JP3952385B2

JP3952385B2 - Surface mount antenna and communication device equipped with the same

Info

Publication number: JP3952385B2
Application number: JP2002173810A
Authority: JP
Inventors: 博志青山; 慶子菊地; 保規高木; 英俊萩原
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2001-06-15
Filing date: 2002-06-14
Publication date: 2007-08-01
Anticipated expiration: 2022-06-14
Also published as: JP2003069331A

Description

【０００１】
【発明の属する技術分野】
本発明はセラミックスや樹脂等の誘電体又は磁性体を基体とする小型アンテナに関し、特にインピーダンス整合機能を給電電極に付与した表面実装型アンテナ及びそれを搭載し通信機器に関する。
【０００２】
【従来の技術】
GHz帯を搬送波とするGPS(Global Positioning System)や無線LAN (Local Area Network)等には、表面実装型アンテナが使用されている。携帯端末機器の小型化は急激なスピードで進められており、表面実装型アンテナも同様に小形低背であると同時に放射効率が良くかつ指向性がなくて広帯域であることが要求されている。しかしながら従来の表面実装型アンテナは、小形低背化を進めると特性が劣化するので、十分な小型低背化を実現するには必ずしも満足でなかった。
【０００３】
一般にこの種のアンテナの放射電極長は1/4波長に相当するように設定される。これは、1/4波長にするとアンテナの放射効率が最大になるためで、1回の充電により電池をできるだけ長時間使用し得ることが必要な携帯端末機器では特に重要である。誘電体の基体上に放射電極を配置すると、その実効長さは比誘電率ε_rの平方根に反比例することが知られており、これは波長短縮効果と呼ばれている。波長短縮効果を用いれば、アンテナの放射電極を短くでき、アンテナを小型低背化できる。
アンテナの伝搬周波数が低くなるほど、基体に比誘電率の大きな材料を用いることによりアンテナを小型化することができる。しかしながら、現実には高誘電率材料の使用には限度があり、実際には約4程度の比誘電率ε_rを有する誘電体基体が実用化されているに過ぎない。これは、比誘電率ε_rがこれより大きくなるとインピーダンス整合の問題が生じるためである。高比誘電率の表面実装型アンテナでは給電点における入力インピーダンスが大幅に変化し易いので、小型化とともにインピーダンス整合の問題を解決するのは困難であった。
【０００４】
例えば、例えば図21に示すように、特開平9-219610号公報に記載の表面実装型アンテナは、ほぼ直方体状の基体90の上面91にほぼL字状又はほぼコ字状に屈曲し、一端が開放され他端が接地された放射電極92と、放射電極92を励振するためにギャップ96を介して基体90上面に形成された給電電極94とを有し、給電電極94の一端は給電線99に接続されている。図22に示すようにその等価回路は、放射電極92の放射抵抗R及びインダクタンスL、放射電極92と地導体との間で形成されるキャパシタンスC、及び放射電極92と給電電極94との間で形成されるキャパシタンスCi’からなる並列共振回路である。
このアンテナにおいては、送信回路（図示せず）からの高周波電力は、回路基板の給電線99を介して給電電極94に伝達され、放射電極92と地導体とで形成する共振回路に入力され、並列共振して放射電極92から電磁波として放射される。給電点98において電圧反射が生じないように、インピーダンス整合をとる必要がある。
【０００５】
給電電極94の送信回路側からみた入力インピーダンス、すなわち給電点98における入力インピーダンスを、特性インピーダンス(50Ω)に一致させるインピーダンス整合手段として、種々のものが提案されている。例えば、図21に示すアンテナでは、放射電極92と給電電極94は容量結合されており、図22の等価回路に示す通り放射電極92のインダクタンスLをキャンセルするように、放射電極92と給電電極94間のキャパシタンスCi’が設定される。
しかしながら、図21に示す従来のアンテナでは、給電電極と放射電極とは直接接続せずにキャパシタンス結合だけしており、インピーダンス整合にインダクタンスは利用されていない。このためこのアンテナを小型低背化すると、インピーダンス整合が容易な高特性のアンテナとすることができない。またGPSや無線LAN等に利用するアンテナでは基本的に無指向性が必要であり、放射効率や利得の向上及び帯域幅の拡大も必要である。従来この点の配慮及び検討は十分でなかった。
【０００６】
また、インピーダンスの不整合が生じた場合、新たな整合回路を送受信回路とアンテナとの間に挿入することがあるが、新たな整合回路の追加はアンテナ装置を大型化させるという問題がある。インピーダンス整合回路に関して、特開2000-286615号公報は、基体を積層構造とし、層間に整合回路を内蔵した小型アンテナを開示している。しかしながら、これではアンテナの構造が複雑化するだけでなく、製造コストの増加を招くと言う問題がある。
WO01/24316A1公報には、基体上面に第1の放射電極（給電側放射電極）と第2の放射電極（無給電側放射電極）を有し、2つの放射電極間が複共振状態にあり、さらに基体側面に整合回路用電極を有するアンテナを開示している。このアンテナでは、第1の放射電極（給電側放射電極）と整合電極とはインピーダンス整合位置で直接接続されているが、給電電極はキャパシタンスを有しておらず、もっぱらインダクタンスを操作してインピーダンス整合を図っている。このような整合回路を有する電極構成は従来の逆Fアンテナに相当し、元々インピーダンス整合が取り易いアンテナ構造である。
【０００７】
特開平8-186431号及び特開平11-340726号公報では、基体上面に放射導体を形成し、基体底面全体に接地導体を形成した構造を有する単指向性アンテナにおけるインピーダンス整合技術を開示している。しかしながら、このようなアンテナはGPSや無線LAN等の無指向性を必要とする用途には不向きである。これは、例えば基体上面に設けられた給電導体を放射導体が取り囲む配置となっており、キャパシタンスの結合が強く大きくなる構成であることからも分かる。また小型化、放射効率、利得及び帯域幅も考慮されていないので、GPS等に使用するには問題がある。
【０００８】
【発明が解決しようとする課題】
従来のものでは、小型低背化とインピーダンス整合が容易で、且つアンテナ特性の高いものを得ることが出来ていなかった。また、ＧＰＳや無線ＬＡＮ等に利用するアンテナでは基本的に無指向性が必要とされ、放射効率や利得の向上及び帯域幅の拡大も必要である。従来、この点での配慮や検討が十分ではなかった。本発明の目的は、比較的高い誘電率の材料を用いた場合でもインピーダンス整合が容易で小型化できるアンテナであって、特にGPSや無線LAN等に適しており、高利得、広帯域でかつ無指向性を有する表面実装型アンテナを提供することである。
本発明のもう一つの目的は、この表面実装型アンテナを搭載した携帯電話、ヘッドフォン、パソコン、ノートパソコン、デジタルカメラ等用の通信機器を提供することである。
【０００９】
【課題を解決するための手段】
上記目的に鑑み鋭意研究の結果、給電電極をキャパシタンスの他にインダクタンスを有する構造とすることによりインピーダンス整合機能を付与すると、比較的高い誘電率の材料を用いた場合でもインピーダンス整合が容易で無指向性を有する小型の表面実装型アンテナが得られることを発見し、本発明に想到した。
【００１０】
本発明の第一の表面実装型アンテナは、誘電体からなる基体と、前記基体の少なくとも上面に設けられ、他端が開放端となった放射電極と、前記放射電極の一端に直接接続するか容量結合するように前記基体に設けられた接地電極と、前記放射電極とギャップを介して面するように前記基体の少なくとも側面に設けられた給電電極とを具備する表面実装型アンテナであって、前記基体の比誘電率は８を超え５０以下であり、前記給電電極は、一端に給電部を他端に接地部を有し、当該給電部と接地部との間を前記放射電極の開放端側とギャップを介して並ぶ並行部で接続した門型状となし、前記基体の底面における前記接地電極の面積率は３０％以下であり、前記給電部と接地部の長さを調節してインダクタンスを調整すると共に、前記並行部のギャップ間隔及び／又は長さを調節してキャパシタンスを調整したことを特徴とする。
【００１２】
本発明の第ニの表面実装型アンテナは、誘電体又は磁性体からなる基体と、前記基体の少なくとも上面に設けられた放射電極と、前記放射電極の一端に直接接続するか容量結合するように前記基体に設けられた接地電極と、前記放射電極とギャップを介して面するように前記基体の少なくとも側面に設けられた給電電極とを具備し、前記給電電極は、前記基体の対向する側面に設けられた２つのL字状電極と、前記基体の端面に設けられた１つのI字状電極とが連結してなり、一方のL字状電極は一端に給電部を有し、他方のL字状電極は一端に接地部を有し、前記I字状電極は並行部であり、もって前記給電電極は門型状であることを特徴とする。
【００１３】
本発明において、前記給電電極は、前記基体の対向する側面に設けられた第一及び第二の電極と、前記基体の端面に設けられた１つのI字状電極とが連結してなり、第一の電極は一端に給電部を有し、第二の電極は一端は接地部を有し、前記I字状電極は並行部であり、もって前記給電電極は門型状であり、さらに前記基体の端面又は端面及び対向する側面に形成された接地電極部が形成されているのが好ましい。
前記給電電極及び放射電極は、少なくとも一部にミアンダ状、コ字状、L字状、クランク軸状のいずれかの形状を有するのが好ましい。
前記給電電極は、前記放射電極の開放端側にギャップを介して前記基体の側面に設けるのが好ましい。このとき、前記放射電極の開放端付近に給電部を配置することが好ましい。
本発明の好ましい一実施例では、前記放射電極の少なくとも一部は、前記基体の一端から長手方向の他端に向かって連続的及び／又は段階的に実質的に幅を狭めながら延在する。本発明の好ましい別の実施例では、放射電極は前記基体の一端から長手方向の他端に向かって連続的及び／又は段階的に実質的に幅を狭めながら延在し、他端でほぼコ字状に屈曲している。
本発明の好ましい他の一実施例では、前記放射電極は、前記給電電極が形成された側面とは異なる側面を経由して上面に至るように形成されている。このとき、基体の上面に設けられた放射電極を基体の下面に投影したとき、重なり合う接地電極が無いことが好ましい。
本発明のアンテナは、放射電極及び／又は給電電極の角部に丸みを持たせるのが好ましい。
本発明のアンテナは、その基体に前記放射電極の他端とギャップを介して対向する第2の接地電極を設けても良い。
本発明のアンテナ用基体に比誘電率ε_rが6〜50の誘電体を使用することができる。
【００１５】
本発明の通信機器は、上記表面実装型アンテナを回路基板の地導体の無い領域に搭載したアンテナ装置を具備し、前記放射電極が長手方向に延びる前記基体は、前記回路基板の地導体の縁部とギャップを介して並び、前記給電電極は前記地導体側に配置されていることを特徴とする。
本発明の好ましい実施例では、表面実装型アンテナ上で回路基板の地導体と反対側に位置する接地電極部は回路基板の角部側に位置し、接地電極部と回路基板の導体とは線状導体により接続される。
【００１６】
【発明の実施の形態】
以下、本発明を図面に示す実施形態と共に詳細に説明する。
まず、インピーダンス整合が困難になる理由について述べておく。基体に放射電極、接地電極及び給電電極等を配置すると、電極間にキャパシタンスが生成される。給電電極と放射電極との間のキャパシタンスの増大は入力インピーダンスを低下させ、インピーダンスの不整合を引き起こす。キャパシタンスは比誘電率ε_rに比例して増加するので、伝搬周波数を下げるために高誘電率材料を使用するとインピーダンスの不整合が顕著になる。そのため、従来から比誘電率ε_rが4程度の低い誘電体の基体が使用されている。本発明は、限定的ではないが、比誘電率ε_rが6以上、好ましくは20〜50又はそれ以上の誘電材の使用を可能とする。
【００１７】
