JP2001189620A - Array antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an array antenna having a directivity pattern suitable for radar together with impedance matching characteristics over a wide band capable of sufficiently guaranteeing performance against frequency characteristic fluctuation caused by a sever use environment (such as temperature change, for example), to become a problem in the case of loading on an airplane or the like. SOLUTION: This array antenna is composed of a power feeding element provided with a power feeding means, a first power non-feeding element arranged in front of the power feeding element within a wavelength of 0.1, and a second power non-feeding element arranged at the back of the power feeding element at an interval exceeding a wavelength of 0.1 at least.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an array antenna, and more particularly to a means for forming a unidirectional pattern using a parasitic element and broadening a frequency characteristic.

[0002]

2. Description of the Related Art A dipole antenna or a monopole antenna has a simple structure in which a feeding point is provided at a required portion of a linear conductor having a predetermined length, and has an advantage that it can be manufactured at low cost. Conventionally, it has been used for various applications. However, since these antennas have a narrow band characteristic as is well known, they cannot be used for applications that need to operate in a wide frequency bandwidth.

In view of the above problems, a dipole antenna having a configuration in which a parasitic element is arranged close to a feed element in order to improve the bandwidth characteristics is described in reference (1) "Ehine, Kagoshima,"
Multi-frequency Shared Dipole Antenna with Proximity Parasitic Element ", IEICE Transactions B, vol.J71-B, No.11, p.
p.1252-1258, November 1988 ". This antenna uses the current mobile phone system, PDC (Personal Dig).
It was developed for the purpose of sharing one 800MHz band analog system and 1.5GHz band digital system with one antenna in the ital Cellular) system. Since the detailed description of this antenna is described in the above-mentioned document, this will be briefly described below.

FIG. 16 is a perspective view showing a configuration example of a multi-frequency dipole antenna having a proximity parasitic element disclosed in the above-mentioned document. The multi-frequency dipole antenna shown in this example includes a feed dipole antenna 102 having a feed point 101 substantially at the center, and a feed dipole antenna 102
Are arranged on a circumference having a radius a with the center as a center.

The multi-frequency dipole antenna shown in FIG. 1 has a multi-frequency resonance characteristic corresponding to the element length of each of the parasitic elements 103, 104... By setting the radius a to about 0.025 wavelength. In addition, it exhibits an omnidirectional radiation pattern characteristic. FIG. 17 is a diagram showing a return loss characteristic representing an impedance matching state when four parasitic elements are used as an example of the multi-frequency dipole antenna. This characteristic is obtained by setting the radius a to 0.025 wavelength and the feed element
The length of the reference numeral 102 and each of the parasitic elements 103, 104,... Are set to 0.5 wavelength, 0.33 wavelength, 0.29 wavelength, 0.25 wavelength, and 0.22 wavelength, respectively. As is clear from this figure, the characteristic of this multi-frequency dipole antenna is a resonance frequency of 0.95f0 due to the feed element (point a in the figure, where f0 is the design frequency).
In addition to the above, there are resonance frequencies (points indicated by b to e in the same drawing) corresponding to the lengths of the four parasitic elements.

[0006]

However, the above-mentioned conventional multi-frequency dipole antenna has the following problems. That is, the conventional one has an omnidirectional characteristic as a radiation directivity pattern, and thus is not suitable for applications requiring a unidirectional pattern such as radar. In addition, it has characteristics that allow impedance matching only at a plurality of frequencies a to e (multi-frequency shared characteristics), but impedance matching is not possible in other frequency bands. Therefore, for example, there is a problem that the performance cannot be sufficiently guaranteed against frequency characteristic fluctuation due to severe use environment such as a sudden temperature change, which is a problem when mounted on an aircraft. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems related to the conventional multi-frequency dipole antenna, and has as its object to provide an array antenna having a unidirectional pattern with a wide-band impedance matching characteristic.

