JP3613952B2

JP3613952B2 - FM-CW radar equipment

Info

Publication number: JP3613952B2
Application number: JP29841597A
Authority: JP
Inventors: 拓也鈴木
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1997-10-30
Filing date: 1997-10-30
Publication date: 2005-01-26
Anticipated expiration: 2017-10-30
Also published as: JPH11133144A

Description

【０００１】
【発明の属する技術分野】
この発明は例えば走行する車両に搭載され、前方に存在する走行車両や障害物などの位置及び速度情報を検出するのに有効に働く装置としてＦＭ−ＣＷレーダ装置に関するものであり、その原理は「６０ＧＨｚ帯自動車用ミリ波レーダ」（ＦＵＪＩＴＳＵ．ｖｏ１４７、４、ｐｐ．３３２−３３７１９９６年７月）などに詳述され、広く知られている。
【０００２】
【従来の技術】
図４は従来のＦＭ−ＣＷレーダ装置の代表的な系統図を示したもので、図中、１は変調電圧記憶部、２はタイミング制御部、３はＤ／Ａ変換器、４は電圧制御発振器、５は高周波増幅器、６は方向性結合器、７は送信空中線、８は受信空中線、９は受信ミクサ、１０はビデオ増幅器、１１は低域通過型フィルタ、１２はＡ／Ｄ変換器、１３は周波数解析手段、１４は距離・速度計測手段であり、これらの部品１〜３で変調電圧発生部１５を、部品４〜６で送信信号変換部１６を、部品７及び８でアンテナ部１７を、部品９〜１１で受信信号検出部１８を、部品２及び１２〜１４で受信ベースバンド信号処理部１９をそれぞれ構成する。
【０００３】
このＦＭ−ＣＷレーダ装置の動作、原理を概説すると、変調電圧記憶部１には、電圧制御発振器４において、その発振周波数が特定の下限値と上限値の間で直線的かつ周期的に増減する送信信号を励振する変調電圧をディジタルデータとして記憶している。タイミング制御部２はこの変調電圧を所定のタイミングで取り出すタイミング信号をＤ／Ａ変換器３に出力する。この出力タイミング信号を受信したＤ／Ａ変換器３は上記のタイミングで変調電圧記憶部１よりディジタル変調電圧を取り出し、変調電圧をディジタル信号からビット数に対応したアナログ信号に変換し、送受信部の電圧制御発振器の発振周波数を制御する変調電圧として出力する。
【０００４】
電圧制御発振器４は、信号処理部のＤ／Ａ変換器３から入力された変調電圧に比例した発振周波数を有する高周波送信信号を励振し、特定の下限値と上限値の間で直線的かつ周期的に増減する直線周波数変調された高周波送信信号を出力する。高周波増幅器５は電圧制御発振器４からの高周波送信信号を入力し、この高周波送信信号と周波数及び位相が時間的に同期しかつ高周波増幅された信号を出力する。方向性結合器６はこの高周波増幅された信号を所定の電力比で２つの高周波送信信号に分割する。この方向性結合器６の出力信号の一方は送信空中線７により電磁波に変換され、目標物に照射される。
【０００５】
照射された電磁波は送信空中線７から相対距離Ｒに存在しかつ相対速度Ｖで移動する目標物で反射され、目標物とＦＭ−ＣＷレーダ装置との相対速度Ｖに比例したドップラシフトを受けて、かつ目標物との相対距離Ｒに比例した時間２^＊Ｒ／Ｃ（Ｃ：光速）だけ遅れて、受信空中線８で受信され受信高周波信号に変換される。このとき目標物とＦＭ−ＣＷレーダ装置との速度差により生じる周波数偏移は２^＊ｆｃ^＊Ｖ／Ｃ（ｆｃ：送信信号の中心周波数）となる。
【０００６】
ＦＭ−ＣＷレーダ装置から距離Ｒ、相対速度Ｖで移動する目標物からの受信高周波信号は受信ミクサ９において、上記の方向性結合器６の出力である送信高周波信号と混合され、受信ベースバンド信号に変換される。この受信ベースバンド信号はビデオ増幅器１０で所定の利得で増幅された後、低域通過型フィルタ１１により、計測に不要な高周波部分を遮断して、目標情報を含む受信ビート周波数のみを取り出される。
【０００７】
図５は従来のＦＭ−ＣＷレーダ装置の送信空中線７から目標物へ照射される送信信号２８と目標物から反射してくる受信信号２９の周波数の時間変化を示したものであり、図中のｆ_ｕは送信周波数の上限値、ｆ_１はその下限値である（この上限値と下限値の差を変調帯域幅Ｂとする）。送信信号２８は周波数が直線的に増加する区間３０、周波数が一定の値となる区間３１、周波数が直線的に減少する区間３２の３つの区間からなり（これらの区間を以後、それぞれｕｐチャープ、ＣＷ、ｄｏｗｎチャープとする）、１周期（時間３Ｔｍ／２）を構成する。受信信号２９は送信信号２８がＦＭ−ＣＷレーダ装置から目標までの距離Ｒを伝播し、反射して戻ってくる電波伝播時間の遅れに相当する時間偏移３３（τとする）と、両者の速度差から生ずるドップラシフトにより周波数偏移３４（Δｆ_ｖとする）を受ける。
受信信号検出部１８からの出力として得られた受信ベースバンド信号は上記の送信信号２８と受信信号２９の周波数の差分をとった信号（ビート信号）に相当する。このビート信号の周波数の時間的な変化を図６に示す。図中３５がビート信号を表している。図５における各チャープに対応した区間３０、３１、３２では上記の相対距離Ｒによる周波数成分Δｆ_ｒと速度ドップラによる周波数成分Δｆ_ｖによって定まるビート周波数ｆ_ｕｐ、ｆ_ＣＷ、ｆ_ｄｏｗｎが得られる。上記の周波数成分及び各チャープのビート周波数はそれぞれ次式のように与えられる。
【０００８】
【数１】

