JP3532309B2 - 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 suitable for transmitting microwave charged waves, and particularly suitable for transmitting and receiving radio waves between the ground and a broadcasting satellite.

[0002]

2. Description of the Related Art Broadcast satellites (hereinafter referred to as B
S: Broadcasting Satellite) has been launched into a so-called geostationary orbit about 36,000 km above the equator of the earth. For this reason, the radio wave reaching the ground from the BS (hereinafter, this is referred to as satellite wave or BS wave) is extremely weak.

For the above-mentioned reasons, it is necessary to use an antenna having high gain and little influence of external noise (external radio waves) for receiving satellite waves. Generally, a circularly polarized radio wave is used for the BS wave, and it is necessary to use an antenna of a type corresponding to this as a transmitting / receiving antenna.

[0004]

The above-mentioned conditions are satisfied,
As an example of an antenna suitable for receiving BS waves, Japanese Patent Laid-Open No. Hei 4
A slot antenna as disclosed in Japanese Patent No. 68604 has been proposed. Although a spiral dielectric is indispensable as a constituent element of the planar antenna described in this publication. Since it is extremely difficult to form the spiral dielectric accurately, it is difficult to form a planar antenna having a high gain and excellent directivity and polarization characteristics.

Further, as an example in which the above-mentioned problems are solved, a flat antenna feeding circuit shown in Japanese Patent Laid-Open No. 6-244634 has been proposed. According to the planar antenna feeding circuit described in this publication, by providing the cavity resonator and the phase adjusting mechanism, it is possible to arrange the slot group formed in the radiation surface side conductor on a plurality of concentric circles, In addition, the spiral dielectric is unnecessary.

However, the characteristic of an antenna is originally determined by its size and various numerical values (for example, permittivity etc.) representing the properties peculiar to the material forming the antenna. On the other hand, in the conventional planar antenna including the above-mentioned publication, such various numerical values are not clearly shown.

That is, for example, the dimensions of each part of the planar antenna suitable for receiving BS waves and other numerical values have not been established.
It was impossible to reproduce a planar antenna with sufficient characteristics. The present invention has been made under such a background, and an object thereof is to provide a planar antenna suitable for transmitting and receiving satellite broadcast waves using a frequency of approximately 12 GHz band.

[0008]

In order to solve the above-mentioned problems, in the invention according to claim 1, a radiation plate having a radiation slot formed of a conductor and a radiation plate spaced apart from each other are provided in parallel. A conductor plate facing each other, and an annular portion formed by a conductor to form a cavity inside and projecting between the radiating plate and the conductor plate, and having an outer central portion of the conductor plate facing the radiating plate. a cavity resonator mounted, through the hollow bottom comprising a power supply means for supplying a high frequency current project 12GHz band in the cavity, and a phase adjusting means attached to said cavity bottom in the cavity inside, the Radiation slot is concentric with the ring as an axis
Is formed on the radiation plate, the inner diameter L of the annular portion is 29 mm or more and 31 mm,
The distance G from the radiation plate to one end of the annular portion is 1 mm or more and 3 mm or less, the axial length D of the annular portion is 4 mm or more and 6 mm or less, and The sum of the distance G and the length D is 5 mm or more and 8 mm or less.

According to the second aspect of the invention,
The planar antenna according to claim 1, wherein an annular dielectric material is inserted between the radiation plate and the conductor plate, except for the annular portion and a portion corresponding to the cavity. .

Further, in the invention described in claim 3,
3. The planar antenna according to claim 1, wherein the radiation slot includes a plurality of minute slots arranged in a circle centered on an axis of the annular portion of the radiation plate. It is characterized by being a slot group.

According to the invention of claim 4,
In the planar antenna according to a third aspect of the present invention, the radiation slot is composed of a plurality of the minute slot groups having the same center and different diameters.

Further, in the invention according to claim 5,
In the planar antenna according to any one of claims 1 to 4,
The high frequency current in the 12 GHz band is approximately 11.7 GHz
To 12 GHz.

Further, in the invention according to claim 6,
In the planar antenna according to any one of claims 1 to 5,
The power feeding means and the phase adjusting means are respectively located at a distance of ¼ of the inner diameter L from the axial position of the cavity, with an included angle of 135 °, and the radiation plate is the conductor plate. A circularly polarized radiation electromagnetic field having directivity is generated on the plane side symmetrical with.

