JP3462959B2 - Planar antenna - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar antenna applicable to mobile communication devices, small information terminals, and other wireless devices having a planar antenna, and more particularly to a planar antenna, particularly a tapered shape of a tapered slot antenna. It relates to a planar antenna with improved directivity even when the antenna length is short.

[0002]

2. Description of the Related Art Planar antennas, particularly tapered slot antennas, have a structure in which the slot width of a slot line is widened with an inclination (tapered shape), and is parallel to the antenna surface (direction of travel of the slot line). It is one that emits electromagnetic waves. Since this planar antenna has a structure similar to that of a slot line, it does not require a ground conductor on the back surface unlike a microstrip line, and can be easily integrated with a feed line or a matching circuit of a uniplanar structure.

As a planar antenna, it has been heretofore shown in FIGS.
Those shown in are reported in papers and the like. FIG. 5 is a LTSA type with a linear tapered shape, FIG. 6 is a vivaldi type with an exponentially tapered shape, and FIG. 7 is a CWSA type with an exponentially expanded tapered shape and a constant width at the tip. FIG. 8 shows a BLTSA type in which a taper shape is formed by bending a straight line in several steps and expanding. As a result of prototyping a planar antenna using these tapered shapes, it is reported that a highly directional antenna with a low sidelob level was obtained.

Further, in JP-A-5-114810 "Broadband continuous flare notched phased array radiating element having a controlled reflection loss shape", a tapered shape is formed so as to give a high pass Chebyshev approximate reflection coefficient vs. frequency characteristic. Disclosed antennas are disclosed. The radiating element disclosed in this publication makes it possible to obtain a broadband, well-matched radiating element with a shortest optimum length for a given maximum mismatch over the band of interest.

[0005]

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention
Even if the taper-shaped antenna shown in FIGS. 5 to 8 is produced at a high frequency such as Hz, it is difficult to obtain a highly directional antenna as reported in papers and the like. Particularly, an antenna having an antenna length of about 3 to 4 wavelengths has a problem that directivity is deteriorated and it is difficult to downsize the antenna.

[0006] Further, in Japanese Patent Application Laid-Open No. 5-114810, the above-mentioned effect that a wide band well-matched radiating element having a shortest optimum length with respect to a predetermined maximum mismatch over a related band can be obtained is provided. Since the tapered shape is expressed by a very complicated calculation formula, there are problems in the following points.

That is, the calculation formula for giving the above-mentioned taper shape requires the value of the characteristic impedance with respect to the line width of the slot line, but in the generally used approximation formula of the characteristic impedance of the slot line on the low dielectric constant substrate, Since it has a discontinuity at the point of /λ=0.075, it cannot be used in the calculation formula disclosed in the above publication (C
characteristic Impedance o
f Wide Slotline on Low Pe
rmitity Substrate, MTT-
34 No. 8, pp. 900-902, 1986).
Therefore, the characteristic impedance of the slot line must be obtained using strict three-dimensional electromagnetic field analysis.
It is very difficult for general researchers to calculate the taper shape disclosed in the above publication.

As described above, the conventional tapered shape of the planar antenna is easy to make, but the desired characteristics cannot be obtained (FIGS. 5 to 8), or the complicated tapered shape is frustrating even for trying the experiment. However, there was a problem (Japanese Patent Laid-Open No. 5-114810).

Therefore, the present invention has been made in view of the above, and a first object of the present invention is to express a taper shape with a simple functional form.

A second object is to achieve impedance matching and improve directivity.

[0011]

The tapered shape of a planar antenna controls the directivity of the antenna by performing impedance matching between the input and output of the antenna and controlling the leakage of electromagnetic waves into the free space. Considering the impedance matching as the center, it is considered that the tapered shape of the planar antenna has an exponential function. However, considering the improvement of directivity, the tapered shape has a tapered shape such as the CWSA shown in FIG.
It is considered that a shape that encloses an electromagnetic wave, such as BLTSA shown in FIG. On the other hand, the LTSA shown in FIG.
Can be said to be in an intermediate position with respect to the CWSA shown in FIG. 7 and the BLTSA shown in FIG. Therefore, there are merits and demerits to those listed as the prior art.

Therefore, the inventor of the present invention simultaneously achieves the objects of impedance matching and improvement of directivity by utilizing the characteristics of the conventional planar antenna.
The impedance matching should be performed by leaving the basic tapered shape of CWSA (Fig. 7) and BLTSA (Fig. 8) with high directivity, and by performing exponentially gentle connection to the tapered shape. Found out.

In order to achieve the above object, the planar antenna according to claim 1 of the present invention has a structure in which the slot width of the slot line is expanded in a taper shape, and the plane antenna radiates an electromagnetic wave in the traveling direction of the slot line. In the antenna, as a result of exponentially expressing the tapered shape based on the tapered shape of CWSA (FIG. 7), the tapered shape is

[Equation 3] (However, x is the position coordinate in the radiation direction of the antenna, a, c
Are Fermi-Dirac function forms represented by arbitrary constants and b is a negative constant.

