Composite Antenna Device

Abstract

Provided is a composite antenna apparatus having a structure that, while minimizing any increase in size, makes it possible to improve gain characteristics, etc., of individual antennas.　The composite antenna apparatus has a patch antenna 32 as a first antenna, and a plurality of second antennas; e.g., a pair of planar elements 41, 42. This composite antenna apparatus also has, as a first conductor part, a three-dimensional base plate 20 or a flat base plate 50 to form the base plate of the patch antenna 32 and the pair of planar elements 41, 42. Each of the plurality of planar elements 41, 42 comprises a second conductor part different from the first conductor part. The patch antenna 32 is provided on the first conductor part, and at least some of the first conductor part is positioned between the second conductor parts.

Description

[Technical field]

[0001] The present invention relates to a composite antenna device that is disposed in a spatially limited portion of a vehicle, such as an instrument panel (abbreviated as "instrument panel"). [Background technology]

[0002] As an example of this type of prior art, Patent Document 1 discloses a composite antenna device that integrates multiple antennas that share a common ground plate. When multiple antennas share a common ground plate (a conductor that functions as a ground for the antennas, the same applies below), interference between the antennas becomes a problem. In the composite antenna device disclosed in Patent Document 1, one antenna is positioned offset from the center of the ground plate toward the center of the vehicle cabin by at least 1 / 4 of the front-to-rear length of the ground plate, and the other antenna is positioned offset from the center of the ground plate on the opposite side to the one antenna by at least 1 / 4 of the front-to-rear length of the ground plate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-124577 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the composite antenna device disclosed in Patent Document 1, the feed points of the multiple antennas are at approximately the same height relative to the ground, and the direction in which the main coverage area of ​​the radio waves extends is also the same. In such an arrangement, when the frequencies of the radio waves used are close to each other, the coverage areas overlap and interference between the antennas is likely to occur, so the distance between the antennas cannot be reduced to prevent interference. In other words, the area of ​​the ground plate cannot be reduced. Therefore, the size of the antenna, including the ground plate, must be increased.

[0005] An object of the present invention is to improve the characteristics of each antenna in a composite antenna device while preventing the device from becoming large in size. [Means for solving the problem]

[0006] A first aspect of the present invention provides a composite antenna device comprising a first antenna, a plurality of second antennas having a different operating frequency band and a different direction of extension of a main coverage area from that of the first antenna, and a first conductor portion serving as a ground plane for the first antenna and the second antennas, each of the plurality of second antennas having a second conductor portion, the first antenna being provided on the first conductor portion, and at least a portion of the first conductor portion being positioned between the second conductor portions.

[0007] A composite antenna device according to a second aspect of the present invention comprises a first antenna, a second antenna having a different frequency band and a different direction in which its main coverage area extends from that of the first antenna, a first conductor portion that serves as a base plate for the first antenna and the second antenna, and a second conductor portion that serves as the second antenna, wherein the first conductor portion has a planar portion on which the first antenna is mounted and an inclined surface portion that is inclined at a predetermined angle relative to the planar portion on the side opposite to the side on which the first antenna is mounted, the second conductor portion is electrically conductive with the inclined surface portion, and the second conductor portion has an insulating substrate and a conductor formed on the surface of the substrate.

[0008] A composite antenna device according to a third aspect of the present invention comprises a first antenna, a second antenna whose main coverage area extends in a direction different from that of the first antenna, a first conductor portion that serves as a base plate for the first antenna and the second antenna, and a second conductor portion that serves as the second antenna, wherein the first conductor portion has a planar portion on which the first antenna is mounted, and the second antenna is positioned on the opposite side of the planar portion from the side on which the first antenna is mounted, and the first antenna is a patch antenna, and the second antenna is an antenna for cellular communication. Effect of the Invention

[0009] The composite antenna device makes it possible to improve the characteristics of each antenna while preventing an increase in size. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is an exploded perspective view illustrating an example of the structure of the complex antenna device according to the embodiment. [Diagram 2] 3A to 3C are front, rear and side views illustrating the structure of a planar element of the composite antenna device. [Diagram 3] FIG. 2 is a perspective view showing an example of the external configuration of the composite antenna device with a radome removed. [Figure 4] 1A to 1C are six views, including a rear view, a top view, a front view, a bottom view, a left side view, and a right side view, for explaining an example of the external configuration of a composite antenna device with a radome removed. [Diagram 5] 4 is a diagram showing antenna gain characteristics on the horizontal plane of a cellular communication antenna of a composite antenna device. [Figure 6] 1 is a schematic diagram of a composite antenna device according to an embodiment of the present invention; [Figure 7] FIG. 4 is a schematic diagram of a composite antenna device according to a first modified example. [Figure 8] FIG. 11 is a diagram showing antenna gain characteristics in the horizontal plane of the complex antenna device according to the first modification. [Figure 9] FIG. 11 is a diagram showing inter-port isolation characteristics of the composite antenna device according to the first modification. [Figure 10] FIG. 4 is a schematic diagram of a composite antenna device according to a comparative example. [Figure 11] FIG. 11 is a diagram showing inter-port isolation characteristics in the comparative example. [Figure 12] FIG. 11 is a schematic diagram of a complex antenna device according to a second modification. [Figure 13] FIG. 11 is a VSWR characteristic diagram of a composite antenna apparatus according to Modification 2. [Figure 14] 13 is a schematic diagram of a complex antenna device according to Modifications 3 to 7. FIG. [Figure 15] FIG. 23 is a schematic diagram of a complex antenna device according to Modification 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the composite antenna device will be described. The composite antenna device of this embodiment is installed in the cabin of a vehicle, for example, on the instrument panel of the vehicle, and is connected to electronic devices on the vehicle side via multiple coaxial cables. An example of the structure of the composite antenna device is shown in an exploded perspective view of FIG. 1. For convenience of explanation, hereinafter, three orthogonal axes, the X-axis, the Y-axis, and the Z-axis, are defined with respect to the installation location of the composite antenna device. In these three orthogonal axes, the +Z direction is the upward direction as viewed from the ground, the -Z direction is the downward direction as viewed from the ground, the +X-axis direction is the forward direction, the -X-axis direction is the backward direction, the +Y-axis direction is the leftward direction, and the -Y-axis direction is the rightward direction. In addition, there are cases where a plane including the X-axis and the Y-axis is described as a horizontal plane. In this case, the horizontal plane is a plane parallel to the ground.

