WO2000026993A1 - Marqueur de radiofrequences a transfert de puissance optimale - Google Patents

Marqueur de radiofrequences a transfert de puissance optimale Download PDF

Info

Publication number
WO2000026993A1
WO2000026993A1 PCT/US1998/023121 US9823121W WO0026993A1 WO 2000026993 A1 WO2000026993 A1 WO 2000026993A1 US 9823121 W US9823121 W US 9823121W WO 0026993 A1 WO0026993 A1 WO 0026993A1
Authority
WO
WIPO (PCT)
Prior art keywords
antenna
stub
tag
length
loading
Prior art date
Application number
PCT/US1998/023121
Other languages
English (en)
Inventor
Michael John Brady
Dah-Weih Duan
Daniel J. Friedman
Harley Kent Heinrich
Venkata S. Rao Kodakula
Original Assignee
Intermec Ip Corp.
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 Intermec Ip Corp. filed Critical Intermec Ip Corp.
Priority to PCT/US1998/023121 priority Critical patent/WO2000026993A1/fr
Priority to US09/423,063 priority patent/US6285342B1/en
Publication of WO2000026993A1 publication Critical patent/WO2000026993A1/fr

Links

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
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/0701—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips at least one of the integrated circuit chips comprising an arrangement for power management
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/077—Constructional details, e.g. mounting of circuits in the carrier
    • G06K19/07749—Constructional details, e.g. mounting of circuits in the carrier the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/077—Constructional details, e.g. mounting of circuits in the carrier
    • G06K19/07749—Constructional details, e.g. mounting of circuits in the carrier the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
    • G06K19/07773—Antenna details
    • G06K19/07786—Antenna details the antenna being of the HF type, such as a dipole
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
    • H01Q1/38—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith formed by a conductive layer on an insulating support
    • 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
    • H01Q19/22—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 using a secondary device in the form of a single substantially straight conductive element
    • 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
    • H01Q19/22—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 using a secondary device in the form of a single substantially straight conductive element
    • H01Q19/24—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 using a secondary device in the form of a single substantially straight conductive element the primary active element being centre-fed and substantially straight, e.g. H-antenna
    • 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
    • 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
    • H01Q9/28—Conical, cylindrical, cage, strip, gauze, or like elements having an extended radiating surface; Elements comprising two conical surfaces having collinear axes and adjacent apices and fed by two-conductor transmission lines

