Antenna equipment

Abstract

To provide a technology capable of ensuring good characteristics in a wide band without deteriorating isolation in a specific frequency band in an antenna device in which a plurality of monopole antennas are arranged side by side.SOLUTION: An antenna device 1 includes a circuit board 12 having a ground area, a first antenna element 18a having a base end side connected to a first feeding point provided on the circuit board 12 and forming a first monopole antenna, a second antenna element 18b having a proximal end connected to a second feeding point provided on the circuit board 12 and forming a second monopole antenna, and a connecting portion 20 connecting the tip portion of the first antenna element 18a and the tip portion of the second antenna element 18b.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an antenna device in which a plurality of monopole antennas are arranged in parallel.

Background Art

[0002] Along with the increase in functionality and performance of vehicles, antenna devices that accommodate a plurality of antennas in a common housing have become widespread (see Patent Document 1). Antennas corresponding to various applications such as GPS (Global Positioning System) for providing position information, ETC (Electronic Toll Collection System) and VICS (Vehicle Information and Communication System) for realizing ITS (Intelligent Transport Systems) are increasingly being standardly equipped on vehicles. The plurality of these antennas are accommodated in a single housing. Note that although ETC and VICS are registered trademarks, their notation will be omitted in the following description.

[0003] In the antenna device described in Patent Document 1, an ETC antenna and a GPS antenna are arranged at the center of a common housing, and a pair of TEL antennas (monopole antennas) are arranged on both left and right sides thereof. Providing a plurality of TEL antennas facilitates compatibility with MIMO (Multiple Input Multiple Output). MIMO is a technology that spatially multiplexes and transmits signals using a plurality of transmitting and receiving antennas, and can achieve improvement in the transmission speed and quality of communication data.

[0004] Incidentally, as the number of in-vehicle devices increases along with the increase in functionality of vehicles, it is required to miniaturize the antenna device as much as possible to achieve space saving. For the pair of TEL antennas as described above, it is also desirable that the interval between the antenna elements can be reduced as much as possible. On the other hand, when a plurality of antennas are arranged in parallel, it is necessary to ensure isolation over a wide bandwidth between the antennas.

[0005] Conventionally, to ensure isolation between two antennas, techniques have been proposed such as adjusting the isolation by interposing circuits or elements near the feed point between the antenna elements (see Patent Documents 2 and 3), and reducing mutual influence by bringing the tips of the antenna elements close together and capacitively coupling them (see Patent Document 4). In addition to these, there is also a method of ensuring isolation by arranging adjacent antenna elements orthogonally. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-218799 [Patent Document 2] Japanese Patent Publication No. 2014-112824 [Patent Document 3] Japanese Patent Publication No. 2012-175317 [Patent Document 4] International Publication No. 2019 / 107553 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the technologies described in Patent Documents 2 to 4 generally tend to have a limited frequency band in which good impedance characteristics (radiation efficiency) and good isolation can be achieved simultaneously. On the other hand, arranging adjacent antenna elements orthogonally leads to constraints on equipment configuration, making it difficult to meet the demand for miniaturization of antenna devices.

[0008] The present invention has been made in view of these problems, and one of its objectives is to provide a technology that can ensure good characteristics over a wide bandwidth without degrading the isolation of a specific frequency band in an antenna device in which multiple monopole antennas are installed side by side. [Means for solving the problem]

[0009] One aspect of the present invention is an antenna device. This antenna device comprises a circuit board having a ground region; a first antenna element whose base end is connected to a first feed point provided on the circuit board and which forms a first monopole antenna; a second antenna element whose base end is connected to a second feed point provided on the circuit board and which forms a second monopole antenna; and a connecting portion that connects the tip of the first antenna element and the tip of the second antenna element. [Effects of the Invention]

[0010] According to the present invention, in an antenna device in which multiple monopole antennas are arranged in parallel, good characteristics can be ensured over a wide bandwidth without degrading the isolation of a specific frequency band. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view showing an overview of the antenna device according to the first embodiment. [Figure 2] This is a plan view showing the configuration of the antenna unit. [Figure 3] This figure shows the results of the frequency characteristics analysis of the TEL antenna. [Figure 4] This is a plan view showing the configuration of the antenna unit according to the second embodiment. [Figure 5] This is a plan view showing the configuration of the antenna unit in a modified example. [Figure 6] This diagram illustrates the relationship between the linewidth and frequency characteristics of a meander structure. [Figure 7] This diagram illustrates the relationship between the meander width of a meander structure and its frequency characteristics. [Figure 8] This is a perspective view showing the configuration of the antenna unit according to the third embodiment. [Figure 9] This is a plan view showing the configuration of the antenna unit in a modified example. [Figure 10] This is a plan view showing the configuration of an antenna unit related to other modifications. [Figure 11]Shows an analysis of the operational effects of the first embodiment and the results thereof. [Figure 12] Shows an analysis of the operational effects of the first embodiment and the results thereof. [Figure 13] Shows an analysis of the operational effects of the second embodiment and the results thereof. [Figure 14] It is a plan view illustrating the configuration of an antenna unit according to Modification 6. [Figure 15] It is a diagram illustrating the effect obtained by the configuration of Modification 6. DESCRIPTION OF EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description of the embodiments and modifications thereof, substantially identical components are denoted by the same reference numerals, and descriptions thereof are omitted as appropriate.