[0012] FIG. 1 is an exploded perspective view showing an example of the structure of a composite antenna device. 1, the composite antenna device has a radio wave transparent radome 10 and a base 11. The radome 10 has a rectangular planar portion 101 parallel to the horizontal plane, a first side portion 102 inclined downward from the front short side of the planar portion 101, a second side portion 103 inclined downward from the rear short side of the planar portion 101, a third side portion 104 inclined downward from the right long side of the planar portion 101, and a fourth side portion 105 inclined downward from the left long side of the planar portion 101. The first side portion 102, the second side portion 103, the third side portion 104, and the fourth side portion 105 are an example of an inclined surface portion that is inclined at a predetermined angle (for example, approximately 90 degrees downward) with respect to the flat portion 101 and extends in a direction away from the flat portion. The lower ends of the first side portion 102, the second side portion 103, and the third side portion 104 are open with the fourth side portion 105 as one side. The lower length of the fourth side portion 105 is longer than the lower lengths of the first side portion 102, the second side portion 103, and the third side portion 104. The lower end of the first side portion 102 is formed with a notch 106 for positioning and holding coaxial cables 331, 332, 431, and 432 described later.

[0013] The base 11 has a flat portion 111 which is parallel to the flat portion 101 of the radome 10 in order to seal the lower opening of the radome 10 and has a projected area (projected area on the ground) substantially equal to the area of ​​the opening of the radome 10. The flat portion 111 is provided with a holding structure for holding the three-dimensional ground plate 20, the antennas, and the electronic circuits, which will be described later, i.e., three screw receiving portions 113, 114, and 115, each of which is reinforced with a partition plate. In addition, a protruding body 116 is formed in front of the flat portion 111, protruding upward in order to hold the coaxial cables 331, 332, 431, and 432, which will be described later. A left side surface portion 112 is formed from the left long side of the flat portion 111, and is inclined downward at approximately 90 degrees. The base 11 is fixed to the electronic circuit board 31 from the bottom side with screws 131 and 132.

[0014] This composite antenna device includes a three-dimensional ground plate 20, which is an example of a first conductor. The three-dimensional ground plate 20 is made of a conductive member held by the base 11. The three-dimensional ground plate 20 has a planar portion 21 parallel to the horizontal plane, a first side portion 22 inclined downward from the front short side of the planar portion 21, a second side portion 23 inclined downward from the rear short side of the planar portion 21, a third side portion 24 inclined downward from the right long side of the planar portion 21, and a fourth side portion 25 inclined downward from the left long side of the planar portion 21. In this example, the height and width of the three-dimensional ground plate 20 are at least about λ / 6 and at least about (2 / 5)λ, respectively, where λ is the wavelength of the minimum frequency used in the planar elements 41 and 42 described later.

[0015] The three-dimensional ground plate 20 needs to be accommodated in the internal accommodation space of the radome 10. Therefore, the short side size (length in the Y-axis direction) of the first side portion 22 and the second side portion 23 is slightly shorter than the short side size of the radome 10 and the base 11. Also, the long side size (length in the X-axis direction) of the third side portion 24 and the fourth side portion 25 is slightly shorter than the long side size of the radome 10 and the base 11. A part of the lower end of the first side portion 22 is cut out slightly larger than the notch 106 of the radome 10 and the protruding body 116 of the base 11. A substantially rectangular opening window 26 is formed in the approximate center of the flat portion 21. The shape and size of this opening window 26 are the same as the outline shape of a substantially rectangular prism-shaped patch antenna 32 which is an example of a first antenna, but are slightly larger than the patch antenna 32.

[0016] The patch antenna 32 is a planar antenna (unit) for circular polarization that is arranged parallel or approximately parallel to the ground, and the direction in which the coverage area extends is upward (Z-axis direction). In this example, a general-purpose planar antenna for a Global Navigation Satellite System (hereinafter referred to as "GNSS") is used as the patch antenna 32. The patch antenna 32 is used in either the frequency band of GPS (Global Positioning System; frequency band 1575.397 to 1576.443 MHz) or the frequency band of GNSS (frequency band 1597.807 to 1605.6305 MHz). The operating frequency of the patch antenna 32 can be changed as appropriate.

[0017] The patch antenna 32 is fixed to an electronic circuit board 31 to which two coaxial cables 331, 332 are connected, and is positioned so that the portion other than the electronic circuit board 31 is exposed from the opening window 26 of the flat portion 21 of the three-dimensional ground plate 20. An electronic circuit including a feeding point to the patch antenna 32 and a ground pattern are also formed on the electronic circuit board 31. Since the two coaxial cables 331, 332 are simply split, only one coaxial cable may be used.

[0018] The height (thickness) of the electronic circuit board 31 and the planar portion 21 of the three-dimensional ground plate 20 is thinner than the height (thickness) of the patch antenna 32. Therefore, when the electronic circuit board 31 is fixed together with the three-dimensional ground plate 20 to the screw receiving portions 113, 114, 115 of the base 11 with the screws 123, 124, 125, almost the entire portion of the patch antenna 32 in the height direction is exposed from the opening window portion 26. In addition, the power supply point of the patch antenna 32 is at almost the same height as the planar portion 21 of the three-dimensional ground plate 20. Furthermore, when the electronic circuit board 31 is fixed with the screws, its ground pattern is conductive with the three-dimensional ground plate 20. Therefore, the three-dimensional ground plate 20 acts as a ground plate (ground) for the patch antenna 32.

[0019] A pair of planar elements 41, 42, which are an example of a second conductor portion, are arranged parallel to the left side surface portion 112 of the base 11 together with coaxial cables 431, 432, respectively. The structure of the planar elements 41, 42 will be described with reference to Fig. 2. Fig. 2 is a front view, a rear view, and a side view of the structure of the planar element 41.