Definitions

  • This invention relates to the field of antenna design. More specifically, the invention relates to
  • antenna is used in radio frequency tags.
  • Figure 1 is a graph of the output voltage of a typical antenna and front end circuit.
  • the antenna produces a voltage when excited by an electromagnetic
  • This voltage is commonly called the open-circuit voltage across the antenna terminals.
  • IF intermediate frequency
  • DC direct current
  • Front end and antenna combinations have various designs depending on the application
  • Figure I shows the voltage output of a front end
  • This voltage output has
  • the antenna/front end combination is designed to disturb an electromagnetic field as little as possible.
  • a field sensor measures the strength of
  • the front end is tuned so that it is out of resonance with the antenna.
  • antenna is loaded with a mismatched load (front end) that limits how much the electromagnetic
  • antennas operate over the bandwidth 120 to receive/transmit
  • the bandwidth 120 of the antenna is
  • the front end is designed to resonate with the antenna over the operation
  • the front end is variably tunable over a plurality
  • RFID radio frequency identification
  • a front end output voltage that is above a threshold voltage in order to power the RFID circuit.
  • modulated signal envelope
  • the carrier typically are spaced at a large fraction of the resonant wavelength (e.g. 0.4 lambda, the carrier
  • the antenna/front end combination has to produce a minimum
  • antenna/front end combination is not optimal, it will have a limited range (distance) over which
  • the prior art attempts to match the antenna and front end impedances in a variety of ways.
  • the prior art uses impedance matching circuits using discrete components, e.g.,
  • the impedance matching circuit can comprise distributed
  • Chip manufacturing processes are expensive to design and implement.
  • An object of this invention is an improved antenna apparatus.
  • An object of this invention is an improved antenna apparatus, used in combination with
  • a radio frequency front end that can be tuned to produce an optimal voltage output and power
  • An object of this invention is an improved antenna apparatus, used in combination with
  • a radio frequency front end that can be tuned to produce an optimal voltage output and power
  • An object of this invention is an improved antenna apparatus, used in combination with
  • a radio frequency front end that can be tuned to produce an optimal voltage and power transfer
  • This invention is an antenna used as a voltage and power source that is designed to operate with arbitrary load, or front end.
  • the invention is particularly useful where it is difficult
  • the antenna preferably a dipole antenna, has one or more (number of) loading bars that
  • antenna input impedance is changed by adjusting the loading bar length, width, and/or spacing
  • Vp to operate the front end and connected circuitry.
  • the antenna input impedance is reduced to the point at which Vp no longer increases.
  • one or more stubs is added to one or more of the
  • the stubs act as two-conductor transmission line that is terminated either in
  • the short-circuited stub(s) acts as a lumped inductor (capacitor)
  • the guided wavelength has a known relation to the
  • the open-circuited stub(s) acts as a lumped
  • stubs and zero or more open-circuit stubs are added to one or more of the antenna elements to
  • the reactive part of the antenna input impedance is changed to equal the negative
  • the loading bar changes vary the real part of the antenna
  • the length of the antenna can change (increase or
  • the antenna impedance only a minimal amount. Further, adding the stubs changes the reactive
  • the invention essentially decouples the tuning of
  • Figure 1 is a graph showing a prior art representation of the frequency response of a prior
  • Figure 2 is a block diagram of a radio frequency
  • Figure 3 is a block diagram of a preferred antenna
  • FIG. 4 is a block diagram showing one novel structure of the present antenna using
  • Figure 5 comprising Figures 5A - 5D, shows variations of the loading bar structures.
  • Figure 6 is a block diagram showing a short-circuit
  • Figure 6A and an open-circuit stub (Figure 6B) structure.
  • Figure 7 comprising Figures 7A and 7B, shows variations of the stub structures.
  • Figure 8 is a diagram showing preferred dipole antenna with both loading bars and a
  • Figure 9 is a diagram showing an alternative preferred meander dipole with a single
  • Figure 2 is a block diagram showing a system 200 with a transmitter or base station 210
  • Block 210 is any radio frequency transmitter/transponder that is well known in the art.
  • the transmitter includes an RF source 211 and RF amplifier 212 that sends RF power to the
  • the transmitter 210 can also have an optional receiver section 218 for
  • the transmitter 210 transmits an RF signal
  • the transmitter carrier also has a transmitting carrier
  • the transmitting bandwidth will be referred to as a transmitting bandwidth.
  • the transmitting bandwidth will be referred to as a transmitting bandwidth.
  • FIG. 2B is a block diagram of a receiver 230, specifically an RFID tag, comprising the
  • an RF processing section i.e., the front end, 232 and a
  • the antenna 250 and front end 232 make up the antenna/front
  • the front end 232 can be any known front end design used with an antenna. Typically, in RFID applications using passive tags, the front end 232 converts the electromagnetic field
  • the signal processing component 234 of the RFID circuit can be any known RFID
  • Figure 3A is a block diagram showing a preferred front end 332 and the novel antenna
  • the antenna comprises a dipole antenna 340 with one or more optional stubs 350 on one
  • One or more optional loading bars 360 are placed
  • the front end 332 is electrically connected to the antenna 250. In this preferred embodiment
  • the front end 332 comprises diodes Dl, D2, and D3, and capacitors Cp and Cs.
  • the diodes Dl, D2, and D3 have a low series resistance and a low
  • the series resistance is less than 30 ohms and the parasitic capacitance is less than 500 femto farads.
  • these diodes are Schottky diodes that are
  • the capacitors, Cp and Cs, are also known semiconductor processing techniques.
  • the capacitors, Cp and Cs, are also known semiconductor processing techniques.
  • the capacitors, Cp and Cs, are also known semiconductor processing techniques.
  • Cs can be discrete devices.
  • Diodes Dl and D2 and capacitor Cp form a voltage doubler circuit that rectifies the
  • diodes Dl and D2 produce the voltage Vp that is equal to or
  • Voc is the open-circuit voltage produced at the antenna terminals (370A, 370B) from the
  • Voc is an AC voltage whereas Vp is a DC voltage.
  • magnitude of Vp is equal to or less than the peak to peak value of Voc.
  • the capacitor, Cp is large enough to be treated as a short-circuit at the carrier frequency
  • the value of Cp is between 10 pf and
  • Diodes Dl and D3 and capacitor Cs form a second voltage doubler circuit that also
  • a DC voltage, Vs is developed across capacitor Cs.
  • Vs low frequency AC voltage
  • Voc is the open-circuit voltage produced from the electromagnetic field 220.
  • the value of Cs is
  • the carrier 38.4 kiloHertz. More preferably the range of Cs is between 1.5 pf and 10 pf.
  • Figure 3B is a circuit diagram of a circuit 390 that models the combination 260 of the
  • the circuit comprises a voltage, Voc; an antenna
  • loading bar(s) 360 are chosen so that the DC voltage developed in the front end; e.g. Vp and Vs,
  • the optimum voltage is the
  • Vp voltage necessary to power the signal processing component 234 at a given distance from the base station antenna 215 and the optimum power is the maximum possible power
