Planar Antenna

Abstract

To provide a planar antenna capable of widening a radiation direction and achieving wider band characteristics.SOLUTION: A planar antenna 1 comprises: a dielectric substrate 3 that has a first surface and a second surface; a resonance part 5 that has two resonators 51 and 53 configured by microstrip lines arranged on the first surface; an antenna part 7 arranged on the first surface and that has radiation elements 71 and 73 connected with the resonance part 5; and a ground layer formed on the second surface. The antenna part 7 has two or more resonance directions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a planar antenna having one or more radiating elements. [Background technology]

[0002] Wireless harnesses are expected to be a fundamental solution to problems such as wire jamming in wired wiring at moving parts inside mechatronic devices such as robot arms (see, for example, Non-Patent Document 1). In particular, wireless harnesses that use millimeter waves are seen as promising for application to devices such as robot arms, from the perspective of effective use of frequency resources. In such wireless harnesses, the use of planar antennas is desirable from the perspectives of integration with wireless modules and cost reduction. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Hiroshi Ban, Shoichi Kitazawa, and Kiyoshi Kobayashi, "Wireless Harness Technology Useful for Resource and Energy Conservation," IEICE Communications Magazine, No. 25, pp. 25-32, 2013 Summary of the Invention [Problem to be solved by the invention]

[0004] When a planar antenna mounted on a device whose orientation changes, such as a robot arm, has narrow directivity, the radiation direction changes when the device changes orientation, which can affect transmission quality. To reduce such an effect on transmission quality, a planar antenna mounted on a device whose orientation changes is required to have radiation characteristics that enable transmission and reception regardless of the orientation of the device. In other words, it is preferable for the planar antenna to have a wide radiation direction.

[0005] Furthermore, microstrip antennas, which are common planar antennas, have the problem of having a narrow bandwidth of less than a few percent. Methods for widening the frequency bandwidth of planar antennas such as microstrip antennas include increasing the thickness of the dielectric substrate or increasing the antenna width (the length in the direction perpendicular to the direction of the current in the resonant mode). In other words, these methods lower the antenna's radiation Q value. However, in high-frequency bands such as the millimeter-wave band, where the thickness of the dielectric substrate is limited, the lower limit of the radiation Q value is naturally set, making it difficult to achieve wideband characteristics compatible with a wide frequency band, such as the 60 GHz band, which is unlicensed, using a planar antenna alone.

[0006] The present invention has been made in response to the above circumstances, and has an object to provide a planar antenna having wider radiation characteristics and wider band characteristics. [Means for solving the problem]

[0007] In order to achieve the above object, a planar antenna according to one embodiment of the present invention comprises a dielectric substrate having a first surface and a second surface, a resonance section having two or more resonators formed by microstrip lines arranged on the first surface, an antenna section having one or more radiating elements arranged on the first surface and connected to the resonance section, and a ground layer formed on the second surface, wherein the antenna section has two or more resonance directions.

[0008] With this configuration, the radiation direction can be widened by having two or more different resonance directions. Therefore, even if the planar antenna is mounted on a device whose orientation changes, such as a robot arm, it can transmit and receive signals properly. In addition, by providing two or more resonators in front of the radiating element, a broadband can be achieved.

[0009] In the planar antenna according to an aspect of the present invention, the antenna section may have two or more radiating elements with different resonance directions.

[0010] With this configuration, the radiation direction can be widened by using two or more radiation elements with different resonance directions.

[0011] In the planar antenna according to an aspect of the present invention, the antenna section may have two radiating elements whose resonance directions are orthogonal to each other.

[0012] With this configuration, it becomes possible to radiate a plurality of orthogonal polarized waves, thereby widening the radiation direction.

[0013] In addition, in a planar antenna according to one aspect of the present invention, the antenna section has a radiating element of a dual resonance mode whose resonance directions are orthogonal to each other, and the ground layer may have an opening in at least a portion of the area corresponding to the radiating element in a planar view.

