JP5267063B2 - Array antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a flat gain frequency characteristic while suppressing the increase of an antenna area, concerning an array antenna for radiating a circularly-polarized wave. <P>SOLUTION: The array antenna 100 includes: an antenna element 11 for radiating an elliptically-polarized wave; and an antenna element 12 for radiating the elliptically-polarized wave whose rotary direction is the same as that of the elliptically-polarized wave to be radiated by the antenna element 11 while the longitudinal axial direction is different. The antenna elements 11 and 12 are also different from each other in frequency (peak frequency) where a maximum gain is obtained in a gain frequency characteristic. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an array antenna.

  Patent Documents 1 to 5 and Non-Patent Document 1 disclose patch antennas or slot antennas suitable for radiation of high-frequency signals such as millimeter waves. Among these, Patent Document 1 and Non-Patent Document 1 disclose array antennas that can radiate circularly polarized waves. More specifically, the array antennas disclosed in these documents have a plurality of antenna elements each radiating elliptically polarized waves. The elliptical polarization characteristics (axial ratio and inclination thereof) of each antenna element are adjusted so as to cancel the deviation of the axial ratio due to mutual coupling between the antenna elements and obtain circular polarization as the entire array antenna. Each antenna element has a dielectric resonator as a radiating element, and the shape of the opening of the dielectric resonator is elliptical in order to radiate elliptically polarized waves. The array antennas of Patent Literature 1 and Non-Patent Literature 1 can change the orientation of the major axis of elliptically polarized waves by rotating the orientation of the opening of the dielectric resonator disposed on the waveguide feed line.

  Patent Document 2 discloses a slot antenna in which a dielectric resonator as a radiating element is arranged on a conductor plate in which a cross-shaped slot is formed. Further, the slot antenna of Patent Document 2 can radiate circularly polarized waves without changing the shape of the radiating element by making the shape of the two rectangular slots crossing each other constituting the cross-shaped slot asymmetric. Yes. Further, as a specific method for adjusting the shape of the rectangular slot, it is disclosed to adjust the length of the rectangular slot in the longitudinal direction or the short direction.

JP 2004-356880 A JP 2000-36708 A JP 2003-324111 A Japanese Patent Laid-Open No. 61-7707 JP 2006-287452 A Uchimura, H. Shino, N. Miyazato, K, "Novel Circular Polarized Antenna Array Substrates for 60GHz-band", Microwave Symposium Digest, 2005 IEEE MTT-S International, pp.1875-1878

  In recent years, with the spread of broadband technology and high-quality video content, the amount of information distributed has been increasing. For example, in a wireless device mainly used indoors, which is applied to a wireless LAN (Local Area Network) or the like, demand for high-speed data communication of Gbps class is increasing. When using a radio indoors, it is necessary to solve the multipath problem. Multipath is a problem because communication quality deteriorates due to reflected incoming waves reflected by walls and furniture. In order to suppress deterioration in communication quality due to multipath, circularly polarized waves that can selectively receive direct incoming waves are widely used.

  In general, the frequency characteristic of antenna gain often has a peak. If the frequency characteristic of the gain has a peak, the power emission in the frequency band used for communication is not uniform, which leads to deterioration in communication quality. Since such a problem becomes remarkable in Gbps class communication using a wide band, an antenna having a flat gain frequency characteristic is required.

  As described above, circularly polarized antennas used for indoor Gbps-class data communication and the like require flat gain frequency characteristics over a wide band. An object of the present invention is to provide an array antenna capable of radiating circularly polarized waves, in which the flatness of gain frequency characteristics is obtained while suppressing an increase in antenna area.

  Note that Patent Document 1 and Non-Patent Document 1 disclose that each antenna can be obtained by individually changing the direction of a plurality of dielectric resonators whose openings are elliptical in order to obtain a good circularly polarized wave. It discloses that the major axis direction of the elliptically polarized wave of the element is changed. Patent Document 2 discloses obtaining a good circularly polarized wave by adjusting the shapes of two rectangular slots constituting the cross slot. However, none of Patent Documents 1 to 5 and Non-Patent Document 1 described above disclose that the gain frequency characteristics of individual antenna elements are different in order to obtain a flat gain frequency characteristic over a wide band.

