JP2011217205A - Planar antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar antenna which can be configured in a small size and at low cost and can be operated in a plurality of frequency bands as an antenna of an apparatus related to RFID for instance.SOLUTION: On the surface of a dielectric substrate 12 provided with a ground conductor 18 on the back surface, a U-shaped strip line 14 and a patch conductor 16 extending from one end of the U-shaped strip line 14 to the other end of the U-shaped strip line are formed. A microstrip line type loop antenna to be operated at a first frequency is configured by the U-shaped strip line 14, and a patch antenna to be operated at a second frequency is configured by the patch conductor 16.

Description

  The present invention relates to a planar antenna that can be configured to be small and inexpensive and can operate 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.

  As conventional planar antennas, for example, antennas described in Patent Documents 1 and 2 are known.

  The one described in Patent Document 1 has a radiating conductor on one side and a grounding conductor on the other side, and has a patch antenna that operates in the frequency band of 2.45 GHz band used in the radio wave system, and a coiled conductor. Then, it is disclosed that an antenna operating in a 13.56 MHz frequency band used in an electromagnetic induction system is stacked via a dielectric holding base.

  In the one described in Patent Document 2, a rectangular 13.56 MHz coil antenna is formed on the upper surface of a dielectric substrate along the peripheral portion, and a circular 2.4 GHz patch antenna is formed at the center of the dielectric substrate. And forming a ground plane corresponding to the patch antenna on the back surface of the dielectric substrate.

  Thus, in the conventional planar antenna, the combination of the patch antenna and the coiled conductor is adapted to handle two frequencies.

JP 2008-125115 A JP 2005-51536 A

  An object of the present invention is to provide a planar antenna having a novel configuration that is small and inexpensive and can be operated at a desired frequency of one frequency or more.

  In order to achieve the above object, a planar antenna according to the present invention as claimed in claim 1 is characterized in that a U-shaped stripline and one end of the U-shaped stripline are formed on the surface of a dielectric substrate having a ground conductor on the back surface. And a U-shaped stripline extending toward the other end of the U-shaped stripline, and the U-shaped stripline forms a microstrip line type loop antenna that operates at the first frequency. An operating patch antenna is configured.

  According to a second aspect of the present invention, in the planar antenna according to the first aspect, the outer periphery of the U-shaped stripline, or in parallel with the U-shaped stripline, or spaced apart from a ground conductor, A coiled conductor that operates in a frequency band different from that of the antenna and performs transmission by an electromagnetic induction method is provided.

  According to a third aspect of the present invention, there is provided a planar antenna having a U-shaped stripline on the surface of a dielectric substrate having a ground conductor on the back surface, and the U-shaped stripline facing the U-shaped stripline. A second U-shaped strip line continuously connected from one end is formed, and a gap is formed between the other end of the U-shaped strip line and the other end of the second U-shaped strip line; Patch conductors extending from one end of the U-shaped strip line and the second U-shaped strip line toward the other end of the U-shaped strip line and the second U-shaped strip line are formed. The two U-shaped strip lines are slightly different in length, and the U-shaped strip line and the second U-shaped strip line form a double loop for the first frequency. Generating a circularly polarized wave in the first frequency, characterized in that.

  According to a fourth aspect of the present invention, in the planar antenna according to the third aspect, a patch antenna that operates at a second frequency is configured by the patch conductor.

  According to a fifth aspect of the present invention, in the planar antenna according to the third or fourth aspect, the outer periphery of the U-shaped strip line and the second U-shaped strip line, or the U-shaped strip line and the second U-shaped strip line. A coiled conductor that operates in a frequency band different from that of the antenna and performs transmission by an electromagnetic induction system is provided in parallel with the letter-shaped stripline or apart from the ground conductor.

  ADVANTAGE OF THE INVENTION According to this invention, the planar antenna which can be comprised small and cheaply is realizable. Further, the U-shaped strip line constitutes a loop antenna radiating element, and the patch conductor is constituted as a patch antenna radiating element, whereby an antenna that operates at two frequencies can be constructed. Furthermore, by providing a coiled conductor, it can be configured as an antenna that operates at two or more frequencies.

  In addition, the planar antenna of the present invention can be used as an antenna for RFID-related devices as an antenna that operates at a frequency of 13.56 MHz, 950 MHz, or a UHF band in the vicinity thereof, 2.45 GHz.

1 is a perspective view of a planar antenna according to a first embodiment of the present invention. It is a top view of a 1st embodiment. It is a side view of a 1st embodiment. In the first embodiment, it is a simulation result of return loss characteristics from 800 MHz to 2.6 GHz when the first frequency is 950 MHz and the second frequency is 2.45 GHz. In 1st Embodiment, it is a simulation result of a radiation characteristic when the 1st frequency is 950 MHz and the 2nd frequency is 2.45 GHz. It is a perspective view showing the modification of 1st Embodiment. It is a block diagram of a 1st embodiment. It is a disassembled perspective view showing another modification of 1st Embodiment. It is a perspective view showing another modification of 1st Embodiment. It is a perspective view of the planar antenna which concerns on 2nd Embodiment of this invention. It is a top view of a 2nd embodiment. It is explanatory drawing showing the electric current distribution in the 1st frequency vicinity of 2nd Embodiment. In 2nd Embodiment, it is a simulation result of the return loss characteristic from 800 MHz to 2.6 GHz when the 1st frequency is 950 MHz and the 2nd frequency is 2.45 GHz. In 2nd Embodiment, it is a simulation result of the axial ratio characteristic of 900-970 MHz when the 1st frequency is 950 MHz. In 2nd Embodiment, it is a simulation result of a radiation characteristic when the 1st frequency is 950 MHz and the 2nd frequency is 2.45 GHz.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
1 to 3 show a planar antenna according to a first embodiment of the present invention. In the figure, the planar antenna 10 has a U-shaped strip line 14 and a patch conductor 16 formed on the surface of a dielectric substrate 12. At least a portion of the back surface of the dielectric substrate 12 facing the U-shaped strip line 14 and the patch conductor 16 is a ground conductor 18.

Specifically, the U-shaped strip line 14 includes a first horizontal side portion 14A (length L1, width W) and a first vertical side portion 14B (length L2) orthogonal to the first horizontal side portion 14A. , Width W) and a second horizontal side portion 14C (length L3, width W) orthogonal to the first vertical side portion 14B and parallel to the first horizontal side portion 14A. The length L1 + L2 + L3 corresponds to the wavelength λ _{1 of} the first frequency (for example, 950 MHz) corresponding to about one wavelength of the wavelength λ _{g1 in} consideration of the wavelength shortening rate due to the dielectric constant of the dielectric substrate 12. Yes.

The patch conductor 16 (width a, length b) extends from the end of the first lateral side 14A, which is one end of the U-shaped stripline 14, to the second lateral side 14C, which is the other end of the U-shaped stripline 14. It extends toward the end of the. The base end portion of the patch conductor 16 is a tapered portion 16a (length g) that becomes narrower toward the first lateral side portion 14A. Then, the length b of the patch conductor 16 is set to 1 / of the wavelength λ _{g2 in} consideration of the wavelength shortening rate due to the dielectric constant of the dielectric substrate 12 with respect to the wavelength λ _{2 of} the second frequency (for example, 2.45 GHz). This corresponds to two wavelengths.

  Power feeding is performed from the transmitting / receiving circuit to the vicinity of the proximal end portion of the patch conductor 16 through the matching circuit 30 (see FIG. 7) using the power feeding coaxial line 20.

  In the planar antenna 10 configured as described above, by performing balanced feeding at the first frequency, the U-shaped stripline 14 corresponds to one wavelength thereof, so that the microstripline type that operates at the first frequency is used. A loop antenna is configured, and radiation of a linearly polarized wave having the first frequency can be performed. In addition, by performing balanced feeding at the second frequency, the patch conductor 16 corresponds to ½ wavelength, so that a patch antenna that operates at the second frequency is configured, and radiation of linearly polarized waves at the second frequency is achieved. It can be performed.

  4 and 5 show simulation results of the return loss characteristic and the radiation characteristic of 800 MHz to 2.6 GHz when the first frequency is 950 MHz and the second frequency is 2.45 GHz. Various parameters at this time are: L1 = 49 mm, L2 = 57 mm, L3 = 45.5 mm, W = 8 mm, a = 13 mm, b = 32 mm, c = 46.5 mm, f = 5 mm, g = 2.5 mm, dielectric The thickness h of the body substrate 12 is 3.2 mm, and the dielectric constant of the dielectric substrate 12 is 4.3.

  FIG. 4 shows that unnecessary resonance characteristics are shown in the vicinity of 1.8 GHz, but resonance characteristics are obtained at 950 MHz and 2.45 GHz. With a return loss characteristic of 950 MHz and 2.4 GHz, a bandwidth of −10 dB or less is about 2.0%. Moreover, 45 degree directivity linearly polarized wave can be confirmed in FIG. 5 from 950 MHz.

  As a result, an antenna compatible with two frequencies can be obtained, and when the second frequency is not used, an antenna corresponding to one frequency of only the first frequency can be obtained.