[0014] This configuration allows two different resonance directions to be achieved with a single radiating element, and also makes it possible to change the radiation Q value corresponding to each resonance direction by changing the size of the aperture.

[0015] In the planar antenna according to one aspect of the present invention, the ground layer may have an opening in at least a part of a portion corresponding to the radiating element in plan view.

[0016] With this configuration, it becomes possible to transmit and receive radio waves from the ground layer side as well.

[0017] In the planar antenna according to an aspect of the present invention, the resonating portion may have two or more half-wave resonators.

[0018] With this configuration, for example, the resonator section can be configured by two short-circuited half-wave resonators arranged in parallel.

[0019] In the planar antenna according to one aspect of the present invention, one end of the radiating element in the resonance direction may be short-circuited to the ground plane.

[0020] With this configuration, it is possible to increase the gain of the component in the direction perpendicular to the dielectric substrate. [Effects of the Invention]

[0021] According to a planar antenna according to one aspect of the present invention, it is possible to widen the radiation direction and achieve wider band characteristics. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a plan view showing the configuration of a planar antenna according to an embodiment of the present invention; [Figure 2] FIG. 10 shows a coupling topology of the planar antenna according to the embodiment. [Figure 3A] FIG. 10 is a diagram showing an example of a radiation pattern of one of the radiation elements in the embodiment; [Figure 3B] FIG. 10 is a diagram showing an example of a radiation pattern of one of the radiation elements in the embodiment; [Figure 4A] FIG. 10 shows an example of the radiation patterns of two radiating elements according to the embodiment. [Figure 4B] FIG. 10 shows an example of the radiation patterns of two radiating elements according to the embodiment. [Figure 5] FIG. 10 is a diagram showing an example of frequency characteristics of a planar antenna according to the embodiment; [Figure 6] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 7] FIG. 10 is a diagram showing another example of the ground layer in the embodiment; [Figure 8A] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 8B] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 9A] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 9B] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 10A]FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 10B] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 11A] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 11B] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 12] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 13] FIG. 10 is a plan view showing another example of the configuration of the planar antenna according to the embodiment. [Figure 14] FIG. 10 shows a robot arm on which a planar antenna according to the embodiment is mounted. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, a planar antenna according to the present invention will be described using embodiments. In the following embodiments, components with the same reference numerals are the same or equivalent, and repeated description may be omitted. The planar antenna according to this embodiment has one or more radiating elements having two or more different resonance directions, and two or more resonators in front of the one or more radiating elements.

[0024] 1 is a plan view showing the configuration of a planar antenna 1 according to this embodiment. The planar antenna 1 according to this embodiment includes a dielectric substrate 3, a resonator unit 5, an antenna unit 7, and a ground layer 9. This planar antenna 1 is a microstrip antenna. The frequency of the radio waves transmitted and received by the planar antenna 1 is not particularly limited, but may be, for example, a frequency in the range of 1 GHz to 300 GHz, or a frequency in the millimeter wave band (30 to 300 GHz).

[0025] The dielectric substrate 3 is a flat substrate and has a first surface which is the surface shown in Fig. 1 and a second surface which is the surface opposite to the first surface. The first surface is sometimes called the front surface, and the second surface is sometimes called the back surface.

[0026] The resonator unit 5 has two or more resonators configured with microstrip lines arranged on the first surface of the dielectric substrate 3. FIG. 1 shows a case in which the resonator unit 5 has two resonators 51 and 53, which are linear half-wave resonators arranged in parallel so that their resonance directions are parallel. The other resonators will be described later. Both ends of the resonators 51 and 53 are short-circuited to the ground layer 9 by vias 50. Therefore, the resonators 51 and 53 are both-end-short-circuited microstrip half-wave resonators. The upstream resonator 51 is connected to an input line 11 configured with a microstrip line. The resonators 51 and 53 are also connected by a connection line 51a configured with a microstrip line.

