JP3861785B2

JP3861785B2 - Antenna device

Info

Publication number: JP3861785B2
Application number: JP2002282692A
Authority: JP
Inventors: 敬之稲葉
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2002-09-27
Filing date: 2002-09-27
Publication date: 2006-12-20
Anticipated expiration: 2022-09-27
Also published as: JP2004117246A

Description

【０００１】
【発明の属する技術分野】
この発明は、追尾レーダや航空管制レーダにおいて低高度目標を追尾するとき，直接波と海面反射（あるいは地面反射）によるマルチパス現象により受信信号が消滅し目標追尾が困難となる現象を回避するレーダフェージング対策技術に関するのものである。
【０００２】
【従来の技術】
低高度目標を追尾するときのマルチパス環境を説明する図を図１１に示す．このような状況では，直接波と海面反射波は同一ビーム内の僅少な角度差となる．一方，ドップラ周波数差や時間遅延差はほぼ無視できる（観測できない）大きさとなる．すなわち，直接波と海面反射波は位相のみシフトした完全相関信号に近い状況となっている．このようなマルチパス環境では目標の位置（距離・高度）によっては，マルチパス現象により電力が消滅するフェージングが発生する．このようなマルチパス環境では，送受信ビーム方向を目標より上方にむけることでフェージングを緩和する方法が考えられる．しかし，直接波と海面反射波方法のビーム利得差の信号が得られるのみであり，フェージング対策としては十分でない．
【０００３】
アレーアンテナを用いたフェージング対策として空間ダイバーシティ法が知られている．空間ダイバーシティ法には，アレーアンテナで一番受信状態が良いアンテナを選択するだけの選択方式，および等利得合成，最大比合成法(MRC: Maximal ratio combining)がある．最大比合成法は，アレーアンテナ各素子で得られた信号の位相をそろえ，かつS/Nで重み付けがなされる最も高性能な空間ダイバーシティ法である．最大比合成法を用いたフェージング対策は，[1]唐沢好男，井上隆，神谷幸宏，田野哲，“ソフトウエアアンテナ[２]，”信学技報，RCS98-152，pp7-12, Nov.1998．[2]神谷幸宏，唐沢好男，“ソフトウエアアンテナ[３]，”信学技報，AP-98-139, pp65-72, Jan. 1998.[3] 唐沢好男，“ITSミリ波車車間通信における路面反射フェージングとスペースダイバシティに関する基礎的検討，”信学論B, vol.J83-B, No.4, pp.518-524, April, 2000. にて報告されている．図１２は，アレーアンテナで受信した信号に最大比合成法を適用するこれら従来法のアンテナ装置の構成を説明する図である．図１２において，１はアレーアンテナ，２は移相器，３は合成器，４は周波数変換装置，５はA/D変換機，６はビーム形成装置，７は送信機である．
【０００４】
アレーアンテナ１で受信された信号は，移相器２で送受信ビーム方向を目標より上方にむけるビームステアリングのための位相が与えられ，合成器３で電力合成されビーム形成される．合成器によるビーム形成された信号は周波数変換装置で，RF信号からベースバンド信号に周波数変換される．ベースバンド信号はA/D変換機５でデジタル化されたデジタル信号が得られる．複数の周波数を利用する周波数ダイバーシティ法である．図１３は送信周波数を変えることでフェージングが発生する距離が変わること説明する図である．上図は，ある送信周波数f0に対しf0+10%の周波数，下図はf0-10%の周波数を用いたときの相対受信電力の距離依存性である．このように周波数を変えることで，ある位置にいる目標に対し受信電力が得られる周波数が存在することが分かる．複数の周波数を用いる周波数の制御方法は，図１４のタイミングチャートで示すよに，送信パルス毎にf1，f2,・・と周波数を変える周波数ホッピング法（frequency hopping）と，送受信系が十分な帯域をもつ場合は，一つのパルス内でf1+f2+・・fkという複数の周波数を多重化して送信する周波数多重法がある．周波数ホッピングは，予め定められた周波数の順で順次送信するものであるが，その類似方式として周波数アジリティ法があり，受信電力が得られる周波数となるまでランダムに周波数を変更する方式である．周波数多重は送受信系に広い帯域が必要となるため，複数の周波数を用いる従来法としては，周波数ホッピングが用いられている．
【０００５】
図１５は第二の従来法の一例として，周波数ホッピングを用いたアンテナ装置の構成を説明する図であり，１〜７は図１２と同じものであり，８は電力算出装置，９は電力加算器である．電力算出装置８では，各パルス毎に，各周波数f1,f2,・・fkで送信した信号を,個別に電力を算出する．電力加算器９では，各周波数各周波数f1,f2,・・fkで送信した信号電力をそのまま全て加算する．周波数によっては，フェージングが発生しない，パルスが含まれるため，全て加算した信号はフェージングが緩和されることが期待される．
【０００６】
【発明が解決しようとする課題】
上記の第一の従来法におけるアンテナ装置は，ビーム指向性により直接波と海面反射波の到来角度差から受信電力を得る方法である．しかし，目標高度が低く距離が遠いと直接波と海面反射波の角度差は僅少となり，ビーム指向性の差ではフェージング対策として不十分である．
【０００７】
一方，複数の周波数を用いる，第二の従来法では，ある周波数で得られた信号の電力を求め，電力が得られる周波数を選択する（周波数アジリティ法），あるいは予め定められた周波数で送信したパルスの受信信号電力を全て加算する方法（周波数ホッピング）である．周波数を変更すればフェージングが発生する距離が変化することは前記したが，直接波と海面反射波の路長差と海面反射時の位相シフトの関係によっては，複数の周波数を用いてもいずれの周波数においても電力が得られないという状況も発生しうる．このように，複数の周波数を利用し，各周波数で電力を求めた後に加算する従来法２でもフェージング対策として十分でないという問題がある．
【０００８】
この発明は、上記のような課題を解決するためになされたものであり，フェージング対策を行うものであり，この中で，単一の周波数のみを用いる解決法と，複数の周波数を用いる解決法とを示す．
【０００９】
【課題を解決するための手段】
第１の発明は，レーダパルスを送受信するアレーアンテナと，前記アレーアンテナにより送受信された信号の振幅・位相を制御する移相器と，前記位相器の出力信号を電圧合成する合成器と，前記合成器の出力信号を周波数変換する周波数変換装置と，前記周波数変換装置の出力信号を最大S/N（Signal to Noise ratio）で合成するためのウエイトを推定する空間最大比合成ウエイト推定装置と，前記空間最大比合成ウエイト推定装置により推定されたウエイトに従い前記周波数変換装置の出力信号を合成する空間最大比合成装置とを備えるアンテナ装置である．
【００１０】
【発明の実施の形態】
実施の形態１．
図１はこの第一発明の実施の形態を示すもので、図において、１〜７は従来法と同じである．１０は空間最大比合成ウエイト推定装置，１１は空間最大比合成装置である．
【００１１】
アレーアンテナ１で送信した周波数f1の送信パルスは，目標から反射し同じくアレーアンテナ１に入射し受信信号となる．アレー素子数をN，サブアレー数をM（図１では一例としてM＝４としている．），サブアレー内の素子数をNsとする．アレーアンテナに入力する受信信号のうち目標が含まれる受信信号（サンプル数をTとする．）を行列形式でXr∈Ｃ^N ^× ^Tとする．ここで，Ｃ^N ^× ^Tは，複素数を要素としたN行T列の行列であることを表す．受信信号Xrは，位相器２に入力される．移相器２では，送信方向と同じ方向に受信ビーム指向する各サブアレー別のビームステアリング操作を行う．ここで，ステアリングベクトルをＢ(θ) ∈Ｃ^N ^× ^Tと書く．合成器３では，サブアレーの出力信号として，“数１”が得られる．
【００１２】
【数１】