[0007]

According to a first aspect of the present invention, there is provided an array antenna according to the present invention, comprising: a feed element having at least feed means, and at least 0.1 wavelength in front of the feed element. And a second parasitic element arranged behind the feed element at an interval exceeding 0.1 wavelength. The invention according to claim 2 of the array antenna according to the present invention includes a feed element having at least feed means, and a feed element 0.1 in front of the feed element.
It comprises a first parasitic element functioning as a director arranged within a wavelength and a second parasitic element functioning as a reflector arranged behind the feeding element at an interval exceeding 0.1 wavelength. Claim 3 of the array antenna according to the present invention
The invention according to claim 1 or claim 2, wherein in the array antenna according to claim 1 or claim 2, a third parasitic element is arranged within 0.1 wavelength behind the feed element. Array antenna. The invention according to claim 4 of the array antenna according to the present invention is a monopole in which the feed element and each parasitic element are erected on a ground plate in the array antenna according to claim 1, claim 2 or claim 3. Antenna. The invention according to claim 5 of the array antenna according to the present invention is the array antenna according to claim 1, claim 2, claim 3 or claim 4, wherein the feed element and each parasitic element are provided on a dielectric substrate surface. It is formed using a conductor pattern.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. In the array antenna according to the present invention, the element length and arrangement interval of the antennas to be arranged are important parameters as described later, and the shape of the antenna element is a dipole, a monopole, an inverted F shape, an inverted L shape. , Top-load type monopole, any linear shape such as S-shaped, or circular, elliptical, triangular, square, rhombic or any closed curve shape (specific antenna shapes other than the above, Information and Communication Engineers, Antenna Engineering Handbook, p.2, "Section 1.3 Antenna Classification"
See description). Further, as disclosed in JP-A-9-55621, a combination of a plurality of types of antenna elements may be used.

[0009] Here, as an example of the element shape, it is necessary to install the antenna on a ground plate. However, since the surface of the moving body can be used as the ground plate, a monopole antenna suitable for mounting on a moving body such as an aircraft. Is applied to the array antenna according to the present invention. Figure
FIG. 1 is a side view of a configuration showing a basic embodiment of an array antenna according to the present invention configured using a monopole antenna. The array antenna shown in this example has a predetermined element length erected on the ground plate 11 and has a feed point to a required portion.
A first parasitic element 14 having a required element length of λ0 / 4 or less, which is disposed at a position away from the power supply element 13 by a distance A1 forward, and a power supply element 13 including the power supply element 13; It comprises a second parasitic element 15 having a required element length of λ0 / 4 or more, which is disposed at the rear thereof and separated by the distance Lr. Here, λ0 means the wavelength at the design frequency f0, and each element was configured using a linear conductor having a radius ra = 2.1 mm.

Such an arrangement in which a parasitic element of λ0 / 4 or less is disposed in front of the feed element and a parasitic element of λ0 / 4 or more is disposed in the rear thereof is known as a Yagi-Uda antenna. It is known that since the Yagi-Uda antenna operates based on the endfire array as a basic principle, it is necessary to set the distance between the feeding element and the parasitic element to 0.15 to 0.25λ0 (for this arrangement interval condition). Is also described in the above-mentioned reference (1), p. 1252, left column, preface, lines 6 to 7).

On the other hand, the array antenna according to the present invention
Unlike the operation principle of the conventional Yagi-Uda antenna, the first parasitic element 14 has an arrangement interval A1 with the feed element 13 of 0.1λ0 or less, so that the impedance characteristic is broadened and a predetermined frequency band is set. Is configured to function as a director only in the case of. Hereinafter, the function of each parasitic element will be described in detail. Each characteristic shown in FIG. 2 and subsequent figures is a value obtained by a simulation based on the moment method unless otherwise specified.

First, the function of the first parasitic element 14 will be described. FIG. 2 is a diagram illustrating frequency characteristics of return loss of a two-element array antenna including the first parasitic element 14 and the feed element 13 with respect to a 50Ω line. In the characteristics shown in this figure, the element length of the feed element 13 is Hf = 0.25λ0, and the arrangement interval is
Assuming that A1 = 0.05λ0, the length H1 of the first parasitic element 14 is λ0 / 4
It is changed in the following range. This return loss characteristic has a resonance point whose frequency depends on the feed element length Hf around 0.95f0, and is generally used to show antenna band performance.VSWR ≦ 2 (RL ≦ −9.54 dB, (RL means return loss) and evaluate the band (the band below the auxiliary line of VSWR = 2 in the figure).
It can be seen that the band shows a wide band characteristic of% to 60%. Also, H1 is 0.
If shorter than 14λ0, a predetermined high frequency (f / f0
= 1.7 or f / f0 = 1.9), VSWR ≦ 2
The dual frequency characteristics are shown.