With the tapered shape represented by the above function form, it is possible to realize a shape in which the line width of the slot line, which increases exponentially at first, changes gradually and at a constant width.

A planar antenna according to a second aspect of the present invention has a structure in which a slot width of a slot line is expanded in a taper shape, and the planar antenna radiating an electromagnetic wave in the traveling direction of the slot line is a BLTSA (Fig. As a result of expressing the tapered shape as an exponential function (Fermi-Dirac function) based on the tapered shape of 8), the tapered shape is

[Equation 4] (However, x is the position coordinate in the radiation direction of the antenna, a, c
Is an arbitrary constant and b is a negative constant).

In the case of the taper shape expressed by the above function form, the line width of the slot line which linearly increases initially has a steep slope halfway and then returns to the original slope again.
It is possible to realize a shape in which the taper shape changes gradually while retaining the characteristics of the ST taper shape.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a planar antenna according to the present invention will be described below in detail with reference to the drawings.

[First Embodiment] The planar antenna according to the first embodiment of the present invention is a CWSA.
The tapered shape is expressed as an exponential function (Fermi-Dirac function) based on the tapered shape of FIG. 1 is a perspective view showing a configuration of a planar antenna according to Embodiment 1 of the present invention, and FIG. 2 is a plan view showing a configuration of a planar antenna according to Embodiment 1 of the present invention.

The planar antenna 10 shown in FIG. 1 and FIG.
A substrate 11 made of a dielectric material and a conductor portion 12 formed on the substrate 11 and having a tapered slot portion 13 for radiating or entering an electromagnetic wave are provided. The tapered slot portion 13 includes an input portion 13a, a curved portion 13b, and an opening portion 13
and c. The taper shape of the tapered slot 13 is based on the taper shape of CWSA (FIG. 7), and the taper shape is an exponential function (Fermi
The result expressed as Dirac function),

[Equation 5] (However, x is the position coordinate in the radiation direction of the antenna, a, c
Is an arbitrary constant and b is a negative constant).

In the planar antenna 10 according to the first embodiment, the substrate 11 is made of polyimide and has a thickness of 50 μm.
m, and the dielectric constant is 3.6. The conductor portion 12 formed on the substrate 11 is a copper foil having a thickness of 5 μm, and is formed on only one surface of the substrate 11. Also, the tapered slot portion 13
Are formed by removing the conductor portion 12 by etching or the like.

Further, the planar antenna 1 according to the first embodiment
0, the opening 13c of the tapered slot portion 13
Has a width of 5 mm, the antenna length is 20 mm, and the slot width of the input portion 13a is 50 μm.

The functional form that gives the tapered shape of the tapered slot portion 13 of the planar antenna 10 is

[Equation 6] (However, x is represented by a position coordinate (mm), 0 ≦ x ≦ 20).

The planar antenna 10 having the above structure is
For example, it is used by being connected to a high frequency circuit (not shown) via a transmission line (not shown) in a mobile communication device, a small information terminal, or the like.

As described above, with the taper shape expressed by the above function form, the line width of the slot line is exponentially increased at first, and then the shape gradually changing with a constant width is realized. can do. Therefore, according to this taper shape, since a smooth connection like an exponential function (Fermi-Dirac function) is performed with respect to the taper shape of the CWSA (Fig. 7), the basic characteristic of the CWSA with high directivity (Fig. 7) Impedance matching can be performed while leaving the shape. Therefore, the tapered shape can be described by a simple functional form, and a planar antenna with high directivity can be realized even if the antenna length is short.

[Second Embodiment] A planar antenna according to a second embodiment of the present invention is a BLTS.
The tapered shape is expressed as an exponential function (Fermi-Dirac function) based on the tapered shape of A (FIG. 8). FIG. 3 is a perspective view showing the configuration of the flat antenna according to the second embodiment of the present invention, and FIG. 4 is a plan view showing the configuration of the flat antenna according to the second embodiment of the present invention.

The planar antenna 30 shown in FIG. 3 and FIG.
A substrate 11 made of a dielectric material and a conductor portion 12 formed on the substrate 11 and having a tapered slot portion 31 for radiating or entering an electromagnetic wave are provided. The tapered slot portion 31 includes an input portion 31a, a curved portion 31b, and an opening portion 31.
and c. The tapered shape of the tapered slot portion 31 is expressed as an exponential function (Fermi-Dirac function) based on the tapered shape of BLTSA (FIG. 8).

[Equation 7] (However, x is the position coordinate in the radiation direction of the antenna, a, c
Is an arbitrary constant and b is a negative constant).