According to the invention of claim 7,
In the planar antenna according to any one of claims 1 to 5,
The power feeding means and the phase adjusting means are respectively located at a distance of ¼ of the inner diameter L from the axial position of the cavity, with an included angle of 135 °, and the radiation plate is the conductor plate. It is characterized in that it has a reception characteristic of a circularly polarized wave having directivity on the plane side symmetrical with.

[0015]

According to the present invention, a radiation plate having a radiation slot, a conductor plate spaced apart from and parallel to the radiation plate, and a cavity formed inside by a conductor are formed between the radiation plate and the conductor plate. A cavity resonator that has a protruding annular portion and is attached to the outer center portion of a conductor plate that faces the radiation plate, a power feeding means that penetrates the bottom of the cavity and projects into the cavity to feed high-frequency current, and a cavity inside the cavity. A plane antenna is constituted by the phase adjusting means attached to the bottom, the inner diameter L of the annular portion is 29 mm or more and 31 mm or less, and the distance G from the radiation plate to one end of the annular portion is 1 mm or more and 3 Mm or less, the axial length D of the annular portion is 4 mm or more and 6 mm or less,
And the sum of the distance G and the length D is 5 mm or more and 8
By forming the electric power feeding means and the phase adjusting means at a distance of ¼ of the inner diameter L from the axial position of the cavity and forming an included angle of 135 ° with each other,
For a frequency of approximately 11.7 GHz to 12 GHz, a radiation field of circularly polarized wave having directivity is generated, or a receiving characteristic of circularly polarized wave having directivity is realized, and a high gain is obtained.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a planar antenna 1 according to an embodiment of the present invention.
1A is a front view, and FIG. 1B is A in FIG.
FIG. 1C is a detailed configuration diagram in a broken line frame 6a (described later) in FIG. 1A.

2 in FIG. 1 (a) and FIG. 1 (b).
Is a disc-shaped conductor plate, and the front side of the radiation plate 2 (see FIG.
An annular portion 2a projects on the left side in (b).
A radiation plate 3 of a conductor having a diameter equal to the inner diameter of the annular portion 2a is placed on one end side of the annular portion 2a. This radiation plate 3
An annular dielectric 4 is sandwiched between the conductive plate 2 and the conductor plate 2, and there is no gap between the outer periphery of the radiation plate 3 and the annular portion 2a, and the end of the radial waveguide formed by the dielectric 4 is formed. The part is completely short-circuited. In the present invention, the dielectric 4 includes
For example, foamed polyethylene having a relative dielectric constant of 1.17 to 2.3 is used.

A plurality of slot groups 6, 6 ... (Radiation slots) arranged concentrically are formed on the radiation plate 3 (shown by a chain line in FIG. 1A). As shown in FIG. 1C, this slot group 6 (micro slot group) has a plurality of micro slots (elongated small holes) 6b, 6b ... Which penetrate the radiation plate 3 arranged with a predetermined regularity. I am configuring.

On the back surface of the planar antenna 1 (on the right side in FIG. 1B), a cavity resonator 7 formed by a conductor having a cylindrical appearance, with a part thereof penetrating the central portion of the conductor plate 2. Is attached. 2A and 2B are diagrams showing a detailed configuration of the cavity resonator 7. FIG. 2A is a side sectional view and FIG. 2B is a front view (front perspective view).

2 (a) and 2 (b),
8 is the front side of the cavity resonator 7 (upper side in FIG. 2A)
It is an annular portion that protrudes to the outside. When the cavity resonator 7 is attached to the conductor plate 2, the annular portion 8 penetrates the conductor plate 2,
The end portion 8a has a gap length G from the radiation plate 3.
It is inserted up to the position of (distance from the radiation plate to one end of the annular portion).

The inside of the annular portion 8 is a cavity 9, the inner diameter of which is L, and from the bottom portion 10 of the cavity resonator 7 to the annular portion 8
To the end 8a of the (the length of the annular portion in the axial direction:
(Depth) is D.

Further, the bottom portion 10 of the cavity resonator 7 has a feed pin 11 (feed means) penetrating the bottom portion 10 and protruding toward the cavity 9 side.
Similarly, the phase adjusting pin 1 of the conductor rod protruding toward the cavity 9 side
2 (phase adjusting means) is attached. The power supply pin 11 is composed of a semi-rigid cable, a coaxial cable, or the like, and both the power supply pin 11 and the phase adjustment pin 12 are at a distance of L / 4 from the central axis O of the annular portion 8 and 135 ° to each other. It is attached without the included angle (Fig. 2
(See (b)).

