Antenna and noncontact tag
EP1826866A4 (en) * 2004-12-14 2007-11-28 Fujitsu Ltd Antenna and noncontact tag
US7570225B2 (en) 2004-12-14 2009-08-04 Fujitsu Limited Antenna and non-contact tag
EP1895620A1 (en) * 2005-06-16 2008-03-05 Fujitsu Limited Rfid tag antenna and rfid tag
EP1895620A4 (en) * 2005-06-16 2009-07-01 Fujitsu Ltd Rfid tag antenna and rfid tag
CN101233532B (en) * 2005-08-02 2011-04-06 Nxp股份有限公司 Antenna structure, transponder and method of manufacturing an antenna structure
WO2007015205A1 (en) 2005-08-02 2007-02-08 Nxp B.V. Antenna structure, transponder and method of manufacturing an antenna structure
US7663567B2 (en) 2005-08-02 2010-02-16 Nxp B.V. Antenna structure, transponder and method of manufacturing an antenna structure
US7750862B2 (en) 2005-11-10 2010-07-06 Nxp B.V. Broadband antenna for a transponder of a radio frequency identification system
WO2007054900A2 (en) 2005-11-10 2007-05-18 Nxp B.V. Broadband antenna for a transponder of a radio frequency identification system
WO2007054900A3 (en) * 2005-11-10 2007-08-09 Nxp Bv Broadband antenna for a transponder of a radio frequency identification system
US7385399B2 (en) 2006-02-27 2008-06-10 Siemens Aktiengesellschaft Radio-frequency antenna arrangement for acquisition of a magnetic resonance signal
DE102006009043B4 (en) * 2006-02-27 2008-10-30 Siemens Ag Radio-frequency antenna arrangement for detecting a magnetic resonance signal and magnetic resonance system with such a radio-frequency antenna arrangement
DE102006009043A1 (en) * 2006-02-27 2007-09-06 Siemens Ag High frequency antenna device for receiving magnetic resonance signal, has high frequency antenna tuned with resonant frequency by tuning device and with two electrodes which are connected by discrete tuning device
EP1850275A2 (en) * 2006-04-26 2007-10-31 Fujitsu Ltd. Tag-use antenna and tag using the same
US7928921B2 (en) 2006-04-26 2011-04-19 Fujitsu Limited Tag-use antenna and tag using the same
EP1850275A3 (en) * 2006-04-26 2009-07-22 Fujitsu Ltd. Tag-use antenna and tag using the same
WO2008073218A1 (en) * 2006-12-11 2008-06-19 Massachusetts Institute Of Technology Rf power extracting circuit and related techniques
DE102007037614B4 (en) * 2007-08-09 2014-03-13 Continental Automotive Gmbh Multipart antenna with circular polarization
US8284111B2 (en) 2007-08-09 2012-10-09 Continental Automotive Gmbh Multipart antenna with circular polarization
AU2013248243B2 (en) * 2007-08-22 2016-04-14 Sensormatic Electronics Llc RFID antenna for use adjacent to conductive elements
US8866616B2 (en) 2007-08-22 2014-10-21 Tyco Fire & Security Gmbh RFID tag having antenna with co-planar radiation pattern
WO2009025700A1 (en) * 2007-08-22 2009-02-26 Sensormatic Electronics Corporation Rfid antenna for use adjacent to conductive elements
US8289163B2 (en) 2007-09-27 2012-10-16 3M Innovative Properties Company Signal line structure for a radio-frequency identification system
EP2212969A1 (en) * 2007-10-11 2010-08-04 3M Innovative Properties Company Rfid tag with a modified dipole antenna
US8717244B2 (en) 2007-10-11 2014-05-06 3M Innovative Properties Company RFID tag with a modified dipole antenna
EP2212969A4 (en) * 2007-10-11 2010-12-29 3M Innovative Properties Co Rfid tag with a modified dipole antenna
WO2009077312A1 (en) * 2007-12-19 2009-06-25 Continental Automotive Gmbh Multi-part antenna having a circular polarization
US8803760B2 (en) 2007-12-19 2014-08-12 Continental Automotive Gmbh Multi-part antenna having a circular polarization
JP2016105647A (en) * 2009-04-14 2016-06-09 株式会社村田製作所 Wireless IC device
US8711046B2 (en) 2010-07-01 2014-04-29 Tyco Fire & Security Services GmbH Wide bandwidth hybrid antenna for combination EAS and RFID label or tag
WO2012002998A1 (en) * 2010-07-01 2012-01-05 Sensormatic Electronics, LLC Wide bandwidth hybrid antenna for combination eas and rfid label or tag
US10062025B2 (en) 2012-03-09 2018-08-28 Neology, Inc. Switchable RFID tag
US10878303B2 (en) 2012-03-09 2020-12-29 Neology, Inc. Switchable RFID tag
EP2845264A1 (en) * 2012-05-01 2015-03-11 Corning Incorporated Discontinuous loop antennas suitable for radio-frequency identification (rfid) tags, and related components, systems, and methods
EP2845265A1 (en) * 2012-05-01 2015-03-11 Corning Incorporated Discontinuous loop antennas suitable for radio-frequency identification (rfid) tags, and related components, systems, and methods
JP2015092802A (en) * 2013-11-08 2015-05-14 三菱電機株式会社 Rectenna device
US9543654B2 (en) 2014-05-14 2017-01-10 Universal Scientific Industrial (Shanghai) Co., Ltd. NFC antenna
TWI584525B (en) * 2014-05-14 2017-05-21 Universal Scientific Industrial (Shanghai) Co Ltd Nfc antenna
US10622707B2 (en) 2014-10-03 2020-04-14 Cambridge Consultants Limited Antenna for implant and associated apparatus and methods
GB2537345A (en) * 2014-10-03 2016-10-19 Cambridge Consultants Inc Antenna for implant and associated apparatus and methods
US11670839B2 (en) 2014-10-03 2023-06-06 Cambridge Consultants Limited Antenna for implant and associated apparatus and methods
WO2018197832A1 (en) * 2017-04-28 2018-11-01 Drayson Technologies (Europe) Limited Loop rectenna
CN110768000A (en) * 2019-09-27 2020-02-07 宁波大学 Ultrahigh frequency RFID (radio frequency identification) tag antenna for wirelessly measuring dielectric constant

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