【０００９】
【数２】

【００１０】
【数３】

【００１１】
【数４】

【００１２】
【数５】

【００１３】
受信信号検出部１８内の低域通過型フィルタ１１の出力ベースバンド信号は、タイミング制御部２からＤ／Ａ変換器３に出力された上記のタイミング信号と時間的に同期したタイミング信号に基づいて、Ａ／Ｄ変換器１２に入力され、アナログ信号からディジタル信号に変換される。離散化・量子化された受信ベースバンド信号は周波数解析手段１３にて離散フーリエ変換により信号周波数の分析が行われ、図７（Ｂ）及び（Ｃ）のように目標の相対距離Ｒによる周波数成分３７（＝Δｆ_ｒ）と図７（Ａ）のように速度ドップラによる周波数成分３８（＝Δｆ_ｖ）ドップラ周波数を含む周波数スペクトルとして出力される。検出された周波数スペクトルは距離・速度計測手段１４により、次式の組み合わせ計算を行うことによりＦＭ−ＣＷレーダ装置から目標までの相対距離Ｒ及び相対速度Ｖを算出することが可能となる。
【００１４】
【数６】

【００１５】
【数７】

【００１６】
【発明が解決しようとする課題】
従来のＦＭ−ＣＷレーダ装置はこのように構成されかつ動作するから、このＦＭ−ＣＷレーダ装置を車両に搭載した図８に示すように、受信信号検出部１８の出力として得られる受信ベースバンド信号に、送信空中線７と受信空中線８との間の相互結合（電磁波の漏れ込み）３８や通常送信空中線７及び受信空中線８前方に配置されるレドーム３９の反射４０などにより生ずる直流及び低周波成分が含まれており、ＦＭ−ＣＷレーダ装置から特定の距離に存在しかつ相対速度で移動する目標の受信ビ−ト信号の振幅レベルが図９の４１（ｂ）に示すように、上記の直流及び低周波成分４２の振幅レベルに比べて低い場合、当該目標物の検出が不可能となるという問題があった。
【００１７】
図１０は上記のＦＭ−ＣＷレーダ装置を搭載した自車両と道路及び先行走行車両の相対的な位置関係を示した図である。図中の４３はＦＭ−ＣＷレーダ装置、４４は自車両、４５は先行走行車両、４６は道路、４７、４８は送信波及び受信波をそれぞれ表している。送信中心周波数ｆ_ｃを６０．５ＧＨｚ、変調帯域幅Ｂを１５０ＭＨｚ、掃引時間Ｔｍを８．４ｍｓとしたＦＭ−ＣＷレーダ装置４３を搭載した車両４４の前方を図１０のように相対速度４０ｋｍ／ｈで先行車両４５が遠ざかる場合、前述のｕｐチャープ、ＣＷ、ｄｏｗｎチャープにおけるビート周波数の相対距離Ｒに対する変化は図１１のようになる。この図において、直流及び低周波の漏れ込み５２により７００Ｈｚ以下のビート周波数をもつ目標信号が検出できないとすると、先行車両がＦＭ−ＣＷレーダ装置より１６ｍから２１ｍの距離範囲に位置する場合はｄｏｗｎチャープの受信ベースバンド信号５０が検出できないため、測距・測速度が不可能となる。図１２における５３は上記と同様の条件で受信ベースバンド信号が検出できないために生ずる不検知領域を示している。図中の横軸の相対速度、縦軸の相対速度を持つ移動目標からの受信信号レベルが十分な大きさであっても検知が不可能となる。以上のように、直流及び低周波の漏れ込みによって発生する不検知領域は実用上の必然的な問題となり、改善が望まれている。
【００１８】
この発明はかかる問題に鑑みてなされたものであり、目標物の距離や速度の如何に関わらず、受信ベースバンド信号に含まれる直流及び低周波により発生する上記の目標物の不検知領域を低減することを目的とする。
【００１９】
【課題を解決するための手段】
第１の発明によるＦＭ−ＣＷレーダ装置は、周波数の変動幅が異なる少なくとも２種類の変調帯域幅を有する送信信号を励振するための異なる少なくとも２種類の変調電圧を発生する変調電圧発生手段を備えたものである。
また、第２の発明によるＦＭ−ＣＷレーダ装置は、周波数の変動幅が異なる少なくとも２種類の変調帯域幅を有する送信信号を励振するための異なる少なくとも２種類の変調電圧を記憶する変調電圧記憶部と、この異なる少なくとも２種類の変調電圧を所定のタイミングで切り替えて出力するタイミング制御器と、変調電圧をディジタル信号からアナログ信号に変換するＤ／Ａ変換器と、タイミング制御器の変調電圧出力タイミングと同期したタイミングで変調帯域幅の異なる受信信号毎のベースバンド信号を入力し、このベースバンド信号をアナログからディジタルに変換するＡ／Ｄ変換器と、ベースバンド信号を離散フーリエ変換により周波数分析を行い、周波数スペクトルとして出力する周波数解祈手段と、周波数スペクトルを変調帯域幅の異なる受信信号毎に算出係数を変えて、距離・速度計算を行う距離・速度計測手段とを備えたものである。
また、第３の発明によるＦＭ−ＣＷレーダ装置は、従来のＦＭ−ＣＷレーダ装置の信号処理部内の変調電圧発生部及び受信ベースバンド信号処理部の構成を以下のように変更したものである。
【００２０】
即ち、電圧制御発振器において、ｕｐチャープ、ＣＷ、ｄｏｗｎチャープの１周期毎に送信中心周波数を起点とした特定の変調帯域幅を有する送信信号と、上記の変調帯域幅とは異なる変調帯域幅を有する送信信号を励振する少なくとも２種類の変調電圧を記憶する変調電圧記憶部と、これらの変調電圧信号を所定の周期毎に切り替えるタイミングでタイミング信号を発生させるタイミング制御部と、変調電圧記憶部から上記のタイミング信号に基づいて出力変調電圧を切り替えるスイッチと、上記のタイミング信号に基づいて変調電圧を入力し、アナログーディジタル変換を行い、電圧制御発振器に出力するＤ／Ａ変換器とを備えたものである。
【００２１】
一方、受信ベースバンド信号処理部は上記のタイミング制御部により、上記の異なる変調電圧により励振される異なる変調帯域幅を有する受信ベースバンド信号を上記のタイミングでＡ／Ｄ変換器へ入力させ、かつ上記の変調帯域幅に対応した周波数解析、相対距離・相対速度計算を行う周波数解析手段及び距離・速度計測手段とを備えたものである。
【００２２】
【発明の実施の形態】
実施の形態１．
