JPH07245521A - Plane antenna - Google Patents

Abstract

PURPOSE:To realize a broad directivity independently of a dielectric of a board and to make the size of the antenna small. CONSTITUTION:The antenna is formed by laminating sequentially a lower ground conductor 3, a lower dielectric layer 2, a radiation conductor 1, an upper dielectric layer 4 and an upper ground conductor 5. The lower ground conductor 3, the lower dielectric layer 2, the radiation conductor and the upper dielectric layer 4 are formed as a disk and the upper ground conductor 5 is formed as a torus. Then the upper ground conductor 5 and the lower ground conductor 3 are connected at their outer circumferential parts with a cylindrical side face ground conductor 6. Furthermore, the inner circumference (a) of the upper ground conductor 5 is set to an inner side of the outer circumference (b) of the radiation conductor 1. Moreover, the radiation conductor 1 and the lower ground conductor 3 are connected at their centers by a short-circuit conductor rod 7, which is used to make the operation stable mainly and not especially required and then may be omitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar antenna suitable for application to microwave band wireless communication terminal equipment.

[0002]

2. Description of the Related Art Conventionally, an antenna system in the field of microwave band wireless communication has a simple structure and is durable.
A flat antenna having a low profile is widely known. Further, in the field of mobile communication using satellites, an antenna element having a wide-angle directivity is required for moving a mobile body.

By the way, in a circular patch antenna or the like as one of the above planar antennas, a magnetic current wave source can be made small and a wide angle directivity can be realized by using a substrate having a high dielectric constant. However, the conventional circular patch antenna has a drawback in that there is no degree of freedom in selecting a substrate with respect to the directional opening angle because the directional opening angle depends on the dielectric constant of the substrate.

In response to such a problem, a planar antenna, an example of which is shown in FIG. 5, has already been reported as a structure that is not affected by the dielectric constant of the substrate (Journal of the Institute of Electronics, Information and Communication Engineers B-II Vol. J72-B-II N
o. 9 pp. 462-467 September 1989).

In the conventional planar antenna, for example, a circular ground conductor 23 and a ring-shaped radiation conductor 21 are arranged via a circular dielectric layer 22, and the outer periphery of the ground conductor 23. And the outer periphery of the radiation conductor 21 is the short-circuit conductor 2
7 are connected and formed.

The feeding point 10 is disposed on the X-axis of the radiation conductor 21 at a position offset from the origin O, and is connected to the core of the feeding connector 11 through the conductive pin 12. The ground side of the power supply connector 11 is connected to the ground conductor 23.

In the planar antenna constructed as above, the inner diameter (a) and the outer diameter (b) of the ring-shaped radiating conductor 21.
The opening angle of directivity can be changed by changing the ratio of. That is, wide-angle directivity can be realized without being affected by the dielectric constant of the substrate.

[0008]

However, in the above-described conventional planar antenna, the size of the antenna is relatively large, and for example, it is not suitable for portable mobile communication equipment.

The present invention has been made in view of the above points, and an object thereof is to provide a planar antenna having a size smaller than that of the conventional planar antenna.

[0010]

The first means of the present invention is to provide a lower ground conductor 3, a lower dielectric layer 2, and a radiation conductor 1.
And the upper dielectric layer 4 and the upper ground conductor 5 formed in a ring shape are sequentially laminated and arranged.
The lower ground conductor 3 and the lower ground conductor 3 are connected by a cylindrical side ground conductor 6 arranged on the outer periphery thereof, and the upper ground conductor 5 is connected.
The inner ring (a) is a plane antenna which is set inside the outer shell (b) of the radiation conductor 1.

According to a second means of the present invention, in the planar antenna according to the first means, the radiation conductor 1 and the lower ground conductor 3 are connected by a rod-shaped short-circuit conductor 7 arranged at the center thereof. It is a planar antenna characterized in that

A third means according to the present invention is the planar antenna according to the first means, wherein the radiation conductor 1 is formed in an annular shape, and the inner ring (c) of the radiation conductor 1 is formed of the upper ground conductor 5. It is a planar antenna characterized by being set inside the inner ring (a).

According to a fourth aspect of the present invention, in the flat antenna according to the third aspect, the radiation conductor 1 and the lower ground conductor 3 are arranged in a tubular shape along the inner ring of the radiation conductor. The planar antenna is characterized by being connected by the short-circuit conductor 17 of.

