JP3947613B2 - Antenna beam combining method and antenna - Google Patents

Description

で表される。ここで、−１≦ｓｉｎθ_n ≦１であり、誘電体の場合（β／ｋ₀ ）は１より大きい定数であるから、θ_n が有効な解を持つために通常はｎ＝−１とする。
【００２６】
これらの式から、漏れ波の放射ビームの方向はストリップ周期ｄで決まることが判る。また、漏れ波の単位長さ当りの放射量（漏れ波定数）はストリップ幅ｓで決まることが知られている。
【００２７】
この実施形態のアレー型のアンテナ２０を構成する１本１本の各アンテナは、放射特性が異なる漏れ波型のアンテナユニットを、その放射面が同一方向に向いた状態で各アンテナユニットの地板導体と誘電体とが１本の連続したイメージ線路を形成するように縦列に接続したものであり、その合成ビームがコセカントビームをとなるようにしている。
【００２８】
ここで、そのビームの合成方法について説明する。
ｎ番目のアンテナユニットの振幅がａ_n で均一、位相定数がβ_n 、長さがＬとし、ｕ、ｕ_n を、
sin θ＝ｕ、 sin θ_n ＝ｕ_n ＝β_n ／ｋ₀
と定義すると、そのアンテナユニットの指向性は、
Ｅ_n ＝ａ_n sin 〔（ｕ−ｕ_n ）ｋ₀ Ｌ／２〕／〔（ｕ−ｕ_n ）ｋ₀ Ｌ／２〕
となる。
【００２９】
このアンテナユニットをＮ個縦列に接続すると、アンテナ全体の指向性は、
Ｅ（ｕ）＝Σ_n ａ_n ｅ^jP（sin Ｕ）／Ｕ …（１）
となる。ただし、Σ_n はｎ＝１〜Ｎまでの総和を表し、Ｕ＝（ｕ−ｕ_n ）ｋ₀ Ｌ／２、Ｐ＝（Ψ_n −ｋ₀ ｕＺ_n ）であり、Ψ_n はＺ＝Ｚ_n に到達する伝送波の位相である。
【００３０】
ここで、所望の合成ビームを定義する領域をｕ空間でＮ−１に等分し、その領域の両端を含む各分割点にｕ_n （ｎ＝１、２、…、Ｎ）を割当て、その間隔（分割幅）をΔｕとして、アンテナユニットの長さＬをλ₀ ／Δｕに選ぶと、式（１）の第２項（sin Ｕ）／Ｕは直交標本関数となり、ｕ＝ｕ_n では、ｎ番目のビームのみが大きさ１となり、他のビームは零となる。
【００３１】
したがって、振幅ａ_n をｕ_n における所望の指向性のレベルに選べば、ｕ₁ 、ｕ₂ 、…、ｕ_N の標本点においては所望の指向性に一致するパターンが得られる。
【００３２】
Ｎ＝３の場合の簡単な例を示すと、図３のように、ｕ＝０．２〜０．４までの範囲を所望の合成ビーム（希望パターン）Ｐｒを定義する領域とし、その間を２つの領域に等分し（Δｕ＝０．１）、各アンテナユニットの長さＬをλ₀ ／Δｕ＝１０λ₀ に選ぶ。
【００３３】
そして、第１のアンテナユニットの振幅ａ₁ を希望パターン（コセカントビーム）のｕ＝０．２のレベルに対応するように設定し、第２のアンテナユニットの振幅ａ₂ を希望パターンのｕ＝０．３のレベルに対応するように設定し、さらに、第３のアンテナユニットの振幅ａ₃ を希望パターンのｕ＝０．４のレベルに対応するように設定する。
【００３４】
このように設定すると、図３に示しているように、第１のアンテナユニットの指向性Ｅ₁ のメインローブＭ₁ の最大点（ｕ＝０．２）で、第２、第３のアンテナユニットの指向性Ｅ₂ 、Ｅ₃ の電界が零となり、同様に、第２のアンテナユニットの指向性Ｅ₂ のメインローブＭ₂ の最大点（ｕ＝０．３）では、第１、第３のアンテナユニットの指向性Ｅ₁ 、Ｅ₃ の電界が零となり、第３のアンテナユニットの指向性Ｅ₃ のメインローブＭ₃ の最大点（ｕ＝０．４）では、第１、第２のアンテナユニットの指向性Ｅ₁ 、Ｅ₂ の電界が零となる。
【００３５】
このため、１本のアンテナ全体の合成パターンは、ｕ＝０．２、０．３、０．４の位置（各分割点の位置）で希望パターンＰｒと一致し、他の位置では希望パターンＰｒを中心にして上下に変化する特性となり、希望パターンＰｒ（コセカントビーム）に沿った特性が得られる。
【００３６】
なお、アンテナユニットは伝送路を一端側から他端側へ電波を進行させながら電波を漏出させているから、単位長さ当りの漏れ量が均一であると、電波が進行するにつれてその振幅が小さくなり、完全に均一な振幅分布を得ることはできない。そのために、１つのアンテナユニット内でのストリップ幅ｓ（金属ストリップの長さ）を給電側から僅かずつ増加させ、給電側から遠くなるほど漏れ量を増やして均一の振幅分布を得るようにしている。
【００３７】
図１に示した実施形態のアンテナ２０は、長さＬが等しい５つのアンテナユニットＵ₁ 〜Ｕ₅ を縦列に接続したものであり、希望パターンの定義領域を４つに分け、その両端を含む５つの各分割点ｕ₁ 〜ｕ₅ （図示せず）に対応した放射角θ₁ 〜θ₅ が各アンテナユニットの最大放射角となり、各分割点における希望パターンのレベルが各アンテナユニットの最大強度となるようにストリップ周期ｄとストリップ幅ｓを設定したものである。
【００３８】
即ち、図４に示すように、誘電体２３の最も給電部２２側に形成されたアンテナユニットＵ₁ の誘電体表面には、その漏れ波のメインローブＭ₁ の最大放射方向が希望パターンＰｒの定義領域の端の分割点ｕ₁ に対応した角度θ₁ となり、その強度が分割点ｕ₁ における希望パターンＰｒのレベルに対応した値ａ₁ となるストリップ周期ｄ₁ とストリップ幅ｓ₁ で金属ストリップ２４が設けられている。
【００３９】
また、アンテナユニットＵ₁ に続くアンテナユニットＵ₂ の誘電体表面には、その漏れ波のメインローブＭ₂ の最大放射方向が希望パターンＰｒの定義領域のの端から２番目の分割点ｕ₂ に対応した角度θ₂ となり、その強度が分割点ｕ₂ における希望パターンＰｒのレベルに対応した値ａ₂ になるストリップ周期ｄ₂ とストリップ幅ｓ₂ で金属ストリップ２４が設けられている。
【００４０】
以下同様にして、アンテナユニットＵ₃ 〜Ｕ₅ の誘電体表面には、各アンテナユニットＵ₃ 〜Ｕ₅ の漏れ波のメインローブＭ₃ 〜Ｍ₅ の最大放射方向が希望パターンＰｒの定義領域の各分割点ｕ₃ 〜ｕ₅ にそれぞれ対応した角度θ₃ 〜θ₅ となり、その強度が分割点ｕ₃ 〜ｕ₅ における希望パターンＰｒのレベルに対応した値ａ₃ 〜ａ₅ になるストリップ周期ｄ₃ 〜ｄ₅ とストリップ幅ｓ₃ 〜ｓ₅ で金属ストリップ２４が設けられている。
【００４１】
また、各アンテナユニットのストリップ幅ｓ₁ 〜ｓ₅ は、前記したように、各アンテナユニット毎に振幅分布が均一となるように僅かずつ変化させているので、１つのアンテナユニットの最大放射方向では、他のアンテナユニットから放射される電波の強度は零となり、希望パターンに近似した合成ビームが得られる。なお、図４は各アンテナユニットＵ₁ 〜Ｕ₅ のビームを極座標上に示したものである。
【００４２】
図５、図６は、５つのアンテナユニットＵ₁ 〜Ｕ₅ を縦列接続したアンテナのサブローブを含めた垂直面の合成パターンをｕ軸上で示したもので、図５の特性は、遠距離からの監視が可能なように０°近傍の放射レベルを高く（２６ｄＢ）設定したときのものであり、偏差がやや大きいが希望パターンに沿った特性が得られている。また、図６の特性は、比較的近距離からの監視用に０°付近の放射レベルをやや低く（２１ｄＢ）設定したものであり、図５に示した特性に対して偏差が大幅に減って、希望パターンＰｒに非常に近い特性が得られている。なお、図５、図６の縦軸は、θ＝０、即ち、ｚ軸方向の放射レベルを基準（０ｄＢ）にしたときの相対値である。
【００４３】
これら図５、図６の特性は、一本の誘電体２３上に５つのアンテナユニットを縦列に形成したときのものであるが、一本の誘電体２３上に８つのアンテナユニットを縦列に形成したときの特性例を図７に示す。この１本のアンテナの特性は、図５のアンテナと同様に、遠距離からの監視が可能なように０°近傍の放射レベルを高く（２６ｄＢ）設定したときのものであり、図５の特性と比べて短い周期で変化しているが希望パターンからの偏差量は小さく、希望パターンＰｒに非常に近い特性が得られている。
