JP2019193167A - Patch antenna and in-vehicle antenna device - Google Patents

Abstract

To provide a small, low-profile patch antenna capable of stable reception of signals in a plurality of frequency bands without incurring cost increases due to a complicated holding structure, expensive materials, and use of difficult-to-form materials.SOLUTION: A first radiating element 11 is provided on an upper surface of a dielectric body 12 having both sides. A second radiating element 13 is provided on a lower surface of the dielectric body 12. Between the second radiating element 13 and a ground conductor 15, a resin base 14 having a relative dielectric constant smaller than that of the dielectric body 12 is disposed. The first radiating element 11 and the second radiating element 13 receive signals in different frequency bands.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a patch antenna and a vehicle-mounted antenna device.

In recent years, development of ITS (Intelligent Transport Systems) and ADAS (advanced driver assistance systems) using vehicle position information acquired by GNSS (Global Navigation Satellite System) has been promoted. In such a system, it is important to increase the accuracy of vehicle position information. A simple means for improving the accuracy of vehicle position information is to receive GNSS signals from a plurality of satellites in the vehicle and complement each other. However, in the case of an in-vehicle antenna device, the installation area is limited. That is difficult.
That is, each GNSS signal from the satellite is carried in a different frequency band. Amplifiers and the like are also adjusted for the frequency band. For this reason, if antennas and amplifiers are arranged as many as the number of frequency bands to be received, the in-vehicle antenna device becomes large.
In order to solve such a problem, in the in-vehicle antenna device disclosed in Patent Document 1, two patch antennas each having a radiating element mounted on one side of a dielectric are stacked in two stages to amplify a received GNSS signal. Gain peaks are obtained in one frequency band.

US Patent Application Publication No. 2006/220970

  Many patch antennas use ceramic as a dielectric for mounting a radiating element. Ceramics are generally expensive because a process such as firing at a high temperature is indispensable for forming. Since it becomes very hard after molding and firing, it is difficult to form a screw hole for holding it after the fact. For this reason, the structure in which the patch antennas are stacked in two stages like the in-vehicle antenna device disclosed in Patent Document 1 not only increases the material cost, but also keeps the two-stage patch antenna stably over a long period of time. Therefore, the holding structure for the vehicle becomes complicated, which causes an increase in cost of the entire vehicle-mounted antenna device. The in-vehicle antenna device disclosed in Patent Document 1 is more than doubled if the same ceramic material is used for the height of the patch antenna, and the in-vehicle antenna device cannot be reduced in height.

The present invention is a compact and low profile capable of stably receiving signals in a plurality of frequency bands without increasing the cost due to the complicated holding structure and the increased use of ceramic materials that are expensive and difficult to process. An object is to provide a patch antenna.
Another object of the present invention is to provide a vehicle-mounted antenna device that can be easily reduced in size and height even when a plurality of patch antennas are mounted.

  The patch antenna of the present invention includes a first radiating element that receives a signal in a first frequency band, a second radiating element that receives a signal in a second frequency band different from the first frequency band, the first radiating element, And a dielectric disposed between the second radiating elements, wherein the first radiating element and the second radiating element are each separated from a ground conductor.

  According to the present invention, since one radiating element is disposed between two radiating elements and is also away from the ground conductor, the patch antenna having one dielectric and one radiating element is stacked in two stages. A patch antenna with the same operating characteristics as a case can be realized with a small size and low cost, and a holding structure is easily realized compared to a case where a patch antenna having one dielectric and one radiation element is stacked in two stages. Can do. In addition, by mounting such a patch antenna, it is possible to realize a vehicle-mounted antenna device that can be easily reduced in size and height, and that is inexpensive, and further, a vehicle-mounted antenna device that easily holds such a patch antenna. Can be realized.

(A) is a top view of the patch antenna according to the present embodiment, (b) is a side view. The disassembled perspective view of the patch antenna which concerns on this embodiment. The gain characteristic figure of the patch antenna which concerns on this embodiment. The simulation figure which shows the gain change at the time of changing the material of a base. The simulation figure which shows the gain change at the time of changing the thickness of a base. (A)-(d) is the figure which showed the example of a variation of the shape of an antenna component. (A) is a top view of the patch antenna according to Modification 4, and (b) is a side view. The simulation figure which shows the gain change in the patch antenna of the modification 4. The simulation figure which shows the axial ratio change in the patch antenna of the modification 4.