[0013] In the following embodiments, an example of a vehicle antenna device (hereinafter simply referred to as "antenna device") in which two monopole antennas are arranged side by side is illustrated. The monopole antenna exemplified herein is a TEL antenna. In order to secure isolation between the two monopole antennas over a wide band, the two antenna elements are connected to each other at ends opposite to their respective feeding points. Details thereof will be described below.

[0014] [First Embodiment] Fig. 1 is a perspective view illustrating an outline of the antenna device according to the first embodiment. In the following description, for convenience, the positional relationship in the antenna device may be expressed in the front-rear, up-down, and left-right directions based on the state where the antenna device is mounted on a vehicle.

[0015] Antenna device 1 includes an antenna unit 10 containing a plurality of antennas. Antenna unit 10 is housed in a case not shown in the drawings. The case includes a lower case on which antenna unit 10 is placed, and an upper case attached to the lower case so as to cover antenna unit 10 from above. Both the upper case and the lower case are made of radio wave-transmissive resin.

[0016] The antenna unit 10 is configured by mounting a single GPS antenna 14 and a pair of TEL antennas 16a and 16b on a circuit board 12. Hereafter, unless otherwise specified, the TEL antennas 16a and 16b will simply be referred to as "TEL antenna 16". The circuit board 12 has a ground area, which will be described later, and functions as a ground plate.

[0017] The GPS antenna 14 is a patch antenna for GPS. The TEL antennas 16a and 16b are monopole antennas for telephone use and include antenna elements 18a and 18b, respectively. Antenna element 18a functions as the "first antenna element" and forms the first monopole antenna. Antenna element 18b functions as the "second antenna element" and forms the second monopole antenna. Hereafter, unless otherwise specified, antenna elements 18a and 18b will simply be referred to as "antenna element 18". Antenna elements 18a and 18b are arranged symmetrically on the left and right sides of the circuit board 12.

[0018] By providing multiple TEL antennas 16 in this manner, MIMO compatibility can be achieved. Antenna elements 18a and 18b are connected at their ends by a connector 20 to improve isolation (details will be described later). Connectors 22, each having a power supply port for one antenna, are provided protruding from the lower front end of the circuit board 12. The antenna device 1 is installed in the instrument panel of a vehicle (not shown), etc.

[0019] Figure 2 is a plan view showing the configuration of the antenna unit. Figure 2(A) shows the configuration of this embodiment, and Figure 2(B) shows the configuration of a comparative example. As shown in Figure 2(A), the circuit board 12 is a polygonal printed circuit board in plan view, and has a stepped shape in which the width of the front half is greater than the width of the rear half. The circuit board 12 has a shape symmetrical with respect to the center line L. The antenna unit 10 as a whole has a shape symmetrical with respect to the center line L. A ground area 24 is provided on the surface of the circuit board 12. The ground area 24 is common to the pair of TEL antennas 16.

[0020] A GPS antenna 14 is arranged in a narrow region of the rear half of the circuit board 12. The GPS antenna 14 is a dielectric patch antenna, constructed by placing a radiating electrode 28 on the surface of a dielectric layer 26. The radiating electrode 28 is provided parallel to the top surface of the circuit board 12. A feed point is provided on the radiating electrode 28. A through hole is provided that penetrates the dielectric layer 26, and a feed pin connecting the feed point to a feed line provided on the back surface of the circuit board 12 is inserted through it. In this embodiment, a single-point fed circular polarization patch antenna is used as the GPS antenna 14, but a two-point fed patch antenna may also be used. Note that a known patch antenna is used for the GPS antenna 14, so a detailed explanation thereof is omitted.

[0021] Feed points P1 and P2 are provided at both the left and right ends of the large front portion of the circuit board 12, and the base ends of the antenna elements 18a and 18b are connected to them. Feed point P1 functions as the "first feed point," and feed point P2 functions as the "second feed point." The pair of TEL antennas 16 are arranged on both the left and right sides of the GPS antenna 14. The pair of antenna elements 18 have a symmetrical structure with respect to the center line L.

[0022] The antenna element 18 is a conductive plate having an elongated rectangular (strip-shaped) body 30, with one end of the body 30 extending inward (towards the center line L) to form a wide base end 32. The inner end of the base end 32 is bent upward at a right angle to form a feed point 34. The feed point of antenna element 18a is connected to the feed point P1, and the feed point 34 of antenna element 18b is connected to the feed point P2. In this embodiment, these connections are made by soldering. The tip 36 of antenna element 18a and the tip 36 of antenna element 18b are integrally connected via a connecting part 20. The connecting part 20 is a conductive plate having a width similar to that of the body 30 and is connected perpendicular to the antenna elements 18a and 18b.