A fifth means according to the present invention is the planar antenna according to the fourth means, wherein the tubular short-circuit conductor 17 is used.
Is a planar antenna characterized by being divided into a plurality of parts.

According to a sixth means of the present invention, in the planar antenna according to any one of the first to fifth means, the shape of the inner ring of the upper ground conductor 5, the radiation conductor 1 and the outer circumference is
It is a planar antenna characterized by being configured in a circular or rectangular shape.

A seventh means according to the present invention is the planar antenna according to the second means, wherein the size of the inner ring (a) of the upper ground conductor 5 and the outer shell (b) of the radiation conductor 1 is set to Jn. ′ (Kb) [Nn ′ (ka) Jn (kb) −Jn ′ (ka)
Nn (kb)] + Jn (kb) [Nn '(ka) Jn' (kb)
-Jn '(ka) Nn' (kb)] = 0 where k is the wave number Jn ', Nn' is obtained by the differential form of the Bessel function of the first and second types It is a planar antenna.

An eighth means according to the present invention is the planar antenna according to the third means, wherein the inner ring (a) of the upper ground conductor 5 and the outer shell (b) and inner ring (c) of the radiation conductor 1 are arranged.
The magnitude of [Nn '(ka) Jn (kb) -Jn' (ka) Nn (kb)]
[Nn '(kc) Jn' (kb) -Jn '(kc) Nn' (k
b)] + [Nn '(ka) Jn' (kb) -Jn '(ka) N
n '(kb)] [Nn' (kc) Jn (kb) -Jn '(kc)
Nn (kb)] = 0 where k is the wave number Jn 'and Nn' is a plane antenna characterized by being obtained by the differential form of the Bessel functions of the first and second types.

A ninth means of the present invention is the planar antenna according to the fourth means, wherein the inner ring (a) of the upper ground conductor 5 and the outer shell (b) and inner ring (c) of the radiation conductor 1 are used.
The magnitude of [Nn '(ka) Jn (kb) -Jn' (ka) Nn (kb)]
[Nn (kc) Jn '(kb) -Jn (kc) Nn' (kb)]
+ [Nn '(ka) Jn' (kb) -Jn '(ka) Nn'
(kb)] [Nn (kc) Jn (kb) -Jn (kc) Nn (k
b)] = 0 where k is the wave number Jn 'and Nn' is a plane antenna characterized by being obtained by the differential form of the Bessel functions of the first and second types.

A tenth means according to the present invention is characterized in that, in the planar antenna according to any one of the first to ninth means, the cylindrical side-surface grounding conductor 6 is divided into a plurality of parts. It is a planar antenna.

[0020]

According to this, the lower ground conductor, the lower dielectric layer, the radiation conductor, the upper dielectric layer, and the upper ground conductor formed in a ring shape are sequentially laminated and arranged. The lower ground conductor and the lower ground conductor are connected by a cylindrical side ground conductor arranged on the outer periphery thereof, and the inner ring of the upper ground conductor is set inside the outer shell of the radiating conductor. Wide-angle directivity can be realized without being influenced by the ratio, and the size can be reduced.

[0021]

Embodiments of the planar antenna of the present invention will be described below with reference to theoretical calculation formulas and drawings.

In FIG. 1, A in FIG. 1 shows the front structure of the planar antenna according to the first embodiment. B of the same drawing shows the sectional structure of the planar antenna taken along the line α-α.

As shown in FIGS. 1A and 1B, in the first embodiment, the lower ground conductor 3, the lower dielectric layer 2, the radiation conductor 1, the upper dielectric layer 4, and the upper ground conductor 5 are sequentially arranged. It is constructed by stacking. Lower ground conductor 3, lower dielectric layer 2,
The radiation conductor 1 and the upper dielectric layer 4 are each formed in a circular shape, and the upper ground conductor 5 is formed in an annular shape. Furthermore, the upper ground conductor 5 and the lower ground conductor 3 are
At the outer peripheral portion thereof, a cylindrical side-face ground conductor 6 is connected.

The inner circumference (a) of the upper ground conductor 5 is
It is set inside the outer circumference (b) of the radiation conductor 1. The radiation conductor 1 and the lower ground conductor 3 are connected by a rod-shaped short-circuit conductor 7 at the center thereof, but this is mainly for stabilizing the operation and is not particularly necessary. It may be omitted.

