Antenna and radar module

Abstract

Provided is an antenna comprising: at least one planar antenna element connected to a feed line; and at least one parasitic antenna element disposed so as to face the planar antenna element with a dielectric layer interposed therebetween.

Description

Antenna and radar module

[0001] The present disclosure relates to an antenna and a radar module. This application claims priority based on Japanese Application No. 2024-189059 filed on October 28, 2024, and incorporates all the descriptions set forth in the said Japanese application.

[0002] Patent Document 1 discloses a common-line type array antenna used for a millimeter-wave radar.

[0003] Japanese Unexamined Patent Application Publication No. 2019-186656

[0004] The antenna according to an embodiment includes at least one planar antenna element connected to a power supply line and at least one non-powered antenna element disposed opposite to the planar antenna element via a dielectric layer.

[0005] Figure 1 is a block diagram showing an example of a radar module. Figure 2 is a perspective view of a circuit board including a transmitting antenna according to the first embodiment. Figure 3 is a cross-sectional view of the main part of the circuit board, showing a cross-section along the X-Z plane including the line III-III in Figure 2. Figure 4 is a plan view showing the antenna portion of the circuit board. Figure 5 is a perspective view of a circuit board including a transmitting antenna according to the second embodiment. Figure 6 is a plan view showing the antenna portion of the circuit board. Figure 7 is a perspective view of a circuit board including a transmitting antenna according to the third embodiment. Figure 8 is a plan view showing the antenna portion of the circuit board. Figure 9 is a cross-sectional view of the main part of a circuit board according to the fourth embodiment. Figure 10 is a diagram showing a modified example of the first embodiment. Figure 11 is a diagram showing a modified example of the first embodiment. Figure 12 is an example of a graph showing the frequency characteristics of the return loss for Example 1 and Comparative Example 1, respectively. Figure 13 is an example of a graph showing the directivity in the horizontal plane for Example 1 and Comparative Example 1, respectively. Figure 14 is an example of a graph showing the directivity in the vertical plane for Example 1 and Comparative Example 1, respectively. Figure 15 is an example of a graph showing the frequency characteristics of the return loss for Example 2 and Comparative Example 2. Figure 16 is an example of a graph showing the directivity in the horizontal plane for Example 2 and Comparative Example 2. Figure 17 is an example of a graph showing the directivity in the vertical plane for Example 2 and Comparative Example 2. Figure 18 is an example of a graph showing the directivity in the horizontal plane for Example 3. Figure 19 is an example of a graph showing the directivity in the horizontal plane for Example 1. Figure 20 is an example of a graph showing the directivity in the vertical plane for Example 3. Figure 21 is an example of a graph showing the directivity in the vertical plane for Example 1. Figure 22 is an example of a graph showing the frequency characteristics of the return loss for Example 4. Figure 23 is an example of a graph showing the directivity in the horizontal plane for Example 4. Figure 24 is an example of a graph showing the directivity in the vertical plane for Example 4.

[0006] [Problems this disclosure aims to solve] Millimeter-wave radar is sometimes installed in vehicles such as automobiles for the purpose of object detection. Automotive millimeter-wave radar is pre-allocated with usable frequency bands of 76-77 GHz and 77-81 GHz.

[0007] However, the combline-type array antennas used in the conventional examples described above are structurally disadvantageous for use in wideband applications because they are forward-wave fed, and there were cases where the usable frequency band could not be effectively utilized.

[0008] Therefore, this disclosure aims to provide an antenna that can be used over a wider bandwidth.

[0009] [Effects of this disclosure] According to this disclosure, it is possible to obtain an antenna that can be used in a wider bandwidth.

[0010] [Description of Embodiments in this Disclosure] First, the contents of the embodiments will be listed and described. [Summary of Embodiments]

[0011] (1) The antenna according to the embodiment comprises at least one planar antenna element connected to a feed line, and at least one parasitic antenna element positioned opposite the planar antenna element via a dielectric layer. With the above configuration, resonance occurs in the parasitic antenna element positioned opposite the planar antenna element. At this time, if the resonant frequency of the parasitic antenna element and the frequency of the signal radiated from the planar antenna element are different from each other, the frequency band that the antenna can transmit and receive can be expanded. As a result, the usable frequency band of the antenna is made wider.

[0012] (2) In addition, in the antenna described in (1) above, the parasitic antenna element may have a first surface facing the planar antenna element and a second surface opposite the first surface that constitutes a radiating surface. In this case, the radiated waves from the second surface and the radiated waves from the planar antenna element can be radiated in the same direction.

[0013] (3) In the antenna described in (1) or (2) above, the dielectric layer may include a fluororesin layer. In this case, it is advantageous to obtain broadband frequency characteristics.

[0014] (4) In any one of the antennas described in (1) to (3) above, the relative permittivity of the dielectric layer may be 3.4 or less. In this case, it is more advantageous to obtain broadband frequency characteristics.

[0015] (5) In any one of the antennas described in (1) to (4) above, the dielectric loss tangent of the dielectric layer may be 0.003 or less. In this case as well, it is more advantageous to obtain broadband frequency characteristics.

[0016] (6) In any one of the antennas described in (1) to (5) above, when the planar antenna element is viewed from above, the parasitic antenna element may have a contour surrounding the planar antenna element. In this case, the entire planar antenna element faces the parasitic antenna element, so that resonance can be effectively generated in the parasitic antenna element.

[0017] (7) In any one of the antennas described in (1) to (6) above, if there are multiple planar antenna elements, the multiple planar antenna elements may be arranged in a comb line configuration along the direction in which the feed line extends. In this case, the multiple planar antenna elements function as an array antenna. This forms a beam that points in a predetermined direction.

[0018] (8) In the antenna described in (7) above, if the plurality of planar antenna elements have a rectangular shape with a pair of first sides that intersect in the direction in which the feed line extends, and the parasitic antenna element has a rectangular shape with a pair of second sides that intersect in the direction in which the feed line extends, when viewing the planar antenna elements on which the parasitic antenna elements are positioned opposite each other from a planar perspective, the pair of first sides may be located between the pair of second sides. In this case, the positional relationship between the planar antenna elements and the parasitic antenna elements can suppress the shift in directivity caused by the shift along the longitudinal direction of the feed line.

[0019] (9) In the antenna described in (7) above, the plurality of planar antenna elements include a first group of planar antenna elements and a second group of planar antenna elements including the same number of planar antenna elements as the first group of planar antenna elements, and the feed line has a feed point, a first line extending from the feed point in a first direction, and a second line extending from the feed point in a second direction opposite to the first direction, and the first group of planar antenna elements is connected to the first line and the second group of planar antenna elements is connected to the second line, then the first group of planar antenna elements and the second group of planar antenna elements may be point-symmetric with respect to the longitudinal center of the feed line. In this case, when the frequency of the fed signal changes, the directivity of the first group of planar antenna elements and the directivity of the second group of planar antenna elements change so as to be symmetric with respect to the center of the feed line. Therefore, the changes in directivity in the first planar antenna element group and the changes in directivity in the second planar antenna element group cancel each other out, resulting in no change in the antenna's directivity. Thus, it is possible to suppress the shift in the antenna's directivity that occurs in response to changes in frequency.