【００４４】
なお、アンテナユニットＵ₁ 〜Ｕ₅ を縦列に接続した１本のアンテナの水平面の放射特性は路上監視用としては広すぎるため、この実施形態のアレー型のアンテナ２０では、前記したように誘電体２３からなるアンテナを平行に複数本（図１では６本）並べ、各誘電体２３毎に５つのアンテナユニットＵ₁ 〜Ｕ₅ をそれぞれ形成して、水平面の放射パターンを路上監視用として最適な広がり幅に設定している。
【００４５】
このため、アンテナ２０からは、水平面の指向特性が道路幅にほぼ対応した幅で、垂直面の指向特性がコセカント関数に近くなり、遠方の車両には強い電波が放射され、近傍の車両には弱い電波が放射されて、道路の長さ方向の広い範囲でほぼ等しい感度で車両からの反射波を受信することができる。
【００４６】
このアンテナ２０を構成する１本１本のアンテナは、低伝送損失の漏れ波型アンテナユニットを縦列接続した構造であるので、アンテナ全体としても低伝送損失である。また、平面構造であって、その表面処理のみで簡単に製作でき、設計、製造および設置が容易でコストが低く、しかも、装荷体としての金属ストリップは印刷技術やエッチング技術によって高い寸法精度で形成することができるので、ビームの合成精度も高い。
【００４７】
また、金属ストリップの周期と長さによって、各アンテナユニットの放射特性を任意に設定することができ、複雑な放射特性が容易に得られる。
【００４８】
また、イメージ線路では、誘電体外部の電磁界は指数関数的に減少するので、これを用いた漏れ波型のアンテナの誘電体の側面側への電波の漏れは非常に少なく、この実施形態のように複数本のアンテナを並列に配置してアレー化した場合でも隣接するアンテナ同士の干渉による放射パターンの乱れが少なく、逆にグレーティングローブが発生しないように隣接するアンテナの間隔をより接近させて配置することができ、アンテナ全体を小型化できる。
【００４９】
【他の実施の形態】
前記実施形態では、５つ（および８つ）のアンテナユニットを縦列に接続した場合について説明したが、垂直面の目標放射特性がより複雑な場合にはユニット数を増加し、垂直面の目標放射特性がより単純な場合にはユニット数を減少してもよく、目標とする垂直面の放射特性に応じて種々変更可能である。
【００５０】
また、前記実施形態では、水平面の放射特性を狭くするために本発明のアンテナを並列に設けていたが、これは、目標とする水平面の放射特性に応じて種々変更可能であり、水平面の放射特性が広くてもよい場合には１本だけにしてもよい。
【００５１】
また、前記実施形態では、誘電体表面から電磁波を漏出させるための装荷体として金属ストリップを用いていたが、図８に示すように、誘電体２３の表面に装荷体として所定高さｈの高段部２４′を一定間隔で設けてコルゲート（波型）状に形成することによって、漏れ波型のアンテナユニットを構成することができる。
【００５２】
この場合、高段部２４′の間隔ｄ（コルゲート周期という）と、高段部２４′の長さｓ（コルゲート幅という）とは、前記実施形態の金属ストリップのストリップ周期およびストリップ幅にそれぞれ相当しており、前記した２つの式がそのまま使用でき、アンテナユニットの放射方向はコルゲート周期ｄで決まり、放射量はコルゲート幅ｓと高段部２４′の高さｈとで決まる。
【００５３】
また、前記実施形態の給電部２２は、地板導体の表面側に設けられていたが、入力された電磁波を地板導体の背面側で分岐して、表面側の各誘電体の一端に給電する折り返しホーン型の給電部を用いてもよい。
【００５４】
また、前記実施形態では、イメージ線路に電波を漏出させるための装荷体を設けた漏れ波型のアンテナユニットを縦列に接続していたが、漏れ波型のアンテナである導波管スロットアンテナに本発明を適用することもできる。
【００５５】
導波管スロットアンテナは、基本波を伝送する所定長の導波管の一側面にスロットを長さ方向に沿って複数設けて電波を漏出させるアンテナであり、漏れ波の放出方向は、
θ_n ＝sin ^-1〔（β／ｋ₀ ）＋（２ｎ−１）λ₀ ／２ｄ_n 〕
（通常はビームを１つだけにするためにｎ＝−１を使う）
となるが、基本的な動作はイメージ線路に装荷体を設けた場合と同様である。
【００５６】
図９はこのような導波管スロットアンテナを１つのアンテナユニットとして
、５つのアンテナユニットＵ₁ 〜Ｕ₅ を、各アンテナユニットの導波管が１本の伝送路を形成するように、縦列に接続したものである。
【００５７】
このアンテナにおいても、各アンテナユニットＵ₁ 〜Ｕ₅ のスロット３０の間隔ｄ₁ 〜ｄ₅ およびスロット幅ｓ₁ 〜ｓ₅ を、希望パターンＰｒのｕ空間における定義領域を４つに等分割する分割幅Δｕで漏れ波の自由空間波長λ₀ を除算した値に、各アンテナユニットＵ₁ 〜Ｕ₅ の長さＬを一致させ、各アンテナユニットＵ₁ 〜Ｕ₅ の漏れ波のメインローブの最大放射方向が希望パターンＰｒの定義領域の各分割点にそれぞれ対応した角度となり、その強度が各分割点における希望パターンＰｒのレベルに対応した値になるように設定することで、希望パターンに近似した合成ビームを得ることができる。
【００５８】
このアンテナでは、ほぼ同一長さのスロットが一定間隔に設けられた導波管スロットアンテナを縦列に接続して、所望のパターンを得るようにしているから、設計も容易で加工もし易い。
【００５９】
なお、前記実施形態では、各アンテナユニットの振幅分布をそれぞれ均一にするために、金属ストリップの長さ（ストリップ幅）を僅かずつ増加していたが、アンテナユニット内の金属ストリップの長さを全て同一にしても、合成パターンが希望パターンに対して掛け離れることはないので、設計をより簡単化するために、各アンテナユニット毎の金属ストリップの長さを同一にしてもよい。
【００６０】
また、厳密な合成精度が要求されていない場合には、所望のビーム特性を適度な間隔でＮ−１に分割し、その両端を含む分割点に各アンテナユニットの放射ビームの放射角をほぼ一致させるとともに、各アンテナユニットの放射ビームの放射強度を合成した各放射角毎の合成放射強度が各分割点の放射強度に近くなるように、各アンテナユニットを形成してもよい。この場合には、一つのアンテナユニットのメインローブの最大放射角において、他のアンテナユニットの放射強度が零とならない場合があるが、製造上の精密な加工が不要で安価に所望のビーム特性に近い特性のアンテナが得られる。これは、装荷体として誘電体の表面に高段部を設けたアンテナユニットや導波管にスロットを設けたアンテナユニットの場合でも同様である。
【００６１】
【発明の効果】
以上説明したように、本発明の請求項１のアンテナのビーム合成方法および請求項３のアンテナは、縦列に接続された漏れ波型の複数のアンテナユニットの各伝送体の長さを、放射角θに対しｕ＝sin θとなる値ｕについての所望のビーム特性の合成対象領域をＮ−１に等分割したときの分割幅で漏れ波の自由空間波長を除算した値にほぼ等しく設定し、各アンテナユニットの最大放射角度とその放射強度が、合成対象領域の両端を含むＮ個の分割点の放射角と放射強度にほぼ一致するように各アンテナユニットの漏出部を設定している。
【００６２】
このため、１つのアンテナユニットのメインローブの最大点では他の全てのアンテナユニットの放射強度が最小となり、各アンテナユニットのメインローブの最大点が所望のパターン上の点に一致して、その合成パターンを所望のパターンに極めて近いものとすることができ、複雑な任意のビームを容易に且つ精度よく合成することができる。
【００６３】
また、本発明の請求項２のアンテナでは、縦列に接続された漏れ波型の複数Ｎのアンテナユニットは、放射ビームの放射角が、所望のビーム特性の合成対象領域をＮ−１に分割したときの両端を含むＮ個の分割点の放射角にそれぞれほぼ一致し、各アンテナユニットの放射ビームの放射強度を合成した各放射角毎の合成放射強度が各分割点の放射強度に近くなるように形成されているため、製造上の精密な加工が不要で安価に所望のビーム特性に近い特性のアンテナが得られる。