The feeding point 10 is arranged at a position appropriately offset from the origin O on the X axis of the radiation conductor for impedance matching, and through the conductor pin 12 penetrating the lower dielectric layer 2, a feeding connector as a feeding port. 11
Is connected to the core wire. The ground side of the power supply connector 11 is connected to the lower ground conductor 3. Instead of the conductor pin 12, a through hole may be used for connection. Input and output of signal power is performed through the power supply connector 11.

The first embodiment of the planar antenna of the present invention is
It is configured as described above. Then, in the first embodiment, the size of each part is obtained as follows.

The size of a planar antenna is usually obtained by solving the equation of the internal electric field between the ground conductor and the radiating conductor for boundary conditions. In the case of a planar antenna having a circular or circular radiating conductor, its internal electric field can be expressed in the cylindrical coordinate system as:

[0028]

[Equation 1] Ez = Eo cos (nφ) [AnJn (kρ) + Bn
Nn (kρ)] where Ez: z component of internal electric field Jn, Nn: Bessel functions of the first and second types ρ, φ: Diameter and azimuth angle in cylindrical coordinates An, Bn: arbitrary coefficient Eo: amplitude k: Is the wave number. The thickness (h) of the substrate (dielectric layer) is derived on the assumption that it is sufficiently smaller than the wavelength.

That is, from Maxwell's equation,
The wave equation is

[Equation 2] Can be written.

This equation (2) is converted into cylindrical coordinates (ρ, φ,
z)

[Equation 3] Becomes

Here, the electric field inside the antenna has only the z component, and since the thickness (h) of the substrate is sufficiently smaller than the free space wavelength λ ₀ , it does not change along the z direction. Therefore,

[Equation 4] Assuming that the variables can be transformed into

[0032]

[Equation 5]

The formula of [Equation 5] is

[Equation 6] It is separated into two formulas. n is called a separation constant.

Two independent solutions to R (ρ) in the first equation of the equation (6) are represented as Jn (kρ) and Nn (kρ). Jn (kρ) is the Bessel function or the Bessel function of the first kind, Nn (kρ) is the Neumann function, or the second
It is called the seed Bessel function.

Therefore, the general solution of R (ρ) is

[Expression 7] R (ρ) = AnJn (kρ) + BnNn (kρ) An and Bn are undetermined coefficients.

The solution to Ψ (φ) in the second equation of equation (6) is

(8) Ψ (φ) = Cn sin (nφ) + Dn cos (nφ) = E
n cos [n (φ−φ ₀ )]. Cn, Dn, and En are undetermined coefficients.

Therefore, the solution of [Equation 3] is

[Equation 9] Ez = En cosn (φ−φ ₀ ) [AnJn (kρ)
+ BnNn (kρ)].

If φ _0, which is the reference of φ, is placed on the x-axis, that is, φ ₀ = 0, the equation of [Equation 9] becomes the equation of [Equation 1] described above, and this equation is for the planar antenna. It is a general formula for the internal electric field.

Therefore, in the first embodiment described above, the internal electric field E of the region is calculated from the above equation (1).
_z1 is

[Equation 10] E _z1 = E ₀₁ cos (nφ) [AnJn (kρ) + B
nNn (kρ)].

On the other hand, in the region, Nn (kρ) is ρ
It becomes infinite at = 0 and is physically unsuitable. Therefore Bn
= 0 and the internal electric field E _z2 is

It is expressed as E _z2 = E ₀₂ cos (nφ) Jn (kρ).

Therefore, the boundary condition for the antenna to resonate in the region is

[Equation 12] Is.

Therefore, the boundary condition for the antenna to resonate in the region is

[Equation 13] Is.

The boundary conditions for the antenna to resonate in the region are:

[Equation 14]

[0044]

[Equation 15] Is.

Therefore, the four boundary conditions are defined by the above [Equation 1]
0] [Equation 11] By applying the equation, the resonance condition of the antenna

## EQU16 ## Jn '(kb) [Nn' (ka) Jn (kb) -J
n '(ka) Nn (kb)] + Jn (kb) [Nn' (ka) J
n '(kb) -Jn' (ka) Nn '(kb)] = 0, where k is the wave number Jn', and Nn 'is the differential form of the Bessel functions of the first and second types.