[0020] (10) In any one of the antennas described in (7) to (9) above, if there are multiple of the at least one parasitic antenna elements, the multiple parasitic antenna elements may be arranged in correspondence with the multiple planar antenna elements. In this case, resonance can be generated in the multiple parasitic antenna elements.

[0021] (11) An antenna, which is an embodiment from another perspective, comprises a combline type array antenna section having a feed line and a plurality of planar antenna elements connected to the feed line, and at least one parasitic antenna element positioned opposite the planar antenna elements via a dielectric layer. With the above configuration, the frequency band that can be transmitted and received by the antenna can be expanded, and as a result, it becomes possible to use it in a wider bandwidth.

[0022] (12) A radar module, which is an embodiment from another perspective, includes a circuit board including an antenna having at least one planar antenna element connected to a power supply line and at least one unpowered antenna element positioned opposite the planar antenna element via a dielectric layer, and a radar circuit that transmits and receives radar signals using the antenna. With the above configuration, by using an antenna that can be used in a wider bandwidth, it is possible to widen the frequency band used for object detection.

[0023] (13) In the radar module described in (12) above, if the circuit board comprises an antenna layer including the planar antenna element, the dielectric layer, and the parasitic antenna element, and a substrate having a first main surface and a second main surface opposite to the first main surface, and the antenna layer is provided on the first main surface side, the radar circuit may be provided on the second main surface side. In this case, the arrangement of the radar circuit can be made less likely to affect the arrangement of the antenna.

[0024] (14) In the radar module described in (12) above, if the circuit board comprises the planar antenna element, the dielectric layer, and an antenna layer including the parasitic antenna element, the radar circuit may be provided on the antenna layer. In this case, the thickness of the circuit board can be reduced.

[0025] [Details of Embodiments] Preferred embodiments will be described below with reference to the drawings. At least some of the embodiments described below may be combined as desired. [About the Radar Module] Figure 1 is a block diagram showing an example of a radar module. This radar module 1 is used, for example, in an on-board millimeter-wave radar mounted on a vehicle. The radar module 1 comprises a plurality of transmitting antennas 2, a plurality of receiving antennas 4, and a radar circuit 6.

[0026] Multiple transmitting antennas 2 and multiple receiving antennas 4 are connected to a radar circuit 6. The radar circuit 6 generates a predetermined radar signal and transmits the radar signal via the multiple transmitting antennas 2. The radar circuit 6 receives reflected wave signals via the multiple receiving antennas 4. The reflected wave signal is the signal that has been reflected by an object or the like from the radar signal transmitted from the multiple transmitting antennas 2. The reflected wave signal received by the radar circuit 6 is processed and used to detect the distance, direction, speed, etc., to an object.

[0027] [About the First Embodiment] Figure 2 is a perspective view of a circuit board including a transmitting antenna 2 according to the first embodiment. Figure 2 shows one of the multiple transmitting antennas 2. In the following description, one transmitting antenna 2 will be described, but the other transmitting antennas 2 and the multiple receiving antennas 4 have the same configuration as one transmitting antenna 2. Also, in the following description, the transmitting antenna 2 will be simply referred to as antenna 2.

[0028] In Figure 2, the circuit board 10 is a board having various parts included in the radar module 1, such as the antenna 2. In the following explanation, the three mutually orthogonal directions in each figure will be referred to as the X direction, Y direction, and Z direction. Also, as shown in Figure 1, one direction of the X direction will be the X1 direction, and the opposite direction of the X1 direction will be the X2 direction. One direction of the Y direction will be the Y1 direction, and the opposite direction of the Y1 direction will be the Y2 direction. One direction of the Z direction will be the Z1 direction, and the opposite direction of the Z1 direction will be the Z2 direction.

[0029] The circuit board 10 includes a first dielectric layer 12, a second dielectric layer 14, a substrate 16, and a third dielectric layer 18. The first dielectric layer 12, the second dielectric layer 14, the substrate 16, and the third dielectric layer 18 are stacked in order along the Z2 direction.

[0030] Antenna 2 comprises an array antenna section 20 and a plurality of passive antenna elements 22. The array antenna section 20 is provided between a first dielectric layer 12 and a second dielectric layer 14. The array antenna section 20 is a conductor pattern (conductor layer) and is made of a conductive material such as copper. The array antenna section 20 includes a plurality of planar antenna elements 24 and a feed line 26. The plurality (four in the illustrated example) of planar antenna elements 24 have a rectangular shape with their longest side aligned along the Y direction. The dimensions of the four planar antenna elements 24 are the same. The four planar antenna elements 24 are arranged side by side along the X direction. The feed line 26 extends along the X direction. The four planar antenna elements 24 are connected to the feed line 26. The X1 direction end 26a of the feed line 26 is connected to the planar antenna element 24 located at the X1 direction end of the four planar antenna elements 24. The end 26b of the power supply line 26 on the X2 direction side has a power supply point 27.

[0031] Multiple parasitic antenna elements 22 are provided on the surface of the first dielectric layer 12 facing the Z1 direction. The multiple parasitic antenna elements 22 are conductor patterns (conductor layers) and are made of a conductive material such as copper. The multiple (four in the illustrated example) parasitic antenna elements 22 have a rectangular shape with their longest side aligned with the Y direction. The dimensions of the four parasitic antenna elements 22 are the same. The four parasitic antenna elements 22 are not connected to a feed line or the like. Therefore, the four parasitic antenna elements 22 do not receive power from a feed line or the like.

[0032] When the four planar antenna elements 24 are viewed from above, the four parasitic antenna elements 22 are arranged so as to overlap the four planar antenna elements 24. Therefore, the four planar antenna elements 24 and the four parasitic antenna elements 22 are arranged facing each other via the first dielectric layer 12. The four planar antenna elements 24 and the four parasitic antenna elements 22 will be described in detail later.

[0033] Figure 3 is a cross-sectional view of the main part of the circuit board 10, showing a cross-section along the X-Z plane including the III-III line in Figure 2. The III-III line is a straight line passing through the center of the power supply line 26 in the width direction (Y direction).

[0034] As described above, the circuit board 10 includes a first dielectric layer 12, a second dielectric layer 14, a substrate 16, and a third dielectric layer 18. The substrate 16 is, for example, a layer made of glass epoxy. The substrate 16 is made up of multiple layers (not shown). Wiring and the like necessary for the radar module 1 are provided inside the substrate 16. The substrate 16 has a first main surface 16a facing in the Z1 direction and a second main surface 16b facing in the Z2 direction. The second main surface 16b is the opposite surface of the first main surface 16a. Grounding conductor plates 30 and 32 are provided on the first main surface 16a and the second main surface 16b, respectively. The grounding conductor plates 30 and 32 are, for example, conductive plates (conductor layers) made of copper or the like.

[0035] The second dielectric layer 14 is provided on the ground conductor plate 30. That is, the ground conductor plate 30 is interposed between the second dielectric layer 14 and the first main surface 16a. The second dielectric layer 14 has a main body layer 14a and an adhesive layer 14b. The adhesive layer 14b is provided on the ground conductor plate 30. The main body layer 14a is provided on the adhesive layer 14b.

[0036] An array antenna section 20 is provided on the main body layer 14a. The array antenna section 20 is a conductive pattern as described above. The array antenna section 20 is provided on a portion of the main body layer 14a, as shown in Figure 2.

