JP4516246B2 - antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an antenna, and more particularly to a basic radiating element or a general fixed element of a mobile telephone base station antenna that requires a high-gain performance with a flat shape and a stable frequency characteristic over a wide band or multiple frequencies. The present invention relates to an antenna effective when applied to a communication antenna.
[0002]
[Prior art]
FIG. 14 is a perspective view showing an example of a conventional microstrip array antenna with a parasitic element used as a basic radiating portion of a mobile telephone base station antenna.
In the _figure, 11 1, 11 _2, microstrip element consisting of unbalanced planar _circuit, 12 1, 12 _2, the microstrip _line, 13 1, 13 ₂ is inputted to the coaxial connector (not shown) Power supply terminals for transmitting the power to the microstrip lines (12 ₁ , 12 ₂ ), 14 ₁ and 14 ₂ are parasitic elements, and 15 is a dielectric substrate.
As shown in the figure, the other surface of the dielectric substrate 15 whose one surface is covered with a metal foil is radiated in the fundamental mode (the smallest shape at the coordinates in the diagram and in the Z direction) at the operating frequency. It is well-known that a microstrip element 11 composed of an unbalanced planar circuit excited in a mode in which the power is maximized is disposed, and an antenna that emits unidirectional radiation in a low posture is provided by supplying power to at least one end face. Street.
Further, based on the principle of directivity product, by arranging microstrip elements (11 ₁ , 11 ₂ ) in the X direction shown in FIG. The sharpness is increased, the gain is increased, and the microstrip elements (11 ₁ , 11 ₂ ) are arranged in the Y direction shown in FIG. Is sharpened and the gain is increased, so that it is often used when a high attitude and a high gain characteristic are required.
[0003]
[Problems to be solved by the invention]
In the antenna described above, the microstrip elements (11 ₁ , 11 ₂ ) made of an unbalanced planar circuit have resonance characteristics and therefore have a narrow frequency characteristic.
When the antenna of the mobile phone base station is used for both transmission and reception, stable characteristics are required over a wide frequency range. Therefore, as shown in FIG. 14, parasitic elements (14 ₁ , 14 ₂ ) are replaced with microstrip elements. It is arranged so as to be parallel to (11 ₁ , 11 ₂ ) to improve the frequency characteristics or increase the thickness of the dielectric of the dielectric substrate 15 to make the resonance characteristics moderate. Measures are taken.
However, in any case, in order to form the microstrip element 11, it is necessary to use an expensive dielectric substrate 15 having good high frequency characteristics, and a plurality of elements are arranged to increase the gain. However, there is a problem that the cost increases.
The present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is to limit the use of a dielectric substrate having good high frequency characteristics and an expensive dielectric substrate used in a conventional antenna. The object is to provide a very lightweight and economical antenna.
The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.
[0004]
[Means for Solving the Problems]
Of the inventions disclosed in this application, the outline of typical ones will be briefly described as follows.
That is, the present invention provides a reflector, a dipole element disposed substantially in parallel with the reflector on the front surface of the reflector, and a distance from the dipole element on the side opposite to the reflector of the dipole element. An antenna including first and second parasitic elements disposed substantially parallel to the dipole element, wherein the dipole element includes the first and second parasitic elements. One open end is disposed with the projection surface of the first parasitic element and the other open end overlaps with the projection surface of the second parasitic element when projected onto the projected surface. The first and second parasitic elements satisfy λo ≦ L ≦ 2λo, where L is the perimeter and λo is the free space wavelength of the operating frequency.
[0005]
The present invention also provides a reflecting plate, first and second dipole elements arranged in a point-symmetric manner substantially in parallel with the reflecting plate on the front surface of the reflecting plate, and the reflecting plate of the first dipole element. On the opposite side of the first dipole element, spaced apart from the first dipole element, and substantially parallel to the first dipole element, and the second dipole element An antenna comprising third and fourth parasitic elements arranged on a side opposite to the reflector plate at a distance from the second dipole element and substantially parallel to the second dipole element; In the first dipole element, when the first and second parasitic elements are projected onto the surface on which the first dipole element is disposed, one open end is projected from the first parasitic element. Surface and the other open end are said second unpaid The second dipole element is disposed so as to overlap the projection surface of the element, and the second dipole element is opened when the third and fourth parasitic elements are projected onto the surface on which the second dipole element is disposed. The first through fourth parasitic elements are arranged such that the end overlaps with the projection surface of the third parasitic element, and the other open end overlaps with the projection surface of the fourth parasitic element. When the perimeter is L and the free space wavelength of the used frequency is λo, λo ≦ L ≦ 2λo is satisfied.