【００６４】
また、各アンテナユニットの伝送体が、地板導体上に誘電体を配置したイメージ線路によって形成され、漏出部が誘電体の表面に装荷された装荷体によって形成された構造のアンテナでは、伝送損失が少なく、平面構造であるため、設計、製造および設置が容易でコストが低く、複雑な放射特性を高い精度で得られる。また、イメージ線路では、誘電体外部の電磁界は指数関数的に減少するので、隣接するアンテナユニット同士の同士の干渉が少なく、アンテナユニット同士を接近させてグレーティングローブを発生させないようにすることができる。それにより、水平面内で希望する指向性を得るようにアンテナユニットを配置することができ、アンテナ全体を小型化することができる。
【００６５】
また、各アンテナユニットの伝送体が導波管によって形成され、漏出部が導波管の表面に設けられたスロットによって形成された構造のアンテナでは、各アンテナユニット内のスロットの寸法および周期をほぼ一様にすることができ、アンテナ素子間の相互結合を考慮しないで済み、設計、製造が容易でコストを下げることができる。
【図面の簡単な説明】
【図１】 本発明の一実施形態の１本１本のアンテナから構成されるアレー型のアンテナの斜視図
【図２】イメージ線路の信号の伝搬状態を説明するための側面図
【図３】本発明のビーム合成方法を説明するための図
【図４】一実施形態の各アンテナユニットの放射特性を示す図
【図５】実施形態の垂直面の合成放射特性の一例を示す図
【図６】実施形態の垂直面の合成放射特性の一例を示す図
【図７】ユニット数を増加したときの垂直面の合成放射特性の一例を示す図
【図８】他の実施形態の要部の斜視図
【図９】他の実施形態の要部の斜視図
【図１０】ミリ波を使用した路上車両監視システムを説明するための概略図
【符号の説明】
２０ アンテナ
２１ 地板導体
２２ 給電部
２３ 誘電体
２４ 金属ストリップ
Ｕ₁ 〜 Ｕ₅ アンテナユニット[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an antenna mainly used in a millimeter wave band and suitable for use in a road vehicle monitoring radar or a high-speed wireless access base station that requires a complicated radiation pattern.
[0002]
[Prior art]
For example, in a road vehicle monitoring system using a millimeter wave, as shown in FIG. 10, a traveling vehicle is monitored by emitting a radio wave from an antenna 1 to a road 2 and receiving a reflected wave from a vehicle 3 traveling on the road. Is doing.
[0003]
In such a monitoring system, the width of the radiation pattern on the horizontal plane is narrow so as not to receive reflected waves from other than the monitoring target, and the level is almost equal in a wide range from a distant position (several hundred meters) to the vicinity of the antenna 1. Therefore, it is required that the radiation pattern P on the vertical plane be close to the cosecant function.
[0004]
In order to obtain such a radiation pattern of a shaped beam, conventionally, a reflector antenna (parabolic antenna), a waveguide slot array antenna, a microstrip array antenna, or the like is used.
[0005]
In the case of array antennas such as waveguide slot array antennas and microstrip array antennas, the excitation amplitude and phase of each antenna element are obtained by calculation based on the directivity synthesis theory, and individual antennas are realized so as to realize them. The excitation of the element is controlled.
[0006]
For example, in a waveguide slot array antenna, the phase and amplitude of an electromagnetic wave radiated for each slot are calculated, and the size and position of each slot are determined based on the calculation result. In the microstrip array antenna, excitation is controlled by the feed line length and impedance of each antenna element.
[0007]
[Problems to be solved by the invention]
However, each antenna described above has the following problems.
[0008]
(B) The reflector antenna is difficult to design the mirror surface and the feeding horn, and it is necessary to use a special mirror surface to make the complex radiation pattern described above, which increases the production cost and has a three-dimensional structure. Is also troublesome.
[0009]
(B) As described above, the waveguide slot array antenna has a complicated design because the size and position of each slot are determined. In addition, since mutual coupling occurs between the antenna elements arranged in parallel, it is difficult to realize a desired excitation distribution in consideration of this influence. In particular, in the high frequency band such as the millimeter wave band, it is difficult to achieve individual excitation distribution. In order to precisely match the excitation amplitude and phase of the antenna element, strict manufacturing accuracy is required and the cost increases.