[0020] The planar element 41 has a pair of planar antenna patterns 411, 412 and a pair of ground patterns 414, 415 formed on both sides of a printed circuit board 410, for example. The antenna patterns 411, 412 have wideband characteristics. In this example, the contours of the antenna patterns 411, 412 are at least partially curved, and the planar element 41 has wideband characteristics by adopting a semi-elliptical shape. The pair of antenna patterns 411, 412 are disposed in a direction away from the planar portion 21, for example, in substantially the same plane as the fourth side portion 25 of the three-dimensional ground plate 20. The pair of antenna patterns 411, 412 are electrically connected to each other via a conductive via hole 413. The pair of ground patterns 414, 415 are also electrically connected to each other via a conductive via hole 416. The antenna patterns 411, 412 are electrically connected to each other through a via hole 416, and are arranged to face the ground patterns 414, 415, which are further electrically connected to the three-dimensional ground plate 20. This provides an effect similar to that of a pseudo biconical antenna. In addition, the ground patterns 414, 415 and the electrically connected three-dimensional ground plate 20 provide an effect as if another antenna element were virtually arranged to face each other. This allows for a broadband.

[0021] The central portions of the pair of antenna patterns 411, 412 are notched in a convex shape. This is a mounting hole 418 for the left side surface portion 112 of the base 11. An engagement portion 118 is formed in a portion of the left side surface portion 112 of the base 11 that corresponds to the mounting hole 418. This engagement portion 118 has a head and a foot portion that elastically supports the head. The head of the engagement portion 118 has a length in the front-rear direction that passes through the front-rear hole of the mounting hole 418. The foot portion has a length in the front-rear direction that passes through the vertical hole of the mounting hole 418, and a length in the left-right direction that is the thickness of the planar element 41. Therefore, after the head of the engagement portion 118 is penetrated through the mounting hole 418, the planar element 41 can be easily engaged with the left side surface portion 112 of the base 11 by simply displacing it slightly upward (when disengaging, the engagement portion is displaced in the opposite direction). A locking portion 119, which will be described later, is also formed below the engaging portion 118, and locks the planar element 41 engaged with the engaging portion 118 so as not to move.

[0022] The signal line (center conductor) of the coaxial cable 431 is electrically connected to the portion of the pair of antenna patterns 411, 412 that is closest to the ground patterns 414, 415. The ground line (outer conductor) of the coaxial cable 431 is electrically connected to the pair of ground patterns 414, 415. The pair of ground patterns 414, 415 are also electrically connected to the fourth side surface portion 25 of the three-dimensional ground plate 20. Therefore, the planar element 41 operates as an antenna (second antenna) with the ground patterns 414, 415 and the three-dimensional ground plate 20 as ground side elements and the pair of antenna patterns 411, 412 as signal side elements. In this example, the antenna formed by the planar element 41 and the three-dimensional ground plate 20 is operated as a cellular communication antenna that enables transmission and reception in the frequency band of 1.7 GHz to 6.0 GHz, which is higher than the patch antenna 32 but close to the low frequency band of the used frequency.

[0023] 2 shows the structure of the planar element 41, and the structure of the planar element 42 is the same as that of the planar element 41 shown in FIG. 2. That is, a pair of antenna patterns (antenna pattern 421 on the front side, omitted on the back side; hereinafter, sometimes referred to as "pair of antenna patterns 421") formed on both sides of the printed circuit board 420 are disposed in a direction away from the planar portion 21, substantially on the same plane as the fourth side portion 25 of the three-dimensional ground plate 20. The antenna patterns are electrically connected to each other via a via hole similar to the conductive via hole 413. In addition, the signal line of the coaxial cable 432 is electrically connected to a portion of the pair of antenna patterns 421 that is closest to the pair of ground patterns (ground pattern 424 on the front side, omitted on the back side; hereinafter, sometimes referred to as "pair of ground patterns 424").

[0024] In addition, the ground line of the coaxial cable 432 is electrically connected to the pair of ground patterns 424. The pair of ground patterns 424 are also electrically connected to the fourth side surface portion 25 of the three-dimensional ground plate 20. Therefore, the planar element 42 operates as an antenna (e.g., another second antenna) with the pair of ground patterns 424 and the three-dimensional ground plate 20 as ground side elements and the pair of antenna patterns 421 as signal side elements. In this example, the antenna formed by the planar element 42 and the three-dimensional ground plate 20 is operated as a cellular communication antenna that enables transmission and reception in the frequency band of 1.7 GHz to 6.0 GHz, which is higher than the patch antenna 32 but close to the low frequency band used.

[0025] An attachment hole 428 is formed in the planar element 42, and the planar element 42 is attached to the base 11 via this attachment hole 428. An engagement portion 128 is formed in the left side surface portion 112 of the base 11 at a location corresponding to the attachment hole 428. This engagement portion 128 has the same structure as the engagement portion 118, and a lock portion 129 (e.g., having the same structure as the lock portion 119) described below is provided below.

[0026] The planar elements 41 and 42 share the three-dimensional ground plane 20 as a common ground-side element, and are disposed approximately perpendicular to the ground. Therefore, the projected area onto the ground is approximately the sum of the thicknesses of the printed circuit boards 410 and 420 and the thicknesses of the antenna patterns 421 and 422, making them less susceptible to the influence of the ground. In addition, the extension direction of the main coverage areas of the planar elements 41 and 42 is also approximately parallel to the ground (approximately a horizontal plane).

[0027] Although the frequency bands used by the high-frequency side of patch antenna 32 and the low-frequency side of each cellular communication antenna are close to each other, interference is unlikely to occur because the directions in which the main coverage areas of patch antenna 32 and the two cellular communication antennas extend are different. However, since the frequency bands used by the cellular communication antennas are close to each other, in this embodiment, the feeding points of planar element 41 and planar element 42 are separated by a distance of ¼ or more of the wavelength of the radio waves for cellular communication in order to suppress mutual interference.

[0028] 3 and 4 show an example of the configuration of the composite antenna device with the radome 10 removed. FIG. 3 is a perspective view showing an example of the external configuration of the composite antenna device with the radome 10 removed. FIG. 4 is a structural explanatory diagram showing the external configuration of the composite antenna device with the radome 10 removed from the back, top, front, bottom, left side, and right side. In these figures, the locking parts 119 and 129 are also shown. As is clear from these figures, the composite antenna device includes a three-dimensional ground plate 20 having a characteristic shape and structure and a plurality of antennas. The three-dimensional ground plate 20 has a flat portion 21 parallel or approximately parallel to the ground, and a first side portion 22, a second side portion 23, a third side portion 24, and a fourth side portion 25 perpendicular or approximately perpendicular to the ground, and these surfaces are integrally formed from a conductive material. Therefore, the three-dimensional ground plate 20 acts as a ground plate for a patch antenna 32 as a first antenna protruding from the flat portion 21. Furthermore, in the planar elements 41 and 42 arranged substantially on the same plane as the fourth side surface portion 25 of the three-dimensional ground plate 20, the ground patterns 414 and 415 of the planar element 41 and a pair of ground patterns 424 of the planar element 42 are conductive with the three-dimensional ground plate 20. Therefore, the three-dimensional ground plate 20 also functions as ground side elements of two cellular communication antennas serving as second antennas with the planar elements 41 and 42 as signal side elements.

