Patent Application
20180054001
The present invention relates to a wideband planar circularly polarized antenna and an antenna device. For more information, it particularly relates to a wideband planar circularly polarized antenna of printed board type and an antenna device, which are capable of being used in WiFi (Wireless Fidelity, brand name) in the band of 2.0 GHz to 5.0 GHz, WiMAX (Worldwide Interoperability for Microwave access), UWB (Ultra Wide Band) wireless communication in the band of 3.1 GHz to 10.6 GHz and the like.
Circular polarization has been used for GPS radio wave, satellite radio wave for satellite digital broadcasting and radio wave for ETC and various kinds of circularly polarized antennas have been proposed (See Patent Document 1).
In recent years, the circular polarization has been widely utilized into wireless LAN represented by WiFi, and wireless communication such as WiMAX and UWB for use of middle-range communication, mobile communication etc. Since a thin and light-weight circularly polarized antenna installed in the wireless communication equipment is required, a planar antenna formed by a printed board etc. is becoming mainstream.
Several wideband planar circularly polarized antennas corresponding thereto have been proposed. For example, non-patent document 1 which the inventors have proposed describes a rectangular antenna element that is obliquely arranged. Non-patent document 2 describes a rectangular antenna element in which a sub pattern of nested structure is formed. Non-patent document 3 describes an antenna element of rectangular loop pattern.
An elliptical antenna element has been known as the wideband planar linearly polarized antenna (see non-patent document 4).
The above-mentioned wideband planar circularly polarized antennas and antenna devices have some problems as follows.
The non-patent document 1 discloses a rectangular monopole antenna of printed board type, which is a simple rectangular antennal element and has an advantage such that antenna characteristics are hardly affected by manufacturing errors in the mass production. It has achieved a frequency band of 1.75 GHz to 4.22 GHz as a frequency bandwidth (1.73 GHz to 4.27 GHz as a frequency bandwidth satisfying return loss of 10 dB or less and axial ratio (AR) of 3 dB or less) but that bandwidth is no yet satisfied.
In the non-patent documents 2 and 3, a frequency bandwidth is wide but shapes of their antenna elements are complicated because the sub pattern or the rectangular loop is required to be formed. Therefore, they are easily affected by manufacturing errors in the mass production, and particularly, this causes a problem such that axial ratio characteristic, which represents circular polarization characteristics, is instable.
In addition, as shown in the non-patent document 4, the elliptical antenna element in a monopole antenna configuration is known for the wideband planar linearly polarized antenna. In such a case, an electric field having a vector direction to a major axis of the elliptical patch occurs as radiation from the elliptical patch and an electric field having a direction to the major axis of the elliptical patch also occurs from the ground conductor part because electric current passes through the ground conductor part symmetrically in relation to the major axis of the elliptical patch or a microstrip line. Therefore, it can radiate only the linearly polarized wave of which electrical field has a direction to the major axis of the elliptical patch. It cannot radiate any circular polarization, therefore cannot be used for any circularly polarized antenna of UHF band or SHF band.
The present invention solves such past problems and has an object to provide a wideband planar circularly polarized antenna and antenna device, each of which has a simply shaped antenna element and acquires a wide frequency bandwidth.
In order to solve the above-mentioned problems, a wideband planar circularly polarized antenna according to the invention claimed in claim 1 includes a patch conductor formed on a front surface of a dielectric substrate so to be obliquely arranged in relation to an orthogonal axis of the dielectric substrate, the patch conductor having a smooth contour and a shape having a longitudinal direction, a microstrip line for feeding power to a bottom part of the patch conductor, and a ground conductor plate formed on a back surface of the dielectric substrate wherein they are configured such that an amplitude of an electric field radiated from each of the patch conductor and the ground conductor plate is the same and a phase between the electric field radiated from the patch conductor and the electric field radiated from the ground conductor plate is about 90 degrees.
The wideband planar circularly polarized antenna claimed in claim 2 is characterized in that a total of lengths of the microstrip line and a major axis of the patch conductor is configured to be almost equal to a length of a diagonal line of the ground conductor plate such that the amplitude of the electric field radiated from each of the patch conductor and the ground conductor plate is the same.
The wideband planar circularly polarized antenna claimed in claim 3 is characterized in that the patch conductor is inclined by a predetermined gradient θ such that the phase between the electric field radiated from the patch conductor and the electric field radiated from the ground conductor plate is about 90 degrees and a direction of the major axis of the patch conductor is almost orthogonal to the diagonal line of the ground conductor plate.
The wideband planar circularly polarized antenna claimed in claim 4 is characterized in that the gradient θ of the patch conductor is selected to be within a range of 40 degrees≦θ≦80 degrees.