【００１３】
ここで，アレーアンテナ１がリニアアレーの場合を例とすると，Ｂ(θ) ∈Ｃ^N ^× ^Tは，“数２”となる
【００１４】
【数２】

【００１５】
ここで，行列の右肩のTは転置行列を表し，θは電波の入射角，ｄはアレーアンテナの各アンテナの間隔，λは送信波の波長を示す．また，合成器３の出力は，“数３”となる．
【００１６】
【数３】

【００１７】
ここで，submatrix(X,a:b,c:d)は，マトリックスの〜行，〜ｄ列のサブマトリックスを切り出す操作を表す．第一の発明では，“数３”で書かれる合成器出力信号は，ベースバンドへ周波数変換されＡ／Ｄ変換された後，空間最大比合成装置１０に入力される．空間最大比合成装置では，合成器３出力であるサブアレー間の信号に最大比合成が適用される．空間最大比合成について説明する．各サブアレーの出力Ymを一つの行列に纏めて，空間最大比合成への入力データ行列Z ∈Ｃ^N ^× ^Tを，“数４”と記述する．
【００１８】
【数４】

【００１９】
このデータ行列を用いて空間最大比合成ウエイト推定装置１１では，空間最大比合成ウエイトを求めるために，zに関する相関行列_Rを，“数５”で求める．
【００２０】
【数５】

【００２１】
さらに，相関行列Rの最大固有値に対応する固有ベクトルW1を求めることで，空間最大比合成のウエイトベクトルが得られる．こうして得られた空間最大比合成ウエイトは，空間最大比合成装置１０に入力され，空間最大比合成装置ではこのウエイトベクトルを用い図２のタイミング図に示すように，目標の有無に関わらず送信パルスと送信パルス間の全ての距離サンプルrに亙り“数６”の処理を行う．
【００２２】
【数６】

