JP3971966B2

JP3971966B2 - Vehicle antenna apparatus and design method thereof

Info

Publication number: JP3971966B2
Application number: JP2002196205A
Authority: JP
Inventors: 浩飯島; 亮吉土居
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: 2007-09-05
Anticipated expiration: 2022-07-04
Also published as: JP2004040571A

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小値を求めるステップと、
（ｇ）前記極小値を与える、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小値となる、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を設置した。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を設置し、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、極小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）とで減衰量は極小値を有している。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、極小値を有している。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）とで極小値を有している。
【００３１】
以上のように減衰量が分布する極小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、減衰量が極小値をとる距離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、極小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）とで減衰量は極小値を有している。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、極小値を有している。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）で極小値を有している。
【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
４４ＥＴＣ用ユニット
４６アンテナモジュール[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an antenna device for a vehicle, and more 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 antenna for ITS (GPS, VICS, ETC, etc.) in a vehicle. Some vehicle windshields (window glass) have a transparent conductive film (metal film) formed to reduce the heat caused by solar radiation or to add a defrosting function to the glass. . In the case of such a windshield with a transparent conductive film, there is a problem that radio waves are 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 cut-out portion that transmits radio waves is provided in the windshield. ing. An example is shown in FIG. In the figure, 2 indicates a windshield, and 4 and 6 indicate film notches.
[0004]
Japanese Patent Application Laid-Open No. 8-210042 also discloses forming a region through which electromagnetic rays are transmitted through a window glass for a vehicle.
[0005]
[Problems to be solved by the invention]
However, the dimensions of such a film notch have not been studied in detail, so they are quite large, and the color difference between the transparent conductive film portion and the portion without the transparent conductive film is different. There is a problem that the notch is conspicuous and the appearance of the vehicle is impaired.
[0006]
Furthermore, the radio wave for ETC (Electronic Toll Collections) is about 5.8 GHz, λ (spatial wavelength) is about 52 mm, the radio wave for VICS (Vehicle Information and Communication System) is about 2.5 GHz, and λ is The radio wave for GPS (Grobal Position System) is about 1.6 GHz, λ is about 187 mm, and the radio wave used for both is a short wavelength.
[0007]
Note that circularly polarized waves are used for ETC and GPS radio waves, and linearly polarized waves (vertically polarized waves or horizontally polarized waves) are used for VICS radio waves.
[0008]
In general, a planar antenna is attached to a position away from the window glass for a vehicle antenna that receives such short-wave radio waves.
[0009]
The window glass (dielectric material) reflects radio waves with respect to radio waves with short wavelengths as described above. It is predicted that the influence of such a reflected wave on the transmission / reception characteristics of the antenna changes depending on the dimension of the film notch 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 notch portion of the transparent conductive film of the window glass is 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 apparatus that can reduce the size of a film notch portion of a transparent conductive film to an inconspicuous level and can satisfactorily transmit and receive radio waves.
[0012]
Still another object of the present invention is to provide a method for designing a vehicle antenna device as described above.
[0013]
[Means for Solving the Problems]
The inventor of the present application has a transmission / reception characteristic of a vehicle antenna device including a film notch portion in which a transparent conductive film of a window glass is not formed and an antenna that receives radio waves transmitted through the film notch portion. When the distance d is changed while keeping the dimension of the film notch portion constant based on the prediction that it depends on the size of the notch portion and the distance d between the window glass and the antenna, the maximum transmission / reception characteristic value is obtained. We found that the values were distributed.
[0014]
Therefore, by changing the dimension of the film notch and the distance d between the window glass and the antenna, the transmission / reception characteristic value of the antenna is measured, and the dimension of the film notch as a candidate from the maximum value, and the window glass The distance d between the antenna and the antenna is selected, and the optimum dimension and distance d of the film notch can be determined from these candidates in consideration of the antenna mounting position in the vehicle.
[0015]
According to one 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, and the film notch are transmitted. A design method for an antenna device for a vehicle comprising an antenna for receiving radio waves. This design method is
(A) preparing a plurality of measurement window glasses each provided with a film cutout of different dimensions, and the antenna;
(B) installing the antenna in an environment where radiated radio waves exist, and measuring a reception voltage of the antenna;
(C) Of the plurality of measurement window glasses, one measurement window glass is arranged on the side where the radio wave arrives with respect to the antenna, and the measurement window glass and the antenna Measuring the received voltage of the antenna while changing the distance between;
(D) obtaining an attenuation amount 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);
Determining a pole minimum value of the attenuation amount obtained for (f) the respective measurement window glass,
(G) said providing a very small value, of the distance between the dimension of the film notch, and the the measurement window glass and the antenna, and selecting the optimum dimensions and distances, the selected size vehicle A dimension of a film notch formed in a part of the transparent conductive film of the window glass for the vehicle, and the selected distance as a distance between the vehicle window glass and the antenna;
Is included.
[0016]
According to another aspect of the present invention, there is provided 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 the film cutout portion. An antenna device for a vehicle comprising an antenna for receiving a coming radio wave, wherein the antenna has an attenuation amount of a reception voltage when receiving the radio wave transmitted through the film notch having a predetermined dimension. It is installed at a position away from the window glass, which is a small value.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a method for designing a vehicle antenna device of the present invention will be described.
[0018]
As an example, a method for designing an ETC antenna device will be described. First, a window glass without a transparent conductive film in which no transparent conductive film was formed and a window glass with a transparent conductive film provided with a film notch in 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. 10 is a window glass, 12 is a transparent conductive film, and 14 is a film notch.
[0020]
As described above, since circularly polarized waves are used for ETC radio waves, the shape of the film notch must have the same length parallel to the polarization direction and the length orthogonal to the polarization direction. A square is an example.
[0021]
The dimension of one side of the square of the film notch 14 is a. Two types of a = 30 mm (≈0.6λ) and a = 50 mm (≈1λ) were prepared.
[0022]
First, as shown in FIG. 3A, a planar antenna 20 is placed in a measurement environment, for example, an anechoic chamber, and a 50Ω resistor is connected to the 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 received voltage V _ref induced in the resistance was measured. This voltage is a reference for the attenuation calculation described later.
[0023]
Next, as shown in FIG. 3 (B), the radio wave is separated by a distance d from the antenna 20 on the side coming radiated position, was placed a transparent conductive film without a window glass 8. The distance d is a distance from the surface of the window glass 8 to the surface of the planar antenna 20. While changing the value of d, radio waves that arrived from the opposite direction of the window glass 8 and passed through the window glass were received, and the received voltage V of the antenna was measured.
[0024]
Next, as shown in FIG. 3 (C), the radio wave is separated by a distance d from the antenna 20 on the side coming radiated position, the transparent conductive film with the window glass 10 which is film notch 14 provided installation Then, while changing the value of d, a radio wave that arrived from the opposite direction of the window glass 10 and passed through the film notch 14 was received, and the received voltage V of the antenna was measured. This was performed for each of the two types of window glasses with transparent conductive films described above.
[0025]
From the above measured values, how much the received voltage is attenuated when a window glass without a transparent conductive film or a window glass with a transparent conductive film provided with a film notch is provided, compared to when no window glass is provided. The amount of attenuation indicating whether or not it has been calculated was 20 log (V / V _ref ). The calculation results are shown in Table 1.
[0026]
[Table 1]