The wideband planar circularly polarized antenna claimed in claim 5 is characterized in that the gradient θ of the patch conductor is selected so as to be 50 degrees, 60 degrees or their intermediate degrees.
The wideband planar circularly polarized antenna claimed in claim 6 is characterized in that the shape of the patch conductor is an elliptical shape.
An antenna device claimed in claim 7 is characterized in that the device installs the wideband planar circularly polarized antenna according to claims 1 through 6.
According to this invention, a wideband planar circularly polarized antenna can be realized by configuration such that the amplitude of the electric field radiated from each of the patch conductor and the ground conductor plate is the same, the patch conductor is inclined by a predetermined gradient and the phase between the electric field radiated from the patch conductor and the electric field radiated from the ground conductor plate is about 90 degrees.
Accordingly, the antenna has a very simple structure and is thin and light-weighted so that it is possible to provide the planar antenna that is superior in portability. Further, regarding circular polarization characteristics, the frequency bandwidth satisfying that VSWR (Standing Wave Ratio) is 2 or less and the axial ratio is 3 dB or less becomes 88.4%, which can realize frequency wideband (a band of 2.1 GHz to 5.5 GHz or 3.1 GHz to 10.6 GHz) that cannot have been realized in the past.
Additionally, since an even radiation directivity which doesn't depend on the frequency can be acquired in the zenith direction, this planar antenna has a feature such that it can be installed without considering the direction of the antenna.
The following will describe an embodiment of a wideband planar circularly polarized antenna according to the present invention.
The wideband planar circularly polarized antenna according to the present invention realizes wideband circularly polarization characteristics by configuration such that the amplitude of the electric field radiated from each of the patch conductor and the ground conductor plate is the same (Condition 1) and the phase between the electric field radiated from the patch conductor and the electric field radiated from the ground conductor plate is about 90 degrees (Condition 2). In this embodiment, a case where the phase between the electric field radiated from the patch conductor and the electric field radiated from the ground conductor plate is 90 degrees will be described.
The Condition 1 will be described. The patch conductor generates the electric field having a direction along the major axis and the ground conductor plate generates the electric field having a direction along the diagonal line thereof. So, if a length of the patch conductor including a microstrip line and a length of the diagonal line of the ground conductor plate are selected to be almost equal each other, the amplitude of the electric field radiated from the patch conductor and radiated from the ground conductor plate will be almost equal each other.
The Condition 2 will be described. Radio waves radiated from the patch conductor and the ground conductor plate will have a shift by ωt=90 degrees if the direction of the major axis of the patch conductor is set at about right angles to the diagonal direction of the ground conductor plate. Accordingly, these two orthogonal electric fields have a phase of 90 degrees, which generates circular polarization. In order to set the major axis direction of the patch conductor at about right angles to the diagonal direction of the ground conductor plate, the patch conductor is inclined by θ in relation to the dielectric substrate.
This planar antenna 10 is configured so as to include a rectangular dielectric substrate 20, a patch conductor 30 (as an antenna element) adhesively formed on a front surface 20a thereof, a microstrip line 40 connecting to this patch conductor 30, and a ground conductor plate 50 adhesively formed on a back surface 20b of the dielectric substrate 20.
As the dielectric substrate 20, a rectangular substrate having a length W1, a width W2 and a thickness h is used. Its relative electric permittivity is sr. In this embodiment, a printed board is used as the dielectric substrate 20.
The patch conductor 30 has a smooth contour and a shape having a longitudinal direction. In this embodiment, it has an elliptical shape determined by lengths of a major axis t1 and a minor axis t2. A microstrip line 40 having a predetermined width s is connected to the patch conductor 30 and a signal to be transmitted or received is fed through the microstrip line 40. A feeding point 60 is provided at a predetermined point of the microstrip line 40.
The patch conductor 30 is arranged around a middle portion of the dielectric substrate 20 so to be inclined by θ to an orthogonal axis of the dielectric substrate 20 (namely, it is inclined by θ on the basis of a focus (x0, y0) of the patch conductor). In this embodiment, a case of θ=50 degrees will be indicated.
It is set so that the major axis of the patch conductor 30 passes through a middle point P of the dielectric substrate 20 and the focus (x0, y0) of the patch conductor 30 is positioned slightly above the middle point P. In addition, the connecting position relation with the patch conductor 30 and the microstrip line 40 is selected so that an end edge of the microstrip line 40 is positioned at a peripheral end edge, which is slightly shifted to right side from the major axis t1, of the patch conductor 30. In other words, a position of the microstrip line 40 connected to the patch conductor 30 is shifted by Sp from the middle P of the antenna (the middle point of the dielectric substrate 20).