Although not shown, the front surface of the planar antenna 1 and the side surface (outer peripheral surface) thereof are covered with a radome made of a material having extremely small permittivity and magnetic permeability.

When a high-frequency current of a predetermined frequency is supplied to the feeding pin 11 of the flat antenna 1 described above, FIG.
A circularly polarized radiation electromagnetic field (electromagnetic wave, radio wave) having directivity in the direction of arrow B shown in (b) is generated. Further, as a matter of course, a high frequency current can be taken out from the power feeding pin 11 as a receiving antenna having directivity with respect to an electromagnetic wave from the arrow B direction.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the planar antenna 1 of the present invention, the frequency bandwidth, the gain, the gain D, the inner diameter L, and the gap length G (hereinafter, these values will be referred to as “values”) of the cavity 9 with respect to a certain frequency. Reflection loss and goodness of polarization are determined.

Therefore, with the configuration shown in FIG.
Each characteristic of the planar antenna 1 of the present invention was measured. In the configuration shown in FIG. 3, a high frequency current is supplied from the network analyzer 13 to the power supply pin 11, and the disk 3'having a slightly smaller diameter is used.
The radiated electromagnetic field was detected by the probe 14 from the gap 5 part at a constant distance from the end part of the radial waveguide formed by. At this time, the plane antenna 1 was rotated from 0 ° to 360 ° in the direction of arrow C around the axis O of the annular portion 8 and the phase change of the radiated electromagnetic field in the circumferential direction was measured.

An embodiment in which each value is different will be described below. Here, in each of the following embodiments, a so-called satellite broadcasting frequency band (hereinafter referred to as a BS band) wave, that is, a frequency of approximately 11.7 GHz to 12 GHz is used.
The description will be given assuming that the antenna is applied to an antenna that transmits and receives radio waves up to.

A. First Embodiment FIG. 4 shows an inner diameter L of 30 mm and a gap length G of 1.5 m.
It is a figure which shows the relationship with respect to frequency when m and the depth D are 5.8 mm. As shown in FIG. 4, according to the present embodiment, the reflection loss is less than −20 dB in the BS band, and it can be said that the characteristic is good.

FIG. 5, FIG. 6 and FIG. 7 show changes and amplitudes of the phase (φ) in the circumferential direction of the detected electromagnetic wave when the frequency is 11.7 GHz, 11.85 GHz or 12 GHz in the same embodiment. It is a figure which shows (M). Needless to say, when the plane antenna 1 is rotated as shown in FIG. 3, the phase of the detected electromagnetic wave changes uniformly, and a phase difference of 360 ° is obtained in one round, which is close to the condition that the amplitude is constant. As a result, good circular polarization characteristics are obtained, and it can be said that this embodiment also has good characteristics satisfying these conditions.

B. Second Example FIG. 8 is a diagram showing the relationship between frequency and reflection loss when the inner diameter L is 30 mm, the gap length G is 2 mm, and the depth D is 6 mm. In this embodiment, the gap length G and the depth D are large as compared with the first embodiment described above, and therefore the sum of the gap length G and the depth D is also large, but as shown in FIG. It can be said that the reflection loss at -20 dB or less is a good characteristic.

FIG. 9, FIG. 10 and FIG. 11 show changes and amplitudes of the phase (φ) in the circumferential direction of the detected electromagnetic wave when the frequency is 11.7 GHz, 11.85 GHz or 12 GHz in the same embodiment. It is a figure which shows (M).
As can be seen from FIGS. 9 to 11, in this embodiment, the phase and amplitude characteristics are slightly disturbed. this is,
Although not shown, it is considered that an unnecessary transmission mode is generated between the bottom 10 of the cavity and the radiation plate 3, and this tendency becomes remarkable as the sum of the gap length G and the depth D increases.

C. Third Embodiment FIG. 12 shows that the inner diameter L is 30 mm, the gap length G is 3 mm,
It is a figure which shows the relationship of frequency vs. reflection loss in case depth D is 5 mm. As shown in FIG. 12, even in the present embodiment, the reflection loss in the BS band is -20 dB or less, and it can be said that the characteristic is good.

FIGS. 13, 14 and 15 show frequencies of 11.7 GHz and 11.85 GHz in the same embodiment, respectively.
Alternatively, when the frequency is 12 GHz, it is a diagram showing changes in the phase (φ) and amplitude (M) in the circumferential direction of the detected electromagnetic wave. Also in this embodiment, since the gap length G is larger and the sum of the gap length G and the depth D is larger than that in the first embodiment,
Disturbances are seen in the phase and amplitude characteristics as in the second embodiment.