[0037] The first dielectric layer 12 is provided on the second dielectric layer 14. In other words, the array antenna portion 20 is interposed between the first dielectric layer 12 and the second dielectric layer 14. The first dielectric layer 12 has a main body layer 12a and an adhesive layer 12b. The adhesive layer 12b is provided on the second dielectric layer 14 so as to cover the array antenna portion 20. The main body layer 12a is provided on the adhesive layer 12b.

[0038] Multiple parasitic antenna elements 22 are provided on the first dielectric layer 12. Therefore, the first dielectric layer 12 is interposed between the multiple parasitic antenna elements 22 and the array antenna section 20 (multiple planar antenna elements 24). In other words, the antenna 2 is included in the antenna layer 15 provided on the second dielectric layer 14. The antenna layer 15 includes the array antenna section 20, the first dielectric layer 12, and the multiple parasitic antenna elements 22.

[0039] The adhesive layers 14b and 12b are layers composed of adhesive. Preferably, the adhesives constituting the adhesive layers 14b and 12b can be pressed onto the substrate 16 and the second dielectric layer 14 at a temperature of 200 degrees Celsius or less. The main body layers 14a and 12a include a fluororesin layer composed of fluororesin.

[0040] The relative permittivity of the first dielectric layer 12 and the second dielectric layer 14 is preferably 3.4 or less. Furthermore, the dielectric loss tangent of the first dielectric layer 12 and the second dielectric layer 14 is preferably 0.003 or less.

[0041] The difference between the relative permittivity of the main layers 14a and 12a and the relative permittivity of the adhesive layers 14b and 12b is preferably 0.1 or less. The relative permittivity of the adhesive layers 14b and 12b (main layers 14a and 12a) can be calculated based on the relative permittivity of the dielectric layers 14 and 12 and the relative permittivity of the main layers 14a and 12a (adhesive layers 14b and 12b). The dielectric loss tangent values ​​of the adhesive layers 14b and 12b and the dielectric loss tangent values ​​of the main layers 14a and 12a are preferably 0.004 or less and 0.003 or less, respectively. The dielectric loss tangent values ​​of the adhesive layers 14b and 12b (main layers 14a and 12a) can be calculated based on the dielectric loss tangent values ​​of the dielectric layers 14 and 12 and the dielectric loss tangent values ​​of the main layers 14a and 12a (adhesive layers 14b and 12b).

[0042] The adhesive layers 14b, 12b and the main body layers 14a, 12a may contain fillers. The constituent materials of the fillers are, for example, silica and titanium oxide. The relative permittivity and dielectric loss tangent values ​​of the first dielectric layer 12 and the second dielectric layer 14 can be adjusted by adjusting the filler content.

[0043] Also, in FIG. 3, the thickness T1 is preferably not less than the thickness T2 and not more than three times the thickness T2. The thickness T1 is the thickness of the portion of the first dielectric layer 12 that is interposed between the wireless power feeding antenna element 22 and the array antenna portion 20. The thickness T2 is the thickness of the portion of the second dielectric layer 14 that is interposed between the ground conductor plate 30 and the array antenna portion 20. When the thickness T1 is smaller than the thickness T2, there is a possibility that appropriate resonance cannot be generated in the four wireless power feeding antenna elements 22. Also, when the thickness T1 is larger than three times the thickness T2, the distance between the four wireless power feeding antenna elements 22 and the four planar antenna elements 24 becomes too large, and there is a possibility that appropriate resonance cannot be generated in the four wireless power feeding antenna elements 22. By setting the thickness T1 to be not less than the thickness T2 and not more than three times the thickness T2, appropriate resonance can be generated in the four wireless power feeding antenna elements 22. Note that the resonance of the wireless power feeding antenna element 22 will be described later.

[0044] The third dielectric layer 18 is provided on the ground conductor plate 32. That is, the ground conductor plate 32 is interposed between the third dielectric layer 18 and the second main surface 16b. The third dielectric layer 18 has a main body layer 18a and an adhesive layer 18b. The adhesive layer 18b is provided on the ground conductor plate 32. The main body layer 18a is provided on the adhesive layer 18b. The adhesive layer 18b is formed of the same adhesive as the adhesive layers 14b and 12b. Also, the main body layer 18a is formed of the same fluororesin as the main body layers 14a and 12a.

[0045] An IC (Integrated Circuit) chip 36 for radar is mounted on the main body layer 18a. The IC chip 36 is a chip including the radar circuit 6. The IC chip 36 is mounted at a position facing the power feeding line 26 of the array antenna portion 20. The IC chip 36 is connected to the ground conductor plate 32 via a via 38. Also, the IC chip 36 is connected to the end portion 26b of the power feeding line 26 via a via 40. The connection point between this power feeding line 26 and the via 40 is the power feeding point 27.

[0046] The vias 38 and 40 are columnar members made of a conductive material such as copper. The via 38 penetrates the third dielectric layer 18 and electrically connects the IC chip 36 and the ground conductor plate 32. The via 40 penetrates the third dielectric layer 18, the ground conductor plate 32, the base material 16, the ground conductor plate 30, and the second dielectric layer 14, and electrically connects the IC chip 36 and the power supply line 26. The IC chip 36 (radar circuit 6) supplies power to the array antenna section 20 via the via 40. That is, the IC chip 36 gives a signal (radar signal) to the array antenna section 20.

[0047] FIG. 4 is a plan view showing a portion of the antenna 2 of the circuit board 10. In FIG. 4, the first dielectric layer 12 is removed, and the surface of the second dielectric layer 14 facing in the Z1 direction and the array antenna section 20 on the second dielectric layer 14 are shown. Also, in FIG. 4, the contour lines C of the four non-powered antenna elements 22 are shown by two-dot chain lines.

[0048] As described above, the antenna 2 includes the array antenna section 20 and the four non-powered antenna elements 22. As described above, the array antenna section 20 includes the four planar antenna elements 24 and the power supply line 26. The four planar antenna elements 24 are arranged side by side along the X direction. The pitch in the X direction of the four planar antenna elements 24 is set to about λ / 2, where λ is the in-substrate wavelength of the transmitted signal. Note that the pitch in the X direction of the four planar antenna elements 24 is the distance between the centers in the X direction of a pair of adjacent planar antenna elements 24. The four planar antenna elements 24 are connected to the side portions 26c and 26d of the power supply line 26. λ is set to a predetermined value within the wavelength band (frequency band) of the transmitted signal.

[0049] The four planar antenna elements 24 are provided so as to project alternately from the side portions 26c and 26d in a plan view. That is, the four planar antenna elements 24 are arranged in a comb-line type along the direction in which the power supply line 26 extends.

[0050] In this embodiment, the four planar antenna elements 24 are referred to as the first planar antenna element 24a, the second planar antenna element 24b, the third planar antenna element 24c, and the fourth planar antenna element 24d, in order from the planar antenna element 24 closest to the feed point 27. The first planar antenna element 24a and the third planar antenna element 24c are connected to the side portion 26c. The second planar antenna element 24b and the fourth planar antenna element 24d are connected to the side portion 26d. The fourth planar antenna element 24d is connected to the end portion 26a of the feed line 26.

[0051] The feed line 26 connects four planar antenna elements 24 in series. Therefore, the four planar antenna elements 24 are fed sequentially, starting with the first planar antenna element 24a, which is closest to the feed point 27. The four planar antenna elements 24 radiate the given signal as radio waves.

[0052] As described above, when the four planar antenna elements 24 are viewed from above, the four parasitic antenna elements 22 are arranged so as to overlap with the four planar antenna elements 24. Therefore, in Figure 4, the region enclosed by the four contour lines C of the four parasitic antenna elements 22 overlaps with the four planar antenna elements 24.

[0053] More specifically, the four contour lines C surround the four planar antenna elements 24. The first planar antenna element 24a has a pair of first long sides 42 and a pair of first short sides 44. Of the pair of first short sides 44, the first short side 44 on the feed line 26 side runs along the side portion 26c. The contour line C of the unpowered antenna element 22 corresponding to the first planar antenna element 24a has a pair of second long sides c1 and a pair of second short sides c2. Here, we describe the first planar antenna element 24a and the contour line C corresponding to the first planar antenna element 24a, but the other planar antenna elements 24 and contour lines C have a similar configuration.

[0054] The positions of the pair of first long sides 42 in the X direction coincide with the positions of the pair of second long sides c1 in the X direction. The pair of first short sides 44 are located between the pair of second short sides c2. Therefore, the second long side c1 is longer than the first long side 42. As a result, the contour line C surrounds the planar antenna element 24. Note that the fact that the contour line C surrounds the planar antenna element 24 includes not only the case where the planar antenna element 24 is included within the region of the contour line C, but also the case, as shown in Figure 4, where some sides of the planar antenna element 24 coincide with some sides of the contour line C that correspond to these sides, and the planar antenna element 24 is included within the region of the contour line C.

[0055] The center of the contour line C (passive antenna element 22) in the Y direction coincides with the center of the Y direction of the range obtained by adding the first long side 42 of the planar antenna element 24 and the Y-width of the feed line 26. The long side dimension of the passive antenna element 22 (length of the second long side c1) is set so that the resonant frequency of the passive antenna element 22 is different from the frequency of the signal radiated from the planar antenna element 24. The long side dimension of the planar antenna element 24 (length of the first long side 42) is set according to the frequency of the fed signal. In this embodiment, the long side dimension of the passive antenna element 22 is longer than the long side dimension of the planar antenna element 24 (length of the first long side 42). As a result, the resonant frequency of the passive antenna element 22 is different from the frequency of the signal radiated from the planar antenna element 24.

[0056] To obtain the circuit board 10 configured as described above, all layers constituting the circuit board 10 may be laminated using a build-up method, or the layers other than the four parasitic antenna elements 22 may be laminated using a build-up method, and then the four parasitic antenna elements 22 may be placed on the first dielectric layer 12. In this case, the four parasitic antenna elements 22 can be easily laminated by bonding them to the first dielectric layer 12 with an adhesive layer or the like. Alternatively, a substrate obtained by mounting the four parasitic antenna elements 22 and the array antenna section 20 on the first dielectric layer 12 may be prepared in advance, and the circuit board 10 may be obtained by laminating this substrate on the second dielectric layer 14. In this case, the alignment of the four parasitic antenna elements 22 and the four planar antenna elements 24 becomes easier. Furthermore, a circuit board 10 may be obtained by first preparing a substrate obtained by mounting four passive antenna elements 22 on the first dielectric layer 12 and a substrate obtained by mounting an array antenna section 20 on the second dielectric layer 14, and then stacking these substrates.

[0057] According to the above configuration, the four parasitic antenna elements 22 and the four planar antenna elements 24 are arranged facing each other via the first dielectric layer 12. Therefore, the radiated waves from the four planar antenna elements 24 cause resonance in the four parasitic antenna elements 22. Here, as described above, the resonant frequencies of the four parasitic antenna elements 22 and the resonant frequencies of the signals radiated from the four planar antenna elements 24 are different from each other, so the transmittable frequency band of antenna 2 can be expanded. As a result, the usable frequency band of antenna 2 is made wider.

[0058] Furthermore, in this embodiment, as shown in Figure 3, each of the four parasitic antenna elements 22 has a first surface 22a facing the planar antenna element 24 and a second surface 22b opposite to the first surface 22a that constitutes the radiating surface. Therefore, the radiated waves from the second surface 22b and the radiated waves from the planar antenna element 24 can be radiated in the same direction.

[0059] Furthermore, in this embodiment, since the four planar antenna elements 24 are arranged in a comb-line configuration along the direction in which the power supply line 26 extends (X direction), the four planar antenna elements 24 function as an array antenna. As a result, a beam is formed that is oriented in a direction intersecting the installation surface (X-Y plane) on which the multiple planar antenna elements are provided.

[0060] Furthermore, in this embodiment, the antenna layer 15 is provided on the first main surface 16a side of the substrate 16, and the IC chip 36 (radar circuit 6) is provided on the second main surface 16b side of the substrate 16. This makes it possible to suppress the influence of the arrangement of the IC chip 36 on the arrangement of the antenna 2. In other words, since multiple antennas 2 can be arranged regardless of the arrangement of the IC chip 36, the degree of freedom when arranging multiple antennas 2 is increased, such as arranging multiple antennas 2 as close together as possible.

[0061] Furthermore, in this embodiment, when the four planar antenna elements 24 are viewed from above, the four parasitic antenna elements 22 have a contour line C that surrounds the four planar antenna elements 24. Therefore, the entirety of the four planar antenna elements 24 faces the four parasitic antenna elements 22, which allows for effective resonance to be generated in the four parasitic antenna elements 22.

[0062] When viewing the four planar antenna elements 24 from a planar perspective, the contour lines C of each of the four parasitic antenna elements 22 do not need to surround the planar antenna elements 24, as long as they overlap with the planar antenna elements 24. For example, if a pair of first long sides 42 of the planar antenna elements 24 are located between a pair of second long sides c1 of the parasitic antenna elements 22, the planar antenna elements 24 may have portions that extend beyond the contour line C. By having a pair of first long sides 42 of the planar antenna elements 24 located between a pair of second long sides c1 of the parasitic antenna elements 22, it is possible to suppress the shift in directivity caused by the positional relationship between the planar antenna elements 24 and the parasitic antenna elements 22 shifting along the longitudinal direction (X direction) of the feed line 26.

[0063] Furthermore, the positioning of a pair of first long sides 42 between a pair of second long sides c1 includes not only the case where the pair of first long sides 42 are located inside the pair of second long sides c1, but also the case where the pair of first long sides 42 and the pair of second long sides c1 coincide, as shown in Figure 4.