  • the invention further permits the antenna 250 to be designed for
  • the voltage provided to the load, the RFID circuit e.g., either Vp or
  • ; is the voltage multiplying factor, e.g., 2 for a front end with a voltage doubler, 4 for a
  • the voltage VDC is maximum when the imaginary
  • the real part of the antenna impedance, Ra cannot be zero. This is
  • the voltage, Voc is determined by the following:
  • the effective height, heff, is uniquely determined by the
  • the loading bar 360 is added to the dipole 340 to reduce
  • one or more loading bars 360 are provided.
  • Ra is reduced from about 73 ohms to about 15
  • Ra is further reduced to less than 10 ohms.
  • Voc The minimum voltage, is determined by the requirements to operate the arbitrarily
  • Voc is the product of heff and Ei, heff must be maintained above a minimum level given the Ei
  • Vp must be above 1.5 volts to read data from a Electrically Erasable
  • CMOS complementary metal-oxide-semiconductor
  • the antenna must maintain the respective Voc described above
  • the (optional) back scattering requirement is determined by the distance 240, the
  • R is the maximum detection range (e.g. 240)
  • P miI1 is the minimum power required for the
  • G is the gain of the base station antenna
  • ⁇ is the wavelength of the RF signal 220, and ⁇ is the effective absorbing area of the
  • Ra is in the range between 10 ohms
  • the stub 350 is provided with or without loading bar(s) 360, to adjust the imaginary part (reactance) of the antenna, Xa, to cancel the effect of the
  • the stub 350 adjusts Xa to be
  • the resonant frequency of the antenna also changes and the size of the
  • the reactance of the antenna can be adjusted to
  • the effective height of the antenna 250, heff can be maintained virtually
  • Figure 4 is a block diagram of one preferred embodiment of the present receiving
  • antenna 250 e.g. mounted on a substrate.
  • the substrate can be any known substrate and the
  • antenna any type of conductive material, e.g. metal wires, printed metal on circuit (PC) boards,
  • PC printed metal on circuit
  • Figure 4 shows a dipole antenna 400 with a number 450 of (one or more) loading bars
  • Various geometric properties of the loading bar include: the length of a loading
  • Thickness of the conductive lamination, not shown, is not considered significant for these
  • lamination is a small percentage of the width of the antenna 401 or loading bars 410 and
  • the antenna (250, 400) is shown as a dipolar antenna.
  • the invention is shown as a dipolar antenna.
  • the front end must be designed to provide a DC isolation (e.g.
  • Complements of antennas are those antennas where the conductive portion is replaced by non
  • a number 450, i.e., one or more, loading bars 410 are placed adjacent (within a distance
  • a loading bar 410 is characterized by its length 420, width 430, and the distance 440 to
  • the effect of loading bars 410 is to suppress (reduce) the real part of the antenna input
  • the spacing 440 is between one and five times the width 401 of the
  • the spacing 440 is less than 25% of the wavelength of the
  • operating frequency i.e., the frequency 125 to which the antenna is tuned to resonate.
  • the spacing 440 is less than 10% of this wavelength, and in a still more
  • the spacing 440 is less than 3% of this wavelength. Furthermore, the spacing 440 is less than 3% of this wavelength. Furthermore, the
  • the antenna can be
  • the suppression effect increases as the length 420 increases. (The length 420 here
  • the effective length i.e., the length of the loading bar that is within the spacing distance 440
  • the effect is less significant when the length 420 becomes larger than the length 405 of the antenna 400.
  • the length of loading bars 420 is chosen to be similar to or smaller than
  • antenna 401 will suppress Ra.
  • the real part of the antenna input impedance is suppressed more with a larger
  • 450 are: one or two. The smaller the number 450 of loading bars 410, the less area the antenna
  • the spacing 460 between the loading bars 410 is chosen to
  • this loading bar spacing 460 can be varied to affect the
  • FIG. 5 is a block diagram that shows alternative embodiments of the optional loading
  • the loading bars 410 are adjacent to the antenna 400.
  • Adjacent means that at least some part (i.e., the effective part) of the loading bar is within a
  • Figure 5 A shows loading bars 410 of various shapes. Note that any combination of
  • Loading bar 510 is a non-linear loading bar, e.g. having one or more
  • Loading bar 520 is linear.
  • Loading bar 530 has one or more locations with a varying
  • Loading bar 535 is made of two or more sections that are not electrically connected
  • loading bars can be electrically connected. In some embodiments, this might be done
  • FIG. 5B shows loading bars (510,
  • FIG. 5C shows a loading bar 540 that
  • FIG. 5D shows loading bars with various lengths (420A, B),
  • the loading effect of the loading bars is caused by the accumulated effect of
  • the area is also determined by the number 450 of loading bars.
  • Figure 6A is a block diagram of a closed- or short-circuited tuning stub 600 that is part
  • Figure 6B shows an alternative tuning stub
  • a tuning stub may be treated as a transmission line comprising two transmission-line
  • a tuning stub can be treated as a lumped, reactive
  • the termination 620 could be a short-circuited termination 622, or an
  • ZO is the characteristic impedance of the stub transmission line
  • tan is the tangent trigonometrical function
  • beta is the phase constant of the stub transmission
  • w is the width of the transmission line conductors 614.
  • phase constant of the stub transmission line, beta is determined by
  • lambda_g is the guided wavelength that is related to the medium that surrounds the
  • the guided wavelength can be determined by well known techniques. Pi is
  • the impedance of a stub is given by
  • ZO is the characteristic impedance of the stub transmission line
  • cot is the cotangent trigonometrical function
  • beta is the phase constant of the stub transmission
  • one or more stubs is added to one or more of the antenna elements.
  • stubs act as two-conductor transmission line and are terminated either in a short-circuit or open-
  • the short-circuit stub(s) acts as a lumped inductor (capacitor) when the length of the
  • transmission line is within odd (even) multiples of one quarter guided wavelength of the
  • the open-circuit stub(s) acts a lumped capacitor (inductor) when the length
  • the length of a tuning stub 612 is often constrained to be
  • open-circuited stub is negative according to equation (4), making the stub behave like a
  • the reactance of the tuning stub changes sign when the length of the stub changes
  • the substrate material can be chosen to produce the desired reactance value. (The substrate material changes
  • the tuning stub basically behaves like a lumped circuit element. It may be used to
  • a tuning stub functions independently of the loading bars. While loading bars
  • the tuning stubs mainly change the reactive
  • FIG. 7 shows variations of the use of tuning stubs. Note that the tuning stubs can be
  • Figure 7(a) shows a dipole antenna containing multiple
  • the stubs can have different geometrical parameters, e.g. spacing 116,
  • the stub 710 has a
  • FIG. 7(b) shows tuning stubs on both arms (340A, 340B) of a dipole antenna 250.
  • One or more of the stubs on each of the arms 340 can have different geometrical parameters
  • the stubs can also be placed 720 on opposite sides of either of the arms 340.
  • large loop antenna (e.g., more than one wavelength in length) does have an effect on the
  • FIG. 8 is a block diagram of one preferred embodiment of the antenna 250.
  • this width 801 is the same as the width 801 of the antenna. For 2.44 gigaHertz, this width 801 is chosen to be
  • the first loading bar is spaced from the antenna at a
  • the second loading bar is
  • loading bars are chosen to be equal to that of the antenna mainly for manufacturing
  • the lengths of the loading bars 820 are
  • loading bars 820 affects both the antenna radiation pattern symmetry and Ra, the magnitude of
  • the effect on symmetry is greater than that on Ra.
  • Ra significantly.
  • Ra can be "tuned” by changing the other geometrical parameters of
  • a single stub 880 is placed at a distance 806 from the antenna connection 870. This
  • distance 806 has little effect on the antenna input impedance for most of the length of the
  • the distance 806 is chosen so that the stub is not too close to the end of the
  • antenna impedance will not change significantly with respect to the position of a given stub
  • the stub 880 is located at a 806 within 70 per cent
  • the single stub 880 has a line width 814 that is one half of -the
  • the center-to-center spacing 816 is about the same as the antenna
  • the transmission line length 812 is about 10 percent of the antenna length
  • the termination 820 is a short-circuit which
  • Figure 9 is a diagram showing an alternative preferred embodiment of a meander dipole
  • Meander dipoles have arms that are not straight
  • This embodiment uses a single 950 loading bar
  • the loading bar is placed at a
  • the length of the loading bar 920 is the same as the linear distance 925 spanned by the meander
  • a single stub 980 is located on one of the arms of the meander dipole at a distance 906
  • the transmission line length 912 is chosen, as before, to be about 10
  • the stub width 914 is equal to the line width
  • the stub spacing 916 is equal to twice the line width 901 of the antenna.
  • the termination is a short-circuit so that the stub appears as a lumped inductor. (Note that the
  • An antenna comprising:
  • an antenna section that has one or more elements and one or more antenna terminals
  • the antenna tuned to receive a radio frequency signal having a wavelength, an impedance across
  • the antenna terminals having a real and a reactive part
  • each loading bar having an effective length
  • the antenna distance being less than one quarter of the wavelength
  • any one of the loading bars has any one or more of
  • antenna section and a second placement on a second side of the antenna section.
  • antenna types a dipole, a monopole, a folded dipole, a loop, and a meander dipole.
  • a type antenna of any of the following antenna types a dipole, a monopole, a folded dipole, a loop, and a meander dipole.
  • each of the loading bars has a bar width
  • a antenna comprising:
  • an antenna section that has one or more elements and one or more antenna terminals
  • the antenna tuned to receive a radio frequency signal having a wavelength, an impedance across
  • the antenna terminals having a real and a reactive part
  • each loading bar having an effective length
  • the antenna distance being less than one quarter of the wavelength
  • each of the stubs contributing a reactance to the reactive part.
  • the termination is an open-circuit
  • the stub
  • the termination is a short-circuit
  • the stub
  • the termination is an open-circuit
  • stub contributes an inductance to the impedance.
  • conductor width increases the reactance contributed to the reactive part.
  • element length being the distance from the antenna terminal to the end, and one or more of the
  • stubs is located within 70% of the element length from the antenna terminal.
  • antenna types a dipole, a monopole, a folded dipole, a loop, and a meander dipole.
  • a dipole a monopole, a folded dipole, a loop, and a meander dipole.
  • An antenna comprising:
  • an antenna section means, that has one or more elements and two or more antenna
  • the loading bar having an effective length, the loading bar being within an antenna distance to at least one
  • the antenna distance being less than one
  • a radio frequency tag having an antenna with one or more antenna terminals, the
  • antenna terminals electrically connected to a front end, and the front end electrically connected
  • the antenna further comprising:
  • antenna tuned to receive a radio frequency signal having a wavelength, an impedance across the
  • antenna terminals having a real and a reactive part
  • each loading bar having an effective length
  • the antenna distance being less than one quarter of the wavelength
  • An antenna comprising:
  • an antenna section that has one or more elements and one or more antenna terminals
  • the antenna tuned to receive a radio frequency signal having a wavelength, an impedance across
  • the antenna terminals having a real and a reactive part
  • each of the stubs having two conductors each with a conductor width, a stub length, a stub spacing between the
  • each of the stubs contributing a reactance to the reactive part.
  • the termination is a short-circuit
  • the stub
  • the termination is an open-circuit
  • the stub
  • the termination is a short-circuit
  • the stub
  • the termination is an open-circuit
  • stub contributes an inductance to the impedance.
  • conductor width increases the reactance contributed to the reactive part.
  • element length being the distance from the antenna terminal to the end, and one or more of the
  • stubs is located within 70% of the element length from the antenna terminal.
  • antenna types a dipole, a monopole, a folded dipole, a loop, and a meander dipole.
  • antenna section is a complementary aperture type antenna including any of the following: a dipole, a monopole, a folded dipole, a loop, and
  • An antenna comprising:
  • an antenna section means that has one or more element means and one or more
  • the antenna section means for being tuned to receive a radio frequency
  • each of the stub means for contributing a reactance
  • a radio frequency tag having an antenna with one or more antenna terminals, the
  • antenna terminals the antenna terminals electrically connected to a front end, and the front end
  • the antenna further comprising:
  • the antenna tuned to receive a radio frequency signal having a wavelength
  • each of the stubs contributing a reactance to the reactive part.
  • a tag as in claim 39, where the antenna has a line width and the conductor width is
  • the stub spacing is less than three times the line width
  • stub length is less than one half the guided wavelength.
  • the invention relates to radio frequency identification (RFID) systems and, more particularly, to RFID systems that employ a high gain antenna.
  • RFID radio frequency identification
  • Radio Frequency Identification (RFID) transponders are operated in conjunction with RFID base stations for a variety of inventory-control, security and other purposes.
  • RFID Radio Frequency Identification
  • an item having a tag associated with it for example, a container with a tag placed inside it, is brought into a "read zone" established by the base station.
  • the RFID base station generates a continuous wave electromagnetic disturbance at a carrier frequency. This disturbance is modulated to correspond to data that is to be communicated via the disturbance.
  • the modulated disturbance which carries information and may be sometimes referred to as a signal, communicates this information at a rate, referred to as the data rate, which is lower than the carrier frequency.
  • the transmitted disturbance will be referred to hereinafter as a signal or field.
  • the RFID base station transmits an interrogating RF signal which is modulated by a receiving tag in order to impart information stored within the tag to the signal.