【００２３】
次に，電力P(r)は，“数７”となる．
【００２４】
【数７】

【００２５】
サブアレー構成による空間最大比合成装置の動作である．空間最大比合成によりフェージング対策が図られたS/Nの良い信号が得られる．一般的には，この空間最大比合成装置の出力は，距離方向に閾値処理が適用され目標検出が検出される．また，S/Nが向上したことにより目標検出サンプルの区間の中で，より正確な距離の測定が可能となる．また，サブアレー構成とすることで，数５の相関行列の固有ベクトル計算などの次元が削減され，計算量が著しく低減されている．この実施の形態１では，図２に示すように各送信パルスに対し以上を繰り返す．
【００２６】
単一の周波数を用いれば、アレーアンテナをサブアレー構成とする方法を採用しているため，マルチパス環境で空間最大比合成を採用しフェージングによる受信信号の消滅を回避する上で，送受信系ハードウエアの削減，空間最大比合成ウエイト計算負荷低減を可能とする効果がある．図３は，単一の周波数を用いる受信空間最大比合成，および送受信空間最大比合成の効果を示す図である．図３の(a)は，目標高度を一定として横軸は目標までの距離であり，縦軸は受信相対電力である．実線は，フルDBF（Degital Beam forminng：サブアレー構成でなく，各放射素子での受信信号をベースバンドまで周波数変換し最大比合成したもの．）による受信空間最大比合成法で得られる受信電力である．点線は，同じく送受信空間最大比合成法，破線は参考としてのモノパルス和信号，一点鎖線は同じく参考としてのマルチパスのない自由空間でのモノパルス和信号である．図３は，目標高度が低く，遠方にある場合であり，直接波と海面反射波の角度がほとんど０であるため空間最大比合成は，自由空間でもノモパルス和信号とう同等となるレベルまでの電力回復は得られていない．しかし，角度差が大きかったり（すなわち目標高度がもう少し高い場合），アレーアンテナの開口径が大きければ，図中の近距離で見られるように空間最大比合成法でも電力回復が期待できる．図３の(b)(c)は，サブアレー構成による空間最大比合成の効果を説明する図である．図３(b)はフルDBFに比べた２サブアレー構成での利得低下を，(c)は同様にフルDBFに比べた４サブアレー構成での利得低下の例を示す．いずれも，フルＤＢＦに比べ利得の低下は少なく，第一の発明によるサブアレー構成での空間最大比合成でも十分満足する効果が得られることが可能である．
【００２７】
実施の形態２．
実施の形態２は，構成は図１と同じであるが，図４のタイミング図に示すように受信信号から得られた空間最大比合成ウエイトを，つぎの送信波の送信ウエイトとして用いることを特徴としており，送信と受信双方で空間最大比合成を実現するものである．
【００２８】
実施の形態３．
実施の形態３は第二の発明（周波数ホッピング空間・周波数最大比合成）の実施例である．図５はこの実施の形態を示すもので、図において、１〜７は従来法と同じである．１２は空間・周波数最大比合成ウエイト推定装置，１３は空間・周波数最大比合成装置である．第二の発明では，第一の発明と同様にサブアレー構成によりパルス毎に周波数ホッピングを行い送信したときの受信パルスデータを保持しておいて，空間・周波数最大比合成法を実現する方法である．
【００２９】
図６は，この実施の形態３の，送受信および処理タイミングを説明する図である．図６に示すように，送信パルスの周波数をf1,f2・・・fxとパルス毎で変更し送信する．この間，各送信パルスの目標反射からのアレーアンテナに入力する受信信号は，第一の発明と同様に，位相器２で送信方向と同じ方向に受信ビーム指向する各サブアレー別のビームステアリング操作される．周波数番号をとすると，サブアレー番号での合成器３出力は，式(１)と同様にYm,k∈Ｃ¹ ^× ^Tが得られる．空間・周波数最大比合成装置１２では，このYm,k∈Ｃ¹ ^× ^Tを，全ての周波数での送受信が完了するまで保持しておく．次に，これらを列方向にならべて行列V∈Ｃ^MK ^× ^T作成する．
【００３０】
数８”で定義した次元の列ベクトルに対し，空間最大比合成と同じ数(5)〜(7)の処理を行う．こうして，各周波数，および各サブアレーで得られた受信信号の最大比合成が容易に実現可能となる
【００３１】
【数８】