[0006]
When the dipole element is brought close to the reflecting plate in parallel, a large electric field is generated between the open end of the dipole element and the reflecting plate, although the direction of each vector is different. Further, when the parasitic element resonates, a strong electric field is generated between the opposing end of the parasitic element and the reflecting plate.
Accordingly, when a pair of parasitic elements are arranged in parallel to the reflector as in the present invention and the dipole element is interposed between the parasitic element and the reflector, the open end of the dipole element is obtained. Of the dipole element, the electric field generated at the end of the open end of the dipole element is applied to each parasitic element corresponding to the end. Can be combined.
By appropriately adjusting the resonance frequency of the dipole element and the parasitic element and the positional relationship between them, the band in which the frequency characteristic is stabilized can be adjusted based on the principle of the double tuning circuit.
[0007]
Since the parasitic element is excited in the fundamental mode of the microstrip antenna by the unbalanced planar circuit, for example, when it is a square, there is one side when no dielectric is interposed between the parasitic element and the reflector. The length is ½ wavelength in the free space wavelength used, and the perimeter of the contour is two wavelengths.
The radiation from the parasitic element is due to the magnetic current generated in the space between the outline of the element and the corresponding reflector, so the outer shape of the parasitic element is not limited to a square. Even if the shape of the parasitic element is a maximum of two wavelengths, the shape of the parasitic element may be a circle, a polygon, or the like.
If a dielectric is interposed between the parasitic element and the reflecting plate, the size of the parasitic element can be reduced, and it is effective to widen the band to some extent, but a dielectric having a very large relative dielectric constant is interposed. In this case, the wideband characteristic is lost and the gain of the element is also reduced. Therefore, the length of the outline of the parasitic element should preferably be longer than one wavelength and smaller than two wavelengths in the free space wavelength to be used. is there.
That is, when the circumference of the parasitic element is L and the free space wavelength of the use frequency is λo, it is necessary to satisfy 1λo ≦ L ≦ λo.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.
[Embodiment 1]
FIG. 1 is a perspective view showing an antenna according to Embodiment 1 of the present invention.
In Figure _1, 1 1 to 1 ₃ the plate-like conductor, the dielectric substrate 2, 3 microstrip line, the feed terminal _4, 5 1, _{5 2} a pair of parasitic element, 7 reflector 10 The dipole element 20 is a notch.
In the dipole element 10, two plate conductors (1 ₁ , 1 ₂ ) are arranged on one surface of the dielectric substrate 2, and each conductor has a notch portion at 20 points shown in FIG. which are connected to the plate-shaped conductor 1 _3.
And two plate-shaped conductors (1 _{1, 1 2),} the plate-shaped conductor 1 ₃ (in FIG. 1, the surface facing the reflecting plate 7) on a surface of the dielectric substrate 2 is provided.
Shape formed by two plate-shaped conductors (1 _{1, 1 2)} of the notch portion plate conductor 1 _3, in order to excite the equilibrium current, to become symmetrical with respect to Y-Z plane Is desirable.
[0009]
The dielectric substrate 2 is disposed so as to be parallel to the reflecting surface of the reflecting plate 7.
In order to maintain the parallel distance between the reflecting plate 7 and the dielectric substrate 2, for example, a solid dielectric is appropriately filled between the reflecting plate 7 and the dielectric substrate 2, or a spacer made of an appropriate material is used. The both are joined together by interposing.
FIG. 2 is a diagram showing the shapes of the two plate-like conductors (1 ₁ , 1 ₂ ), the plate-like conductor 1 ₃ , and the microstrip line 3 shown in FIG.
As shown in FIG. 2 (a), the plate-like conductor 1 _3, at its front end, a longitudinal slot 21 of the plate-like conductor 1 ₃ is provided.
An end portion facing each of the two plate-shaped conductors (1 _{1, 1 2),} at the front end portion of the plate-like conductor 1 _3, provided continuously to the divided portion in the longitudinal direction of the slot 21.