  • the receiving tag then transmits the modulated, answering, RF signal to the base station.
  • RFID tags may be active, containing their own RF transmitter, or passive, having no transmitter.
  • Passive tags i.e., tags that rely upon modulated back-scattering to provide a return link to an interrogating base station, may include their own power sources, such as a batteries, or they may be "field-powered", whereby they obtain their operating power by rectifying an interrogating RF signal that is transmitted by a base station.
  • both types of tag have minimum RF field strength read requirements, or read thresholds, in general, a field-powered passive system requires at least an order of magnitude more power in the interrogating signal than a system that employs tags having their own power sources.
  • the read threshold for a field-powered passive tag is typically substantially higher than for an active tag.
  • field-powered passive tags do not include their own power source, they may be substantially less expensive than active tags and because they have no battery to "run down", field-powered passive tags may be more reliable in the long term than active tags. And, finally, because they do not include a battery, field-powered passive tags are typically much more "environmentally- friendly”.
  • field-powered passive tag RFID systems provide cost, reliability, and environmental benefits, there are obstacles to the efficient operation of field-powered passive tag RFID systems.
  • it is often difficult to deliver sufficient power from a base station to a field-powered passive tag via an interrogating signal.
  • the amount of power a base station may impart to a signal is limited by a number of factors, not the least of which is regulation by the Federal Communication Commission (FCC).
  • FCC Federal Communication Commission
  • RFID tags are often affixed to the surface of or placed within, a container composed of RF absorptive material.
  • RFID tags should typically include a resonant antenna.
  • conventional RFID tags include resonant antennas, such as resonant dipole antennas, that require more space than "form factor" driven application will permit.
  • Garment tagging is one application in which the tag, in order not to interfere with marketing or to avoid damaging the garments, should be made as small as practicable: essentially invisible to a potential customer.
  • Many other applications, including, parcel tagging and keychain tags also require compact tags. All these potential application areas require the use of a low cost tag that can be interrogated from a distance.
  • Field powered tags are particularly susceptible to variations ins an interrogating signal's field strength. That is, field powered RFID tags are generally designed to operate at as great a distance as possible. Providing a relatively long read range is a significant advantage for an RFID tag system. RFID tags are therefore generally designed to operate at from a long distance. When operating at a great distance, the tags will dissipate very little energy, employing only miniscule currents to operate. Somewhat ironically, when an attempt is made to operate such a tag in close proximity to a base station, the significantly increased current levels which result from the much stronger field strength of the interrogating signal can cause an RFID tag to malfunction.
  • An RFID tag integrated circuit may, for example, include clock and data recovery circuitry. If the IC's bias supply varies due variations in the field strength of the interrogating signal, the clock circuitry, and other circuitry may be disrupted in a manner that causes the tag to be misread.
  • a low cost RFID tag that provides relatively high performance, that is, relatively long read/write distances and stable operation in close proximity to a base station, and can be made essentially "invisible" for applications such as garment tagging, keychain tags, parcel tags, etc., would therefore be highly desirable.
  • Patents assigned to the assignee of the present invention include 5,528,222; 5,550,547; 5,552,778; 5,554,974; 5,538,803; 5,563,583; 5,565,847; 5,606,323 5,521,601; 5,635,693; 5,673,037; 5,682,143; 5,680,106; 5,729,201; 5,729,697; 5,736,929 5,739,754; and 5,767,789.
  • Patent applications assigned to the assignee of the present invention include: application USP 5,673,037; No. 08/621,784, filed on March 25, 1996 entitled, "Thin Radio Frequency Transponder with Leadframe Antenna Structure" by Brady et al.
  • a radio-frequency identification (RFID) transponder (tag) in accordance with the principles of the invention includes a resonant wire antenna that is confined to an area which has no dimension long enough to accommodate a resonant antenna.
  • the antenna is coupled to RFID circuitry which, in the illustrative embodiment, is implemented as an RFID tag integrated circuit (IC).
  • IC RFID tag integrated circuit
  • the tag IC and the antenna are mounted on the same side of a substrate.
  • the arms of the antenna are contorted in one way or another in order to fit the antenna into the limited available space on the substrate.
  • the new RFID tag antenna is formed in a manner that increases its electrical length to the point that it is a half wavelength resonant antenna, in spite size restrictions imposed by the RFID tag.
  • the antenna may be implemented as a "bent dipole” antenna, with the tag IC attached so that the lengths of the two antenna arms on either side of the chip are identical in length or, optionally, with arms having different lengths.
  • antenna configurations include: a Z shaped antenna, whereby the ends of a dipole are "bent” to fit within the tag area, a meander dipole, whereby sections of a dipole antenna are bent to fit within the tag area, and a meander dipole with bent sections of non-uniform length, spiral type loops, a "squeezed dipole", whereby the dipole arms are formed by "squeezing" a loop antenna.
  • An antenna that is a combination of "straight dipole” and meander antenna may be employed, as well as other combinations of the above antenna configurations, with or without loading bars or stubs, to create resonant antennas within the relatively confined space provided by a miniature RFID tag.
  • a ground plane may be added to the opposite side of the substrate in order to enhance the gain of the antenna and to make the tags applicable to metallic surfaces.
  • a plurality of antennas may also be combined on the tag to provide wider operational bandwidths.
  • the new RFID tag may also include a stabilized reference, which enhances the operation of a field-powered RFID tag.
  • FIG. 10 is a conceptual block diagram of an RFID system in accordance with the principles of the invention.
  • FIG 11 is a top plan view of an exemplary RFID tag which employs RFID tag circuitry in the form of an RFID tag integrated circuit (IC) connected to a meander antenna;
  • IC RFID tag integrated circuit
  • Figure 12 is a top plan view of an illustrative embodiment of an RFID tag that employs a combination of a straight dipole and meander antennas
  • Figure 13 is a top plan view of an illustrative embodiment of an RFID tag that includes a non-uniform meander antenna
  • Figure 14 is a top plan view of an illustrative embodiment of an RFID tag that employs a bent dipole antenna
  • Figure 15 is a top plan view of an illustrative embodiment of an RFID tag that employs spiral antennas
  • Figure 16 is a top plan view of an illustrative embodiment of an RFID tag that employs a "z-shaped" antenna;
  • Figure 17 is a top plan view of an illustrative embodiment of an RFID tag that employs an antenna which is a combination of spiral and non-uniform meander antennas;
  • Figure 18 is a top plan view of an illustrative embodiment of an RFID tag that employs an antenna that is a combination of a non-uniform meander and pinched dipole antennas;