Therefore, in the equation (16), when ka, which is a parameter for determining the opening angle of directivity, is 1.0, kb is 1.58, which is the conventional value shown in FIG. With the planar antenna according to the technology, ka = 1.
Compared to kb = 3.46 obtained for the case of 0, it is half or less. Note that FIG. 2 shows an example of eigenvalue (kb) characteristics of the conventional planar antenna and the planar antenna of the present invention, which are obtained by calculation. As is clear from the figure, the size of the planar antenna of the present invention is half or less that of the conventional planar antenna.

Thus, according to the above-described device, the lower ground conductor 3, the lower dielectric layer 2, the radiation conductor 1, the upper dielectric layer 4, and the upper ground conductor 5 formed in an annular shape are sequentially laminated. And the upper side ground conductor 5 and the lower side ground conductor 3 are connected by a cylindrical side surface ground conductor 6 arranged on the outer periphery thereof,
The inner ring (a) of the upper ground conductor 5 is replaced by the outer ring (b) of the radiation conductor 1.
By setting it to the inner side, the substrate (dielectric layer 2,
Wide-angle directivity can be realized without being affected by the dielectric constant of 4),
Moreover, the size can be reduced.

In the first embodiment described above,
As a size, the outer circumference (b) of the radiation conductor 1 is 30.0 m
m, and the thickness (h) of the substrate (dielectric layers 2 and 4) is 0.8.
The inner circumference of the upper grounding conductor 5 was made in the case of mm
Obtain the resonance frequency (fr) when the value in (a) is changed sequentially.
The values are as follows. However, the substrate (dielectric
The material of the body layer is Chuko Flow (Teflon glass fiber)
) And use ε _r= 2.6, tan δ = 1.8 × 1
0^-3(1 GHz).

(1) a = 15.0 mm fr =
1.64 GHz (2) a = 18.0 mm fr = 1.61 GH
z (3) a = 22.0 mm fr = 1.62 GH
z (4) a = 26.0 mm fr = 1.68 GH
z

On the other hand, for example, the same frequency as (1) (1.6
In the case of an annular cavity antenna having an outer diameter (b) / inner diameter (a) = 2.0 at 4GFz), a computer simulation shows that the outer diameter (b) = 70.7 mm and the inner diameter (a) = 35.7 mm. Becomes

In the case of circular patch antennas having the same frequency, the diameter is 32.9 mm, and the frequency of the circular patch antenna having a diameter of 30.0 mm is fr = 1.83 GHz.

Therefore, from these results, a small size can be obtained at the same frequency, and a low resonance frequency at the same diameter means that a smaller size can be achieved.

Next, a second embodiment of the flat antenna of the present invention will be described with reference to FIG.

In FIG. 3, A in FIG. 3 shows the front structure of the planar antenna according to the second embodiment. B of the same drawing shows the sectional structure of the planar antenna taken along the line α-α.

As shown in FIGS. 3A and 3B, in the second embodiment, as in the first embodiment, the lower ground conductor 3, the lower dielectric layer 2, the radiation conductor 1, and the upper dielectric are formed. The layer 4 and the upper ground conductor 5 are sequentially laminated and configured. The lower ground conductor 3, the lower dielectric layer 2, and the upper dielectric layer 4 are each formed in a circular shape, and the radiation conductor 1 and the upper ground conductor 5 are formed in an annular shape. The upper ground conductor 5 and the lower ground conductor 3 are connected to each other by a cylindrical side ground conductor 6 on the outer peripheral portion thereof.

The inner circumference (a) of the upper ground conductor 5 is
The outer circumference (b) of the radiation conductor 1 is set inside, and the inner circumference (c) of the radiation conductor 1 is set further inside thereof.

The feeding point 10 is arranged at a position appropriately offset from the origin O on the X axis of the radiation conductor for impedance matching, and through the conductor pin 12 penetrating the lower dielectric layer 2, a feeding connector as a feeding port. 11
Is connected to the core wire. The ground side of the power supply connector 11 is connected to the lower ground conductor 3. Instead of the conductor pin 12, a through hole may be used for connection. Input and output of signal power is performed through the power supply connector 11.

The second embodiment of the planar antenna of the present invention is constructed as described above. Also in this second embodiment, as in the first embodiment, if the boundary condition is substituted into the expression of [Equation 1] and the equation is solved, kb can be obtained. Again, the same as in the first embodiment. In addition, since it is smaller than the kb of the conventional planar antenna, the antenna size is small.