  An array antenna according to one aspect of the present invention includes a first antenna element that radiates elliptically polarized waves, and an elliptical wave that has the same turning direction as the elliptically polarized waves radiated by the first antenna element and has different major axis directions. And a second antenna element that radiates polarized waves. Further, the first and second antenna elements have different frequencies (hereinafter referred to as peak frequencies) at which the gain is maximized in the gain frequency characteristics.

  According to the shifted aspect of the present invention, in an array antenna capable of emitting circularly polarized waves, gain frequency characteristics can be flattened while suppressing an increase in antenna area.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary for the sake of clarity.

<First Embodiment>
The array antenna 100 according to the present embodiment has a patch antenna by slot feeding as each antenna element. The structure of the array antenna 100 is schematically shown in FIGS. FIG. 1 is a plan view of the array antenna 100 as viewed from the radiating element side. 2 is a cross-sectional view of the antenna element 11 taken along line AA in FIG.

  The array antenna 100 includes at least a pair of antenna elements 11 and 12. The antenna element 11 includes a radiating element 101, a feed element 103, and a feed line 105. Similarly, the antenna element 12 includes a radiating element 102, a feed element 104, and a feed line 106. As shown in FIG. 2, the antenna element 11 has a four-layer structure. Specifically, there are a radiating element 101, a feeding element 103, and a feeding line 105 in order from the top, and a ground conductor plate 117 is disposed in the lowermost layer. A dielectric 119 is disposed between the respective layers. The laminated structure of the antenna element 12 is the same as that of the antenna element 11 shown in FIG. Although only two antenna elements 11 and 12 are shown in FIG. 1, the number of antenna elements included in the array antenna 100 is not necessarily two, and may include more elements.

  The transmission lines 105 and 106 supply high frequency power to the power feeding elements 103 and 104. The feed element 103 is a conductor plate in which a cross-shaped slit 103a facing the X-axis and Y-axis directions is formed. Similarly, a cross-shaped slit 104 a is also formed in the power feeding element 104. Here, the directions of the X axis, the Y axis, and the Z axis are as shown in FIGS. Specifically, the X axis is from the left to the right in FIG. 1, the Y axis is from the bottom to the top in FIG. 1, and the Z axis is from the back to the front in FIG. The main surfaces of the flat radiating elements 101 and 102 and the feeding elements 103 and 104 are parallel to the XY plane formed by the X axis and the Y axis.

  The power feeding elements 103 and 104 in which the cross slits 103a and 104a are formed respectively feed the high-frequency electric field to the radiation elements 101 and 102 by dividing the high-frequency electric field into components in the X-axis direction and components in the Y-axis direction. The main surfaces of the radiating elements 101 and 102 are rectangular and have two resonance modes that are independent of each other in the X-axis direction and the Y-axis direction. Thereby, an elliptically polarized wave is generated.

  In addition, since the frequency (peak frequency) at which the gain peak is obtained in the gain frequency characteristic is different between the antenna elements 11 and 12, the sizes of the radiating elements 101 and 102 are different from each other. In the present embodiment, the description will be made assuming that the peak frequency of the antenna element 11 is present on the lower frequency side than the peak frequency of the antenna element 12.

  The widths W11 and W12 in the short direction are adjusted for the two rectangular slits in the X direction and the Y direction that constitute the cross-shaped slit 103a. Similarly, the widths W21 and W22 in the lateral direction of the two rectangular slits in the X direction and the Y direction constituting the cross-shaped slit 104a are adjusted. By adjusting the slit width in the short direction of each rectangular slit, the input power in the X-axis direction and the input power in the Y-axis direction to the radiation elements 101 and 102 can be adjusted.

  3A and 3C show an example of the relationship between the electric field supplied from the feeding element 103 to the radiating element 101 and the elliptically polarized electric field 111 radiated from the radiating element 101. FIG. Similarly, FIGS. 3B and 3D show an example of the relationship between the electric field supplied from the feeding element 104 to the radiating element 102 and the elliptically polarized electric field 112 radiated from the radiating element 102. For example, the input power Ex (107) in the X-axis direction and the input power Ey in the Y-axis direction to the radiation element 102 are adjusted by adjusting the slit widths W11 and W12 in the short direction of the two rectangular slits constituting the slit 103a. (109) can be adjusted. The major axis direction AL1 of the elliptically polarized wave 111 radiated from the radiating element 102 is the direction of the vector sum E (113) of Ex (107) and Ey (109). As an example, the angle formed by the major axis direction AL1 of the elliptically polarized wave 111 and the major axis direction AL2 of the elliptically polarized wave 112 shown in FIGS. 3A and 3B is smaller than 90 degrees, but the major axis direction AL1 and The angle formed by AL2 should be substantially 90 degrees. Specifically, the angle formed by the major axis directions AL1 and AL2 is preferably in the range of 70 degrees to 110 degrees. As a result, the axial ratio of the combined electric field of the antenna elements 11 and 12 can be suppressed to be close to circular polarization.

  Subsequently, the effects of widening the circularly polarized wave and widening the gain characteristic obtained by the array antenna 100 according to the present embodiment will be described below. As described above, the array antenna 100 includes an antenna element 11 that radiates elliptically polarized waves and has a gain peak on the relatively low frequency side, and an antenna element 12 that radiates elliptically polarized waves and has a gain peak on the high frequency side. Including. 4A and 4B show elliptical polarization patterns 111 and 112 of the antenna elements 11 and 12 at 63 GHz. 4A and 4B, the white arrows indicate the direction of the electric field radiated during the initial input phase with respect to the antenna elements 11 and 12, respectively. In the example of FIG. 4, at 63 GHz, the angle between the long axis directions AL1 and AL2 is approximately 100 degrees. The electric field direction φ radiated when the initial input phase (input phase is 0 degree) is 40 degrees and 80 degrees in the antenna elements 11 and 12, respectively. The angle formed by the electric field direction φ radiated from the antenna elements 11 and 12 at the same time is preferably within a range of +/− 50 degrees. The axial ratio of the combined electric field of the antenna elements 11 and 12 can be effectively reduced by aligning the radiation electric field directions at the same time. The direction of the radiation electric field can be adjusted by adjusting the feeding phase for the antenna elements 11 and 12.

  As described above, the antenna elements 11 and 12 are patch antennas by slot feeding. The major axis directions AL1 and AL2 of the elliptical polarization patterns 111 and 112 are adjusted by adjusting the power in the X-axis direction and the Y-axis direction from the slot power supply. In the example of FIGS. 4A and 4B, the angle formed by the major axis directions AL1 and AL2 is approximately 70 degrees.

  FIG. 5 shows the analysis results of the gain frequency characteristics of the antenna elements 11 and 12 and the gain frequency characteristics after arraying. The broken line in FIG. 5 indicates the gain of the antenna element 11, the alternate long and short dash line indicates the gain of the antenna element 12, and the solid line indicates the gain after arraying. The antenna 1 (ANT1) in FIG. 5 represents the antenna element 11, and the antenna 2 (ANT2) represents the antenna element 12. In the example of FIG. 5, the gain characteristics after arraying are higher than the middle (about 63 GHz) between the peak frequency (about 61 GHz) of the antenna element 11 (ANT1) and the peak frequency (about 65 GHz) of the antenna element 12 (ANT2). The gain is flattened.

  FIG. 6 shows changes in the frequency characteristics of the axial ratio before and after the arraying. The broken line in FIG. 6 indicates the axial ratio of the antenna element 11, the alternate long and short dash line indicates the axial ratio of the antenna element 12, and the solid line indicates the axial ratio after arraying. As shown in FIG. 6, in the present embodiment, the frequency at which the axial ratio of the antenna element 11 is minimized (about 60 GHz in FIG. 6) and the frequency at which the axial ratio of the antenna element 12 is minimized (about 61. 5 GHz) is different. Further, the frequency region where the axial ratio of the antenna element 11 is 3 dB or less (about 56 to 64 GHz in FIG. 6) and the frequency region where the axial ratio of the antenna element 12 is 3 dB or less (about 60 to 69 GHz in FIG. 6) overlap. Designed to cover different areas while holding areas. Due to the axial ratio characteristics of the antenna elements 11 and 12, circular polarization characteristics over a wide band after arraying can be obtained. In the example of FIG. 6, the axial ratio characteristic after arraying becomes a minimum value at 64 GHz, and the 3 dB bandwidth is 4.5 GHz.

  As already described, by adjusting the input power phase to the antenna elements 11 and 12 so that the direction of the radiation electric field at the same time is the same, the effect of reducing the axial ratio after arraying is increased. For comparison, FIGS. 8 and 9 show frequency characteristics of gain and axial ratio obtained by arraying antenna elements having the elliptical polarization pattern shown in FIGS. 7A and 7B. In the two polarization patterns shown in FIGS. 7A and 7B, the major axis directions AL1 and AL2 are the same. In this case, the gain characteristic shown in FIG. 8 is flattened in a region between peak gain frequencies. However, as shown in FIG. 9, the 3 dB bandwidth of the axial ratio is as narrow as 2 GHz. 5 and 6 and FIGS. 8 and 9, it can be seen that the array antenna 100 can realize flattening of the gain characteristics and widening of the circularly polarized radiation band.

<Second Embodiment>
FIG. 10 is a plan view schematically showing an array antenna 200 according to the second embodiment of the present invention. The array antenna 200 includes antenna elements 21 and 22. The difference between the array antenna 200 and the array antenna 100 described above is that phase control circuits 207 and 208 are arranged on the feed lines 105 and 106 of the array antenna 200. Phase control circuits 207 and 208 change the phase of power supplied to the power feeding elements 103 and 104. The phase control circuits 207 and 208 can be realized by, for example, a variable capacitor or a variable inductor. By arranging the phase control circuits 207 and 208, the phase of the power supplied to the power feeding elements 103 and 104 can be easily adjusted. For this reason, it becomes easy to align the phase of the radiation electric field described in the first embodiment, and it becomes easy to increase the effect of reducing the axial ratio of the combined electric field after arraying.

<Third Embodiment>
FIG. 11 is a plan view schematically showing an array antenna 300 according to the third embodiment of the present invention. The array antenna 300 includes antenna elements 31 and 32. In the array antenna 300, the feed line 105 has a redundant line 307 and the feed line 106 has a redundant line 308 in order to adjust the phase of power supplied to the antenna elements 31 and 32. The lengths of the redundant lines 307 and 308 may be determined so that the phase difference of the power supplied to the antenna elements 31 and 32 becomes a desired value. The desired phase difference is a phase difference necessary for aligning the radiation electric field direction at the same time of the antenna elements 31 and 32 within a predetermined range. By providing the redundant lines 307 and 308, it becomes easy to increase the effect of reducing the axial ratio of the combined electric field after arraying. In FIG. 11, the redundant path is provided in both of the feed lines 105 and 106, but the redundant path may be provided only in one of the feed lines.

<Fourth embodiment>
FIG. 12 is a plan view schematically showing an array antenna 400 according to the fourth embodiment of the present invention. The array antenna 400 includes antenna elements 41 and 42. In the array antenna 400, the feed line 105 has a stub 407 and the feed line 106 has a stub 408 in order to adjust the phase of power supplied to the antenna elements 41 and 42. The shapes of the stubs 407 and 408 may be determined so that the phase difference of the power supplied to the antenna elements 41 and 42 becomes a desired value. The desired phase difference is a phase difference necessary for aligning the radiation electric field directions at the same time of the antenna elements 41 and 42 within a predetermined range. By providing the stubs 407 and 408, it becomes easy to increase the effect of reducing the axial ratio of the combined electric field after arraying. In FIG. 12, stubs are provided in both of the feed lines 105 and 106, but stubs may be provided in only one of the feed lines.

