JP2004040571A

JP2004040571A - Antenna device for vehicle, and its designing method

Info

Publication number: JP2004040571A
Application number: JP2002196205A
Authority: JP
Inventors: Hiroshi Iijima; 飯島　浩; Ryokichi Doi; 土居　亮吉
Original assignee: Nippon Sheet Glass Co Ltd
Current assignee: Nippon Sheet Glass Co Ltd
Priority date: 2002-07-04
Filing date: 2002-07-04
Publication date: 2004-02-05
Anticipated expiration: 2022-07-04
Also published as: JP3971966B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for designing an antenna device for a vehicle which can reduce the dimensions of a film cut part into an inconspicuous extent and can transmit and receive radio waves satisfactorily. <P>SOLUTION: The transmitting and receiving characteristics of this antenna device for a vehicle provided with the film cut part with no transparent conductive film of window glass formed and an antenna for receiving the radio waves through the film cut part depend upon the dimensions of the film cut part and a distance d between the window glass and the antenna. When the distance d is varied while the dimensions of the film cut part are constant, maximum values of transmitting and receiving characteristic values are distributed. Then, the dimensions of the film cut part and the distance d are changed to measure the transmitting and receiving characteristics of the antenna. The dimensions of the film cut part and distances d to be the candidates are selected among the maximum values, and optimum dimensions of the film cut part and an optimum distance d are determined among the candidates by actually taking into consideration positions for mounting the antenna in the vehicle. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、車両用アンテナ装置、特に透明導電膜が形成された窓ガラスに取り付けられるＩＴＳ（Ｉｎｔｅｌｌｉｇｅｎｔ　ｔｒａｎｓｐｏｒｔ　ｓｙｓｔｅｍｓ）用のアンテナ装置およびその設計方法に関する。
【０００２】
【従来の技術】
現在、車両内にＩＴＳ用のアンテナ（ＧＰＳ，ＶＩＣＳ，ＥＴＣ等）を取り付けることにより、さまざまな情報サービスを受けることができるようになっている。車両のウインドシールド（窓ガラス）には、太陽の日射による暑さ軽減のため、あるいは、ガラスに霜とり機能を付加するなどの目的で、透明導電膜（金属膜）が形成されたものがある。このような透明導電膜つきウインドシールドの場合、透明導電膜によって電波が減衰しアンテナが機能しなくなるという問題点がある。
【０００３】
このような問題点を解決する方法として、特開２００２−２０１４２号公報に開示されているように、部分的に透明導電膜を切り欠いて、電波を透過させる膜切欠き部をウインドシールドに設けている。図１に、その一例を示す。図中、２は、ウインドシールドを、４，６は膜切欠き部を示す。
【０００４】
また、特開平８−２１００４２号公報にも、車両用の窓ガラスに電磁線を透過させる領域を形成することが開示されている。
【０００５】
【発明が解決しようとする課題】
しかし、このような膜切欠き部の寸法については、詳細な検討がなされることがなかったため、かなり大きいものであり、また透明導電膜部分と透明導電膜なし部分では色目が違うため、膜切欠き部が目立ち、車両の外観を損なうという問題点がある。
【０００６】
さらに、ＥＴＣ（Ｅｌｅｃｔｒｏｎｉｃ　Ｔｏｌｌ　Ｃｏｌｌｅｃｔｉｏｎｓ）用の電波は約５．８ＧＨｚで、λ（空間波長）は約５２ｍｍであり、ＶＩＣＳ（Ｖｅｈｉｃｌｅ　Ｉｎｆｏｒｍａｔｉｏｎ　ａｎｄ　Ｃｏｍｍｕｎｉｃａｔｉｏｎ　Ｓｙｓｔｅｍ）用の電波は、約２．５ＧＨｚで、λは約１２０ｍｍであり、ＧＰＳ（Ｇｒｏｂａｌ　Ｐｏｓｉｔｉｏｎ　Ｓｙｓｔｅｍ）用の電波は約１．６ＧＨｚで、λは約１８７ｍｍであり、いずれも用いられる電波は短波長である。
【０００７】
なお、ＥＴＣおよびＧＰＳ用の電波には円偏波が用いられ、ＶＩＣＳ用の電波には直線偏波（垂直偏波または水平偏波）が用いられている。
【０００８】