本発明は、高誘電率の材料を基体に使用することにより放射電極と給電電極との間のキャパシタンスが増加しても、給電電極を長くすることによりそのインダクタンスを増大させてキャパシタンスの増分をキャンセルし、インピーダンス整合を図るものである。従来のこの種のアンテナの給電電極は、等価回路上キャパシタンスのみを与える構成であったが、本発明によりキャパシタンスに加えインダクタンスが獲得できる形状とした。具体的には、給電電極を帯状に形成してインダクタンスを得やすくするとともに、給電電極の一部をギャップを介して放射電極に並ばせることにより、キャパシタンスの調整を可能とした。また帯状の給電電極の一端を給電部とし、他端を接地部とすることにより、図2に示すように並列成分L₂と直列成分L₁、C_iとを設け、インピーダンス整合の設計を容易にして、開発期間を短縮化できた。
【００１８】
表面実装型アンテナには用途に応じて種々の形態があるので、インピーダンス整合条件は、それらの広汎な要件を満足する必要がある。上記したように、本発明の給電電極は並列成分L₂と直列成分L₁、C_iとの組合わせと見なせる。この給電電極をミアンダ状、コ字状、L字状、クランク軸状、又はこれらの組合せにすることにより、インピーダンス整合条件に限定されることなくインダクタンスとキャパシタンスを任意に設定できる。例えば、キャパシタンスとインダクタンスとをほぼ同じにしたり、どちらか一方を大としたりできる。インダクタンスは給電電極の長さに比例し、キャパシタンスは給電電極と放射電極との対向長さの関数である。従って、本発明の給電電極を用いてインピーダンス整合を行う場合、まず等価回路中のL₁、L₂、C_iのうちどれをどの程度増減すべきかを決める。次にL₁、L₂は給電電極の長さに比例し、C_iは給電電極と放射電極との対向長さの関数であることを利用すると、インピーダンス整合のために望ましいパラメータを満足する給電電極の形状を容易に設定することができる。
【００１９】
本発明の一実施例によるアンテナ構成では、放射電極は基体の少なくとも上面に設けられ、その一端は接地されて他端は開放端になっている。このアンテナ構造は、放射電極の接地端の近傍に給電電極が接続された逆F型アンテナに近いように見えるが、本発明では放射電極と給電電極は離隔して容量結合している点で基本的に逆F型構造と相違する。なお、給電電極は基体の側面の一面に形成する方が電極を印刷形成する際に印刷ずれ等がなく製造容易で特性上も安定する。
本発明では放射電極と給電電極との間の距離や並行長さ及び／又は給電電極の脚長さや形状を適宜設定することにより、インピーダンス整合を容易にしている。これにより帯域幅BWを任意に選択できる。BW∝1/Q及びQ = R√(C/L)の関係があるので、容量結合度合いや電極長さに基づきＣ又はC/Lを制御すれば、帯域幅ＢＷを広げることができる。例えば、放射電極の開放端付近に給電電極の給電部側を配置すれば、放射端はインダクターと見なされインダクタンス分（L）を大きくとることができる。同じ共振周波数での設計であればその分キャパシタンス分（C）を小さくしてＱ値を高めることができる。よって、帯域幅を広げることができる。
【００２０】
本発明の表面実装型アンテナは、優れた無指向性を有するために、底面に半田付け用の接地電極をほとんど有さないことを特徴とする。裏面全体に接地電極が形成されていると、上面の放射電極とのキャパシタンス結合により、アンテナの無指向性が失われる。具体的には、底面における接地電極の総面積／底面の全面積の比は30％以下が好ましく、20％以下がより好ましい。また底面の。うち上面に設けられた放射電極の下の領域には実質的に接地電極がないのが好ましい
また、放射電極の開放端にギャップを介して第2の接地電極を対向させて配置することもできる。この場合、対向する接地電極との容量結合が強いため、近傍に給電電極を配置しても比較的影響が少ない。従って、大幅に伝搬周波数を調整する場合、放射電極と第２の接地電極との結合度を調整することにより周波数の主調整を行い、また放射電極と給電電極との結合度を調整することにより周波数の微調整を行う。
【００２１】
本発明において基体の比誘電率ε_rは6〜50の範囲が好ましい。この比誘電率ε_rは、誘電体の温度係数、基体の加工精度等を考慮して決めたものであるが、材質、加工精度等が向上すれば、当然その上限値も引き上げられる。このような比誘電率ε_rを有する基体は、例えば22.22重量％のMgO、5.13重量％のCaCO₃、48.14重量％のTiO₂及び24.51重量％のZnOの各原料からなる素体を焼成し、焼成基体として36.6モル％のMgO、3.4モル％のCaO、40モル％のTiO₂及び20モル％のZnOからなる誘電セラミック(比誘電率ε_r：21)により形成することができる。
高誘電体の基体を使用すると、放射電極の放射効率が低下する。放射効率の低下を抑制するために、自由空間への放射を高めるように放射電極及び接地電極を構成したり、高誘電体と低誘電体を複合化した基体を使用したりする。
【００２２】
次に、図面に基づき本発明の実施の形態について説明する。
図1は本発明の第1の実施例による表面実装型アンテナを示す斜視図である。このアンテナ1Aは、直方体状の基体1の上面に配設された放射電極2と、放射電極2の一端に接続された接地電極3と、側面に放射電極2と所定間隔G1を介して形成された給電電極4とを有する。放射電極2の他端は開放端20となっている。アンテナ1Aは逆Fアンテナと似た構成を有するが、給電電極4がギャップG1を介している点で逆Fアンテナと異なる。基体1の底面1aには半田付け用電極以外の電極は配置されておらず、またアンテナも回路基板上の地導体のない領域に実装されるので、いかなる方向にもほぼ均一な放射電界パターンを示す無指向性が得られる。
給電電極4は、帯状の電極を2ヵ所で屈曲した門型（コ字型）の形状を有し、放射電極2の縁部23にほぼ並行して対向する並行部41を有する。給電電極4は一端の給電部43に送受信回路(図示せず)の給電線に接続される給電点40を有するとともに、他端の接地部44に地導体に接続される接地端42を有する。給電電極4の給電部43及び接地部44は主としてインダクタンスを生成し、放射電極2と並行部41とは主としてキャパシタンスを生成する。従って、本発明による表面実装型アンテナは図2に示す等価回路を有する。
【００２３】
インダクタンスL₁、L₂は給電電極の脚部43、44で形成され、キャパシタンスC_iは放射電極２と給電電極4の並行部41との間で形成される。従って、脚部43、44や並行部41の長さ及び形状を適宜設定してL₁、L₂及びC_iを変化させることにより、給電点40から放射電極2をみた入力インピーダンスZ_inを50 Ωに一致させることができる。このように放射電極２と給電電極4との間のキャパシタンスに加えて、給電電極４のインダクタンスを操作して入力インピーダンスの整合を独自に行えることは、本発明の重要な特徴である。なお以下の実施例でも同様であるが、給電点40と接地点42の位置は左右逆になっていても良い。また並行部41は放射電極2との間でギャップを介して並んでいれば良く、平行である必要はない。
【００２４】
図3は第2の実施例による表面実装型アンテナを示す斜視図であり、図4はその放射電極の展開図であり、図5はこのアンテナの等価回路を示す図である。
本実施例の表面実装型アンテナ1BはGPS用であり、直方体状の基体1と、その上面1c及び隣接する側面1dに形成した放射電極2と、放射電極2の一端に接続された接地電極3と、基体1の長手方向側面1bから上面1cにかけて門型に形成された給電電極4とを有する。給電電極4は側面1b側面のみに設けても良い。門型の給電電極4の配置及び形状はインピーダンス整合と広帯域化のバランスをとって決める。本実施例の放射電極2は、基体1の一端から長手方向に連続的及び／又は段階的に実質的に幅を狭めながら延びる形状を有する。図4の展開図に示すように、放射電極2は、基体1の上面1cに設けられた放射電極部21と、隣接する側面1dに連続的に形成した放射電極部22とからなり、放射電極部22も若干先端に向かって幅を狭めている。このように基体1の上面1cだけでなく隣接する側面1dにも徐々に幅が狭まる放射電極2を形成することにより、多重共振を誘起し、小型化とともに、より無指向性にすることができる。
接地電極3と放射電極２とは非接触の容量結合により接続されていても良い。接地電極3は基体１の一端面1eの周りを取り囲む四面に設けても良い。底面1aに形成された接地電極3は半田付け用電極も兼ねており、回路基板の地導体に接続される。給電電極4も基体1の底面1aに接地電極部50を有し、接地電極部50は回路基板との半田付け用電極として作用する。
【００２５】
本実施例では、給電電極4は、幅1 mmで等価長さが10 mmの門型（コ字状）である。図6(a) 〜(c) は給電電極4の種々の形状を示す。図6(a)はコ字状の給電電極4の例を示し、左右の脚部に生じるインダクタンスL₁, L₂はほぼ等しい。図6(b)及び(c)に示す形状はそれぞれ左右の脚部の長さが異なるもので、導体の長さによりインダクタンスを調整する例である。図6(b)は、右側の脚部をミアンダ状として、L₁＜L₂としたものである。また図6(c)は、左側の脚部をクランク状に、右側の脚部をミアンダ状として、L₁＞L₂としたものである。インダクタンスを用いて調整する場合、入力インピーダンスを増加させたい場合にはL₁を増加させ、逆に入力インピーダンスを減少させたい場合にはL₂を増加させる。
【００２６】
また、給電電極4の中央並行部41は本発明の特徴の一つである。中央並行部41によりＣ及びC_iを任意に設定することができる。すなわち、キャパシタンスC_iはおおむね並行部41の長さWに比例し、並行部41と放射電極2との距離G₁に反比例する。従って、C_iを増加させる場合、並行部41を長くするか、並行部41と放射電極2との距離G₁を縮める。またC_iを減少させる場合、その逆とする。このように並行部41の長さWや並行部41と放射電極2との距離G₁を変えることにより、C_iを調整できる。
【００２７】
本実施例は放射電極2にも特徴がある。放射電極2の基本形状は、高周波電流の流れ（基体1の長手方向）に対して垂直方向の電極長さ、すなわち幅を一定とせずに、開放端20側に接近するに従い徐々に減少させた形状としている。給電電源から給電電極4を介して供給された高周波電流は、放射電極2のインダクタンスと大地との間で形成されるキャパシタンスで決まる周波数で共振を起こし、空間に電磁エネルギとして放射される。この時、接地電極3と開放端20を節と腹とする電流分布モードになる。放射電極2の幅が一定ならば、この電流分布モードは1つしか存在しないが、放射電極2の幅が一定でないと、アンテナには図5に示すように複数のインダクタンスLr₁, Lr₂, Lr₃, …とキャパシタンスCr₁, Cr₂, Cr₃, …による共振回路が等価的に形成される。各共振回路の共振周波数はかなり接近しているため、共振が連続して複数存在するような状態になり、結果的に広帯域の共振特性が得られる。
【００２８】
図７は本発明の第3の実施例による表面実装型アンテナを示す。上記実施例と同じ部分には同一符号を付し、それらの説明を省略する。上記実施例と同様に放射電極24は基体1の一端から長手方向他端に向かって連続的及び／又は段階的に実質的に幅を狭めながら延びるほぼ台形状を有し、給電電極4は基体1の側面1b及び上面1cに渡って設けられている。この実施例では給電電極4はU字状であるので、並行部41と放射電極24との間隔は一定ではなく、キャパシタンスは少なめである。このように放射電極24と給電電極4とは平行でなくても良く、一部が並んでいれば良い。これを略並行と呼んでいる。また、放射電極の段階的に狭まるとは、例えば階段状に段差を持って狭まる形状がある。
【００２９】
図8は本発明の第4の実施例による表面実装型アンテナを示す。上記実施例と同じ部分には同一符号を付し、それらの説明を省略する。放射電極25はマイクロストリップ状であり、その一端は接地され、他端20は開放されている。上記実施例ではいずれも誘電体基体1の上面1cの全長にわたって放射電極2が設けられているが、放射電極の長さは所望周波数の1/4波長に選べば良く、必ずしも基体1の全長に設ける必要はない。本実施例では、基体1よりも放射電極25が短い。これにより、伝搬中心周波数を下げるための調整代をとることができる。また基体1の端部に寸法不良や欠け等の欠陥があっても、放射電極25の形成に問題がない。
【００３０】
図9は本発明の第5の実施例による表面実装型アンテナを示す。上記実施例と同じ部分には同一符号を付し、それらの説明を省略する。放射電極26の開放端20にギャップG2を介して対向するように第2の接地電極5が形成されている。これにより、放射電極26の開放端20と地導体との間に大きく安定したキャパシタンスが形成され、周波数の大幅な調整ができる。微調整は給電電極4のインダクタンス及びキャパシタンスで行えば良い。
放射電極26の開放端20と第2の接地電極5とのギャップG2によりキャパシタンスがある分、放射電極26が短くても（インダクタンスが小さくても）、所望の周波数が得られる。そのため、このような構造の表面実装型アンテナは小型化に適している。
給電電極4は基体1の側面1bから上面1cにかけて形成しているが、条件に応じて側面1bのみに設けても良い。これは前記実施例に共通して言える。給電電極4を側面1bのみに設ける場合、スクリーン印刷等で形成する際に繋ぎ目の精度等に注意を払わなくて良く、工程数が減るので、製造面でも好ましい。
【００３１】
図10〜12は本発明の第6〜8の実施例による表面実装型アンテナを示す。図の左側に斜視図、右側に展開図を示し、上記実施例と同じ部分には同一符号を付し、それらの説明を省略する。これらの実施例では、帯状の放射電極2は基体1の側面1dから上面1cまで形成されている。
図10に示す第6実施例では、基体1の上面1cの端部にはL字状電極部27が設けられており、隣接する側面1dにL字状電極28が連続的に形成されている。給電電極4はそれぞれ給電端及び接地端となる脚部43，44と中央並行部41を有する門型（コ字）状であり、基体1の側面1bのL字状電極部27の開放端側に並んで形成されている。
図11に示す第7実施例では、基体1の上面1cの端部にはL字状電極部27が設けられており、隣接する側面1dにL字状電極29が連続的に形成されている。
また図12に示す第8実施例では、基体1の上面1cの端部にはL字状電極部27が設けられており、隣接する側面1dにI字状電極30が連続的に形成されている。なお給電電極4の形状については、第7及び第8の実施例は第6実施例と実質的に同じである。
電極51はアンテナを回路基板に固定するための半田付け用電極であるが、図11及び12の例では回路基板との接合強度を上げるために半田付け用電極52が追加されている。電極51，52は回路基板の地導体に接続されない。図10〜12の例では、インダクタンスを大きくするために放射電極はL字状である。図11の例ではL字状放射電極部29と門型の給電電極4の屈曲部は丸められている。曲率Rを持たせるのは放射電極だけでも良い。基体1を低背化した場合、図12に示すように、半田付け用電極52を接続電極31を介して放射電極30に直接連続させると、アンテナ特性に大きな変化がなく安定する。
【００３２】
図11に示すようにL字状電極部29の屈曲部に丸みRを持たせると、放射利得が向上する。ほぼL字状、コ字状、ミアンダ状又はクランク状の屈曲部分を有する従来の放射電極では、直線部分と屈曲部分とが不等幅であり、角張ったままで連結している。これはインピーダンスが不連続に変化することを意味し、その不連続性により進行波の一部が反射される。このため、入力した高周波の反射ロスが大きく、利得の低下が見られた。この問題を解消するために、屈曲部分に丸みを持たせると線路はほぼ等幅となり、インピーダンスの不連続性を回避できることが分かった。あるいは角部を切り落とした角面取りを施すことでも効果があることが分かった。屈曲部分での反射ロスの発生が抑制されると、アンテナの放射電極を流れる共振電流の伝送損失が低減され、利得が向上する。
【００３３】
図13及び14は本発明の第9及び10の実施例による表面実装型アンテナを示す。上記実施例と同じ部分には同一符号を付し、それらの説明を省略する。これらの実施例では、放射電極33と給電電極4に特徴がある。放射電極33は主として基体1の上面1cに設けられており、図3に示す例と同様に接地電極3と接続する一端から長手方向の他端に向かって連続的及び／又は段階的に実質的に幅を狭めながら延びる放射電極部33aと、左端部分でコ字状又はUターン状に屈曲した放射電極部33bとからなる。このような放射電極33により、台形状の放射電極部33aで広帯域の共振特性が得られ、屈曲した放射電極部33bでインダクタンスを補充できる。電極51はアンテナを回路基板に固定するための半田付け用電極であって、必要最小限に設ける。
本実施例では放射電極33の外周と基体1の稜線との間に0.2〜0.5 mm程度の隙間が設けられている。この隙間により、電極印刷が容易になり、印刷ずれが生じ難くなる。また基体1の縁部の変形や欠け等による電極剥離を防止できる。印刷ずれや電極剥離を防ぐことにより、伝搬周波数のばらつきを抑制することができる。放射電極33を基体1の上面1cのみに設ける構成は、側面にも放射電極を設ける構成に比べて回路基板の地導体とのキャパシタンス結合が減るので、高利得が得られる。
【００３４】
図13に示すように、側面1bに設けられた門型の給電電極4は放射電極部33bの開放端20と対向する。図14に示す給電電極4は、一端に給電端43を有し側面1bに設けられたL字状電極部41と、端面1fに設けられたI字状電極部42と、一端に接地端44を有し側面1dに設けられたL字状電極部45とからなる。門型の給電電極4は、2側面1b, 1dと端面1fに渡って設けられた電極部41, 42, 45からなるコ字状並行部41を有し、並行部41はコ字状放射電極33bに対向している。このような給電電極4により、放射電極33のコ字状部のほぼ全体に渡ってキャパシタンス結合することができるので、アンテナの小型化に有利である。また同一のキャパシタンス値に対しては、放射電極33との間隔を広くとれ、印刷ずれ等に起因するキャパシタンス値のばらつき、及び伝搬周波数のばらつきを低減できる。
図15は実施例11の表面実装型アンテナを示す。この例では給電電極4の構成が他の例のものと異なる。すなわち給電電極4は、基体1の側面1bに設けられた給電端43及び接地端44を有するＦ字状電極部41と、端面1f及び側面1dに形成された直線状電極部42, 45とからなる。この実施例の給電電極は、インピーダンス整合と同時に複共振を用いた広帯域化が可能である。
なお、上記した各実施例のアンテナ構成を組み合わせることも可能であり、本発明の範囲内で他の実施例を種々構成することが出来る。
【００３５】
図16は実施例12の表面実装型アンテナを示す。帯状の放射電極133は、側面1dに長手方向に形成されたクランク軸状の電極部133dと、上面1cに形成されたL字状電極部133cとからなり、全体的にはコの字状である。このように放射電極133は基体1の上面1cから側面1dまで屈曲状に延在するので、全長を長くすることができる。その結果、同じ帯域幅ではアンテナ基体1のサイズを小さくすることができる。
給電電極104の給電部143及び接地部144の位置関係は上記実施例と逆であり、給電点140が基体のほぼ中央部に位置し、放射電極133の開放端の近傍に給電部143が位置するようにしている。また上面1cに形成されたL字状電極部133cを下面1aに投影したとき接地電極32と重ならないようにしている。これらにより、帯域幅の向上と無指向性が良好でGPS用アンテナとしてバランスのとれたものとなる。また放射電極133の開放端と給電電極104の並行部141とは接近している。幅広の並行部141とすることにより、インピーダンス整合が容易であり、利得も若干向上する。
本実施例では並行部141は幅が広くて長方形に近い形状を有するが、給電電極104の形状は、回路基板側の実装位置や導体パターンの配置及び放射電極構造等により種々変更することができる。また回路基板や放射電極133の仕様が変更されても、給電点140と接地点142との間で給電電極104の配置、形状、大きさ等を適宜設定することにより、インダクタンスとキャパシタンスを適当に調整してインピーダンス整合を容易に取ることができる。
【００３６】
図17は、図1の表面実装型アンテナ（本発明）及び図21の表面実装型アンテナ（従来例）について、シミュレーションにより求めた入力インピーダンスZ_inと基体の比誘電率ε_rとの関係を示す。本発明では高誘電率の基体を使用することに伴うキャパシタンスの増加をインダクタンスにより適宜キャンセルでき、比誘電率ε_rが50程度までの高誘電体を使用することができる。従来の比誘電率ε_rが4程度の場合に比べると、5倍以上のε_rを有する誘電材を使用でき、アンテナの小型化に大きな効果がある。なお高温域で安定な誘電材が開発されたり、加工技術が改善されると、入力インピーダンスZ_inの上限値は更に上昇する。また高誘電材と低誘電材の複合材が開発されたときにも、上限値が引き上げられると予想される。
【００３７】
次に、上記した表面実装型アンテナを回路基板に実装する構成について説明する。
図18は図3に示すアンテナ1Bを回路基板6上に実装した状態を示す。なお図18ではアンテナ以外の部品は省略されている。アンテナ1Bは、回路基板6の地導体がない露出部65上で地導体62の縁部63と若干のギャップを介して長手方向に並ぶように配置されている。その際、給電電極4は地導体62側に位置し、放射電極2の開放端20は地導体62から遠い位置にある。門型の給電電極4の一端は給電線61に接続され、他端は地導体62に接続される。これにより、給電電源60から供給された高周波信号は、給電線61を経て給電電極4に供給され、給電端40から並行部41を介して放射電極2側に向かう電流と接地端42を介して地導体62に向かう電流とに分かれ、インピーダンスの整合を図るとともに放射電極2を励振させる。その結果、放射電極2の開放端20から電磁波が空間に放射される。
【００３８】
従来はアンテナを地導体62の縁部に垂直に配置することが多かった。この場合デッドスペースが大きくなり、設計の自由度が小さいことは言うまでもない。ところが本発明では、アンテナを地導体62の縁部から僅かに離隔して、それに平行に配置することにより、アンテナにより実質的に占有される面積（デッドスペースを含む）は格段に減少し、実装レイアウトの自由度及び密度が上がるので、アンテナ装置の省スペース化を図ることができる。
給電電極4の給電部43及び接地部44の左右配置は基板6の給電線61と地導体62の配置に応じて変更しても良いが、少なくとも給電電極4を給電線61側に配置し、地導体62とアンテナ基体1の長手方向を並行にすることは、小さい占有面積で本発明の効果を得るために必要である。無指向性とするために、本発明のアンテナは地導体62の無い露出部65に実装するのが望ましい。
このようにアンテナを実装した回路基板6を図19に模式的に示す携帯電話やパソコン等の内部に搭載することにより、GPSや無線LAN機能を備えた通信機器として利用できる。
【００３９】
図20は図16に示すアンテナを図18と異なる回路基板6上に実装した例を示す。図18と同一な部分には同一符号を付してある。アンテナ1Lは、回路基板6上の地導体62が形成されていない露出部65上で、地導体62の縁部63とアンテナ基体1が若干のギャップを介して並ぶように配置されている。
給電電極4は地導体62側の基体1の側面1bに形成されており、給電電極104の給電端140は給電線61に接続され、接地端142は地導体62に接続されている。放射電極133と接続する接地電極32のうち回路基板6の角部側に位置する部分は、回路基板6の地導体62と線状電極66により接続されている。線状電極66はインダクタンスの作用をし、アンテナ基体1の小型化を容易にする。また同じ基体1ではより低誘電率の材料を用いて帯域幅を拡大できる。金属領域51’, 53’はアンテナ基体1を回路基板6に半田により固定するために設けられている。
【００４０】
図3に示す実施例2、図11に示す実施例7及び図16に示す実施例12について、アンテナの特性試験を行った。また放射電極2の一部を図23に示すようにミアンダ状にした以外図3に示すものと同じアンテナを比較例1として、アンテナの特性試験を行った。アンテナ基体は、比誘電率εrが21のセラミックス誘電体により形成し、その基体寸法は実施例２及び比較例1では長さ15 mm×幅3 mm×厚さ3 mmとし、実施例7、12では長さ10 mm×幅3 mm×厚さ2 mmとした。伝搬周波数の中心周波数を1.575 GHz±1 MHzとし、電圧定在波比2 (VSWR = 2)での帯域幅BW(MHz)、平均利得(dBi)及び指向性を測定した。VSWRの測定は、アンテナ実装基板の一端に設けた給電端子と、ネットワークアナライザの入力端子とを、同軸ケーブル（特性インピーダンス50Ω）を介して接続し、前記給電端子においてネットワークアナライザ側からみた、アンテナの散乱パラメータ（Scattering Parameter）を測定することにより、この値に基いてVSWRを算出した。また、利得の測定に際しては、電波無響暗室内で被試験アンテナ（送信側）の給電端子に信号発生器を接続し、前記アンテナから放射された電力を受信用基準アンテナで受信することにより測定した。被試験アンテナからくる受信電力をPaとし、既知の利得Grを有する送信用基準アンテナにより測定した受信電力をPrとすると、被試験アンテナの利得Gaは、Ga＝Gr×Pa／Prで表される。指向性については、被試験アンテナ素子を回転テーブルに搭載し、被試験アンテナを回転させながら上記の利得測定を行うことにより、図18に示すように、Ｘ、ＹおよびＺ軸を中心として回転させたときの回転角度に対する利得をそれぞれ測定した。また図19のように携帯電話等の通信機器に搭載することを想定して、特性の金属依存性を調べた。測定結果を表1に示す。
【００４１】
【表１】

【００４２】
以上の結果より、実施例2、7、12のアンテナは、比較的高い比誘電率の基体を有しながら、インピーダンス整合が容易に取れることが分かった。また実施例2、7、12のアンテナは比較例1のものに比べ実施例2、7が帯域幅はやや狭いものの、高い放射利得が得られ、金属接近による利得低下も少なく、安定したアンテナ特性が得られた。実施例7では基体寸法を約2/3と小さくしたにもかかわらず、帯域幅及び利得ともに良好であった。無指向性については、三者とも３軸共に利得がほぼ円に近く指向性のない無指向特性が得られた。以上より実施例2、7、12、特に実施例12のアンテナについて帯域幅、放射利得、指向性及び金属依存性の全てにおいてバランスのとれた良好な結果が得られた。尚、比較例1の放射利得が低い原因は、インピーダンス整合が容易ではなく、整合用のインダクタンスを稼ぐために放射電極をミアンダ状にしたことであると考える。
また、以上により図10〜図16に示したような放射電極を採用することにより、基体の大きさを、長さ１０mm×幅３mm×厚さ２mm程度あるいはそれ以下の小型化ができることが分かった。
【００４３】
本発明の他の実施例としては、基体は直方体に限るものでなく適宜の形状がある。材料は磁性体、樹脂体、またこれらの積層基板としても良い。また、帯域幅を広げたり周波数調整のために放射電極側辺の開放端に形成した並行部２３ａあるいは基体をトリミングすることが有効である。
放射電極は、台形状、階段状、曲線状、ミアンダ状、一部ミアンダ状、クランク状等種々の形状が考えられるが、長手方向に連続的および／または段階的に実質的に幅を狭めながら延びる形状を有していることが望ましい。また、放射電極の一端側は必ずしも連続的に接地電極を形成する必要はなく、非連続とした容量結合となし最終的に接地できていれば良い。また、第１あるいは第２の接地電極は、最小限その端面が覆われ接地面に連接して接地できていれば良いが、基体端面からの電界の放射を抑制する効果を得るためには基体端部において端面とその廻りの四面を覆うように形成しておくと良い。
本発明のアンテナは回路基板の地導体がない領域に実装すれば最大の特性が期待できるが、設計によってはある程度特性を犠牲にしてでも地導体上に実装する場合もある。上記各実施例のアンテナ構成は組み合わせても良く、本発明の範囲内で種々の変更を加えることもできる。
【００４４】
【発明の効果】
以上のように本発明によれば、従来問題となっていた高誘電体を基体に使用した場合のインピーダンスの整合が容易となり、小型軽量であり高利得、広帯域で且つ無指向性をもった表面実装型アンテナを得ることができる。また、ＧＰＳや無線ＬＡＮ等に用いた場合にアンテナの特性を充分引き出した通信機器となる。
【図面の簡単な説明】
【図１】本発明の第１の実施例を示す表面実装型アンテナの斜視図である。
【図２】第１実施例のアンテナの等価回路図である。
【図３】本発明の第２の実施例を示す表面実装型アンテナの斜視図である。
【図４】図３の放射電極の展開図である。
【図５】第２実施例のアンテナの等価回路図である。
【図６】本発明における給電電極の他の実施例である。
【図７】本発明の第３の実施例を示す表面実装型アンテナの斜視図である。
【図８】本発明の第４の実施例を示す表面実装型アンテナの斜視図である。
【図９】本発明の第５の実施例を示す表面実装型アンテナの斜視図である。
【図１０】本発明の第６の実施例を示す表面実装型アンテナの斜視図と展開図である。
【図１１】本発明の第７の実施例を示す表面実装型アンテナの斜視図と展開図である。
【図１２】本発明の第８の実施例を示す表面実装型アンテナの斜視図と展開図である。
【図１３】本発明の第９の実施例を示す表面実装型アンテナの斜視図と展開図である。
【図１４】本発明の第１０の実施例を示す表面実装型アンテナの斜視図と展開図である。
【図１５】本発明の第１１の実施例を示す表面実装型アンテナの斜視図と展開図である。
【図１６】本発明の第１２の実施例を示す表面実装型アンテナの斜視図と展開図である。
【図１７】比誘電率と入力インピーダンスの関係である。
【図１８】本発明のアンテナを回路基板に実装した状態を示す実装図である。
【図１９】本発明のアンテナを通信機器に搭載する概念図である。
【図２０】本発明の他のアンテナを他の回路基板に実装した状態を示す実装図である。
【図２１】従来の表面実装型アンテナの一例を示す斜視図である。
【図２２】従来の上記アンテナの等価回路図である。
【図２３】比較例1の表面実装型アンテナの放射電極を示す展開図である。
【符号の説明】
１Ａ、１Ｂ、１Ｃ、１Ｄ、１Ｅ、１Ｆ、１Ｇ、１Ｈ、１Ｉ、１Ｊ、１Ｋ、１Ｌ：表面実装型アンテナ
１、９０：誘電体基体
２、２１、２４、２５、２６、２７、３３、９２：放射電極
２２、２８、２９、３０：側面放射電極、３１：接続電極
２０、９７：放射電極の開放端
２３：放射電極の側辺
２３ａ：放射電極側辺に形成した並行部
３２、５１、５２、５３：固定用電極
３８，３９：延長電極
３、３２、９３：接地電極
４、９４：給電電極、９５：給電端子電極
４０、９８：給電点
４１、１４１：給電電極の並行部分（並行部）
４２：接地点
４３、１４３：給電端となる脚部（給電部）
４４、１４４：接地端となる脚部（接地部）
５：第２の接地電極
６：回路基板、１０：基体の稜線
６０：給電電源、６１、９９：給電線、６２：接地導体
６３：接地導体の境界線、６４：接地導体の延長部、６５：回路基板の露出部
６６：線状導体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a small antenna having a dielectric or magnetic material such as ceramics or resin as a base, and more particularly to a surface-mounted antenna having an impedance matching function provided to a feeding electrode and a communication device equipped with the same.
[0002]
[Prior art]
Surface mount antennas are used in GPS (Global Positioning System), wireless LAN (Local Area Network), etc., which use the GHz band as a carrier wave. Miniaturization of portable terminal devices is proceeding at a rapid speed, and surface-mounted antennas are also required to have a small size and a low profile, as well as good radiation efficiency, no directivity, and a wide bandwidth. However, since the characteristics of the conventional surface mount antenna deteriorate as the size and height of the antenna are reduced, it is not always satisfactory to realize a sufficiently small size and height.
[0003]
Generally, the radiation electrode length of this type of antenna is set to correspond to a quarter wavelength. This is because the radiation efficiency of the antenna is maximized when the wavelength is set to 1/4, and is particularly important in a portable terminal device that needs to be able to use the battery as long as possible by one charge. When a radiation electrode is placed on a dielectric substrate, its effective length is the relative permittivity ε _r It is known that it is inversely proportional to the square root of, which is called the wavelength shortening effect. If the wavelength shortening effect is used, the radiation electrode of the antenna can be shortened, and the antenna can be reduced in size and height.
As the propagation frequency of the antenna decreases, the antenna can be reduced in size by using a material having a large relative dielectric constant for the substrate. However, in reality, there is a limit to the use of high dielectric constant materials, and in practice the relative dielectric constant ε is about 4 _r Only a dielectric substrate having the above has been put into practical use. This is the relative dielectric constant ε _r This is because an impedance matching problem arises when the value is larger than this value. In a surface mount antenna with a high relative dielectric constant, the input impedance at the feed point is likely to change significantly, and thus it is difficult to reduce the size and solve the problem of impedance matching.
[0004]
For example, as shown in FIG. 21, for example, a surface-mounted antenna described in Japanese Patent Laid-Open No. 9-219610 is bent in an approximately L shape or an approximately U shape on an upper surface 91 of a substantially rectangular parallelepiped base 90, and has one end The radiation electrode 92 is open and the other end is grounded, and the power supply electrode 94 is formed on the upper surface of the base body 90 via the gap 96 to excite the radiation electrode 92. One end of the power supply electrode 94 is a power supply line. Connected to 99. As shown in FIG. 22, the equivalent circuit includes a radiation resistance R and an inductance L of the radiation electrode 92, a capacitance C formed between the radiation electrode 92 and the ground conductor, and between the radiation electrode 92 and the feeding electrode 94. It is a parallel resonant circuit composed of formed capacitance Ci ′.
In this antenna, high-frequency power from a transmission circuit (not shown) is transmitted to the feed electrode 94 via the feed line 99 of the circuit board, and input to the resonance circuit formed by the radiation electrode 92 and the ground conductor, The electromagnetic waves are radiated from the radiation electrode 92 in parallel resonance. It is necessary to perform impedance matching so that voltage reflection does not occur at the feeding point 98.
[0005]
Various impedance matching means for matching the input impedance viewed from the transmission circuit side of the feeding electrode 94, that is, the input impedance at the feeding point 98, with the characteristic impedance (50Ω) have been proposed. For example, in the antenna shown in FIG. 21, the radiation electrode 92 and the feed electrode 94 are capacitively coupled, and the radiation electrode 92 and the feed electrode 94 are canceled so as to cancel the inductance L of the radiation electrode 92 as shown in the equivalent circuit of FIG. A capacitance Ci ′ is set between them.
However, in the conventional antenna shown in FIG. 21, the feeding electrode and the radiating electrode are not directly connected but only capacitively coupled, and inductance is not used for impedance matching. For this reason, if this antenna is reduced in size and height, it cannot be made a high-performance antenna with which impedance matching is easy. In addition, antennas used for GPS, wireless LAN, and the like basically require omnidirectional characteristics, and it is necessary to improve radiation efficiency and gain, and to increase bandwidth. Conventionally, consideration and examination of this point have not been sufficient.
[0006]
In addition, when impedance mismatch occurs, a new matching circuit may be inserted between the transmission / reception circuit and the antenna. However, the addition of the new matching circuit has a problem of increasing the size of the antenna device. Regarding the impedance matching circuit, Japanese Patent Laid-Open No. 2000-286615 discloses a small antenna in which a base is a laminated structure and a matching circuit is built in between layers. However, this not only complicates the antenna structure, but also increases the manufacturing cost.
WO01 / 24316A1 has a first radiating electrode (feeding side radiating electrode) and a second radiating electrode (non-feeding side radiating electrode) on the upper surface of the substrate, and the two radiating electrodes are in a double resonance state. Furthermore, an antenna having a matching circuit electrode on the side surface of the substrate is disclosed. In this antenna, the first radiating electrode (feeding side radiating electrode) and the matching electrode are directly connected at the impedance matching position, but the feeding electrode has no capacitance, and impedance matching is performed by manipulating the inductance exclusively. I am trying. The electrode configuration having such a matching circuit corresponds to a conventional inverted-F antenna, and originally has an antenna structure that facilitates impedance matching.
[0007]
Japanese Patent Application Laid-Open Nos. H8-186431 and H11-340726 disclose impedance matching technology in a unidirectional antenna having a structure in which a radiation conductor is formed on the top surface of a substrate and a ground conductor is formed on the entire bottom surface of the substrate. . However, such an antenna is not suitable for applications that require omnidirectionality, such as GPS and wireless LAN. This can also be seen from the configuration in which, for example, the radiation conductor surrounds the power supply conductor provided on the upper surface of the base body, and the coupling of the capacitance is strongly increased. Moreover, since miniaturization, radiation efficiency, gain, and bandwidth are not taken into consideration, there is a problem in using for GPS and the like.
[0008]
[Problems to be solved by the invention]
In the prior art, it has not been possible to obtain a compact and low profile and easy impedance matching and high antenna characteristics. In addition, antennas used for GPS, wireless LAN, and the like basically require omnidirectional characteristics, and it is necessary to improve radiation efficiency and gain, and to increase bandwidth. Conventionally, consideration and examination on this point have not been sufficient. An object of the present invention is an antenna that can be easily reduced in impedance even when a material having a relatively high dielectric constant is used and can be miniaturized, and is particularly suitable for GPS, wireless LAN, etc., and has a high gain, a wide bandwidth, and an omnidirectionality. It is an object of the present invention to provide a surface mount antenna having the characteristics.
Another object of the present invention is to provide a communication device for a mobile phone, a headphone, a personal computer, a notebook personal computer, a digital camera or the like equipped with this surface mount antenna.
[0009]
[Means for Solving the Problems]
As a result of diligent research in view of the above-mentioned purpose, when the impedance matching function is provided by making the feeding electrode have an inductance in addition to the capacitance, impedance matching is easy and omnidirectional even when a relatively high dielectric constant material is used. The present inventors have found that a small surface-mount antenna having the characteristics can be obtained, and have arrived at the present invention.
[0010]
The first surface mount antenna of the present invention is a dielectric. Body And a substrate provided on at least the upper surface of the substrate. The other end became an open end A radiation electrode; a ground electrode provided on the base so as to be directly connected or capacitively coupled to one end of the radiation electrode; and provided on at least a side surface of the base so as to face the radiation electrode through a gap. A surface-mounted antenna comprising a feeding electrode, The substrate has a relative dielectric constant of more than 8 and 50 or less, The feed electrode feeds at one end Part To the other end Part Have The power feeding part and the grounding part Between And a gate-like shape connected to the open end side of the radiation electrode through a parallel portion arranged through a gap, The area ratio of the ground electrode on the bottom surface of the substrate is 30% or less. In addition, the inductance is adjusted by adjusting the length of the power supply unit and the grounding unit, and the capacitance is adjusted by adjusting the gap interval and / or the length of the parallel unit. It is characterized by that.
[0012]
First of the present invention D The surface-mount antenna is provided on the base body so as to be directly connected to or capacitively coupled to a base body made of a dielectric material or a magnetic body, a radiation electrode provided on at least the upper surface of the base body, and one end of the radiation electrode. A grounding electrode, and a feeding electrode provided on at least a side surface of the base so as to face the radiation electrode through a gap, and the feeding electrode is provided on two side faces facing the base. An L-shaped electrode is connected to one I-shaped electrode provided on the end face of the base. One L-shaped electrode has a power feeding portion at one end, and the other L-shaped electrode is one end. The I-shaped electrode is a parallel portion, and the feeding electrode has a gate shape.
[0013]
In the present invention, the power feeding electrode is formed by connecting a first electrode and a second electrode provided on opposite side surfaces of the base body and one I-shaped electrode provided on an end face of the base body, One electrode has a feeding part at one end, the second electrode has a grounding part at one end, the I-shaped electrode is a parallel part, and the feeding electrode has a gate shape, and further the base It is preferable that a ground electrode portion formed on the end face or the end face and the opposite side face is formed.
It is preferable that at least a part of the feeding electrode and the radiation electrode have a meander shape, a U shape, an L shape, or a crankshaft shape.
The feeding electrode is preferably provided on the side surface of the base body with a gap on the open end side of the radiation electrode. At this time, it is preferable to arrange a power feeding portion in the vicinity of the open end of the radiation electrode.
In a preferred embodiment of the present invention, at least a part of the radiation electrode extends from one end of the substrate toward the other end in the longitudinal direction while being substantially narrowed continuously and / or stepwise. In another preferred embodiment of the invention, the radiation electrode extends from one end of the substrate to the other end in the longitudinal direction in a continuous and / or stepwise manner with a substantially narrowing width, with the other end being substantially co-axial. It is bent in a letter shape.
In another preferred embodiment of the present invention, the radiation electrode is formed so as to reach the upper surface via a side surface different from the side surface on which the feeding electrode is formed. At this time, it is preferable that there is no overlapping ground electrode when the radiation electrode provided on the upper surface of the substrate is projected onto the lower surface of the substrate.
In the antenna of the present invention, it is preferable to round the corners of the radiation electrode and / or the feeding electrode.
In the antenna of the present invention, a second ground electrode facing the other end of the radiation electrode via a gap may be provided on the base.
The dielectric constant ε of the antenna substrate of the present invention _r A dielectric of 6-50 can be used.
[0015]
A communication device according to the present invention includes an antenna device in which the surface-mounted antenna is mounted in an area without a ground conductor on a circuit board, and the base in which the radiation electrode extends in a longitudinal direction is an edge of the ground conductor on the circuit board. It arranges via a part and a gap, The said feeding electrode is arrange | positioned at the said ground conductor side, It is characterized by the above-mentioned.
In a preferred embodiment of the present invention, the ground electrode portion located on the opposite side of the ground conductor of the circuit board on the surface-mounted antenna is located on the corner side of the circuit board, and the ground electrode portion and the conductor of the circuit board are not connected to each other. Connected by a conductor.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with embodiments shown in the drawings.
First, the reason why impedance matching becomes difficult will be described. When a radiation electrode, a ground electrode, a feeding electrode, and the like are arranged on the substrate, a capacitance is generated between the electrodes. Increasing the capacitance between the feed electrode and the radiating electrode lowers the input impedance and causes impedance mismatch. Capacitance is dielectric constant ε _r Therefore, when a high dielectric constant material is used to lower the propagation frequency, impedance mismatch becomes significant. Therefore, the relative dielectric constant ε _r A dielectric substrate having a low value of about 4 is used. Although the present invention is not limited, the dielectric constant ε _r Allows the use of 6 or more, preferably 20-50 or more dielectric materials.
[0017]
Even if the capacitance between the radiating electrode and the feeding electrode is increased by using a high dielectric constant material for the substrate, the present invention increases the inductance of the feeding electrode by increasing the capacitance, thereby canceling the increase in capacitance. Thus, impedance matching is achieved. The conventional feeding electrode of this type of antenna has a configuration that provides only a capacitance on an equivalent circuit. However, according to the present invention, the feeding electrode has a shape capable of acquiring an inductance in addition to the capacitance. Specifically, the feeding electrode is formed in a strip shape so that the inductance can be easily obtained, and the capacitance can be adjusted by arranging a part of the feeding electrode on the radiation electrode through a gap. In addition, by using one end of the belt-shaped power supply electrode as a power supply unit and the other end as a grounding unit, a parallel component L as shown in FIG. ₂ And series component L ₁ , C _i To facilitate impedance matching design and shorten the development period.
[0018]
Since there are various forms of surface mount antennas depending on the application, the impedance matching condition needs to satisfy these extensive requirements. As described above, the feeding electrode of the present invention has the parallel component L. ₂ And series component L ₁ , C _i Can be regarded as a combination. By making the power supply electrode into a meander shape, a U shape, an L shape, a crankshaft shape, or a combination thereof, inductance and capacitance can be arbitrarily set without being limited to impedance matching conditions. For example, the capacitance and the inductance can be made substantially the same, or one of them can be made larger. Inductance is proportional to the length of the feed electrode, and capacitance is a function of the opposing length of the feed and radiation electrodes. Therefore, when impedance matching is performed using the feeding electrode of the present invention, first, the L ₁ , L ₂ , C _i Decide which of these should be increased or decreased. Then L ₁ , L ₂ Is proportional to the length of the feed electrode and C _i Is a function of the opposing length of the feed electrode and the radiation electrode, it is possible to easily set the shape of the feed electrode that satisfies the desired parameters for impedance matching.
[0019]
In the antenna configuration according to an embodiment of the present invention, the radiation electrode is provided on at least the upper surface of the base, and one end thereof is grounded and the other end is an open end. This antenna structure appears to be close to an inverted F-type antenna in which a feeding electrode is connected in the vicinity of the grounding end of the radiation electrode. However, in the present invention, the basic point is that the radiation electrode and the feeding electrode are separated and capacitively coupled. This is different from the inverted F structure. The feeding electrode is formed on one side surface of the substrate so that there is no printing misalignment or the like when the electrode is printed, and the manufacturing is easy and the characteristics are stable.
In the present invention, impedance matching is facilitated by appropriately setting the distance and parallel length between the radiation electrode and the feeding electrode and / or the leg length and shape of the feeding electrode. Thereby, the bandwidth BW can be arbitrarily selected. Since there is a relationship of BW∝1 / Q and Q = R√ (C / L), the bandwidth BW can be widened by controlling C or C / L based on the degree of capacitive coupling and the electrode length. For example, if the power supply portion side of the power supply electrode is arranged near the open end of the radiation electrode, the radiation end is regarded as an inductor, and the inductance (L) can be increased. If the design is performed at the same resonance frequency, the capacitance (C) can be reduced accordingly and the Q value can be increased. Therefore, the bandwidth can be increased.
[0020]
The surface-mounted antenna of the present invention is characterized by having almost no grounding electrode for soldering on the bottom surface in order to have excellent omnidirectionality. If the ground electrode is formed on the entire back surface, the antenna non-directionality is lost due to capacitance coupling with the radiation electrode on the top surface. Specifically, the ratio of the total area of the ground electrode on the bottom surface to the total area of the bottom surface is preferably 30% or less, and more preferably 20% or less. Also on the bottom. It is preferable that there is substantially no ground electrode in the region below the radiation electrode provided on the upper surface.
Further, the second ground electrode can be disposed opposite to the open end of the radiation electrode via a gap. In this case, since capacitive coupling with the opposing ground electrode is strong, even if the power feeding electrode is arranged in the vicinity, the influence is relatively small. Therefore, when adjusting the propagation frequency significantly, the main adjustment of the frequency is performed by adjusting the coupling degree between the radiation electrode and the second ground electrode, and the coupling degree between the radiation electrode and the feeding electrode is adjusted. Make fine adjustments to the frequency.
[0021]
In the present invention, the relative dielectric constant ε of the substrate _r Is preferably in the range of 6-50. This dielectric constant ε _r Is determined in consideration of the temperature coefficient of the dielectric, the processing accuracy of the substrate, and the like, but the upper limit is naturally raised if the material, the processing accuracy, etc. are improved. Such a relative dielectric constant ε _r A substrate having, for example, 22.22 wt% MgO, 5.13 wt% CaCO _Three 48.14 wt% TiO ₂ And 24.51% by weight of ZnO raw material were fired, and 36.6 mol% MgO, 3.4 mol% CaO, 40 mol% TiO were used as the calcined substrate. ₂ And a dielectric ceramic composed of 20 mol% ZnO (relative permittivity ε _r : 21).
When a high dielectric substrate is used, the radiation efficiency of the radiation electrode is reduced. In order to suppress a decrease in radiation efficiency, a radiation electrode and a ground electrode are configured so as to increase radiation to free space, or a substrate in which a high dielectric material and a low dielectric material are combined is used.
[0022]
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing a surface mount antenna according to a first embodiment of the present invention. This antenna 1A is formed with a radiation electrode 2 disposed on the upper surface of a rectangular parallelepiped base 1, a ground electrode 3 connected to one end of the radiation electrode 2, and a radiation electrode 2 on a side surface with a predetermined gap G1. Power supply electrode 4. The other end of the radiation electrode 2 is an open end 20. The antenna 1A has a configuration similar to that of the inverted F antenna, but differs from the inverted F antenna in that the feeding electrode 4 is interposed via the gap G1. No electrode other than the soldering electrode is arranged on the bottom surface 1a of the base 1, and the antenna is mounted on the circuit board without a ground conductor, so that a substantially uniform radiation electric field pattern is formed in any direction. The omnidirectionality shown is obtained.
The feeding electrode 4 has a gate-shaped (U-shaped) shape in which a strip-shaped electrode is bent at two locations, and has a parallel portion 41 facing the edge 23 of the radiation electrode 2 substantially in parallel. The feed electrode 4 has a feed point 40 connected to a feed line of a transmission / reception circuit (not shown) at a feed part 43 at one end, and a ground end 42 connected to a ground conductor at a ground part 44 at the other end. The power feeding part 43 and the ground part 44 of the power feeding electrode 4 mainly generate inductance, and the radiation electrode 2 and the parallel part 41 mainly generate capacitance. Therefore, the surface mount antenna according to the present invention has an equivalent circuit shown in FIG.
[0023]
Inductance L ₁ , L ₂ Is formed by the

legs

43 and 44 of the feed electrode and the capacitance C _i Is formed between the radiation electrode 2 and the parallel part 41 of the feeding electrode 4. Therefore, set the length and shape of the

legs

43, 44 and the parallel part 41 as appropriate. ₁ , L ₂ And C _i By changing the input impedance Z, the radiation electrode 2 is viewed from the feed point 40. _in Can be matched to 50 Ω. Thus, in addition to the capacitance between the radiation electrode 2 and the feeding electrode 4, it is an important feature of the present invention that the input impedance matching can be uniquely performed by manipulating the inductance of the feeding electrode 4. The same applies to the following embodiments, but the positions of the feeding point 40 and the ground point 42 may be reversed left and right. Moreover, the parallel part 41 should just be located in a line with the radiation electrode 2 via the gap, and does not need to be parallel.
[0024]
FIG. 3 is a perspective view showing a surface mount antenna according to the second embodiment, FIG. 4 is a development view of the radiation electrode, and FIG. 5 is a diagram showing an equivalent circuit of the antenna.
The surface mount antenna 1B of the present embodiment is for GPS, a rectangular parallelepiped base 1, a radiation electrode 2 formed on the upper surface 1c and the adjacent side surface 1d, and a ground electrode 3 connected to one end of the radiation electrode 2 And a feeding electrode 4 formed in a gate shape from the longitudinal side surface 1b to the upper surface 1c of the base 1. The feeding electrode 4 may be provided only on the side surface 1b. The arrangement and shape of the gate-type feeding electrode 4 are determined by balancing impedance matching and broadening the bandwidth. The radiation electrode 2 of the present embodiment has a shape extending from one end of the substrate 1 in a longitudinal direction while being substantially narrowed continuously and / or stepwise. As shown in the development view of FIG. 4, the radiation electrode 2 includes a radiation electrode portion 21 provided on the upper surface 1c of the base 1, and a radiation electrode portion 22 continuously formed on the adjacent side surface 1d. The portion 22 is also narrowed slightly toward the tip. In this way, by forming the radiation electrode 2 whose width is gradually narrowed not only on the upper surface 1c of the substrate 1 but also on the adjacent side surface 1d, multiple resonance can be induced, and miniaturization and more non-directivity can be achieved. .
The ground electrode 3 and the radiation electrode 2 may be connected by non-contact capacitive coupling. The ground electrode 3 may be provided on four surfaces surrounding the periphery of the one end surface 1e of the substrate 1. The ground electrode 3 formed on the bottom surface 1a also serves as a soldering electrode and is connected to the ground conductor of the circuit board. The power supply electrode 4 also has a ground electrode portion 50 on the bottom surface 1a of the base 1, and the ground electrode portion 50 acts as a soldering electrode with the circuit board.
[0025]
In this embodiment, the feeding electrode 4 is a gate shape (U-shape) having a width of 1 mm and an equivalent length of 10 mm. 6A to 6C show various shapes of the feeding electrode 4. FIG. 6 (a) shows an example of the U-shaped feeding electrode 4, and the inductance L generated at the left and right legs. ₁ , L ₂ Are almost equal. The shapes shown in FIGS. 6B and 6C are examples in which the lengths of the left and right legs are different, and the inductance is adjusted by the length of the conductor. Fig. 6 (b) shows the right leg with a meander shape. ₁ <L ₂ It is what. FIG. 6 (c) shows the left leg as a crank and the right leg as a meander. ₁ > L ₂ It is what. When adjusting using inductance, if you want to increase the input impedance, ₁ If you want to decrease the input impedance ₂ Increase.
[0026]
Further, the central parallel portion 41 of the feeding electrode 4 is one of the features of the present invention. C and C by central parallel part 41 _i Can be set arbitrarily. That is, capacitance C _i Is generally proportional to the length W of the parallel part 41 and the distance G between the parallel part 41 and the radiation electrode 2 ₁ Inversely proportional to Therefore, C _i The parallel part 41 is lengthened or the distance G between the parallel part 41 and the radiation electrode 2 is increased. ₁ Shrink. Also C _i Vice versa. Thus, the length W of the parallel part 41 and the distance G between the parallel part 41 and the radiation electrode 2 ₁ By changing C _i Can be adjusted.
[0027]
This embodiment is also characterized by the radiation electrode 2. The basic shape of the radiating electrode 2 was gradually decreased as the electrode length in the direction perpendicular to the flow of the high-frequency current (longitudinal direction of the substrate 1), that is, the width was not constant, and approached to the open end 20 side. It has a shape. The high-frequency current supplied from the power supply via the power supply electrode 4 resonates at a frequency determined by the capacitance formed between the inductance of the radiation electrode 2 and the ground, and is radiated as electromagnetic energy into the space. At this time, it becomes a current distribution mode in which the ground electrode 3 and the open end 20 are nodes and antinodes. If the width of the radiation electrode 2 is constant, there is only one current distribution mode, but if the width of the radiation electrode 2 is not constant, the antenna has a plurality of inductances Lr as shown in FIG. ₁ , Lr ₂ , Lr _Three ,… And capacitance Cr ₁ , Cr ₂ , Cr _Three , ... are equivalently formed. Since the resonance frequencies of the respective resonance circuits are quite close to each other, a state in which a plurality of resonances exist continuously is obtained, and as a result, a broadband resonance characteristic is obtained.
[0028]
FIG. 7 shows a surface mount antenna according to a third embodiment of the present invention. The same parts as those in the above embodiment are denoted by the same reference numerals, and the description thereof is omitted. As in the above embodiment, the radiation electrode 24 has a substantially trapezoidal shape extending from one end of the substrate 1 to the other end in the longitudinal direction while being substantially narrowed in a continuous and / or stepwise manner. 1 over the side surface 1b and the upper surface 1c. In this embodiment, since the feeding electrode 4 is U-shaped, the distance between the parallel part 41 and the radiation electrode 24 is not constant, and the capacitance is small. As described above, the radiation electrode 24 and the power supply electrode 4 do not have to be parallel, but only need to be partially aligned. This is called approximately parallel. In addition, the narrowing of the radiation electrode in steps includes, for example, a shape that narrows with a step in a step shape.
[0029]
FIG. 8 shows a surface mount antenna according to a fourth embodiment of the present invention. The same parts as those in the above embodiment are denoted by the same reference numerals, and the description thereof is omitted. The radiation electrode 25 has a microstrip shape, one end of which is grounded and the other end 20 is opened. In any of the above embodiments, the radiation electrode 2 is provided over the entire length of the upper surface 1c of the dielectric substrate 1, but the length of the radiation electrode may be selected to be a quarter wavelength of the desired frequency, and is not necessarily the entire length of the substrate 1. There is no need to provide it. In this embodiment, the radiation electrode 25 is shorter than the substrate 1. As a result, an adjustment allowance for lowering the propagation center frequency can be taken. Further, even if there is a defect such as a dimension defect or chipping at the end of the substrate 1, there is no problem in forming the radiation electrode 25.
[0030]
FIG. 9 shows a surface mount antenna according to a fifth embodiment of the present invention. The same parts as those in the above embodiment are denoted by the same reference numerals, and the description thereof is omitted. A second ground electrode 5 is formed so as to face the open end 20 of the radiation electrode 26 via a gap G2. Thereby, a large and stable capacitance is formed between the open end 20 of the radiation electrode 26 and the ground conductor, and the frequency can be adjusted greatly. Fine adjustment may be performed by the inductance and capacitance of the feeding electrode 4.
Since there is a capacitance due to the gap G2 between the open end 20 of the radiation electrode 26 and the second ground electrode 5, a desired frequency can be obtained even if the radiation electrode 26 is short (even if the inductance is small). Therefore, the surface mount antenna having such a structure is suitable for miniaturization.
The feeding electrode 4 is formed from the side surface 1b to the upper surface 1c of the base 1, but may be provided only on the side surface 1b depending on conditions. This can be said in common with the above embodiments. When the power supply electrode 4 is provided only on the side surface 1b, it is not necessary to pay attention to the accuracy of joints when forming by screen printing or the like, and the number of processes is reduced, which is preferable in terms of manufacturing.
[0031]
10 to 12 show surface mount antennas according to sixth to eighth embodiments of the present invention. A perspective view is shown on the left side of the figure, and a developed view is shown on the right side. The same parts as those in the above embodiment are given the same reference numerals, and the description thereof is omitted. In these embodiments, the strip-shaped radiation electrode 2 is formed from the side surface 1d to the upper surface 1c of the base 1.
In the sixth embodiment shown in FIG. 10, an L-shaped electrode portion 27 is provided at the end of the upper surface 1c of the base 1, and an L-shaped electrode 28 is continuously formed on the adjacent side surface 1d. . The feeding electrode 4 has a gate-shaped (U-shaped) shape having

leg portions

43 and 44 and a central parallel portion 41 as a feeding end and a grounding end, respectively, and the open end side of the L-shaped electrode portion 27 on the side surface 1b of the base 1 Are formed side by side.
In the seventh embodiment shown in FIG. 11, an L-shaped electrode portion 27 is provided at the end of the upper surface 1c of the base 1, and an L-shaped electrode 29 is continuously formed on the adjacent side surface 1d. .
In the eighth embodiment shown in FIG. 12, an L-shaped electrode portion 27 is provided at the end of the upper surface 1c of the substrate 1, and the I-shaped electrode 30 is continuously formed on the adjacent side surface 1d. Yes. As for the shape of the feeding electrode 4, the seventh and eighth embodiments are substantially the same as the sixth embodiment.
The electrode 51 is a soldering electrode for fixing the antenna to the circuit board. In the examples of FIGS. 11 and 12, a soldering electrode 52 is added to increase the bonding strength with the circuit board. The electrodes 51 and 52 are not connected to the ground conductor of the circuit board. In the examples of FIGS. 10 to 12, the radiation electrode is L-shaped in order to increase the inductance. In the example of FIG. 11, the bent portions of the L-shaped radiation electrode portion 29 and the gate-shaped feeding electrode 4 are rounded. Only the radiation electrode may have the curvature R. When the substrate 1 is lowered in height, as shown in FIG. 12, if the soldering electrode 52 is directly connected to the radiation electrode 30 via the connection electrode 31, the antenna characteristics are stable without being greatly changed.
[0032]
As shown in FIG. 11, when the bent portion of the L-shaped electrode portion 29 is rounded R, the radiation gain is improved. In a conventional radiation electrode having a bent portion that is substantially L-shaped, U-shaped, meandered, or crank-shaped, the straight portion and the bent portion have unequal widths and are connected while being angular. This means that the impedance changes discontinuously, and a part of the traveling wave is reflected by the discontinuity. For this reason, the reflection loss of the input high frequency was large, and the gain was reduced. In order to solve this problem, it has been found that if the bent portion is rounded, the line becomes substantially equal in width and impedance discontinuity can be avoided. Or it turned out that it is effective also to give the chamfering which cut off the corner | angular part. When the occurrence of reflection loss at the bent portion is suppressed, transmission loss of the resonance current flowing through the radiation electrode of the antenna is reduced, and the gain is improved.
[0033]
13 and 14 show surface mount antennas according to ninth and tenth embodiments of the present invention. The same parts as those in the above embodiment are denoted by the same reference numerals, and the description thereof is omitted. In these embodiments, the radiation electrode 33 and the feeding electrode 4 are characterized. The radiation electrode 33 is mainly provided on the upper surface 1c of the base 1, and is substantially continuously and / or stepwise from one end connected to the ground electrode 3 to the other end in the longitudinal direction, similarly to the example shown in FIG. The radiation electrode portion 33a extends while narrowing the width, and the radiation electrode portion 33b bent in a U-shape or a U-turn shape at the left end portion. With such a radiation electrode 33, a broadband resonance characteristic can be obtained by the trapezoidal radiation electrode portion 33a, and the inductance can be supplemented by the bent radiation electrode portion 33b. The electrode 51 is a soldering electrode for fixing the antenna to the circuit board, and is provided to the minimum necessary.
In this embodiment, a gap of about 0.2 to 0.5 mm is provided between the outer periphery of the radiation electrode 33 and the ridgeline of the base 1. This gap facilitates electrode printing and makes it difficult for printing misalignment to occur. Further, electrode peeling due to deformation or chipping of the edge of the substrate 1 can be prevented. By preventing printing misalignment and electrode peeling, variations in propagation frequency can be suppressed. The configuration in which the radiation electrode 33 is provided only on the upper surface 1c of the substrate 1 has a higher gain than the configuration in which the radiation electrode is also provided on the side surface, because capacitance coupling with the ground conductor of the circuit board is reduced.
[0034]
As shown in FIG. 13, the gate-shaped feeding electrode 4 provided on the side surface 1b faces the open end 20 of the radiation electrode portion 33b. The feeding electrode 4 shown in FIG. 14 has a feeding end 43 at one end and an L-shaped electrode portion 41 provided on the side surface 1b, an I-shaped electrode portion 42 provided on the end surface 1f, and a grounding end 44 at one end. And an L-shaped electrode portion 45 provided on the side surface 1d. The gate-shaped feeding electrode 4 has a U-shaped parallel portion 41 composed of

electrode portions

41, 42, 45 provided over two

side surfaces

1b, 1d and an end surface 1f, and the parallel portion 41 is a U-shaped radiation electrode. It faces 33b. With such a feeding electrode 4, capacitance coupling can be achieved over almost the entire U-shaped portion of the radiation electrode 33, which is advantageous for downsizing of the antenna. Further, with respect to the same capacitance value, the distance from the radiation electrode 33 can be widened, and variations in capacitance value and propagation frequency due to printing misalignment can be reduced.
FIG. 15 shows a surface-mounted antenna of Example 11. In this example, the configuration of the feeding electrode 4 is different from that of the other examples. That is, the feeding electrode 4 includes an F-shaped electrode portion 41 having a feeding end 43 and a grounding end 44 provided on the side surface 1b of the base 1, and

linear electrode portions

42 and 45 formed on the end surface 1f and the side surface 1d. Become. The power supply electrode of this embodiment can be broadened using double resonance simultaneously with impedance matching.
It should be noted that the antenna configurations of the above-described embodiments can be combined, and various other embodiments can be configured within the scope of the present invention.
[0035]
FIG. 16 shows a surface-mounted antenna of Example 12. The band-shaped radiation electrode 133 is composed of a crankshaft-shaped electrode portion 133d formed in the longitudinal direction on the side surface 1d and an L-shaped electrode portion 133c formed on the upper surface 1c, and is generally U-shaped. is there. Thus, since the radiation electrode 133 extends in a bent shape from the upper surface 1c to the side surface 1d of the base 1, the entire length can be increased. As a result, the antenna base 1 can be reduced in size with the same bandwidth.
The positional relationship between the power feeding part 143 and the grounding part 144 of the power feeding electrode 104 is opposite to that of the above embodiment, the power feeding point 140 is located at the substantially central part of the substrate, and the power feeding part 143 is located near the open end of the radiation electrode 133. Like to do. Further, the L-shaped electrode portion 133c formed on the upper surface 1c is not overlapped with the ground electrode 32 when projected onto the lower surface 1a. As a result, the bandwidth is improved and the omnidirectionality is good, and the GPS antenna is balanced. Further, the open end of the radiation electrode 133 and the parallel part 141 of the feeding electrode 104 are close to each other. By using the wide parallel portion 141, impedance matching is easy and the gain is slightly improved.
In the present embodiment, the parallel portion 141 has a shape that is wide and close to a rectangle, but the shape of the feeding electrode 104 can be variously changed depending on the mounting position on the circuit board side, the arrangement of the conductor pattern, the radiation electrode structure, and the like. . Even if the specifications of the circuit board and the radiation electrode 133 are changed, the inductance and capacitance can be appropriately set by appropriately setting the arrangement, shape, size, etc. of the feeding electrode 104 between the feeding point 140 and the grounding point 142. It is possible to easily adjust the impedance matching.
[0036]
17 shows the input impedance Z obtained by simulation for the surface mount antenna of the present invention (invention) of FIG. 1 and the surface mount antenna of FIG. 21 (conventional example). _in And dielectric constant ε of the substrate _r Shows the relationship. In the present invention, the increase in capacitance associated with the use of a high dielectric constant substrate can be canceled as appropriate by the inductance, and the relative dielectric constant ε _r High dielectrics up to about 50 can be used. Conventional dielectric constant ε _r Is more than 5 times ε compared to the case of 4 _r Can be used, which has a great effect on miniaturization of the antenna. If a stable dielectric material is developed at high temperatures or if the processing technology is improved, the input impedance Z _in The upper limit of is further increased. It is also expected that the upper limit will be raised when composites of high and low dielectric materials are developed.
[0037]
Next, a configuration for mounting the surface mount antenna described above on a circuit board will be described.
FIG. 18 shows a state where the antenna 1B shown in FIG. 3 is mounted on the circuit board 6. In FIG. 18, parts other than the antenna are omitted. The antenna 1B is arranged on the exposed portion 65 of the circuit board 6 where there is no ground conductor so as to be aligned in the longitudinal direction with a slight gap from the edge 63 of the ground conductor 62. At that time, the feeding electrode 4 is located on the ground conductor 62 side, and the open end 20 of the radiation electrode 2 is located far from the ground conductor 62. One end of the gate-type power supply electrode 4 is connected to the power supply line 61, and the other end is connected to the ground conductor 62. Thereby, the high-frequency signal supplied from the power supply 60 is supplied to the power supply electrode 4 through the power supply line 61, and the current from the power supply end 40 to the radiation electrode 2 side via the parallel portion 41 and the grounding end 42. The current is directed to the ground conductor 62, and impedance matching is achieved and the radiation electrode 2 is excited. As a result, electromagnetic waves are radiated into the space from the open end 20 of the radiation electrode 2.
[0038]
Conventionally, the antenna is often arranged perpendicular to the edge of the ground conductor 62. In this case, it goes without saying that the dead space becomes large and the degree of freedom in design is small. However, in the present invention, by disposing the antenna slightly away from the edge of the ground conductor 62 and in parallel therewith, the area substantially occupied by the antenna (including the dead space) is significantly reduced, and the mounting is implemented. Since the degree of freedom and density of the layout increase, the space of the antenna device can be saved.
The left and right arrangement of the feeding part 43 and the grounding part 44 of the feeding electrode 4 may be changed according to the arrangement of the feeding line 61 and the ground conductor 62 of the substrate 6, but at least the feeding electrode 4 is arranged on the feeding line 61 side, Paralleling the longitudinal direction of the ground conductor 62 and the antenna base 1 is necessary to obtain the effect of the present invention with a small occupied area. In order to make it omnidirectional, the antenna of the present invention is preferably mounted on the exposed portion 65 without the ground conductor 62.
By mounting the circuit board 6 on which the antenna is mounted in this manner inside a mobile phone, a personal computer or the like schematically shown in FIG. 19, it can be used as a communication device having a GPS or wireless LAN function.
[0039]
FIG. 20 shows an example in which the antenna shown in FIG. 16 is mounted on a circuit board 6 different from FIG. The same parts as those in FIG. 18 are denoted by the same reference numerals. The antenna 1L is arranged on the exposed portion 65 where the ground conductor 62 is not formed on the circuit board 6 so that the edge 63 of the ground conductor 62 and the antenna base 1 are arranged with a slight gap.
The power supply electrode 4 is formed on the side surface 1 b of the base 1 on the ground conductor 62 side, the power supply end 140 of the power supply electrode 104 is connected to the power supply line 61, and the ground end 142 is connected to the ground conductor 62. Of the ground electrode 32 connected to the radiation electrode 133, the portion located on the corner side of the circuit board 6 is connected to the ground conductor 62 of the circuit board 6 by the linear electrode 66. The linear electrode 66 acts as an inductance and facilitates the miniaturization of the antenna base 1. Further, the bandwidth of the same substrate 1 can be increased by using a material having a lower dielectric constant. The metal regions 51 ′ and 53 ′ are provided to fix the antenna base 1 to the circuit board 6 by soldering.
[0040]
Antenna characteristics tests were conducted on Example 2 shown in FIG. 3, Example 7 shown in FIG. 11, and Example 12 shown in FIG. Further, an antenna characteristic test was carried out using the same antenna as shown in FIG. 3 as Comparative Example 1 except that a part of the radiation electrode 2 was formed in a meander shape as shown in FIG. The antenna substrate is formed of a ceramic dielectric having a relative dielectric constant εr of 21. The substrate dimensions in Example 2 and Comparative Example 1 are 15 mm long × 3 mm wide × 3 mm thick. Then, the length was 10 mm x width 3 mm x thickness 2 mm. The bandwidth BW (MHz), average gain (dBi), and directivity were measured at a voltage standing wave ratio of 2 (VSWR = 2), with the center frequency of the propagation frequency being 1.575 GHz ± 1 MHz. The VSWR measurement is performed by connecting the power supply terminal provided at one end of the antenna mounting board and the input terminal of the network analyzer via a coaxial cable (characteristic impedance 50Ω). The VSWR was calculated based on this value by measuring the scattering parameter. When measuring gain, connect a signal generator to the power supply terminal of the antenna under test (transmitting side) in an anechoic chamber and receive the power radiated from the antenna with the receiving reference antenna. did. When the received power coming from the antenna under test is Pa and the received power measured by a transmission reference antenna having a known gain Gr is Pr, the gain Ga of the antenna under test is expressed as Ga = Gr × Pa / Pr . With regard to directivity, the antenna element under test is mounted on a turntable, and the gain measurement is performed while rotating the antenna under test. As shown in FIG. The gain with respect to the rotation angle was measured. Also, as shown in FIG. 19, the metal dependence of the characteristics was examined on the assumption that it is mounted on a communication device such as a mobile phone. Table 1 shows the measurement results.
[0041]
[Table 1]

[0042]
From the above results, it was found that the antennas of Examples 2, 7, and 12 can easily achieve impedance matching while having a substrate having a relatively high relative dielectric constant. In addition, the antennas of Examples 2, 7 and 12 have higher radiation gain, less gain reduction due to metal approach, and stable antenna characteristics although Examples 2 and 7 have a slightly narrower bandwidth than those of Comparative Example 1. was gotten. In Example 7, both the bandwidth and the gain were good although the substrate size was reduced to about 2/3. As for the omnidirectionality, the omnidirectional characteristics without any directivity were obtained in all three axes, with the gain almost nearly circular. From the above, good results were obtained that were balanced in all of the bandwidth, radiation gain, directivity, and metal dependence of the antennas of Examples 2, 7, and 12, particularly Example 12. The reason why the radiation gain of Comparative Example 1 is low is considered to be that impedance matching is not easy and that the radiation electrode is formed in a meander shape in order to obtain matching inductance.
Further, it has been found that the size of the substrate can be reduced to about 10 mm in length, 3 mm in width, 2 mm in thickness or less by adopting the radiation electrode as shown in FIGS. .
[0043]
In another embodiment of the present invention, the substrate is not limited to a rectangular parallelepiped, and has an appropriate shape. The material may be a magnetic body, a resin body, or a laminated substrate thereof. It is also effective to trim the parallel part 23a or the base formed at the open end of the side of the radiation electrode in order to widen the bandwidth or adjust the frequency.
The radiation electrode may have various shapes such as a trapezoidal shape, a stepped shape, a curved shape, a meander shape, a partial meander shape, a crank shape, etc., while the width is substantially narrowed continuously and / or stepwise. It is desirable to have an extending shape. Further, it is not always necessary to form a ground electrode continuously on one end side of the radiation electrode, as long as it is a non-continuous capacitive coupling and finally can be grounded. The first or second ground electrode may be grounded at least as long as its end face is covered and connected to the ground face. In order to obtain the effect of suppressing the emission of the electric field from the end face of the base body, It is preferable that the end portion is formed so as to cover the end surface and the four surrounding surfaces.
The antenna of the present invention can be expected to have the maximum characteristics if it is mounted on an area of the circuit board where there is no ground conductor. However, depending on the design, the antenna may be mounted on the ground conductor even if the characteristics are sacrificed to some extent. The antenna configurations of the above embodiments may be combined, and various modifications can be made within the scope of the present invention.
[0044]
【The invention's effect】
As described above, according to the present invention, impedance matching becomes easy when a high dielectric, which has been a problem in the past, is used for a substrate, and it is small and light, has a high gain, a wide bandwidth, and an omnidirectional surface. A mounted antenna can be obtained. In addition, when used for GPS, wireless LAN, or the like, a communication device that sufficiently draws out the characteristics of the antenna is obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view of a surface mount antenna according to a first embodiment of the present invention.
FIG. 2 is an equivalent circuit diagram of the antenna of the first embodiment.
FIG. 3 is a perspective view of a surface mount antenna according to a second embodiment of the present invention.
4 is a development view of the radiation electrode of FIG. 3; FIG.
FIG. 5 is an equivalent circuit diagram of the antenna of the second embodiment.
FIG. 6 is another embodiment of the power feeding electrode in the present invention.
FIG. 7 is a perspective view of a surface mount antenna showing a third embodiment of the present invention.
FIG. 8 is a perspective view of a surface mount antenna showing a fourth embodiment of the present invention.
FIG. 9 is a perspective view of a surface mount antenna according to a fifth embodiment of the present invention.
FIGS. 10A and 10B are a perspective view and a developed view of a surface mount antenna according to a sixth embodiment of the present invention. FIGS.
FIGS. 11A and 11B are a perspective view and a development view of a surface mount antenna according to a seventh embodiment of the present invention. FIGS.
FIGS. 12A and 12B are a perspective view and a developed view of a surface mount antenna according to an eighth embodiment of the present invention. FIGS.
FIGS. 13A and 13B are a perspective view and a development view of a surface mount antenna according to a ninth embodiment of the present invention. FIGS.
FIGS. 14A and 14B are a perspective view and a developed view of a surface mount antenna according to a tenth embodiment of the present invention. FIGS.
FIGS. 15A and 15B are a perspective view and a developed view of a surface mount antenna according to an eleventh embodiment of the present invention. FIGS.
FIGS. 16A and 16B are a perspective view and a development view of a surface mount antenna according to a twelfth embodiment of the present invention. FIGS.
FIG. 17 is a relationship between relative permittivity and input impedance.
FIG. 18 is a mounting diagram showing a state where the antenna of the present invention is mounted on a circuit board.
FIG. 19 is a conceptual diagram of mounting the antenna of the present invention on a communication device.
FIG. 20 is a mounting diagram showing a state in which another antenna of the present invention is mounted on another circuit board.
FIG. 21 is a perspective view showing an example of a conventional surface mount antenna.
FIG. 22 is an equivalent circuit diagram of the conventional antenna.
23 is a development view showing radiation electrodes of a surface-mounted antenna according to Comparative Example 1. FIG.
[Explanation of symbols]
1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I, 1J, 1K, 1L: Surface mount antenna
1, 90: Dielectric substrate
2, 21, 24, 25, 26, 27, 33, 92: radiation electrode
22, 28, 29, 30: Side radiation electrode, 31: Connection electrode
20, 97: Open end of radiation electrode
23: Side of radiation electrode
23a: Parallel portion formed on the side of the radiation electrode
32, 51, 52, 53: Fixing electrode
38, 39: Extension electrode
3, 32, 93: Ground electrode
4, 94: Feed electrode, 95: Feed terminal electrode
40, 98: Feeding point
41, 141: parallel part of power supply electrode (parallel part)
42: Ground point
43 and 143: Leg portions (feeding portions) serving as feeding ends
44, 144: Leg part (grounding part) to be a grounding end
5: Second ground electrode
6: Circuit board, 10: Base line of substrate
60: Power supply, 61, 99: Power supply line, 62: Ground conductor
63: boundary line of ground conductor, 64: extension part of ground conductor, 65: exposed part of circuit board
66: Linear conductor

Claims

A dielectric or Ranaru substrate, provided on at least the upper surface of the substrate, and the radiation electrode and the other end is an open end, the provided on the substrate so as either capacitive coupling directly connected to one end of the radiation electrode A surface mount antenna comprising a ground electrode and a feed electrode provided on at least a side surface of the base so as to face the radiation electrode through a gap, wherein the base has a relative dielectric constant of more than 8 and 50 or less, the feeding electrode has a ground portion at the other end of the feeding portion at one end, connects the ground portion the feeding portion at the open end side and a parallel portion arranged with a gap of said radiation electrode the gate-shaped and pear, the area ratio of the ground electrode at the bottom surface of the substrate Ri der than 30%, with adjusting the inductance by adjusting the length of the grounding portion and the feeding portion, the gap of the parallel portion Adjust spacing and / or length Surface mount antenna, characterized in that to adjust the capacitance Te.

A base made of dielectric or magnetic material, a radiation electrode provided on at least the upper surface of the base, a ground electrode provided on the base so as to be directly connected or capacitively coupled to one end of the radiation electrode, and the radiation A surface mount antenna comprising an electrode and a feed electrode provided on at least a side surface of the base so as to face through a gap, wherein the feed electrode is provided on two side faces opposed to the base. An L-shaped electrode is connected to one I-shaped electrode provided on the end face of the base. One L-shaped electrode has a power feeding portion at one end, and the other L-shaped electrode is one end. A surface-mount antenna having a grounding portion, the I-shaped electrode being a parallel portion, and the feeding electrode having a gate shape.

3. The surface-mount antenna according to claim 1, wherein the feeding electrode includes first and second electrodes provided on opposite side surfaces of the base body, and one I-shape provided on an end surface of the base body. The first electrode has a power feeding part at one end, the second electrode has a grounding part at one end, and the I-shaped electrode is a parallel part, so that the power feeding electrode Is a gate-shaped, and further has a ground electrode portion formed on the end face or end face of the substrate and on the opposite side face.

The surface mount antenna according to any one of claims 1 to 3, wherein the feeding electrode has at least a part of any one of a meander shape, a U shape, an L shape, and a crankshaft shape. A surface mount antenna.

5. The surface mount antenna according to claim 1, wherein the feed electrode has a feed portion disposed near an open end of the radiation electrode. 6.

6. The surface-mounted antenna according to claim 1, wherein at least a part of the radiation electrode is substantially continuously and / or stepwise from one end of the base toward the other end in the longitudinal direction. A surface-mounted antenna that extends while narrowing its width.

7. The surface mount antenna according to claim 1, wherein the radiation electrode reaches the upper surface via a side surface different from the side surface on which the feeding electrode is formed. .

8. A surface-mounted antenna according to claim 1, wherein at least a region below the open end of the radiation electrode provided on the upper surface of the substrate is substantially free from a ground electrode. Mountable antenna.

9. The surface-mount antenna according to claim 1, wherein the radiation electrode has a meander-shaped, U-shaped, L-shaped or crankshaft-shaped bent portion. .

10. The surface mount antenna according to claim 1, wherein corners of the radiation electrode and / or feed electrode are rounded.

11. The surface mount antenna according to claim 1, further comprising a second ground electrode facing the other end of the radiation electrode via a gap.

A communication device including an antenna device in which the surface-mounted antenna according to any one of claims 1 to 11 is mounted in a region without a ground conductor of a circuit board, wherein the base electrode extends in the longitudinal direction. A communication device, wherein the circuit board is arranged with a gap between an edge of a ground conductor of the circuit board and a gap, and the power supply electrode is disposed on the ground conductor side.

The communication device according to claim 12 , wherein the ground electrode positioned on the surface mounting antenna on the side opposite to the ground conductor of the circuit board is disposed on a corner side of the circuit board, and A communication device, wherein the circuit board is connected to a conductor by a linear conductor.