[0023] Specifically, the antenna element 18a has a base end 32 (corresponding to the "first base end") connected to the circuit board 12 and a main body 30 (corresponding to the "first extension") extending from the base end 32 to the rear of the circuit board 12. The antenna element 18b has a base end 32 (corresponding to the "second base end") connected to the circuit board 12 and a main body 30 (corresponding to the "second extension") extending from the base end 32 to the rear of the circuit board 12. The connecting portion 20 connects the tip 36 of the antenna element 18a and the tip 36 of the antenna element 18b in the left-right direction of the circuit board 12.

[0024] In the manufacture of the antenna unit 10, the conductor plate is punched out into a square frame shape with one side open, and the open end is bent to integrally form the antenna elements 18a, 18b and the connecting part 20. In a modified example, the antenna elements 18a and 18b may be formed individually, and the connecting part 20 may be joined by welding or the like.

[0025] Each feed point P1 and P2 is connected to a feed line mounted on the circuit board 12. The feed lines for each antenna are provided as microstrip lines on the back surface of the circuit board 12 and are connected to the respective feed ports of the connector 22.

[0026] Three cables, connected to an in-vehicle unit (not shown), are connected to connector 22 (see Figure 1). These cables are all coaxial cables and are connected via connector 22 to the respective feed lines of the GPS antenna 14 and a pair of TEL antennas 16. The inner conductors of the coaxial cables for the TEL antennas 16 are connected to the feed points (P1, P2) via connector 22, and the outer conductors are connected to the ground area 24 via connector 22.

[0027] In this embodiment, as shown in the figure, the antenna elements 18a and 18b are connected to the circuit board 12 at their respective base ends 32, while their respective main bodies 30 extend outward from the circuit board 12. This allows for proper adjustment of the distance between the antenna elements 18a and 18b.

[0028] By appropriately setting the spacing between the antenna elements 18a and 18b, which are arranged side by side, the circuit board 12 can be housed in the area enclosed by the antenna elements 18a and 18b and the connection portion 20 in a plan view (inside the contours of these projected areas). In other words, the circuit board 12 has a width that fits between the antenna elements 18a and 18b and a size that fits within the aforementioned area. The spacing between the antenna elements 18a and 18b is set to such an extent that there is virtually no capacitive coupling between them. The GPS antenna 14 is spaced apart from both antenna elements so that, in a plan view, it does not overlap with the projected planes of the antenna elements 18a and 18b.

[0029] As shown in Figure 2(B), the antenna unit 110 in the comparative example differs from this embodiment in that it does not have a connecting portion for connecting the pair of antenna elements 18a and 18b. The presence or absence of this connecting portion 20 affects the isolation of the left and right TEL antennas 16. The results of the analysis performed to verify this will be described below.

[0030] Figure 3 shows the results of the frequency characteristics analysis of the TEL antenna 16. Figure 3(A) shows the isolation (dB) analysis results, and Figure 3(B) shows the radiation efficiency (dB) analysis results. In each figure, the solid line shows the characteristics of this embodiment, and the dashed line shows the characteristics of the comparative example. The horizontal axis in each figure represents frequency.

[0031] Generally, isolation is considered good if it can be secured by an absolute value of 10 dB or more. In this respect, while the comparative example fails to secure 10 dB in the frequency range below 1200 MHz, this embodiment secures 10 dB across the entire frequency range shown in the figure, including below 1200 MHz.

[0032] On the other hand, regarding radiation efficiency, a higher numerical value is considered better. In this respect, both this embodiment and the comparative example show good performance in the frequency range of 1600 MHz and above. However, in the frequency range of lower than 1600 MHz, a significant improvement is observed in this embodiment. According to this embodiment, it can be seen that not only isolation but also radiation efficiency is improved in the range of 800 MHz to 1200 MHz.

[0033] As described above, according to this embodiment, by physically connecting the tips of the antenna elements (opposite the feed point) of two adjacent monopole antennas, good characteristics (radiation efficiency) can be ensured over a wide bandwidth without degrading isolation in the low frequency band. Space can also be effectively utilized by placing the circuit board 12 between the two monopole antennas (more specifically, the area surrounded by the two antenna elements and the connection point).

