JP2004364229A - Two-element antenna with cardioid directivity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a two-element antenna with cardioid directivity that has directivity with a high front-to-rear ratio over a wide frequency band, that is, null (zero) in the opposite direction of a main beam regardless of a distance between the two-element antennas. <P>SOLUTION: When one of the element antennas has a feeding amplitude of a, the other element antenna has a feeding amplitude of -a, and a difference in feeding phase between the two element antennas is set at 360 d/λ(degree). Alternatively, the two element antennas are made equal in the feeding amplitude, and the difference in feeding phase is set at 360 d/λ±180(degree). Further, the distance between the two-element antennas is set to be not larger than λ/2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

ただし、ｋは電波の伝搬定数でｋ＝２π／λである。上記（数１）は係数を省いて次のように変形される。

【０００４】
（数２）よりφ＝０ではＤ（０）＝１となりビームの最大方向となる。一方、φ＝π（＝１８０°）ではＤ（π）＝ｃｏｓ（２πｄ／λ）となり、ｄ＝λ／４（＝０．２５λ）のときだけゼロになりカージオイド指向性になる。しかし、一般にｄがλ／４以外ではカージオイド指向性にならない。
【０００５】
例えば、ｄ＝０．２λの場合には、図２の従来の２素子アンテナの指向性は図３の５のようになる。すなわち、ビームの後方ではヌル（零点）が埋まり、いわゆるビームの前後比が悪い不完全なカージオイド指向性である。あるいは、ある周波数でｄ＝λ／４にしたとしても、このアンテナを広い周波数帯域にわたって使用する場合には他の周波数でヌル（零点）が埋まる。
【０００６】
【発明が解決しようとする課題】
従来のカージオイド型２素子アンテナは、上記のように２つの素子アンテナの間隔がλ／４でなければならず、かつ広い周波数帯域にわたってカージオイド指向性が得られないという欠点があった。
【０００７】
この発明は、このような欠点を解決するためになされたもので、２つの素子アンテナ間の間隔に制約がなく、かつ広い周波数帯域にわたって前後比の高いカージオイド指向性を有する２素子アンテナを提供するものである。
【０００８】
【課題を解決するための手段】
この発明に係るカージオイド型指向性を持つ２素子アンテナは、従来の２素子アンテナとは異なる給電振幅と給電位相が与えられる。
【０００９】
【作用】
この発明においては、２つの素子アンテナ間の距離をλ／２以下の任意とし、２つの素子アンテナの給電位相を従来と比べて進み・遅れを逆にし、さらに給電振幅を一方をａとすれば他方を−ａとするものである。
【００１０】
【実施例】
以下、本発明によるカージオイド型指向性を持つ２素子アンテナについて、図面を参照して説明する。
図４は本発明の実施例の２素子アンテナである。図４で、６は第１素子アンテナ、７は第２素子アンテナ、８は２素子アンテナである。第１素子アンテナ６の給電位相は−１８０ｄ／λ（度）で、第２素子アンテナ７の給電位相は１８０ｄ／λ（度）である。これらは、図２の従来の２素子アンテナの場合と給電位相の正負が逆である。また、第１素子アンテナ６の給電振幅は１で、第２素子アンテナ７の給電振幅は−１である。
【００１１】
各素子アンテナの指向性を無指向性と仮定すれば、図４の２素子アンテナの指向性Ｄ（φ）は次のようになる

ただし、ｋは電波の伝搬定数でｋ＝２π／λである。上記（数３）は変形すると係数を省いて次のようになる。

この
【数４】より、φ＝π＝１８０°では、指向性は素子間の距離ｄや波長λに関係なく、常にゼロになることが分かる。これが本発明によるカージオイド型指向性を持つ２素子アンテナの最大のすぐれた特長である。従来の２素子アンテナの場合の指向性である上記（数２）と比較すると、式全体のｃｏｓがｓｉｎに変わり、ｃｏｓφの符号が−から＋に変わっていることが分かる。
【００１２】
また、φ＝０がビームの最大方向であり、そのレベルは上記（数４）より、