[0027] The antenna unit 7 is disposed on the first surface of the dielectric substrate 3 and includes one or more radiating elements connected to the resonator unit 5. The antenna unit 7 is typically connected to the final resonator 53 of the resonator unit 5. The antenna unit 7 has two or more different resonance directions. That is, two or more different resonance directions are realized by one or more radiating elements included in the antenna unit 7. The resonance direction refers to the direction of current in the resonance mode. The two different resonance directions may or may not be orthogonal. When the antenna unit 7 has two or more radiating elements, the resonance directions of at least two of the radiating elements are different. In this embodiment, the case where the radiating elements included in the antenna unit 7 are in a single resonance mode will be mainly described, and the case where the radiating elements are in a double resonance mode will be described later. The shape of the radiating elements may be, for example, rectangular, square, elliptical, or circular. In this embodiment, the case where the radiating elements are rectangular will be mainly described. FIG. 1 illustrates the case where the antenna unit 7 has two rectangular radiating elements 71 and 73. Other radiating elements will be described later. The radiating elements 71 and 73 have the same shape and are arranged so that their resonance directions, indicated by the solid double-headed arrows, are orthogonal. Therefore, the planar antenna 1 can transmit and receive multiple orthogonally polarized waves. The radiating elements 71 and 73 are connected to the resonator 53 by connection lines 71a and 73a, respectively, which are microstrip lines. Furthermore, if the polarization directions of the radio waves radiated from two or more radiating elements of the antenna unit 7 are orthogonal, the two or more radiating elements do not need to be excited in phase; however, if the polarization directions of the two or more radiating elements are not orthogonal, it is preferable that the two or more radiating elements be excited in phase.

[0028] The ground layer 9 is a ground conductor formed on the second surface of the dielectric substrate 3. The ground layer 9 may be formed over the entire second surface of the dielectric substrate 3, or an opening may be provided in part of the ground layer 9. In the planar antenna 1 of FIG. 1, it is assumed that the ground layer 9 (not shown) is formed over the entire second surface of the dielectric substrate 3. The ground layer 9 having an opening will be described later.

[0029] Fig. 2 is a diagram showing the coupling topology of the planar antenna 1 shown in Fig. 1. In Fig. 2, each node represents a resonator or a radiating element, and each link represents a coupling. In Fig. 2, nodes 1 and 2 correspond to resonators 51 and 53, respectively, and two nodes 3 correspond to radiating elements 71 and 73.

[0030] In the rectangular radiating elements 71 and 73 shown in FIG. 1, the resonant frequency f 03 can be adjusted, and the radiation Q value Q of the radiating elements 71 and 73 can be adjusted by adjusting the length in the direction perpendicular to the resonance direction (the length indicated by the double-headed dashed arrow. Hereinafter, the length in this direction may be referred to as the "width"). r The two radiating elements 71 and 73 are coupled to the resonator 53 at two points. The coupling coefficient k 23 It is possible to adjust the coupling coefficient k between the two radiating elements 71 and 73 by making the distance from one end of the resonator 53 to the connection position of the radiating element 71 in the resonance direction of the resonator 53 (the left-right direction in FIG. 1) the same as the distance from the other end of the resonator 53 to the connection position of the radiating element 73, i.e., by making the connection positions of the radiating elements 71 and 73 symmetrical in the resonance direction of the resonator 53. 23 can be made the same.

[0031] The electric field distribution of the resonator 53, both ends of which are short-circuited to the ground plane 9, is even symmetric about the center of the resonator 53, so that the two radiating elements 71 and 73 are excited in phase. 23If the same, the two radiating elements 71 and 73 are excited with the same amplitude.

[0032] The resonators 51 and 53 are coupled by being connected by a connection line 51a that is shorter than half the wavelength, and the length of the connection line 51a and the connection position of the connection line 51a determine the coupling coefficient k 12 The resonant frequency f of the resonators 51 and 53 can be adjusted. 01 , f 02 can be adjusted by changing the length of each line. Furthermore, the external Q factor Q e can be adjusted by the connection position of the input line 11 to the resonator 51.