[0064] In Figure 4, the following dimensions are set appropriately according to the frequency of the transmitted signal, radiation characteristics, etc.: • Length dimension L1 of the feed line 26 (dimension in the X direction) • Width dimension W1 of the feed line 26 (dimension in the Y direction) • Length dimension L2 of the portion of the feed line 26 from end 26b to the first planar antenna element 24a • Length dimension L3 of the portion of the feed line 26 between a pair of adjacent planar antenna elements 24 • Short side dimension W2 of the planar antenna element 24 (dimension in the X direction) • Long side dimension L4 of the planar antenna element 24 (dimension in the Y direction) • Short side dimension W3 of the unpowered antenna element 22 (dimension in the X direction) • Long side dimension L5 of the unpowered antenna element 22 (dimension in the Y direction)

[0065] [Regarding the Second Embodiment] Figure 5 is a perspective view of a circuit board including a transmitting antenna 2 according to the second embodiment. Figure 6 is a plan view showing the portion of the antenna 2 on the circuit board 10. Note that Figure 5 shows one of the multiple transmitting antennas 2. Also, in Figure 6, the first dielectric layer 12 has been removed, and the surface of the second dielectric layer 14 facing the Z1 direction and the array antenna portion 20 on the second dielectric layer 14 are shown. Also, in Figure 6, the outline C of the parasitic antenna element 22 is shown by a dashed line.

[0066] This embodiment differs from the first embodiment in that it has two planar antenna elements 24. In this embodiment as well, the transmittable frequency band of the antenna 2 can be expanded, making it possible to use it in a wider bandwidth.

[0067] [Regarding the Third Embodiment] Figure 7 is a perspective view of a circuit board including a transmitting antenna 2 according to the third embodiment. Figure 8 is a plan view showing the portion of the antenna 2 on the circuit board 10. Note that Figure 7 shows one of the multiple transmitting antennas 2. Also, in Figure 8, the first dielectric layer 12 has been removed, and the surface of the second dielectric layer 14 facing the Z1 direction and the array antenna portion 20 on the second dielectric layer 14 are shown. Also, in Figure 8, the contour line C of the unpowered antenna element 22 is shown by a dashed line.

[0068] This embodiment differs from the second embodiment in that the plurality of planar antenna elements 24 include a first planar antenna element group 54 and a second planar antenna element group 56, and the first planar antenna element group 54 and the second planar antenna element group 56 are provided on the feed line 26 with the feed point 27 in between. In this embodiment, two planar antenna elements 24 are provided at each end of the feed line 26.

[0069] The power supply line 26 of this embodiment has a first line 50 and a second line 52. The first line 50 extends from the power supply point 27 in the X1 direction (first direction). Therefore, the first line 50 is provided on the end 26a side of the power supply line 26. The second line 52 extends from the power supply point 27 in the X2 direction (second direction). Therefore, the second line 52 is provided on the end 26b side of the power supply line 26. The first line 50 connects two planar antenna elements 24 included in the first planar antenna element group 54 in series. The second line 52 connects two planar antenna elements 24 included in the second planar antenna element group 56 in series. The length of the first line 50 is λ / 2 shorter than the length of the second line 52. λ is the in-board wavelength of the transmitted signal as described above. Therefore, the feed point 27 is offset in the X1 direction by approximately λ / 4 relative to the center point 53. The center point 53 is the center point of the antenna 2 (feed line 26) in the X direction (longitudinal direction).

[0070] The first planar antenna element group 54 includes a first planar antenna element 24a and a second planar antenna element 24b. The first planar antenna element 24a and the second planar antenna element 24b are connected to the first transmission line 50. Similar to the second embodiment, the first planar antenna element 24a and the second planar antenna element 24b are arranged in a comb line configuration along the direction in which the first transmission line 50 extends.

[0071] The second planar antenna element group 56 includes a fifth planar antenna element 24e and a sixth planar antenna element 24f. The fifth planar antenna element 24e and the sixth planar antenna element 24f are connected to the second line 52. The fifth planar antenna element 24e is located closer to the feed point 27 than the sixth planar antenna element 24f. The fifth planar antenna element 24e is connected to the side portion 26d. The sixth planar antenna element 24f is located further from the feed point 27 than the fifth planar antenna element 24e. The sixth planar antenna element 24f is connected to the side portion 26c. Therefore, the second planar antenna element group 56 is arranged in a comb line shape along the direction in which the second line 52 extends.

[0072] In this embodiment as well, four parasitic antenna elements 22 are arranged opposite each other, corresponding to the four planar antenna elements 24. In Figure 8, the region enclosed by the four contour lines C of the four parasitic antenna elements 22 overlaps with the four planar antenna elements 24. More specifically, the four contour lines C enclose the four planar antenna elements 24. Therefore, resonance occurs in the four parasitic antenna elements 22, expanding the frequency bandwidth that antenna 2 can transmit. As a result, the usable frequency bandwidth of antenna 2 is broadened.

[0073] Here, the first planar antenna element group 54 and the second planar antenna element group 56 are point-symmetric with respect to the center point 53. Furthermore, the positions of the four parasitic antenna elements 22, which are provided in correspondence with the four planar antenna elements 24, are also point-symmetric with respect to the center point 53.

[0074] In this embodiment, the first planar antenna element 24a and the second planar antenna element 24b of the first planar antenna element group 54 are connected in series to the first transmission line 50. Therefore, the first planar antenna element group 54 is supplied with signals in the order of the first planar antenna element 24a and the second planar antenna element 24b. Here, the pitch in the X direction between the first planar antenna element 24a and the second planar antenna element 24b is a fixed value. Therefore, when the frequency of the supplied signal changes, the wavelength of the signal within the substrate also changes, and the relationship between the phase of the signal radiated from the first planar antenna element 24a and the phase of the signal radiated from the second planar antenna element 24b also changes. When the relationship between the phase of the signal radiated from the first planar antenna element 24a and the phase of the signal radiated from the second planar antenna element 24b changes, the directivity of the first planar antenna element group 54 changes.

[0075] Similarly, the fifth planar antenna element 24e and the sixth planar antenna element 24f of the second planar antenna element group 56 are connected in series to the second transmission line 52. Therefore, the second planar antenna element group 56 is fed in the order of the fifth planar antenna element 24e and the sixth planar antenna element 24f. Consequently, in the second planar antenna element group 56 as well, when the frequency of the supplied signal changes, the relationship between the phase of the signal radiated from the fifth planar antenna element 24e and the phase of the signal radiated from the sixth planar antenna element 24f also changes, and the directivity of the second planar antenna element group 56 changes.

[0076] For example, if antenna 2 includes only the first planar antenna element group 54, the directivity of antenna 2 will change in response to changes in the signal frequency. In contrast, according to this embodiment, the first planar antenna element group 54 and the second planar antenna element group 56 are point-symmetric with respect to the center point 53. Therefore, when the frequency of the fed signal changes, the directivity of the first planar antenna element group 54 and the directivity of the second planar antenna element group 56 change in a way that is symmetric with respect to the center point 53. Thus, the changes in the directivity of the first planar antenna element group 54 and the changes in the directivity of the second planar antenna element group 56 cancel each other out, and as a result, there is no change in the directivity of antenna 2. The directivity of antenna 2 is oriented in the direction of the feed point 27. Therefore, it is possible to suppress the shift in the directivity of antenna 2 in response to changes in frequency.

[0077] [Regarding the Fourth Embodiment] Figure 9 is a cross-sectional view of the main part of the circuit board 10 according to the fourth embodiment. This embodiment differs from the first embodiment in that the IC chip 36 (radar circuit 6) is provided on the antenna layer 15. As shown in Figure 9, the first dielectric layer 12 of this embodiment has a hole 12c. The hole 12c penetrates the first dielectric layer 12 in the Z direction. The IC chip 36 is provided in the region of the second dielectric layer 14 corresponding to the hole 12c. Therefore, the IC chip 36 is housed in the hole 12c. The IC chip 36 and the feed point 27 of the array antenna unit 20 are connected by a transmission line 25. The array antenna unit 20 is powered via the transmission line 25.