  • Figure 19 is a top plan view of an illustrative embodiment of an RFID tag that employs a pinched dipole antenna.
  • Figure 20 is a top plan view of an illustrative embodiment of an RFID tag that employs bent meander antenna.
  • An RFID system in accordance with the principles of the present invention is illustrated in the conceptual block diagram of Fig. 10.
  • An RF base station 1000 includes an RF transmitter 1002, an RF receiver 1004, and an antenna 1006 connected to the transmitter 1002 and receiver 1004.
  • An RF tag 1016 such as may be used in conjunction with the base station 1000 includes an RF front end 1010, a signal processing section 1012, and a spiral antenna 1014 which provides high gain, low axial ratio, high directivity operation over a relatively wide frequency band.
  • the base station 1000 interrogates the tag 1016 by generating an RF signal having a carrier frequency F c .
  • the carrier frequency F c is chosen based on a number of factors known in the art, including the amount power permitted at that frequency by FCC regulations.
  • the RF signal is coupled to the antenna 1006 and transmitted to the tag 1016.
  • the tag may be employed in a number of applications, but is particularly suited to industrial or warehousing applications in which the tag may be mounted within a plastic container that is, in turn, mounted on or within a pallet.
  • the container associated with the tag 1016 is typically moved into a "read zone" within which it is intended that the RF tag will be successfully interrogated.
  • the RF signal emitted by the antenna 1006, will, ostensibly, be received by the tag antenna 1014 and, if the RF signal's field strength meets a read threshold requirement, the RF tag will respond to the reception of the signal by modulating the RF carrier to impart information about the associated container onto the back-scattered RF field, which propagates to the base station 1000.
  • the RF signal transmitted by the base station 1000 must have sufficient field strength, taking into account the polarization of the signal and of the tag's antenna, at the location of the tag 1016 for the tag to detect the RF signal.
  • the intenogating signal's field strength generally must be great enough for the tag 1016 to rectify the signal and to use the signal's energy for the tag's power source.
  • the RFID tag 1100 includes an RFID integrated circuit (IC) 1102 that is affixed in a conventional manner to a substrate 1104.
  • a meander antenna 1106 which, as discussed in the parent case, may employ one or more loading bars, such as loading bar 1108 and/or one or more tuning stubs, such as the tuning stub 1110, to tune the IC/antenna to resonance at a preferred operational wavelength is connected to antenna terminals on the tag IC 1102.
  • the illustrated meanders are rectangular, the meanders may be of any of a variety of shapes, including sinusoidal, clipped rectangular, and triangular.
  • tuning stubs such as tuning stub 1110 may be placed in any of a wide variety of locations along the antenna 1106 and in any of a wide variety of orientations.
  • the use of an antenna 1106, such as a meander antenna, rather than a straight dipole antenna, permits the antenna 1106 to be of a length which supports resonant operation. Consequently, the tag may be successfully read at a greater distance, sometimes as much as an order of magnitude greater, than a tag using a non- resonant antenna. If, for example, the RFID system employs a carrier frequency of 915 MHz, the corresponding signal wavelength would be approximately 32 cm and the half wavelength needed for resonant operation would be approximately 16 cm.
  • the electrical length of the antenna should equal half the wavelength of the carrier frequency: 16 cm in this example. If the longest dimension of the tag 1100, the diameter of the tag in this exemplary embodiment, is less than 16 cm, the meander configuration permits the inclusion of an antenna that has a total length equal to half a wavelength. For example, if the diameter of the tag 1100 is 100 mm and a meander antenna having an average of 10 mm per meander is employed, sixteen meanders, may be employed to provide the necessary antenna length.
  • a half wavelength of approximately 6 cm corresponds to a carrier frequency of 2.45 GHz and six meanders of 10 mm each would provide the length necessary for a resonant antenna at 2.45 GHz.
  • the meanders are placed too closely to one another, the antenna's performance will be severely degraded.
  • the minimal meander required to provide the a half wavelength antenna may be employed.
  • the combination straight dipole/meander antenna of Figure 12 provides the necessary antenna length without any unnecessary meander.
  • the meander sections may be placed relatively close to the tag IC 1102, or may be moved further toward the perimeter of the tag 1200. The degree to which the antenna's length is devoted to straight dipole section and to meander sections may vary according to the intended application.
  • a tag IC 1300 illustrated in the top plan view of Figure 13 includes a non-uniform meander antenna 1302.
  • the non-uniform meander antenna 1302 may employ one or more lading bars, such as loading bar 1108, and/or one or more tuning stubs, such as tuning stub 1110 illustrated in Figure 11.
  • the non-uniform meander antenna 1302 permit resonant operation in the relatively confined space of a small RFID tag 1300.
  • the non-uniform meander may better utilize the available space on a surface of the tag 1300, thereby permitting the use of a smaller tag at a given carrier frequency.
  • the RFID tag 1400 of Figure 14 employs a "bent dipole" antenna 1402.
  • the bent dipole avoids the interference problems associated with the meander antennas of previous figures yet provides the necessary antenna length to meet the desired half wavelength threshold.
  • a bent dipole antenna 1402 may be employed with a tag that that provides more room than a tag such as might employ the meander or non-uniform meander tags previously described.
  • a loading bar 1404 and tuning stub 1406 are also employed in this illustrative embodiment to match the impedances of the tag IC 1102 and the antenna 1402.
  • a tag 1500 illustrated in the top plan view of Figure 15 employs a spiral antenna 1502, which may be an Archimedes spiral, for example.
  • the spiral type antenna provides flexibility in matching the impedances of the antenna and tag IC, as well as providing flexibility in obtaining circular polarization, when desired.
  • the antenna 1502 provides sufficient antenna length in the confined space available from an RFID tag 1500.
  • a somewhat Z-shaped antenna 1602 is employed by an RFID tag 1600 of Figure 16 to provide sufficient antenna length in a confined space.
  • the antenna 1700 is a combination of the non-uniform meander and spiral antennas described above and the antenna 1802 of figure 18 is a combination of a "pinched dipole" antenna and a non-uniform meander antenna.
  • the RFID tag 1900 of Figure 19 employs a pinched dipole antenna 1902 and the RFID tag 2000 of Figure 20 employs a bent meander antenna 2002.
  • any of the antenna configurations discussed above may be used in cooperation with a ground plane located on the opposite side of the substrate 1104.
  • a plurality of antennas may be combined on the same substrate to provide circular or dual linear antennas with wider bandwidths than a single antenna may be able to provide.
  • the wire antennas may be replace by their slot counterparts, whereby the wire is replaced by a slot in a conductive surface, such as a metallized surface. In such a case, the slot may be "backed up" by a ground plane or cavity for improved gain and bandwidth performance.