図１はこの発明の実施の形態１を示すＦＭ−ＣＷレーダ装置の構成図であり、１は変調電圧記憶部、２０はスイッチ、２はタイミング制御部、３はＤ／Ａ変換器であり、これらの部品１〜３及び部品２０で変調電圧発生部１５を構成する。また、図中の１２はＡ／Ｄ変換器、１３は周波数解析手段、１４は距離・速度計測手段であり、これらの部品１２〜１４及び部品２で受信ベースバンド信号処理部１９を構成する。なお、この発明は従来のＦＭ−ＣＷレーダ装置の一部を変更したものであるため、従来のものと同一機能を有する部品については、同一の符号を付してその説明を省略する。
【００２３】
変調電圧記憶部１には、図２の２１のように出力送信周波数が特定の下限値ｆ_１と上限値ｆ_ｕの間で直線的かつ周期的に増減するように電圧制御発振器４を制御する変調電圧と、２２のように出力送信周波数が下限２ｆ_ｌ −ｆ_ｃと上限値２ｆ_ｕ −ｆ_ｃの間で直線的かつ周期的に増減するように電圧制御発振器４を制御する変調電圧が記憶されている。電圧制御発振器４は印加電圧に比例した周波数を有する高周波送信信号を励振する電圧制御発振器である。上記の２種類の変調帯域幅を有する送信信号の周波数の時間変化は図２に示すように、時間Ｔｍ／２毎に周波数が直線的に増加する区間２３、周波数が一定の値となる区間２４、周波数が直線的に減少する区間２５の３つの区間からなり、１周期（時間３Ｔｍ／２）を構成する。
【００２４】
タイミング制御部２はこれらの変調電圧を図２に示す１周期毎（時間３Ｔｍ／２）に切り替えるタイミング信号を発生し、スイッチ２０に出力する。タイミング信号を受信したスイッチ２０はそれまでに接続していた端子と別のもう一方の端子に接続を切り替えて、変調電圧記憶部１からそれまで読み込んでいた変調電圧（これを＃１とする）とは別のもう一方の変調電圧（これを＃２とする）の読み込みを開始し、この変調電圧＃２をＤ／Ａ変換器３に転送する。スイッチを切り替えて３Ｔｍ／２時間後に、再びタイミング制御部２からタイミング信号が発生し、このタイミング信号に基づいて再びスイッチ２０を切り替えて、変調電圧＃１がＤ／Ａ変換器３に転送される。以後同様に、時間３Ｔｍ／２毎にスイッチ２０が切り替わり、変調電圧＃１と＃２が交互にＤ／Ａ変換器３に転送される。
【００２５】
Ｄ／Ａ変換器３は変調電圧記憶部１から読み込んだディジタルの変調電圧信号を所定のビット数に相当するアナログ変調電圧信号に変換する。変換された変調電圧信号は従来のＦＭ−ＣＷレーダ装置と同様に電圧制御発振器４に出力される。
【００２６】
送信信号変換部１６では従来のＦＭ−ＣＷレーダ装置と同様に、変調電圧に比例した発振周波数を有する高周波送信信号を出力し、高周波増幅を行った後、送信空中線７より目標物に送信波として照射される。目標物から相対速度に比例したドップラシフトを受けて反射し、相対距離に比例した電波伝播時間の遅れをもった反射波は再び受信空中線８で受信され、受信信号検出部１８にて周波数変換、中間周波数増幅、濾波された後、受信ベースバンド信号が出力される。この際得られる受信ベースバンド信号は上記の変調電圧の１周期即ち３Ｔｍ／２時間毎に異なる変調帯域幅を有している。
【００２７】
上記の異なる変調帯域幅を有する受信ベースバンド信号は、受信ベースバンド信号処理部１９内のタイミング制御部２により、時間３Ｔｍ／２毎の単位でＡ／Ｄ変換器１２へ入力され、ディジタル信号に変換する。離散化・量子化された受信ベースバンド信号は周波数解析手段１３にて離散フーリエ変換により信号周波数の分析が行われ、目標のドップラ周波数を含む周波数スペクトルとして出力される。検出された周波数スペクトルは距離・速度計測手段１４により、上記の変調帯域幅に対応した相対距離・相対速度計算が行われ（具体的には、数６及び数７の計算が行われ）、目標の位置・速度情報を得る。
【００２８】
上記の２種類の異なる変調帯域幅を有する受信ベースバンド信号には、前述のように直流及び低周波成分の漏れ込みが含まれており、この周波数帯域に目標の受信ビート信号が得られた場合、受信ビート信号スペクトルが直流及び低周波成分のフロアノイズに隠れてしまい、当該目標物の検出が不可能となる。例えば送信中心周波数ｆｃを６０．５ＧＨｚ、掃引時間Ｔｍを８．４ｍｓとし、２つの変調帯域幅Ｂを１５０ＭＨｚ及び３００ＭＨｚに設定した場合、直流及び低周波の漏れ込みによりフロアノイズの拡がりが７００Ｈｚとすると、ビート信号が検出できないために生ずる不検知領域は図３の２６ようになる。図中の変調帯域幅３００ＭＨｚの送信信号に対する不検知領域を、変調帯域幅１５０ＭＨｚの場合の不検知領域５３に比べた場合、同一相対速度に対して目標を検知できない相対距離は半分となる。以上のように変調帯域幅を大きくすることにより、不検知領域を低減することが可能となる。
【００２９】
一方、変調電圧発生部１５と受信ベースバンド信号処理部１９において、送信信号の変調帯域幅を時間３Ｔｍ／２毎に切り替えて、相対距離・相対速度計測を行うことにより、異なる変調帯域幅に対する目標の不検知領域は図３のように、時間３Ｔｍ／２毎に領域２６と領域５３に変化するため、図中の領域２７以外の不検知領域に存在する目標は、相対距離・相対速度を２回計測する内の１回は検出されることになる。即ち、図中の領域２７以外の不検知領域は時間的に半分に低減されたことになる。
【００３０】
【発明の効果】
第１乃至第３の発明によれば、ＦＭ−ＣＷレーダ装置において受信ベースバンド信号に直流及び低周波成分が混入し、目標のドップラ周波数スペクトルが検出できない不検出領域を時間的に低減することができる。
【００３１】
また、第３の発明によれば、変調電圧発生部の出力変調電圧のみを変化させることにより送信信号の変調帯域幅を制御し、送信信号変換部、受信信号検出部及びアンテナ部のハードウエア部品を変更する必要がないため、従来のＦＭ−ＣＷレーダ装置からの構成部品変更や改修の規模が小さく、かつ受信ベースバンド信号の検波方式を変更していないために、信号の送受信におけるＳ／Ｎの劣化を少なくすることができる。
【００３２】