The microstrip line 40 is adhesively formed to extend parallel to a vertically side end edge of the dielectric substrate 20 and reach a horizontally side end edge thereof. The feeding point 60 is provided at a position that is away from the horizontally side end edge by Sd (and the position that is away from the middle point P of the dielectric substrate 20 by Sp).
The ground conductor plate 50 is adhesively formed at a certain position on the back surface 20b of the dielectric substrate 20 not to overlap with the patch conductor 30 adhesively formed on the front surface 20a, and to cover a smaller area than the dielectric substrate.
Specifically, the ground conductor plate 50 is formed to have an area (d*(L1+L2)) to cover a half or less of the dielectric substrate 20. In this embodiment, the ground conductor plate 50 corresponding to a lower peripheral portion of the patch conductor 30 is cut to be a shape around the lower peripheral portion (almost U-shape) not to overlap with the lower peripheral portion of the patch conductor 30. As a result thereof, that will be a curved shape having predetermined gaps g1, g2 between the lower peripheral portion of the patch conductor 30 and the ground conductor plate 50. These gaps g1, g2 are selected so that they are slightly different from each other (g1>g2).
Electric supply to the microstrip line 40 is fed from the back surface 20b of the dielectric substrate 20. Accordingly, as shown in
The ground conductor plate 50 has a nearly rectangular shape and a length of the diagonal line joining vertexes q1, q2 is fixed by a long side (L1+L2) and a short side d, which are selected so that the length of the diagonal line is almost equal to the above-described total of lengths of the microstrip line 40 and the major axis of the patch conductor 30.
Thus, the patch conductor 30 is inclined by θ; the position of the microstrip line is shifted from the middle P of the antenna by Sp; the focus position (x0, y0) of the patch conductor 30 is shifted upward from the middle P of the antenna; a size of the ground conductor plate 50 is selected so that the major axis t1 of the patch conductor 30 is almost at right angle to the diagonal line of the ground conductor plate 50; and the length of the patch conductor 30 including the microstrip line 40 is set to be around the above-mentioned length of the diagonal line.
It is to be noted that an angle between the major axis t1 and the diagonal line of the ground conductor plate 50 is not a right angle in
By thus setting each size etc. of the planar antenna 10, the (condition 1) that the amplitude of the electric field radiated from each of the patch conductor 30 and the ground conductor plate 50 is the same, and the (condition 2) that the phase between the electric field radiated from the patch conductor and the electric field radiated from the ground conductor plate is 90 degrees, are both satisfied.
The following will describe an example of specifications (parameters) of the wideband planar circularly polarized antenna 10 thus configured.
Vertical length W1 of the dielectric substrate 20 is 50 mm.
Horizontal length W2 of the dielectric substrate 20 is 60 mm.
Thickness h of the dielectric substrate 20 is 1.6 mm.
Relative electric permittivity a of the dielectric substrate 20 is 2.6.
Major axis t1 of the patch conductor 30 is 20 mm.
Minor axis t2 of the patch conductor 30 is 10 mm.
Gradient θ of the patch conductor 30 is 50 degrees.
Width S of the microstrip line 40 is 4 mm.
Length L1 of the ground conductor plate 50 is 30 mm.
Length L2 of the ground conductor plate 50 is 30 mm.
Length d of the ground conductor plate 50 is 23 mm.
Gap g1 is 0.6 mm.
Gap g2 is 0.4 mm.
Distance Sd up to the feeding point 60 is 3 mm.
Shift Sp between the feeding point 60 and the middle point P is 7.5 mm.
The following will describe various kinds of characteristics of the wideband planar circularly polarized antenna 10 according to the invention.
On the other hand, on the ground conductor plate 50, the electric currents flow only in a direction from an upper left to a lower right, therefore it is comprehended that the electric currents passing through the ground conductor plate 50 contribute to the radiation at the phase angle of ωt=10 degrees.
On the other hand, on the patch conductor 30, the electric currents flow in a direction from a lower left to an upper right from the microstrip line 40 on a left side peripheral portion and a right side peripheral portion. Therefore, the electric currents passing through the patch conductor 30 contribute to the radiation at the phase angle of ωt=100 degrees.
On the other hand, on the ground conductor plate 50, the electric currents flow only in a direction from a lower right to an upper left, therefore it is comprehended that the electric currents passing through the ground conductor plate 50 contribute to the radiation at the phase angle of ωt=190 degrees.
On the other hand, on the patch conductor 30, the electric currents flow in a direction from an upper right to a lower left to the microstrip line 40 on a left side peripheral portion and a right side peripheral portion. Therefore, it is comprehended that the electric currents passing through the patch conductor 30 contribute to the radiation at the phase angle of ωt=280 degrees.