D. Fourth Embodiment FIG. 16 shows that the inner diameter L is 30 mm, the gap length G is 1 mm,
It is a figure which shows the relationship of frequency versus reflection loss in case depth D is 4 mm. In this embodiment, the gap length G is smaller than that in the first embodiment, and therefore the gap length G
And the sum of depth D is also small. As shown in FIG. 16, in this embodiment, the reflection loss of −20 dB or less is narrow in the frequency bandwidth, and the reflection loss is large as a whole.

FIGS. 17, 18 and 19 show frequencies of 11.7 GHz and 11.85 GHz in the same embodiment, respectively.
Alternatively, when the frequency is 12 GHz, it is a diagram showing changes in the phase (φ) and amplitude (M) in the circumferential direction of the detected electromagnetic wave. As can be seen from FIGS. 17 to 19, the phase and amplitude characteristics are also disturbed in this embodiment. The tendency as seen in this embodiment becomes more remarkable as the gap length G is smaller and the sum of the gap length G and the depth D is smaller.

E. Fifth Embodiment FIG. 20 shows an inner diameter L of 29 mm and a gap length G of 1.5 m.
It is a figure which shows the relationship with respect to frequency when m and the depth D are 5.8 mm. As shown in FIG. 20, according to this embodiment, the frequency band in which the reflection loss is less than −20 dB is higher than that of the above-described first embodiment (see FIG. 4).
The tendency as seen in this embodiment becomes more remarkable as the inner diameter L becomes smaller.

F. Sixth Embodiment FIG. 21 shows an inner diameter L of 31 mm and a gap length G of 1.5 m.
It is a figure which shows the relationship with respect to frequency when m and the depth D are 5.8 mm. As shown in FIG. 21, according to this embodiment, the frequency band in which the reflection loss is less than −20 dB is lower than that of the first embodiment (see FIG. 4) described above.
The tendency as seen in this example becomes more remarkable as the inner diameter L increases.

From the above-mentioned respective embodiments, when the planar antenna 1 of the present invention is used for transmitting and receiving BS charged waves, the following tendencies are shown when the depth D and the gap length G of the cavity 9 are changed. I understand. When the gap length G is increased, the polarization characteristic is disturbed. When the gap length G is reduced, the reflection loss increases. When the depth D is increased, the unnecessary transmission mode occurs. When the depth D is reduced, the polarization characteristic is disturbed.

Furthermore, the following relationship is also found between the gap length G and the depth D. When the gap length G + the depth D becomes large, an unnecessary transmission mode occurs. When the gap length G + the depth D becomes smaller, the polarization characteristics are disturbed.

When the inner diameter L is changed, the following tendency is shown. When the inner diameter L is increased, the frequency band in which the reflection loss of -20 dB is guaranteed shifts to the lower side. When the inner diameter L is reduced, the frequency band in which the reflection loss of -20 dB is guaranteed shifts to the higher side.

As described above, when transmitting and receiving BS charged waves in the planar antenna 1 of the present invention, the cavity 9 is used.
When the depth D, the inner diameter L, and the gap length G satisfy the following conditions, the frequency bandwidth, the reflection loss, and the polarization characteristics are good. (A) Regarding the gap length G and the depth D 5 ≦ G + D ≦ 8 (1) where 1 ≦ G ≦ 3 (2) and 4 ≦ D ≦ 6 (both units are mm) .. (3) (b) Regarding inner diameter L 29 ≦ L ≦ 31 (unit is mm) (4)

[0042]

As described above, according to the present invention,
Radiation having a radiation plate having a radiation slot, a conductor plate facing the radiation plate in parallel and facing each other, and an annular portion formed by a conductor to form a cavity inside and projecting between the radiation plate and the conductor plate. By a cavity resonator attached to the outer center of the conductor plate facing the plate, a power feeding means that penetrates the cavity bottom and projects into the cavity to supply a high-frequency current, and a phase adjusting means attached to the cavity bottom inside the cavity. A planar antenna is configured, the inner diameter L of the annular portion is 29 mm or more and 31 mm or less, the distance G from the radiation plate to one end of the annular portion is 1 mm or more and 3 mm or less, and the axial direction of the annular portion. Has a length D of 4 mm or more and 6 mm or less and a sum of the distance G and the length D of 5 mm or more and 8 mm or less,
By forming the power feeding means and the phase adjusting means at a distance of a quarter of the inner diameter L from the position of the axis of the cavity with an included angle of 135 ° to each other, for example, satellite broadcasting currently used in Japan. In the 12 GHz band, which is the frequency band, the phase difference in the circumferential direction of the planar antenna is uniform and 36
It is possible to radiate an electromagnetic wave that changes by 0 ° and has a constant amplitude, and it is possible to realize a planar antenna with less reflection loss.