更に変調電圧発生部では、記憶部への変調電圧の追加と、記憶部からの読み出しの切り替えだけで送信信号の変調帯域幅を制御できるため、タイミング制御器のタイミング信号発生周期やタイミング信号品質に対する性能・条件は変更されないため、容易にこの発明の構成が実現できる。同時に受信ベースバンド信号処理部では、相対距離・相対速度の算出係数の変更のみで目標の位置・速度情報が得られるため、従来のＦＭ−ＣＷレーダ装置と比べて信号処理負荷が大きく増大しない。
【図面の簡単な説明】
【図１】この発明によるＦＭ−ＣＷレーダ装置の実施の形態１の構成を示すシステムブロック図である。
【図２】この発明によるＦＭ−ＣＷレーダ装置の実施の形態１の送信信号の変調周波数の時間変化を示す図である。
【図３】この発明によるＦＭ−ＣＷレーダ装置の実施の形態１の不検知領域を示す図である。
【図４】従来のＦＭ−ＣＷレーダ装置の構成を示すシステムブロック図である。
【図５】従来のＦＭ−ＣＷレーダ装置の送信信号と受信信号の周波数の時間変化を示す図である。
【図６】従来のＦＭ−ＣＷレーダ装置のビート信号の周波数の時間変化を示す図である。
【図７】従来のＦＭ−ＣＷレーダ装置のビート信号の周波数スペクトルを示す図である。
【図８】従来のＦＭ−ＣＷレーダ装置の受信ベースバンド信号へ直流及び低周波の漏れ込みが混入する原理を示す図である。
【図９】従来のＦＭ−ＣＷレーダ装置の直流及び低周波の漏れ込みとビート信号の周波数スペクトルの関係を説明するための図である。
【図１０】従来のＦＭ−ＣＷレーダ装置を搭載した自車両と先行車両との位置関係を示す図である。
【図１１】従来のＦＭ−ＣＷレーダ装置のビート信号と相対距離の関係を示す図である。
【図１２】従来のＦＭ−ＣＷレーダ装置の不検知領域を示す図である。
【符号の説明】
１変調電圧記憶部、２タイミング制御部、３Ｄ／Ａ変換器、４電圧制御発振器、５高周波増幅器、６方向性結合器、７送信空中線、８受信空中線、９受信ミクサ、１０ビデオ増幅器、１１低域通過型フィルタ、１２Ａ／Ｄ変換器、１３周波数解析手段、１４距離・速度計測手段、１５変調電圧発生部、１６送信信号変換部、１７アンテナ部、１８受信信号検出部、１９受信ベースバンド信号検出部、２０スイッチ、２１１５０ＭＨｚ変調波形、２２３００ＭＨｚ変調波形、２３ｕｐチャープ、２４ＣＷ、２５ｄｏｗｎチャープ、２６変調帯域幅３００ＭＨｚのときの不検知領域、２７変調帯域幅１５０ＭＨｚ、３００ＭＨｚの両方が検知できない領域、２８送信信号、２９受信信号、３０ｕｐチャープ、３１ＣＷ、３２ｄｏｗｎチャープ、３３遅延時間、３４周波数偏移、３５ビート信号、３６ドップラシフト、３７距離による周波数偏移、３８送信アンテナから受信アンテナヘの漏れ込み、３９レドーム、４０レドームによる反射、４１ビート周波数、４２直流及び低周波の漏れ込みによるフロアノイズ、４３従来のＦＭ−ＣＷレーダ装置、４４自車両、４５先行走行車両、４６２車線の道路、４７送信波、４８受信波、４９ｕｐチャープのビート周波数、５０ｄｏｗｎチャープのビート周波数、５１ＣＷのビート周波数、５２直流及び低周波の漏れ込みによる不検知領域、５３変調帯域幅１５０ＭＨｚのときの不検知領域。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an FM-CW radar device as a device that is mounted on a traveling vehicle and works effectively to detect position and speed information of a traveling vehicle or an obstacle existing in front of the vehicle. 60 GHz band automotive millimeter wave radar "(FUJITSU.vo147, 4, pp.332-337 July 1996) and the like, and is widely known.
[0002]
[Prior art]
FIG. 4 shows a typical system diagram of a conventional FM-CW radar apparatus, in which 1 is a modulation voltage storage unit, 2 is a timing control unit, 3 is a D / A converter, and 4 is voltage control. Oscillator, 5 is a high frequency amplifier, 6 is a directional coupler, 7 is a transmission antenna, 8 is a reception antenna, 9 is a reception mixer, 10 is a video amplifier, 11 is a low-pass filter, 12 is an A / D converter, Reference numeral 13 denotes frequency analysis means, and reference numeral 14 denotes distance / speed measurement means. These components 1 to 3 are the modulation voltage generator 15, the components 4 to 6 are the transmission signal converter 16, and the components 7 and 8 are the antenna portion 17. The components 9 to 11 constitute the reception signal detection unit 18, and the

components

2 and 12 to 14 constitute the reception baseband signal processing unit 19.
[0003]
The operation and principle of this FM-CW radar apparatus will be outlined. In the voltage control oscillator 4, the oscillation frequency of the modulation voltage storage unit 1 increases and decreases linearly and periodically between a specific lower limit value and an upper limit value. The modulation voltage for exciting the transmission signal is stored as digital data. The timing control unit 2 outputs a timing signal for extracting the modulation voltage at a predetermined timing to the D / A converter 3. The D / A converter 3 that has received this output timing signal extracts the digital modulation voltage from the modulation voltage storage unit 1 at the above timing, converts the modulation voltage from the digital signal to an analog signal corresponding to the number of bits, and Output as a modulation voltage for controlling the oscillation frequency of the voltage controlled oscillator.
[0004]
The voltage controlled oscillator 4 excites a high frequency transmission signal having an oscillation frequency proportional to the modulation voltage input from the D / A converter 3 of the signal processing unit, and linearly and periodically between a specific lower limit value and an upper limit value. A high-frequency transmission signal that is linearly frequency-modulated and increased or decreased is output. The high frequency amplifier 5 receives a high frequency transmission signal from the voltage controlled oscillator 4 and outputs a signal whose frequency and phase are synchronized with each other in time and amplified. The directional coupler 6 divides the high frequency amplified signal into two high frequency transmission signals at a predetermined power ratio. One of the output signals of the directional coupler 6 is converted into an electromagnetic wave by the transmission antenna 7 and irradiated to the target.
[0005]
The irradiated electromagnetic wave is reflected by a target that exists at a relative distance R from the transmission antenna 7 and moves at a relative speed V, and undergoes a Doppler shift proportional to the relative speed V between the target and the FM-CW radar device. Further, it is delayed by a time 2 ^* R / C (C: speed of light) proportional to the relative distance R to the target, and is received by the receiving antenna 8 and converted into a received high-frequency signal. At this time, the frequency shift caused by the speed difference between the target and the FM-CW radar apparatus is 2 ^* fc ^* V / C (fc: center frequency of transmission signal).
[0006]
A reception high-frequency signal from a target moving at a distance R and a relative speed V from the FM-CW radar apparatus is mixed with a transmission high-frequency signal which is an output of the directional coupler 6 in the reception mixer 9 to obtain a reception baseband signal. Is converted to This received baseband signal is amplified with a predetermined gain by the video amplifier 10, and then a high-frequency portion unnecessary for measurement is blocked by the low-pass filter 11, and only the received beat frequency including target information is extracted.
[0007]
FIG. 5 shows the time change of the frequency of the transmission signal 28 irradiated to the target from the transmission antenna 7 of the conventional FM-CW radar apparatus and the reception signal 29 reflected from the target. f _u is an upper limit value of the transmission frequency, and f ₁ is a lower limit value thereof (a difference between the upper limit value and the lower limit value is defined as a modulation bandwidth B). The transmission signal 28 includes three sections, a section 30 in which the frequency increases linearly, a section 31 in which the frequency becomes a constant value, and a section 32 in which the frequency decreases linearly (these sections are referred to as up chirp, CW, down chirp) and one period (time 3 Tm / 2). The received signal 29 includes a time shift 33 (tau) corresponding to a delay in the radio wave propagation time in which the transmission signal 28 propagates the distance R from the FM-CW radar device to the target, and is reflected back. Due to the Doppler shift resulting from the speed difference, a frequency shift 34 (denoted as Δf _v ) is applied.
The reception baseband signal obtained as an output from the reception signal detector 18 corresponds to a signal (beat signal) obtained by taking the difference in frequency between the transmission signal 28 and the reception signal 29 described above. FIG. 6 shows temporal changes in the frequency of the beat signal. In the figure, 35 represents a beat signal. In

sections

30, 31, and 32 corresponding to each chirp in FIG. 5, beat frequencies f _up , f _CW , and f _down determined by the frequency component Δf _r by the relative distance R and the frequency component Δf _v by the velocity Doppler are obtained. The frequency component and the beat frequency of each chirp are given by the following equations, respectively.
[0008]
[Expression 1]

[0009]
[Expression 2]

[0010]
[Equation 3]

[0011]
[Expression 4]

[0012]
[Equation 5]

[0013]
The output baseband signal of the low-pass filter 11 in the reception signal detection unit 18 is based on the timing signal synchronized in time with the timing signal output from the timing control unit 2 to the D / A converter 3. The A / D converter 12 converts the analog signal into a digital signal. The received baseband signal that has been discretized and quantized is subjected to signal frequency analysis by discrete Fourier transform in the frequency analysis means 13, and the frequency component due to the target relative distance R as shown in FIGS. 7B and 7C. 37 (= Δf _r ) and a frequency spectrum including a frequency component 38 (= Δf _v ) Doppler frequency due to velocity Doppler as shown in FIG. 7A. The distance / velocity measuring means 14 calculates the relative distance R and the relative speed V from the FM-CW radar apparatus to the target by performing a combination calculation of the following equation by the distance / speed measuring means 14.
[0014]
[Formula 6]

[0015]
[Expression 7]