FIG. 3 is a diagram showing a first example in which the arrangement interval A1 is used as a parameter.
FIG. 7 is a diagram showing a bandwidth of VSWR ≦ 2 with respect to the length H1 of the parasitic element 14 of FIG. As a parameter related to the first parasitic element 14, when H1 is set to about 0.1475λ0 when A1 = 0.05λ0, the maximum bandwidth (about 60%) is obtained.

FIG. 4 shows that A1 = 0.05 at which the maximum bandwidth is obtained.
At λ0, a diagram showing a frequency characteristic of a front (−x-axis direction) and a rear (+ x-axis direction) gain ratio Gd / Gr representing the front-back ratio of the directivity pattern to the length H1 of the first parasitic element 14. It is. Contrary to the basic principle of the Yagi-Uda antenna, the first parasitic element 14 is arranged close to the feed element 13 so that Gd / Gr
Is almost 0dB (meaning omnidirectional pattern), but 1.3
In the frequency band above 6f0, no matter what value H1 is set to, G
It has been found that there is an optimum value of d / Gr ≧ 20 dB and that the bandwidth satisfying Gd / Gr ≧ 10 dB indicating a unidirectional pattern has a value of about 18% with respect to f0. In other words, it has been thought that, as in the case of the multi-frequency dipole antenna shown in FIG. To exhibit unidirectionality in a higher frequency region than f0 (f / f0 = 1), that is, Yagi
Despite being different from the basic arrangement of the Uda antenna, they have found that there is a frequency band in which the parasitic element 14 arranged close to functions as a director.

As described above, the arrangement interval A1 and the element length H1 of the first parasitic element 14 are each set to a required length, for example, A1 =
By setting 0.05λ0 and H1 = 0.1475λ0, it is possible to realize a wide band of the impedance characteristic (return loss characteristic) and to operate the first parasitic element 14 as a director for forming a directional pattern. . Hereinafter, the first parasitic element 14 is referred to as a director.

Next, the function of the second parasitic element 15 will be described. The parasitic element 15 functions as a reflector for forming a broadband directional pattern in cooperation with the director 14 described above. Hereinafter, the second parasitic element 15 is referred to as a reflector.

FIG. 5 is a diagram showing the frequency characteristics of Gd / Gr in a two-element array antenna composed of the feeding element 13 and the reflector 15 using the element length H4 of the reflector as a parameter. Figure
As is apparent from FIG. 5, by setting the element length H4 to a required length, the reflector 15 can function so that Gd / Gr becomes maximum at a frequency lower than f0. In addition,
FIG. 7 shows a case where Lr = 0.2λ0 as an example of the arrangement interval. However, in the range of Lr = 0.15λ0 to 0.25λ0, there is almost no difference in Gd / Gr characteristics.

On the other hand, as described above, the director 14 is
As shown in FIG. 4, the two-element array antenna arranged close to 13 has a larger Gd / Gr on the higher frequency side than the frequency f0, but has a Gd / Gr of almost 0 dB below the frequency f0. By adding the reflector 15 having the required element length H4, the Gd / Gr characteristics can be increased over a wide frequency range.

As a basic embodiment, the two parasitic elements of the three-element array antenna according to the present invention shown in FIG. 1 are set to the required parameters described above, and each is set to the director 14.
And reflector 15, it is possible to realize broadband characteristics having the following directivity pattern. As an example, the parameters of the director 14 are set to A1 = 0.05λ0 and H1 = 0.1475λ0 at which the VSWR band is optimal, and the reflector
The characteristics when the element length of No. 15 is set to H4 = 0.275λ0 will be described.

FIG. 6 is a graph showing G in the three-element array antenna (basic embodiment) according to the present invention set to the above parameters.
FIG. 9 is a diagram illustrating the frequency characteristic of d / Gr using the distance Lr between reflectors as a parameter. For comparison, the figure also shows characteristics without the reflector 15 and experimental values (Δ marks) of a type 1 shape described later for comparison. The Gd / Gr characteristic is 1.36f0 due to the operation of the reflector 15 shown in FIG.
It is greatly improved in the following frequency bands and exhibits a directivity pattern over a wide band. In particular, when Lr = 0.2λ0, the bandwidth of VSWR ≦ 2 (RL ≦ −9.54 dB) is broadly as 1: 1.67, which is almost the same as the characteristic without the reflector 15, as described later, which is advantageous from the impedance matching characteristic. Therefore, this shape is set as type 1 representing the basic embodiment, and the shape parameters are shown in Table 1.