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  • Engineering & Computer Science (AREA)
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  • Microelectronics & Electronic Packaging (AREA)
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  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Variable-Direction Aerials And Aerial Arrays (AREA)

Abstract

L'invention concerne une antenne utilisée en tant que source de tension et de puissance, conçue pour fonctionner avec une charge arbitraire ou un circuit frontal. Ladite antenne comporte une ou plusieurs barres de charge (950) qui sont placées à côté d'éléments (400) de l'antenne, avec un certain écartement (940). La partie réelle de l'impédance d'entrée de l'antenne est modifiée par réglage de la longueur (920) de la largeur et/ou de l'écartement (940) des barres de charge (950) et/ou du nombre de celles-ci. Ces modifications sont effectuées pour réduire la partie réelle de l'impédance d'entrée de l'antenne de façon qu'elle soit suffisamment petite pour développer une tension adéquate, Vp, destinée à faire fonctionner le circuit frontal et les autres circuits connectés. Un ou plusieurs tronçons (980) sont ajoutés à au moins un des éléments d'antenne. Ces tronçons (980) jouent le rôle d'une ligne de transmission à deux conducteurs et se terminent soit par un court-circuit ou par un circuit ouvert.
PCT/US1998/023121 1998-10-30 1998-10-30 Marqueur de radiofrequences a transfert de puissance optimale WO2000026993A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/US1998/023121 WO2000026993A1 (fr) 1998-10-30 1998-10-30 Marqueur de radiofrequences a transfert de puissance optimale
US09/423,063 US6285342B1 (en) 1998-10-30 1999-10-29 Radio frequency tag with miniaturized resonant antenna

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Cited By (13)

* Cited by examiner, † Cited by third party
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EP1168237A2 (fr) * 2000-06-19 2002-01-02 Supersensor (Proprietary) Limited Transpondeur à large bande et grande impédance pour système d'identification électronique
US6784813B2 (en) 2001-02-12 2004-08-31 Matrics, Inc. Method, system, and apparatus for remote data calibration of a RFID tag population
EP1522950A2 (fr) * 2003-10-08 2005-04-13 Toshiba Tec Kabushiki Kaisha Module d'étiquette à radiofréquence, article avec un module d'étiquette à radiofréquence et lecteur correspondant
US6999028B2 (en) * 2003-12-23 2006-02-14 3M Innovative Properties Company Ultra high frequency radio frequency identification tag
WO2006050411A1 (fr) * 2004-11-02 2006-05-11 Sensormatic Electronics Corporation Antenne microruban rfid en champ proche en forme de serpentin
WO2007000461A1 (fr) * 2005-06-27 2007-01-04 Etilux S.A. Ensemble d'un support metallique et d'un dispositif emetteur-recepteur.
EP1455644A4 (fr) * 2001-09-10 2007-05-02 Univ Pittsburgh Appareil permettant la mise sous tension d'une station a distance et procede associe
WO2009011599A1 (fr) * 2007-07-18 2009-01-22 Times-7 Holdings Limited Marqueur rfid
US7847697B2 (en) 2008-02-14 2010-12-07 3M Innovative Properties Company Radio frequency identification (RFID) tag including a three-dimensional loop antenna
US8289163B2 (en) 2007-09-27 2012-10-16 3M Innovative Properties Company Signal line structure for a radio-frequency identification system
US8717244B2 (en) 2007-10-11 2014-05-06 3M Innovative Properties Company RFID tag with a modified dipole antenna
JP2016105647A (ja) * 2009-04-14 2016-06-09 株式会社村田製作所 無線ｉｃデバイス
WO2020100402A1 (fr) * 2018-11-12 2020-05-22 Ｎｅｃプラットフォームズ株式会社 Antenne, dispositif de communication sans fil et procédé de formation d'antenne