[0029] Although the projection area of ​​the three-dimensional ground plate 20 on the ground is smaller than the projection area of ​​a flat ground plate having the same surface area as the three-dimensional ground plate 20, the three-dimensional ground plate 20 functions as a ground plate for the patch antenna 32, whose surface area is larger than the projection area. Therefore, the operating characteristics of the patch antenna 32, such as the VSWR characteristics, are much more stable than a patch antenna having a ground plate without the first side portion 22 to the fourth side portion 25. In addition, the gain in the upward direction (Z-axis direction) of the patch antenna 32 can be improved compared to a patch antenna having a ground plate without the first side portion 22, the second side portion 23, the third side portion 24, and the fourth side portion 25, that is, a ground plate having the size of the flat portion 21. As a result, the reception accuracy of the patch antenna 32 can be further improved.

[0030] Since the three-dimensional ground plate 20 also functions as the ground plate for each cellular communication antenna, simply ensuring a size of λ / 4 or more for the wavelength λ of the smallest frequency of the frequencies used will have the effect of suppressing leakage current over almost the entire frequency range. Coaxial cables are sometimes used in high frequency bands to connect electronic circuits or as power feed lines. In this case, the potential difference between the outer conductor and the ground can become significant, and unintended currents can flow through the coaxial cables. Such currents become leakage currents, which can lead to unintended radiation and loss.

[0031] For this reason, in the past, when performing cellular communications at high frequencies such as the 700 MHz band, it was essential to provide leakage current countermeasures such as ferrite cores to the coaxial cable used for power supply. However, ferrite cores are not only expensive, but also heavy and large. Moreover, considering the snake's limitations, at current levels, the effect of ferrite cores cannot be expected at frequencies above 1.7 GHz.

[0032] In the composite antenna device of this embodiment, the three-dimensional ground plate 20, which has an electrically larger area than that used in the conventional case of 700 MHz, is electrically connected to the outer conductors of the coaxial cables 431 and 432. Therefore, the generation of unnecessary currents propagating through the coaxial cables 431 and 432 is suppressed, and it is not necessary to take measures against leakage current even in high frequency bands exceeding 1.7 GHz. As a result, the entire device configuration including the radome 10 and the base 11 can be made small and simple. The fact that it is possible to improve the characteristics of each antenna while making the composite antenna device small and simple can be an extremely useful effect, considering that the mounting area is generally limited in the design of vehicle-mounted antennas.

[0033] FIG. 5 shows the antenna gain characteristic diagram of the horizontal plane of the cellular communication antenna of this embodiment. In FIG. 5, the vertical axis is gain [dBi], and the horizontal axis is frequency [MHz]. Also, "port 1" represents the feed point of the planar element 41, and "port 2" represents the feed point of the planar element 42. A solid line 511 indicates the antenna gain characteristic of the horizontal plane observed at port 1, and a dashed line 512 indicates the antenna gain characteristic of the horizontal plane observed at port 2. That is, the gain of port 1 is the antenna gain in a substantially horizontal direction with respect to the ground as seen from the feed point of the planar element 41, and the gain of port 2 is the antenna gain in a substantially horizontal direction with respect to the ground as seen from the feed point of the planar element 42. As shown in FIG. 5, in the cellular communication antenna of this embodiment, it can be seen that the gain near the feed points of the two planar elements 41 and 42 is stably around 0 [dBi] or more over the entire range of the 1.7 GHz to 6 GHz band.

[0034] In addition, the main coverage area of ​​the patch antenna 32 extends upward, whereas the main coverage area of ​​each cellular communication antenna extends approximately parallel to the ground, so mutual interference between the antennas is suppressed even if the frequency bands used are close to each other.

[0035] Furthermore, since the planar elements 41 and 42 acting as the signal side elements of the cellular communication antennas are disposed below the fourth side surface portion 25 of the three-dimensional ground plate 20, the patch antenna 32 and the signal side element of the cellular communication antenna are disposed on opposite sides of the ground (the three-dimensional ground plate 20 in this example). As a result, even in the limited space inside the vehicle, for example, it is possible to maintain the VSWR characteristics and upper gain of the patch antenna 32 while ensuring a sufficient electromagnetic distance between the patch antenna 32 and the cellular communication antenna. In other words, it is possible to maintain a sufficient level of isolation between the antennas.

[0036] In addition, the position of the feed point of each cellular communication antenna is lower than the feed point of the patch antenna 32, and both feed points are separated in the height direction, so that the isolation between the feed points can also be improved. That is, the feed point of each cellular communication antenna is on the opposite side of the ground from the side where the patch antenna 32 is provided, and both feed points are located in directions away from each other. Therefore, the isolation between the feed points can also be improved. When viewed from the horizontal direction (Y-axis direction), the patch antenna 32 is located between the two cellular communication antennas (planar elements 41, 42). In this way, the feed point of the patch antenna 32 is separated from the feed point of the cellular communication antenna in the horizontal direction as well, so that the isolation between the antennas can be further improved.

[0037] <Variation 1> The configuration of the composite antenna device of the present invention is not limited to the example described in this embodiment, and can be modified in various ways without departing from the gist of the invention. Several modified examples are described below. For convenience, the same components or functional components as those of the composite antenna device of this embodiment are given the same reference numerals. A typical configuration example of the composite antenna device of this embodiment is also shown.

[0038] Fig. 6 is a schematic diagram of a composite antenna device of this embodiment. In this composite antenna device, a three-dimensional ground plate 20 has a first side portion 22, a second side portion 23, a third side portion 24, and a fourth side portion 25 each extending downward from a flat portion 21. Fig. 7 is a schematic diagram of a composite antenna device according to Modification 1, and as shown in Fig. 7, the composite antenna device according to Modification 1 has a configuration in which the first side portion 22 and the second side portion 23 of the composite antenna device of this embodiment are removed.