[0027]
However, d / λ is a value obtained by normalizing the distance d by the spatial wavelength λ.
[0028]
FIG. 4 shows this in a graph. The vertical axis represents attenuation [dB], and the horizontal axis represents d / λ. 0 dB is the attenuation when the window glass is not installed. The vertical axis indicates that the amount of attenuation increases as the numerical value increases in the negative direction.
[0029]
As it can be seen from this graph, the transparent conductive film without glazing, and in any film notch is of the transparent conductive film with a window glass provided, with a change in d / lambda, so that very small values are distributed It can be seen that it has fluctuated.
[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). attenuation between has a very small value. In the case of a window glass with a transparent conductive film provided with a film notch of a = 30 mm, d / λ = 0.1 and d / λ = 0. 6, it has a very small value. In the case of a window glass with a transparent conductive film provided with a film cutout portion of a = 50 mm, d / λ = 0.2, that is, d = 0.2λ (= 10.4 mm), and d / λ = 0. 6, i.e., has a very small value in a d = 0.6λ (= 31.2mm).
[0031]
The fact that changes a very small value of the attenuation amount is distributed as described above, is a new finding by the present inventors have found, as described above, the reflected wave from the surface of the glass have caused Conceivable.
[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 amount of attenuation is almost the same as the window glass without a transparent conductive film, In the case of a window glass with a transparent conductive film provided with a film cutout portion of a = 50 mm, the amount of attenuation is almost equal to that of the window glass without a transparent conductive film in the range of d / λ> 0.2.
[0033]
In this way, the attenuation curve of the window glass having a film cutout portion of a = 30 mm and the attenuation curve of the window glass having a film cutout portion of a = 50 mm intersect at d / λ = 0.2. The reason for this is considered to be due to the influence of the radio wave reflected at the edge of the cut-out portion of the transparent conductive film in addition to the above-described reflected wave from the glass.
[0034]
As described above, for the window glass without a transparent conductive film and the window glass with a transparent conductive film provided with a film cutout, if the attenuation is determined, the attenuation is determined by the dimension a of the film cutout, and the window glass It can be seen how it fluctuates depending on the distance d to the antenna. Then, it can be seen that the distance d attenuation takes a very small value is a candidate for proper installation position of the antenna.
[0035]
Among these installation positions, in this embodiment, in the case of a window glass with a transparent conductive film having a film cutout portion of a = 30 mm, d = 0.1λ (= 5.2 mm) is the attenuation amount at that time. Is optimal because it is almost the same as the attenuation of the 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, the amount of attenuation at that time is almost the same as the amount of attenuation of the window glass without a transparent conductive film, and it is understood that it is optimal. Which one to select is determined by the location where the film notch is provided in the transparent conductive film of the window glass and the position of the antenna provided in the vehicle. In any case, the dimension of the film notch is approximately the same as the spatial wavelength or smaller than the spatial wavelength, and is small enough that the film notch is not conspicuous.
[0036]
In the above embodiment, the shape of the film notch is square, but the shape is not limited to this, and a circular film notch having the same area as the area of the square film notch may be used. Good.
[0037]
In the embodiment described above, the attenuation is calculated for the window glass without a transparent conductive film. This is referred to in comparison with the attenuation of the window glass with a transparent conductive film provided with a film notch. If the transmission / reception characteristics are maintained as an antenna device even if the attenuation is larger than the attenuation of the window glass without a transparent conductive film, it is possible to obtain the attenuation for the window glass without a transparent conductive film. Obviously, it is not essential.
[0038]
The above is an embodiment of a design method for an ETC antenna device. However, it is easily understood by those skilled in the art that a VICS and GPS antenna device can be designed in the same manner. Let's go.
[0039]
Regarding the design of the VICS antenna device, two types of window glass having a film cutout portion of a = 30 mm and 50 mm were prepared, and radio waves having a frequency of 2.5 GHz (λ = 120 mm), which is a linearly polarized wave for VICS, were 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. The calculation results are shown in Table 2.
[0040]
[Table 2]