[0010]
(C) In the case of a microstrip array antenna, similarly to the waveguide slot array antenna, the excitation control of individual antenna elements is complicated, the feed loss is large, the frequency band is narrow, and the power is high. There is a problem that it is difficult to use.
[0011]
The present invention has been made in view of these circumstances. An antenna beam combining method capable of easily forming a complicated radiation pattern, a loss, a design, manufacture and installation are easy and cost is low. The purpose is to provide an antenna.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the antenna beam combining method according to claim 1 of the present invention comprises:
A leakage wave type N antenna unit composed of a transmission body forming an electromagnetic wave transmission path and a plurality of leakage portions formed along the length direction on the surface of the transmission body, and the radiation surface of the leakage wave is in the same direction A beam combining method of antennas, which are connected in a column in a state of facing the antenna and combine desired beams as one antenna ,
A value obtained by dividing the free space wavelength of the leaky wave by the division width when the synthesis target region of the desired beam characteristic for the value u where u = sin θ with respect to the radiation angle θ is equally divided into N−1; Set the length of the transmission body of multiple antenna units to be almost equal,
The length and period of the leakage portion of each antenna unit are set so that the maximum radiation angle and the radiation intensity of each antenna unit substantially coincide with the radiation angles and radiation strengths of N division points including both ends of the synthesis target region. By setting, the desired beam is obtained.
[0013]
The antenna according to claim 2 of the present invention is
Leaky wave type N antenna units each comprising a transmission body forming an electromagnetic wave transmission path and a plurality of leakage portions formed along the length direction on the surface of the transmission body are arranged to emit leakage waves of each antenna unit. It is connected in series so as to form a single continuous transmission path with the surfaces facing in the same direction, and is fed with electromagnetic waves from one end side of the single continuous transmission path to obtain a desired antenna as one antenna . An antenna that emits electromagnetic waves with beam characteristics,
The length of the transmission body of the plurality of antenna units is a division width when the synthesis target region of the desired beam characteristic for a value u where u = sin θ with respect to the radiation angle θ is equally divided into N−1. It is set approximately equal to the value obtained by dividing the free-space wavelength of the leaky wave, and the length and period of the leaking portion of each antenna unit are the maximum radiation angle and radiation intensity of each antenna unit including N at both ends of the synthesis target region. It is set so as to almost coincide with the radiation angle and the radiation intensity of each division point.
[0014]
The antenna according to claim 3 of the present invention is the antenna according to claim 2 or 3,
The transmission body of each antenna unit is formed by an image line having a rod-shaped dielectric disposed on the surface of a ground plane conductor, and the leakage portion is a plurality of loads loaded on the surface of the dielectric along the length direction at a substantially constant period. It is formed by the loaded body.
[0015]
The antenna according to claim 4 of the present invention is the antenna according to claim 2 or 3,
The transmission body of each antenna unit is formed by a waveguide that transmits a fundamental mode, and the leakage portion is formed by a plurality of slots provided on the surface of the waveguide along the length direction at substantially constant intervals. ing.
[0016]
The antenna according to claim 5 of the present invention is
A plurality of antennas according to any one of claims 2 to 5 are arranged side by side in parallel to form an array.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a millimeter-wave array antenna 20 used in a traveling vehicle monitoring system.
[0018]
The antenna 20 is formed on a rectangular ground plane conductor 21 as shown in FIG.
[0019]
A horn-type power feeding section 22 is provided on the top surface 21 a of the ground plane conductor 21. A branch circuit by a waveguide (not shown) is formed inside the power supply unit 22 and a plurality of paths (six paths in this embodiment) of electromagnetic waves input from the connection port 22a provided on the upper surface side. And in-phase power is supplied to one end of each dielectric 23 described later.
[0020]
Between the lower portion of the power feeding portion 22 and the lower portion of the surface 22a of the ground plane conductor 22, a dielectric 23 having a predetermined length, for example, formed in a rectangular bar shape having a rectangular cross section with alumina or the like, has one side surface on the surface of the ground plane conductor 21. a plurality of (Figure 1, six) are provided in parallel in parallel in a state of being in contact with 21a. One end 23 a of each dielectric 23 is formed in a tapered shape (see FIG. 4) for matching with the power feeding unit 22.
[0021]
In this way, the circuit in which the rod-shaped dielectric 23 is arranged on the ground plane conductor 21 forms a transmission path called an image line. As shown in FIG. 2, the electromagnetic wave fed from the one end 23a side of the dielectric 23 is It is transmitted toward the other end 23b.
[0022]
On the surface of each dielectric 23, a metal strip 24 having the same width as that of the dielectric 23 is intermittently formed along the length direction as a loaded body.
[0023]
In this manner, the metal strips 24 are provided on the surface of the dielectric 23 constituting the image line at predetermined intervals, or the surface of the dielectric 23 is corrugated (corrugated) as will be described later. A large number of spatial harmonics are generated, and some of them are output from the surface of the dielectric 23 as leakage waves. The leakage wave radiation pattern is determined by the distance d (referred to as strip period) between the metal strips and the length s (referred to as strip width) of the metal strip.
[0024]
That is, the spatial harmonic β _n is given by
β _n = β + 2nπ / d (−∞ ≦ n ≦ ∞)
(Where β is the phase constant of the dielectric line)
The leakage wave is radiated when β _n is smaller than the free space wavenumber k ₀ .
[0025]
The radiation direction of the leaky wave is such that the length direction z of the dielectric 23 is a positive angular direction with the axis x orthogonal to the surface of the dielectric 23 as a reference, and the free space wavelength of the leaky wave is λ ₀ . The following formula,

It is represented by Here, since −1 ≦ sin θ _n ≦ 1 and the dielectric (β / k ₀ ) is a constant larger than 1, in order to have an effective solution, θ _n is normally set to n = −1. .
[0026]
From these equations, it can be seen that the direction of the leakage wave radiation beam is determined by the strip period d. Further, it is known that the amount of radiation per unit length of leakage wave (leakage wave constant) is determined by the strip width s.
[0027]
Each antenna constituting the array-type antenna 20 of this embodiment is a leaky wave type antenna unit having different radiation characteristics, and the ground plane conductor of each antenna unit with its radiation surface facing in the same direction. And the dielectric are connected in series so as to form one continuous image line, and the combined beam becomes a cosecant beam.
[0028]
Here, a method of combining the beams will be described.
n-th uniform amplitude of the antenna units in a _{n, n} phase constant beta, is a L length, u, and u _n,
sin θ = u, sin θ _n = u _n = β _n / k ₀
If defined, the directivity of the antenna unit is
E _n = a _n sin [(u−u _n ) k ₀ L / 2] / [(u−u _n ) k ₀ L / 2]
It becomes.
[0029]
When this antenna unit is connected in N columns, the directivity of the whole antenna is
_{E (u) = Σ n a} n e jP (sin U) / U ... (1)
It becomes. However, sigma _n denotes the total sum of up to n = 1~N, U = (u -u n) k 0 L / 2, is _{P = (Ψ n -k 0 uZ} n), Ψ n is Z = Z _This is the phase of the transmitted wave that reaches _n .
[0030]
Here, the region defining the desired combined beam is equally divided into N−1 in the u space, and u _n (n = 1, 2,..., N) is assigned to each division point including both ends of the region, intervals (division width) as Delta] u, choose the length L of the antenna unit to the lambda ₀ / Delta] u, the second term of formula (1) (sin U) / U becomes a quadrature sampling function, the u = u _n, Only the n-th beam has a size of 1 and the other beams are zero.
[0031]
Therefore, if you choose the amplitude a _n on the level of desired directivity in _{u n, u 1, u 2} , ..., in the sample point u _N obtained pattern matching the desired directivity.
[0032]
A simple example in the case of N = 3 shows a range where u = 0.2 to 0.4 as a region for defining a desired composite beam (desired pattern) Pr as shown in FIG. Equally divided into two regions (Δu = 0.1), and the length L of each antenna unit is selected as λ ₀ / Δu = 10λ ₀ .
[0033]
Then, the amplitude a ₁ of the first antenna unit is set so as to correspond to the level of u = 0.2 of the desired pattern (cosecant beam), and the amplitude a ₂ of the second antenna unit is set to u = of the desired pattern. The level is set so as to correspond to the level of 0.3, and the amplitude a ₃ of the third antenna unit is set so as to correspond to the level of u = 0.4 of the desired pattern.
[0034]
With this setting, as shown in FIG. 3, the second and third antenna units at the maximum point (u = 0.2) of the main lobe M ₁ of the directivity E ₁ of the _first antenna unit. Similarly, at the maximum point (u = 0.3) of the main lobe M ₂ of the directivity E ₂ of the second antenna unit, the electric fields of the directivities E ₂ and E ₃ become zero. At the maximum point (u = 0.4) of the main lobe M ₃ of the directivity E ₃ of the third antenna unit, the electric fields of the directivities E ₁ and E ₃ of the antenna unit become zero. The electric fields of the unit directivities E ₁ and E ₂ become zero.
[0035]
Therefore, one of the synthetic patterns of the entire antenna, u = position of 0.2, 0.3, 0.4 matches the desired pattern Pr in (the position of each dividing point), in other locations desired pattern Pr Thus, the characteristic changes along the vertical direction, and the characteristic along the desired pattern Pr (cosecant beam) is obtained.
[0036]
Note that the antenna unit leaks radio waves while propagating radio waves from one end side to the other end side of the transmission path. Therefore, if the amount of leakage per unit length is uniform, the amplitude decreases as the radio waves travel. Thus, a completely uniform amplitude distribution cannot be obtained. For this purpose, the strip width s (the length of the metal strip) in one antenna unit is increased little by little from the power supply side, and the amount of leakage increases as the distance from the power supply side increases to obtain a uniform amplitude distribution.
[0037]
The antenna 20 of the embodiment shown in FIG. 1 is obtained by connecting _five antenna units U _{1 to} U ₅ having the same length L in a column, dividing the definition area of a desired pattern into four, and including both ends thereof. Radiation angles θ _{1 to} θ ₅ corresponding to _five division points u _{1 to} u ₅ (not shown) are the maximum radiation angles of each antenna unit, and the desired pattern level at each division point is the maximum intensity of each antenna unit. The strip period d and the strip width s are set so that
[0038]
That is, as shown in FIG. 4, the maximum radiation direction of the main lobe M ₁ of the leaky wave is the desired pattern Pr on the dielectric surface of the antenna unit U ₁ formed closest to the feeding portion 22 of the dielectric 23. A metal strip having a strip period d ₁ and a strip width s ₁ having an angle θ ₁ corresponding to the dividing point u ₁ at the end of the definition area and a strength a ₁ corresponding to the level of the desired pattern Pr at the dividing point u ₁ . 24 is provided.
[0039]
Further, on the dielectric surface of the antenna unit U ₂ following the antenna unit U ₁ , the maximum radiation direction of the main lobe M ₂ of the leaky wave is at the second division point u ₂ from the end of the definition area of the desired pattern Pr. The metal strip 24 is provided with a strip period d ₂ and a strip width s ₂ that have a corresponding angle θ ₂ and whose intensity is a value a ₂ corresponding to the level of the desired pattern Pr at the dividing point u ₂ .
[0040]
In the same manner, the dielectric surface of the antenna unit U ₃ ~U _5, the maximum radiation direction of the main lobe M ₃ ~M ₅ of leaky wave of the antenna units U ₃ ~U ₅ is defined regions of desired pattern Pr each respective division point u ₃ ~u ₅ the corresponding angle theta ₃ through? _5, and the strip cycle d of the intensity is a value a ₃ ~a ₅ corresponding to the level of the desired pattern Pr at the division point u ₃ ~u ₅ Metal strips 24 are provided with _{3 to} d ₅ and strip widths s _{3 to} s ₅ .
[0041]
Also, as described above, the strip widths s _{1 to} s ₅ of each antenna unit are changed little by little so that the amplitude distribution is uniform for each antenna unit, so that in the maximum radiation direction of one antenna unit, The intensity of radio waves radiated from other antenna units becomes zero, and a combined beam approximating the desired pattern can be obtained. FIG. 4 shows the beams of the antenna units U _{1 to} U ₅ on polar coordinates.
[0042]
FIG. 5 and FIG. 6 show on the u-axis the combined pattern of the vertical plane including the sub-lobe of the antenna in which the _five antenna units U _{1 to} U ₅ are connected in cascade. The characteristics of FIG. In this case, the radiation level in the vicinity of 0 ° is set high (26 dB) so that monitoring can be performed, and the characteristics along the desired pattern are obtained although the deviation is slightly large. Further, the characteristics shown in FIG. 6 are obtained by setting the radiation level near 0 ° to be slightly low (21 dB) for monitoring from a relatively short distance, and the deviation is greatly reduced with respect to the characteristics shown in FIG. A characteristic very close to the desired pattern Pr is obtained. The vertical axes in FIGS. 5 and 6 are relative values when θ = 0, that is, the radiation level in the z-axis direction is set as a reference (0 dB).
[0043]
The characteristics shown in FIGS. 5 and 6 are obtained when five antenna units are formed in a column on one dielectric 23, but eight antenna units are formed in a column on one dielectric 23. FIG. 7 shows an example of the characteristics when this is done. The characteristic of this single antenna is similar to the antenna of FIG. 5 when the radiation level near 0 ° is set high (26 dB) so that monitoring from a long distance is possible. However, the deviation from the desired pattern is small and a characteristic very close to the desired pattern Pr is obtained.
[0044]
Since the radiation characteristics of the horizontal plane of _one antenna in which the antenna units U _{1 to} U ₅ are connected in series are too wide for road monitoring, the array-type antenna 20 of this embodiment has a dielectric as described above. A plurality of antennas 23 (six in FIG. 1) are arranged in parallel, and five antenna units U _{1 to} U ₅ are formed for each dielectric 23 to optimize the horizontal radiation pattern for monitoring on the road. The spread width is set.
[0045]
For this reason, the antenna 20 has a horizontal plane whose directivity characteristic substantially corresponds to the road width, the vertical plane directivity characteristic is close to a cosecant function, and a strong radio wave is radiated to a distant vehicle. A weak radio wave is radiated, and a reflected wave from the vehicle can be received with almost equal sensitivity over a wide range in the length direction of the road.
[0046]
Each antenna constituting the antenna 20 has a structure in which leakage wave type antenna units with low transmission loss are connected in cascade, so that the entire antenna has low transmission loss. In addition, it has a flat structure and can be easily manufactured only by its surface treatment. It is easy to design, manufacture and install, and the cost is low. Moreover, the metal strip as a loaded body is formed with high dimensional accuracy by printing and etching techniques. Therefore, the beam synthesis accuracy is also high.
[0047]
Further, the radiation characteristics of each antenna unit can be arbitrarily set according to the period and length of the metal strip, and complicated radiation characteristics can be easily obtained.
[0048]
Further, in the image guide, the dielectric external electromagnetic field because it decreases exponentially, radio wave leakage is very small to the side surface side of the dielectric leaky wave type antenna using the same, this embodiment less disturbance of radiation pattern due to interference of adjacent antenna the worker even when the array by being arranged a plurality of antennas in parallel, as the spacing between adjacent antenna as contrary to the grating lobe does not occur The antennas can be arranged closer to each other, and the entire antenna can be reduced in size.
[0049]
[Other embodiments]
In the above-described embodiment, the case where five (and eight) antenna units are connected in series has been described. However, when the target radiation characteristic of the vertical plane is more complicated, the number of units is increased and the target radiation of the vertical plane is increased. If the characteristics are simpler, the number of units may be reduced, and various changes can be made depending on the radiation characteristics of the target vertical plane.
[0050]
Further, in the above embodiment, the antenna of the present invention is provided in parallel in order to narrow the radiation characteristic of the horizontal plane, but this can be variously changed according to the radiation characteristic of the target horizontal plane, and the radiation of the horizontal plane is possible. If the characteristics may be wide, only one may be used.
[0051]
In the above embodiment, the metal strip is used as the loading body for leaking electromagnetic waves from the dielectric surface. However, as shown in FIG. 8, the surface of the dielectric 23 has a height of a predetermined height h as the loading body. By providing the step portions 24 ′ at regular intervals and forming a corrugated shape, a leaky wave type antenna unit can be configured.
[0052]
In this case, the interval d (referred to as corrugation period) of the high step portion 24 ′ and the length s (referred to as corrugation width) of the high step portion 24 ′ correspond to the strip period and strip width of the metal strip of the above embodiment, respectively. Thus, the above two equations can be used as they are, the radiation direction of the antenna unit is determined by the corrugated period d, and the radiation amount is determined by the corrugated width s and the height h of the high step portion 24 '.
[0053]
In addition, the power supply unit 22 of the above embodiment is provided on the surface side of the ground plane conductor. However, the input electromagnetic wave is branched on the back side of the ground plane conductor to supply power to one end of each dielectric on the surface side. A horn-type power feeding unit may be used.
[0054]
In the above embodiment, the leaky wave type antenna units provided with a loading body for leaking radio waves to the image line are connected in series. However, the present invention is not limited to the waveguide slot antenna which is a leaky wave type antenna. The invention can also be applied.
[0055]
A waveguide slot antenna is an antenna that leaks radio waves by providing a plurality of slots along the length direction on one side surface of a waveguide having a predetermined length for transmitting a fundamental wave.
θ _n = sin ⁻¹ [(β / k ₀ ) + (2n−1) λ ₀ / 2d _n ]
(Usually n = -1 to have only one beam)
However, the basic operation is the same as that when the loading body is provided on the image line.
[0056]
In FIG. 9, such a waveguide slot antenna is used as one antenna unit, and five antenna units U _{1 to} U ₅ are arranged in series so that the waveguide of each antenna unit forms one transmission line. Connected.
[0057]
In this antenna, equally dividing the distance d ₁ to d ₅ and the slot width s ₁ ~s ₅ slot 30 of the antenna units U ₁ ~U _5, the four defined areas in the u space the desired pattern Pr division The length L of each antenna unit U _{1 to} U ₅ is made equal to the value obtained by dividing the free space wavelength λ ₀ of the leaky wave by the width Δu, and the maximum radiation of the main lobe of the leaky wave of each antenna unit U _{1 to} U ₅ The synthesis is approximated to the desired pattern by setting the direction to be an angle corresponding to each division point of the definition area of the desired pattern Pr and setting the intensity to a value corresponding to the level of the desired pattern Pr at each division point. A beam can be obtained.
[0058]
In this antenna, waveguide slot antennas having slots of substantially the same length provided at regular intervals are connected in series to obtain a desired pattern, so that it is easy to design and process.
[0059]
In the above embodiment, in order to make the amplitude distribution of each antenna unit uniform, the length (strip width) of the metal strip is slightly increased. However, the length of the metal strip in the antenna unit is all increased. Even if they are the same, the composite pattern does not diverge from the desired pattern, so that the length of the metal strip for each antenna unit may be the same in order to simplify the design.
[0060]
If strict synthesis accuracy is not required, the desired beam characteristics are divided into N-1 at appropriate intervals, and the radiation angles of the radiation beams of the respective antenna units substantially coincide with the division points including both ends thereof. In addition, each antenna unit may be formed so that the combined radiation intensity for each radiation angle obtained by synthesizing the radiation intensity of the radiation beam of each antenna unit is close to the radiation intensity at each division point. In this case, at the maximum radiation angle of the main lobe of one antenna unit, the radiation intensity of the other antenna unit may not become zero, but precise processing in manufacturing is not required and the desired beam characteristics can be obtained at low cost. An antenna with close characteristics can be obtained. The same applies to an antenna unit in which a high step portion is provided on the surface of a dielectric as a loading body or an antenna unit in which a slot is provided in a waveguide.
[0061]
【The invention's effect】
As described above, the antenna beam combining method according to the first aspect of the present invention and the antenna according to the third aspect include the length of each transmission body of a plurality of leaky wave type antenna units connected in series as the radiation angle. set substantially equal to the value obtained by dividing the free space wavelength of the leaky wave by the division width when the synthesis target region of the desired beam characteristic for the value u where u = sin θ with respect to θ is equally divided into N-1. The leakage portion of each antenna unit is set so that the maximum radiation angle and the radiation intensity of each antenna unit substantially coincide with the radiation angles and radiation strengths of N division points including both ends of the synthesis target region.
[0062]
For this reason, at the maximum point of the main lobe of one antenna unit, the radiation intensity of all the other antenna units is the minimum, and the maximum point of the main lobe of each antenna unit coincides with a point on the desired pattern and is combined The pattern can be made very close to the desired pattern, and a complex arbitrary beam can be synthesized easily and accurately.
[0063]
Further, in the antenna according to claim 2 of the present invention, the leaky wave type plural N antenna units connected in tandem divided the region to be synthesized having a desired beam characteristic into N−1 in the radiation angle of the radiation beam. So that the radiation angles of the N division points including both ends substantially coincide with each other, and the combined radiation intensity for each radiation angle obtained by synthesizing the radiation intensity of the radiation beam of each antenna unit is close to the radiation intensity of each division point. Therefore, it is possible to obtain an antenna having characteristics close to the desired beam characteristics at low cost without requiring precise manufacturing.
[0064]
In addition, in the antenna having a structure in which the transmission body of each antenna unit is formed by an image line in which a dielectric is disposed on a ground plane conductor and the leakage portion is formed by a loading body loaded on the surface of the dielectric, transmission loss is reduced. Since there are few plane structures, design, manufacture, and installation are easy, cost is low, and complicated radiation characteristics can be obtained with high accuracy. In addition, in the image line, the electromagnetic field outside the dielectric decreases exponentially, so there is less interference between adjacent antenna units, and it is possible to prevent the antenna units from approaching each other to generate a grating lobe. it can. Thereby, the antenna unit can be arranged so as to obtain the desired directivity in the horizontal plane, and the entire antenna can be reduced in size.
[0065]
Further, in an antenna having a structure in which the transmission body of each antenna unit is formed by a waveguide and the leakage portion is formed by a slot provided on the surface of the waveguide, the size and period of the slot in each antenna unit are approximately the same. It can be made uniform, it is not necessary to consider the mutual coupling between the antenna elements, it is easy to design and manufacture, and the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a perspective view of an array type antenna including one antenna according to an embodiment of the present invention. FIG. 2 is a side view for explaining a signal propagation state of an image line. FIG. 4 is a diagram illustrating a beam combining method according to the present invention. FIG. 4 is a diagram illustrating radiation characteristics of each antenna unit according to an embodiment. FIG. 5 is a diagram illustrating an example of combined radiation characteristics of a vertical plane according to the embodiment. FIG. 7 is a diagram showing an example of the combined radiation characteristic of the vertical plane according to the embodiment. FIG. 7 is a diagram showing an example of the combined radiation characteristic of the vertical plane when the number of units is increased. FIG. 9 is a perspective view of the main part of another embodiment. FIG. 10 is a schematic diagram for explaining a road vehicle monitoring system using millimeter waves.
20 antenna 21 ground plane conductor 22 feeding portion 23 dielectric 24 metal strip U ₁ to U ₅ antenna unit

Claims (5)

A leakage wave type N antenna unit composed of a transmission body forming an electromagnetic wave transmission path and a plurality of leakage portions formed along the length direction on the surface of the transmission body, and the radiation surface of the leakage wave is in the same direction A beam combining method of antennas, which are connected in a column in a state of facing the antenna and combine desired beams as one antenna ,
A value obtained by dividing the free space wavelength of the leaky wave by the division width when the synthesis target region of the desired beam characteristic for the value u where u = sin θ with respect to the radiation angle θ is equally divided into N−1; Set the length of the transmission body of multiple antenna units to be almost equal,
The length and period of the leakage portion of each antenna unit are set so that the maximum radiation angle and the radiation intensity of each antenna unit substantially coincide with the radiation angles and radiation strengths of N division points including both ends of the synthesis target region. A beam combining method for an antenna, wherein the desired beam is obtained by setting. Leaky wave type N antenna units each comprising a transmission body forming an electromagnetic wave transmission path and a plurality of leakage portions formed along the length direction on the surface of the transmission body are arranged to emit leakage waves of each antenna unit. It is connected in series so as to form a single continuous transmission path with the surfaces facing in the same direction, and is fed with electromagnetic waves from one end side of the single continuous transmission path to obtain a desired antenna as one antenna . An antenna that emits electromagnetic waves with beam characteristics,
The length of the transmission body of the plurality of antenna units is a division width when the synthesis target region of the desired beam characteristic for a value u where u = sin θ with respect to the radiation angle θ is equally divided into N−1. It is set approximately equal to the value obtained by dividing the free-space wavelength of the leaky wave, and the length and period of the leaking portion of each antenna unit are the maximum radiation angle and radiation intensity of each antenna unit including N at both ends of the synthesis target region. An antenna characterized in that it is set so as to substantially coincide with the radiation angle and radiation intensity of each division point . The transmission body of each antenna unit is formed by an image line having a rod-shaped dielectric disposed on the surface of a ground plane conductor, and the leakage portion is a plurality of loads loaded on the surface of the dielectric along the length direction at a substantially constant period. The antenna according to claim 2 or 3, wherein the antenna is formed by a loaded body . The transmission body of each antenna unit is formed by a waveguide that transmits a fundamental mode, and the leakage portion is formed by a plurality of slots provided on the surface of the waveguide along the length direction at substantially constant intervals. claim 2 or claim 3 antennas, wherein the are. An antenna comprising a plurality of antennas according to any one of claims 2 to 4 arranged side by side in parallel .

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