In the planar antenna 30 according to the second embodiment, the substrate 11 is made of polyimide and has a thickness of 50 μm.
m, and the dielectric constant is 3.6. The conductor portion 12 formed on the substrate 11 is a copper foil having a thickness of 5 μm, and is formed on only one surface of the substrate 11. Also, the tapered slot portion 31
Are formed by removing the conductor portion 12 by etching or the like.

Further, the planar antenna 3 according to the first embodiment
0, the opening 31c of the tapered slot 31
Has a width of 5 mm, the antenna length is 20 mm, and the slot width of the input section 31a is 50 μm.

The function form that gives the tapered shape of the tapered slot portion 31 of the planar antenna 30 is

[Equation 8] (However, x is represented by a position coordinate (mm), 0 ≦ x ≦ 20).

The plane antenna 30 having the above structure is
For example, it is used by being connected to a high frequency circuit (not shown) via a transmission line (not shown) in a mobile communication device, a small information terminal, or the like.

As described above, in the case of the taper shape expressed by the above function form, the line width of the slot line which initially increases linearly has a steep slope on the way and then changes to the original slope again. The shape can be realized. Therefore, according to this taper shape, BLAST (Fig. 8)
Since a smooth exponential (Fermi-Dirac function) connection is made to the tapered shape of, the impedance matching can be performed while leaving the basic shape of BLAST (FIG. 8) having high directivity. Therefore, the tapered shape can be described by a simple functional form, and a planar antenna with high directivity can be realized even if the antenna length is short.

[0032]

As described above, according to the planar antenna (Claim 1) of the present invention, the slot line has a structure in which the slot width is expanded in a taper shape, and electromagnetic waves are radiated in the traveling direction of the slot line. In a flat antenna, the taper shape is

[Equation 9] (However, x is the position coordinate in the radiation direction of the antenna, a, c
Is a Fermi-Dirac function form expressed by an arbitrary constant and b is a negative constant. Therefore, at first, the line width of the slot line is exponentially increased, and thereafter, gently,
In addition, it is possible to realize a shape that changes with a certain width. Therefore, according to this taper shape, CWS
Since a smooth connection like an exponential function (Fermi-Dirac function) was performed on the tapered shape of A (Fig. 7),
Impedance matching can be performed while leaving the basic shape of CWSA (FIG. 7) having high directivity. Therefore, the tapered shape can be described by a simple functional form, and a planar antenna with high directivity can be realized even if the antenna length is short.

According to the planar antenna of the present invention (claim 2), the planar antenna having a structure in which the slot width of the slot line is expanded in a taper shape and radiating electromagnetic waves in the traveling direction of the slot line is tapered. The shape of

[Equation 10] (However, x is the position coordinate in the radiation direction of the antenna, a, c
, Which is an arbitrary constant and b is a negative constant), is a Fermi-Deluxe function form. Therefore, at first, the line width of the slot line that increases linearly becomes steep on the way, It is possible to realize a shape that changes to an inclination. Therefore, according to this tapered shape, BLAS
Since we performed a smooth exponential (Fermi-Dirac function) connection to the taper shape of T (Fig. 8),
Impedance matching can be performed while leaving the basic shape of BLAST (FIG. 8) having high directivity. Therefore, the tapered shape can be described by a simple functional form, and a planar antenna with high directivity can be realized even if the antenna length is short.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a planar antenna according to a first embodiment of the present invention.

FIG. 2 is a plan view showing the configuration of the planar antenna according to the first embodiment of the present invention.

FIG. 3 is a perspective view showing a configuration of a planar antenna according to a second embodiment of the present invention.

FIG. 4 is a plan view showing a configuration of a planar antenna according to a second embodiment of the present invention.

FIG. 5 is a plan view showing a configuration of a conventional planar antenna LTSA.

FIG. 6 is a plan view showing a configuration of a conventional planar antenna, vivaldi.

FIG. 7 is a plan view showing a configuration of a CWSA which is a conventional planar antenna.

FIG. 8 is a plan view showing the configuration of a BLTSA which is a conventional planar antenna.

[Explanation of symbols]

10,30 planar antenna 11 board 12 conductor 13,31 Tapered slot 13a, 31a input section 13b, 31b Curved part 13c, 31c opening

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01Q 13/16 JISST file (JOIS)

Claims (2)

(57) [Claims] 1. In a planar antenna having a structure in which a slot width of a slot line is expanded in a taper shape and radiating an electromagnetic wave in a traveling direction of the slot line, the shape of the taper is (However, x is the position coordinate in the radiation direction of the antenna, a, c
Is a Fermi-Dirac function form represented by an arbitrary constant and b is a negative constant). 2. In a planar antenna having a structure in which a slot width of a slot line is expanded in a taper shape, and radiating an electromagnetic wave in a traveling direction of the slot line, the taper shape is expressed by (However, x is the position coordinate in the radiation direction of the antenna, a, c
Is a Fermi-Dirac function form represented by an arbitrary constant and b is a negative constant).