Hereinafter, an embodiment in the case where the present invention is applied to a patch antenna capable of receiving GNSS signals of a plurality of frequency bands by one will be described.
The patch antenna of the present embodiment receives a 1.2 GHz band GNSS signal as an example of the first frequency band and a 1.6 GHz band GNSS signal as an example of the second frequency band from the satellite. An element that receives a GNSS signal in the 1.2 GHz band is referred to as a “first radiating element”, and an element that receives a GNSS signal in the 1.6 GHz band is referred to as a “second radiating element”. Each radiating element is a radiating element for receiving circularly polarized waves, and is composed of a two-dimensional conductor pattern. The conductor pattern may have a structure equivalent to, for example, a microstrip line with both ends open, or may be a meander shape, a fractal shape, a planar shape, or a combination of these. In the present embodiment, it is assumed that the rectangular conductor pattern resonates in a frequency band in which the length of one side coincides with an integral multiple of ½ wavelength.

  There are various embodiments of the patch antenna 1, but in the present embodiment, it is assumed that the patch antenna 1 is housed in a radio wave transmissive antenna case and is implemented as an antenna component of a vehicle-mounted antenna device. The shape and size of the antenna case depend on the shape and size of the enclosed antenna when an antenna whose received frequency band is lower than the patch antenna 1 is enclosed. In this specification, it is assumed that “upper” is vertically upward and “lower” is vertically downward (ground direction) with respect to a vehicle-side mounting surface (for example, a vehicle roof) to which the antenna case is attached.

<Configuration example of patch antenna>
1A and 1B are external views of a patch antenna 1 according to the present embodiment. FIG. 1A is a top view and FIG. 1B is a side view. FIG. 2 is an exploded perspective view of the patch antenna 1.
The patch antenna 1 of the present embodiment has a structure in which a first radiating element 11 and a second radiating element 13 having different sizes are arranged with a single dielectric 12 interposed therebetween. In other words, the dielectric 13 is present between the first radiating element 11 and the second radiating element 13. The dielectric 12 is made of, for example, a ceramic having a relative dielectric constant of about 20, and is a rectangular column shape having a side length of 46 mm in a plane parallel to the ground conductor 15 and a vertical height from the ground conductor 15, that is, a thickness of 7 mm. It is molded into. In the quadrangular prism shape, a surface portion including a point farthest from the ground conductor 15 is referred to as a “first surface”, and a surface portion including a point closest to the ground conductor 15 is referred to as a “second surface”.

  The first radiating element 11 is a conductor pattern having a side length of 25 mm in a plane parallel to the ground conductor 15, and is mounted almost at the center of the first surface of the dielectric 12. The second radiating element 13 is a conductor pattern having a side length of 46 mm in a plane parallel to the ground conductor 15, and is mounted on almost the entire second surface of the dielectric 12. A known method can be used for mounting the first radiating element 11 and the second radiating element 13 on the dielectric 12.

  If the second radiating element 13 and the ground conductor 15 are in surface contact with no gap, the second radiating element 13 does not operate as a radiating element (if there is a corresponding gap, it operates as a radiating element). That is, the patch antenna 1 is the same as a normal patch antenna including a radiating element for one frequency band. In the present embodiment, a base 14 made of an insulating member is provided between the second radiating element 13 and the ground conductor 15 so that the second radiating element 13 is electrically separated from the ground conductor 15. Is interposed. Since the base 14 is an insulating member, even if the dielectric 12 (second radiating element 13) is joined to the base 14, there is no problem such as a short circuit.

  For the insulating member, for example, a resin having a hardness that can be screwed can be used. Resin is an inexpensive insulating member and can be easily molded by injection molding or the like. In addition, subsequent molding and processing such as scraping off a part of a pre-formed shape is easy. The periphery of a hard member or a wiring member can also be molded.