[0078] In this embodiment, since the IC chip 36 is provided on the antenna layer 15, the IC chip 36 is not placed on the second main surface 16b side of the substrate 16, and there is no need to provide the third dielectric layer 18. This reduces the thickness of the circuit board 10. Also, since the IC chip 36 is provided on the antenna layer 15, there is no need to provide vias 40 that penetrate the substrate 16 as in the first embodiment, and power can be supplied to the antenna 2 with a simple configuration such as a transmission line 25.

[0079] [Regarding Modifications] Figures 10 and 11 show modifications of the first embodiment. Figure 10(a) differs from the first embodiment in that the sizes of the four planar antenna elements 24 are different from each other, and the sizes of the four passive antenna elements 22 are different from each other. In Figure 10(a), the short side dimension W2 of the planar antenna elements 24 decreases in stages from the first planar antenna element 24a to the fourth planar antenna element 24d. Conversely, the long side dimension L4 of the planar antenna elements 24 increases in stages from the first planar antenna element 24a to the fourth planar antenna element 24d.

[0080] The four parasitic antenna elements 22 have contour lines that surround the four planar antenna elements 24. The short side dimension W3 and long side dimension L5 of each of the four parasitic antenna elements 22 are adjusted to match the size of the corresponding planar antenna elements 24.

[0081] As in this embodiment, by adjusting the size of the four planar antenna elements 24, the radiation amount of each of the four planar antenna elements 24 is adjusted, and the directivity of the antenna 2 is adjusted. The radiation amount of the planar antenna elements 24 mainly depends on the short side dimension W2. The short side dimension W2 of the fourth planar antenna element 24d, located at the end 26a of the feed line 26, is the smallest. The function of the fourth planar antenna element 24d is prioritized over its function of radiating radio waves, in order to adjust the reflection of the fed signal at the end 26a. For this reason, the short side dimension W2 of the fourth planar antenna element 24d is set to be relatively small.

[0082] Figure 10(b) shows the antenna 2 obtained by moving the four parasitic antenna elements 22 in Figure 10(a) parallel toward the feed line 26. As a result of the parallel movement of the four parasitic antenna elements 22 toward the feed line 26, each of the four planar antenna elements 24 has a portion 60 that does not face the parasitic antenna elements 22 and a portion 61 that faces the parasitic antenna elements 22. Thus, the parasitic antenna elements 22 may have a portion 60 that does not face the parasitic antenna elements 22, as long as there is a portion 61 that overlaps with and faces the planar antenna elements 24.

[0083] Therefore, as shown in Figure 10(b), the parasitic antenna element 22 may be moved along the direction (Y direction) that intersects the longitudinal direction of the feed line 26. By moving the parasitic antenna element 22 in this way, it is possible to fine-tune the direction of the antenna 2's directional orientation. In Figure 10(b), the parasitic antenna element 22 is moved within a range where the pair of first long sides 42 of the planar antenna element 24 are located between the pair of second long sides c1 of the parasitic antenna element 22.

[0084] Figure 10(c) shows a case where the feed line 26 in Figure 10(a) has a zigzag shape, and the portion of the feed line 26 between adjacent pairs of planar antenna elements 24 is inclined with respect to the longitudinal direction (X direction) of the feed line 26. In this case, the aperture of the antenna 2 in the X and Y directions becomes smaller. As a result, the beam width of the antenna 2 in the X and Y directions can be widened.

[0085] Figure 11(a) shows the case where three planar antenna elements 24 are provided only on the side 26d of the feed line 26. In this example, three passive antenna elements 22 are provided corresponding to the three planar antenna elements 24. In this case, the pitch of the three planar antenna elements 24 in the X direction is set to λ, which is the in-board wavelength of the transmitted signal.

[0086] Figure 11(b) shows an antenna 2 with matching elements 62 provided corresponding to the four planar antenna elements 24 in Figure 10(a). As shown in Figure 11(b), the four matching elements 62 have a rectangular shape. The four matching elements 62 are provided on the opposite side of the feed line 26 to which the four planar antenna elements 24 are connected. Therefore, the planar antenna elements 24 and the matching elements 62 are provided so as to straddle the feed line 26. In this case, impedance matching can be performed for each planar antenna element 24 by the matching elements 62.

[0087] [Verification Test] Next, we will explain the verification test conducted on the effect of antenna 2. As for the test method, a model of one antenna 2 was constructed, and the return loss and directivity at the feed point 27 were determined by computer simulation using this model. By comparing the obtained simulation results, the effect of the arrangement of the unpowered antenna elements was verified.

[0088] Models were constructed for the following four embodiments and two comparative examples. (Embodiment 1) In Embodiment 1, the antenna 2 shown in the first embodiment is used. In Figure 3, the circuit board was modeled with a configuration in which the portion of the circuit board 10 on the Z2 side of the ground conductor plate 30 was replaced with a ground conductor having a thickness of 400 μm. The first dielectric layer 12 was an air layer, and its layer thickness (thickness in the Z direction) was 300 μm. The second dielectric layer 14 had a thickness of 127 μm in the Z direction, a relative permittivity of 2.98, and a dielectric loss tangent of 0.0008. The ground conductor plate 30, the planar antenna element 24, and the parasitic antenna element 22 were made of copper with a thickness of 30 μm.

[0089] The dimensions of each part of antenna 2 are as follows (see Figure 4): • Length L1 of feed line 26: 5.75 mm • Width W1 of feed line 26: 0.21 mm • Length L2 from end 26b to first planar antenna element 24a: 1.0 mm • Length L3 between pair of planar antenna elements 24: 0.65 mm • Short side W2 of planar antenna element 24: 0.7 mm • Long side L4 of planar antenna element 24: 1.08 mm • Short side W3 of unpowered antenna element 22: 0.7 mm • Long side L5 of unpowered antenna element 22: 1.50 mm

[0090] Furthermore, the center of the unpowered antenna element 22 in the Y direction coincides with the center of the Y direction of the region obtained by adding the first long side of the planar antenna element 24 and the feed line 26. Also, the positions in the X direction of the pair of first long sides 42 coincide with the positions in the X direction of the pair of second long sides c1 (see Figure 4).

[0091] (Example 2) Example 2 uses the antenna 2 shown in the second embodiment. The dimensions of each part of the antenna 2 are the same as in Example 1, except for the dimensions listed below (see Figure 6). - Length of the feed line 26 L1: 4.16 mm - Length from end 26b to the first planar antenna element 24a L2: 2.19 mm - Length between the pair of planar antenna elements 24 L3: 0.57 mm The settings of Example 2, other than those listed above, are the same as in Example 1.

[0092] (Example 3) Example 3 uses the antenna 2 shown in the third embodiment. The dimensions of each part of the antenna 2 are the same as in Example 1, except for the dimensions described below (see Figure 8). - Length dimension L1 of the feed line 26: 6.1 mm - Length dimension L6 from the first planar antenna element 24a to the fifth planar antenna element 24e: 2.0 mm The settings of Example 3, other than those mentioned above, are the same as in Example 1.