が、ｄがλ／４以上λ／２未満でもヌル（零点）が１つのカージオイド指向性になることが分かる。
【００１３】
図５は、本発明の実施例に２素子アンテナの指向性であり、素子アンテナの距離がｄ＝０．２λの場合である。従来例の図３と異なり、図５のカージオイド指向性９ではφ＝１８０°方向に完全なヌル（零点）が形成されている。
【００１４】
なお、上記の図４の実施例では、第１素子アンテナ６の給電振幅を１、第２素子アンテナ７の給電振幅を−１としたが、一般に一方がａであれば、他方が−ａであればよい。また、実施例では、第１素子アンテナ６の給電位相を−１８０ｄ／λ（度）で、第２素子アンテナ７の給電位相を１８０ｄ／λ（度）としたが、２つの素子アンテナの給電位相の差が３６０ｄ／λであればよい。
【００１５】
さらに、使用する周波数帯域が比較的狭い場合には、上記の給電振幅が正負逆であることを位相に置き換えて、一方の位相を０とするとき他方の位相を１８０度とし、この位相差１８０度と上記３６０ｄ／λの位相差の両方を加味して互いの給電位相を決めてももちろん構わない。すなわち、２つの素子アンテナの給電振幅が等しく、給電位相の差が３６０ｄ／λ±１８０（度）であればよい。
【００１６】
また、素子アンテナ６，７のアンテナ形式は特に示さなかったが、例えば、ダイポールアンテナ、モノポールアンテナ、マイクロストリップアンテナ、ループアンテナなど全ての種類のアンテナを用いて本発明を実施することができる。さらに、偏波についても任意であり、垂直偏波、水平偏波、あるいは円偏波を用いてこの発明は実施することができる。
【００１７】
【発明の効果】
以上のようにこの発明によれば、２つの素子アンテナに適切な給電振幅と給電位相を与えるために、２つの素子アンテナ間の距離がλ／４に固定されることなく、かつ広い周波数帯域にわたって前後比の高いカージオイド指向性を実現することができる。
【図面の簡単な説明】
【図１】カージオイド指向性の説明図である。
【図２】従来の２素子アンテナの説明図である。
【図３】従来の不完全なカージオイド指向性の説明図である。
【図４】本発明による２素子アンテナの説明図である。
【図５】本発明によるカージオイド指向性の説明図である。
【符号の説明】
１；カージオイド指向性
２；第１素子アンテナ
３；第２素子アンテナ
４；２素子アンテナ
５；不完全カージオイド指向性
６；第１素子アンテナ
７；第２素子アンテナ
８；２素子アンテナ
９；カージオイド指向性[0001]
[Industrial applications]
The present invention relates to a two-element antenna having one main beam and directivity having radiation null (zero point) in a direction opposite to the main beam, that is, a cardioid type directivity. The present invention relates to a two-element antenna having a cardioid type directivity that is not restricted and can maintain a high directivity of a front-to-back ratio of an antenna radiation beam over a wide frequency band.
[0002]
[Prior art]
FIG. 1 shows the cardioid directivity. In FIG. 1, the circumferential direction is the observation angle (degree), and the radial direction is the amplitude (dB value). The cardioid directivity 1 is a directivity having a main beam and a null (zero point) of radiation in a direction opposite to the main beam as shown in FIG. Such characteristics are that the antenna radiates radio waves well in front of the antenna or receives radio waves from the front well, and there is no radiation to the rear of the antenna or no radio waves from the rear. It has a high effect. An antenna having such characteristics is used as a train-side antenna that communicates with a base station antenna in front of (or behind) a train, for example, in a Shinkansen train radio system. Alternatively, such cardioid directivity has only one zero point of radiation, and may be used for an antenna for direction finding utilizing this characteristic.
[0003]
FIG. 2 shows a conventional two-element antenna having such cardioid directivity. In FIG. 2, 2 is a first element antenna, 3 is a second element antenna, and 4 is a two-element antenna composed of these two element antennas. The distance between the two element antennas 2 and 3 is d, the wavelength of the radio wave is λ, and the observation angle is φ as shown in the figure. The feeding phase of the first element antenna 2 is 180 d / λ (degree), and the feeding phase of the second element antenna 3 is -180 d / λ (degree). The power supply amplitudes are both 1. The two-element antenna 4 is a so-called two-element endfire array antenna that directs a beam in the φ = 0 direction. At this time, the radiation directivity of the two-element antenna 4 is as follows, assuming that the directivity of each element antenna is non-directional.

Here, k is a propagation constant of a radio wave, and k = 2π / λ. The above (Equation 1) is modified as follows by omitting the coefficient.

[0004]
From (Equation 2), when φ = 0, D (0) = 1 and the beam is in the maximum direction. On the other hand, when φ = π (= 180 °), D (π) = cos (2πd / λ), and becomes zero only when d = λ / 4 (= 0.25λ), resulting in cardioid directivity. However, in general, the cardioid directivity is not obtained when d is other than λ / 4.
[0005]
For example, when d = 0.2λ, the directivity of the conventional two-element antenna in FIG. 2 is as shown in 5 in FIG. That is, a null (zero point) is buried behind the beam, which is a so-called imperfect cardioid directivity having a poor front-to-back ratio of the beam. Alternatively, even if d = λ / 4 at a certain frequency, when this antenna is used over a wide frequency band, nulls (zero points) are filled at other frequencies.
[0006]
[Problems to be solved by the invention]
As described above, the conventional cardioid two-element antenna has a disadvantage that the distance between the two element antennas must be λ / 4 and that cardioid directivity cannot be obtained over a wide frequency band.
[0007]
The present invention has been made in order to solve such a drawback, and provides a two-element antenna having a cardioid directivity with a high front-to-back ratio over a wide frequency band, without any restriction on the interval between the two element antennas. Is what you do.
[0008]
[Means for Solving the Problems]
The two-element antenna having cardioid directivity according to the present invention is provided with a different feeding amplitude and feeding phase from the conventional two-element antenna.
[0009]
[Action]
In the present invention, if the distance between the two element antennas is arbitrarily equal to or less than λ / 2, and the feed phases of the two element antennas are reversed in lead and lag as compared with the conventional case, and one of the feed amplitudes is a. The other is -a.
[0010]
【Example】
Hereinafter, a two-element antenna having cardioid directivity according to the present invention will be described with reference to the drawings.
FIG. 4 shows a two-element antenna according to the embodiment of the present invention. In FIG. 4, reference numeral 6 denotes a first element antenna, 7 denotes a second element antenna, and 8 denotes a two-element antenna. The feeding phase of the first element antenna 6 is -180 d / λ (degree), and the feeding phase of the second element antenna 7 is 180 d / λ (degree). These are opposite in the polarity of the feeding phase from the case of the conventional two-element antenna of FIG. The power supply amplitude of the first element antenna 6 is 1, and the power supply amplitude of the second element antenna 7 is -1.
[0011]
Assuming that the directivity of each element antenna is omni-directional, the directivity D (φ) of the two-element antenna of FIG.