【００３２】
実施の形態４．
実施の形態４は第二の発明（周波数ホッピング空間・周波数最大比合成）の別の実施例である．図７は，この実施の形態４の，送受信および処理タイミングを説明する図である．実施の形態４は，実施の形態２と３を組み合せたものである．実施の形態３による周波数ホッピングした送信パルス列を送信する．そのパルス列から空間・周波数最大比合成ウエイト推定装置で推定したウエイトを受信の空間・周波数最大比合成に持ちいるのみにならず，次の送信パルスは空間・周波数最大比合成ウエイトの要素のうち振幅の大きな要素に対応する周波数と，その要素を送信ウエイトとして用いるものである．続く送受信は，実施の形態２を繰り返しつつ，電力をモニタすることで，空間最大比合成だけでは，フェージングによる受信電力の回復が困難となり周波数を変更すべきかを判断する．周波数を変更すべきと判断された場合は，次の送信パルスとして実施の形態４の初めと同様に周波数ホッピングした送信パルス列を送信する実施の形態３を実施するものである．以下，同様の制御を繰り返す．このように制御することで，実施の形態２にくらべ周波数ホッピングを併用しているためフェージング改善効果が大きく，かつ周波数ホッピングした送信を繰り返す実施の形態３に比べ，実施の形態２の空間周波数最大比合成で十分な場合は，それを，繰り返すことになり，全体としての電力利用効率を向上させることが可能である．
【００３３】
実施の形態５．
実施の形態５は，第三の発明（周波数多重空間・周波数最大比合成）の実施例である．図８この実施の形態を示すもので、図において、１〜７は図５の実施の形態３と同じである．１２は空間・周波数最大比合成ウエイト推定装置，１３は空間・周波数最大比合成装置である．１４は周波数多重して送信されたパルスの受信信号を各周波数に弁別する周波数弁別装置である．第三の発明は，空間・周波数最大比合成ウエイト推定装置，空間・周波数最大比合成装置の機能としては，第二の発明と同様である．図９を用いて実施の形態５（すなわち第三の発明）を説明する．図９は送受信および処理タイミングを説明する図である．実施の形態５では，実施の形態３で各送信パルスを周波数ホッピングした周波数を同時に一つの送信パルスで周波数多重化して送信するものである．送受信系が広い帯域をもち，複数の周波数を同時に送信可能な場合に適用可能となる．周波数弁別により各周波数に弁別された各サブアレーの信号を，空間・周波数最大比合成ウエイト推定装置１２にて，第二の発明と同じ数(8)を作成する．第二の発明と同様にして得られた空間・最大比合成ウエイトを用いて，空間・周波数最大比合成装置１３にて受信信号を合成する．こうして，各周波数，および各サブアレーで得られた受信信号の最大比合成が１パルスにて容易に実現可能となる．更に，この空間・周波数最大比合成ウエイトを，送信機７，位相器２に入力し，次の送信時の周波数多重パルスのウエイトとして用いることで送信の空間・周波数最大比合成が可能となる．これを繰り返すことで，送受信の空間・周波数最大比合成が実現可能となる．
【００３４】
図１０は，複数の周波数を利用する第二の発明の効果を説明する図である．図１０(a)は，図３(a)と同様の図であり，実線は周波数ホッピングを用いたときのフルDBFによる空間・周波数最大比合成による受信電力である．周波数は，中心周波数をf0(=6GHz)として，f0-10%，f0，f0+10％の３種を用いた例である．点線は参考としてのモノパルス和信号，一点鎖線は同じく参考としてのマルチパスのない自由空間でのモノパルス和信号である．この図から，空間・周波数最大比合成により全ての距離範囲において自由空間でのモノパルス和信号以上の受信電力が得られることが確認される．同様に，図１０(b)は，周波数ホッピング空間・周波数最大比合成，または周波数多重空間・周波数最大比合成であるサブアレー構成による空間・周波数最大比合成の効果を説明する図である．図１０(b)は，フルDBFに比べた２および４サブアレーでの利得の低下と，従来の第二の方法（周波数ホッピングしたパスルの各電力を加算する方法．ノンコヒーレントF/Hと呼ぶ．）での利得の低下を説明する図である．２，および４サブアレーでもフルDBFに比べて利得の低下は，2dB以下に止まっているが，第二の従来法（ノンコヒーレントF/H）では，近距離で10dB近いフェージングが発生している．この理由は，図１０(c) は，３種の各周波数での受信電力を示す．図１０(c)から明らかなように，使用した３種の周波数のいずれにおいても電力のヌルとなる距離が一致してしまったため，第二の従来法ではフェージングによる電力の消滅を回避しきれないことが分かる．このように，空間・周波数最大比合成によりこのような悪条件下でも自由空間でのモノパルス和信号以上の電力が得られるという効果が得られる．
【００３５】
【発明の効果】
上記によりフェージング対策を行うことができる．
【図面の簡単な説明】
【図１】実施の形態１および２を示すアンテナ装置のブロック図である．
【図２】実施の形態１の動作タイミングを説明する図である．
【図３】実施の形態１および２の効果を説明する図である
【図４】実施の形態２の動作タイミングを説明する図である．
【図５】実施の形態３および４を示すアンテナ装置のブロック図である．
【図６】実施の形態３の動作タイミングを説明する図である．
【図７】実施の形態４の動作タイミングを説明する図である．
【図８】実施の形態５を示すアンテナ装置のブロック図である．
【図９】実施の形態５の動作タイミングを説明する図である．
【図１０】実施の形態４または５の効果を説明する図である．
【図１１】マルチパス環境の電波伝播を説明する図である．
【図１２】従来の第一の技術によるアンテナ装置のブロック図である．
【図１３】マルチパス環境での受信電力の周波数依存性を説明する図である．
【図１４】周波数ホッピング送信と周波数多重送信のタイミングを説明する図である．
【図１５】従来の第二の技術によるアンテナ装置のブロック図である．
【符号の説明】
１アレーアンテナ，２移相器，３合成器，４周波数変換装置，５A/D変換機，６ビーム形成器，７送信機，８電力算出器，９電力加算器，１０空間最大比合成ウエイト推定装置，１１空間最大比合成装置，１２空間・周波数最大比合成ウエイト推定装置，１３空間・周波数最大比合成装置，１４目標[0001]
BACKGROUND OF THE INVENTION
This invention avoids the phenomenon that when tracking low altitude targets in tracking radar or air traffic control radar, the received signal disappears due to multipath phenomenon caused by direct wave and sea surface reflection (or ground reflection), and target tracking becomes difficult. It relates to fading countermeasure technology.
[0002]
[Prior art]
Figure 11 illustrates the multipath environment when tracking a low altitude target. In such a situation, the direct wave and the sea surface reflected wave have a slight angular difference in the same beam. On the other hand, the Doppler frequency difference and time delay difference are almost negligible (not observable). In other words, the direct wave and the sea surface reflected wave are close to the perfectly correlated signal shifted only in phase. In such a multipath environment, depending on the target position (distance and altitude), fading that causes the power to disappear due to the multipath phenomenon occurs. In such a multipath environment, fading can be mitigated by moving the transmit and receive beam directions upward from the target. However, only the signal of the beam gain difference between the direct wave and the sea surface reflected wave method can be obtained, and it is not enough as a countermeasure against fading.
[0003]
Spatial diversity method is known as a countermeasure against fading using array antenna. Spatial diversity methods include selection methods that only select the best receiving antenna among array antennas, and equal gain combining and maximum ratio combining (MRC). The maximum ratio combining method is the highest-performance spatial diversity method in which the phase of the signal obtained from each element of the array antenna is aligned and weighted by S / N. Fading countermeasures using the maximum ratio combining method are as follows: [1] Yoshio Karasawa, Takashi Inoue, Yukihiro Kamiya, Satoshi Tano, “Software Antenna [2],” IEICE Technical Report, RCS98-152, pp7-12, Nov .1998. [2] Yukihiro Kamiya, Yoshio Karasawa, “Software Antenna [3],” IEICE Technical Report, AP-98-139, pp65-72, Jan. 1998. [3] Yoshio Karasawa, “ITS Millimeter-Wave Car Basic study on road surface reflection fading and space diversity in inter-vehicle communication, "Science theory B, vol.J83-B, No.4, pp.518-524, April, 2000. FIG. 12 is a diagram for explaining the configuration of these conventional antenna apparatuses that apply the maximum ratio combining method to signals received by an array antenna. In FIG. 12, 1 is an array antenna, 2 is a phase shifter, 3 is a combiner, 4 is a frequency converter, 5 is an A / D converter, 6 is a beam forming device, and 7 is a transmitter.
[0004]