[0093] (Example 4) A pair of antennas having the same configuration as antenna 2 shown in Figure 10(a) were used, arranged in a point-symmetric manner with respect to the center of the feed line 26, as in Example 2. Thus, Example 4 has eight planar antenna elements 24 arranged in a point-symmetric manner with respect to the center of the feed line 26. The physical properties of the first dielectric layer 12 were made the same as those of the second dielectric layer 14. Thus, the relative permittivity of the first dielectric layer 12 was set to 2.98 and the dielectric loss tangent to 0.0008. Of the settings in Example 4, all other settings were the same as those in Example 1.

[0094] (Comparative Example 1) Comparative Example 1 is a configuration in which the four parasitic antenna elements 22 of Example 1 are omitted.

[0095] (Comparative Example 2) Comparative Example 2 is a configuration in which the two passive antenna elements 22 of Example 2 are omitted.

[0096] (Comparison between Example 1 and Comparative Example 1) Figure 12 is an example of a graph showing the frequency characteristics of the return loss for Example 1 and Comparative Example 1, respectively. The horizontal axis of Figure 12 represents frequency. The vertical axis of Figure 12 represents S11, which is the S-parameter when the feed point 27 is the input terminal.

[0097] In Figure 12, in Comparative Example 1, the S11 (return loss) in the range of approximately 77 GHz to 78 GHz is -15 dB or less. The return loss in other frequency bands is greater than -15 dB. The frequency band in which the return loss is -15 dB or less can be determined to be the usable frequency band of the antenna. Therefore, the usable frequency band BW11 of Comparative Example 1 is the range of approximately 77 GHz to 78 GHz in which the return loss is -15 dB or less. The bandwidth of frequency band BW11 is approximately 1.05 GHz.

[0098] In contrast, in Example 1, the return loss in the range of 74 GHz to 83 GHz is -15 dB or less. In other words, the usable frequency band BW1 of Example 1 includes the entire frequency band (76-77 GHz and 77-81 GHz) that is allocated as a usable frequency band for automotive millimeter-wave radar. The bandwidth of frequency band BW1 is approximately 9.67 GHz. From these results, it can be seen that Example 1 is usable over a wider bandwidth than Comparative Example 1.

[0099] Figure 13 is an example of a graph showing the directivity in the horizontal plane for each of Example 1 and Comparative Example 1. The vertical axis in Figure 13 represents the gain. The horizontal axis in Figure 13 represents the elevation angle when the azimuth angle on the X-Y plane is 90 degrees, with the feed point 27 as the origin (see Figure 2). Therefore, an angle of 0 degrees on the horizontal axis represents the Z1 direction with the feed point 27 as the reference, and an angle of 90 degrees on the horizontal axis represents the Y1 direction with the feed point 27 as the reference. Here, the Y-Z plane is referred to as the horizontal plane. Figure 13 also shows a graph when the frequency of the fed signal is 79 GHz.

[0100] As shown in Figure 13, there is no significant difference between the directivity in the horizontal plane of Example 1 and that of Comparative Example 1. Furthermore, the gain near the peak angle of Example 1 is greater than that of Comparative Example 1.

[0101] Figure 14 is an example of a graph showing the directivity in the vertical plane for each of Example 1 and Comparative Example 1. The vertical axis in Figure 14 represents the gain. The horizontal axis in Figure 14 represents the elevation angle when the azimuth angle on the X-Y plane is 0 degrees, with the feed point 27 as the origin (see Figure 2). Therefore, an angle of 0 degrees on the horizontal axis represents the Z1 direction with the feed point 27 as the reference, and an angle of 90 degrees on the horizontal axis represents the X1 direction with the feed point 27 as the reference. Here, the X-Z plane is referred to as the vertical plane. Figure 14 also shows a graph when the frequency of the fed signal is 79 GHz.

[0102] As shown in Figure 14, there is no significant difference between the directivity in the vertical plane of Example 1 and the directivity in the vertical plane of Example 1. Furthermore, the gain near the peak angle and the gain of the side lobes in Example 1 are greater than those in Comparative Example 1.

[0103] (Comparison between Example 2 and Comparative Example 2) Figure 15 is an example of a graph showing the frequency characteristics of the return loss for Example 2 and Comparative Example 2, respectively. The horizontal axis of Figure 15 represents frequency. The vertical axis of Figure 15 shows S11 as the return loss.

[0104] In Figure 15, the usable frequency band BW12 of Comparative Example 2 is in the range of approximately 77 GHz to 78 GHz, similar to the frequency band BW11 of Comparative Example 1. The bandwidth of frequency band BW12 is approximately 1.01 GHz. In contrast, in Example 2, the return loss in the range of 69 GHz to 81 GHz is -15 dB or less. In other words, the usable frequency band BW2 of Example 2 includes the entire frequency band (76-77 GHz and 77-81 GHz) allocated as usable frequency bands for automotive millimeter-wave radar. The bandwidth of frequency band BW2 is approximately 12.7 GHz. From these results, it can be seen that Example 2 is usable over a wider bandwidth than Comparative Example 2.

[0105] Figure 16 is an example of a graph showing the directivity in the horizontal plane for both Example 2 and Comparative Example 2. The vertical and horizontal axes of Figure 16 are the same as in Figure 13. Figure 16 also shows a graph for a powered signal with a frequency of 79 GHz.

[0106] As shown in Figure 16, there is no significant difference between the horizontal directivity of Example 2 and the horizontal directivity of Example 2. Furthermore, the gain near the peak angle of Example 2 is greater than that of Comparative Example 2. Conversely, in the region where the angle is greater than 45, the gain of Comparative Example 2 is greater than that of Example 2.

[0107] Figure 17 is an example of a graph showing the directivity in the vertical plane for both Example 2 and Comparative Example 2. The vertical and horizontal axes are the same as in Figure 14. Figure 17 also shows a graph for a powered signal with a frequency of 79 GHz.

[0108] As shown in Figure 17, there is no significant difference between the directivity in the vertical plane of Example 2 and the directivity in the vertical plane of Example 2. Furthermore, the gain of Example 2 is greater than that of Comparative Example 1.

[0109] (Comparison of Example 3 and Example 1) Figure 18 is an example of a graph showing the directivity in the horizontal plane of Example 3. The vertical and horizontal axes of Figure 18 are the same as in Figure 13. Figure 18 shows the directivity of Example 3 when six signals of different frequencies, ranging from 76 GHz to 81 GHz in 1 GHz increments, are supplied. In Figure 18, when the peak angle was determined for the directivity of each frequency, the peak angle was found to be within the range of -0.1° to -0.3°. Therefore, the variation range of the peak angle is 0.2°.

[0110] Figure 19 is an example of a graph showing the directivity in the horizontal plane of Example 1. The vertical and horizontal axes of Figure 19 are the same as in Figure 13. As with Figure 18, Figure 19 also shows the directivity of Example 1 when six signals of different frequencies, ranging from 76 GHz to 81 GHz in 1 GHz increments, are supplied. When the peak angle was determined for the directivity of each frequency in Figure 19, the peak angle was found to be within the range of -3.8° to 3.0°. Therefore, the range of variation in the peak angle is 6.8°.