By configuring the base 14 with resin, a holding structure for the ground conductor 15 can be easily realized. For example, a plurality of holding structures for the base 14 using screws can be provided in any part that does not affect the operating characteristics of the first radiating element 11 and the second radiating element 13. Therefore, it is possible to easily realize a holding structure without displacement over a long period of time.
The base 14 may be made of any material as long as it is an insulator (excluding conductors and magnetic bodies). The base 14 of this embodiment is made of a resin having a relative dielectric constant of about 4.3, has a side length of 47 mm in a plane parallel to the ground conductor 15, and has a vertical height from the ground conductor 15, that is, a thickness of It is assumed that it is formed into a 5 mm square column shape.

  The ground conductor 15 is a conductor plate having a larger area than the base 14 and may be called a ground plane. The ground conductor 15 becomes a ground potential by connecting a coaxial ground side during power feeding, and forms a patch antenna by pairing with the first radiating element 11 and the second radiating element 13. The projected area of the base 14 on the ground conductor 15 is larger than the projected area of the dielectric 12. That is, the area of each component when the patch antenna 1 is viewed from above decreases in the order of the ground conductor 15, the base 14, the dielectric 12, the second radiating element 13, and the first radiating element 11. The area of the second radiating element 13 may be smaller than the area of the second surface of the dielectric 12.

<Gain characteristics>
Next, operation characteristics of the patch antenna 1 configured as described above, particularly gain characteristics for each frequency will be described. FIG. 3 is a gain characteristic diagram of the patch antenna 1. The horizontal axis represents frequency (GHz), and the vertical axis represents gain ( _dBic ). “DB _ic ” represents the magnitude of the circular polarization gain. A solid line 101 represents a change in gain at each frequency.
As shown in FIG. 3, the patch antenna 1 has a peak in both the 1.2 GHz band and the 1.6 GHz band. That is, the gain characteristic is almost the same as that of a patch antenna having a conventional structure in which two patch antennas for 1.2 GHz and two patch antennas for 1.6 GHz band are stacked.

<Effect of this embodiment>
As described above, the patch antenna 1 according to the present embodiment includes only one dielectric 12 that is expensive and difficult to process, but has two patch antennas (two dielectrics) stacked as in the conventional structure. Equivalent gain characteristics can be obtained. Since there is no need to overlap two dielectrics, there is no need to make the holding structure of the patch antenna 1 complicated. In addition, since only one expensive dielectric 12 is provided, the manufacturing cost of the patch antenna 1 can be significantly reduced. Moreover, by mounting such a patch antenna 1, the effect that the vehicle-mounted antenna can be easily reduced in size and height is obtained.

In the present embodiment, since the second radiating element 13 and the ground conductor 15 are electrically separated by the resin base 14, the second radiating element 13 does not become a ground potential. It can be used for receiving signals in the second frequency band.
When two patch antennas are stacked as in the conventional structure, the upper patch antenna and the lower patch antenna are generally physically different sizes. For example, when the lower patch antenna is larger than the upper patch antenna, the dielectric of the lower stage is larger than that of the upper patch antenna. On the other hand, in the patch antenna 1 of the present embodiment, the second radiating element 13 is mounted on the dielectric 12, and the second radiating element and the ground conductor 15 are electrically separated by the base 14, The base 14 and the second radiating element 13 do not need to be physically different sizes, and the base 14 does not need to be physically larger than the second radiating element 13. Therefore, it is possible to select a physically smaller dielectric size with respect to the conventional structure in which two patch antennas are stacked, and it is possible to obtain an effect that the size and height can be reduced as compared with the conventional structure.

  In addition, when two dielectric patch antennas such as ceramics of the same type are stacked as in the conventional structure, the radiating element of the lower patch antenna tends to be larger than the radiating element of the upper patch antenna. In this case, the reception frequency band of the radiating element of the upper patch antenna needs to be higher than the reception frequency band of the radiating element of the lower patch antenna. In contrast, in the patch antenna 1 of the present embodiment, the height direction of the radiating element is such that the first radiating element 11 is for the 1.2 GHz band and the second radiating element 13 is for the 1.6 GHz band. There is no restriction on the frequency band that can be received according to the positional relationship. Therefore, according to this embodiment, the effect that the freedom degree of design of the patch antenna 1 improves is acquired.