[0016]
[Problems to be solved by the invention]
Since the conventional FM-CW radar apparatus is configured and operates in this manner, the received baseband signal obtained as the output of the received signal detector 18 as shown in FIG. 8 in which this FM-CW radar apparatus is mounted on a vehicle. In addition, the direct coupling and low frequency components generated by the mutual coupling (electromagnetic wave leakage) 38 between the transmitting antenna 7 and the receiving antenna 8, the reflection 40 of the radome 39 disposed in front of the normal transmitting antenna 7 and the receiving antenna 8, etc. The amplitude level of a target received beat signal that is present at a specific distance from the FM-CW radar apparatus and moves at a relative speed is shown in 41 (b) of FIG. When the amplitude level of the low frequency component 42 is low, there is a problem that the target cannot be detected.
[0017]
FIG. 10 is a diagram showing a relative positional relationship between the host vehicle on which the FM-CW radar device is mounted, a road, and a preceding traveling vehicle. In the figure, 43 represents an FM-CW radar device, 44 represents the host vehicle, 45 represents a preceding vehicle, 46 represents a road, and 47 and 48 represent transmission waves and reception waves, respectively. 60.5GHz transmission center frequency _{f c,} 150 MHz modulation bandwidth B, the relative velocity 40 km / h as shown in FIG. 10 the front of the vehicle 44 equipped with the FM-CW radar device 43 of the sweep time Tm was 8.4ms When the preceding vehicle 45 moves away, the change of the beat frequency with respect to the relative distance R in the above-mentioned up chirp, CW, and down chirp is as shown in FIG. In this figure, if a target signal having a beat frequency of 700 Hz or less cannot be detected due to DC and low-frequency leakage 52, the chirp is down when the preceding vehicle is located in the range of 16 to 21 m from the FM-CW radar device. Since the received baseband signal 50 cannot be detected, distance measurement and speed measurement are impossible. Reference numeral 53 in FIG. 12 indicates a non-detection area that occurs because a reception baseband signal cannot be detected under the same conditions as described above. Detection is impossible even if the received signal level from the moving target having the relative speed on the horizontal axis and the relative speed on the vertical axis in the figure is sufficiently large. As described above, the non-detection region generated by leakage of direct current and low frequency becomes an inevitable problem in practical use, and improvement is desired.
[0018]
The present invention has been made in view of such a problem, and reduces the above-described non-detection region of the target generated by direct current and low frequency included in the received baseband signal regardless of the distance and speed of the target. The purpose is to do.
[0019]
[Means for Solving the Problems]
The FM-CW radar apparatus according to the first invention includes modulation voltage generating means for generating at least two different modulation voltages for exciting transmission signals having at least two types of modulation bandwidths having different frequency fluctuation ranges. It is a thing.
Further, the FM-CW radar apparatus according to the second invention is a modulation voltage storage unit for storing at least two different modulation voltages for exciting transmission signals having at least two modulation bandwidths having different frequency fluctuation ranges. A timing controller that switches and outputs at least two different modulation voltages at a predetermined timing, a D / A converter that converts the modulation voltage from a digital signal to an analog signal, and a modulation voltage output timing of the timing controller A baseband signal for each received signal with a different modulation bandwidth is input at a timing synchronized with the A / D converter that converts the baseband signal from analog to digital, and frequency analysis is performed on the baseband signal by discrete Fourier transform. And frequency output means to output as a frequency spectrum and the frequency spectrum to the modulation band Changing the calculated coefficients for each reception signals of different widths, in which a distance and speed measurement means for performing distance and speed calculations.
The FM-CW radar apparatus according to the third invention is obtained by changing the configurations of the modulation voltage generation unit and the reception baseband signal processing unit in the signal processing unit of the conventional FM-CW radar apparatus as follows.
[0020]
That is, in the voltage controlled oscillator, a transmission signal having a specific modulation bandwidth starting from the transmission center frequency for each period of up chirp, CW, and down chirp and a modulation bandwidth different from the above modulation bandwidth A modulation voltage storage unit that stores at least two types of modulation voltages for exciting a transmission signal, a timing control unit that generates a timing signal at a timing at which these modulation voltage signals are switched at predetermined intervals, and a modulation voltage storage unit those of a switch for switching the output modulated voltage based on the timing signal, and inputs the modulated voltage based on the timing signal, performs analog-to-digital converter, and a D / a converter which outputs a voltage controlled oscillator It is .
[0021]
On the other hand, the reception baseband signal processing unit causes the timing control unit to input reception baseband signals having different modulation bandwidths excited by the different modulation voltages to the A / D converter at the above timing, and those with frequency analysis corresponding to the modulation bandwidth, and a frequency analyzing means and the distance and speed measurement means for performing a relative distance and a relative speed calculation.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a block diagram of an FM-CW radar apparatus showing Embodiment 1 of the present invention, wherein 1 is a modulation voltage storage unit, 20 is a switch, 2 is a timing control unit, and 3 is a D / A converter. These components 1 to 3 and the component 20 constitute a modulation voltage generator 15. In the figure, 12 is an A / D converter, 13 is frequency analysis means, 14 is distance / speed measurement means, and these parts 12 to 14 and part 2 constitute a reception baseband signal processing unit 19. Since the present invention is obtained by changing a part of a conventional FM-CW radar apparatus, parts having the same functions as those of the conventional FM-CW radar apparatus are denoted by the same reference numerals and description thereof is omitted.
[0023]
The modulation voltage storage unit 1 controls the voltage controlled oscillator 4 so that the output transmission frequency linearly and periodically increases and decreases between a specific lower limit value f ₁ and an upper limit value f _u as indicated by 21 in FIG. and modulation voltage linearly and periodically modulated voltage for controlling the voltage controlled oscillator 4 to increase or decrease the stored between the output transmission frequency is lower 2f _l -f _c and the upper limit value 2f _u -f _c as 22 Has been. The voltage controlled oscillator 4 is a voltage controlled oscillator that excites a high-frequency transmission signal having a frequency proportional to the applied voltage. As shown in FIG. 2, the time change of the frequency of the transmission signal having the two types of modulation bandwidths described above is a section 23 in which the frequency increases linearly every time Tm / 2, and a section 24 in which the frequency becomes a constant value. , Which consists of three sections 25 in which the frequency decreases linearly, and constitutes one period (time 3 Tm / 2).
[0024]
The timing control unit 2 generates a timing signal for switching these modulation voltages for each cycle (time 3 Tm / 2) shown in FIG. The switch 20 that has received the timing signal switches the connection to the other terminal different from the terminal that has been connected so far, and the modulation voltage that has been read from the modulation voltage storage unit 1 (this is assumed to be # 1). Reading of the other modulation voltage (which will be referred to as # 2) is started, and this modulation voltage # 2 is transferred to the D / A converter 3. After 3 Tm / 2 hours after switching the switch, a timing signal is generated again from the timing control unit 2, and the switch 20 is switched again based on this timing signal, and the modulation voltage # 1 is transferred to the D / A converter 3. . Thereafter, similarly, the switch 20 is switched every 3 Tm / 2, and the modulation voltages # 1 and # 2 are transferred to the D / A converter 3 alternately.