That is, a notch 20 in the width direction of the plate conductor is provided between the opposing ends of the two plate conductors (1 ₁ , 1 ₂ ), and the inner ends of the conductors divided by the notch 20 (FIG. 2). 22 of (a); to a feed point), the front end portion of the plate-like conductor 1 _3, is divided portions in the longitudinal direction of the slot 21 are connected.
[0010]
The microstrip line 3 constitutes a feeding circuit, and as shown in FIG. 2B, the other surface of the dielectric substrate 2 (the surface facing the parasitic elements (5 ₁ , 5 ₂ ) in FIG. 1). Provided.
The microstrip line 3, with a portion of the plate-shaped conductor 1 _3, the equilibrium by the branch conductors respectively - constitute the - unbalanced conversion circuit (unbalanced conversion balanced by microstrip line).
Microstrip line 3, the coaxial feed pipe _61, a signal connected to the radio via the feed terminal 4, to excite the dipole elements 10.
FIG. 1 shows an example in which the dielectric substrate 2 is used to form the dipole element 10. However, if the dipole element is balanced and fed, the shape of the element is plate, columnar, cylindrical. Any type of balanced-unbalanced converter may be selected from the shape and loss.
[0011]
A pair of parasitic elements (5 ₁ , 5 ₂ ) arranged so as to be parallel to the reflector 7 constitute the dipole element 10 so that the dipole elements 10 can match the electric power induced in each element. two plate-like conductors (1 _{1, 1 2),} it is desirable to disposed symmetrically symmetry plane of the plate-like conductor 1 ₃ with a cutout portion (Y-Z plane).
In addition, the end portion of the dipole element 10 (that is, the end portions of the two plate conductors (1 ₁ , 1 ₂ ) that are not opposite to each other) is formed by the pair of parasitic elements (5 ₁ , 5 ₂ ) and the reflector 7. Arranged to be sandwiched.
That is, when the pair of parasitic elements (5 ₁ , 5 ₂ ) is projected onto the surface on which the _two plate conductors (1 ₁ , 1 ₂ ) constituting the dipole element 10 are arranged, the plate conductor 1 ₁ end which is not connected with the plate conductor 1 ₃ is arranged so as to overlap the first parasitic element 5 ₁ of the projection plane, the end portion not connected to the plate-shaped conductor 1 ₃ of the plate-shaped conductor 1, _second It arrange | positions so that it may overlap with the projection surface of ₂ parasitic elements 52.
[0012]
In order to arrange the dipole element 10 and the pair of parasitic elements (5 ₁ , 5 ₂ ), a conductor foil pattern is formed by applying a conductor on a dielectric plate and using an etching technique used in a method for forming a printed wiring board. There is a method of mechanically connecting to the reflector 7 by interposing an insulating support material at an important point.
In the case of dipole elements 10, a portion of the coaxial waveguide _61, by adding a flange 6 _2, which a reflector 7 may be fixed to.
The center portion of the parasitic element (5 _{1, 5 2),} since the electric field distribution is minimized, if this portion, so that the vertical to the parasitic element (5 _{1, 5 2),} metal or the like There is no problem even if it is connected to the reflector 7 using the conductor.
[0013]
FIG. 3 is a graph showing an example of the frequency characteristic of the return loss of the antenna according to the present embodiment.
The graph shown in FIG. 3 shows the dimensions of each part of the antenna shown in FIG. 1. (1) The parasitic elements (5 ₁ , 5 ₂ ) have one side of 0.34λo (λo; free space wavelength at the used center frequency). square, the distance between the reflector 7 and (2) parasitic element ₍₅ 1, _{5 2),} 0.106Ramudao, the distance between (3) the parasitic element _{5 1} and the parasitic element _{5 2,} 0. 472λo, (4) the width of the plate-like conductor (1 ₁ , 1 ₂ ) is 0.047λo, (5) the total length of the plate-like conductor (1 ₁ , 1 ₂ ) is 0.395λo, (6) the dipole element 10 The distance between the surface formed by the reflector 7 and the reflector 7 is 0.047λo, (7) the length of the side of the reflector 7 parallel to the dipole element 10 is 1.18λo, and the length of the side orthogonal to this is 0. In the case of a rectangular reflector of 885λo, the frequency characteristics of the return loss at the feed terminal 4 are shown. Than is.
The use center frequency (fo) is the center frequency of the upper limit frequency and the lower limit frequency that are planned to be used.
From the graph shown in FIG. 3, it can be seen that the specific bandwidth with respect to the used center frequency (λo), in which the return loss is better than 14 dB (VSWR 1.5 or less), is 30% or more, and the bandwidth is increased.
[0014]
FIG. 4 is a graph showing the directivity characteristic in the magnetic field plane (YZ plane shown in FIG. 1) of the antenna used when measuring the graph shown in FIG. 3, and the measurement result at a frequency of 0.915 fo. Is shown.
FIG. 5 is a graph showing the directivity characteristics in the magnetic field plane (YZ plane shown in FIG. 1) of the antenna used when measuring the graph shown in FIG. 3, and the measurement result at 1.085 fo. Is shown.
Both directivity characteristics have a power half-value angle (beam width) of about 70 °, indicating that it is stable against changes in frequency.
FIG. 6 is a graph showing directivity characteristics in the electric field plane (XZ plane shown in FIG. 1) of the antenna used when measuring the graph shown in FIG. 3, and the measurement result at a frequency of 0.915 fo. Is shown.
FIG. 7 is a graph showing the directivity characteristics in the electric field plane of the antenna (XZ plane shown in FIG. 1) used when measuring the graph shown in FIG. 3, and the measurement result at a frequency of 1.085 fo. Is shown.
Both directivity characteristics have a power half-value angle of about 45 ° and are found to be stable against changes in frequency.
The reason why the beam width of the electric field in-plane directivity is sharper than that in the magnetic field in-plane is based on the principle of directivity product, and a pair of parasitic elements (5) arranged in the X direction by the dipole element 10. ₁ , 5 ₂ ) is also a proof of effective excitation.
[0015]
[Embodiment 2]
FIG. 8 is a perspective view showing an antenna according to the second embodiment of the present invention.
_8, 1 1 to 1 ₃ the plate-like _conductor, 3 1, _{3 2} microstrip line, the feed terminal _4, 5 1 to 5 ₄ are parasitic element, 7 _reflector 10 1, 10 ₂ It is a dipole element.
The first dipole element 10 ₁ and the second dipole element 10 ₂ are arranged point-symmetrically with respect to the feeding terminal 4, but the first dipole element 10 ₁ and the second dipole element 10 ₂ are The structure is the same as that of the dipole element 10 shown in FIG.
End of the dipole element 10 ₁ (i.e., the two plate-shaped conductors ₍₁ 1, _{1 2)} opposite to not end of) is sandwiched between a reflector 7 pair of parasitic element ₍₅ 1, _{5 2)} arranged to be, also, the ends of the dipole elements 10 ₂ (i.e., two plate-shaped conductor ₍₁ 4, ₁ opposed to not end of ₅₎₎ is a pair of parasitic element ₍₅ 3, _{5 4} ) And the reflector 7.
That is, the pair of parasitic element ₍₅ 1, _{5 2),} two plate-shaped conductors ₍₁ 1, _{1 2)} when projected onto the surface is arranged, plate-shaped conductor _{1 1} of the plate-like conductor _{1 3} end which is not connected with is arranged so as to overlap the first parasitic element 5 ₁ of the projection plane, the end not connected to the plate-shaped conductor 1 ₃ of the plate-shaped conductor 1 ₂ is the second parasitic element 5 _When a pair of parasitic elements (5 ₃ , 5 ₄ ) is projected onto a surface on which two plate-like conductors (1 ₄ , 1 ₅ ) are arranged, they are arranged so as to overlap with the _two projection planes. conductor 1 ₄ plate conductor 1 ₆ end which is not connected with is arranged so as to overlap the third parasitic element ₃ of the projection plane, not connected to the plate-shaped conductor 1 ₆ plate-shaped conductor 1 ₅ end Are arranged so as to overlap the projection surface of the _fourth parasitic element 54.
[0016]
The antenna of this embodiment is an antenna shown in FIG. 1 arranged in two rows with a spacing of 0.472 λo in the Y direction.
FIG. 9 is a graph showing an example of the frequency characteristic of the return loss of the antenna according to the present embodiment.
The graph shown in FIG. 9 shows the dimensions of each part of the antenna shown in FIG. 8, as in the antenna shown in FIG. 1, (1) a parasitic element (5 _{1 to} 5 ₄ ) and a square with a side of 0.34λo. , (2) the distance between the reflector 7 and the parasitic elements _{(5 1 ~5 4), 0.106λo} , (3) the parasitic element _{5 1} the spacing between parasitic element _{5 2} and the parasitic element 5 ₃ and the distance between the parasitic element _{5 4, 0.472λo,} the width of (4) plate-shaped conductor _{(1 1, 1 2, 1} 4, 1 5), 0.047λo, (5) a plate-like conductor The total length of (1 ₁ , 1 ₂ , 1 ₄ , 1 ₅ ) is 0.395λo, (6) the distance between the surface formed by the dipole element (10 ₁ , 10 ₂ ) and the reflector 7 is 0.047λo, ( 7) Frequency of return loss at the feed terminal 4 when the reflector 7 is a square reflector having a side length of 1λo. It shows the characteristics.
From the graph shown in FIG. 9, it can be seen that the band width is about 35%, which is about 35%, with respect to the center frequency of use where the return loss is better than 14 dB (VSWR 1.5 or less).
[0017]
FIG. 10 is a graph showing the directivity characteristics in the magnetic field plane (YZ plane shown in FIG. 8) of the antenna used when measuring the graph shown in FIG. 9, and the measurement result at a frequency of 0.915 fo. Is shown.
FIG. 11 is a graph showing the directivity characteristics in the magnetic field plane (YZ plane shown in FIG. 8) of the antenna used when measuring the graph shown in FIG. 9 , and the measurement result at 1.085 fo. Is shown.
Both of the directivity characteristics have a power half-value angle (beam width) of about 50 ° and are found to be stable against changes in frequency.
FIG. 12 is a graph showing the directivity characteristics in the electric field plane (XZ plane shown in FIG. 8) of the antenna used when measuring the graph shown in FIG. 9, and the measurement result at a frequency of 0.915 fo. Is shown.
FIG. 13 is a graph showing the directivity characteristics within the electric field plane (XZ plane shown in FIG. 8) of the antenna used when measuring the graph shown in FIG. 9, and the measurement result at a frequency of 1.085 fo. Is shown.
Both directivity characteristics have a power half-value angle of about 50 ° and are found to be stable against changes in frequency.
It can be seen that by arranging the parasitic elements (5 _{1 to} 5 ₄ ) vertically and horizontally at equal intervals like the antenna of the present embodiment, substantially the same directivity can be obtained in both the magnetic field plane and the electric field plane.
[0018]
As described above, it is possible to increase the gain of the antenna by a simple method in which the pair of parasitic elements (5 _{1 to} 5 ₄ ) are arranged on the dipole elements (10, 10 ₁ , 10 ₂ ). In addition, since it is possible to realize a wide band based on the principle of a double-tuned circuit of dipole elements (10, 10 ₁ , 10 ₂ ) and parasitic elements (5 _{1 to} 5 ₄ ), microstrip The high-frequency characteristics required to be used for the array antenna are good, the use of an expensive dielectric substrate can be limited, and an extremely light and economical antenna can be realized.
As described above, the radiation from the parasitic element (5 _{1 to} 5 ₄ ) is due to the magnetic current generated in the space between the outline of the element and the reflecting plate corresponding thereto, so that the parasitic element The outer shape of (5 _{1 to} 5 ₄ ) is not limited to a square, and even if it is a shape other than a square, if the length of the outline of the parasitic element is a maximum of two wavelengths, the outer shape is circular and many It may be a shape such as a square.
Although the invention made by the present inventor has been specifically described based on the above-described embodiment, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. Of course.
[0019]
【The invention's effect】
The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.
According to the present invention, it is possible to limit the use of an expensive dielectric substrate that is used in a conventional antenna and has good high-frequency characteristics, and can provide an extremely lightweight and economical antenna. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an antenna according to a first embodiment of the present invention.
2 is a diagram showing the shapes of two plate-like conductors (1 ₁ , 1 ₂ ), a plate-like conductor 1 ₃ , and a microstrip line 3 shown in FIG.