Here, k is a propagation constant of a radio wave, and k = 2π / λ. When the above (Equation 3) is transformed, the following is obtained by omitting the coefficient.

From this, it can be seen that, when φ = π = 180 °, the directivity is always zero irrespective of the distance d between the elements and the wavelength λ. This is the most outstanding feature of the two-element antenna having cardioid directivity according to the present invention. Comparing with the above-mentioned (Equation 2) which is the directivity in the case of the conventional two-element antenna, it can be seen that cos in the entire expression changes to sin, and the sign of cos φ changes from-to +.
[0012]
Φ = 0 is the maximum direction of the beam, and its level is given by (Equation 4)

However, it can be seen that even when d is λ / 4 or more and less than λ / 2, a null (zero point) becomes one cardioid directivity.
[0013]
FIG. 5 shows the directivity of a two-element antenna according to the embodiment of the present invention, in which the distance between the element antennas is d = 0.2λ. Unlike the conventional example of FIG. 3, in the cardioid directivity 9 of FIG. 5, a complete null (zero point) is formed in the φ = 180 ° direction.
[0014]
In the embodiment of FIG. 4 described above, the feed amplitude of the first element antenna 6 is set to 1 and the feed amplitude of the second element antenna 7 is set to −1, but generally, if one is a, the other is −a. I just need. In the embodiment, the feeding phase of the first element antenna 6 is -180 d / λ (degree) and the feeding phase of the second element antenna 7 is 180 d / λ (degree). Should be 360d / λ.
[0015]
Further, when the frequency band to be used is relatively narrow, the fact that the power supply amplitude is opposite in polarity is replaced with a phase. When one phase is set to 0, the other phase is set to 180 degrees, and the phase difference is set to 180 degrees. It is a matter of course that both power supply phases may be determined in consideration of both the degree and the phase difference of 360 d / λ. That is, it is only necessary that the two element antennas have the same feeding amplitude and the difference between the feeding phases is 360 d / λ ± 180 (degrees).
[0016]
Although the antenna types of the element antennas 6 and 7 are not particularly shown, the present invention can be implemented using all types of antennas such as a dipole antenna, a monopole antenna, a microstrip antenna, and a loop antenna. Furthermore, the polarization is arbitrary, and the present invention can be implemented using vertical polarization, horizontal polarization, or circular polarization.
[0017]
【The invention's effect】
As described above, according to the present invention, in order to provide appropriate feed amplitude and feed phase to the two element antennas, the distance between the two element antennas is not fixed to λ / 4 and over a wide frequency band. Cardioid directivity with a high front-to-back ratio can be realized.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of cardioid directivity.
FIG. 2 is an explanatory diagram of a conventional two-element antenna.
FIG. 3 is an explanatory diagram of a conventional incomplete cardioid directivity.
FIG. 4 is an explanatory diagram of a two-element antenna according to the present invention.
FIG. 5 is an explanatory diagram of cardioid directivity according to the present invention.
[Explanation of symbols]
1; cardioid directivity 2; first element antenna 3; second element antenna 4; two-element antenna 5; incomplete cardioid directivity 6; first element antenna 7; second element antenna 8; Cardioid directivity

Claims (2)

When the distance between the two element antennas is d, the wavelength of the radio wave is λ, and the feeding amplitude of one element antenna is a, the feeding amplitude of the other element antenna is − a, wherein the difference between the feeding phases of the two element antennas is 360 d / λ (degrees), and the distance d between the two element antennas is λ / 2 or less. A two-element antenna with a characteristic. When the distance between the two element antennas is d and the wavelength of the radio wave is λ, the difference between the feeding phases of the two element antennas is 360 d / λ ± 180 (degrees). And a distance d between the two-element antennas is λ / 2 or less, wherein the two-element antenna has cardioid directivity.

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