[0021]

[Table 1]

FIG. 7 is a graph showing the return loss frequency characteristics of the three-element array antenna (basic embodiment) according to the present invention, using the distance Lr between the reflectors 15 as a parameter. The figure also shows the characteristics without the reflector 15 for comparison. When Lr = 0.15λ0, the characteristics are slightly deteriorated as compared with the case without the reflector 15, but when the reflector 15 is separated from the feeding element 13 by a predetermined distance or more as in Lr = 0.25λ0, it is almost the same as that without the reflector 15. VSWR ≤ 2 (RL ≤ -9.5) in a wide band with a frequency of approximately 0.9f0 to 1.5f0.
4dB). In any case, in the range of Lr shown in the figure, the array antenna according to the present invention has wideband characteristics.

FIG. 8 shows a horizontal plane of the type 1 according to the present invention.
FIG. 4 is a view showing a radiation pattern on (a surface including the ground plate 11). Here, “MoM” indicates a calculated value, and “Measured” indicates an experimental value. The figure shows data for 0.91f0 and 1.50f0, which are frequencies substantially at the lower and upper limits of the VSWR ≦ 2 band, and each radiation pattern shows good unidirectionality.

Next, the second embodiment of the array antenna according to the present invention will be described.
A second embodiment will be described. FIG. 9 is a side view showing the configuration of the second embodiment of the array antenna according to the present invention.
The array antenna shown in this figure has a third parasitic element having a required element length H2 between a feed element 13 and a second parasitic element (reflector) 15 in the configuration of the basic embodiment shown in FIG. Feed element
16 is arranged at a position away from the feed element 13 by a distance A2.

In the four-element array antenna, the element length H2 of the third parasitic element 16 is changed to the element length H of the first parasitic element 14.
It is characterized by being shorter than 1. As is clear from FIG. 2, the parasitic element is arranged closer to the feed element, and the shorter the element length, the more the resonance frequency on the high frequency side appears on the high frequency side. The bandwidth of the loss characteristic is expanded to a higher frequency side to further increase the bandwidth. To explain with a specific example, the above type1
7, the band of return loss characteristic of VSWR ≤ 2 (RL ≤ -9.54dB) is in the range of 0.9f0 to 1.5f0, and the return loss characteristic in the range of more than 1.5f0. Becomes almost 0 dB (total reflection). Therefore, A2 =
A third parasitic element having an element length H2 = 0.125λ0 shorter than the first parasitic element 14 is disposed at a position separated by 0.05λ0.
(Hereinafter, this shape is referred to as type 2.) From Fig. 2, the element length is set to 0.
If it is set to 125λ0, the resonance point on the high frequency side appears near 1.68f0 on the higher frequency side than 1.5f0, so that it is added to the return loss characteristics of type 1 and the band is expanded.

FIG. 10 is a diagram showing the return loss characteristics of this type2. This figure also shows the characteristics of the shape of type 2 in which the element length H1 of the director 14 is finely adjusted and H1 = 0.14λ0 (hereinafter, this shape is referred to as type 3). The shape parameters of type2 and type3 are shown in Table 1 above.
Are shown together with type1. The return loss characteristics of type 2 are improved over those of type 1 in the frequency band of 1.54f0 to 1.81f0 for the reasons described above. Also, in type 3 where the element length H1 of the director is finely adjusted,
VSWR = 2 (RL = -9.54 dB) A little deterioration in characteristics around frequency 1.60f0, but VSWR ≤ 2 (RL ≤ -9.54 dB)
Has a bandwidth of 1: 1.93, which is wider than type1. This broadband characteristic of type 3 is supported by the experimental values indicated by Δ. The configuration of H2 <H1 has been described above. In short, if H2 and H1 are set to different lengths, the characteristics of the respective parasitic elements are combined, and as a result, the return loss characteristic is broadened.

Next, the second embodiment of the array antenna according to the present invention will be described.
A third embodiment will be described. FIG. 11 is a side view showing the configuration of an array antenna according to a third embodiment of the present invention. The array antenna shown in this figure has a further required element length H3 in the configuration of the second embodiment shown in FIG.
A fourth parasitic element 17 having the following arrangement is arranged at a predetermined interval A3 in front of the first parasitic element 14.