  Since the base 14 used in the present embodiment uses a resin having a hardness that can be screwed, the holding structure using a screw or the like to hold the base 14 can be designed arbitrarily and afterwards, From this point of view, the effect of improving the degree of freedom in designing the patch antenna 1 can be obtained.

<Modification 1>
In the present embodiment, an example in which the material of the base 14 is a resin having a relative dielectric constant of 4.3 has been described. However, an insulating member such as air or alumina, that is, a material having a different relative dielectric constant is used. be able to. In the case of air, the base 14 is composed of a resin frame (skeleton) or a small spacer. FIG. 4 is a simulation diagram showing the relationship between the frequency (horizontal axis: GHz) and the gain (vertical axis: dB _ic ) of the patch antenna 1 for each material of the base 14. The solid line 101 is a characteristic in the case of the above-described resin (relative permittivity 4.3), the short broken line 102 is a characteristic in the case of air (relative permittivity 1), and the long broken line 103 is an alumina (relative permittivity 9.5). The characteristics of the case are shown.

  As shown in FIG. 4, even if the base 14 is replaced with a material having a different relative dielectric constant, that is, even if the material of the insulating material constituting the base 14 is changed, the peak gain in the 1.2 GHz band is increased. There is no big difference. On the other hand, the magnitude of the peak gain in the 1.6 GHz band is highest when the base 14 is alumina (long broken line 103), the second is resin (solid line 101), and the third is air. Case (short dashed line 102). That is, if attention is paid only to the gain of the patch antenna 1, the base 14 can be made of a material having a high relative dielectric constant such as alumina. However, alumina is expensive like ceramic, and the manufacturing cost increases. . In the case of air, a frame and the like must be prepared separately, which leads to an increase in cost. The resin base 14 that can be easily molded and processed is the most excellent in cost performance.

<Modification 2>
In the present embodiment, an example in which the height of the base 14 (made of a resin having a side length of 47 mm in a plane parallel to the ground conductor 15) is 5 mm has been described. The size can be changed as appropriate depending on the size of the antenna case and the relationship with the antennas in other frequency bands to be included. FIG. 5 is a simulation diagram showing the relationship between the frequency (horizontal axis: GHz) and the gain (vertical axis: dB _ic ) of the patch antenna 1 when the thickness of the base 14 is changed. The solid line 101 indicates the characteristic in the case of 5 mm, the broken line 104 indicates the characteristic in the case of 2 mm, and the alternate long and short dash line 105 indicates the characteristic in the case of 8 mm.

When the thickness of the base 14 is changed, the electrical length between the first radiating element 11 and the ground conductor 15 is changed. However, since the relative permittivity of the base 14 is lower than that of the dielectric 12, the electrical length between the first radiating element 11 and the ground conductor 15 mainly depends on the size of the dielectric 12. Therefore, the change in the gain characteristic of the first radiating element 11 due to the change in the thickness of the base 14 is smaller than the change in the gain characteristic of the second radiating element 13.
In fact, as shown in FIG. 5, even if the thickness of the base 14 was changed, there was no great difference in the magnitude of the peak gain in the 1.2 GHz band. There was no significant difference in the magnitude of the gain at the peak in the 1.6 GHz band, whether the thickness of the base 14 was 5 mm (solid line 101) or 8 mm (one-dot chain line 105).

On the other hand, when the thickness of the base 14 is 2 mm (broken line 104), the gain of the patch antenna 1 is slightly smaller than when the thickness of the base 14 is 5 mm (solid line 101) and 8 mm (dashed line 105). Besides decreasing, the frequency at which the gain reaches a peak shifts to the lower side. Since the gain level is irrelevant in frequency bands other than the 1.2 GHz band and the 1.6 GHz band, if the thickness of the base 14 is about 5 mm, it is not necessary to make the thickness higher than that. It can contribute to the conversion.
Needless to say, it may be about 2 mm or more and about 5 mm or less for use in receiving signals of a low frequency in the 1.6 GHz band.

<Modification 3>
In the present embodiment, an example has been described in which all of the dielectric 12, the base 14, and the ground conductor 15 have a quadrangular shape when viewed from above. It can be appropriately changed according to the operating characteristics.
6A to 6D are top views showing variations of the top view of the patch antenna 1. FIG. Both the first radiating element 11 and the second radiating element 13 are rectangular conductor patterns as viewed from above.
FIG. 6A shows an example in which the dielectric 12 and the ground conductor 15 are rectangular, but the base 24 is circular. The base 24 becomes a circumscribed circle of the dielectric 12. Therefore, the areas when viewed from above the dielectric 12 and the base 24 are substantially the same.
FIG. 6B shows an example in which the base 14 and the ground conductor 15 are rectangular, but the dielectric 22 is circular. The dielectric 22 becomes an inscribed circle of the base 14.
FIG. 6C shows an example in which the dielectric 12 has a quadrangular shape, but the base 24 and the ground conductor 25 have a circular shape. The base 24 becomes a circumscribed circle of the dielectric 12.
FIG. 6D shows an example in which the dielectric 22, the base 24 and the ground conductor 25 are circular. The inner diameter increases in the order of the dielectric 22, the base 24, and the ground conductor 25.

  According to the simulations of the present inventors, the patch antenna of the first embodiment can be used as long as the area of the base 24 is substantially equal to the area of the dielectric 12 even when the variation in the shape of each part seen from above changes. Similar to 1, it has been found that gain peaks appear in the 1.2 GHz band and the 1.6 GHz band. Therefore, the shape of the antenna case that accommodates the patch antenna 1, the installation space, or the fixed structure can be changed to any part shape, and the degree of freedom in designing the patch antenna 1 can be improved.

<Modification 4>
As described above, the resin base 14 is easier to mold and process than the dielectric 12. Since the second radiating element 13 faces the base 14, both ends thereof are close to each other. Since the base 14 described in the first embodiment has a relative permittivity of 4.3 and air has a relative permittivity of 1.0, the gain of the second radiating element 13 is relatively high at the boundary between both ends. It is affected by the difference in dielectric constant. Therefore, in Modification 4, the influence of the size of the base 14 on the second radiating element 13 will be described.

  FIG. 7A is a top view of the patch antenna according to the modified example 4, and FIG. 7B is a side view seen from the direction of 180 degrees when the upper side of the sheet of FIG. Although the ground conductor 15 is omitted, it corresponds to FIG. The patch antenna has a part shape viewed from above, in which the first radiating element 11 and the dielectric 12 (the same applies to the second radiating element 13 on the second surface) are square, and the bases 241, 242, and 243 are circular. It is an example in the case of a shape. The length of one side of the first radiating element is 25 mm, and the length of one side of the dielectric 12 and the second radiating element 13 is 47 mm. The inner diameter is 44 mm for the base 241, 56 mm for the base 242, and 68 mm for the base 243. The area of the base 242 is substantially the same as the base 14 of the first embodiment. The dielectric 12 has a thickness of 7 mm, and the bases 241, 242, and 243 have a thickness of 5 mm.

FIG. 8 is a simulation diagram showing the relationship between the frequency (horizontal axis: GHz) and the gain (vertical axis: dB _ic ) of the patch antenna according to Modification 4. FIG. 9 is a simulation diagram showing the relationship between the frequency (horizontal axis: GHz) of the patch antenna according to the modification 4 and the antenna axial ratio (vertical axis: dB _ic ). The antenna axial ratio is an index representing how close to the perfect circular polarization, and can be said to be equal (substantially perfect circular polarization) as long as it is within 3 dB in the received frequency band. In these drawings, the solid line 101 is the characteristic in the case of the base 14 of the first embodiment, the short broken line 202 is the characteristic in the case of the base 241, the one-dot chain line 203 is the characteristic in the case of the base 242, and the long broken line 204 is the base. The characteristic in the case of the base 243 is shown.

As shown in FIGS. 8 and 9, the patch antenna (one-dot broken line 203) in the case of the base 242 has a gain of 1.2 GHz band and 1.6 GHz similarly to the patch antenna 1 (solid line 101) of the first embodiment. Peaks are shown in both bands, and the antenna axial ratio is almost equal. That is, if the areas were almost the same, there was no change in gain characteristics or antenna axial ratio.
On the other hand, in the patch antenna (short broken line 202) in the case of the base 241, the frequency indicating the gain peak changes from the 1.6 GHz band to the high frequency band. In the patch antenna (long broken line 204) in the case of the base 243, the frequency indicating the gain peak changes from the 1.6 GHz band to the lower frequency band. The antenna axial ratio is almost equal between 1.0 GHz and 1.6 GHz, but the patch antenna (short dashed line 202) in the case of the base 241 becomes more uniform in the higher frequency band. In the patch antenna (long broken line 204), the lower the frequency band, the more uniform.

  This is because the size or position of the first radiating element 11 or the second radiating element 13 is generally changed when it is desired to change the operating characteristics of the patch antenna 1, for example, the gain characteristics or the axial ratio. Even if it does not do so, it means that the object can be achieved by adjusting the area and thickness viewed from above the base 14 which is relatively easy to process and inexpensive. In particular, the gain characteristics of the second radiating element 13 can be greatly changed by changing the area of the base 14 or the like.

<Modification 5>
In the present embodiment, the first radiating element 11 and the second radiating element 13 are arranged with the dielectric 12 interposed therebetween, and the first radiating element 11 and the second radiating element 13 are separated from the ground conductor 15, respectively. Although it has been described that the gain of the antenna 1 has two peaks, the gain of the two radiating elements 11 and 13 can be three or more.
For example, a part of at least one of the conductor patterns of the first radiating element 11 and the second radiating element 13 may be a slot or slit having a different electrical length from the entire conductor pattern (the length that causes the above two gain peaks). Or it is set as a combination of these. In the slot and slit, the length of the inner wall starting from the feeding point is the electrical length. Thereby, three or more frequency bands can be obtained in which the gain reaches a peak.

<Other variations>
The above description is an example in which the shapes of the first radiating element 11, the dielectric 12, the second radiating element 13, the base 14, and the ground conductor 15 are square or circular when viewed from above. The quadrangular shape and the circular shape are typical examples of the shape, and the same description can be applied to the substantially rectangular shape, the substantially circular shape or the elliptical shape, and the substantially elliptical shape.
In addition, the shape of the first embodiment is not limited to a quadrangular shape, but may be a triangular shape or a polygonal shape (or substantially polygonal shape) having a pentagonal shape or more as long as the area of the base is substantially equal to the area of the dielectric 12. The gain characteristic is almost the same as that of the patch antenna 1.
In the above description, the example in which the relative permittivity of the base 14 is lower than the relative permittivity of the dielectric 12 has been described. However, it is not always necessary to do so. Depending on the application, the relative permittivity of the base 14 may be higher than the relative permittivity of the dielectric 12.

The patch antenna of the present invention is mounted on the first surface, a dielectric having a ground conductor, a first surface including a point farthest from the ground conductor, and a second surface including a point closest to the ground conductor. a first radiating element for receiving a signal of a first frequency band, is mounted on the second surface, and a second radiating element for receiving a signal of the first frequency band is different from the second frequency band, further comprising a Features.

Claims (7)

A first radiating element for receiving a signal in a first frequency band;
A second radiating element for receiving a signal in a second frequency band different from the first frequency band;
A dielectric disposed between the first radiating element and the second radiating element,
The patch antenna according to claim 1, wherein the first radiating element and the second radiating element are separated from a ground conductor. In the dielectric, a first surface including a point farthest from the ground conductor and a second surface including a point closest to the ground conductor are formed,
The first radiating element is disposed on the first surface;
The second radiating element is disposed on the second surface with a size larger than that of the first radiating element,
The patch antenna according to claim 1.   The patch antenna according to claim 1 or 2, further comprising a base interposed between the dielectric and the ground conductor and made of an insulating member. The base is made of a resin having a hardness capable of being screwed,
The patch antenna according to claim 3.   The patch antenna according to claim 3 or 4, wherein a projected area of the base on the ground conductor is larger than the projected area of the dielectric.   The patch antenna according to any one of claims 3 to 5, wherein a thickness of the base in a direction from the ground conductor to the dielectric is about 2 mm or more and about 5 mm or less. An antenna case,
A patch antenna housed in the antenna case,
The patch antenna is a patch antenna according to any one of claims 1 to 6,
In-vehicle antenna device.