[0041]
FIG. 5 shows this in a graph. As it can be seen from this graph, the transparent conductive film without glazing, and in any film notch is of the transparent conductive film with a window glass provided, with a change in d / lambda, so that very small values are distributed It can be seen that it has fluctuated.
[0042]
In the case of a window glass without a transparent conductive film, the amount of attenuation is d / λ = 0.2, that is, d = 0.2λ (= 24 mm), and d / λ = 0.7, that is, d = 0.7λ (84 mm). It has a very small value. If the transparent conductive film with glazing film notch of a = 30 mm is provided, just as in the case of the transparent conductive film without glazing, with d / lambda = 0.2, it has a very small value ing. If the transparent conductive film with glazing film notch of a = 50 mm is provided, d / λ = 0.7, i.e. has a very small value at d = 0.7λ (= 84mm).
[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), and the attenuation at that time is almost equal to the attenuation of the window glass without a transparent conductive film. Therefore, in the case of a window glass with a transparent conductive film having a film cutout portion of a = 50 mm, d = 0.7λ (= 84 mm), and the attenuation at that time is that of the window glass without a transparent conductive film. It turns out to be optimal because it is almost equal to the attenuation.
[0044]
In the above 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 orthogonal to the polarization direction. It can be shortened to ½ of the length of the direction. For example, a square film notch having a length of one wavelength on one side can have a longitudinal length of ½ wavelength when the radio wave is vertically polarized. Therefore, in this case, the shape of the film notch 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]
The transparent conductivity of the window glass in the case of a = 30 mm, d = 5.2 mm, and the case of a = 50 mm, d = 31.2 mm, which are selected in the embodiment of the design method of the ETC antenna device described above. The optimum place where the film notch is provided in the film and the optimum place where the antenna is installed will be described with reference to FIG.
[0047]
In the following description, two examples are described simultaneously for convenience, but one example is actually selected.
[0048]
FIG. 6A is a front view of the windshield (window glass) 2, and a square film notch 30 having a side of 50 mm is provided at the upper center of the windshield 2 or a square having a side of 30 mm. The film notch 32 is provided at the lower left end of the windshield 2.
[0049]
As described above, the reason why the larger film cutout 30 is provided in the upper center of the windshield 2 is that the film cutout is not so conspicuous in the upper part of the windshield and the ETC flat antenna is installed in the room. This is for attaching to the back side of the mirror.
In addition, since the film notch is easily noticeable at the lower part of the windshield 2, it is desirable to provide the film notch 32 having a smaller dimension.
[0050]
FIG. 6B shows the mounting position of the planar antenna in the vehicle. A 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 back side of the indoor 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 that receives 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 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 planar antenna was attached using the back side of the indoor mirror or a support pillar for the attachment was prepared, but not limited to this method, if it can be installed by a method that can maintain the optimum distance Any method is acceptable. For example, as shown in FIG. 7, an antenna module 46 including an ETC antenna 42 and an ETC unit 44 that is an electric system may be attached to the back surface of the windshield.
[0053]
The above is the embodiment of the antenna device for ETC, but it will be easily understood by those skilled in the art that the VICS and GPS antenna devices can be similarly configured.
[0054]
In the above embodiment, the shape of the film notch is square, but the shape is not limited to this, and other shapes such as a rectangle, a circle, and an ellipse may 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 inconspicuously small, and depending on the size of the film notch, the window glass and the antenna Therefore, the attenuation of the window glass with a transparent conductive film provided with a film notch can be improved to be substantially equal to the attenuation of the window glass without a transparent conductive film.
[Brief description of the drawings]
FIG. 1 is a view showing a windshield for explaining a film notch.
2A and 2B are a plan view and a cross-sectional view showing a part of a window glass provided with a film notch.
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 an attenuation amount in designing an ETC antenna device.
FIG. 5 is a graph showing the amount of attenuation when designing a VICS antenna device.
FIG. 6 is a view for explaining the antenna device of the present invention, and shows a film notch portion of the 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 notch

