JP2003017931A - Planar antenna structure - Google Patents

Abstract

(57) [PROBLEMS] To reduce the transmission and reception efficiency of a planar antenna and to reduce the directivity characteristics of the antenna without being reduced.
A planar antenna structure having high durability is provided. The planar antenna structure includes a glass plate provided with a transparent conductive film so as to surround the planar antenna, and in the case of the planar antenna structure having a microstrip antenna (MSA), the shortest distance to the inner peripheral edge of the transparent conductive film 13 at each position on the outer peripheral edge of the radiating conductor 11a is ₀ the free space wavelength of the radio wave lambda used for transmission and reception in _{MSA11, 1/20 · λ 0} ~λ 0
It is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar antenna structure in which a planar antenna is mounted on a dielectric substrate, and more particularly, a planar antenna in which a high frequency planar antenna suitable for microwave communication and millimeter wave communication is mounted on a glass plate. Regarding the structure.

[0002]

2. Description of the Related Art Today, due to the demand for high speed and large capacity communication,
High-frequency communication, which transmits and receives radio waves using microwaves and millimeter waves, is rapidly expanding. As an antenna for transmitting and receiving radio waves, for example, a microstrip antenna (hereinafter, referred to as a microstrip antenna) having a circular or rectangular patch-shaped radiation conductor and a grounding conductor arranged so as to face the radiation conductor with a dielectric material sandwiched therebetween. A strip antenna is referred to as MSA) is preferably used. This MSA is also called a patch antenna.

This MSA can be manufactured using a printed circuit board or the like, and has a planar structure, so that it is widely used as a small and thin antenna. For example, the MSA is an automatic toll collection system (ETC), that is, a system that automatically collects tolls by performing wireless communication using a 5.8 GHz frequency band on highways and toll roads. It is often used for. More specifically, the MSA is mounted on a vehicle as an antenna on an in-vehicle device when performing wireless communication with a roadside device provided at a tollgate in an ETC, or is housed in a housing and mounted on a dashboard of the vehicle. Placed on top.

[0004]

However, antennas such as MSA installed on the dashboard are not preferable in terms of design when viewed from the inside or outside of the vehicle, and hinder the driver's visual field, as well as the mounting position and direction. Therefore, there is a problem of directivity characteristics such that the characteristics of the antenna are not constant. On the other hand, it is possible to attach the MSA to the window glass plate of the vehicle or to attach it to the vehicle by adhering it. However, when attaching the MSA to the window glass plate of the vehicle, as shown below, the problem of the directivity characteristics of the antenna Occurs.

That is, when the MSA is to be attached to a window glass plate of a vehicle, it is desired that the MSA be small because of its design and limited installation space in the vehicle. Not only the conductor but also the ground conductor must be reduced. In fact, a small MS
When the directional characteristics of the MSA in the planar antenna structure in which A is attached in close contact with the glass plate are measured, an angle of ± 70 degrees to 80 degrees (0 in the direction perpendicular to the mounting surface of the glass plate is 0 as shown in FIG. In the range of 10 degrees), the relative received power is lowered and the antenna directional characteristics do not form a gentle mountain shape. The reason for this is "small planar antennas"
(The Institute of Electronics, Information and Communication Engineers, author Misao Haishi et al., P. 131), the size of the ground conductor of the MSA is about the same as or smaller than the free space wavelength λ ₀ of transmitted and received radio waves. As a result, the transmitted and received radio waves undergo high-order multiple diffraction under the influence of the end of the ground conductor, and
It is considered that the surface wave is generated by causing multiple reflection inside the glass plate. That is, the reason why the directional characteristic of the antenna does not form a gentle mountain shape is basically because the ground conductor of the MSA is made small. However, as described above, it is impossible to make the ground conductor of the MSA large in view of the design and the limited mounting space in the vehicle.

Further, a window glass plate used in a vehicle or the like is provided with a visually almost transparent conductive film having a function of reflecting heat rays in order to maintain the temperature in the vehicle compartment, or is energized and heated to conduct window heating. A visually almost transparent conductive film having an antifogging function of preventing fogging of glass may be provided. Since this conductive film has low radio wave permeability, when the MSA is attached on the window glass plate provided with the conductive film, the effect of the conductive film lowers the transmission / reception efficiency of the MSA, and in the worst case, transmission / reception cannot be performed. There is a problem that it becomes impossible. In this way, glass that is good in design, does not hinder the driver's field of view, is compact, does not deteriorate the directional characteristics of the antenna, and has a transparent conductive film formed to have a heat ray reflection function and an antifogging function. Planar antenna structures with an antenna attached to a plate are not available today.

In order to solve the above problems, the present invention provides a planar antenna including a radiation conductor and a ground conductor,
For example, a planar antenna structure mounted on a dielectric substrate such as a glass plate provided with a conductive film for a heat ray reflection function or an anti-fog function, and for example, a position of the antenna mounting position such as in front of a driver's seat of a vehicle. It is possible to provide a planar antenna structure that can be mounted in a restricted place, does not reduce the transmission / reception efficiency of the antenna, is compact, and does not deteriorate the directional characteristics of the antenna, and has good durability. To aim.

[0008]

In order to achieve the above object, the present invention provides a planar antenna provided with a radiating conductor and a ground conductor, a planar antenna provided with the planar antenna, and a conductive film surrounding the planar antenna. A planar antenna structure having a dielectric substrate provided with, and the shortest distance to the inner peripheral edge of the conductive film at each position of the outer peripheral edge of the radiation conductor is used for transmission or reception by the planar antenna. If the free space wavelength of the radio wave is λ ₀ , then 1/20 · λ ₀
There is provided a planar antenna structure characterized by being ˜λ ₀ .

The present invention also provides a planar antenna structure having a planar antenna provided with a radiation conductor and a ground conductor, and a dielectric substrate provided with a conductive film so as to surround the planar antenna. A planar antenna, wherein the radiation conductor and the ground conductor are provided on a surface of the dielectric substrate so that the ground conductor surrounds a part or all of the radiation conductor on the surface of the dielectric substrate with a space therebetween; Provided is a planar antenna structure, wherein the conductive film surrounds a ground conductor.

Further, the dielectric substrate is preferably a glass plate, for example, a glass plate for vehicles. More preferably, it is a vehicle windshield plate, and the planar antenna is preferably formed on the vehicle interior side of the vehicle windshield plate. The vehicle glass plate may be a laminated glass plate. Further, it is preferable that the planar antenna is arranged within a range of 100 mm from an edge of the vehicle windshield plate. Further, the planar antenna has a center in a left-right direction when the vehicle windshield plate is mounted on the vehicle. It is preferably arranged within a range of 100 mm to the left and right around the line. Here, it is preferable that the conductive film is transparent or semi-transparent, and the conductive film is provided on substantially the entire one surface of the glass plate other than the region where the planar antenna is arranged.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The planar antenna structure of the present invention will be described below in detail with reference to the preferred embodiments shown in the accompanying drawings.

1 and 2 show a planar antenna structure 10 using an MSA which is a first embodiment of the planar antenna structure of the present invention. 1 is a plan view of the planar antenna structure 10, and FIG. 2 is a cross-sectional view of the planar antenna structure 10 taken along the line AA ′ shown in FIG.

The planar antenna structure 10 includes an MSA 11 for transmitting and receiving radio waves and a glass plate 1 to which the MSA 11 is attached.
2 and the MSA on the glass plate surface where the MSA 11 is attached.
The transparent conductive film 13 is provided on substantially the entire glass surface excluding the attachment area 11. In addition, MSA
Reference numeral 11 corresponds to the planar antenna in the present invention, and glass plate 12 corresponds to the dielectric substrate in the present invention.

The MSA 11 has a circular or square patch-shaped radiation conductor 11a, a ground conductor 11b, and a dielectric substrate 11c for a planar antenna of the MSA 11, and the radiation conductor 11
This is a known planar antenna in which the surface a and the surface of the ground conductor 11b are arranged to face each other with the dielectric substrate for planar antenna 11c interposed therebetween. The radiation conductor 11a and the ground conductor 11b are
It is formed in a predetermined shape with a copper foil or a conductive film made of silver, gold, or the like. A resin material, a material such as ceramic or sapphire is used for the planar antenna dielectric substrate 11c.

The glass plate 12 has a region in which the transparent conductive film 13 is not formed corresponding to the size and the shape of the outer periphery of the MSA 11, and this region in which the transparent conductive film 13 is not formed serves as a mounting region for the MSA 11. Such a transparent conductive film 13 may be formed by, for example, forming a transparent conductive film layer on the entire surface of the glass plate 12 in advance, and
The non-formation region is formed by removing the transparent conductive film layer in the mounting region of SA11, or masking the non-formation region in advance and providing the conductive film layer in the other region. Therefore, the transparent conductive film 13 is provided around the MSA 11 mounted on the glass plate 12.
It is configured to surround 1.

The transparent conductive film 13 may be an oxide semiconductor thin film such as a transparent tin oxide (SnO ₂ ) conductive film. Although the glass plate 12 is used as an example of the dielectric substrate in the present embodiment, the dielectric substrate of the present invention is a substrate made of a non-conductive material, for example, a resin material, a material such as ceramic or sapphire. Any of them may be used. The conductive film in the present invention corresponding to the transparent conductive film 13 does not necessarily have to be transparent, and may be semitransparent or opaque. For example, Cr, Ti,
Single layer metal conductive film or nitride thin film of a thin metal layer such as Ag, Au, Al, Cu or Ni, or TiO ₂
It may be a metal conductive film having a plurality of structures in which thin metal layers such as / Ag / TiO ₂ and ZnO / Ag / ZnO are laminated in a sandwich shape with transparent dielectric layers from above and below.

The MSA 11 is attached to the glass surface on which the transparent conductive film 13 is formed, with the surface of the radiating conductor 11a of the MSA 11 as the attachment surface, by the double-sided tape 14 or the like. Therefore, as shown in FIG. 2, the ground conductor 11b is arranged on the surface of the planar antenna dielectric substrate 11c that does not directly face the glass plate 12. The radiation conductor 11a is connected to the central conductor 18 of the connector, and the ground conductor 11b is connected to the outer conductor of the connector 17. The connector 17 is connected to a coaxial cable (not shown), and further connected to a circuit and equipment.

Here, the shortest distance to the inner peripheral edge of the transparent conductive film 13 at each position of the outer peripheral edge of the radiating conductor 11a, for example, the separation distance d in FIG. 2, is the freedom of radio waves used for transmission or reception by the MSA 11. 1/2 with spatial wavelength λ ₀
Is set to ₀ · λ 0 ~λ 0. More preferably 1
It is set to / 8 · λ ₀ to 1/2 · λ ₀ . By setting the shortest distance in this way, the transparent conductive film 13 can reduce the influence of surface waves due to multiple reflection inside the glass plate 12, and the transparent conductive film 13 can be formed between the radiation conductor 11a and the ground conductor 11b. It does not affect the electric field created. Therefore, the directivity characteristic of the antenna is improved as described later.

In such a planar antenna structure 10,
Since the transparent conductive film 13 having low radio wave transmission is removed in the mounting area of the MSA 11, the transmission / reception efficiency of the antenna does not decrease, and the glass plate 12 as a dielectric is used.
The radio wave that has passed through can be received by the MSA 11, and the radio wave can be transmitted. Moreover, MSA11
Since the transparent conductive film 13 is provided on the outer periphery of the glass plate 12, even if the ground conductor 11b is small, it does not cause high-order multiple diffraction under the influence of the end of the ground conductor 11b. It is not affected by surface waves due to multiple reflection. Therefore, the disturbance of the directivity characteristic of the MSA 11 is reduced, and a gentle chevron-shaped directivity characteristic can be obtained, as shown in Example 1 described later. This is a directivity characteristic similar to the case where the ground conductor of MSA11 is large.
With the transparent conductive film 13 around, the same effect as that of enlarging the ground conductor 11b can be obtained. Therefore, the ground conductor 11
b can be made small, that is, the region where the transparent conductive film 13 is not formed can be made small.
It is also preferable from the viewpoint of the design when attaching 11. Further, since the ground conductor 11b is small, a compact MSA
And a compact planar antenna structure can be realized.

Here, it is preferable that the transparent conductive film 13 is connected to the ground conductor 11b by being as close as possible to the periphery of the MSA 11, but it is not always necessary to be connected.
In addition, a direct current may flow through the transparent conductive film 13 for antifogging function and the like. In addition, the glass plate 12 of the MSA 11
The adhesive may be used instead of the double-sided tape 14 and may be attached by another attaching member.

FIG. 3 and FIG. 4 show a planar antenna structure 20 which is a second embodiment of the planar antenna structure of the present invention.
Is shown. 3 is a plan view of the planar antenna structure 20, and FIG. 4 is a cross-sectional view of the planar antenna structure 20 taken along line BB ′ shown in FIG.

The plane antenna structure 20 includes a plane antenna 21 for transmitting and receiving radio waves, a glass plate 22 for arranging the plane antenna 21, and an area for arranging the plane antenna 21 on a glass plate surface for arranging the plane antenna 21. Except that the transparent conductive film 23 is provided on almost the entire glass surface. The flat antenna 21 corresponds to the flat antenna of the present invention, and the glass plate 22 corresponds to the dielectric substrate of the present invention.

For the planar antenna 21, the glass plate 2
2 is a plane antenna in which the radiation conductor 25 and the ground conductor 26 are formed on one surface of the second antenna 2, and the details will be described later. The glass plate 22 has a region where the transparent conductive film 23 is not formed, which corresponds to the size of the planar antenna 21 and the shape of the outer periphery,
This portion is the area where the planar antenna 21 is arranged. Then, as shown in FIG. 4, the transparent conductive film 23 is provided so as to overlap with the ground conductor 26 of the planar antenna 21 and is electrically connected thereto. Such a transparent conductive film 23 is, for example,
After providing a layer of the transparent conductive film on the entire surface of the glass plate 22 in advance,
The layer of the transparent conductive film in the region where the planar antenna 21 is arranged is removed to form a region where the transparent conductive film is not formed. Therefore, the transparent conductive film 23 is configured to surround the flat antenna 21 around the flat antenna 21 arranged on the glass plate 22.

Here, as shown in FIG. 3, the planar antenna 21 is a planar antenna formed on the same surface as the surface of the glass plate 22 on which the transparent conductive film 23 is formed. The planar antenna 21 includes an island-shaped radiation conductor 25 having a square radiation conductor main body 25a and a strip-shaped projection 25b projecting from the radiation conductor main body 25a, and the radiation conductor 25.
And a grounding conductor 26 which is formed on the same surface as the above and surrounds all of the radiation conductors 25 with a constant distance therebetween.

A feeding portion 27 is provided at an end of the protruding portion 25b, and a coaxial cable is provided through a surface mounting type connector (not shown) and a connector (not shown) on the same side as the island-shaped radiation conductor 25. Connected to the center conductor of. Further, the ground conductor 26 is connected to the outer conductor of the coaxial cable, and the coaxial cable is connected to a circuit or a device. Also,
The projecting portion 25b forms, together with the ground conductor 26, a coplanar waveguide (CPW) which is a known transmission line in which the ground conductor is formed on both sides of the strip-shaped center conductor with a certain distance therebetween. It functions as a strip-shaped center conductor for the coplanar waveguide.

The width W and the length L _a of the radiation conductor main body 25a of the planar antenna 21 as described above are determined as _follows.
The radio waves are set to resonate according to the wavelength of the radio waves transmitted and received in. When the free space wavelength of the center frequency of the desired frequency band for transmission / reception is λ _M , the length L _a of the radiating conductor main body 25a is k · (λ _M / 4 in order to improve the transmission / reception efficiency of the antenna. ) -K · λ _M (k is the glass plate 12)
It is preferable that it is within the range of (shortening rate). By setting the length L _a in this range, the gain of several dB is improved as compared with the case of setting the length outside this range. The width W of the radiating conductor main body 25a is λ _H, which is the free space wavelength of the highest frequency in the desired frequency band for transmission and reception, and λ _{L, which} is the minimum free space wavelength of the desired frequency band for transmission and reception. At this time, it is preferably in the range of k · (λ _H / 4) to k · λ _L.

On the other hand, of the protruding portion 25b forming the CPW,
The length L _b protruding from the radiating conductor main body 25a is defined as follows: If the free space wavelength of the radio wave transmitted and received by the planar antenna 21, for example, the free space wavelength of the center frequency is λ _M, and the shortening rate in the glass plate 22 is k, k · λ _M / 2 or less.
In this way, by defining the upper limit of the length L _b as k · λ _M / 2, the transmission / reception efficiency of the antenna can be secured, and a compact planar antenna can be formed.

Here, the shortening rate k relates to the propagation velocity of the radio wave propagating on the dielectric substrate, so that the reactance component of the input impedance of the antenna becomes 0 at the desired radio wave frequency. That is, it refers to the ratio of making the size of an antenna manufactured using a dielectric substrate smaller than the size of the antenna that would be expected without the dielectric substrate so that the antenna resonates. Here, the shortening rate k is k = ε _r , where ε _r is the effective relative permittivity of the dielectric substrate.
It can be represented by ^(-1/2) .

Further, the ground conductor 26 is the circumference of the radiation conductor 25.
Enclose the enclosure with a certain distance. That is, the ground conductor 26
Is a constant distance g from the edge of the radiation conductor body 25a._appSeparation
And a constant distance g from the edge of the protrusion 25b._apfSet apart
To be Interval g_appIs the input impedance of the planar antenna 21.
It is set to have good dance characteristics and is almost glass.
The vicinity of the thickness of the plate 12 is preferable. On the other hand, the interval g_apfIs a rush
It is set by the ratio with the width of the projecting portion 25b, and this interval g
_apfAnd the width of the protrusion 25b is the same as the width of the protrusion 25b and the ground conductor.
Characteristic impedance in CPW formed by body 26
Dance is a given value, usually used in high frequency transmission lines
The ratio of the glass plate so that the characteristic impedance is 50Ω.
Consider the permittivity and the conductivity and thickness of the radiating conductor and the ground conductor.
It is set carefully. For this CPW, see "Microstri
p Lines and Slotines "(Artech House Publisher, Author
K.C.Gupta et al.).

In the planar antenna 21, the radiation conductor main body 25a has a square shape as shown in FIG.
It may have a rectangular shape such as a rectangular shape, and further, as shown in FIG.
It may be circular as shown in FIG. Furthermore, ETC
When transmitting and receiving circularly polarized radio waves as shown in
As shown in FIGS. 5B to 5E, the radiation conductor main body 25a
It is also possible to provide a cutout portion 30, a protrusion portion 31 or the like in a part of the above, and use a degenerate element or a perturbation element to cope with circular polarization. Besides, the radiation conductor main body 25a may be formed in a square shape, and a slot may be provided in the central portion of the square shape, and a method similar to the circular polarization technique in a normal MSA can be used. Furthermore, as shown in FIG.
The radiation conductor body 25a has a square shape, and the radiation conductor body 25a and the ground conductor 26 are spaced apart from each other by the distances g _app1 , g _app2.
As shown in FIG. 5G, or by changing the distance between the radiation conductor main body 25a and the ground conductor 26 in the antenna length direction as shown in FIG. The capacitance may be changed depending on the distance from the ground conductor 26, and the same effect as that of the degenerate element or the perturbation element may be obtained to cope with circular polarization.

Further, as shown in FIG. 5 (h), the protrusion 2
In order to perform impedance matching between the radiation conductor body 25a and the radiation conductor body 25a, the protrusion 25b of the radiation conductor body 25a is considered in consideration of the influence of the gap g _app between the radiation conductor body 25a and the surrounding ground conductor 26. A notch 32 may be provided in a portion connected to the so that the edge of the protrusion 25b extends into the inside of the radiation conductor main body 25a. In this case, the notch 30 or the protrusion 31 may be provided in a part of the radiation conductor body 25 described above.