[0033] As shown in Figures 3A and 3B, the radiating element 71 on the right side of Figure 1 radiates mainly x-component polarized waves in the front direction of the planar antenna 1 (i.e., the +z direction), and further radiates z-component polarized waves in the ±x directions of Figure 1. In contrast, the radiating element 73 on the left side of Figure 1 radiates mainly y-component polarized waves in the front direction of the planar antenna 1, and further radiates z-component polarized waves in the ±y directions of Figure 1. Therefore, the z-component polarized waves of the two radiating elements 71 and 73 are not orthogonal and are excited in phase. In this way, when two radiating elements 71 and 73 are used, as shown in Figures 4A and 4B, x-component and y-component polarized waves are simultaneously radiated in the front direction of the planar antenna 1, and z-component polarized waves are radiated in the horizontal direction of the xy plane (in reality, a launch angle occurs due to the influence of the ground layer 9).

[0034] Therefore, by appropriately designing the resonant frequencies and radiation Q values ​​of the radiating elements 71 and 73, and the resonant frequencies and external Q values ​​of the resonators 51 and 53, and the coupling coefficients, it becomes possible to radiate three orthogonal polarized waves while suppressing return loss within a specified frequency bandwidth. In other words, it becomes possible to widen the radiation direction.

[0035] Next, we will explain the specific methods for determining the resonant frequencies and radiation Q values ​​of radiating elements 71 and 73, the resonant frequencies and external Q values ​​of resonators 51 and 53, and each coupling coefficient. The normalized coupling matrix [M] in the frequency domain of the prototype low-pass filter of the coupling topology in Figure 2 is expressed by the following equation. Note that this normalized coupling matrix is ​​a matrix composed of normalized coupling coefficients that do not depend on the center frequency or bandwidth.

number

[0036] In the coupling topology of Fig. 2, the value of each matrix element of the normalized coupling matrix is ​​determined by determining the transfer function and the number of resonators. The number of resonators refers to the number when considering not only the resonators included in the resonance unit 5 but also the radiating elements included in the antenna unit 7 as resonators. In Fig. 2, the two radiating elements 71 and 73 are symmetrical, so only one radiating element is considered. Therefore, in the example of Fig. 2, the number of resonators is three, resulting in the above normalized coupling matrix [M]. In the following explanation, we will explain the case where the transfer function is a Chebyshev function with a predetermined passband ripple width and the number of resonators is three.

[0037] By using the relationship between each matrix element of the normalized coupling matrix of the prototype low-pass filter and each matrix element of the coupling matrix of the band-pass filter, it is possible to calculate the coupling coefficient, resonant frequency, and external Q values ​​of the input and output sides of the band-pass filter having the resonator unit 5 and antenna unit 7. This will be explained below. Here, if the center frequency of the band-pass filter is f0 and the frequency bandwidth is Δf, then the coupling coefficient k between the resonators 51 and 53 is i,i+1 (Here, i=1) is expressed by the following equation. The center frequency f0 can be determined as desired by the designer. On the other hand, the frequency bandwidth Δf is determined by the radiation Q value of the radiating element 71, as will be described later. Also, commas (,) in the subscripts of the coupling coefficient, etc. are added for convenience to make it easier to distinguish between two subscripts.

number

[0038] Furthermore, the coupling coefficient k between the resonator 53 and the radiating element 71 (or the radiating element 73) i,i+1 (Here, i=2) divides the power into two for the radiating elements 71 and 73, so the coefficient "1 / √2" is multiplied as shown in the following equation. Even if the coupling coefficient with the resonator 53 differs for each of the radiating elements 71 and 73, the coupling coefficient etc. can be found by multiplying by the corresponding coefficient as if the number of resonators were three.

number

[0039] The radiation Q value Q of the radiating element 71 (or the radiating element 73) r is the element M of the normalized coupling matrix N,L (N is the number of resonators, here N=3), and it is expressed as follows:

number

[0040] Therefore, the element M of the normalized coupling matrix N,L is determined, the upper limit of the realizable frequency bandwidth Δf is the radiation Q value Q of the physically realizable radiating element 71 (or radiating element 73). r The radiation quality factor Q is determined by r The lower limit of is determined depending on the thickness of the dielectric substrate 3. The radiation Q value Q r may be determined.

[0041] Similarly, the external quality factor Q e is the element M of the normalized coupling matrix S1 is expressed as follows using the following equation:

number

[0042] The resonance frequency f between the radiating element 71 (or the radiating element 73) and the resonators 51 and 53 0i is the diagonal element of the normalized coupling matrix M ii (Here, i=1, 2, 3) can be obtained by solving the following equation.

number

[0043] In this way, the coupling coefficients, resonant frequencies, radiation Q values, and external Q values ​​are determined according to the elements of the normalized coupling matrix. The determined coupling coefficients, etc. determine the connection position of the input line 11, the lengths of the resonators 51 and 53, the position and length of the connecting line 51a, the connection positions of the connecting lines 71a and 73a, and the widths and lengths in the resonance direction of the radiating elements 71 and 73. Therefore, by configuring the planar antenna 1 according to these determined details, it is possible to realize a planar antenna 1 that has the desired band characteristics of center frequency f0 and frequency bandwidth Δf, is capable of radiating three orthogonal polarized waves, and has reduced return loss.

[0044] Figure 5 shows the total gain of the three components at the front of the planar antenna 1 designed in this way, and the reflection coefficient S 11 5 shows the change in impedance depending on the frequency. As shown in FIG. 5, the planar antenna 1 has the frequency selection characteristics of a band-pass filter. It also achieves a flat gain characteristic with low frequency dependency within a predetermined frequency band. As with a band-pass filter, the frequency bandwidth can be widened by adjusting the degree of coupling between multiple resonators including radiating elements. Therefore, the stronger the coupling, the wider the frequency bandwidth. Therefore, the planar antenna 1 according to this embodiment can achieve good impedance matching over a wider frequency bandwidth than a planar antenna having only a single radiating element.

[0045] In addition, when cross-coupling between resonators (i.e., coupling between non-adjacent resonators) is used, a transmission zero (attenuation pole) can be generated in the stopband, resulting in a sharper frequency selection characteristic.

[0046] In the above explanation, the case where the coupling coefficients, resonant frequencies, radiation Q values, and external Q values ​​of the band-pass filter having three resonators shown in Fig. 1 are calculated using the values ​​of the matrix elements of the normalized coupling matrix of the prototype low-pass filter has been described, but it is clear that the coupling coefficients, resonant frequencies, radiation Q values, and external Q values ​​of band-pass filters of other configurations can also be calculated in a similar manner using the values ​​of the matrix elements of the normalized coupling matrix of the prototype low-pass filter. Therefore, it goes without saying that for planar antennas 1 of configurations other than that shown in Fig. 1, the resonators of the resonant unit 5 and the radiating elements of the antenna unit 7 can be regarded as band-pass filters, and a planar antenna 1 with reduced return loss can be similarly realized.

[0047] As described above, the planar antenna 1 according to this embodiment includes the antenna section 7 having the radiating elements 71 and 73 and the resonator section 5 having the two resonators 51 and 53 arranged in front of the antenna section 7, thereby widening the radiation direction and achieving a wider frequency band. Furthermore, good impedance matching characteristics can be achieved within a predetermined frequency band, and flat gain characteristics can also be obtained. Furthermore, by using the connection wire 51a to connect the resonators 51 and 53, slight manufacturing errors do not significantly affect the characteristics, as is the case with narrow gap structures. Furthermore, by employing a double-short circuit structure for the resonators 51 and 53, deviations in the resonant frequency due to etching accuracy at the ends of the resonators 51 and 53 can be minimized.