このような短波長の電波を受信する車両用アンテナには、通常、平面アンテナが、窓ガラスから離れた位置に取り付けられて、用いられる。
【０００９】
上述のような短波長の電波に対し、窓ガラス（誘電体）は、電波を反射するようになる。このような反射波のアンテナの送受信特性への影響は、膜切欠き部の寸法と、窓ガラスとアンテナとの間の距離に依存して変化することが予測される。
【００１０】
したがって、ＩＴＳ用のアンテナ装置は、窓ガラスの透明導電膜の膜切欠き部の寸法をできるだけ小さくすると共に、窓ガラスとアンテナとの間の距離を、良好に電波を送受信できるように設計することが要求されている。
【００１１】
本発明の目的は、目立たない程度に透明導電膜の膜切欠き部の寸法を小さくし、および、良好に電波を送受信することを可能にした車両用アンテナ装置を提供することにある。
【００１２】
本発明のさらに他の目的は、上記のような車両用アンテナ装置を設計する方法を提供することにある。
【００１３】
【課題を解決するための手段】
本願発明者らは、窓ガラスの透明導電膜が形成されていない膜切欠き部と、膜切欠き部を透過してくる電波を受信するアンテナとを備える車両用アンテナ装置の送受信特性は、膜切欠き部の寸法と、窓ガラスとアンテナとの間の距離ｄとに依存するという予測のもとに、膜切欠き部の寸法を一定にして距離ｄを変えた場合、送受信特性値の極大値が分布することを見出した。
【００１４】
したがって、膜切欠き部の寸法、および窓ガラスとアンテナとの間の距離ｄを変えて、アンテナの送受信特性値を測定し、その極大値から候補となる膜切欠き部の寸法、および窓ガラスとアンテナとの間の距離ｄを選び、これら候補の中から、実際に車両内のアンテナ取り付け位置を考慮して、最適な膜切欠き部の寸法および距離ｄを決定することができる。
【００１５】
本発明の一態様は、実質的全面に透明導電膜が形成された車両用窓ガラスの前記透明導電膜の一部に形成された膜切欠き部と、前記膜切欠き部を透過してくる電波を受信するアンテナとを備える車両用アンテナ装置の設計方法である。この設計方法は、
（ａ）異なる寸法の膜切欠き部がそれぞれ設けられた複数枚の測定用窓ガラスと、前記アンテナとを準備するステップと、
（ｂ）放射されてくる電波が存在する環境内に前記アンテナを設置し、アンテナの受信電圧を測定するステップと、
（ｃ）前記複数枚の測定用窓ガラスのうち１枚の測定用窓ガラスを、前記アンテナに対して、前記電波の到来してくる側に配置し、前記測定用窓ガラスと前記アンテナとの間の距離を変えながら、前記アンテナの受信電圧を測定するステップと、
（ｄ）前記ステップ（ｂ）で測定した受信電圧に対する、前記ステップ（ｃ）で測定した受信電圧の減衰量を求めるステップと、
（ｅ）前記（ｃ），（ｄ）のステップを繰り返すステップと、
（ｆ）前記各測定用窓ガラスについて求められた減衰量の極大値を求めるステップと、
（ｇ）前記極大値を与える、前記膜切欠き部の寸法、および前記測定用窓ガラスと前記アンテナとの間の距離のうち、最適な寸法および距離を選択し、選択した寸法を前記車両用窓ガラスの透明導電膜の一部に形成された膜切欠き部の寸法とし、前記選択した距離を、前記車両用窓ガラスと前記アンテナとの間の距離とするステップと、
を含んでいる。
【００１６】
本発明の他の態様は、実質的全面に透明導電膜が形成された車両用窓ガラスの前記透明導電膜の一部に形成された膜切欠き部と、前記膜切欠き部を透過してくる電波を受信するアンテナとを備える車両用アンテナ装置であって、前記アンテナは、所定の寸法を有する前記膜切欠き部を透過してくる電波を受信する場合に、受信電圧の減衰量が極大値となる、前記窓ガラスから離れた位置に設置されている。
【００１７】
【発明の実施の形態】
本発明の車両用アンテナ装置の設計方法の実施の形態を説明する。
【００１８】
一例として、ＥＴＣ用アンテナ装置の設計方法について述べる。まず、透明導電膜が全く形成されていない透明導電膜なし窓ガラスと、透明導電膜が形成されていない膜切欠き部を設けた透明導電膜つき窓ガラスとを用意した。透明導電膜つき窓ガラスは、合わせガラスよりなり、重ね合わされたガラス板の間に透明導電膜が設けられている。
【００１９】
図２に、膜切欠き部が設けられた窓ガラスの一部を示す。（Ａ）は平面図、（Ｂ）は断面図である。１０は窓ガラスを、１２は透明導電膜を、１４は膜切欠き部を示す。
【００２０】
前述したようにＥＴＣ用の電波には円偏波が用いられるので膜切欠き部の形状は、偏波方向に平行な長さと、偏波方向と直交する長さを同じにしなければならない。正方形は、その一例である。
【００２１】
膜切欠き部１４の正方形の一辺の寸法をａとする。ａ＝３０ｍｍ（≒０．６λ）ものと、ａ＝５０ｍｍ（≒１λ）のものを、２種類準備した。
【００２２】
まず、図３（Ａ）に示すように、測定環境、例えば電波暗室に平面アンテナ２０を置き、アンテナの出力端子に５０Ωの抵抗を接続する。そして、このアンテナに向かってＥＴＣ用の円偏波である周波数５．８ＧＨｚ（λ＝５２ｍｍ）の電波を放射し、抵抗に誘起する受信電圧Ｖ_ｒｅｆ　を測定した。この電圧は、後述する減衰量計算の基準となる。
【００２３】
次に、図３（Ｂ）に示すように、電波が放射されてくる側にアンテナ２０から距離ｄだけ離れた位置に、透明導電膜なし窓ガラス８に設置した。なお、距離ｄは、窓ガラス８の表面から平面アンテナ２０の表面までの距離である。ｄの値を変えながら、窓ガラス８の反対方向から到来し、窓ガラスを透過した電波を受信し、アンテナの受信電圧Ｖを測定した。
【００２４】
次に、図３（Ｃ）に示すように、電波が放射されてくる側にアンテナ２０から距離ｄだけ離れた位置に、膜切欠き部１４が設けられた透明導電膜つき窓ガラス１０に設置し、ｄの値を変えながら、窓ガラス１０の反対方向から到来し、膜切欠き部１４を透過する電波を受信し、アンテナの受信電圧Ｖを測定した。これは、前述した２種類の透明導電膜つき窓ガラスについて、それぞれ行った。
【００２５】
以上の測定値から、透明導電膜なし窓ガラス、あるいは膜切欠き部が設けられた透明導電膜つき窓ガラスを設けた場合に、窓ガラスを設けない場合に比べて、受信電圧がどれだけ減衰したかを示す減衰量を、２０ｌｏｇ（Ｖ／Ｖ_ｒｅｆ　）で計算した。計算結果を表１に示す。
【００２６】
【表１】