The signal received by the array antenna 1 is given a phase for beam steering in which the phase of the transmission / reception beam is directed above the target by the phase shifter 2, and the power is synthesized by the combiner 3 to form a beam. The signal formed by the combiner is frequency converted from the RF signal to the baseband signal by a frequency converter. The baseband signal is a digital signal digitized by the A / D converter 5. This is a frequency diversity method using multiple frequencies. FIG. 13 is a diagram for explaining that the distance at which fading occurs is changed by changing the transmission frequency. The upper figure shows the distance dependence of the relative received power when the f0 + 10% frequency is used for a certain transmission frequency f0, and the lower figure is the f0-10% frequency. By changing the frequency in this way, it can be seen that there is a frequency at which received power can be obtained for a target at a certain position. As shown in the timing chart of FIG. 14, the frequency control method using a plurality of frequencies is a frequency hopping method in which the frequency is changed to f1, f2,. If there is, there is a frequency multiplexing method in which multiple frequencies f1 + f2 + ·· fk are multiplexed and transmitted within one pulse. Frequency hopping is to transmit sequentially in the order of a predetermined frequency, but there is a frequency agility method as a similar method, and the frequency is changed randomly until the received power is obtained. Since frequency multiplexing requires a wide bandwidth in the transmission / reception system, frequency hopping is used as a conventional method using multiple frequencies.
[0005]
FIG. 15 is a diagram for explaining the configuration of an antenna device using frequency hopping as an example of the second conventional method. 1 to 7 are the same as those in FIG. 12, 8 is a power calculation device, and 9 is power addition. It is a vessel. The power calculation device 8 calculates the power of each signal transmitted at each frequency f1, f2,... Fk for each pulse. The power adder 9 adds all the signal powers transmitted at the respective frequencies f1, f2,. Depending on the frequency, fading does not occur, and pulses are included. Therefore, it is expected that fading is alleviated for the signals that are all added.
[0006]
[Problems to be solved by the invention]
The antenna device in the first conventional method is a method of obtaining the received power from the difference in the arrival angle between the direct wave and the sea surface reflected wave by the beam directivity. However, if the target altitude is low and the distance is long, the angle difference between the direct wave and the sea surface reflected wave becomes small, and the difference in beam directivity is insufficient as a countermeasure against fading.
[0007]
On the other hand, in the second conventional method using a plurality of frequencies, the power of a signal obtained at a certain frequency is obtained, and the frequency at which the power can be obtained is selected (frequency agility method), or transmitted at a predetermined frequency. This is a method (frequency hopping) that adds all the received signal power of the pulse. As described above, if the frequency is changed, the distance at which fading occurs changes. However, depending on the relationship between the path length difference between the direct wave and the sea surface reflected wave and the phase shift at the time of sea surface reflection, any frequency can be used. A situation where power cannot be obtained even at a frequency may occur. As described above, the conventional method 2 which uses a plurality of frequencies and adds power after obtaining the power at each frequency is not sufficient as a fading countermeasure.
[0008]
The present invention has been made in order to solve the above-described problems, and is a countermeasure for fading. Among them, a solution using only a single frequency and a solution using a plurality of frequencies are provided. It shows.
[0009]
[Means for Solving the Problems]
The first invention is an array antenna that transmits and receives radar pulses, a phase shifter that controls the amplitude and phase of signals transmitted and received by the array antenna, a combiner that performs voltage synthesis on the output signal of the phase shifter, A frequency converter for frequency-converting the output signal of the synthesizer, a spatial maximum ratio synthesis weight estimator for estimating a weight for synthesizing the output signal of the frequency converter with a maximum S / N (Signal to Noise ratio), An antenna device comprising: a spatial maximum ratio synthesis device that synthesizes an output signal of the frequency converter according to the weight estimated by the spatial maximum ratio synthesis weight estimation device.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIG. 1 shows an embodiment of the first invention. In the figure, 1 to 7 are the same as in the conventional method. 10 is a space maximum ratio combining weight estimation device, and 11 is a space maximum ratio combining device.
[0011]
The transmission pulse of frequency f1 transmitted by the array antenna 1 is reflected from the target and is incident on the array antenna 1 as a reception signal. Assume that the number of array elements is N, the number of subarrays is M (M = 4 as an example in FIG. 1), and the number of elements in the subarray is Ns. Of the received signals that are input to the array antenna, the received signal that includes the target (the number of samples is T) is Xr∈C ^N ^× ^T in matrix form. Here, C ^N ^× ^T represents an N-row T-column matrix with complex numbers as elements. Received signal Xr is input to phase shifter 2. In the phase shifter 2, the beam steering operation is performed for each subarray in which the receiving beam is directed in the same direction as the transmission direction. Here, the steering vector is written as B (θ) ∈ C ^N ^× ^T. In the synthesizer 3, "Equation 1" is obtained as the output signal of the subarray.
[0012]
[Expression 1]