  Alternatively, as shown in FIG. 6, a coiled conductor for the HF band (13.56 MHz) on the surface of the dielectric substrate 12 around the outer periphery of the strip line 14 and the patch conductor 16 and not facing the ground conductor 18. 34 can be formed. In this case, as shown in FIG. 7, by transmitting power from the transmission / reception circuit 36 to the coiled conductor 34, transmission by an electromagnetic induction method at 13.56 MHz can be performed, and an antenna for two frequencies or three frequencies is obtained. be able to.

  Alternatively, as shown in FIG. 8, the coiled conductor 34 is provided on a plane separated from the ground conductor 18 by a spacer with respect to the dielectric substrate 12, or, as shown in FIG. It is also possible to provide in parallel with the strip line 14 in a portion not facing the ground conductor 18 on the surface.

  Although the dielectric substrate 12 is affected by the dielectric loss of tan δ, the dielectric substrate 12 is increased in thickness by increasing the thickness of the dielectric substrate 12 (3 mm or more) and decreasing the Q to increase the gain. Therefore, it is possible to provide an inexpensive and small antenna. Then, as an RFID-related device operating at a frequency of 950 MHz or a nearby UHF band, a frequency of 2.45 GHz and a nearby frequency, and a frequency of 13.56 MHz or a nearby HF band, for example, as a reader-side antenna or an IC By combining with a chip, it can be used as an antenna on the tag side or card side.

(Second Embodiment)
10 and 11 show a planar antenna according to the second embodiment of the present invention. In this embodiment, in addition to the first embodiment, a second U-shaped strip line 24 is continuously formed from one end of the U-shaped strip line 14.

  The second U-shaped strip line 24 is specifically similar to the U-shaped strip line 14, specifically with respect to the first lateral side portion 24A (length L5, width W) and the first lateral side portion 24A. A first vertical side portion 14B (length L2, width W) orthogonal to each other and a second horizontal side portion 24C (length L4, width W) orthogonal to the first vertical side portion 24B and parallel to the first horizontal side portion 24A. It consists of a radiating element consisting of

  While one end of the first lateral side portion 14A and one end of the first lateral side portion 24A are continuous, between the other end of the U-shaped strip line 14 and the other end of the second U-shaped strip line 24 A gap 26 is formed, and the U-shaped strip line 14 and the second U-shaped strip line 24 form a rectangular loop with a gap 26.

  The patch conductor 16 (width a, length b) has an end portion of the first lateral side portion 14A which is one end of the U-shaped strip line 14 and a first lateral side portion which is one end of the second U-shaped strip line 24. From the end of 24 </ b> A toward the end of the second lateral side 14 </ b> C that is the other end of the U-shaped strip line 14 and the end of the second lateral side 24 </ b> C that is the other end of the second U-shaped strip line 24. That is, it extends toward the gap 26.

The combined length L1 + 2L2 + L3 + L4 + L5 of the U-shaped strip line 14 and the second U-shaped strip line 24 is a wavelength λ _{1 of} the first frequency (for example, 950 MHz) of the wavelength due to the dielectric constant of the dielectric substrate 12. The U-shaped stripline 14 and the second U-shaped stripline 24 constitute a double loop of the first frequency, corresponding to about two wavelengths λ _{g1 in} consideration of the shortening rate. However, the lengths of the U-shaped strip line 14 and the second U-shaped strip line 24 are slightly different, that is, the length L1 of the first lateral side portion 14A and the length L5 of the first lateral side portion 24A. Further, the length L3 of the second lateral side portion 14C and the length L4 of the second lateral side portion 24C are different. Accordingly, the positions of the gap 26 and the patch conductor 16 are shifted from the left and right center to the left and right, and the area A1 of the region surrounded by the U-shaped stripline 14 and the patch conductor 16 and the second U-shaped stripline 24 and the patch The area A2 of the region surrounded by the conductor 16 is also different. The area ratio between the areas A1 and A2 is about 1: 0.92 (or 0.87 to 0.94).

  Power feeding is performed from the vicinity of the base end portion of the patch conductor 16 using the power feeding coaxial line 20.

  In the planar antenna 10 configured as described above, by performing balanced feeding at the first frequency, two resonance frequency characteristics appear in the double loop due to capacitive coupling by the gap 26. When this phase difference is 90 degrees, circular polarization near the first frequency can be generated.

  FIG. 12 shows the relationship between the change in frequency near the first frequency and the current distribution. In this example, the area A1 on the left side is smaller than the area A2 on the right side, and as shown in FIG. 12 (a), the contribution of radiation from the right loop is made to a frequency smaller than the first frequency. High and horizontal radiation is large. On the other hand, as shown in FIG. 12B, for the frequency higher than the first frequency, the contribution of radiation from the left loop is high, and the radiation from the vertical direction is large. Therefore, in the vicinity of the first frequency corresponding to the middle, contributions from both loops are obtained, and circular polarization can be generated by having a phase difference of 90 degrees. Here, it is preferable that the difference between the resonance frequencies of the right and left loops is about 5% of the first frequency.