The characteristics of the five-element array antenna can be further improved by appropriately adjusting the parameters related to the fourth parasitic element 17. As an example, a fourth parasitic element 17 is added to the type 3 shape,
The characteristics when A3 and H3 are varied will be described. First, in the range of 0.03λ0 to 0.2λ0 in the interval A3, H3 was varied and antenna characteristics were examined. As a result, when H3> H1, the bandwidth of the characteristic is rapidly deteriorated. However, when A3 is set to, for example, about 0.1λ0 to 0.15λ0 under the condition of H3 <H1, the return loss characteristic is further improved.

FIG. 12 is a diagram showing an example of return loss frequency characteristics in the third embodiment relating to the above parameters. In this characteristic, parameters related to the fourth parasitic element 17 are set to A3 = 0.1λ0 and H3 = 0.115λ0 (hereinafter, this shape is referred to as type4). According to the figure, type4 is VSWR ≦ 2 (RL
≤-9.54 dB) has a broadband performance close to one octave of 1: 1.93, which is fully supported by experimental values (Δ marks).

FIG. 13 is a diagram showing the Gd / Gr frequency characteristics of the type 4 shape together with the characteristics of type 1 and type 3. As a guide of the unidirectional pattern, for example, when evaluated at Gd / Gr ≧ 10 dB, the bandwidth of type 4 is greatly improved over type 3 and
It is about the same performance as.

Next, the directional gain of the array antenna of each of the above embodiments will be described. FIG. 14 is a diagram showing the frequency characteristics of the directional gain Gd of the type 1, type 3, and type 4 array antennas according to the present invention. Each directivity gain Gd has a maximum value near 0.86f0 and 1.63f0, and the shapes of type1 and type4 have a broadband performance of 1: 2.28 and 1: 2.1 and 1 octave or more as a bandwidth of Gd ≧ 8 dBi, respectively. Have.

Further, Table 2 shows the performance comparison between the array antenna according to the present invention and the conventionally proposed optimized Yagi-Uda antenna. However, the conventional one is optimized for the configuration of the six-element dipole Yagi-Uda antenna. Reference (2) "Konan, Mutsushima," One design method of Yagi-Uda antenna by nonlinear programming ", The values described in the IEICE Transactions (B), vol. J61-B, No. 1, pp. 9-16, Jan. 1978. "were used. An array antenna according to the present invention,
For example, the characteristics of type 4 consisting of 5 elements are wider than the conventional optimized characteristics using 6 elements, and in particular, the VSWR characteristics (return loss characteristics) are much larger than those of the conventional optimized. To be improved.

[0033]

[Table 2]

As described above, in the array antenna according to the present invention, by sequentially increasing the parasitic elements having a required element length at predetermined intervals, the antenna characteristics,
In particular, the improvement of the bandwidth with respect to the return loss characteristic (impedance characteristic) is remarkable. Therefore, it will be unnecessary to particularly explain that the antenna characteristics can be further improved (broadband) by further increasing the number of elements as compared with the configuration shown in the above embodiment.

In the above embodiment, the case where the array antenna is formed by using the linear conductor having the radius ra has been described. However, the present invention is not limited to this example. For example, the relative dielectric constant εr The dielectric substrate is vertically erected on a ground plate, and a conductor pattern constituting an array antenna shape according to the present invention such as the above-described type 1 to type 4 is formed on one surface of the substrate by copper foil by etching or the like. You may.
Hereinafter, this will be described.

FIG. 15 is a side view showing an example in which the array antenna of the basic embodiment is formed using a dielectric substrate. In the array antenna shown in this example, a dielectric substrate 20 is erected on the ground plate 11, and a feed element 22 and each parasitic element 23 having a required feed point 21 on one surface of the dielectric substrate 20 are provided.
24 are formed. Note that there is no conductor pattern on the surface opposite to the one surface. In this case, since the wavelength of the shape parameter is reduced to approximately λ / √εr to 0.95λ, the distance between the feeding element and each parasitic element, the feeding element length, and the length of each parasitic element in the basic embodiment described above. Also about 1 / √εr ~
It has to be reduced to 0.95. Further, a plate-like conductor may be held on one surface of a dielectric such as a foam material by an adhesive or the like, and the above-mentioned conductor pattern may be formed by the plate-like conductor. In this case, since εr ≒ 1, the distance between the feeding element and each parasitic element, the length of the feeding element and the length of each parasitic element need not be reduced.

[0037]

According to the present invention, as described above, a feed element and a plurality of parasitic elements each having a required element length are arranged at predetermined intervals, and have a directivity pattern while having a simple structure. This is very effective in realizing an array antenna with wide band characteristics.

[Brief description of the drawings]

FIG. 1 shows a basic embodiment (3) of an array antenna according to the present invention.
Side view showing (element configuration)

FIG. 2 is a frequency characteristic diagram of return loss in a two-element array antenna including a first parasitic element and a feed element used in a basic embodiment according to the present invention.

FIG. 3 is a diagram showing a bandwidth characteristic of VSWR ≦ 2 in a two-element array antenna including a first parasitic element and a feed element used in the basic embodiment according to the present invention;

FIG. 4 is a diagram showing frequency characteristics of Gd / Gr in a two-element array antenna including a first parasitic element and a feed element used in a basic embodiment according to the present invention;

FIG. 5 is a diagram showing the frequency characteristics of Gd / Gr in a two-element array antenna including a second parasitic element (reflector) and a feeding element used in the basic embodiment according to the present invention.

FIG. 6 is a diagram showing frequency characteristics of Gd / Gr in the basic embodiment according to the present invention.

FIG. 7 is a diagram showing frequency characteristics of return loss in the basic embodiment according to the present invention.

FIG. 8 is a view showing a radiation pattern in a horizontal plane of a type 1 shape representing a basic embodiment according to the present invention.

FIG. 9 shows a second embodiment of the array antenna according to the present invention.
Side view showing (4-element configuration)

FIG. 10 is a diagram showing frequency characteristics of return loss in a second embodiment (four-element configuration) of the array antenna according to the present invention;

FIG. 11 is a side view showing a third embodiment (five-element configuration) of the array antenna according to the present invention.

FIG. 12 is a diagram showing frequency characteristics of return loss in a third embodiment (five-element configuration) of the array antenna according to the present invention;

FIG. 13 is a diagram showing frequency characteristics of Gd / Gr in a third embodiment (five-element configuration) of the array antenna according to the present invention.

FIG. 14 shows a directional gain of an array antenna according to the present invention.
Diagram showing frequency characteristics of Gd

FIG. 15 is a side view showing an example in which the array antenna of the basic embodiment is configured using a dielectric substrate.

FIG. 16 is a perspective view showing a configuration example of a conventional multi-frequency dipole antenna.

FIG. 17 is a diagram showing return loss characteristics of a conventional multi-frequency shared dipole antenna.

[Explanation of symbols]

 11 Ground plane 12 Feed point 13 Feed element 14 First parasitic element 15 Second parasitic element 16 Third parasitic element 17 Fourth parasitic element element

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Chen Qiang, 1-33-506, Migamimine 1-chome, Taishiro-ku, Sendai, Miyagi Prefecture (72) Inventor Kunio Sawaya 4-2-1, Yawata, Aoba-ku, Sendai, Miyagi F Terms (reference) 5J020 AA03 BA02 BC02 BC08 DA01 DA04 DA08 5J021 AA03 AA04 AA05 AA07 AB02 BA01 GA02 GA08 HA10 JA02 JA03 5J070 AD08 AF06 AK40 BC06

Claims (5)

[Claims] 1. A feeding element having at least feeding means, a first parasitic element arranged within 0.1 wavelength in front of the feeding element, and a second feeding element arranged behind the feeding element at an interval exceeding 0.1 wavelength. An array antenna comprising two parasitic elements. 2. A feeding element having at least feeding means, a first parasitic element functioning as a director disposed within 0.1 wavelength in front of the feeding element, and a wavelength exceeding 0.1 wavelength behind the feeding element. An array antenna including a second parasitic element functioning as a reflector disposed at an interval. 3. The array antenna according to claim 1, wherein a third parasitic element is arranged within 0.1 wavelength behind the feed element. 4. The array antenna according to claim 1, wherein the feed element and each parasitic element are monopole antennas erected on a ground plate. 5. The power feeding element and each of the parasitic elements are formed by using a conductor pattern on a surface of a dielectric substrate.
The array antenna described.