[0013]
Here, taking the case where the array antenna 1 is a linear array as an example, B (θ) ∈ C ^N ^× ^T is “Equation 2”.
[Expression 2]

[0015]
Here, T on the right side of the matrix represents a transposed matrix, θ is the incident angle of the radio wave, d is the spacing between the antennas of the array antenna, and λ is the wavelength of the transmitted wave. The output of the synthesizer 3 is “Equation 3”.
[0016]
[Equation 3]

[0017]
Here, submatrix (X, a: b, c: d) represents the operation of cutting out the submatrix of ~ row and ~ dcolumn of the matrix. In the first invention, the synthesizer output signal written as “Equation 3” is frequency-converted to baseband and A / D converted, and then input to the space maximum ratio synthesizer 10. In the spatial maximum ratio synthesizer, maximum ratio synthesis is applied to the signals between the subarrays that are the outputs of the synthesizer 3. The spatial maximum ratio composition is explained. The output data Ym of each subarray is combined into one matrix, and the input data matrix Z ∈ C ^N ^× ^T for the spatial maximum ratio composition is described as “Equation 4”.
[0018]
[Expression 4]

[0019]
The spatial maximum ratio combined weight estimation device 11 uses this data matrix to determine the correlation matrix_R for z by “Equation 5” in order to determine the spatial maximum ratio combined weight.
[0020]
[Equation 5]

[0021]
Furthermore, by obtaining the eigenvector W1 corresponding to the maximum eigenvalue of the correlation matrix R, the weight vector of the spatial maximum ratio synthesis can be obtained. The space maximum ratio combining weight obtained in this way is input to the space maximum ratio combining apparatus 10, which uses this weight vector and transmits a transmission pulse regardless of the presence or absence of a target as shown in the timing diagram of FIG. Then, the processing of “Equation 6” is performed over all distance samples r between the transmission pulses.
[0022]
[Formula 6]

[0023]
Next, the power P (r) becomes “Equation 7”.
[0024]
[Expression 7]

[0025]
This is the operation of the space maximum ratio synthesizer with a subarray configuration. A signal with good S / N with anti-fading measures can be obtained by combining the spatial maximum ratio. In general, threshold processing is applied to the output of this spatial maximum ratio synthesizer in the distance direction to detect target detection. In addition, the improved S / N enables more accurate distance measurement within the target detection sample interval. In addition, the subarray configuration reduces the dimension of the eigenvector calculation of the correlation matrix of Equation 5, and the amount of calculation is significantly reduced. In the first embodiment, the above is repeated for each transmission pulse as shown in FIG.
[0026]
If a single frequency is used, the array antenna is configured as a sub-array. Therefore, in order to avoid the disappearance of the received signal due to fading by employing spatial maximum ratio combining in a multipath environment, the transmission / reception hardware And the maximum space ratio synthesis weight calculation load can be reduced. Figure 3 shows the effect of reception space maximum ratio combining using a single frequency and transmission / reception space maximum ratio combining. In Fig. 3 (a), the target altitude is constant, the horizontal axis is the distance to the target, and the vertical axis is the received relative power. The solid line is the received power obtained by the reception space maximum ratio combining method using full DBF (Degital Beam forminng: not a subarray configuration, but frequency conversion of received signals at each radiating element to baseband). . The dotted line is the transmission / reception space maximum ratio combining method, the broken line is the monopulse sum signal as a reference, and the alternate long and short dash line is the monopulse sum signal in free space without multipath as a reference. Figure 3 shows the case where the target altitude is low and far away, and since the angle between the direct wave and the sea surface reflected wave is almost zero, the spatial maximum ratio synthesis is the power up to a level equivalent to the nomopulse sum signal even in free space. No recovery has been obtained. However, if the angular difference is large (that is, if the target altitude is a little higher) or the aperture diameter of the array antenna is large, power recovery can be expected even with the spatial maximum ratio combining method as seen at a short distance in the figure. (B) and (c) of Fig. 3 are diagrams for explaining the effect of the spatial maximum ratio combining by the subarray configuration. Fig. 3 (b) shows an example of gain reduction in a 2-subarray configuration compared to a full DBF, and Fig. 3 (c) shows an example of gain reduction in a 4-subarray configuration compared to a full DBF. In either case, the gain is less lowered than the full DBF, and it is possible to obtain a sufficiently satisfactory effect even with the maximum spatial ratio combining in the subarray configuration according to the first invention.
[0027]
Embodiment 2. FIG.
The second embodiment has the same configuration as that of FIG. 1, but uses the spatial maximum ratio combining weight obtained from the received signal as the transmission weight of the next transmission wave as shown in the timing chart of FIG. It realizes the maximum space ratio composition for both transmission and reception.
[0028]
Embodiment 3 FIG.
The third embodiment is an example of the second invention (frequency hopping space / frequency maximum ratio synthesis). FIG. 5 shows this embodiment. In the figure, 1 to 7 are the same as in the conventional method. 12 is a space / frequency maximum ratio combining weight estimation device, and 13 is a space / frequency maximum ratio combining device. In the second invention, similar to the first invention, the sub-array configuration is used to realize the spatial / frequency maximum ratio combining method by holding the received pulse data when transmitting by performing frequency hopping for each pulse. .
[0029]
FIG. 6 is a diagram for explaining transmission / reception and processing timing in the third embodiment. As shown in Fig. 6, the transmission pulse frequency is changed by f1, f2, ... fx for each pulse. During this time, the received signal input to the array antenna from the target reflection of each transmission pulse is subjected to beam steering operation for each subarray that is directed to the reception beam in the same direction as the transmission direction by the phase shifter 2 as in the first invention. . If the frequency number is taken, Ym, k ∈ C ¹ ^× ^T is obtained from the output of the synthesizer 3 at the sub-array number, as in equation (1). The space / frequency maximum ratio synthesizer 12 holds Ym, kεC ¹ ^× ^T until transmission / reception at all frequencies is completed. Next, the matrix V∈C ^MK ^× ^{T is} created by arranging them in the column direction.
[0030]
The same number (5) to (7) of processing as the spatial maximum ratio combining is performed on the column vector of the dimension defined in Equation 8 ″. In this way, the maximum ratio combining of the received signals obtained at each frequency and each subarray is performed. Can be easily realized. [0031]
[Equation 8]

