JP2011217203A - Planar loop antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar loop antenna which can be configured in a small size and at low cost and is operated in a plurality of frequency bands as an antenna of an apparatus related to RFID for instance.SOLUTION: The planar loop antenna includes: a dielectric substrate; a first loop conductor 14 which is formed on one surface of the dielectric substrate and has a gap at a part; a second loop conductor 24 which is formed on the other surface of the dielectric substrate, has a gap at a part and is conducted with the first loop conductor; a reflector 20 which is arranged a predetermined distance away from the dielectric substrate and performs unbalanced feeding at a first frequency with the first loop conductor; and a coil-like conductor 34 which is arranged between the first loop conductor and the second loop conductor within the dielectric substrate, is operated in the frequency band different from the first frequency and performs transmission by an electromagnetic induction system.

Description

  The present invention relates to a planar loop antenna that can be configured in a small size and at low cost and that operates in a plurality of frequency bands, for example, as an antenna of an RFID-related device.

  In recent years, technologies using non-contact IC cards, wireless IC tags, etc. have been actively used. For example, as security applications, they are increasingly used in entrance / exit management, office security management, etc. Applications of built-in RFID reader / writer devices are expanding.

  Known antennas for RFID reader / writer devices include a 13.56 MHz HF band print loop coil, a 950 MHz band resonant dipole antenna, and a 2.45 GHz patch antenna.

  Conventionally, it has been used as a separate device for each band, but a reader / writer device that integrates these devices is indispensable, so it can operate in multiple frequency bands, and is small and inexpensive. The practical application of an integrated planar antenna is desired.

  By the way, as a conventional planar loop antenna, for example, antennas described in Patent Documents 1 to 3 are known.

  In the one described in Patent Document 1, in a circularly polarized loop antenna, a ground plate and a loop conductor are opposed to each other with a dielectric interposed therebetween, and an L-shape extending from a predetermined position of the loop conductor to a loop within a predetermined distance. An element is provided, the central conductor of the feeding coaxial line is connected to the L-shaped element, and the external conductor is connected to the ground plate.

  In the one described in Patent Document 2, in a circularly polarized loop antenna, a grounding plate and a loop conductor are opposed to each other with a dielectric sandwiched between them, close to the loop conductor on the inner side of the loop conductor, and not to the loop conductor. A contact feeding portion conductor pattern is provided, the central conductor of the feeding coaxial line is connected to the feeding portion conductor pattern, and the external conductor is connected to the ground plate.

  In the thing of patent document 3, the 2nd loop element by which the 2nd linear part was loaded was formed in the front side of the 2nd dielectric material by which the back side became the ground conductor, and it was spaced apart above the 2nd loop element. The first dielectric is disposed, and a first loop element loaded with the first straight portion is formed on the front side of the first dielectric, and the central conductor of the feeding coaxial line is connected to the second straight portion and the first straight line. And connecting the outer conductor of the coaxial line for power feeding to the ground conductor, and by making the loop lengths of the first loop element and the second loop element different from each other, the bandwidth is increased.

JP-A-2-214304 Japanese Patent Laid-Open No. 5-110334 JP-A-7-183721

  However, the antennas described in Patent Documents 1 and 2 are antennas that operate at one frequency, and those described in Patent Document 3 are antennas that operate at two frequencies. There is a problem that it cannot be done.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a planar loop antenna that can be configured to be small and inexpensive, and that can also perform transmission using an electromagnetic induction method.

In order to achieve the above object, a planar loop antenna according to the invention of claim 1 comprises:
A dielectric substrate;
A first loop conductor formed on one surface of the dielectric substrate and partially having a gap;
A second loop conductor formed on the other surface of the dielectric substrate, having a gap in part and conducting with the first loop conductor;
A reflector disposed at a predetermined distance from the dielectric substrate and being unbalanced at a first frequency with the first loop conductor;
A coiled conductor disposed between a first loop conductor and a second loop conductor in a dielectric substrate, operating in a frequency band different from the first frequency and performing transmission by an electromagnetic induction method;
It is characterized by comprising.