An example of the effect of the present invention is as shown in FIGS. 4 to 7, and the gain in this case is shown in FIG. The antenna aperture efficiency was obtained from the gain Ga shown in FIG.

[Equation 1] In this case, Di is the antenna effective diameter of the planar antenna 1 (in this case, the diameter of the radial waveguide) and is 23c here.
m and η are aperture efficiencies of the planar antenna 1, and here, 80% at a frequency of 11.85 GHz, and the unit of the gain Ga is d.
It is Bi. Thus, according to the present invention, approximately 12 GH
The effect that a plane antenna suitable for transmitting and receiving satellite broadcast waves using the z-band frequency can be realized can be obtained.

[Brief description of drawings]

FIG. 1 is a planer antenna 1 according to an embodiment of the present invention.
It is a block diagram which shows the structure of.

FIG. 2 is a configuration diagram showing a detailed configuration of a cavity resonator 7 in FIG.

3 is a configuration diagram showing a configuration for measuring a change in phase and amplitude in a circumferential direction of an electric field emitted by a cavity resonator 7 of the planar antenna 1 shown in FIG.

FIG. 4 is a plan view of the planar antenna shown in FIGS. 1 and 2.
Inner diameter L is 30 mm, gap length G is 1.5 mm, depth D
It is a figure which shows the relationship of frequency vs. reflection loss in case of is 5.8 mm (1st Example).

FIG. 5 is a diagram showing changes in phase (φ) and amplitude (M) of a detected electromagnetic wave in the circumferential direction when the frequency is 11.7 GHz in the example.

FIG. 6 is a diagram showing changes in the phase (φ) and amplitude (M) of the detected electromagnetic wave in the circumferential direction when the frequency is 11.85 GHz in the example.

FIG. 7 is a diagram showing changes in phase (φ) and amplitude (M) of a detected electromagnetic wave in the circumferential direction when the frequency is 12 GHz in the example.

FIG. 8 is a plan view of the planar antenna shown in FIGS. 1 and 2.
Inner diameter L is 30 mm, gap length G is 2 mm, depth D is 6
It is a figure which shows the relationship of frequency vs. reflection loss when it is mm (2nd Example).

FIG. 9 is a diagram showing changes in the phase (φ) in the circumferential direction and the amplitude (M) of the detected electromagnetic wave when the frequency is 11.7 GHz in the example.

FIG. 10 shows a frequency of 11.85 GHz in the embodiment.
The phase of the detected electromagnetic wave in the circumferential direction (φ)
It is a figure which shows the change and amplitude (M).

FIG. 11 is a diagram showing changes in the phase (φ) and amplitude (M) in the circumferential direction of the detected electromagnetic wave when the frequency is 12 GHz in the example.

FIG. 12 is a plan view of the planar antenna shown in FIGS. 1 and 2, having an inner diameter L of 30 mm, a gap length G of 3 mm, and a depth D.
It is a figure which shows the relationship between a frequency and a reflection loss when is 5 mm (3rd Example).

FIG. 13 is a diagram showing changes in the phase (φ) in the circumferential direction and the amplitude (M) of the detected electromagnetic wave when the frequency is 11.7 GHz in the example.

FIG. 14 shows a frequency of 11.85 GHz in the embodiment.
The phase of the detected electromagnetic wave in the circumferential direction (φ)
It is a figure which shows the change and amplitude (M).

FIG. 15 is a diagram showing changes in the phase (φ) and amplitude (M) of the detected electromagnetic wave in the circumferential direction when the frequency is 12 GHz in the example.

FIG. 16 is a plan view of the planar antenna shown in FIGS. 1 and 2, having an inner diameter L of 30 mm, a gap length G of 1 mm, and a depth D.
It is a figure which shows the relationship of a frequency vs. reflection loss when is 4 mm (4th Example).