Such a radiation conductor 25 and a ground conductor 26
Is formed by printing a paste containing a conductive metal, such as a silver paste, on the glass plate 22 and baking it. The present invention is not limited to this formation method, and a linear or foil-shaped thin film made of a conductive material such as copper may be formed on the surface of the glass plate 22. In this way, since the baked silver paste is formed as the conductor on the glass plate 22, the glass plate 22, the radiation conductor main body 25a, and the protrusion 2 are formed.
5b and the ground conductor 26, there is no gap between them,
By causing reflection and resonance at each interface due to the air gap,
The transmission / reception characteristics of the planar antenna 21 do not deteriorate.

In this embodiment, the glass plate 22 is used as an example of the dielectric substrate, but the dielectric substrate of the present invention is
Any substrate may be used as long as it is a substrate made of a non-conductive material, for example, a resin material, a material such as ceramics or sapphire. Further, the conductive film in the present invention corresponding to the transparent conductive film 23 does not necessarily have to be transparent, and may be semitransparent or opaque. For example, Cr,
A single layer metal conductive film or nitride thin film of a thin metal layer such as Ti, Ag, Au, Al, Cu or Ni, or T
It may be a metal conductive film having a plurality of structures in which thin metal layers such as iO ₂ / Ag / TiO ₂ and ZnO / Ag / ZnO are laminated in a sandwich shape with transparent dielectric layers from above and below.

In such a planar antenna structure 20,
Since the transparent conductive film 23 having low radio wave transparency is removed in the mounting area of the flat antenna 21, the flat antenna 21 transmits the radio wave transmitted through the glass plate 22 as a dielectric without lowering the transmission / reception efficiency of the antenna. It can receive and can also transmit radio waves. Moreover, since the transparent conductive film 23 is provided on the outer periphery of the planar antenna 21, even if the ground conductor 26 is small, the ground conductor 2
The high-order multiple diffraction does not occur under the influence of the six edges, and the influence of the surface wave due to the multiple reflection inside the glass plate 22 does not occur, and the disturbance of the directivity characteristics of the planar antenna 21 is reduced. To be done. As a result, as shown in Example 2 which will be described later, a gentle mountain-shaped directivity characteristic is obtained. This is the same directivity characteristic as when the ground conductor of the planar antenna 21 is large, and the same effect as when the ground conductor 26 is enlarged by the transparent conductive film 23 around the planar antenna 21 can be obtained. As a result, the ground conductor 26 can be made smaller, so that a compact planar antenna can be realized. Further, the planar antenna 21 and the thin film conductive film 23
Are provided on the same surface of the glass plate 22, so that a compact planar antenna structure having few irregularities on the glass surface can be realized.

In this embodiment, the transparent conductive film 23 is connected so as to overlap the ground conductor 26 of the planar antenna 21, but when a direct current flows through the transparent conductive film 23, the transparent conductive film 23 is connected to the ground conductor 26. May be separated from. Further, an insulating layer may be provided between the transparent conductive film 23 and the ground conductor 26 in order to prevent a short circuit due to migration. However, in any case, it is preferable to perform the operation within the range in which the directivity characteristic of the antenna is not deteriorated.

As described above, the glass plate 12 used in the first embodiment and the glass plate 22 used in the second embodiment are one glass plate. It may be a planar antenna structure in which a planar antenna is attached to a multi-layer glass plate. For example, when a laminated glass plate is used, the transparent conductive film may be formed on the mating surface side and the planar antenna may be arranged on the surface opposite to the mating surface.

The MSA 11 of the first embodiment, the planar antenna 21 of the second embodiment, etc. are formed on the surface of a vehicle windshield plate having a heat ray reflecting function and an antifogging function, for example, as an antenna in ETC. Used. That is, since the vehicle windshield is used as the glass plate 12 or the glass plate 22 and the side on which the MSA 11, the planar antenna 21 and the like are arranged is the inside of the vehicle, durability is improved as compared with the case where it is arranged outdoors. Such MSA 11 and planar antenna 21 are used for narrow area communication (DSRC: Dedicated Short Rang).
e Communication) It may be integrated with a control circuit or the like and provided on the glass plate 12 or the glass plate 22.

The antennas such as the MSA 11 and the planar antenna 21 used in the planar antenna structure of the present invention are
It is preferably used in the ETC that performs wireless communication using the above-mentioned 5.8 GHz frequency band, but is not limited to ETC and can also be used in various data communication using the same frequency band. For example, 800 MHz band (810 to 960 MHz) for car phones, 1.5 GHz for car phones
z band (1.429 to 1.501 GHz), UHF band (3
00 MHz to 3 GHz), and GPS signals of GPS satellites, 1575.42 MHz, can also be used for transmitting and receiving radio waves. Of course, in addition to the above bands, radio waves of microwave frequencies (1 GHz to 3 THz) and millimeter waves (30 G)
(Hz to 300 GHz) can also be used for transmission and reception.

The planar antenna structure 10 (Example 1) and the planar antenna structure 20 (Example 2) are
The antenna was manufactured as described below, and the directivity characteristics of the antenna were examined.

(Example 1) As shown in FIGS. 1 and 2, a laminated glass plate having a thickness of 5 mm and having a transparent conductive film 13 formed thereon was used as the glass plate 12, and the same size as the outer circumference of the MSA 11 to be attached, The transparent conductive film 13 made of a heat ray reflective film having a non-formed area of 30 mm × 30 mm was formed. In this non-formed area, the MSA 11 having a size of 30 mm × 30 mm and a thickness of 2.5 mm is provided with the double-sided tape 14 having a thickness of 0.4 mm
Then, the radiation conductor 11a was attached so as to become the mounting surface. The MSA 11 was adjusted so as to be an antenna capable of transmitting and receiving at a center frequency of 5.8 GHz when attached to the glass plate 12. The shortest distance d to the inner peripheral edge of the transparent conductive film 13 at each position of the outer peripheral edge of the radiation conductor 11a.
Is a free space wavelength λ ₀ (= 5.17c) of 5.8 GHz.
m) was about 1/5 · λ ₀ .

When the directivity characteristic of the antenna at the frequency of 5.8 GHz was measured for the manufactured planar antenna structure 10, the directivity characteristic as shown in FIG. 6 was obtained. As for the relative reception power, the maximum reception power is 0 dB. According to this, compared to the directivity characteristic of the planar antenna structure in which the MSA is closely attached to the glass plate having no transparent conductive film (see FIG. 8), the directivity characteristic of the antenna forms a gentle mountain shape, In the range of the angle ± 70 ° to 80 ° (the direction perpendicular to the mounting surface of the glass plate is 0 °), the relative received power did not decrease as shown in FIG. 8. In this way, the transparent conductive film of the manufactured planar antenna structure 10 functions for heat ray reflection and anti-fog in portions other than the planar antenna, and in order to obtain good antenna directional characteristics in the planar antenna portion. I found it to work.

(Embodiment 2) Next, as shown in FIGS. 3 and 4, after the transparent conductive film is formed on the entire surface of the glass plate 22, a part of the transparent conductive film is removed, and the size is 46 mm × 46 m.
The transparent conductive film non-forming area of m was formed. After that, a planar antenna 21 having a size of a ground conductor of 50 mm × 50 mm, which is formed by firing a silver paste on the non-formation region, is formed.
Was formed. The plane antenna 21 also has a center frequency of 5.8 GHz.
Adjustment was performed so that the antenna can be transmitted and received at z.

When the directivity characteristic of the antenna at the frequency of 5.8 GHz was measured for the manufactured planar antenna structure 20, the directivity characteristic as shown in FIG. 7 was obtained. As for the relative reception power, the maximum reception power is 0 dB. According to this, compared to the directivity characteristic of the planar antenna structure in which the planar antenna 21 is formed on the glass plate without the conductive film 23 (see FIG. 9), the antenna directivity characteristic forms a gentle mountain shape and the angle ± In the range of 50 ° to 60 ° (the direction perpendicular to the mounting surface of the glass plate is 0 °), the relative received power did not decrease as shown in FIG. 9. In this way, the transparent conductive film of the planar antenna structure 20 thus produced is
It was found that the parts other than the planar antenna function for heat ray reflection and anti-fog, and the planar antenna part functions for obtaining good antenna directional characteristics.

Such a planar antenna structure 10, 20
Is applied to a vehicle windshield plate, MSA11
It is preferable that the mounting area of the flat antenna such as the flat antenna 21 and the flat antenna 21 is formed within 100 mm from the edge of the vehicle windshield plate so as not to hinder the visual field of the vehicle driver. 100m left and right centered on the left-right centerline when mounted on
It is preferably formed within the range of m. For example, from the viewpoint of the vehicle driver, the position on the back side of the rearview mirror is particularly preferable in terms of not obstructing the visual field and design.

Although the planar antenna structure of the present invention has been described above in detail, the present invention is not limited to the above-mentioned embodiments, and various improvements and modifications can be made without departing from the scope of the present invention. Of course it's good.

[0046]

As described above in detail, according to the planar antenna structure of the present invention, a high frequency antenna is suitable for a glass plate of a moving body such as a vehicle such as a windshield plate of a vehicle. The antenna directivity characteristics can be improved without lowering the transmission / reception efficiency. Moreover, it is durable and compact. For example, GPS
(Global Positioning Sysytem), VICS (Vehicl
The planar antenna structure is suitable for a dedicated short range communication (DSRC) system such as e information and communication system and ETC. Furthermore, the flat antenna structure of the present invention can be formed not only on a communication system such as a telephone or a glass plate of a mobile body, but also on another dielectric substrate, and can be used for various high frequency applications. It can be used as a structure of an antenna. Furthermore, the glass plate having the conductive film used in the planar antenna structure of the present invention contributes to the improvement of the directivity characteristics of the antenna in the antenna mounting area, and the heat ray reflection function and the anti-fog function in the area other than the antenna mounting area. Have.

[Brief description of drawings]

FIG. 1 is a plan view showing a planar antenna structure using a microstrip antenna which is an example of the planar antenna structure of the present invention.

FIG. 2 is a cross-sectional view of the planar antenna structure taken along the line AA ′ shown in FIG.

FIG. 3 is a plan view showing a planar antenna structure which is another example of the planar antenna structure of the present invention.

FIG. 4 is a cross-sectional view of the planar antenna structure taken along line BB ′ shown in FIG.

5A to 5H are plan views showing another example of the planar antenna in the planar antenna structure shown in FIG.

6 is a diagram showing the directivity characteristic of the antenna in the planar antenna structure shown in FIG.

7 is a diagram showing the directivity characteristic of the antenna in the planar antenna structure shown in FIG.

FIG. 8 is a diagram showing an example of directivity characteristics of a conventional planar antenna.

FIG. 9 is a diagram showing another example of directivity characteristics of a conventional planar antenna.

[Explanation of symbols]

10, 20 Planar antenna structure 11 Microstrip antenna 11a, 25 radiating conductor 11b, 26 Ground conductor 11c Dielectric substrate for planar antenna 12,22 glass plate 13, 23 Transparent conductive film 14 double-sided tape 17 connector 18 center conductor 21 planar antenna 25a Radiating conductor body 25b protrusion 27 power supply 30 Notch 31 protrusion 32 notches

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Claims (2)

[Claims] 1. A planar antenna structure comprising: a planar antenna provided with a radiation conductor and a ground conductor; and a dielectric substrate on which the planar antenna is arranged and a conductive film is provided so as to surround the planar antenna. And, the shortest distance to the inner peripheral edge of the conductive film at each position of the outer peripheral edge of the radiation conductor, when the free space wavelength of the radio wave used for transmission or reception by the planar antenna is λ ₀ ,
Planar antenna structure which is a 1/20 · λ ₀ ~λ _0. 2. A planar antenna structure comprising: a planar antenna provided with a radiation conductor and a ground conductor; and a dielectric substrate provided with a conductive film so as to surround the planar antenna, wherein the planar antenna comprises: The radiation conductor and the ground conductor are provided on the surface of the dielectric substrate so that the ground conductor surrounds a part or all of the radiation conductor on the surface of the dielectric substrate with a space around the ground conductor. A planar antenna structure characterized in that the conductive film surrounds.