[0025]
The D / A converter 3 converts the digital modulation voltage signal read from the modulation voltage storage unit 1 into an analog modulation voltage signal corresponding to a predetermined number of bits. The converted modulation voltage signal is output to the voltage controlled oscillator 4 as in the conventional FM-CW radar apparatus.
[0026]
As in the conventional FM-CW radar apparatus, the transmission signal converter 16 outputs a high-frequency transmission signal having an oscillation frequency proportional to the modulation voltage, performs high-frequency amplification, and then transmits it as a transmission wave from the transmission antenna 7 to the target. Irradiated. A reflected wave having a Doppler shift proportional to the relative velocity and reflected from the target and having a delay in radio wave propagation time proportional to the relative distance is received again by the receiving antenna 8, and the received signal detector 18 converts the frequency. After intermediate frequency amplification and filtering, a received baseband signal is output. The received baseband signal obtained at this time has a different modulation bandwidth for each period of the modulation voltage, that is, every 3 Tm / 2 hours.
[0027]
The reception baseband signal having the different modulation bandwidth is input to the A / D converter 12 by the timing control unit 2 in the reception baseband signal processing unit 19 in units of time 3 Tm / 2 and converted into a digital signal. Convert. The reception baseband signal that has been discretized and quantized is subjected to signal frequency analysis by discrete Fourier transform in the frequency analysis means 13 and output as a frequency spectrum including a target Doppler frequency. The detected frequency spectrum is subjected to relative distance / relative velocity calculation corresponding to the above-described modulation bandwidth by the distance / velocity measuring means 14 (specifically, the equations 6 and 7 are calculated), and the target Get position / velocity information.
[0028]
The reception baseband signal having the two different modulation bandwidths described above includes leakage of direct current and low frequency components as described above, and a target reception beat signal is obtained in this frequency band. The received beat signal spectrum is hidden by the floor noise of direct current and low frequency components, and the target cannot be detected. For example, when the transmission center frequency fc is 60.5 GHz, the sweep time Tm is 8.4 ms, and the two modulation bandwidths B are set to 150 MHz and 300 MHz, the spread of floor noise is 700 Hz due to leakage of direct current and low frequency. The non-detection region that occurs because the beat signal cannot be detected is as shown in FIG. When the non-detection region for the transmission signal with the modulation bandwidth of 300 MHz in the figure is compared with the non-detection region 53 with the modulation bandwidth of 150 MHz, the relative distance at which the target cannot be detected for the same relative speed is halved. As described above, it is possible to reduce the non-detection area by increasing the modulation bandwidth.
[0029]
On the other hand, the modulation voltage generation unit 15 and the reception baseband signal processing unit 19 switch the modulation bandwidth of the transmission signal every time 3 Tm / 2 and measure the relative distance and the relative speed, thereby achieving targets for different modulation bandwidths. As shown in FIG. 3, the non-detection area changes to the area 26 and the area 53 every time 3 Tm / 2. Therefore, the target existing in the non-detection area other than the area 27 in the figure has a relative distance / velocity of 2 One of the measurement times is detected. That is, the non-detection area other than the area 27 in the figure is reduced by half in terms of time.
[0030]
【The invention's effect】
According to the first to third inventions, in the FM-CW radar apparatus, direct current and low frequency components are mixed in the received baseband signal, and the non-detection region where the target Doppler frequency spectrum cannot be detected can be reduced in time. it can.
[0031]
In addition, according to the third aspect of the invention, the modulation bandwidth of the transmission signal is controlled by changing only the output modulation voltage of the modulation voltage generation unit, and the hardware components of the transmission signal conversion unit, the reception signal detection unit, and the antenna unit Since there is no need to change the components, the scale of the component change or modification from the conventional FM-CW radar apparatus is small, and the detection method of the received baseband signal is not changed. Can be reduced.
[0032]
Furthermore, since the modulation voltage generator can control the modulation bandwidth of the transmission signal only by adding the modulation voltage to the storage unit and switching the reading from the storage unit, the timing voltage generation period and timing signal quality of the timing controller can be controlled. Since the performance and conditions are not changed, the configuration of the present invention can be easily realized. At the same time, the reception baseband signal processing unit can obtain target position / velocity information only by changing the relative distance / relative velocity calculation coefficients, and therefore the signal processing load does not increase significantly compared to the conventional FM-CW radar apparatus.
[Brief description of the drawings]
FIG. 1 is a system block diagram showing a configuration of a first embodiment of an FM-CW radar apparatus according to the present invention.
FIG. 2 is a diagram showing a time change of a modulation frequency of a transmission signal in the first embodiment of the FM-CW radar apparatus according to the present invention.
FIG. 3 is a diagram showing a non-detection area of the first embodiment of the FM-CW radar apparatus according to the present invention.
FIG. 4 is a system block diagram showing a configuration of a conventional FM-CW radar apparatus.
FIG. 5 is a diagram showing temporal changes in the frequency of a transmission signal and a reception signal of a conventional FM-CW radar apparatus.
FIG. 6 is a diagram illustrating a time change of a frequency of a beat signal of a conventional FM-CW radar apparatus.
FIG. 7 is a diagram showing a frequency spectrum of a beat signal of a conventional FM-CW radar apparatus.
FIG. 8 is a diagram illustrating the principle of leakage of direct current and low frequency mixed into a received baseband signal of a conventional FM-CW radar apparatus.
FIG. 9 is a diagram for explaining a relationship between direct current and low frequency leakage of a conventional FM-CW radar apparatus and a frequency spectrum of a beat signal.
FIG. 10 is a diagram showing a positional relationship between a host vehicle equipped with a conventional FM-CW radar device and a preceding vehicle.
FIG. 11 is a diagram illustrating a relationship between a beat signal and a relative distance of a conventional FM-CW radar apparatus.
FIG. 12 is a diagram showing a non-detection area of a conventional FM-CW radar apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Modulation voltage memory | storage part, 2 timing control part , 3 D / A converter, 4 voltage control oscillator, 5 high frequency amplifier, 6 directional coupler, 7 transmission antenna, 8 reception antenna, 9 reception mixer, 10 video amplifier, 11 Low-pass filter, 12 A / D converter, 13 Frequency analysis means, 14 Distance / velocity measurement means, 15 Modulation voltage generation section, 16 Transmission signal conversion section, 17 Antenna section, 18 Reception signal detection section, 19 Reception baseband Signal detection unit, 20 switch, 21 150 MHz modulation waveform, 22 300 MHz modulation waveform, 23 up chirp, 24 CW, 25 down chirp, 26 Non-detection area when modulation bandwidth is 300 MHz, 27 Both modulation bandwidth is 150 MHz and 300 MHz Undetectable area, 28 transmission signal, 29 reception signal, 30 up chirp, 31 CW, 32 down chirp, 33 delay time, 34 frequency shift, 35 beat signal, 36 Doppler shift, 37 frequency shift due to distance, 38 leakage from transmitting antenna to receiving antenna, 39 radome, reflection by 40 radome, 41 beat frequency, 42 Floor noise due to leakage of direct current and low frequency, 43 conventional FM-CW radar device, 44 own vehicle, 45 preceding vehicle, 462 two-lane road, 47 transmission wave, 48 reception wave, beat frequency of 49 up chirp, Beat frequency of 50 down chirp, beat frequency of 51 CW, 52 non-detection region due to leakage of direct current and low frequency, 53 non-detection region when modulation bandwidth is 150 MHz.