FIG. 17 is a diagram showing changes in the phase (φ) and amplitude (M) in the circumferential direction of the detected electromagnetic wave when the frequency is 11.7 GHz in the example.

FIG. 18 is a frequency of 11.85 GHz in the example.
The phase of the detected electromagnetic wave in the circumferential direction (φ)
It is a figure which shows the change and amplitude (M).

FIG. 19 is a diagram showing changes in phase (φ) and amplitude (M) of a detected electromagnetic wave in the circumferential direction when the frequency is 12 GHz in the example.

20 is a diagram showing the relationship between frequency and reflection loss when the inner diameter L is 29 mm, the gap length G is 1.5 mm, and the depth D is 5.8 mm in the planar antenna shown in FIGS. 1 and 2. FIG. is there.

21 is a diagram showing the relationship between frequency and reflection loss when the inner diameter L is 31 mm, the gap length G is 1.5 mm, and the depth D is 5.8 mm in the planar antenna shown in FIGS. 1 and 2. FIG. is there.

FIG. 22 is a diagram showing a gain versus frequency Ga in the first example.

[Explanation of symbols]

1 planar antenna 2 conductor plate 3 radiation plate 4 Dielectric 6 slots 6b Micro slot 7 Cavity resonator 8 torus 9 cavities 10 bottom 11 Power supply pin 12 Phase adjustment pin D depth G gap length L inner diameter O axis

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanori Suzuki 1-5-1, Taito, Taito-ku, Tokyo Toppan Printing Co., Ltd. (72) Inventor Naohisa Goto 6-15-1, Dobashi, Miyamae-ku, Kawasaki-shi, Kanagawa Miyamaedaira Palm House A-514 (72) Inventor Makoto Ando 1-1 Kogura 1-kokura, Kawasaki-shi, Kanagawa 1-I- 312 (56) Reference JP-A-6-244634 (JP, A) JP-A-4-207703 ( JP, A) JP 5-283931 (JP, A) JP 5-152813 (JP, A) JP 60-199201 (JP, A) JP 4-54703 (JP, A) JP Flat 5-206727 (JP, A) Actual flat 4-85905 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01Q 13/18 H01Q 13/22

Claims (7)

(57) [Claims] 1. A radiation plate which is formed of a conductor and has a radiation slot, a conductor plate which is spaced apart from the radiation plate and faces the radiation plate in parallel, and a radiation plate and the conductor plate which are formed of a conductor and have a cavity formed therein. A cavity resonator having an annular portion projecting between and being attached to an outer central portion of the conductor plate facing the radiation plate, and a cavity resonator penetrating the cavity bottom and projecting into the cavity 12 GHz
A feeding means for supplying a high-frequency current of a (GHz) band and a phase adjusting means attached to the bottom of the cavity inside the cavity, the radiation slot being concentric with the annular portion as an axis.
Serial is formed on the radiation plate, a and 31 mm of inner diameter (diameter) L 29 millimeters or more of the annular portion, the distance G from the radiation plate to one end of the annular portion and 1 millimeter or more 3 mm or less, the axial length D of the annular portion is 4 mm or more and 6 mm or less, and the sum of the distance G and the length D is 5 mm or more and 8 mm or less. A flat antenna characterized by the above. 2. The ring-shaped dielectric except for the ring-shaped portion and the portion corresponding to the cavity is inserted between the radiation plate and the conductor plate. Plane antenna. 3. The radiation slot is a micro slot group composed of a plurality of micro slots arranged on a circle centered on the axis of the annular portion in the radiation plate. Item 3. The planar antenna according to item 1 or 2. 4. The planar antenna according to claim 3, wherein the radiating slot is composed of a plurality of micro slot groups having the same center and different diameters. 5. The planar antenna according to claim 1, wherein the high frequency current in the 12 GHz band belongs to a frequency of approximately 11.7 GHz to 12 GHz. 6. The radiation means and the phase adjusting means are respectively located at a distance of a quarter of the inner diameter L from the axial position of the cavity with an included angle of 135 °. Generate a circularly polarized radiation electromagnetic field having directivity on a plane side symmetrical with the conductor plate.
The planar antenna according to any one of 1. 7. The radiation means and the phase adjusting means are respectively located at a distance of a quarter of the inner diameter L from the axial position of the cavity, with an included angle of 135 °. The planar antenna according to any one of claims 1 to 5, characterized in that it has a circularly polarized wave reception characteristic having directivity on a surface side symmetrical with the conductor plate.