As being clear from the flowing directions of electric currents shown in
Here, the axial ratio is represented by a ratio of a major axis t1 and a minor axis t2 of elliptically polarized wave. When the axial ratio is 3 dB or less, it is regarded as indicating the circular polarization characteristics. Further, the VSWR (Standing Wave Ratio) means a reflection coefficient of input voltage at the antenna feeding point 60. VSWR=2 corresponds to −10 dB of S parameter (characteristic parameter).
In
Similarly, in
Thus, according to the antenna characteristics shown in
As clearly seen from that figure, the operational frequency bandwidth in the zenith direction of the planar antenna according to the invention is several times broader than the operational frequency bandwidth disclosed in the non-patent document 1, and an even radiation gain characteristic is also obtained therein.
On the other hand, in
Similarly,
In addition,
A wideband antenna is generally required to have an even radiation directivity characteristic in the operational frequency bandwidth. In this invention, it can be confirmed that the almost even radiation directivity characteristic is obtained. Further, as shown in
The embodiment shown in the figures up to
Antenna characteristics of the planar circularly polarized antenna 10 can be fixed by adjusting the gradient θ of the patch conductor 30 in relation to the orthogonal axis of the dielectric substrate 20. Here, the antenna characteristics mean the antenna characteristics satisfying that axial ratio (AR) is 3 or less and standing wave ratio (VSWR) is 2 or less in the high frequency band of 7.0 GHz or more as described above (characteristic parameter S11≦−dB).
Length W1 (=W2) is 19.34 mm;
Thickness is 1.6 mm;
Relative electric permittivity is 2.6; and
Dielectric loss tangent (tan 8) is 0.001.
Other specifications are suitably adjusted according to the gradient θ. In
In all of the gradients θ, the frequency band in which AR value becomes 3 or less is within a range of 7.25 GHz through 10.25 GHz. Among them, as the AR value, the gradient θ is preferably 50 or 60 degrees, more preferably their median (intermediate value from 50 degrees to 60 degrees; not shown). Thus, by adopting the above-mentioned gradients θ (40 degrees to 80 degrees), the wideband can be realized in the UWB high band.
In the case of VSWR, the gradient θ of the patch conductor 30 is also preferably 50 or 60 degrees, more preferably their median (intermediate value from 50 degrees to 60 degrees; not shown).
Accordingly, the frequency bandwidth in which S11 becomes −10 dB in all of the gradients θ is within a range of 7.25 GHz through 10.25 GHz. High frequency bandwidth at UWB-High_Band becomes 88.4% by adopting the above-described gradients θ (40 degrees to 80 degrees), which realizes the wideband. Therefore, the planar antenna in which the gradient θ of the patch conductor 30 is selected to be 40 degrees through 80 degrees is preferable as the antenna characteristics satisfying both of the AR characteristic and the VSWR characteristic. Thereby, it is applicable to any various kinds of radar antennas in which the wideband is desired in the UWB.
By the wideband planar circularly polarized antenna 10 according to the invention in which the elliptical typed planar monopole antenna is thus used, it is easy to manufacture the planar antenna because the antenna is an elliptical typed planar monopole antenna in which the printed board is used as the dielectric substrate 20. It is also possible to realize the thin and light-weight antenna so that the antenna is easy for an installation thereof and is also superior in portability. In addition, since the operational frequency bandwidth as the antenna characteristics can achieve 88.4%, the wideband antenna can be realized. And since an even gain is obtained in radiation directivity on the zenith direction, it can be used without considering the direction of the antenna.
By suitably selecting specifications (parameters) of the wideband planar circularly polarized antenna 10 such as selection of the shape, size of the dielectric substrate 20, and the gradient θ of the patch conductor 30, it is easily possible to set a target frequency band and bandwidth. Accordingly, the wideband planar circularly polarized antenna 10 according to the invention is applicable to a radar antenna, a collision prevention radar antenna for automobile, a vital observation antenna, an ETC antenna, an antenna for satellite and the like. It is applicable to an antenna device in which these wideband planar circularly polarized antennas using the monopole antenna according to the invention, and transmitting and receiving circuits or one of them, are installed.
In addition, although the embodiment in which the patch conductor 30 is inclined by θ to a right side in relation to the orthogonal axis of the dielectric substrate 20 has been described in
In the wideband planar circularly polarized antenna 10 according to the invention, the right hand circularly polarized wave is radiated in the +z axis direction and the left hand circularly polarized wave is radiated in the −z axis direction shown in
Since it is not necessary to take a direction of the antenna into consideration in this invention, it is effectively applicable to a radar antenna, an antenna (wideband planar circularly polarized antenna) for collision prevention radar for automobile, for satellite, for a vital observation, for therapeutic use etc., and the antenna device installing the wideband planar circularly polarized antenna.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-229883 | Nov 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/081845 | 12/11/2015 | WO | 00 |