[0048] Next, a modification of the planar antenna 1 according to this embodiment will be described. [Radiating element with one end shorted] As shown in FIG. 6, the radiating elements 71 and 73 may have one end shorted to the ground plane 9 in the resonant direction. In FIG. 6, the rectangular radiating elements 71 and 73 have one power supply side connected to the ground plane 9 through a via 50, one of the sides perpendicular to the resonant direction. As a result, the antenna unit 7 has two planar inverted-F antennas. In this case, the radiating elements 71 and 73 each operate as a quarter-wave resonant antenna. Therefore, radiation occurs not only from the patch portions on the top surfaces of the radiating elements 71 and 73 but also from the conductive via 50 perpendicular to the ground plane 9. This increases the z-component gain. Furthermore, while the planar antenna 1 of FIG. 1 has slightly higher gain in the x-axis or y-axis direction compared to other directions in the angular characteristics of the z-component gain, the planar antenna 1 of FIG. 6 can also reduce the deviation of the z-component gain due to the angle in the horizontal direction. However, this results in a decrease in the x- and y-component gain and a slight sacrifice in the unidirectionality of the radiation pattern.

[0049] [Ground plane with openings] In the planar antenna 1 shown in FIGS. 1 and 6, the ground plane 9 is formed over the entire rear surface (i.e., the second surface) of the dielectric substrate 3, but this is not necessarily the case. When polarized waves of the x and y components are also radiated toward the rear surface of the planar antenna 1, the ground plane 9 may have openings 9a and 9b in at least a portion of the rear surface of the radiating elements 71 and 73, as shown in FIG. 7. That is, the ground plane 9 may have openings 9a and 9b in at least a portion of the areas corresponding to the radiating elements 71 and 73 in a planar view (i.e., when viewed from the normal direction of the dielectric substrate 3). FIG. 7 illustrates the planar antenna 1 as viewed from the second surface side. By converting the planar antenna 1 into a microstrip antenna having openings 9a and 9b in the ground plane 9, the radiation Q value can be adjusted not only by the width of the radiating elements 71 and 73 but also by the size of the openings 9a and 9b.

[0050] [Multiple track coupling] The resonators 51 and 53 of the planar antenna 1 may be coupled by multiple lines, as shown in FIG. 8A. The input line 11 of the planar antenna 1 shown in FIG. 8A branches into two lines 11a and 11b on the connection side with the resonator 51. The two lines 11a and 11b couple to the resonator 51. The resonators 51 and 53 are also coupled to each other by two connecting lines 51a and 51b. The planar antenna 1 shown in FIG. 8A has a bilaterally symmetrical structure. In this case, as with the planar antenna 1 shown in FIG. 1, the coupling coefficients and resonant frequencies can be calculated from the values ​​of the matrix elements of the normalized coupling matrix. By designing the planar antenna 1 accordingly, it is possible to widen the radiation direction and achieve wider bandwidth characteristics. The same applies to the other planar antennas 1 described below.

[0051] Join at Gap The resonators 51 and 53 of the planar antenna 1 may be coupled by a gap, as shown in FIG. 9A. The input line 11 of the planar antenna 1 shown in FIG. 9A has a line 11c provided on the resonator 51 side in parallel to the resonator 51. The line 11c and the resonator 51 are coupled by a gap therebetween, and the resonators 51 and 53 are also coupled by a gap therebetween. In this way, coupling may be achieved by a gap without a connecting line. The planar antenna 1 shown in FIG. 9A also has a symmetrical structure.

[0052] [Resonator section with open-ended microstrip half-wavelength resonators] The resonators 61 and 63 of the resonator unit 5 of the planar antenna 1 may be open-ended half-wave resonators formed of microstrip lines, as shown in Fig. 10A. In the resonator unit 5 shown in Fig. 10A, the resonators 61 and 63 are coupled by a gap, and the input line 11 and the resonator 61 are also coupled by a gap. In this case, the resonators 61 and 63 do not need to be connected to the ground plane 9, making it easier to manufacture the planar antenna 1. In Fig. 10A, the connection lines 71a and 73a of the radiating elements 71 and 73 are connected to the same position on the resonator 63, so that the radiating elements 71 and 73 are excited with the same phase and amplitude.

[0053] [Resonator section with microstrip quarter-wave resonator] As shown in FIG. 11A, the resonators 81 and 83 included in the resonator unit 5 of the planar antenna 1 may be quarter-wave resonators formed of microstrip lines. In this case, one end of each of the resonators 81 and 83 is short-circuited. That is, one end of each of the resonators 81 and 83 is connected to the ground plane 9 by a via 50. In the resonator unit 5 shown in FIG. 11A, the resonators 81 and 83 are coupled by a gap, and the input line 11 and the resonator 81 are also coupled by a gap. In this case, the length of the resonators 81 and 83 in the resonance direction can be shortened, allowing for a smaller size than the planar antenna 1 shown in FIG. 10A. In FIG. 11A, as in FIG. 10A, the radiating elements 71 and 73 are excited with the same phase and amplitude.

[0054] [Antenna section with more than two radiating elements] As shown in FIG. 12, the antenna unit 7 of the planar antenna 1 may have four radiating elements 75a, 75b, 77a, and 77b. In FIG. 12, the resonant directions of the radiating elements 75a and 75b are the same, and the resonant directions of the radiating elements 77a and 77b are the same. The resonant directions of the radiating elements 75a and 75b are perpendicular to the resonant directions of the radiating elements 77a and 77b. Therefore, the planar antenna 1 shown in FIG. 12 is substantially the same as the planar antenna 1 shown in FIG. 8A. However, since two radiating elements are used for radiation in one resonant direction, it can also be considered as an array antenna for each resonant direction. Note that it is preferable that the power supply to the four radiating elements 75a, 75b, 77a, and 77b is not reverse-phase power supply. While FIG. 12 illustrates a case where the antenna unit 7 has four radiating elements, the antenna unit 7 may have three radiating elements or five or more radiating elements. Furthermore, at least two radiating elements included in the antenna unit 7 may have, for example, resonance directions that are orthogonal to each other. Alternatively, the antenna unit 7 may have two or more radiating elements whose resonance directions are not orthogonal to each other. Note that when the antenna unit 7 has two or more radiating elements whose polarization directions are not orthogonal to each other, it is preferable that each radiating element be excited in the same phase.

[0055] [Antenna section with one radiating element] As shown in FIG. 13, the antenna unit 7 of the planar antenna 1 may have one radiating element 79. The radiating element 79 is a double-resonance mode radiating element with orthogonal resonant directions, indicated by the double arrows, i.e., a square-shaped radiating element. The radiating element 79 is connected to the resonator 53 by connecting lines 79a and 79b formed by microstrip lines. In this case, the size (length of one side) of the radiating element 79 is determined by the resonant frequency of the radiating element 79, so the radiation Q value cannot be changed by the size of the radiating element 79. Therefore, the ground layer 9 of the planar antenna 1 shown in FIG. 13 has an opening in at least a portion corresponding to the radiating element 79 in a planar view. The radiation Q value is adjusted by the size of the opening. Although FIG. 13 shows a case where the radiating element 79 is square-shaped, the radiating element 79 may also be circular, for example.

[0056] [Resonating unit with three or more resonators] The resonator unit 5 of the planar antenna 1 may have three or more resonators. For example, the resonator unit 5 may have resonators 51, 53, and 55 as shown in FIGS. 8B and 9B, resonators 61, 63, and 65 as shown in FIG. 10B, or resonators 81, 83, and 85 as shown in FIG. 11B. In FIG. 8B, the resonators 51 and 55 are connected by two connection lines 55a and 55b. In FIG. 9B, the resonators 51 and 55 are coupled by a gap, and the line 11c of the input line 11 and the resonator 55 are also coupled by a gap. In FIG. 10B, the resonators 61 and 65 are coupled by a gap, and the input line 11 and the resonator 65 are also coupled by a gap. In the resonator unit 5 shown in FIG. 11B, the resonators 81 and 85 are coupled by a gap, and the input line 11 and the resonator 85 are also coupled by a gap. In these examples, the resonator unit 5 has three resonators, but it goes without saying that the resonator unit 5 may have four or more resonators. As the number of resonators in the resonator unit 5 increases, the loss increases. In other words, the gain of the planar antenna 1 decreases. On the other hand, it becomes possible to obtain a steeper frequency selection characteristic.