【００２７】
ただし、ｄ／λは、距離ｄを空間波長λで正規化した値である。
【００２８】
図４には、これをグラフ化して示す。縦軸は減衰量［ｄＢ］、横軸はｄ／λである。０ｄＢは、窓ガラスを設置しない場合の減衰量である。縦軸は、マイナス方向に数値が大きくなるに従って、減衰量が大きくなることを示している。
【００２９】
このグラフからわかるように、透明導電膜なし窓ガラス、および膜切欠き部が設けられた透明導電膜つき窓ガラスのいずれにおいても、ｄ／λの変化に伴って、極大値が分布するように変動していることがわかる。
【００３０】
透明導電膜なし窓ガラスの場合、ｄ／λ＝０．１、すなわちｄ＝０．１λ（＝５．２ｍｍ）と、ｄ／λ＝０．６、すなわちｄ＝０．６λ（３１．２ｍｍ）とで減衰量は極大値を有している。ａ＝３０ｍｍの膜切欠き部が設けられた透明導電膜つき窓ガラスの場合は、透明導電膜なし窓ガラスの場合と全く同様に、ｄ／λ＝０．１、およびｄ／λ＝０．６で、極大値を有している。ａ＝５０ｍｍの膜切欠き部が設けられた透明導電膜つき窓ガラスの場合は、ｄ／λ＝０．２、すなわちｄ＝０．２λ（＝１０．４ｍｍ）と、ｄ／λ＝０．６、すなわちｄ＝０．６λ（＝３１．２ｍｍ）とで極大値を有している。
【００３１】
以上のように減衰量が分布する極大値を有して変動するという事実は、本願発明者が見出した新しい知見であり、前述したように、ガラスの表面からの反射波が原因であると考えられる。
【００３２】
さらに、図４のグラフから次のことがわかる。すなわち、ａ＝３０ｍｍの膜切欠き部が設けられた透明導電膜つき窓ガラスの場合、ｄ／λ＜０．２の範囲では、透明導電膜なし窓ガラスとほぼ同等の減衰量となり、また、ａ＝５０ｍｍの膜切欠き部が設けられた透明導電膜つき窓ガラスの場合、ｄ／λ＞０．２の範囲では、透明導電膜なし窓ガラスとほぼ同等の減衰量となる。
【００３３】
このように、ａ＝３０ｍｍの膜切欠き部を有する窓ガラスの減衰量曲線と、ａ＝５０ｍｍの膜切欠き部を有する窓ガラスの減衰量曲線とが、ｄ／λ＝０．２で交差する理由は、前述したガラスからの反射波に加えて、透明導電膜の膜切欠き部の縁部で反射された電波の影響によるものと考えられる。
【００３４】
以上のように、透明導電膜なし窓ガラス、膜切欠き部を設けた透明導電膜つき窓ガラスについて、減衰量を求めたならば、減衰量が膜切欠き部の寸法ａ、および窓ガラスとアンテナとの間の距離ｄによって、どのように変動するかがわかる。そして、減衰量が極大値をとる距離ｄがアンテナの適切な設置位置の候補であることがわかる。
【００３５】
これら設置位置の中で、本実施の形態では、ａ＝３０ｍｍの膜切欠き部を有する透明導電膜つき窓ガラスの場合、ｄ＝０．１λ（＝５．２ｍｍ）が、そのときの減衰量が透明導電膜なし窓ガラスの減衰量とほぼ同等となるので最適であり、ａ＝５０ｍｍの膜切欠き部を有する透明導電膜つき窓ガラスの場合、ｄ＝０．６λ（＝３１．２ｍｍ）が、そのときの減衰量が透明導電膜なし窓ガラスの減衰量とほぼ同等となるので最適であることがわかる。いずれを選ぶかは、窓ガラスの透明導電膜に膜切欠き部を設ける箇所、車両内に設けるアンテナの位置によって決定される。また、いずれの場合も、膜切欠き部の寸法は、空間波長と同程度か、あるいは空間波長より小さく、膜切欠き部が目立たない程の小さな寸法である。
【００３６】
また、以上の実施の形態では、膜切欠き部の形状は正方形としたが、これに限られるものではなく、正方形の膜切欠き部の面積と同じ面積を有する円形の膜切欠き部としてもよい。
【００３７】
以上説明した実施の形態では、透明導電膜なし窓ガラスについて、減衰量を求めているが、これは膜切欠き部が設けられた透明導電膜あり窓ガラスの減衰量と比較して参考にするためのデータであり、透明導電膜なし窓ガラスの減衰量よりも大きな減衰量であっても、アンテナ装置として送受信特性が保持されるならば、透明導電膜なし窓ガラスについて減衰量を求めることは、必須ではないことは明らかである。
【００３８】
以上は、ＥＴＣ用アンテナ装置の設計方法についての実施の形態であるが、ＶＩＣＳ，ＧＰＳ用アンテナ装置についても、同様の方法で設計が可能であることは、当業者に容易に理解されるであろう。
【００３９】
ＶＩＣＳ用アンテナ装置の設計についても、ａ＝３０ｍｍ，５０ｍｍの膜切欠き部を有する窓ガラスを２種類準備し、ＶＩＣＳ用の直線偏波である周波数２．５ＧＨｚ（λ＝１２０ｍｍ）の電波を用いて、ＥＴＣ用アンテナ装置の場合と同様の測定を行い、測定値から減衰量を計算した。計算結果を表２に示す。
【００４０】
【表２】

【００４１】
図５には、これをグラフ化して示す。このグラフからわかるように、透明導電膜なし窓ガラス、および膜切欠き部が設けられた透明導電膜つき窓ガラスのいずれにおいても、ｄ／λの変化に伴って、極大値が分布するように変動していることがわかる。
【００４２】
透明導電膜なし窓ガラスの場合、ｄ／λ＝０．２、すなわちｄ＝０．２λ（＝２４ｍｍ）と、ｄ／λ＝０．７、すなわちｄ＝０．７λ（８４ｍｍ）とで減衰量は極大値を有している。ａ＝３０ｍｍの膜切欠き部が設けられた透明導電膜つき窓ガラスの場合は、透明導電膜なし窓ガラスの場合と全く同様に、ｄ／λ＝０．２で、極大値を有している。ａ＝５０ｍｍの膜切欠き部が設けられた透明導電膜つき窓ガラスの場合は、ｄ／λ＝０．７、すなわちｄ＝０．７λ（＝８４ｍｍ）で極大値を有している。
【００４３】
したがって、ａ＝３０ｍｍの膜切欠き部を有する透明導電膜つき窓ガラスの場合、ｄ＝０．２λ（＝２４ｍｍ）が、そのときの減衰量が透明導電膜なし窓ガラスの減衰量とほぼ同等となるので最適であり、ａ＝５０ｍｍの膜切欠き部を有する透明導電膜つき窓ガラスの場合、ｄ＝０．７λ（＝８４ｍｍ）が、そのときの減衰量が透明導電膜なし窓ガラスの減衰量とほぼ同等となるので最適であることがわかる。
【００４４】
以上のＶＩＣＳ用アンテナ装置では、膜切欠き部の形状を正方形としたが、ＶＩＣＳ用の電波は直線偏波であるので、偏波方向に平行な向きの長さを、偏波方向と直交する向きの長さの１／２まで短縮することができる。例えば、一辺が１波長の長さを有する正方形の膜切欠き部は、電波が垂直偏波の場合、縦方向の長さを１／２波長とすることができる。したがって、この場合、膜切欠き部の形状は横長の長方形となる。このような長方形の膜切欠き部は、同じ面積を有する楕円形の膜切欠き部としてもよい。
【００４５】
次に、本発明の車両用アンテナ装置の実施の形態を説明する。
【００４６】
前述したＥＴＣ用アンテナ装置の設計方法の実施の形態において選ばれた、ａ＝３０ｍｍ，ｄ＝５．２ｍｍの場合と、ａ＝５０ｍｍ，ｄ＝３１．２ｍｍの場合とについて、窓ガラスの透明導電膜に膜切欠き部を設ける最適な箇所、およびアンテナの最適な設置箇所について、図６を参照して説明する。
【００４７】
なお、以下の説明では、便宜上２つの例を同時に説明するが、実際には１つの例が選択される。
【００４８】
図６（Ａ）は、ウインドシールド（窓ガラス）２の正面図であり、一辺が５０ｍｍの正方形の膜切欠き部３０が、ウインドシールド２の上部中央に設けられるか、あるいは一辺が３０ｍｍの正方形の膜切欠き部３２が、ウインドシールド２の下部左端に設けられる。
【００４９】
このように、寸法が大きい方の膜切欠き部３０をウインドシールド２の上部中央に設けた理由は、ウインドシールドの上部では膜切欠き部があまり目立たないことと、ＥＴＣ用の平面アンテナを室内ミラーの裏側に取り付けるためである。また、ウインドシールド２の下部は、膜切欠き部が目立ちやすいので、寸法が小さい方の膜切欠き部３２を設けるのが望ましい。
【００５０】
図６（Ｂ）は、車両内における平面アンテナの取り付け位置を示す。ウインドシールドの上部中央の膜切欠き部３０を透過してくるＥＴＣ用電波を受信する平面アンテナ３４は、室内ミラー３６の裏側に取り付けられる。このとき、ウインドシールド２と平面アンテナ３４との間の距離ｄは、３１．２ｍｍとなるように設定する。
【００５１】
あるいは、ウインドシールドの下部左端の膜切欠き部３２を透過してくるＥＴＣ用電波を受信する平面アンテナ３８は、運転台上に設けられた支持柱４０に取り付けられる。このとき、ウインドシールド２と平面アンテナ３８との間の距離ｄは、５．２ｍｍとなるように設定する。
【００５２】
以上の例では、平面アンテナを取り付けるのに、室内ミラーの裏側を利用したり、あるいは取り付けのための支持柱を用意したが、このような方法に限らず、最適な距離を保てる方法で設置できればどのような方法でもよい。例えば、図７に示すように、ＥＴＣ用アンテナ４２と、電気系統であるＥＴＣ用ユニット４４とを内蔵させたアンテナモジュール４６を、ウインドシールドの裏面に貼り付けるようにしてもよい。
【００５３】
以上は、ＥＴＣ用アンテナ装置の実施の形態であるが、ＶＩＣＳ，ＧＰＳ用アンテナ装置についても、同じように構成できることは、当業者に容易に理解されるであろう。
【００５４】
また、以上の実施の形態では、膜切欠き部の形状は正方形としたが、これに限られるものではなく、長方形，円形，楕円形など、その他の形状とすることもできる。
【００５５】
【発明の効果】
本発明によれば、透明導電膜つきの窓ガラスに設ける膜切欠き部の寸法を目立たない程度の小さな大きさとすることができ、また、膜切欠き部の寸法に応じて、窓ガラスとアンテナとの間の距離を調整しているので、膜切欠き部が設けられた透明導電膜つき窓ガラスの減衰量を、透明導電膜なし窓ガラスの減衰量とほぼ同等まで改善することができる。
【図面の簡単な説明】
【図１】膜切欠き部を説明するためのウインドシールドを示す図である。
【図２】膜切欠き部が設けられた窓ガラスの一部を示す平面図および断面図である。
【図３】本発明の設計方法に関係した電波暗室での測定を説明するための図である。
【図４】ＥＴＣアンテナ装置の設計の際の減衰量を示すグラフである。
【図５】ＶＩＣＳアンテナ装置の設計の際の減衰量を示すグラフである。
【図６】本発明のアンテナ装置を説明するための図であり、ウインドシールドの膜切欠き部、およびアンテナの設置位置を示す。
【図７】アンテナモジュールを示す図である。
【符号の説明】
２，１０　ウインドシールドまたは窓ガラス
８　透明導電膜なし窓ガラス
１２　透明導電膜
１４，３０，３２　膜切欠き部
２０，３４，３８，４２　平面アンテナ
３６　室内ミラー
４０　支持柱
４４　ＥＴＣ用ユニット
４６　アンテナモジュール[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an antenna device for a vehicle, and particularly to an antenna device for ITS (Intelligent transport systems) attached to a window glass on which a transparent conductive film is formed, and a design method thereof.
[0002]
[Prior art]
At present, various information services can be received by installing an ITS antenna (GPS, VICS, ETC, etc.) in a vehicle. Some windshields (window glass) of vehicles have a transparent conductive film (metal film) formed for the purpose of reducing heat due to the sun's sunlight or for adding a defrost function to the glass. . In the case of such a windshield with a transparent conductive film, there is a problem that the radio wave is attenuated by the transparent conductive film and the antenna does not function.
[0003]
As a method for solving such a problem, as disclosed in Japanese Patent Application Laid-Open No. 2002-20142, a transparent conductive film is partially cut out, and a film cutout for transmitting radio waves is provided in the windshield. ing. FIG. 1 shows an example. In the figure, reference numeral 2 denotes a windshield, and

reference numerals

4 and 6 denote film cutouts.
[0004]
Also, Japanese Patent Application Laid-Open No. Hei 8-210042 discloses that a region for transmitting electromagnetic radiation is formed in a window glass for a vehicle.
[0005]
[Problems to be solved by the invention]
However, the dimensions of such a film cutout portion were rather large because no detailed examination was made, and the color difference between the transparent conductive film portion and the portion without the transparent conductive film was different. There is a problem that the notch is conspicuous and the appearance of the vehicle is impaired.
[0006]
Further, the radio wave for ETC (Electronic Toll Collection) is about 5.8 GHz, the λ (spatial wavelength) is about 52 mm, and the radio wave for VICS (Vehicle Information and Communication System) is about 2.5 GHz, and λ is 2.5 GHz. The radio wave for GPS (Global Position System) is about 1.6 GHz, λ is about 187 mm, and the radio wave used in each case has a short wavelength.
[0007]
Note that circularly polarized waves are used for ETC and GPS radio waves, and linearly polarized waves (vertically or horizontally polarized waves) are used for VICS radio waves.
[0008]
For a vehicle antenna that receives such a short-wavelength radio wave, a planar antenna is usually used by being attached to a position away from a window glass.
[0009]
The window glass (dielectric) reflects radio waves with respect to the short-wavelength radio waves as described above. The effect of such reflected waves on the transmission and reception characteristics of the antenna is expected to change depending on the size of the film cutout portion and the distance between the window glass and the antenna.
[0010]
Therefore, the antenna device for ITS should be designed so that the size of the cutout portion of the transparent conductive film of the window glass is made as small as possible, and the distance between the window glass and the antenna can be transmitted and received satisfactorily. Is required.
[0011]
An object of the present invention is to provide a vehicular antenna device in which the size of a film cutout portion of a transparent conductive film is reduced to an inconspicuous degree, and a radio wave can be transmitted and received satisfactorily.
[0012]
Still another object of the present invention is to provide a method for designing an antenna device for a vehicle as described above.
[0013]
[Means for Solving the Problems]
The inventors of the present application have disclosed a transmission / reception characteristic of a vehicle antenna device including a film cutout portion of a window glass on which a transparent conductive film is not formed, and an antenna for receiving a radio wave transmitted through the film cutout portion. When the distance d is changed while keeping the size of the film notch constant based on the prediction that it depends on the size of the notch and the distance d between the window glass and the antenna, the maximum of the transmission / reception characteristic value is obtained. The values were found to be distributed.
[0014]
Therefore, the transmission / reception characteristic value of the antenna is measured by changing the size of the film notch and the distance d between the window glass and the antenna, and the size of the film notch which is a candidate from the maximum value, and the window glass The distance d between the antenna and the antenna is selected, and from these candidates, the optimum size and distance d of the film notch can be determined in consideration of the antenna mounting position in the vehicle.
[0015]
According to one embodiment of the present invention, a notch formed in a part of the transparent conductive film of a window glass for a vehicle in which a transparent conductive film is formed over substantially the entire surface, and the film is transmitted through the notch. This is a method for designing a vehicle antenna device including an antenna for receiving a radio wave. This design method
(A) preparing a plurality of measurement window glasses provided with film notches of different dimensions, respectively, and the antenna;
(B) installing the antenna in an environment where radiated radio waves are present, and measuring a reception voltage of the antenna;
(C) one of the plurality of measurement window glasses is arranged on the side from which the radio wave comes with respect to the antenna, and the measurement window glass and the antenna are connected to each other; Measuring the received voltage of the antenna while changing the distance between;
(D) obtaining an attenuation of the reception voltage measured in the step (c) with respect to the reception voltage measured in the step (b);
(E) repeating the steps (c) and (d);
(F) obtaining a maximum value of the amount of attenuation determined for each of the measurement window glasses;
(G) An optimal dimension and distance are selected from the dimensions of the membrane notch, giving the maximum value, and the distance between the measurement window glass and the antenna, and the selected dimension is used for the vehicle. The dimensions of the film notch formed in a part of the transparent conductive film of the window glass, the selected distance, the step of the distance between the vehicle window glass and the antenna,
Includes
[0016]
According to another aspect of the present invention, a film notch formed in a part of the transparent conductive film of a vehicle window glass having a transparent conductive film formed on substantially the entire surface thereof, An antenna for receiving an incoming radio wave, wherein the antenna has a maximum amount of attenuation of a received voltage when receiving an electric wave transmitted through the film notch having a predetermined dimension. It is installed at a position away from the window glass.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a method for designing a vehicle antenna device according to the present invention will be described.
[0018]
As an example, a method of designing an ETC antenna device will be described. First, a window glass without a transparent conductive film, on which no transparent conductive film was formed, and a window glass with a transparent conductive film, provided with a film cutout portion, on which no transparent conductive film was formed, were prepared. The window glass with a transparent conductive film is made of laminated glass, and a transparent conductive film is provided between the laminated glass plates.
[0019]
FIG. 2 shows a part of a window glass provided with a film notch. (A) is a plan view and (B) is a cross-sectional view. Reference numeral 10 denotes a window glass, 12 denotes a transparent conductive film, and 14 denotes a film cutout.
[0020]
As described above, since circularly polarized waves are used for ETC radio waves, the shape of the film cutout portion must be the same in length parallel to the polarization direction and perpendicular to the polarization direction. A square is one example.
[0021]
The dimension of one side of the square of the film notch 14 is defined as a. Two types were prepared: a = 30 mm (≒ 0.6λ) and a = 50 mm (≒ 1λ).
[0022]
First, as shown in FIG. 3A, the planar antenna 20 is placed in a measurement environment, for example, an anechoic chamber, and a resistance of 50Ω is connected to an output terminal of the antenna. Then, a radio wave having a frequency of 5.8 GHz (λ = 52 mm), which is a circularly polarized wave for ETC, was radiated toward the antenna, and the reception voltage V _ref induced in the resistance was measured. This voltage is used as a reference for calculating the amount of attenuation described later.
[0023]
Next, as shown in FIG. 3B, a window glass 8 without a transparent conductive film was installed at a position away from the antenna 20 by a distance d on the side from which radio waves were radiated. The distance d is the distance from the surface of the window glass 8 to the surface of the planar antenna 20. While changing the value of d, a radio wave coming from the opposite direction of the window glass 8 and passing through the window glass was received, and the reception voltage V of the antenna was measured.
[0024]
Next, as shown in FIG. 3 (C), at a position away from the antenna 20 by a distance d on the side from which the radio wave is radiated, the window glass 10 with the transparent conductive film provided with the film cutout 14 is installed. Then, while changing the value of d, a radio wave coming from the opposite direction of the window glass 10 and passing through the film notch 14 was received, and the reception voltage V of the antenna was measured. This was performed for each of the two types of window glasses with a transparent conductive film described above.
[0025]
From the above measured values, when a window glass without a transparent conductive film, or a window glass with a transparent conductive film provided with a film cutout is provided, the received voltage is attenuated compared to the case without the window glass. The amount of attenuation indicating whether or not the measurement was performed was calculated using 20 log (V / V _ref ). Table 1 shows the calculation results.
[0026]
[Table 1]

[0027]
Here, d / λ is a value obtained by normalizing the distance d with the spatial wavelength λ.
[0028]
FIG. 4 shows this in a graph. The vertical axis is the attenuation [dB], and the horizontal axis is d / λ. 0 dB is the attenuation when no window glass is installed. The vertical axis indicates that the attenuation increases as the numerical value increases in the minus direction.
[0029]
As can be seen from this graph, in each of the window glass without the transparent conductive film and the window glass with the transparent conductive film provided with the film notch, the maximum value is distributed with the change of d / λ. It can be seen that it fluctuates.
[0030]
In the case of a window glass without a transparent conductive film, d / λ = 0.1, that is, d = 0.1λ (= 5.2 mm), and d / λ = 0.6, that is, d = 0.6λ (31.2 mm) And the attenuation has a maximum value. In the case of a window glass with a transparent conductive film provided with a film notch portion of a = 30 mm, d / λ = 0.1 and d / λ = 0. 6 has a local maximum. In the case of a window glass with a transparent conductive film provided with a film notch of a = 50 mm, d / λ = 0.2, that is, d = 0.2λ (= 10.4 mm) and d / λ = 0. 6, ie, d = 0.6λ (= 31.2 mm), which has the maximum value.
[0031]
The fact that the attenuation fluctuates with the distributed maximum value as described above is a new finding discovered by the present inventor, and as described above, is considered to be caused by the reflected wave from the glass surface. Can be
[0032]
Further, the following can be seen from the graph of FIG. That is, in the case of a window glass with a transparent conductive film provided with a film cutout portion of a = 30 mm, in the range of d / λ <0.2, the attenuation is almost the same as that of the window glass without a transparent conductive film. In the case of a window glass with a transparent conductive film provided with a film notch of a = 50 mm, the attenuation is almost the same as a window glass without a transparent conductive film in the range of d / λ> 0.2.
[0033]
As described above, the attenuation curve of the window glass having the film notch of a = 30 mm and the attenuation curve of the window glass having the film notch of a = 50 mm intersect at d / λ = 0.2. It is considered that the reason for this is that, in addition to the above-mentioned reflected wave from the glass, the influence of the radio wave reflected at the edge of the film cutout portion of the transparent conductive film.
[0034]
As described above, for a window glass without a transparent conductive film, for a window glass with a transparent conductive film provided with a film notch, if the amount of attenuation is determined, the amount of attenuation is the dimension a of the film notch, and the window glass. It can be seen how the distance f varies depending on the distance d from the antenna. Then, it can be seen that the distance d at which the amount of attenuation takes the maximum value is a candidate for an appropriate installation position of the antenna.
[0035]
Among these installation positions, in the present embodiment, in the case of a window glass with a transparent conductive film having a film cutout of a = 30 mm, d = 0.1λ (= 5.2 mm) is an attenuation amount at that time. Is almost equal to the attenuation of a window glass without a transparent conductive film. In the case of a window glass with a transparent conductive film having a film cutout of a = 50 mm, d = 0.6λ (= 31.2 mm) However, it can be seen that the amount of attenuation at that time is almost the same as the amount of attenuation of the window glass without the transparent conductive film, so that it is optimal. Which one to select depends on the location of the film cutout in the transparent conductive film of the window glass and the position of the antenna provided in the vehicle. In each case, the size of the film notch is approximately the same as or smaller than the spatial wavelength, and is small enough to make the film notch inconspicuous.
[0036]
Further, in the above embodiments, the shape of the film notch is a square, but the shape is not limited to this, and the film notch may be a circular film notch having the same area as the area of the square film notch. Good.
[0037]
In the embodiment described above, the attenuation amount is obtained for the window glass without the transparent conductive film, but this is compared with the attenuation amount of the window glass with the transparent conductive film provided with the film cutout portion. Even if the attenuation is larger than that of the window glass without the transparent conductive film, if the transmission / reception characteristics are maintained as the antenna device, it is not possible to obtain the attenuation for the window glass without the transparent conductive film. Obviously, it is not required.
[0038]
Although the above is an embodiment of a method of designing an antenna device for ETC, it is easily understood by those skilled in the art that the antenna device for VICS and GPS can be designed in a similar manner. Would.
[0039]
Regarding the design of the antenna device for VICS, two types of window glasses having film cutouts of a = 30 mm and 50 mm are prepared, and radio waves having a frequency of 2.5 GHz (λ = 120 mm), which is a linearly polarized wave for VICS, are used. Then, the same measurement as in the case of the ETC antenna device was performed, and the attenuation was calculated from the measured value. Table 2 shows the calculation results.
[0040]
[Table 2]

[0041]
FIG. 5 shows this in a graph. As can be seen from this graph, in each of the window glass without the transparent conductive film and the window glass with the transparent conductive film provided with the film notch, the maximum value is distributed with the change of d / λ. It can be seen that it fluctuates.
[0042]
In the case of a window glass without a transparent conductive film, the attenuation is obtained when d / λ = 0.2, that is, d = 0.2λ (= 24 mm), and when d / λ = 0.7, that is, d = 0.7λ (84 mm). Has a maximum value. In the case of a window glass with a transparent conductive film provided with a film notch portion of a = 30 mm, d / λ = 0.2 and a maximum value having a maximum value just like the case of a window glass without a transparent conductive film. I have. In the case of a window glass with a transparent conductive film provided with a film notch of a = 50 mm, the maximum value is obtained at d / λ = 0.7, that is, d = 0.7λ (= 84 mm).
[0043]
Therefore, in the case of a window glass with a transparent conductive film having a film cutout portion of a = 30 mm, d = 0.2λ (= 24 mm), the attenuation at that time is almost equal to the attenuation of the window glass without the transparent conductive film. In the case of a window glass with a transparent conductive film having a film cutout of a = 50 mm, d = 0.7λ (= 84 mm), and the attenuation at that time is the same as that of the window glass without a transparent conductive film. It can be seen that it is optimal because it is almost equal to the amount of attenuation.
[0044]
In the above-mentioned VICS antenna device, the shape of the film notch is square, but since the VICS radio wave is linearly polarized, the length parallel to the polarization direction is set to be orthogonal to the polarization direction. The length of the direction can be reduced to １／. For example, in the case of a square film notch having a length of one wavelength on one side, when the radio wave is vertically polarized, the length in the vertical direction can be set to 波長 wavelength. Therefore, in this case, the shape of the film cutout portion is a horizontally long rectangle. Such a rectangular film notch may be an elliptical film notch having the same area.
[0045]
Next, an embodiment of the vehicle antenna device of the present invention will be described.
[0046]
Regarding the case of a = 30 mm and d = 5.2 mm and the case of a = 50 mm and d = 31.2 mm, which were selected in the above-described embodiment of the method of designing the ETC antenna device, the transparent conductive material of the window glass was used. The optimum location for providing a film notch in the membrane and the optimal location for the antenna will be described with reference to FIG.
[0047]
In the following description, two examples will be described simultaneously for convenience, but one example is actually selected.
[0048]
FIG. 6A is a front view of a windshield (window glass) 2 in which a square film notch 30 having a side of 50 mm is provided in the upper center of the windshield 2 or a square having a side of 30 mm. Is provided on the lower left end of the windshield 2.
[0049]
As described above, the reason why the larger film notch 30 is provided at the center of the upper portion of the windshield 2 is that the film notch is not so conspicuous at the upper part of the windshield 2 and that the flat antenna for ETC is installed indoors. This is for attaching to the back side of the mirror. In addition, since a film cutout portion is easily conspicuous at a lower portion of the windshield 2, it is desirable to provide a film cutout portion 32 having a smaller dimension.
[0050]
FIG. 6B shows a mounting position of the planar antenna in the vehicle. The planar antenna 34 for receiving the ETC radio wave transmitted through the film cutout 30 at the upper center of the windshield is attached to the rear side of the interior mirror 36. At this time, the distance d between the windshield 2 and the planar antenna 34 is set to be 31.2 mm.
[0051]
Alternatively, the planar antenna 38 for receiving the ETC radio wave transmitted through the film cutout 32 at the lower left end of the windshield is attached to a support column 40 provided on the driver's cab. At this time, the distance d between the windshield 2 and the planar antenna 38 is set to be 5.2 mm.
[0052]
In the above example, the back side of the interior mirror was used to attach the planar antenna, or a support column for attachment was prepared, but it is not limited to such a method, and if it can be installed by a method that can keep the optimal distance Any method may be used. For example, as shown in FIG. 7, an antenna module 46 including an ETC antenna 42 and an ETC unit 44 as an electric system may be attached to the back surface of the windshield.
[0053]
Although the above is the embodiment of the antenna device for ETC, it will be easily understood by those skilled in the art that the same configuration can be applied to the antenna device for VICS and GPS.
[0054]
Further, in the above-described embodiment, the shape of the film cutout portion is a square, but the shape is not limited to this, and another shape such as a rectangle, a circle, and an ellipse can be used.
[0055]
【The invention's effect】
According to the present invention, the size of the film notch provided in the window glass with the transparent conductive film can be made as small as inconspicuous, and, depending on the size of the film notch, the window glass and the antenna Is adjusted, the attenuation of the window glass with the transparent conductive film provided with the film cutout portion can be improved to almost the same as the attenuation of the window glass without the transparent conductive film.
[Brief description of the drawings]
FIG. 1 is a view showing a windshield for explaining a film cutout portion.
FIG. 2 is a plan view and a cross-sectional view showing a part of a window glass provided with a film cutout portion.
FIG. 3 is a diagram for explaining measurement in an anechoic chamber related to the design method of the present invention.
FIG. 4 is a graph showing the amount of attenuation when designing an ETC antenna device.
FIG. 5 is a graph showing attenuation in designing a VICS antenna device.
FIG. 6 is a diagram for explaining the antenna device of the present invention, showing a film cutout portion of a windshield and an installation position of the antenna.
FIG. 7 is a diagram showing an antenna module.
[Explanation of symbols]
2, 10 Windshield or window glass 8 Window glass without transparent conductive film 12 Transparent

conductive film

14, 30, 32

Film cutout

20, 34, 38, 42 Planar antenna 36 Interior mirror 40 Supporting column 44 ETC unit 46 Antenna module

Claims

A film cutout portion formed in a part of the transparent conductive film of a vehicle window glass having a transparent conductive film formed on substantially the entire surface, and an antenna for receiving a radio wave transmitted through the film cutout portion. A method for designing a vehicle antenna device comprising:
(A) preparing a plurality of measurement window glasses provided with film notches of different dimensions, respectively, and the antenna;
(B) installing the antenna in an environment where radiated radio waves are present, and measuring a reception voltage of the antenna;
(C) one of the plurality of measurement window glasses is arranged on the side from which the radio wave comes with respect to the antenna, and the measurement window glass and the antenna are connected to each other; Measuring the received voltage of the antenna while changing the distance between;
(D) obtaining an attenuation of the reception voltage measured in the step (c) with respect to the reception voltage measured in the step (b);
(E) repeating the steps (c) and (d);
(F) obtaining a maximum value of the amount of attenuation determined for each of the measurement window glasses;
(G) An optimal dimension and distance are selected from the dimensions of the membrane notch, giving the maximum value, and the distance between the measurement window glass and the antenna, and the selected dimension is used for the vehicle. The dimensions of the film notch formed in a part of the transparent conductive film of the window glass, the selected distance, the step of the distance between the vehicle window glass and the antenna,
A method for designing a vehicle antenna device, comprising:

The step (a) includes a step of further preparing one measuring window glass on which the transparent conductive film is not formed, and in the step (g), the measuring window glass on which the transparent conductive film is not formed. The method of designing an antenna device for a vehicle according to claim 1, wherein an optimal size and an optimal distance are selected so that an attenuation amount substantially equal to the attenuation amount obtained for (1) is obtained.

The method for designing a vehicle antenna device according to claim 1, wherein the radio waves are radio waves for ITS.

The method of designing a vehicle antenna device according to claim 1, wherein the shape of the film notch is a square, a rectangle, a circle, or an ellipse.

The method according to claim 1, wherein the antenna is a planar antenna.

A film cutout portion formed in a part of the transparent conductive film of a vehicle window glass having a transparent conductive film formed on substantially the entire surface, and an antenna for receiving a radio wave transmitted through the film cutout portion. A vehicle antenna device comprising:
The antenna is installed at a position distant from the vehicle window glass when receiving a radio wave transmitted through the film notch having a predetermined dimension, the amount of attenuation of a reception voltage becomes a maximum value. A vehicle antenna device.

The dimensions of the film notch and the distance between the vehicle window glass and the antenna,
(A) preparing a plurality of measurement window glasses provided with film notches of different dimensions, respectively, and the antenna;
(B) installing the antenna in an environment where radiated radio waves are present, and measuring a reception voltage of the antenna;
(C) one of the plurality of measurement window glasses is arranged on the side from which the radio wave comes with respect to the antenna, and the measurement window glass and the antenna are connected to each other; Measuring the received voltage of the antenna while changing the distance between;
(D) obtaining an attenuation of the reception voltage measured in the step (c) with respect to the reception voltage measured in the step (b);
(E) repeating the steps (c) and (d);
(F) obtaining a maximum value of the amount of attenuation determined for each of the measurement window glasses;
(G) An optimal dimension and distance are selected from the dimensions of the membrane notch, giving the maximum value, and the distance between the measurement window glass and the antenna, and the selected dimension is used for the vehicle. The dimensions of the film notch formed in a part of the transparent conductive film of the window glass, the selected distance, the step of the distance between the vehicle window glass and the antenna,
The vehicle antenna device according to claim 6, wherein:

The step (a) includes a step of further preparing one measuring window glass on which the transparent conductive film is not formed, and in the step (g), the measuring window glass on which the transparent conductive film is not formed. The vehicle antenna device according to claim 7, wherein an optimal size and an optimal distance are selected so that an attenuation amount substantially equal to the attenuation amount obtained for (1) is obtained.

The vehicle antenna device according to claim 6, wherein the radio wave is an ITS radio wave.

The vehicle antenna device according to any one of claims 6 to 9, wherein the shape of the film notch is a square, a rectangle, a circle, or an ellipse.

The vehicle antenna device according to any one of claims 6 to 10, wherein the antenna is a planar antenna.