FIG. 3 is a graph showing an example of frequency characteristics of return loss of the antenna according to the first embodiment of the present invention.
4 is a graph showing an example of directivity characteristics in the magnetic field plane (YZ plane shown in FIG. 1) of the antenna according to the first embodiment of the present invention. FIG.
5 is a graph showing another example of directivity characteristics in the magnetic field plane (YZ plane shown in FIG. 1) of the antenna according to the first embodiment of the present invention; FIG.
6 is a graph showing an example of directivity characteristics in the electric field plane (XZ plane shown in FIG. 1) of the antenna according to the first embodiment of the present invention. FIG.
7 is a graph showing another example of directional characteristics in the electric field plane (XZ plane shown in FIG. 1) of the antenna according to the first embodiment of the present invention. FIG.
FIG. 8 is a perspective view showing an antenna according to the second embodiment of the present invention.
FIG. 9 is a graph showing an example of frequency characteristics of the return loss of the antenna according to the second embodiment of the present invention.
FIG. 10 is a graph showing an example of directivity characteristics in the magnetic field plane (YZ plane shown in FIG. 8) of the antenna according to the second embodiment of the present invention.
11 is a graph showing another example of directivity characteristics in the magnetic field plane (YZ plane shown in FIG. 8) of the antenna according to the second embodiment of the present invention. FIG.
12 is a graph showing an example of directivity characteristics in the electric field plane (XZ plane shown in FIG. 8) of the antenna according to the second embodiment of the present invention. FIG.
13 is a graph showing another example of directivity characteristics in the electric field plane (XZ plane shown in FIG. 8) of the antenna according to the second embodiment of the present invention. FIG.
FIG. 14 is a perspective view showing an example of a conventional microstrip array antenna with a parasitic element.
[Explanation of symbols]
1 ₁ to ₁₆ ... plate conductor, 2 ... dielectric substrate, 3, 3 ₁ , 3 ₂ , 12 ₁ , 12 ₂ ... microstrip line, 4, 13 ₁ , 13 ₂ ... feed terminal, 5 _{1 to} 5 ₄ , 14 ₁ , 14 ₂ ... parasitic element, 6 ₁ ... coaxial feeding pipe, 6 ₂ ... flange, 7 ... reflector, 10, 10 ₁ , 10 ₂ ... dipole element, 11 ₁ , 11 ₂ ... microstrip element, 15 ... Dielectric substrate, 20 ... cut, 21 ... slot, 22 ... feed point.

Claims (3)

A reflector,
A dipole element disposed substantially in front of the reflector on the front surface of the reflector;
An antenna comprising first and second parasitic elements arranged on the opposite side of the dipole element from the reflector, spaced apart from the dipole element and substantially parallel to the dipole element,
In the dipole element, when the first and second parasitic elements are projected onto a surface on which the dipole element is disposed, one open end is a projection surface of the first parasitic element, and the other Is arranged so that the open end of the second element overlaps the projection surface of the second parasitic element,
The antenna according to claim 1, wherein the first and second parasitic elements satisfy λo ≦ L ≦ 2λo, where L is a peripheral length and λo is a free space wavelength of a use frequency. A reflector,
First and second dipole elements disposed in front of the reflecting plate in a point-symmetric manner substantially parallel to the reflecting plate;
First and second parasitic elements disposed on the side of the first dipole element opposite to the reflector and spaced apart from the first dipole element and substantially parallel to the first dipole element. When,
Third and fourth parasitic elements disposed on the side of the second dipole element opposite to the reflecting plate, spaced apart from the second dipole element and substantially parallel to the second dipole element. An antenna comprising:
In the first dipole element, when the first and second parasitic elements are projected onto the surface on which the first dipole element is disposed, one open end is projected from the first parasitic element. And the other open end overlaps with the projection surface of the second parasitic element,
In the second dipole element, when the third and fourth parasitic elements are projected onto the surface on which the second dipole element is disposed, one open end is projected from the third parasitic element. And the other open end overlaps with the projection surface of the fourth parasitic element,
The first to fourth parasitic elements satisfy λo ≦ L ≦ 2λo, where L is a peripheral length and λo is a free space wavelength of a use frequency.   3. The antenna according to claim 1, wherein an outer shape of each of the first to fourth parasitic elements is a circular shape or a polygonal shape.

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