[0111] Figure 20 is an example of a graph showing the directivity of Example 3 in a vertical plane. The vertical and horizontal axes of Figure 20 are the same as in Figure 14. In Figure 20, as in Figure 18, the directivity of Example 3 is shown when six signals of different frequencies, ranging from 76 GHz to 81 GHz in 1 GHz increments, are supplied. In Figure 20, when the peak angle was determined for the directivity of each frequency, the peak angle was found to be within the range of 0.1° to 0.3°. Therefore, the variation range of the peak angle is 0.2°.

[0112] Figure 21 is an example of a graph showing the directivity of Example 1 in a vertical plane. The vertical and horizontal axes of Figure 21 are the same as in Figure 14. In Figure 21, as in Figure 18, the directivity of Example 1 is shown when six signals of different frequencies, ranging from 76 GHz to 81 GHz in 1 GHz increments, are supplied. In Figure 21, when the peak angle (peak angle) for the directivity of each frequency was determined, the peak angle was found to be within the range of -4.0° to 5.5°. Therefore, the range of variation in the peak angle is 9.5°.

[0113] As described above, the variation range of the peak angle in the horizontal and vertical planes of Example 3 was 0.2°, while the variation ranges of the peak angle in the horizontal and vertical planes of Example 1 were 6.8° and 9.5°, respectively. Thus, the variation range of the peak angle in the horizontal and vertical planes of Example 3 is significantly smaller than that of Example 1. From these results, it can be confirmed that Example 3 suppresses the shift in the directivity of the antenna 2 in response to changes in frequency.

[0114] (Regarding Example 4) Figure 22 is an example of a graph showing the frequency characteristics of the return loss in Example 4, Figure 23 is an example of a graph showing the directivity in the horizontal plane of Example 4, and Figure 24 is an example of a graph showing the directivity in the vertical plane of Example 4.

[0115] The usable frequency band of Example 4 includes the entire frequency band allocated as usable for automotive millimeter-wave radar. Therefore, it can be confirmed that Example 4 is usable over a wide bandwidth. Furthermore, it can be confirmed that in Example 4 as well, the shift in the directivity of antenna 2 in response to changes in frequency is suppressed.

[0116] In Example 4, the first dielectric layer 12 is not an air layer as in Examples 1-3, but uses the same dielectric material as the second dielectric layer 14. In this case as well, it was confirmed that it can be used over a wide bandwidth.

[0117] [Other] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. For example, in each of the above embodiments, the cases in which the plurality of planar antenna elements 24 and the plurality of parasitic antenna elements 22 have a rectangular shape are illustrated. However, the plurality of planar antenna elements 24 and the plurality of parasitic antenna elements 22 may have other shapes as long as they face each other.

[0118] Furthermore, in each of the above embodiments, examples were given in which the first dielectric layer 12 and the second dielectric layer 14 include a fluororesin layer made of fluororesin. However, the first dielectric layer 12 and the second dielectric layer 14 may be made of other dielectric materials other than fluororesin, such as polyimide, liquid crystal polymer, or PPE resin.

[0119] The scope of the present invention is indicated by the claims, not in the sense described above, and is intended to include the meaning of equivalents to the claims and all modifications within the scope.

[0120] 1 Radar module 2 Transmitting antenna 4 Receiving antenna 6 Radar circuit 10 Circuit board 12 First dielectric layer 12a Main layer 12b Adhesive layer 12c Hole 14 Second dielectric layer 14a Main layer 14b Adhesive layer 15 Antenna layer 16 Substrate 16a First main surface 16b Second main surface 18 Third dielectric layer 18a Main layer 18b Adhesive layer 20 Array antenna section 22 Passive antenna element 22a First surface 22b Second surface 24 Planar antenna element 24a First planar antenna element 24b Second planar antenna element 24c Third planar antenna element 24d Fourth planar antenna element 24e Fifth planar antenna element 24f Sixth planar antenna element 25 Line 26 Feed line 26a End 26b End 26c Side section 26d Side section 27 Feed point 30 Grounding conductor plate 32 Grounding conductor plate 36 IC chip 38 Via 40 Via 42 First long side 44 First short side 50 First line 52 Second line 54 First planar antenna element group 56 Second planar antenna element group 60 Section 61 Section 62 Matching element C Contour line c1 Second long side c2 Second short side

Claims

1. An antenna comprising at least one planar antenna element connected to a power supply line, and at least one passive antenna element positioned opposite the planar antenna element via a dielectric layer.

2. The antenna according to claim 1, wherein the parasitic antenna element has a first surface facing the planar antenna element and a second surface opposite the first surface that constitutes a radiating surface.

3. The antenna according to claim 1 or claim 2, wherein the dielectric layer comprises a fluororesin layer.

4. The antenna according to any one of claims 1 to 3, wherein the relative permittivity of the dielectric layer is 3.4 or less.

5. The antenna according to any one of claims 1 to 4, wherein the dielectric loss tangent of the dielectric layer is 0.003 or less.

6. The antenna according to any one of claims 1 to 5, wherein when the planar antenna element is viewed from above, the unpowered antenna element has a contour surrounding the planar antenna element.

7. The antenna according to claims 1 to 6, wherein the at least one planar antenna element is a plurality of planar antenna elements arranged in a comb line configuration along the direction in which the feed line extends.

8. The antenna according to claim 7, wherein the plurality of planar antenna elements have a rectangular shape with a pair of first sides that intersect in the direction in which the feed line extends, and the parasitic antenna element has a rectangular shape with a pair of second sides that intersect in the direction in which the feed line extends, and when the planar antenna elements in which the parasitic antenna elements are arranged opposite each other are viewed from above, the pair of first sides are located between the pair of second sides.

9. The antenna according to claim 7, wherein the plurality of planar antenna elements include a first group of planar antenna elements and a second group of planar antenna elements including the same number of planar antenna elements as the first group of planar antenna elements, the feed line has a feed point, a first line extending from the feed point in a first direction, and a second line extending from the feed point in a second direction opposite to the first direction, the first group of planar antenna elements is connected to the first line, the second group of planar antenna elements is connected to the second line, and the first group of planar antenna elements and the second group of planar antenna elements are point-symmetric with respect to the longitudinal center of the feed line.

10. The antenna according to any one of claims 7 to 9, wherein the at least one parasitic antenna element is a plurality, and the plurality of parasitic antenna elements are arranged in correspondence with the plurality of planar antenna elements.

11. An antenna comprising a combline-type array antenna section having a power supply line and a plurality of planar antenna elements connected to the power supply line, and at least one passive antenna element positioned opposite the planar antenna elements via a dielectric layer.

12. A radar module comprising: a circuit board including an antenna having at least one planar antenna element connected to a power supply line and at least one passive antenna element positioned opposite the planar antenna element via a dielectric layer; and a radar circuit that transmits and receives radar signals using the antenna.

13. The radar module according to claim 12, wherein the circuit board comprises an antenna layer including the planar antenna element, the dielectric layer, and the parasitic antenna element, and a substrate having a first main surface and a second main surface opposite to the first main surface, the antenna layer being provided on the first main surface side, and the radar circuit being provided on the second main surface side.

14. The radar module according to claim 12, wherein the circuit board comprises the planar antenna element, the dielectric layer, and the antenna layer including the parasitic antenna element, and the radar circuit is provided on the antenna layer.

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