20, 34, 38, 42 Planar antenna 36 Indoor mirror 40 Support pillar 44 Unit for ETC 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 radio waves transmitted through the film cutout portion. A vehicle antenna device design method comprising:
(A) preparing a plurality of measurement window glasses each provided with a film cutout of different dimensions, and the antenna;
(B) installing the antenna in an environment where radiated radio waves exist, and measuring a reception voltage of the antenna;
(C) Of the plurality of measurement window glasses, one measurement window glass is arranged on the side where the radio wave arrives with respect to the antenna, and the measurement window glass and the antenna Measuring the received voltage of the antenna while changing the distance between;
(D) obtaining an attenuation amount 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);
Determining a pole minimum value of the attenuation amount obtained for (f) the respective measurement window glass,
(G) said providing a very small value, of the distance between the dimension of the film notch, and the the measurement window glass and the antenna, and selecting the optimum dimensions and distances, the selected size vehicle A dimension of a film notch formed in a part of the transparent conductive film of the window glass for the vehicle, and the selected distance as a 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 measurement window glass in which a transparent conductive film is not formed. In the step (g), the measurement window glass in which the transparent conductive film is not formed. The design method of the vehicular antenna apparatus according to claim 1, wherein an optimal dimension and distance are selected so that an attenuation amount substantially equal to the attenuation amount obtained with respect to 1 is obtained.

The vehicle antenna device design method according to claim 1, wherein the radio wave is an ITS radio wave.

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

The method for designing a vehicle antenna device 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 radio waves transmitted through the film cutout portion. A vehicle antenna device comprising:
The antenna, when receiving radio waves transmitted through the film notch having a predetermined size, the attenuation of the received voltage becomes extremely small value, is installed in a position away from the window glass for the vehicle A vehicle antenna device.

The dimension of the film notch and the distance between the vehicle window glass and the antenna are:
(A) preparing a plurality of measurement window glasses each provided with a film cutout of different dimensions, and the antenna;
(B) installing the antenna in an environment where radiated radio waves exist, and measuring a reception voltage of the antenna;
(C) Of the plurality of measurement window glasses, one measurement window glass is arranged on the side where the radio wave arrives with respect to the antenna, and the measurement window glass and the antenna Measuring the received voltage of the antenna while changing the distance between;
(D) obtaining an attenuation amount 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);
Determining a pole minimum value of the attenuation amount obtained for (f) the respective measurement window glass,
(G) said providing a very small value, of the distance between the dimension of the film notch, and the the measurement window glass and the antenna, and selecting the optimum dimensions and distances, the selected size vehicle A dimension of a film notch formed in a part of the transparent conductive film of the window glass for the vehicle, and the selected distance as a distance between the vehicle window glass and the antenna;
The vehicle antenna device according to claim 6, which is set by:

The step (a) includes a step of further preparing one measurement window glass in which a transparent conductive film is not formed. In the step (g), the measurement window glass in which the transparent conductive film is not formed. The vehicle antenna device according to claim 7, wherein an optimal dimension and distance are selected so that an attenuation amount substantially equal to the attenuation amount obtained for the above 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 a shape of the film notch is a square, a rectangle, a circle, or an ellipse.

The vehicle antenna device according to claim 6, wherein the antenna is a planar antenna.