In the second embodiment, the equation obtained by substituting the boundary condition into the equation of [Equation 1] is as follows:
become that way.

[0060]

## EQU17 ## [Nn '(ka) Jn (kb) -Jn' (ka) N
n (kb)] [Nn '(kc) Jn' (kb) -Jn '(kc)
Nn '(kb)] + [Nn' (ka) Jn '(kb) -Jn'
(ka) Nn '(kb)] [Nn' (kc) Jn (kb) -J
n ′ (kc) Nn (kb)] = 0, where k is the wave number Jn ′, Nn ′ is the differential form of the Bessel functions of the first and second types

Further, a third embodiment of the planar antenna of the present invention will be described with reference to FIG.

In FIG. 4, A in FIG. 4 shows the front structure of the planar antenna according to the second embodiment. B of the same drawing shows the sectional structure of the planar antenna taken along the line α-α.

As shown in FIGS. 4A and 4B, in the third embodiment, as in the first embodiment, the lower ground conductor 3, the lower dielectric layer 2, the radiation conductor 1, and the upper dielectric are formed. The layer 4 and the upper ground conductor 5 are sequentially laminated and configured. The lower ground conductor 3, the lower dielectric layer 2, and the upper dielectric layer 4 are each formed in a circular shape, and the radiation conductor 1 and the upper ground conductor 5 are formed in an annular shape. The upper ground conductor 5 and the lower ground conductor 3 are connected to each other by a cylindrical side ground conductor 6 on the outer peripheral portion thereof.

The radiation conductor 1 and the lower ground conductor 3 are
The inner peripheral portion is connected by a tubular short-circuit conductor 17. The tubular short-circuit conductor 17 may be divided into a plurality of parts, and for example, a large number of through holes arranged along the inner peripheral portion can be substituted. The inner circumference (a) of the upper ground conductor 5 is set inside the outer circumference (b) of the radiation conductor 1, and the inner circumference (c) of the radiation conductor 1 is set further inside.

The feeding point 10 is arranged at a position appropriately offset from the origin O on the X axis of the radiation conductor for impedance matching, and through the conductor pin 12 penetrating the lower dielectric layer 2, a feeding connector as a feeding port. 11
Is connected to the core wire. The ground side of the power supply connector 11 is connected to the lower ground conductor 3. Instead of the conductor pin 12, a through hole may be used for connection. Input and output of signal power is performed through the power supply connector 11.

The third embodiment of the flat antenna of the present invention is constructed as described above. Also in this third embodiment, as in the first embodiment, if the boundary condition is substituted into the expression of [Equation 1] and the equation is solved, kb is obtained, and again, the same as in the first embodiment. In addition, since it is smaller than the kb of the conventional planar antenna, the antenna size is small.

In the third embodiment, the equation obtained by substituting the boundary condition into the equation of [Equation 1] is as follows:
become that way.

[0068]

[Equation 18] [Nn '(ka) Jn (kb) -Jn' (ka) N
n (kb)] [Nn (kc) Jn '(kb) -Jn (kc) N
n '(kb)] + [Nn' (ka) Jn '(kb) -Jn'
(ka) Nn '(kb)] [Nn (kc) Jn (kb) -Jn
(kc) Nn (kb)] = 0 where k is the wave number Jn ′, Nn ′ is the differential form of the Bessel functions of the first and second types

In all of the embodiments described above, the cylindrical side-face grounding conductor 6 may be divided into a plurality of parts, and for example, a large number of through holes arranged along the outer peripheral portion can be substituted.

In all of the above-mentioned embodiments, the radiation conductor, the ground conductor, and the dielectric layer have a circular shape or an annular shape, but they may have a rectangular shape or another shape. , A similar effect can be obtained. Although the calculation formula in the case of a rectangle is not presented, it can be understood from the above-described circular embodiment that the size can be reduced. Also, the size can be determined by experiment.

Further, the feeding structure may be not only one-point feeding but also plural feedings. Therefore, the same configuration is possible when radiating circularly polarized waves and elliptical polarized waves.
The effect of the present invention can be obtained.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various configurations can be adopted without departing from the gist of the present invention.