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US3689929A (en) * 1970-11-23 1972-09-05 Howard B Moody Antenna structure
US4987424A (en) * 1986-11-07 1991-01-22 Yagi Antenna Co., Ltd. Film antenna apparatus

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US3689929A (en) * 1970-11-23 1972-09-05 Howard B Moody Antenna structure
US4987424A (en) * 1986-11-07 1991-01-22 Yagi Antenna Co., Ltd. Film antenna apparatus

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1168237A3 (fr) * 2000-06-19 2003-02-05 Supersensor (Proprietary) Limited Transpondeur à large bande et grande impédance pour système d'identification électronique
EP1686511A3 (fr) * 2000-06-19 2008-09-03 ZIH Corp. Largeur de bande passante, transpondeur d'impédance d'identification du système électronique élevée
US6891466B2 (en) 2000-06-19 2005-05-10 Christopher Gordon Gervase Turner Broad bandwidth, high impedance transponder for electronic identification system
EP1168237A2 (fr) * 2000-06-19 2002-01-02 Supersensor (Proprietary) Limited Transpondeur à large bande et grande impédance pour système d'identification électronique
US7057511B2 (en) 2001-02-12 2006-06-06 Symbol Technologies, Inc. Method, system, and apparatus for communicating with a RFID tag population
US6784813B2 (en) 2001-02-12 2004-08-31 Matrics, Inc. Method, system, and apparatus for remote data calibration of a RFID tag population
US6956509B2 (en) 2001-02-12 2005-10-18 Symbol Technologies, Inc. Method, system, and apparatus for remote data calibration of a RFID tag population
US7075436B2 (en) 2001-02-12 2006-07-11 Symbol Technologies, Inc. Method, system, and apparatus for binary traversal of a tag population
EP1455644A4 (fr) * 2001-09-10 2007-05-02 Univ Pittsburgh Appareil permettant la mise sous tension d'une station a distance et procede associe
EP1522950A3 (fr) * 2003-10-08 2005-06-01 Toshiba Tec Kabushiki Kaisha Module d'étiquette à radiofréquence, article avec un module d'étiquette à radiofréquence et lecteur correspondant
EP1522950A2 (fr) * 2003-10-08 2005-04-13 Toshiba Tec Kabushiki Kaisha Module d'étiquette à radiofréquence, article avec un module d'étiquette à radiofréquence et lecteur correspondant
US6999028B2 (en) * 2003-12-23 2006-02-14 3M Innovative Properties Company Ultra high frequency radio frequency identification tag
US7215295B2 (en) 2003-12-23 2007-05-08 3M Innovative Properties Company Ultra high frequency radio frequency identification tag
WO2006050411A1 (fr) * 2004-11-02 2006-05-11 Sensormatic Electronics Corporation Antenne microruban rfid en champ proche en forme de serpentin
WO2007000461A1 (fr) * 2005-06-27 2007-01-04 Etilux S.A. Ensemble d'un support metallique et d'un dispositif emetteur-recepteur.
WO2009011599A1 (fr) * 2007-07-18 2009-01-22 Times-7 Holdings Limited Marqueur rfid
US8289163B2 (en) 2007-09-27 2012-10-16 3M Innovative Properties Company Signal line structure for a radio-frequency identification system
US8717244B2 (en) 2007-10-11 2014-05-06 3M Innovative Properties Company RFID tag with a modified dipole antenna
US7982616B2 (en) 2008-02-14 2011-07-19 3M Innovative Properties Company Radio frequency identification (RFID) tag including a three-dimensional loop antenna
US7847697B2 (en) 2008-02-14 2010-12-07 3M Innovative Properties Company Radio frequency identification (RFID) tag including a three-dimensional loop antenna
JP2016105647A (ja) * 2009-04-14 2016-06-09 株式会社村田製作所 無線ｉｃデバイス
WO2020100402A1 (fr) * 2018-11-12 2020-05-22 Ｎｅｃプラットフォームズ株式会社 Antenne, dispositif de communication sans fil et procédé de formation d'antenne
JPWO2020100402A1 (ja) * 2018-11-12 2021-09-24 Ｎｅｃプラットフォームズ株式会社 アンテナ、無線通信機器およびアンテナ形成方法
JP7193169B2 (ja) 2018-11-12 2022-12-20 Ｎｅｃプラットフォームズ株式会社 アンテナ、無線通信機器およびアンテナ形成方法
US11876309B2 (en) 2018-11-12 2024-01-16 Nec Platforms, Ltd. Antenna, wireless communication device, and antenna forming method

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