[0057] [Mixture of gap coupling and line coupling] 8A and 8B illustrate a case where multiple resonators are coupled by a line, and Fig. 9A and 9B illustrate a case where multiple resonators are coupled by a gap, but among the multiple resonators included in the resonance unit 5, some resonators may be coupled by a line and other resonators may be coupled by a gap. For example, if the resonance unit 5 has three resonators 55, 51, and 53 arranged in parallel, as in Fig. 8B and 9B, the resonators 55 and 51 may be coupled by a line and the resonators 51 and 53 may be coupled by a gap.

[0058] [Planar antenna mounted on a robot arm] FIG. 14 is a diagram showing an example in which the planar antenna 1 is mounted on a robot arm 100. As shown in FIG. 14, a plurality of planar antennas 1 are arranged on each arm and tip of the robot arm 100. A signal for controlling the robot arm 100 is transmitted from a base station antenna 101 on the base station. The signal from the base station is received by each planar antenna 1, and motors, actuators, and the like are controlled. Sensor information (e.g., encoder values) within the robot arm 100 is transmitted from the planar antenna 1 of the robot arm 100 to the base station antenna 101. In this case, the positional relationship of the planar antennas 1 changes as the robot arm 100 moves, but the planar antenna 1 according to this embodiment has a wider radiation direction, enabling stable wireless communication at all times.

[0059] [Radiating element shape] In this embodiment, the case where one or more radiating elements of the antenna unit 7 are rectangular has been mainly described, but as described above, the radiating elements may be in a shape other than rectangular, for example, circular or elliptical. Therefore, in the antenna unit 7 described above, for example, an elliptical radiating element may be used instead of the rectangular radiating element.

[0060] Furthermore, the present invention is not limited to the above-described embodiment, and various modifications are possible, and it goes without saying that these modifications are also included within the scope of the present invention. [Industrial Applicability]

[0061] As described above, the planar antenna according to one aspect of the present invention has the effect of being able to widen the radiation direction and achieve wider bandwidth characteristics, making it useful as a planar antenna to be mounted on, for example, a robot arm. [Explanation of symbols]

[0062] 1. Planar antenna 3 Dielectric substrate 5 Resonant part 7 Antenna section 9 Ground Layer 11 Input line 50 Beer 51, 53, 55, 61, 63, 65, 81, 83, 85 resonator 71, 73, 75a, 75b, 77a, 77b, 79 Radiating elements

Claims

1. a dielectric substrate having a first surface and a second surface; a resonator unit having two or more resonators formed by microstrip lines arranged on the first surface; an antenna section disposed on the first surface and having one or more radiating elements connected to the resonator section; a ground layer formed on the second surface, The antenna unit has two radiating elements of the same shape whose resonance directions are perpendicular to each other, A planar antenna, wherein the connection positions of the two radiating elements and the last-stage resonator of the resonance section are symmetrical with respect to the resonance direction of the last-stage resonator.

2. A planar antenna as described in claim 1, wherein both ends of the final stage resonator are short-circuited to the ground layer.

3. 3. The planar antenna according to claim 1, wherein said ground layer has an opening at least in a part of a portion corresponding to said radiating element in a plan view.

4. 4. The planar antenna according to claim 1, wherein said resonator portion has two or more half-wave resonators.

5. 5. The planar antenna according to claim 1, wherein one end of said radiating element in a resonance direction is short-circuited to said ground plane.

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