Claims

In the voltage controlled oscillator, a modulation voltage for storing a modulation voltage for controlling the voltage controlled oscillator so that the oscillation frequency of the output transmission signal to be excited linearly and periodically increases and decreases between a predetermined lower limit value and an upper limit value. A storage unit, a first timing controller that outputs a timing signal for reading the modulation voltage from the modulation voltage storage unit at a predetermined sweep time, and a modulation voltage stored in the modulation voltage storage unit at the above timing. A modulation voltage generator comprising a D / A converter for reading digital-analog conversion and outputting a modulation voltage;
A voltage-controlled oscillator that inputs a modulation voltage from this modulation voltage generator and excites and outputs an output transmission signal having an oscillation frequency proportional to the modulation voltage. The frequency and phase of the output transmission signal are synchronized in time and power is amplified. A high-frequency amplifier that outputs the high-frequency transmission signal, and a transmission signal converter including a directional coupler that distributes and outputs the high-frequency transmission signal to a predetermined power ratio;
An antenna including a transmission antenna that converts the high-frequency transmission signal output from the transmission signal conversion unit into an electromagnetic wave and irradiates the target, and a reception antenna that receives a reflected electromagnetic wave from the target and converts it into a high-frequency reception signal And
A reception mixer that frequency-mixes one of the high-frequency reception signal taken out from the reception antenna and the high-frequency transmission signal from the directional coupler, and outputs a reception baseband signal. Amplifier that outputs a received baseband signal that is synchronized with each other and amplified with a predetermined gain, and a low-pass that extracts a received beat frequency including target information by cutting off a high-frequency portion unnecessary for measurement in the received baseband signal A received signal detector comprising a type filter;
A second timing controller that outputs a timing signal that captures the output signal of the received signal detection unit at every sweep time of the modulation voltage, and an A / D conversion that receives the received baseband signal at this timing and performs analog-digital conversion Frequency analysis means for performing frequency analysis of the received baseband signal discretized and quantized by the A / D converter and separating a plurality of frequency components contained in the signal, and detected by the frequency analysis means A receiving baseband signal processing unit comprising distance / speed measuring means for detecting target position and speed information from the frequency components obtained;
FM-CW radar apparatus comprising:
The modulation voltage storage unit stores at least two different modulation voltages for exciting a transmission signal having at least two types of modulation bandwidths whose frequency widths of the lower limit value and the upper limit value are different from the frequency width,
The switch and the first timing controller switch at least two different modulation voltages at a predetermined timing,
The D / A converter converts the modulation voltage from a digital signal to an analog signal,
The A / D converter inputs the output baseband signal of the reception signal detection unit for each reception signal having a different modulation bandwidth at a timing synchronized with the modulation voltage output timing of the modulation voltage generation unit. Convert the signal from analog to digital,
The frequency praying means analyzes the signal frequency of the received baseband signal by discrete Fourier transform and outputs it as a frequency spectrum including a target Doppler frequency,
The distance / speed measuring means performs distance / speed calculation by changing a calculation coefficient for each received signal having a different modulation bandwidth for the detected frequency spectrum.
An FM-CW radar apparatus characterized by the above.