  Further, by performing balanced feeding at the second frequency, since the patch conductor 16 corresponds to ½ wavelength, linearly polarized radiation at the second frequency can be performed.

  FIGS. 13 to 15 show simulation results of return loss characteristics, axial ratio characteristics, and radiation characteristics from 800 MHz to 2.6 GHz when the first frequency is 950 MHz and the second frequency is 2.45 GHz. Various parameters at this time are as follows: L1 = 51.5 mm, L2 = 57 mm, L3 = 48.5 mm, L4 = 51.5 mm, L5 = 55.5 mm, gap 26 interval d = 7 mm, W = 8 mm, a = 20 mm , B = 32 mm, c1 = 43.5 mm, c2 = 47.5 mm, f = 9 mm, g = 2.5 mm, the thickness h of the dielectric substrate 12 is 3.2 mm, and the dielectric constant of the dielectric substrate 12 is 3 .8.

  From FIG. 13, it can be seen that there are two resonance characteristics near 950 MHz, a circular polarization resonance characteristic is obtained, and a resonance characteristic is obtained at 2.45 GHz. Then, from the axial ratio characteristics of 900 to 970 MHz in FIG. 14, an axial ratio of about 1.5 dB to 2 dB is obtained at 930 MHz in the maximum radiation direction, and the relative bandwidth at which the axial ratio is 3 dB or less is about 2%. It was confirmed that the turning direction was right turning. It was also confirmed that the left turn could be achieved by moving the patch conductor 16 left and right so that A1> A2.

  As a result, it is possible to provide a two-frequency antenna of circularly polarized wave at the first frequency and linearly polarized wave at the second frequency. When the second frequency is not used, the circularly polarized wave of the first frequency is It can also be a single frequency antenna. By providing the circular polarization characteristic, it is not necessary to consider the orientation of the planar antenna 10 with the object (tag or card).

  Further, a coiled conductor 34 for the HF band (13.56 MHz) is provided on the outer periphery of the strip lines 14, 26, or in parallel with the strip lines 14, 26, or with respect to the dielectric substrate 12. It is also possible to provide the antenna on a plane separated from the ground conductor 18 by a spacer, whereby a two-frequency or three-frequency antenna can be obtained.

DESCRIPTION OF SYMBOLS 10 Planar antenna 12 Dielectric board | substrate 14 U-shaped stripline 16 Patch conductor 18 Ground conductor 24 2nd U-shaped stripline 26 Gap 34 Coiled conductor

Claims (5)

  A U-shaped strip line and a patch conductor extending from one end of the U-shaped strip line toward the other end of the U-shaped strip line are formed on the surface of the dielectric substrate provided with the ground conductor on the back surface, A planar antenna, wherein a microstrip line type loop antenna that operates at a first frequency is configured by a U-shaped strip line, and a patch antenna that operates at a second frequency is configured by a patch conductor.   A coil that operates in a frequency band different from that of the antenna and performs transmission by an electromagnetic induction method around the outer periphery of the U-shaped strip line, in parallel with the U-shaped strip line, or apart from the ground conductor. The planar antenna according to claim 1, wherein a planar conductor is provided.   On the surface of the dielectric substrate having the ground conductor on the back surface, a U-shaped strip line and a second end of the U-shaped strip line continuously connected to one end of the U-shaped strip line so as to face the U-shaped strip line. A U-shaped strip line is formed, and a gap is formed between the other end of the U-shaped strip line and the other end of the second U-shaped strip line, and the U-shaped strip line and the second U-shaped strip line are formed. A patch conductor extending from one end of the strip line toward the other end of the U-shaped strip line and the second U-shaped strip line is formed, and the length of the U-shaped strip line and the second U-shaped strip line is slightly In contrast, the U-shaped stripline and the second U-shaped stripline form a double loop with respect to the first frequency to generate a circularly polarized wave at the first frequency. Planar antenna according to claim.   The planar antenna according to claim 3, wherein a patch antenna that operates at a second frequency is constituted by the patch conductor.   The antenna around the outer periphery of the U-shaped strip line and the second U-shaped strip line, in parallel with the U-shaped strip line and the second U-shaped strip line, or separated from the ground conductor. The planar antenna according to claim 3 or 4, further comprising a coiled conductor that operates in a frequency band different from the above and performs transmission by an electromagnetic induction method.