  According to a second aspect of the present invention, in the planar loop antenna according to the first aspect, a first feeding conductor extends from a predetermined portion of the first loop conductor toward the inside of the loop. A center conductor of a first feeding coaxial line is connected, and an outer conductor of the first feeding coaxial line is connected to the reflection plate.

  According to a third aspect of the present invention, in the planar loop antenna according to the first aspect, a first power supply conductor is provided in parallel with the first loop conductor, and the first power supply conductor is a central conductor of the first power supply coaxial line. Is connected to the reflector, and an outer conductor of a first feeding coaxial line is connected to the reflector, and power is fed from the first feeding conductor to the first loop conductor by electromagnetic coupling.

  According to a fourth aspect of the present invention, in the planar loop antenna according to the first aspect, the first feeding conductor extends from a predetermined portion of the first loop conductor toward the inside of the loop, and from the predetermined portion of the second loop conductor. A second power supply conductor extends toward the inside of the loop, and the first loop conductor and the second loop conductor are opposed to each other in the same configuration, and the first power supply conductor and the second power supply are opposed to each other. The conductor is disposed so as not to be opposed to the first conductor and the center conductor of the first feeder coaxial line is connected to one of the first feeder and the second feeder conductor, and the first feeder is connected to the reflector. The outer conductor of the coaxial line for use is connected and has a circular polarization characteristic at the first frequency.

  According to a fifth aspect of the present invention, in the planar loop antenna according to the first aspect, the first loop conductor and the second loop conductor are opposed to each other in the same configuration, and the first loop conductor and the second loop conductor A first power supply conductor and a second power supply conductor are provided in parallel to the two loop conductors, and the first power supply conductor and the second power supply conductor are located at different positions with respect to the first loop conductor and the second loop conductor. The center conductor of the first feeding coaxial line is connected to one of the first feeding conductor and the second feeding conductor, and the outer conductor of the first feeding coaxial line is connected to the reflector. The first loop conductor and the second loop conductor are fed by electromagnetic coupling and have circular polarization characteristics at the first frequency.

  A sixth aspect of the present invention is the planar loop antenna according to any one of the first to third aspects, wherein the second loop conductor has a frequency different from the first frequency between the second loop conductor and the reflector. An unbalanced power supply at a frequency is performed.

  According to a seventh aspect of the present invention, in the planar loop antenna according to the sixth aspect, a second feeding conductor extends from a predetermined portion of the second loop conductor into the loop, and the second feeding conductor is supplied to the second feeding conductor. A central conductor of the coaxial line for connection is connected, and an outer conductor of the second coaxial line for power feeding is connected to the reflecting plate.

  According to an eighth aspect of the present invention, in the planar loop antenna according to the sixth aspect, a second feeding conductor is provided in parallel to the second loop conductor, and the central conductor of the second feeding coaxial line is provided on the second feeding conductor. Is connected, and an outer conductor of a second power feeding coaxial line is connected to the reflector, and power is fed from the second power feeding conductor to the second loop conductor by electromagnetic coupling.

  According to the present invention, it is possible to realize a small and inexpensive antenna that can operate at two or more frequencies. By sandwiching the coiled conductor between the first loop conductor and the second loop conductor, electrostatic shielding can be performed on the electromagnetic induction type coiled conductor when the first loop conductor and the second loop conductor are grounded. it can. Therefore, even when the electric power of the coiled conductor is increased, the electric field in the distance can be attenuated, and the influence of the electric field by the coiled conductor on the surroundings can be reduced.

  In addition, the planar loop antenna of the present invention can be used as an antenna for an RFID-related device as an antenna that operates at a frequency of 13.56 MHz, 950 MHz, or a nearby UHF band.