<Fifth embodiment>
The array antenna according to the present embodiment includes at least a pair of antenna elements (hereinafter referred to as antenna pairs) having different gain frequency characteristics. The structure of the array antenna according to the present embodiment may be the same as that of any of the array antennas 100, 200, 300, and 400 described above.

  FIG. 13 shows the gain frequency characteristic of each antenna element included in the antenna pair and the gain frequency characteristic of the antenna pair after arraying. A graph L51 indicated by a broken line in FIG. 13 indicates the gain of one antenna element having a peak frequency on the low frequency side of the antenna pair. A graph L52 indicated by a one-dot chain line in FIG. 13 indicates the gain of the other antenna element having the peak frequency on the high frequency side of the antenna pair. In addition, a graph L53 indicated by a solid line in FIG. 13 indicates the gain after combining antenna pairs. An intersection 55 of the graphs L51 and L52 is a point where the gains of the two antenna elements included in the antenna pair become equal.

As shown in FIG. 13, the frequency corresponding to the intersection 55 is within the desired band W. Here, the desired band W is a frequency region in which gain flatness is required. The gain G at the intersection 55 satisfies the following expression (1) when the allowable variation value of the gain of the array antenna according to the present embodiment is +/− δ (where δ is a positive value). Has been adjusted.
G_max−δ−3 [dB] ≦ G ≦ G_max + δ−3 [dB] (1)
Here, G_max is the maximum gain value at the peak frequency of each antenna element included in the antenna pair.

  By determining the gain frequency characteristics of the antenna pair as shown in FIG. 13, it is possible to make the fluctuation range of the antenna gain after arraying within +/− δ dB within the desired band W.

<Sixth Embodiment>
The array antenna according to the present embodiment is an array of a plurality of antenna pairs described in the fifth embodiment. FIG. 14 is a graph showing frequency characteristics of the gain of the array antenna according to the present embodiment. The array antenna according to the present embodiment includes a plurality of antenna pairs having different frequency bands in which gain characteristics are flat. As an example, FIG. 14 shows the gain characteristics of an array antenna having two antenna pairs. Graphs L61 and L6 indicated by broken lines in FIG. 14 indicate the antenna gain of the antenna pair adjusted so that the frequency band W61 in which the gain characteristic is flat is relatively on the low frequency side. On the other hand, graphs L63 and L64 indicated by dotted lines in FIG. 14 indicate the antenna gain of the antenna pair adjusted so that the frequency band W62 in which the gain characteristic is flat is relatively on the high frequency side. A graph L65 indicated by a solid line in FIG. 14 indicates an antenna gain obtained by combining the radiated electric fields of two antenna pairs.

  In the gain frequency characteristic of the array antenna according to the present embodiment, two frequency bands W61 and W62 having a gain fluctuation value within +/− δ dB are formed. Further, by making the flat frequency bands W61 and W62 formed by the two antenna pairs close to each other, the gain obtained by one antenna pair described in the fifth embodiment is obtained from the flattened frequency bandwidth W. Further, the antenna gain can be flattened over a wide frequency band. Note that the number of antenna pairs included in the array antenna according to the present embodiment may be three or more. By arraying a plurality of antenna pairs, it is possible to obtain a plurality of frequency bands whose gain fluctuation values are within +/− δ dB.

<Other embodiments>
In each of the above-described embodiments, the array antenna has been described in which not only the frequency characteristics of the gain of a plurality of antenna elements but also the frequency characteristics of the axial ratio are different among the elements. However, an array antenna in which at least the frequency characteristic of gain is different among elements is also included in one of the embodiments of the present invention. According to such an array antenna, the gain frequency characteristic can be flattened while suppressing an increase in antenna area.

  In each of the above-described embodiments, an array antenna in which patch antennas by slot feeding are arrayed is shown. However, it goes without saying that the antenna structure of each antenna element is not limited to the above-described embodiments. That is, each antenna element emits elliptically polarized waves when electric fields in two orthogonal directions (X-axis and Y-axis) are input, and can adjust input power in the X-axis direction and the Y-axis direction. It is only necessary to have a possible antenna structure. For example, the effect of the present invention can be obtained by a patch antenna structure using two-point feeding of a feeding line.

  Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention described above.

It is a top view of the array antenna concerning a 1st embodiment. It is sectional drawing of the antenna element which the array antenna concerning 1st Embodiment has. It is a figure which shows the input electric field to the antenna element which the array antenna concerning 1st Embodiment has, and the radiation electric field of an antenna element. It is a figure which shows the radiation electric field of the antenna element which the array antenna concerning 1st Embodiment has. It is a graph which shows the frequency characteristic of the gain of the array antenna concerning a 1st embodiment. It is a graph which shows the frequency characteristic of the axial ratio of the array antenna concerning 1st Embodiment. It is a figure which shows the radiation electric field of the antenna element which the array antenna which concerns on a comparative example has. It is a graph which shows the frequency characteristic of the gain of the array antenna which concerns on a comparative example. It is a graph which shows the frequency characteristic of the axial ratio of the array antenna which concerns on a comparative example. It is a top view of the array antenna concerning a 2nd embodiment. It is a top view of the array antenna concerning a 3rd embodiment. It is a top view of the array antenna concerning a 4th embodiment. It is a graph which shows the frequency characteristic of the gain of the array antenna concerning a 5th embodiment. It is a graph which shows the frequency characteristic of the gain of the array antenna concerning a 6th embodiment.

Explanation of symbols

100, 200, 300, 400 Array antenna 11, 12, 21, 22, 31, 32, 41, 42 Antenna element 101, 102 Radiation element 103, 104 Feed element 103a, 104a Cross slit 111, 112 Elliptical polarization pattern 105, 106 Feed line 207, 208 Phase control circuit 307, 308 Redundant path 407, 408 Stub

Claims (7)

A first antenna element that radiates elliptically polarized waves;
A second antenna element that radiates elliptically polarized waves radiated by the first antenna element and radiates elliptically polarized waves having the same turning direction and different major axis directions;
It said first and second antenna elements, the gain becomes maximum frequency (hereinafter, referred to as peak frequency) in the gain frequency characteristic different Ri, and frequencies of axial ratio minimum in the frequency characteristics of the axial ratio are different from each other, Array antenna.   2. The array antenna according to claim 1, wherein an angle formed by a major axis direction of elliptically polarized waves radiated from the first and second antenna elements is substantially 90 degrees. The first and second antenna elements are designed so that the frequency region in which the axial ratio is equal to or less than a predetermined value in the frequency characteristic of the axial ratio covers different frequency regions while having overlapping frequency regions. The array antenna according to claim 1 or 2 . Each of the first and second antenna elements includes a feeding element having a cross-shaped slit formed by intersecting two rectangular slits, and a radiating element fed from the feeding element ,
Each cross-shaped slit, the two short-side direction of the rectangular slit are different from each other in length, the array antenna according to any one of claims 1-3.   5. The array antenna according to claim 4, wherein the cross-shaped slit feeds power to the radiating element by dividing a high-frequency electric field into a component in a first direction and a component in a second direction orthogonal to each other.   The apparatus further comprises means for causing a phase difference in a feeding phase with respect to the first and second antenna elements in order to make the radiation field directions of the first and second antenna elements at the same time substantially the same. The array antenna according to any one of 1 to 5. The first and second antenna elements are designed such that the maximum gain values G_max at each of the peak frequencies are substantially the same,
The peak frequency of the second antenna element exists on a higher frequency side than the peak frequency of the first antenna element,
The gain frequency characteristics of the first and second antenna elements are equal to each other in a predetermined frequency band between the peak frequency of the first antenna element and the peak frequency of the second antenna element. Have a common frequency
The gain G of the first and second antenna elements at the common frequency has a predetermined fluctuation range allowed for the gain of the array antenna in the predetermined frequency band ± δ (where δ is a positive value) The array antenna according to any one of claims 1 to 6 , wherein the array antenna is determined so as to satisfy the following formula:
G_max−δ−3 [dB] ≦ G ≦ G_max + δ−3 [dB]

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