[0034] [Second Embodiment] Figure 4 is a plan view showing the configuration of the antenna unit according to the second embodiment. In the antenna unit 210 of this embodiment, the connection portion 220 has an electrical length increasing structure that increases the electrical length. This "electrical length increasing structure" includes a meander structure having a plurality of folded portions 222 in the extending direction of the connection portion 220, and functions as an "antenna characteristic adjustment structure" in which the antenna characteristics are adjusted by setting the line width w1 and meander width w2 of the meander structure. The length of the connection portion 220 along the extending direction (length along the meander shape) is greater than the length of the connection portion 20 in which both tip portions 36 of the antenna elements 18a and 18b are connected in a straight line, as in the first embodiment. In this embodiment, the line width w1 is set to 5 mm and the meander width w2 is set to 20 mm.

[0035] Figure 5 is a plan view showing the configuration of the antenna unit according to a modified example. Figure 5(A) shows Modified Example 1, and Figure 5(B) shows Modified Example 2. Modification 1 involves changing the line width w1 while keeping the meander width w2 of the meander structure unchanged, compared to the second embodiment (Figure 5(A)). The antenna unit 212 includes a connection section 230 having a meander structure. In the illustrated example, the line width w1 is set to 2 mm and the meander width w2 to 20 mm for the meander structure.

[0036] On the other hand, in the second modification, the meander width w2 is changed while the line width w1 of the meander structure remains unchanged compared to the second embodiment (Figure 5(B)). The antenna unit 214 includes a connection section 232 having a meander structure. In the illustrated example, the line width w1 of the meander structure is set to 5 mm and the meander width w2 to 40 mm. As described above, the antenna characteristics can be adjusted by appropriately setting the line width w1 and meander width w2 of the meander structure. Below, the analysis results for verifying this are shown.

[0037] Figure 6 shows the relationship between the line width of the meander structure and the frequency characteristics. Figure 6(A) shows the analysis results for isolation (dB), and Figure 6(B) shows the analysis results for radiation efficiency (dB). In each figure, the solid line shows the characteristics of the first embodiment without a meander structure, and the others show the characteristics of the second embodiment with a meander structure and its modified examples. The meander width w2 is assumed to be constant at 20 mm. Regarding the line width w1, the dotted line shows the case of 5 mm (corresponding to the second embodiment), the dashed line shows 3 mm, and the dashed line shows 2 mm (corresponding to Modification Example 1). The horizontal axis in each figure represents frequency.

[0038] According to this analysis, employing a meander structure significantly improves both isolation and radiation efficiency in the low-frequency range below 1000 MHz. Even in the frequency range of 1700-6000 MHz, isolation of over 10 dB can be secured, and radiation efficiency is comparable to that without a meander structure. In all frequency ranges, slight differences in isolation are observed depending on the linewidth w1.

[0039] Figure 7 shows the relationship between the meander width of the meander structure and the frequency characteristics. Figure 7(A) shows the analysis results for isolation (dB), and Figure 7(B) shows the analysis results for radiation efficiency (dB). The line width w1 is assumed to be constant at 5 mm. For the meander width w2 in each figure, the solid line represents 20 mm (corresponding to the second embodiment), the dotted line represents 30 mm, the dashed line represents 35 mm, and the dashed line represents 40 mm (corresponding to the second modification). The horizontal axis in each figure represents frequency.

[0040] This analysis shows that isolation and radiation efficiency can also be adjusted by adjusting the meander width w2 of the meander structure. In all frequency ranges, there is a slight difference in isolation depending on the meander width w2. In the frequency range below 1200MHz, isolation decreases as the meander width w2 increases. When the meander width w2 is 35mm or more, it becomes impossible to ensure isolation of 10dB or more.

[0041] According to this embodiment, by employing a meander structure at the connection point and adjusting its line width and meander width, it was confirmed that the balance between isolation and radiation efficiency for a pair of monopole antennas can be adjusted, thereby improving their frequency characteristics. In other words, depending on the balance of line width and meander width, the characteristics may be worse than without a meander structure (first embodiment) in certain frequency ranges. For this reason, it is preferable to adjust these according to the specifications (frequency band) of the monopole antenna. In this embodiment, it was found that by setting the line width w1 to 2 mm or more and 5 mm or less, and the meander width w2 to 20 mm or more and 35 mm or less, isolation can be improved, especially in the low-frequency range.

[0042] [Third Embodiment] Figure 8 is a perspective view showing the configuration of the antenna unit according to the third embodiment. The antenna unit 310 of this embodiment has a slightly different structure for the connection portion 320 compared to the connection portion 220 of the second embodiment. The connection portion 320 has stepped portions 322 at both ends so that it is maintained at a higher position than the main body 30 (first extension portion, second extension portion) of the antenna element 18. This allows the cable connected to the in-vehicle device to be passed downward through the connection portion 320 and connected to the connector 22.

[0043] According to this embodiment, the design flexibility for cable routing can be increased. In this case, a sufficient gap is formed between the connection part 320 and the cable to prevent deterioration of antenna performance. In this embodiment, the height of the stepped part 322 is set to 10 mm or more.

[0044] Although preferred embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to these specific embodiments, and various modifications are possible within the scope of the technical concept of the present invention.

[0045] [Differentiation] Figure 9 is a plan view showing the configuration of the modified antenna unit. The antenna unit 410 of the modified example 3 includes a larger circuit board 412 compared to the above embodiment. The circuit board 412 is a rectangular printed circuit board in plan view, and the antenna element 418a (first antenna element), antenna element 418b (second antenna element) and connection part 20 are arranged along the outer edge of the circuit board 412 in plan view.

[0046] The antenna elements 418a, 418b and the connecting portion 20 are each elongated rectangular in shape and are located above the circuit board 412, forming a U-shaped element unit 420 in plan view. The element unit 420 extends parallel to the upper surface of the circuit board 412. The base end portion 432 of each antenna element does not have the wide shape as in the above embodiment. The inner end of the base end portion 432 is bent downward at a right angle to form the feed portion 34. The lower end of the feed portion 34 is connected to the feed points (P1, P2).

[0047] On the upper surface of the circuit board 412, the area enclosed by the antenna elements 418a, 418b and the connection part 20 (inside the projection area of ​​the element unit 420) is sufficiently large, providing ample space to arrange a patch antenna or the like, separate from the GPS antenna 14. Antenna elements such as patch antennas are arranged to avoid circuit components such as chips on the circuit board 412. This modified example increases the design flexibility, such as circuit layout, by utilizing the aforementioned extra space.

[0048] In this modified example, the circuit board 412 is configured to be slightly larger than the element unit 420 in a plan view, with its outer edge located outside the element unit 420. In other modified examples, the circuit board 412 may be configured to be smaller than the element unit 420 in a plan view, with its outer edge located inside the element unit 420. Alternatively, the circuit board 412 may be configured to be such that its outer edge lies within the projection plane of the element unit 420. In any case, the antenna elements 418a, 418b and the connecting portion 20 are arranged along the outer edge of the circuit board 412 in a plan view.

[0049] Furthermore, in this modified example, the antenna element and connection part of the TEL antenna (monopole antenna) are made of a conductive plate, similar to the embodiment described above. However, in other modified examples, they may be made of wiring patterns mounted on the top surface (front), bottom surface (back), or within the layered structure of the circuit board 412. That is, the wiring patterns constituting the antenna element and connection part of the monopole antenna may be arranged along the outer edge of the circuit board 412.

[0050] Figure 10 is a plan view showing the configuration of an antenna unit relating to other modifications. Figure 10(A) shows modification 4, and Figure 10(B) shows modification 5. In these modifications, the frequency characteristics of the TEL antenna (monopole antenna) are adjusted by configuring the antenna element to have a tapered shape in plan view.

[0051] In other words, in the modified example 4, the antenna element 518 has a tapered shape in which its width gradually decreases from the base end 532 towards the tip end 36 in the front-to-back direction (Figure 10(A)). The antenna element 518 also has a tapered shape in which its width decreases as it approaches the feed point P1 in the left-to-right direction.

[0052] On the other hand, in the modified example 5, the antenna element 618 has a tapered shape in which its width gradually increases from the base end 632 towards the tip end 36 in the front-rear direction (Figure 10(B)). In other words, the antenna element 618 has a tapered shape in which its width decreases as it approaches the feed point P1.

[0053] By configuring the antenna elements so that their width decreases as they approach the feed point (P1, P2), it may be possible to improve antenna performance, for example, in high-frequency bands. By adjusting the taper angle of the tapered shape, antenna performance can be improved in specific frequency bands.

[0054] In this modified example, a tapered shape is given as an example of the specific shape of the antenna element, but any stepped shape or other shape is acceptable as long as the width of the antenna element is gradually reduced toward the feed point. Furthermore, depending on the frequency band to be improved, a configuration in which the width of the antenna element is gradually increased is also possible. In addition, as in the above embodiment, a configuration in which the width of the antenna element is gradually reduced or gradually increased is also possible, limited to the vicinity of the feed point.

[0055] Figures 11 and 12 show an analysis of the effects of the first embodiment and the results thereof. Figure 11(A) shows the analytical model of the first embodiment, and Figure 11(B) shows the analytical model of the comparative example. The configuration of the antenna unit 10 according to the first embodiment has already been described. On the other hand, the antenna unit 112 according to the comparative example has a structure in which the connection portion 20 of the first embodiment is divided into left and right antenna elements 118a and 118b by providing a slit in the center. Antenna element 118a functions as the "first antenna element," and antenna element 118b functions as the "second antenna element." In this comparative example, the gap G between the tips of the antenna elements 118a and 118b is 1 mm.

[0056] Figure 12 shows the results of the frequency response analysis. Figure 12(A) shows the isolation (dB) analysis results, and Figure 12(B) shows the radiation efficiency (dB) analysis results. In each figure, the solid line shows the characteristics of the first embodiment, and the dashed line shows the characteristics of the comparative example. The horizontal axis in each figure represents frequency.

[0057] According to this analysis, in the low frequency range of 1200 MHz and below (especially between 800 MHz and 1200 MHz), the first embodiment yielded better results in terms of isolation and radiation efficiency than the comparative example. On the other hand, in the high frequency range, there was almost no difference between the two. This point was also mentioned in the description of the first embodiment.

[0058] In another analysis (not shown), the effect on the other antenna element was investigated by calculating the current distribution when a current was excited at only one of the feed points of the first or second antenna element. Specifically, the feed point P2 (second feed point) of antenna element 118b was set to an excited state, and the feed point P1 (first feed point) of antenna element 118a was set to a non-excited state.

[0059] According to this analysis, when a current is excited at one feed point P2 with a frequency of 900 MHz, in the first embodiment, the current amplitude near the other feed point P1 becomes small, meaning the current waveform can be made into a node, resulting in good isolation. On the other hand, in the comparative example, the current amplitude near feed point P1 becomes large, meaning the current waveform becomes an antinode, resulting in poor isolation. This result is consistent with the analysis results in Figure 12.

[0060] In this analysis, one feed point P2 was excited and the other feed point P1 was not excited, but the same results are obtained when the excited states are reversed. At the same frequency, the current waveform (positional relationship between antinodes and nodes) at the non-excited feed point will be the same.

[0061] In other words, in the first embodiment, the lengths of the antenna element 18a, the antenna element 18b, and the connection part 20 are set such that, in the low frequency region, the waveform of the current excited at the feed point P1 has nodes near the feed point P2, and the waveform of the current excited at the feed point P2 has nodes near the feed point P1.

[0062] Figure 13 shows an analysis of the effects of the second embodiment and its results. Figure 13(A) shows the analysis results for isolation (dB), and Figure 13(B) shows the analysis results for radiation efficiency (dB). In each figure, the solid line shows the characteristics of the second embodiment (specifically, modified example 1 of Figure 5(A)), and the dashed line shows the characteristics of the comparative example. The horizontal axis in each figure represents frequency.

[0063] The configuration of the antenna unit 212 according to the second embodiment (modification 1) has already been described. On the other hand, the antenna unit according to the comparative example has a structure in which the connection portion 230 of modification 1 is divided into left and right antenna elements by providing a slit in the center. One of the antenna elements functions as the "first antenna element," and the other antenna element functions as the "second antenna element." In this comparative example as well, the gap between the tips of the left and right antenna elements is 1 mm.

[0064] According to this analysis, in the frequency range of 1200 MHz and below (especially between 800 MHz and 1200 MHz), the second embodiment (modified example 1) yielded better results in terms of isolation and radiation efficiency than the comparative example.

[0065] In another analysis (not shown), the effect on the other antenna element was verified by calculating the current distribution when a current was excited at only one of the feed points of the first and second antenna elements. According to this analysis, when a current was excited at one feed point P2 with a frequency of 900 MHz, in the second embodiment (modified example 1), the current waveform near the other feed point P1 could be made into a node, resulting in good isolation. On the other hand, in the comparative example, the current waveform near feed point P1 became an antinode, and good isolation could not be obtained. This result is consistent with the analysis results in Figure 13.

[0066] In other words, in the second embodiment (modified version 1), the lengths of the antenna element 18a, antenna element 18b, and connection part 230 are set such that, in the low frequency region, the waveform of the current excited at the feed point P1 has nodes near the feed point P2, and the waveform of the current excited at the feed point P2 has nodes near the feed point P1.

[0067] Figures 11 to 13 show examples of analysis results for specific configurations, but similar results can be obtained for other configurations as well. Specifically, this applies to various configurations where the connection part has a meander structure with different line widths and meander widths, configurations where the ends of the connection part have a rounded R shape, configurations where the connection part slopes from the ends toward the center (configurations where it forms an acute or obtuse angle with respect to the left and right antenna elements, configurations where it approaches or moves away from the patch antenna from the ends toward the center), and other configurations.

[0068] In other words, if the lengths of the first antenna element, the second antenna element, and the connection are set such that the waveform of the current excited at the first feed point forms nodes near the second feed point, and the waveform of the current excited at the second feed point forms nodes near the first feed point, then isolation and radiation efficiency can be improved.

[0069] Figure 14 is a plan view showing the configuration of the antenna unit according to the modified example 6. In this modified example, a metal plate 710 is added to the antenna unit 10 of the first embodiment. The metal plate 710 is a sheet metal component provided so as to face the side of the circuit board 12 opposite to the patch antenna (GPS antenna 14).

[0070] The metal plate 710 has a structure symmetrical with respect to the center line L in a plan view and is positioned within the region enclosed by the antenna elements 18a and 18b and the connecting portion 20. The metal plate 710 may also be positioned at the same height as the antenna elements 18a and 18b. This configuration can improve the gain characteristics and axial ratio characteristics of the patch antenna.

[0071] Figure 15 shows the effects of the configuration of Modified Example 6. Figure 15(A) shows the elevation angle-average gain characteristics (frequency: 1575MHz), Figure 15(B) shows the frequency-zenith gain characteristics, and Figure 15(C) shows the frequency-zenith axial ratio characteristics. In each figure, the solid line shows the characteristics of Modified Example 6, and the dashed line shows the characteristics of the Comparative Example. The horizontal axis in each figure represents frequency. The Comparative Example referred to here is a configuration without the metal plate 710 and corresponds to the first embodiment. The zenith axial ratio is an indicator of the roundness of the received radio waves when a patch antenna receives radio waves in the GNSS frequency band from an artificial satellite, in other words, the degree of distortion.

[0072] According to this modified example, it can be seen that by adding the metal plate 710, the average gain characteristics improve regardless of how the elevation angle of the GNSS antenna (GPS antenna 14) is set (Figure 15(A)). Furthermore, it can be seen that the zenith gain characteristics and zenith axial ratio characteristics improve in the frequency domain corresponding to the GNSS frequency band (Figures 15(B), (C)). In other modifications, the "conductive member" may be made of a conductive resin or other conductive material instead of the metal plate 710.

[0073] In the first embodiment described above, an example was shown in which the antenna element 18 and the connecting portion 20 are integrally molded by punching out a single conductive plate, and the width and thickness of the connecting portion 20 are the same as those of the main body 30 of the antenna element 18. In the modified example, at least one of the width and thickness of the connecting portion 20 may be different from that of the main body 30. The antenna element and the connecting portion may also be molded separately and then joined, in which case materials with different thicknesses may be used for both. Furthermore, the width and thickness of the connecting portion 20 may be changed in the direction of its extension. The shape of the connecting portion 20 may also be changed to a shape other than a rectangle in plan view.

[0074] In the above embodiment, the antenna element 18 is shown extending toward the rear of the circuit board 12, but it may also be configured to extend toward the front of the circuit board 12. Alternatively, it may be configured to extend both toward the front and rear of the circuit board 12. The "front-rear direction of the circuit board" may include both the front and rear of the circuit board.

[0075] In the second embodiment and its modifications described above, a configuration was shown in which the meander structure was applied to the entire area from one end to the other of the connection. Furthermore, a periodic rectangular wave-shaped meander structure was given as an example. In other modifications, the meander structure may be applied not to the entire area of ​​the connection, but only to a portion, such as the central region, the vicinity of the ends, or at predetermined intervals. The meander structure may also be curved wave-shaped or may not have periodicity. The thickness may be partially varied along the meander shape.

[0076] In the second embodiment described above, an example was shown in which the connection part 220 is made of the same metal as the antenna element 18 and further increased in length by using a meander structure (electrical length increasing structure). In a modified example, the electrical length may be adjusted by making the connection part of a different metal from that of the antenna element, without integrally molding the connection part and the antenna element. Alternatively, the electrical length may be adjusted by connecting a metal plate and a circuit element such as a chip inductor to the connection part. Conversely, an electrical length reduction structure may be adopted for the connection part, which shortens the electrical length compared to the case where the first antenna element and the second antenna element are connected in a straight line. That is, the connection part may have an "electrical length adjustment structure" that makes the electrical length different from the case where the first antenna element and the second antenna element are connected in a straight line.

[0077] In the above embodiment, the elements of the GPS antenna 14 were positioned higher than the elements of the TEL antenna 16, but the elements of the GPS antenna 14 may be positioned lower than the elements of the TEL antenna 16. In that case, the feed portion 34 may be bent downward at the base end 32 of the antenna element 18 and connected to the circuit board 12 from above.

[0078] In the above embodiment, a GPS antenna 14 was exemplified as the patch antenna provided on the circuit board 12, but instead, a patch antenna compatible with GLONASS (Global Navigation Satellite System) or other GNSS (Global Navigation Satellite Systems) may be provided. Alternatively, a patch antenna capable of receiving satellite radio such as SiriusXM may be provided. A patch antenna for ETC or VICS may also be provided.

[0079] As shown in Figure 2, if there is sufficient space in the area enclosed by the first antenna element, the second antenna element, and the connection part in a plan view, the circuit board 12 may be made larger in the front-to-back direction to arrange multiple patch antennas in the front-to-back direction. In that case as well, the circuit board 12 should be placed within the area enclosed by the first antenna element, the second antenna element, and the connection part (inside the contour of their projected areas).

[0080] Furthermore, when an ETC antenna is included in multiple patch antennas, the antenna element of that ETC antenna may be tilted relative to the circuit board 12 from the standpoint of directivity. In such cases, it is preferable to position the ETC antenna in front of the other patch antennas.

[0081] In the above embodiment, the antenna element is made of metal, but it may also be made of conductive resin or other conductive material.

[0082] In the above embodiment, so-called inverted L antennas were exemplified as the two monopole antennas, but inverted F antennas may also be used. Furthermore, rod-shaped monopole antennas or tapered monopole antennas may also be used.

[0083] In the above modified examples 3 to 5, the shape of the connection portion 20 is shown to be rectangular, similar to that of the first embodiment. However, it goes without saying that a meander structure (electrical length adjustment structure) may also be used, as in the second embodiment and its modified examples.

[0084] In the above embodiment, the antenna device was described as being installed within the instrument panel, but it may be installed at other locations on the vehicle body. Furthermore, it may be an antenna device installed not only on vehicles but also on ships and other means of transportation.

[0085] In the above embodiment, the two adjacent (parallel) monopole antennas were used as TEL antennas, but other antennas compatible with MIMO may also be used. Furthermore, in the above embodiment, a configuration in which the two monopole antennas extend in the front-to-back direction parallel to the circuit board was illustrated, but they may also extend perpendicular to the circuit board. In that case as well, the circuit board may have a width that fits between the first antenna element and the second antenna element.

[0086] It should be noted that the present invention is not limited to the embodiments and modifications described above, and the components can be modified and implemented without departing from the spirit of the invention. Various inventions may be formed by appropriately combining the multiple components disclosed in the embodiments and modifications described above. In addition, some components may be deleted from all the components shown in the embodiments and modifications described above. [Explanation of symbols]

[0087] 1 Antenna device, 10 Antenna unit, 12 Circuit board, 14 GPS antenna, 16 TEL antenna, 18 Antenna element, 20 Connection part, 22 Connector, 24 Ground area, 32 Base end, 34 Feed part, 36 Tip, 110 Antenna unit, 212 Antenna unit, 214 Antenna unit, 220 Connection part, 222 Folded part, 230 Connection part, 232 Connection part, 310 Antenna unit, 320 Connection part, 322 Stepped part, 410 Antenna unit, 412 Circuit board, 420 Element unit, 432 Base end, 518 Antenna element, 532 Base end, 618 Antenna element, 632 Base end, P1 Feed point, P2 Feed point.

Claims

1. A circuit board having a ground region, A first antenna element, whose base end is connected to a first feed point provided on the circuit board, and which forms a first monopole antenna, The base end of the second antenna element is connected to a second feed point provided on the circuit board, forming a second monopole antenna. A connecting portion that connects the tip of the first antenna element and the tip of the second antenna element, Equipped with, The antenna device is characterized in that the connection portion is configured such that the waveform of the current excited at the first feed point forms a node near the second feed point.

2. The first antenna element has a first base end connected to the first feed point and a first extension portion extending from the first base end in the front-rear direction of the circuit board. The second antenna element has a second base end connected to the second feed point and a second extension extending from the second base end in the front-rear direction of the circuit board. The antenna device according to claim 1, characterized in that the connection portion connects the first extended portion and the second extended portion in the left-right direction of the circuit board on the side opposite to each base end.

3. The antenna device according to claim 1 or 2, characterized in that the circuit board has a width that fits between the first antenna element and the second antenna element.

4. The antenna device according to any one of claims 1 to 3, characterized in that the circuit board is sized to fit within the region enclosed by the first antenna element, the second antenna element, and the connection portion in a plan view.

5. The antenna device according to claim 4, characterized in that a patch antenna is provided on the circuit board.

6. The antenna device according to any one of claims 1 to 5, characterized in that the first antenna element and the second antenna element are each arranged along the outer edge of the circuit board.

7. The antenna device according to any one of claims 1 to 6, characterized in that the connection portion has an electrical length adjustment structure that makes the electrical length different from that when the first antenna element and the second antenna element are connected in a straight line.

8. The antenna device according to any one of claims 1 to 7, characterized in that the connection portion has an electrical length increasing structure that increases the electrical length.

9. The antenna device according to claim 8, characterized in that the electrical length increasing structure includes a meander structure having a plurality of folded portions in the extending direction of the connection portion.

10. The antenna device according to claim 9, characterized in that it includes an antenna characteristic adjustment structure in which the antenna characteristics are adjusted by setting the line width and meander width of the meander structure.

11. The antenna device according to claim 10, characterized in that the meander structure has a line width of 2 mm or more and 5 mm or less, and a meander width of 20 mm or more and 35 mm or less.

12. The antenna device according to any one of claims 1 to 11, characterized in that the lengths of the first antenna element, the second antenna element, and the connection portion are set such that the waveform of the current excited at the first feed point forms a node near the second feed point, and the waveform of the current excited at the second feed point forms a node near the first feed point.

13. The circuit board further comprises a conductive member provided so as to face the side opposite to the patch antenna, The antenna device according to claim 5, characterized in that the conductive member is arranged in a region surrounded by the first antenna element, the second antenna element, and the connecting portion in a plan view.

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