[0039] FIG. 8 shows an antenna gain characteristic diagram in the horizontal plane of the composite antenna device according to the first modification. FIG. 9 shows an isolation characteristic diagram between ports of the composite antenna device according to the first modification. That is, FIG. 8 shows an example of gain [dBi] characteristic in the horizontal plane of the composite antenna device according to the first modification, and FIG. 9 shows an example of isolation between ports [dB], that is, an example of isolation between two cellular communication antennas and an example of isolation between a cellular communication antenna and a patch antenna 32. The feed point of the planar element 41 is "port 1", the feed point of the planar element 42 is "port 2", and the feed point of the patch antenna 32 is "port 3". The horizontal axis is the frequency band [MHz] used. In FIG. 8, a solid line 521 shows an example of gain characteristic in the horizontal plane observed at port 1, and a dashed line 522 shows an example of gain characteristic in the horizontal plane observed at port 2. In FIG. 9, a solid line 611 shows an example of isolation characteristic between port 1 and port 3, and a dashed line 612 shows an example of isolation characteristic between port 2 and port 3.

[0040] With reference to FIG. 8, in the case of the complex antenna device according to the first modification, the gain becomes high overall and stable at frequencies above 2.4 GHz. Therefore, when the antenna characteristics of the patch antenna 32 are more important than the antenna characteristics during cellular communication, the configuration of this embodiment can be adopted, and when the opposite is true, the configuration of variant example 1 can be adopted, thereby increasing the freedom of design.

[0041] <Comparative Example> A comparative example is shown in which the planar elements 41 and 42 extend upward from the planar portion 21 as shown in FIG. 10, instead of extending downward from the planar portion 21 as in the first modified example. FIG. 11 shows the inter-port isolation characteristic diagram for the comparative example shown in FIG. 10. The characteristic diagram in FIG. 11 corresponds to the characteristic diagram in FIG. 9. That is, the solid line 811 is an example of the isolation characteristic between port 1 and port 3, and the dashed line 812 is an example of the isolation characteristic between port 2 and port 3. In general, when the frequency bands used are different, or when the harmonics thereof overlap or are close to each other, but the directions in which the main coverage areas extend are different, mutual interference between antennas can be suppressed. However, when the directions in which the main coverage areas extend overlap as in the comparative example, in this example, when two antennas (second antennas) both used as cellular communication antennas are shared, mutual interference between antennas is not sufficiently suppressed, and further ingenuity is required.

[0042] 9 and 11, depending on the frequency band used, the characteristic of the dashed line 812 in FIG. 11 showing the comparative example (example of the isolation characteristic between port 2 and port 3) appears to be lower in all frequency bands than the characteristic of the dashed line 612 in FIG. 9 showing the modified example 1 (example of the isolation characteristic between port 2 and port 3). On the other hand, the characteristic of the solid line 811 in FIG. 11 (example of the isolation characteristic between port 1 and port 3) has almost the same value as the modified example 1, except for some frequency bands. Therefore, it can be seen that the configuration in which the planar elements 41 and 42 extend downward from the flat portion 21 as in the modified example 1 can expand the frequency band in which the isolation between port 1 and port 3 can be further improved, compared to the configuration of the comparative example.

[0043] <Variation 2> In this embodiment, the two planar elements 41, 42 have been described under the assumption that they are the same size, but as shown in Variation 2 of Fig. 12, one of them, in the illustrated case, planar element 52, may be configured to be larger than planar element 41. In the composite antenna device according to Variation 2 of Fig. 12, a configuration is shown excluding the first side portion 22 and the second side portion 23, but a configuration having at least one of the first side portion 22 and the second side portion 23 may also be used.

[0044] 13 is a VSWR characteristic diagram for the second modification. The vertical axis represents VSWR, and the horizontal axis represents frequency [MHz]. Moreover, solid line 711 indicates an example of the VSWR characteristic observed at port 1 (the feed point of planar element 41), and dashed line 712 indicates an example of the VSWR characteristic observed at port 2 (the feed point of planar element 52). In the illustrated example, in the case of planar element 41, the VSWR becomes 2 or less at about 1.6 GHz, but in the case of planar element 52, the VSWR becomes 2 or less from about 850 MHz. In other words, by adopting a configuration such as that of the second modification, it is possible to make the usable frequency band wider.

[0045] <Variations 3 to 8> In addition to the above-mentioned modifications 1 and 2, various other combinations of shapes of the three-dimensional ground plate 20 and the locations of the planar elements 41, 42 of the complex antenna device are possible, as exemplified in Figs. 14(A)-(F). Modification 3 in FIG. 14(A) is a configuration in which planar elements 41 and 42 are arranged diagonally to each other in a plane that is approximately perpendicular to the flat portion 21 of the three-dimensional ground plate 20. 14(B) is a configuration in which the heights of the third side surface portion 24 and the fourth side surface portion 25 are shorter than those of the other modifications. In this case, it is desirable that the heights of the third side surface portion 24 and the fourth side surface portion 25 are equal to or greater than 1 / 6 of the wavelength λ of the minimum frequency used in the planar elements 41, 42. It is also possible to have a configuration in which the height of only one of the third side surface portion 24 and the fourth side surface portion 25 is shorter than that of the other modifications.

[0046] 14(C) is a configuration in which the planar element 41 and the planar element 42 are arranged perpendicular to each other. That is, in the configuration of the fifth modification, the planar element 41 is arranged so as to be in the same plane as the second side surface portion 23, and the planar element 42 is arranged so as to be in the same plane as the fourth side surface portion 25 which is arranged substantially perpendicular to the second side surface portion 23. With such an arrangement, it becomes easier to ensure isolation between the two planar elements 41, 42. In the sixth modified example of FIG. 14(D), two planar elements 41, 42 (or vice versa) are arranged so as to be in the same plane as the first side surface portion 22 and the second side surface portion 23 that face each other. Variation 7 in Fig. 14(E) and Fig. 14(F) with the Z-axis direction reversed has a configuration in which four planar elements 41, 42, 43, 44 of the same configuration are arranged in a plane perpendicular or approximately perpendicular to the planar portion 21 of the three-dimensional ground plate 20. Variation 7 has a configuration in which the planar elements 41, 42 are arranged so as to be in the same plane as the fourth side surface portion 25, and the planar elements 43, 44 are arranged so as to be in the same plane as the third side surface portion 24 which is approximately parallel to the fourth side surface portion 25, and the planar elements 41, 42 and the planar elements 43, 44 arranged in the same plane are arranged spaced apart from each other.

[0047] Modifications 1 and 2 may be appropriately combined in an arrangement. The number of planar elements 41, 42 may also be changed as desired. In addition, in Modifications 3 to 7 of Fig. 14(A) to (F), the first side surface portion 22 and the second side surface portion 23 may be omitted, or at least one of the first side surface portion 22 and the second side surface portion 23 may be included.

[0048] In the eighth modified example of Fig. 15, a planar ground plate 50 is used as the first conductor portion instead of the three-dimensional ground plate 20. The planar ground plate 50 is roughly equivalent to the three-dimensional ground plate 20 with the inclined surface portions (first side portion 22, second side portion 23, third side portion 24, fourth side portion 25) being placed in the same plane as the planar portion 21. The patch antenna 32, which is the first antenna, is placed on the planar ground plate 50. The two planar elements 41, 42, which are the second antenna, are placed on the same plane as the planar portion 21 with the planar ground plate 50 in between. The planar ground plate 50 acts as a ground plate for the patch antenna 32. The spacing between the two planar elements 41, 42 is greater than or equal to approximately 13 / 60 of the wavelength λ of the minimum usable frequency (=approximately λ / 6+approximately (2 / 5)λ as mentioned above), and the spacing between the planar element 41 and the patch antenna 32, and between the planar element 42 and the patch antenna 32, is greater than or equal to approximately λ / 6 as mentioned above, so that mutual interference is less likely to occur even if the extension direction of the main coverage area is the same.

[0049] <Other Modifications> In this embodiment, an example has been described in which the planar element 41 is realized by forming antenna patterns 411, 412 on both sides of a printed circuit board 410, but the antenna patterns 411, 412 may also be created directly using sheet metal or a mold. The antenna patterns 411 and 412 do not necessarily have to be planar, but may be linear, net-like, fractal-like, or have any other shape that exhibits the same performance as a plane depending on the frequency used. Alternatively, the antenna pattern 411 or the antenna pattern 412 may be provided on only one surface of a single printed circuit board 410 .

[0050] In this embodiment, the second antenna, the cellular communication antenna, has been described as operating in a frequency band of 1.7 GHz or more and 6 GHz or less, but it is also possible to configure a cellular communication antenna that operates in a lower frequency range by increasing the size of at least one of the planar elements.

[0051] In the present embodiment, the planar portion 21 of the three-dimensional ground plate 20 or the planar ground plate 50 is rectangular, but the shape of each ground plate 20, 50 may be a symmetrical shape such as a square, a rectangle, a substantially square, or a substantially rectangular shape, as well as a circle, an ellipse, a substantially circular shape, or a substantially ellipse. In short, a conductive element (e.g., a planar element 41) that exhibits planar or equivalent antenna characteristics may be formed as a second conductive portion on the same surface as a surface formed vertically, substantially vertically, or horizontally with respect to the planar portion of each shape. In addition, when the planar portion 21 is circular, the second conductor portion may be configured to have a curvature that follows the shape of the planar portion.

[0052] In this embodiment, the four side surface portions 22-25 of the three-dimensional base plate 20 are assumed to be integrated, but a gap (slit) may be formed between at least a pair of adjacent side surface portions or between all of the side surface portions 22-25 and the adjacent side surface portions. This gap has the effect of suppressing leakage current flowing through the side surface portions 22-25 while ensuring an area that acts as a base plate.

[0053] In this embodiment, the configuration in which the three-dimensional ground plate 20 or the flat ground plate 50 is provided with two planar elements 41, 42 has been described, but a configuration in which only one planar element is provided may also be used. In this embodiment, an example has been described in which the three-dimensional ground plate 20 or the plane ground plate 50 acts as the ground side element for the two planar elements 41, 42, but the three-dimensional ground plate 20 or the plane ground plate 50 may also act as the ground plate for the two planar elements 41, 42. In this case, the size of the two planar elements 41, 42 is designed so that they can be used as an antenna in a predetermined frequency band.

[0054] In addition, in this embodiment, a configuration has been described in which the planar elements 41, 42 are arranged in the same plane as any of a number of side portions that are inclined at a predetermined angle relative to the planar portion 21 of the three-dimensional base plate 20, but the planar elements 41, 42 may also be arranged to be inclined at a predetermined angle relative to any of the side portions.

[0055] In addition, in the present embodiment, the planar portion 101 of the radome 10 is described as being rectangular in shape, but the planar portion 101 may be changed as appropriate in accordance with the shape of the three-dimensional ground plate 20. The shape of the opening window portion 26 can be changed as appropriate in accordance with the shape of the patch antenna 32. For example, in the case of a circular patch antenna, the shape of the opening window portion may also be circular.

[0056] In the embodiment, the patch antenna 32 is arranged parallel or approximately parallel to the ground, but the patch antenna 32 may be arranged perpendicular or approximately perpendicular to the ground. In this case, the cellular communication antenna, which is the second antenna, is arranged on the opposite side of the ground from the side on which the patch antenna 32 is arranged.

[0057] According to the present specification, the following aspects are provided.

[0058] (Aspect 1-1) The composite antenna device comprises a first antenna, a plurality of second antennas operating in a different frequency band than the first antenna, and a first conductor portion that serves as a ground plane for the first antenna and the second antennas, each of the plurality of second antennas having a second conductor portion, the first antenna being provided on the first conductor portion, and at least a portion of the first conductor portion being located between the second conductor portions. According to aspect 1-1, the first conductor serves as the ground plane for the first antenna and the second antenna, so the antenna size can be made smaller than when the ground planes for the respective antennas are provided separately. At least one pair of the second conductors are arranged with the first conductor between them, so interference between the first antenna and the second antennas and between the second antennas themselves is suppressed. This makes it possible to improve the characteristics of each antenna while suppressing an increase in the antenna size.

[0059] (Aspect 1-2) The complex antenna device according to aspect 1-1, wherein a direction in which the main coverage areas of the plurality of second antennas extend is different from a direction in which the main coverage area of ​​the first antenna extends. According to aspect 1-2, interference between the first antenna and the multiple second antennas is suppressed, and the characteristics of each antenna can be improved.

[0060] (Aspects 1-3) This is a composite antenna device described in aspect 1-1 or aspect 1-2, wherein the first conductor portion has a planar portion on which the first antenna is placed, and the multiple second conductor portions are arranged on the same plane as the planar portion, sandwiching the planar portion. According to aspect 1-3, even if the main coverage areas of the second antennas extend in the same direction, the second antennas can be spaced apart from each other, making it difficult for mutual interference to occur.

[0061] (Aspects 1-4) This is a composite antenna device described in aspect 1-1 or aspect 1-2, wherein the first conductor portion has a planar portion on which the first antenna is placed, and the multiple second conductor portions are arranged on a side of the planar portion different from the side on which the first antenna is placed. According to aspect 1-4, interference between the first antenna and the multiple second antennas and interference between the multiple second antennas are suppressed, making it possible to improve the characteristics of each antenna.

[0062] (Aspects 1-5) In the complex antenna device according to aspect 1-4, the first conductor portion further has an inclined surface portion inclined at a predetermined angle with respect to the flat surface portion, and the plurality of second conductor portions are electrically connected to the inclined surface portion. According to aspect 1-5, the distance between the first antenna and the second antenna can be further increased, thereby suppressing interference between the first antenna and multiple second antennas and between multiple second antennas, thereby improving the characteristics of each antenna.

[0063] (Aspects 1-6) The complex antenna device according to any one of aspects 1-1 to 1-5, wherein a position of a feed point of the second antenna is different from a position of a feed point of the first antenna. According to aspect 1-6, the isolation between the feeding points of the first antenna and the second antenna can be further improved, thereby suppressing interference between the first antenna and multiple second antennas and between multiple second antennas, thereby improving the characteristics of each antenna.

[0064] (Aspects 1-7) The complex antenna device according to any one of aspects 1-1 to 1-6, wherein the feed points of the second conductors are spaced apart from each other by a distance equal to or greater than ¼ of the wavelength of radio waves in the frequency band used by the second antenna. According to aspect 1-7, the isolation between the feed points of the second antennas can be further improved, so that interference between the second antennas is suppressed. Even if the main coverage areas extend in the same direction, interference between the second antennas is suppressed, and the characteristics of each antenna can be improved.

[0065] (Aspects 1-8) This is a composite antenna device described in any one of aspects 1-2 to 1-7, wherein the first conductor portion has a plurality of inclined surface portions inclined at a predetermined angle with respect to the planar portion, and a plurality of the second conductor portions are arranged on at least one of the plurality of inclined surface portions. According to aspect 1-8, it is possible to effectively utilize space while providing multiple antennas.

[0066] (Aspects 1-9) A composite antenna device described in any of aspects 1-2 to 1-7, wherein the first conductor portion has a plurality of inclined surface portions inclined at a predetermined angle with respect to the planar portion, and at least one of the plurality of second conductor portions is arranged on an inclined surface portion different from the inclined surface portions on which the other second conductor portions are arranged. According to aspect 1-9, even if the main coverage areas extend in the same direction, mutual isolation can be ensured, so interference between multiple second antennas is suppressed and the characteristics of each antenna can be improved.

[0067] (Aspects 1-10) At least one of the multiple second conductor portions is a composite antenna device described in any of aspects 1-1 to 1-9, having an insulating substrate, a first conductor formed on the front surface of the substrate, a second conductor formed on the back surface of the substrate, and a conductive via hole that connects the first conductor and the second conductor to each other. According to the embodiment 1-10, the antenna operates like a biconical antenna, making it possible to achieve a wide bandwidth.

[0068] (Aspects 1-11) A composite antenna device according to aspect 1-10, wherein the first conductor and the second conductor are linear or planar. According to the embodiment 1-11, the antenna operates like a biconical antenna, making it possible to achieve a wide bandwidth.

[0069] (Aspects 1-12) A composite antenna device described in any one of aspects 1-1 to 1-11, further comprising a coaxial cable, wherein a central conductor of the coaxial cable is conductive with the second conductor portion and an outer conductor of the coaxial cable is conductive with the first conductor portion. According to aspect 1-12, the first conductor portion acts as a ground for the first antenna and the multiple second antennas, and the second conductor portion operates as an antenna.

[0070] (Aspects 1-13) The composite antenna device according to any one of aspects 1-1 to 1-12, wherein the first antenna and the second antenna use radio waves in a frequency band of 1 GHz or higher. According to aspect 1-13, since the first conductor portion acts as a sufficiently large ground plane, there is no need to take measures against leakage current such as a ferrite core. In addition, since there is no need for measures against leakage current such as a ferrite core, the overall configuration of the antenna device can be made small and simple.

[0071] (Aspects 1-14) The composite antenna device according to any one of Aspects 1-1 to 1-13, wherein the first antenna is a patch antenna and the second antenna is an antenna for cellular communication. According to aspect 1-14, since the frequency band used by the first antenna and the second antenna is a high frequency band, the first conductor acts as a sufficiently large ground plane, and there is no need to implement leakage current countermeasures such as a ferrite core. In addition, since leakage current countermeasures such as a ferrite core are not required, the overall antenna device configuration can be made small and simple.

[0072] (Aspect 2-1) A composite antenna device comprising: a first antenna; a second antenna having a different frequency band used and a different direction in which its main coverage area extends from the first antenna; a first conductor portion that serves as a base plate for the first antenna and the second antenna; and a second conductor portion that serves as the second antenna, wherein the first conductor portion has a planar portion on which the first antenna is placed and an inclined surface portion that is inclined at a predetermined angle relative to the planar portion on the side opposite to the side on which the first antenna is placed, and the second conductor portion is electrically conductive with the inclined surface portion, and the second conductor portion has an insulating substrate and a conductor formed on a surface of the substrate. According to aspect 2-1, the first conductor serves as the ground plane for the first and second antennas, so the antenna size can be made smaller than when the ground planes for each antenna are provided separately. Also, isolation between the first and second antennas can be ensured, and interference between the first and second antennas is suppressed because the directions in which the main coverage areas of the first and second antennas extend are different. This makes it possible to improve the characteristics of each antenna while suppressing an increase in antenna size.

[0073] (Aspect 3-1) A composite antenna device comprising: a first antenna; a second antenna whose main coverage area extends in a direction different from that of the first antenna; a first conductor portion that serves as a base plate for the first antenna and the second antenna; and a second conductor portion that serves as the second antenna, wherein the first conductor portion has a planar portion on which the first antenna is placed, and the second antenna is disposed on the opposite side of the planar portion from the side on which the first antenna is placed, and the first antenna is a patch antenna, and the second antenna is an antenna for cellular communication. According to aspect 3-1, the first conductor serves as the ground plate for the first antenna and the second antenna, so that the antenna size can be reduced compared to the case where the ground plates for each antenna are provided separately. In addition, the first antenna and the second antenna use different frequency bands, and the isolation between the first antenna and the second antenna can be sufficiently ensured, and the directions in which the main coverage areas of the first antenna and the second antenna extend are different, so that interference between the first antenna and the second antenna is suppressed. This makes it possible to improve the characteristics of each antenna while suppressing the increase in antenna size. In addition, since the frequency bands used by the first antenna and the second antenna are high frequency bands, the first conductor acts as a sufficiently large ground plate, and there is no need to take measures against leakage current such as a ferrite core. In addition, since there is no need for measures against leakage current such as a ferrite core, the overall antenna device configuration can be made small and simple.

[0074] (Aspect 3-2) This is a composite antenna device described in aspect 3-1, in which the first conductor portion is connected to the planar portion at one end and further has an inclined surface portion extending at a predetermined angle toward the side opposite the side on which the first antenna is placed relative to the planar portion, the second conductor portion is conductive to the other end of the inclined surface portion, and the position of the feed point of the second antenna is different from the position of the feed point of the first antenna. According to aspect 3-2, the isolation between the feeding points of the first antenna and the second antenna can be further improved, so that interference between the first antenna and the second antenna is suppressed.

[0075] (Aspect 3-3) In the complex antenna device according to aspect 3-2, a distance between the feed point of the first antenna and the feed point of the second antenna is equal to or greater than approximately 1 / 6 of a wavelength of a minimum frequency of the second antenna. According to aspect 3-3, the isolation between the feeding points of the first antenna and the second antenna can be further improved, so that interference between the first antenna and the second antenna is suppressed.

Claims

1. A first antenna; A second antenna using a different frequency band from that of the first antenna; a first conductor portion serving as a ground plane for the first antenna and the second antenna; Equipped with the first conductor portion has a planar portion on which the first antenna is placed, the second antenna has a second conductor portion; the second conductor portion is disposed on the same plane as the planar portion, The second antenna is present in a plurality of locations, At least a portion of the first conductor portion is located between the second conductor portions. Composite antenna device.

2. A first antenna; A second antenna using a different frequency band from that of the first antenna; a first conductor portion serving as a ground plane for the first antenna and the second antenna; Equipped with the first conductor portion has a planar portion on which the first antenna is placed and an inclined surface portion inclined at a predetermined angle with respect to the planar portion, the second antenna has a second conductor portion; The second conductor portion is electrically connected to the inclined surface portion. Composite antenna device.

3. The second antenna is present in a plurality of locations, At least a portion of the first conductor portion is located between the second conductor portions, the second conductor portion is disposed on a side of the planar portion different from a side on which the first antenna is placed. The composite antenna device according to claim 2 .

4. The direction in which the main coverage area of ​​the second antenna extends is different from the direction in which the main coverage area of ​​the first antenna extends. The composite antenna device according to any one of claims 1 to 3.

5. The position of the feed point of the second antenna is different from the position of the feed point of the first antenna. A composite antenna device according to any one of claims 1 to 4.

6. The distance between the power supply points of the second conductor portions is equal to or greater than ¼ of the wavelength of a radio wave in the frequency band used by the second antenna. A composite antenna device according to any one of claims 1 to 5.

7. The first conductor portion has a plurality of inclined surface portions inclined at a predetermined angle with respect to the flat surface portion, A plurality of the second conductor portions are arranged on at least one of the plurality of inclined surface portions. A composite antenna device according to any one of claims 1 to 6.

8. The first conductor portion has a plurality of inclined surface portions inclined at a predetermined angle with respect to the flat surface portion, The second conductor portion is provided in a plurality of portions, At least one of the second conductor portions is disposed on an inclined surface portion different from an inclined surface portion on which the other second conductor portions are disposed. A composite antenna device according to any one of claims 1 to 7.

9. The second conductor portion has an insulating substrate, a first conductor formed on a front surface of the substrate, a second conductor formed on a rear surface of the substrate, and a conductive via hole that electrically connects the first conductor and the second conductor to each other. A composite antenna device according to any one of claims 1 to 8.

10. The first conductor and the second conductor are linear or planar. The composite antenna device according to claim 9.

11. Further comprising a coaxial cable, a central conductor of the coaxial cable is electrically connected to the second conductor portion; The outer conductor of the coaxial cable is electrically connected to the first conductor portion. A composite antenna device according to any one of claims 1 to 10.

12. The first antenna and the second antenna use radio waves in a frequency band of 1 GHz or higher. A composite antenna device according to any one of claims 1 to 11.

13. the first antenna is a patch antenna; The second antenna is an antenna for cellular communication. A composite antenna device according to any one of claims 1 to 12.

14. A first antenna; a second antenna having a different operating frequency band and a different direction of a main coverage area from the first antenna; a first conductor portion serving as a ground plane for the first antenna and the second antenna; a second conductor portion serving as the second antenna, the first conductor portion has a flat surface portion on which the first antenna is placed, and an inclined surface portion inclined at a predetermined angle toward an opposite side to the side on which the first antenna is placed with respect to the flat surface portion, The second conductor portion is electrically connected to the inclined surface portion, The second conductor portion has an insulating substrate and a conductor formed on a surface of the substrate. Composite antenna device.

15. A first antenna; A second antenna having a direction in which a main coverage area extends differently from that of the first antenna; a first conductor portion serving as a ground plane for the first antenna and the second antenna; a second conductor portion serving as the second antenna, the first conductor portion has a planar portion on which the first antenna is placed, and an inclined surface portion connected to the planar portion at one end and extending at a predetermined angle toward an opposite side to the side on which the first antenna is placed with respect to the planar portion, The second conductor portion is electrically connected to the other end of the inclined surface portion. Composite antenna device.

16. the second antenna is disposed on an opposite side of the planar portion from a side on which the first antenna is placed, The position of the feed point of the second antenna is different from the position of the feed point of the first antenna.

16. The composite antenna arrangement of claim 15.

17. A distance between the feed point of the first antenna and the feed point of the second antenna is approximately 1 / 6 or more of a wavelength of a minimum frequency of the second antenna.

17. The composite antenna arrangement of claim 16.

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