[0073]

According to the present invention, a lower ground conductor, a lower dielectric layer, a radiating conductor, an upper dielectric layer, and an annularly formed upper ground conductor are sequentially laminated and disposed. The upper ground conductor and the lower ground conductor are connected by a cylindrical side surface ground conductor arranged on the outer periphery thereof, and the inner ring of the upper ground conductor is set inside the outer shell of the radiating conductor, whereby the dielectric constant of the substrate is improved. Wide-angle directivity can be realized without being affected by the change, and the size can be reduced.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an example of eigenvalue characteristics of a planar antenna of the present invention and a conventional planar antenna.

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

FIG. 4 is a configuration diagram of a third embodiment of a planar antenna according to the present invention.

FIG. 5 is a configuration diagram of an example of a planar antenna according to a conventional technique.

[Explanation of symbols]

 1 Radiation Conductor 2 Lower Dielectric Layer 3 Lower Grounding Conductor 4 Upper Dielectric Layer 5 Upper Grounding Conductor 6 Side Grounding Conductor 7 Shorting Conductor 10 Feeding Point 11 Feeding Connector 12 Conductor Pin 17 Shorting Conductor 21 Radiating Conductor 22 Dielectric Layer 23 Grounding Conductor 27 short-circuit conductor

Claims (10)

[Claims] 1. A lower ground conductor, a lower dielectric layer, a radiation conductor, an upper dielectric layer, and an upper ground conductor formed in a ring shape are sequentially laminated and arranged, and the upper ground conductor and The lower ground conductor is connected by a cylindrical side-face ground conductor arranged on the outer periphery thereof, and the inner ring of the upper ground conductor is set inside the outer shell of the radiation conductor. Planar antenna. 2. The planar antenna according to claim 1, wherein the radiation conductor and the lower ground conductor are connected by a rod-shaped short-circuit conductor arranged at the center thereof. 3. The plane antenna according to claim 1, wherein the radiation conductor is formed in a ring shape, and the inner ring of the radiation conductor is set inside the inner ring of the upper ground conductor. antenna. 4. The planar antenna according to claim 3, wherein the radiation conductor and the lower ground conductor are connected by a tubular short-circuit conductor arranged along an inner ring of the radiation conductor. And a planar antenna. 5. The planar antenna according to claim 4, wherein the tubular short-circuit conductor is divided into a plurality of parts. 6. The planar antenna according to claim 1, wherein the shape of the inner ring of the upper ground conductor, the radiation conductor and the outer circumference is circular or rectangular. Planar antenna. 7. The planar antenna according to claim 2, wherein the inner ring (a) of the upper ground conductor and the outer shell (b) of the radiating conductor have a size of Jn ′ (kb) [Nn ′ (ka). Jn (kb) -Jn '(ka)
Nn (kb)] + Jn (kb) [Nn '(ka) Jn' (kb)
-Jn '(ka) Nn' (kb)] = 0 where k is the wave number Jn 'and Nn' is obtained by the differential form of the Bessel functions of the first and second types. Planar antenna. 8. The planar antenna according to claim 3, wherein the size of the inner ring (a) of the upper ground conductor and the outer shell (b) and inner ring (c) of the radiating conductor is [Nn ′ (ka ) Jn (kb) -Jn '(ka) Nn (kb)]
[Nn '(kc) Jn' (kb) -Jn '(kc) Nn' (k
b)] + [Nn '(ka) Jn' (kb) -Jn '(ka) N
n '(kb)] [Nn' (kc) Jn (kb) -Jn '(kc)
Nn (kb)] = 0 where k is the wave number Jn 'and Nn' is a differential type of the Bessel functions of the first and second types. 9. The planar antenna according to claim 4, wherein the size of the inner ring (a) of the upper ground conductor and the outer shell (b) and inner ring (c) of the radiating conductor is [Nn ′ (ka ) Jn (kb) -Jn '(ka) Nn (kb)]
[Nn (kc) Jn '(kb) -Jn (kc) Nn' (kb)]
+ [Nn '(ka) Jn' (kb) -Jn '(ka) Nn'
(kb)] [Nn (kc) Jn (kb) -Jn (kc) Nn (k
b)] = 0 where k is the wave number Jn ′ and Nn ′ is the differential type of the Bessel functions of the first and second types. 10. The planar antenna according to claim 1, wherein the cylindrical side-surface grounding conductor is divided into a plurality of parts.