It is a disassembled perspective view of the planar loop antenna which concerns on the basic composition 1 of this invention. 2 is a plan view of basic configuration 1. FIG. 2 is a side view of the basic configuration 1. FIG. It is a simulation result of the VSWR characteristic around 950 MHz when the first frequency is 950 MHz in the basic configuration 1. It is a simulation result of the radiation characteristic of 950 MHz when the 1st frequency is 950 MHz in basic composition 1. It is a disassembled perspective view of the planar loop antenna which concerns on the basic composition 2 of this invention. 5 is a plan view of a basic configuration 2. FIG. 3 is a side view of a basic configuration 2. FIG. 1 is an exploded perspective view of a planar loop antenna according to a first embodiment of the present invention (a dielectric substrate is not shown). It is a bottom view of the dielectric substrate of the planar loop antenna which concerns on 1st Embodiment of this invention. 1 is a side view of a planar loop antenna according to a first embodiment of the present invention. 1 is a block diagram of a planar loop antenna according to a first embodiment of the present invention. It is a side view showing the modification of the planar loop antenna which concerns on 1st Embodiment of this invention. It is the top view of the modification of the planar loop antenna which concerns on 1st Embodiment of this invention, and the top view and side view of the one part component. It is a disassembled perspective view of the planar loop antenna which concerns on 2nd Embodiment of this invention (The dielectric material board is abbreviate | omitting illustration). It is a top view of the dielectric substrate of the planar loop antenna which concerns on 2nd Embodiment of this invention. It is a side view of the planar loop antenna which concerns on 2nd Embodiment of this invention. It is a disassembled perspective view of the planar loop antenna which concerns on 3rd Embodiment of this invention (The dielectric material board is abbreviate | omitting illustration). It is a top view of the dielectric substrate of the planar loop antenna which concerns on 3rd Embodiment of this invention. It is a side view of the planar loop antenna which concerns on 3rd Embodiment of this invention. In 3rd Embodiment, it is a simulation result of the gain and axial ratio of 950 MHz vicinity when a 1st frequency is 950 MHz. In 3rd Embodiment, it is a simulation result of a radiation characteristic when the 1st frequency is set to 950 MHz. It is a disassembled perspective view of the planar loop antenna which concerns on 4th Embodiment of this invention (The dielectric material board is abbreviate | omitting illustration). It is a top view of the dielectric substrate of the planar loop antenna which concerns on 4th Embodiment of this invention. It is a side view of the planar loop antenna which concerns on 4th Embodiment of this invention. In 4th Embodiment, it is a simulation result of the gain and axial ratio of 950 MHz vicinity when a 1st frequency is 950 MHz. In 4th Embodiment, it is a simulation result of a radiation characteristic when the 1st frequency is set to 950 MHz. It is a disassembled perspective view of the planar loop antenna which concerns on 5th Embodiment of this invention (The dielectric material board is abbreviate | omitting illustration). It is a top view of the dielectric substrate of the planar loop antenna which concerns on 5th Embodiment of this invention. It is a side view of the planar loop antenna which concerns on 5th Embodiment of this invention. It is a disassembled perspective view of the planar loop antenna which concerns on 6th Embodiment of this invention (The dielectric material board is abbreviate | omitting illustration). It is a top view of the dielectric substrate of the planar loop antenna which concerns on 6th Embodiment of this invention. It is a side view of the planar loop antenna which concerns on 6th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Basic configuration 1)
1 to 3 show a planar loop antenna according to the basic configuration 1 of the present invention. In the figure, the planar loop antenna 10 has a first loop conductor 14 formed on one surface of a dielectric substrate 12.

  Specifically, the first loop conductor 14 includes a first horizontal side portion 14A (length L1, width W) and a first vertical side portion 14B (length L2, L2) orthogonal to the first horizontal side portion 14A. Width W) and second vertical side portion 14C (length L2, width W), and second horizontal side portion orthogonal to the first vertical side portion 14B and second vertical side portion 14C and parallel to the first horizontal side portion 14A. It consists of a rectangular loop radiating element consisting of 14D (length L1, width W), and is formed by copper foil etching. The aspect ratio of length and width is preferably about 2.0 (1.5 to 2.5).

  A gap 15 (distance d) is formed in the central portion of the second lateral side portion 14D. Therefore, the second lateral side portion 14D includes the first portion 14D1 (length L3, width W) and the second portion. It is further divided into a portion 14D2 (length L4, width W). The length L1 + 2L2 + L3 + L4 corresponds to one wavelength of the wavelength λg in consideration of the wavelength shortening rate due to the dielectric constant of the dielectric substrate 12 with respect to the wavelength λ1 of the first frequency (for example, 950 MHz).

  From the center of the first horizontal side portion 14A, the first power supply conductor 16 (width a, length b) extends toward the inside of the loop (from the first vertical side portion 14B and the second vertical side portion 14C). The distance c1, c2), the free end portion of the first power supply conductor 16 is directed toward the gap 15. However, the lateral position of the gap 15 and the lateral position of the first power supply conductor 16 do not have to be exactly the same. Further, the base end portion of the first power supply conductor 16 is a tapered portion 16a (length g) that becomes narrower toward the first lateral side portion 14A.

  A metal reflector 20 is arranged in parallel to the dielectric substrate 12 so as to be separated from the dielectric substrate 12. This distance h1 is preferably about 0.1λ1.

  The central conductor 22a of the first power supply coaxial line 22 is connected to the vicinity of the free end of the first power supply conductor 16 (distance f from the first lateral side portion 14A), and the outside of the first power supply coaxial line 22 The conductor 22b is connected to the metal reflector 20.

  In the planar loop antenna 10 configured as described above, since the first loop conductor 14 corresponds to one wavelength by performing unbalanced feeding at the first frequency from the feeding coaxial line 22, Linearly polarized radiation can be performed. At this time, impedance matching can be performed by the first power supply conductor 16.

  4 and 5 show simulation results by the FDTD method of the VSWR characteristic and the radiation characteristic of 950 MHz in the vicinity of 950 MHz when the first frequency is 950 MHz (the absolute gain is 3 dBi in the Z-axis direction). Various parameters at this time are as follows: L1 = 104 mm, L2 = 57 mm, L3 = L4 = 48.5 mm, W = 8 mm, gap 15 distance d = 7 mm, a = 12.5 mm, b = 32 mm, c1 = c2 = 44 mm, f = 31.5 mm, g = 2.5, the thickness h of the dielectric substrate 12 is 1.6 mm, and the dielectric constant of the dielectric substrate 12 is 4.3.

  It can be seen from FIG. 4 that the resonance characteristic at 950 MHz is obtained, and the specific bandwidth that is 2 or less of VSWR is 5%. In addition, the resonance frequency can be adjusted by changing various dimensions. For example, by shifting the position (c1, c2) of the first power supply conductor 16 from the center in the lateral direction, the resonance frequency fluctuates higher, and the length (b) of the first power supply conductor 16 and the power supply When the position (f) is shortened, the impedance changes and the resonance frequency fluctuates toward the higher side. Therefore, by setting the dimensions of the first loop conductor 14 to resonate with respect to a frequency lower than the target first frequency, and adjusting the position, length, and feeding position of the first feeding conductor 16, It becomes possible to make the resonance frequency coincide with the target first frequency. The resonance frequency can also be adjusted by adjusting the length L1 of the first lateral side portion 14A, which is the length in the longitudinal direction of the rectangular loop, and the dielectric constant and thickness of the dielectric substrate 12.

  Even if there is no gap 15 in this basic configuration, the influence on the characteristics is small.

  By providing a coil for the HF band (13.56 MHz) in parallel with the first loop conductor 14 described above, a two-frequency antenna can be obtained. In addition, a low-grade dielectric substrate can be used, and the antenna can be made inexpensive and small as a whole.

(Basic configuration 2)
6 to 8 show a planar loop antenna according to the basic configuration 2 of the present invention. In this example, instead of the coaxial power feeding of the basic configuration 1, electromagnetic coupling power feeding is performed, and instead of the first power feeding conductor 16, a first extending from the outside of the loop into the loop in parallel with the first loop conductor 14 is performed. A power supply conductor 17 is provided. A central conductor 22 a of the first power supply coaxial line 22 is connected to the proximal end portion of the first power supply conductor 17, and an outer conductor 22 b of the first power supply coaxial line 22 is connected to the metal reflector 20.

  Such a configuration can also be operated in the same manner as the basic configuration 1 and can radiate linearly polarized waves at the first frequency.

  The impedance changes by changing the width of the first power supply conductor 17. Similar to the basic configuration 1, by adjusting the first power supply conductor 17, it becomes possible to match the target first frequency.

  By providing a coil for the HF band (13.56 MHz) in parallel with the first loop conductor 14 and the first power supply conductor 17 described above, a two-frequency antenna can be obtained.

(First embodiment)
9 to 11 show a planar loop antenna according to the first embodiment of the present invention. In this example, in addition to the planar loop antenna of the basic configuration 1, a second loop conductor 24 is provided on the other surface of the dielectric substrate 12.

  The second loop conductor 24 is also configured in the same manner as the first loop conductor 14, and specifically, the first horizontal side 24A, the first vertical side 24B orthogonal to the first horizontal side 24A, and the second A rectangular foil radiating element comprising a vertical side portion 24C and a second horizontal side portion 24D perpendicular to the first vertical side portion 24B and the second vertical side portion 24C and parallel to the first horizontal side portion 24A. Formed from etching. A gap 25 is formed in the central portion of the second horizontal side portion 24D, and is divided into a first portion 24D1 and a second portion 24D2. The length and width of each part are preferably the same as those of the first loop conductor 14.

  The first loop conductor 14 and the second loop conductor 24 are electrically connected to each other when the first lateral side portion 14A and the first lateral side portion 24A are connected by the connection conductor 28 that penetrates the dielectric substrate 12. Yes.

  Further, between the first loop conductor 14 and the second loop conductor 24 in the dielectric substrate 12, parallel to the first loop conductor 14 and the second loop conductor 24, for the HF band (13.56 MHz). A coiled conductor 34 is embedded.

  In the first embodiment configured as described above, linearly polarized waves at the first frequency can be radiated as in the basic configuration.

  Furthermore, by feeding the coiled conductor 34, transmission by an electromagnetic induction method at 13.56 MHz can be performed.

  The coiled conductor 34 is sandwiched between the first loop conductor 14 and the second loop conductor 24, and when the first loop conductor 14 and the second loop conductor 24 are grounded, the coiled conductor 34 is electrostatically charged. Can be shielded. Therefore, even when the electric power of the coiled conductor 34 is increased, a distant electric field can be attenuated within the radio wave regulation value, and the influence of the electric field on the surroundings can be reduced. The magnetic field generated by the coiled conductor 34 can be generated outside without being attenuated by providing the gaps 15 and 25 in the first loop conductor 14 and the second loop conductor 24.

  Regarding the mutual influences of the radio wave system using the first loop conductor 14 and the electromagnetic induction system using the coiled conductor 34, the coiled conductor 34 operates in a magnetic field, and hence the electric field of the surrounding radio wave system. There is little influence, and there is not much fluctuation of the resonance frequency. On the other hand, the radio wave system is affected by the coiled conductor 34, and the resonance frequency may shift and the radiation pattern may also change. However, as shown in FIG. 12, the grounds of the first frequency transmission / reception circuit 36 connected to the first power supply conductor 16 and the electromagnetic induction transmission / reception circuit 40 connected to the coiled conductor 34 are separately provided. Thus, by insulating the two, it is possible to eliminate the influence on the radiation pattern at the first frequency. For the deviation of the resonance frequency, by adjusting the length of the first loop conductor 14 and the second loop conductor 24, the dielectric constant of the dielectric substrate 12, and the substrate thickness, the resonance frequency becomes the resonance frequency at the first frequency. You can make adjustments.

  Further, as shown in FIGS. 12A and 12B, a transmission spiral coil 42 of 13.56 MHz is provided between the dielectric substrate 12 and the reflection plate 20, and non-contact power feeding is performed to the coiled conductor 34. It is also possible not to affect the antenna. The capacitor C is connected to the coiled conductor 34, and the resonance state (f = 1 / 2π√LC = 13.56 MHz) is established by the inductance L and the capacitor C due to the coiled conductor, whereby 13.56 MHz from the spiral coil 42 is obtained. The transmission induced power is amplified by magnetic resonance and multiplied by Q, and a magnetic field proportional to the current is generated from the coiled conductor 34.

  In this way, by providing the coiled conductor 34 in addition to the basic configuration 1 shown in FIGS. Since the influence of the radiation efficiency due to the dielectric loss is small, the dielectric substrate 12 can be realized with a low grade such as FR-4, and an inexpensive and small antenna can be obtained. And as an RFID-related device that operates at a frequency in the HF band near 13.56 MHz, the frequency in the UHF band near 950 MHz, for example, as a reader side antenna or as an antenna on the tag side or card side by combining with an IC chip Can be used.

(Second Embodiment)
Next, FIGS. 13 to 15 illustrate a planar loop antenna according to a second embodiment of the present invention. In this example, unlike the planar loop antenna of the basic configuration 2, the second loop conductor 24 is provided on the other surface of the dielectric substrate 12, and the dielectric substrate 12A (thickness h2 = thickness = stacked on the dielectric substrate 12) is provided. A first power supply conductor extending in parallel to the first loop conductor 14 and the second loop conductor 24 and from the outside of the loop toward the inside of the loop through a gap of 0.8 mm to 1.6 mm and a dielectric constant the same as those of the dielectric substrate 12. 17 is provided.

  A coiled conductor 34 for the HF band (13.56 MHz) is embedded between the first loop conductor 14 and the second loop conductor 24 in the dielectric substrate 12.

  In the second embodiment configured as described above, linearly polarized waves at the first frequency can be radiated as in the basic configuration.

  Furthermore, by feeding the coiled conductor 34, transmission by an electromagnetic induction method at 13.56 MHz can be performed.

  At this time, the coiled conductor 34 is electrostatically shielded by being sandwiched between the first loop conductor 14 and the second loop conductor 24, so that the same action as in the first embodiment can be achieved.

  In this way, by providing the coiled conductor 34 in addition to the basic configuration 2 shown in FIG. 6, it is possible to obtain a dual-frequency antenna, and the same effects as in the first embodiment can be obtained. Further, the first power supply conductor 17 can be used so as to also supply power to the coiled conductor 34.

(Third embodiment)
Next, FIGS. 16 to 18 illustrate a planar loop antenna according to a third embodiment of the present invention. In this example, the second feeding conductor 26 extends from the first lateral side 24A of the second loop conductor 24 to the planar loop antenna of the first embodiment, and the base end thereof is a tapered portion 26a. It has become.

  As shown in the figure, the first loop conductor 14 and the first power supply conductor 16, and the second loop conductor 24 and the second power supply conductor 26 have substantially the same shape and size on the front side and the back side of the dielectric substrate 12. However, the positions of the first power supply conductor 16 and the second power supply conductor 26 are shifted from the center of the left and right, and as a result, when viewed through the dielectric substrate 12 from above, the first power supply conductor 16 16 and the second feeding conductor 26 are displaced from each other.

  A feeding point is set in the vicinity of the free end of the second feeding conductor 26, and the central conductor 22 a of the feeding coaxial line 22 is connected.

  By shifting the positions of the first power supply conductor 16 and the second power supply conductor 26 to the left and right and providing gaps 15 and 25 in the first loop conductor 14 and the second loop conductor 24, respectively, two phase differences of 90 degrees can be obtained. Resonance frequency characteristics appear and circularly polarized waves at the first frequency can be radiated.

  19 and 20 show the simulation results by the FDTD method of the gain and axial ratio in the vicinity of 950 MHz when the first frequency is 950 MHz and the radiation characteristics when the first frequency is 950 MHz. Various parameters at this time are L1 = 101 mm, L2 = 57 mm, L3 = 48 mm, L4 = 48 mm, W = 8 mm, gap distance d = 5 mm, a = 10 mm, b = 32 mm, c1 = 34 mm, c2 = 34 mm F = 30.5 mm, g = 2.5, the thickness h of the dielectric substrate 12 is 1.6 mm, and the dielectric constant of the dielectric substrate 12 is 3.8. Further, h1 = 0.1λ1.

  A left-handed circular polarization characteristic was obtained at 950 MHz. Moreover, the specific bandwidth which becomes 3 dB or less of the axial ratio was 5.8%.

  Further, when the feeding point is changed from the second feeding conductor 26 to the first feeding conductor 16, a right-handed circularly polarized wave characteristic is obtained and the same characteristic is exhibited.

  In this way, in addition to the effects of the first embodiment, in this embodiment, a dual-frequency antenna can be obtained by a circularly polarized radiation radio wave system and an electromagnetic induction system using a coiled conductor 34. By giving the circular polarization characteristic, it is not necessary to consider the orientation of the planar loop antenna 10 with the object (tag or card).

(Fourth embodiment)
Next, FIGS. 21 to 23 illustrate a planar loop antenna according to a fourth embodiment of the present invention. In this example, a second feeding conductor 27 is further provided on the dielectric substrate 12A with respect to the planar loop antenna of the second embodiment.

  The positions of the first power supply conductor 17 and the second power supply conductor 27 are shifted from the left-right center and symmetrical with respect to the left-right center. As a result, when the dielectric substrate 12 is seen through from above, The first power supply conductor 16 and the second power supply conductor 26 are displaced from each other with respect to the first loop conductor 14 and the second loop conductor 24.

  The central conductor 22 a of the power feeding coaxial line 22 is connected to the vicinity of the base end portion of the first power feeding conductor 17.

  By shifting the positions of the first feeding conductor 17 and the second feeding conductor 27 to the left and right and providing gaps 15 and 25 in the first loop conductor 14 and the second loop conductor 24, respectively, two phase differences of 90 degrees can be obtained. Resonance frequency characteristics appear and circularly polarized waves at the first frequency can be radiated.

  24 and 25 show the simulation result by the FDTD method of the gain and axial ratio around 860 MHz when the first frequency is 860 MHz and the radiation characteristics when the first frequency is 860 MHz. Various parameters at this time are L1 = 104 mm, L2 = 57 mm, L3 = 48 mm, L4 = 48 mm, W = 8 mm, gap distance d = 5 mm, a = 13 mm, b = 32 mm, c1 = 32 mm, c2 = 32 mm , G = 2.5, the thickness h + h2 = 2.4 mm of the dielectric substrates 12 and 12A, and the dielectric constant of the dielectric substrate 12 is 3.4. Further, h1 = 0.1λ1.

  A right-handed circular polarization characteristic was obtained at 860 MHz. Further, the specific bandwidth that is 3 dB or less of the axial ratio was 3%.

  Further, when the feeding point is changed from the first feeding conductor 17 to the second feeding conductor 27, a left-handed circularly polarized wave characteristic is obtained, and the same characteristic is exhibited.

  In this way, in addition to the effects of the second embodiment, in this embodiment, a dual-frequency antenna can be provided that uses a circularly polarized radiation radio wave system and an electromagnetic induction system using a coiled conductor 34. By giving the circular polarization characteristic, it is not necessary to consider the orientation of the planar loop antenna 10 with the object (tag or card).

(Fifth embodiment)
26 to 28 show a planar loop antenna according to a fifth embodiment of the present invention. In this example, the second feeding conductor 26 extends from the first lateral side 24A of the second loop conductor 24 to the planar loop antenna of the first embodiment.

  The central conductor 32 a of the second power supply coaxial line 32 is connected to the vicinity of the free end of the second power supply conductor 26, and the outer conductor 32 b of the second power supply coaxial line 32 is connected to the metal reflector 20.

  Similar to the first power supply conductor 16, the resonance frequency can be changed by adjusting the parameters of the position, length, and power supply position of the second power supply conductor 26. The parameters of the second power supply conductor 26 are set so that the second power supply conductor 26 resonates at a second frequency (for example, 915 MHz).

  In the planar loop antenna 10 configured as described above, by performing unbalanced feeding at the first frequency from the first feeding coaxial line 22, linearly polarized radiation at the first frequency is emitted from the first loop conductor 14. In addition, it is possible to radiate linearly polarized waves of the second frequency from the second loop conductor 24 by performing unbalanced feeding of the second frequency from the second feeding coaxial line 32.

  In addition, a coiled conductor 34 for the HF band (13.56 MHz) is embedded between the first loop conductor 14 and the second loop conductor 24 in the dielectric substrate 12, so that the first embodiment is implemented. It is possible to have an electrostatic shielding effect in the same manner as in FIG.

  In this way, in addition to the effects of the first embodiment, it is possible to provide a three-frequency antenna using a radio frequency system of two-frequency linearly polarized radiation and an electromagnetic induction system using a coiled conductor 34.

(Sixth embodiment)
29 to 31 show a planar loop antenna according to a sixth embodiment of the present invention. In this example, a second feeding conductor 27 is further provided on the dielectric substrate 12A with respect to the planar loop antenna of the second embodiment.

  A coiled conductor 34 for the HF band (13.56 MHz) is embedded between the first loop conductor 14 and the second loop conductor 24 in the dielectric substrate 12.

  In the sixth embodiment configured as described above, as in the fifth embodiment, a two-frequency linearly polarized radiation radio wave system and an electromagnetic induction system using a coiled conductor 34 are used for a three-frequency antenna. And the same effects as those of the fifth embodiment can be obtained.

  In addition, the first power supply conductor 17 or the second power supply conductor 27 can be used so as to also supply power to the coiled conductor 34.

10 Planar Loop Antenna 12 Dielectric Substrate 14 First Loop Conductor 16 First Feeding Conductor 17 First Feeding Conductor 20 Reflector 22 First Feeding Coaxial Line 22a Center Conductor 22b Outer Conductor 24 Second Loop Conductor 26 Second Feed Conductor 27 Second feeding conductor 32 Second feeding coaxial line 32a Center conductor 32b Outer conductor 34 Coiled conductor

Claims (8)

A dielectric substrate;
A first loop conductor formed on one surface of the dielectric substrate and partially having a gap;
A second loop conductor formed on the other surface of the dielectric substrate, having a gap in part and conducting with the first loop conductor;
A reflector disposed at a predetermined distance from the dielectric substrate and being unbalanced at a first frequency with the first loop conductor;
A coiled conductor disposed between a first loop conductor and a second loop conductor in a dielectric substrate, operating in a frequency band different from the first frequency and performing transmission by an electromagnetic induction method;
A planar loop antenna comprising:   A first feeding conductor extends from a predetermined portion of the first loop conductor toward the inside of the loop, a center conductor of a first feeding coaxial line is connected to the first feeding conductor, and a first conductor is connected to the reflector. The planar loop antenna according to claim 1, wherein an outer conductor of a feeding coaxial line is connected.   A first feeding conductor is provided in parallel with the first loop conductor, a central conductor of the first feeding coaxial line is connected to the first feeding conductor, and an outer conductor of the first feeding coaxial line is connected to the reflector. The planar loop antenna according to claim 1, wherein the planar loop antenna is connected and fed from the first feeding conductor to the first loop conductor by electromagnetic coupling.   A first power supply conductor extends from a predetermined part of the first loop conductor toward the inside of the loop, and a second power supply conductor extends from the predetermined part of the second loop conductor to the inside of the loop, and the first loop The conductor and the second loop conductor are opposed to each other in the same configuration, and the first power supply conductor and the second power supply conductor are arranged so as not to be opposed to each other, and the first power supply conductor is disposed. A central conductor of the first feeding coaxial line is connected to one of the second feeding conductor and the outer conductor of the first feeding coaxial line is connected to the reflecting plate, and a circularly polarized wave characteristic is obtained at the first frequency. The planar loop antenna according to claim 1, wherein the planar loop antenna has characteristics.   The first loop conductor and the second loop conductor are opposed to each other in the same configuration, and a first feeding conductor and a second feeding conductor are parallel to the first loop conductor and the second loop conductor. The first power supply conductor and the second power supply conductor are arranged at different positions with respect to the first loop conductor and the second loop conductor, and either the first power supply conductor or the second power supply conductor is provided. The central conductor of the first feeding coaxial line is connected to one side, the outer conductor of the first feeding coaxial line is connected to the reflector, and the first loop conductor and the second loop conductor are fed by electromagnetic coupling. The planar loop antenna according to claim 1, wherein the planar loop antenna has circular polarization characteristics at the first frequency.   4. The unbalanced feeding at a second frequency, which is a frequency different from the first frequency, is performed between the second loop conductor and the reflection plate. 5. Plane loop antenna.   A second power supply conductor extends from a predetermined portion of the second loop conductor into the loop, a central conductor of a second power supply coaxial line is connected to the second power supply conductor, and the second power supply conductor is connected to the reflector. The planar loop antenna according to claim 6, wherein an outer conductor of a coaxial line is connected.   A second feeding conductor is provided in parallel with the second loop conductor, a center conductor of the second feeding coaxial line is connected to the second feeding conductor, and an outer conductor of the second feeding coaxial line is connected to the reflector. The planar loop antenna according to claim 6, wherein the planar loop antenna is connected and fed from the second feeding conductor to the second loop conductor by electromagnetic coupling.