[0032]
Embodiment 4 FIG.
Embodiment 4 is another example of the second invention (frequency hopping space / frequency maximum ratio synthesis). FIG. 7 is a diagram for explaining transmission / reception and processing timing in the fourth embodiment. The fourth embodiment is a combination of the second and third embodiments. The transmission pulse train subjected to frequency hopping according to the third embodiment is transmitted. In addition to having the weight estimated from the pulse train by the space / frequency maximum ratio combining weight estimator for reception space / frequency maximum ratio combining, the next transmitted pulse has the amplitude of the elements of the space / frequency maximum ratio combining weight. The frequency corresponding to a large element of and the element is used as the transmission weight. In the subsequent transmission and reception, the power is monitored while repeating the second embodiment, so that it is difficult to recover the received power by fading and the frequency should be changed only by combining the spatial maximum ratio. When it is determined that the frequency should be changed, the third embodiment in which the transmission pulse train frequency-hopped is transmitted as the next transmission pulse in the same manner as in the first embodiment. The same control is repeated thereafter. By controlling in this way, the frequency hopping is used in combination with the second embodiment, so that the fading improvement effect is large, and the spatial frequency maximum of the second embodiment is larger than that of the third embodiment that repeats frequency-hopped transmission. If ratio synthesis is sufficient, it will be repeated and the overall power utilization efficiency can be improved.
[0033]
Embodiment 5 FIG.
The fifth embodiment is an example of the third invention (frequency multiplexing space / frequency maximum ratio synthesis). FIG. 8 shows this embodiment. In the figure, reference numerals 1 to 7 are the same as those in the third embodiment shown in FIG. 12 is a space / frequency maximum ratio combining weight estimation device, and 13 is a space / frequency maximum ratio combining device. 14 is a frequency discriminating device that discriminates the received signal of the pulse transmitted by frequency multiplexing into each frequency. The third invention is the same as the second invention in terms of the functions of the space / frequency maximum ratio combining weight estimation device and the space / frequency maximum ratio combining device. Embodiment 5 (that is, the third invention) will be described with reference to FIG. FIG. 9 is a diagram for explaining transmission / reception and processing timing. In the fifth embodiment, the frequency obtained by frequency hopping each transmission pulse in the third embodiment is simultaneously frequency-multiplexed with one transmission pulse and transmitted. This is applicable when the transmission / reception system has a wide bandwidth and can transmit multiple frequencies simultaneously. The sub-array signals discriminated by frequency by frequency discrimination are created by the spatial / frequency maximum ratio combined weight estimation device 12 in the same number (8) as in the second invention. Using the space / maximum ratio combining weight obtained in the same manner as the second invention, the space / frequency maximum ratio combining device 13 synthesizes the received signal. Thus, the maximum ratio combining of the received signals obtained at each frequency and each sub-array can be easily realized with one pulse. Furthermore, the space / frequency maximum ratio combining weight is input to the transmitter 7 and the phase shifter 2 and used as the weight of the frequency multiplexed pulse at the next transmission, thereby enabling the space / frequency maximum ratio combining of transmission. By repeating this, it is possible to realize the space / frequency maximum ratio synthesis for transmission and reception.
[0034]
FIG. 10 is a diagram for explaining the effect of the second invention using a plurality of frequencies. Fig. 10 (a) is the same diagram as Fig. 3 (a), and the solid line is the received power by the space-frequency maximum ratio combining by full DBF when frequency hopping is used. The frequency is an example using three types, f0-10%, f0, f0 + 10%, where the center frequency is f0 (= 6GHz). The dotted line is the monopulse sum signal as a reference, and the alternate long and short dash line is the monopulse sum signal in free space without multipath as a reference. From this figure, it is confirmed that the received power more than the monopulse sum signal in free space can be obtained in all distance ranges by combining the space and frequency maximum ratio. Similarly, FIG. 10 (b) is a diagram for explaining the effect of the space / frequency maximum ratio combining by the sub-array configuration which is the frequency hopping space / frequency maximum ratio combining or the frequency multiplexing space / frequency maximum ratio combining. Figure 10 (b) shows the gain reduction in 2 and 4 subarrays compared to the full DBF, and the conventional second method (a method of adding each power of a frequency-hopped pulse. This is called non-coherent F / H. ) Is a diagram for explaining the decrease in gain. In the 2nd and 4th subarrays, the gain decrease is less than 2dB compared to the full DBF, but in the second conventional method (non-coherent F / H), fading near 10dB occurs at a short distance. The reason for this is that Fig. 10 (c) shows the received power at each of the three frequencies. As is clear from FIG. 10 (c), the power null distances coincided at any of the three types of frequencies used, so the second conventional method cannot avoid the disappearance of power due to fading. I understand that. In this way, the space / frequency maximum ratio synthesis can produce the power that is higher than the monopulse sum signal in free space even under such adverse conditions.
[0035]
【The invention's effect】
The above measures can be taken for fading.
[Brief description of the drawings]
FIG. 1 is a block diagram of an antenna

device showing Embodiments

1 and 2. FIG.
FIG. 2 is a diagram for explaining the operation timing of the first embodiment.
FIG. 3 is a diagram for explaining the effects of the first and second embodiments. FIG. 4 is a diagram for explaining an operation timing of the second embodiment.
FIG. 5 is a block diagram of an antenna device showing the third and fourth embodiments.
FIG. 6 is a diagram for explaining the operation timing of the third embodiment.
FIG. 7 is a diagram for explaining the operation timing of the fourth embodiment.
FIG. 8 is a block diagram of an antenna apparatus showing a fifth embodiment.
FIG. 9 is a diagram for explaining the operation timing of the fifth embodiment.
FIG. 10 is a diagram for explaining the effect of the fourth or fifth embodiment.
FIG. 11 is a diagram for explaining radio wave propagation in a multipath environment.
FIG. 12 is a block diagram of an antenna apparatus according to the first conventional technique.
FIG. 13 is a diagram illustrating the frequency dependence of received power in a multipath environment.
FIG. 14 is a diagram for explaining the timing of frequency hopping transmission and frequency multiplex transmission.
FIG. 15 is a block diagram of an antenna device according to a second conventional technique.
[Explanation of symbols]
1 array antenna, 2 phase shifter, 3 combiner, 4 frequency converter, 5 A / D converter, 6 beam former, 7 transmitter, 8 power calculator, 9 power adder, 10 spatial maximum ratio combined weight estimation Device, 11 spatial maximum frequency ratio combining device, 12 spatial / frequency maximum frequency ratio combining weight estimation device, 13 spatial / frequency maximum frequency ratio combining device, 14 target

Claims

An array antenna having a plurality of sub-arrays composed of a plurality of array elements and transmitting and receiving radar pulses;
A transmitter for transmitting a transmission pulse train frequency-hopped to the array antenna;
A plurality of phase shifters for controlling the amplitude and phase of signals transmitted and received by the array antenna for each array element, and performing beam steering operation for each sub-array for directing the reception beam in the same direction as the transmission direction;
A synthesizer that synthesizes the output signal of the phase shifter for each sub-array; and
A frequency converter that converts the output signal of the combiner for each sub-array;
The output of each sub-array of the frequency converter is held until transmission / reception at all frequencies subjected to frequency hopping is completed, and these are arranged in the column direction to obtain a correlation matrix and obtain the maximum eigenvalue of the obtained correlation matrix. A spatial / frequency maximum ratio combined weight estimation device for estimating a weight for combining a frequency hopped output signal of the frequency conversion device with maximum S / N (Signal to Noise ratio) by obtaining a corresponding eigenvector;
A spatial / frequency maximum ratio synthesizer for synthesizing the output signals obtained at each frequency and each sub-array of the frequency converter according to the weight estimated by the spatial / frequency maximum ratio synthetic weight estimator;
An antenna device comprising:

After transmitting the transmission pulse train frequency hopped, the transmitter,
Transmitting a transmission pulse train using a frequency corresponding to an element having a large amplitude among the elements of the weight estimated by the space / frequency maximum ratio combined weight estimation device and the element as a transmission weight;
Next, by transmitting a transmission pulse train using the transmission weight and monitoring the power while repeating spatial maximum ratio combining in both transmission and reception, it is difficult to recover the received power due to fading only by combining the spatial maximum ratio, and the frequency should be changed. If it is determined that the frequency should be changed, a transmission pulse train frequency-hopped is transmitted.
The antenna device according to claim 1.

An array antenna having a plurality of sub-arrays composed of a plurality of array elements and transmitting and receiving radar pulses;
A transmitter for transmitting a transmission pulse frequency-multiplexed to the array antenna;
A plurality of phase shifters for controlling the amplitude and phase of signals transmitted and received by the array antenna for each array element, and performing beam steering operation for each sub-array for directing the reception beam in the same direction as the transmission direction;
A synthesizer that synthesizes the output signal of the phase shifter for each sub-array; and
A frequency discriminator for discriminating the frequency multiplexed signal of the output signal of the combiner into each frequency for each sub-array;
A frequency converter for converting the frequency of the output signal discriminated by each frequency by the frequency discriminator for each sub-array;
By obtaining a correlation matrix related to a matrix obtained by arranging the outputs of the respective subarrays discriminated by the respective frequencies from the frequency conversion device in a column direction, and obtaining an eigenvector corresponding to the maximum eigenvalue of the obtained correlation matrix, the frequency conversion device A space / frequency maximum ratio combined weight estimation device for estimating a weight for combining a frequency hopped output signal with maximum S / N (Signal to Noise ratio);
A spatial / frequency maximum ratio synthesizer for synthesizing the output signals obtained at each frequency and each sub-array of the frequency converter according to the weight estimated by the spatial / frequency maximum ratio synthetic weight estimator;
An antenna device comprising: