Gii thiu v RadarNguyn Hng QuangT6-K48

Radar

Radar Vit tt ca Radio Detection And Ranging :l 1b cm bin sng v tuyn ,ni chung(nhng khng hon ton ) hot ng di tn s microwave (> 1 GHz), v l 1 b cm bin cc nhy . y t nhy ch ra rng : b cm bin pht nng lng (sng in t) vo mi trng xung quanh v thu v thng tin thng qua phn tch phn x tr li.

RadarRadar c th c hiu nh 1 cp kt ni truyn thng ch trn 1 ng ,vi kt ni tr v l sng phn x.

B phn pht v thu u c t cng 1 v tr v tn hiu thu l tn hiu phn x .

RadarChng ta c 1 ngten pht ng hng ngha l n pht ng nht v mi hng .Nng lng pht ti 1 khong cch d t my pht ,l c tri rng ng nht trn b mt ca 1 qu cu c bn knh l d ,vi mt nng lng :

Radarngten thc t pht theo 1 hng nht nh :h s tng ch ca ngten (G) l thc o tnh hiu qu ca ngten trong tp trung nng lng pht x ca ngten theo 1 hng xc nh.Mt nng lng s l :

ngten Radar

H s phn xForward signal

Radar

H thng Radar in hnh bao gm :1 my pht v thu sng v tuyn t cng v tr ,thng s dng chung 1 ngten.

RadarSng c pht i v sau my thu s thu tn hiu tr v.Cng ca tn hiu tr v ph thuc vo khong cch ti ch v kch c(in) ca n .Radar xc nh khong cch ti ch nh vo tr thi gian t khi pht cho ti khi nhn c sng phn x li.

Truyn trong khng gian t doNng lng c sn ti u ra ca 1 ngten nhn s l tch s ca mt nng lng ti im vi din tch c nh hng ca ngten.

Truyn trong khng gian t doNu cng 1 ngten s dng cho c pht v thu chng ta c th s dng phng trnh quan h gia din tch chu nh hng v h s tng ch.

Truyn trong khng gian t doThay th phng trnh h s tng ch ngten bng phng trnh tn hao nng lng trong khng gian t do Friis

Radar cross-sectionTm dch :Tit din ca Radar.Thay th din tch chu nh hng (effective area) ca ngten nhn ,trong Radar ,tn hiu c xc nh bi RCS.RCS l thc o din tch phn x hoc in (electrical) ca mc tiu.

Radar cross-sectionN c th t l hoc khng vi kch thc vt l ca mc tiu.N thng c biu din bng m2 hoc dBsmK hiu ca RCS l :

Phng trnh RadarDo vy ,tn hiu phn x c th c xc nh bng mt nng lng ti mc tiu nhn vi RCS

Mt nng lng ti my thu t tn hiu phn x l:

Phng trnh RadarKhi nhn vi vng chu nh hng ca ngten Radar Ta c :

Phng trnh tm xa ca RadarTu vo mc tn hiu nhn c,chng ta c th xc nh c phng trnh cho d v tm c khong cch ln nht m thit b c th d c

Trong Radar thng s dng R - tm xa thay th cho d - khong cch.

SNR(Signal Noise Ratio)Nng lng nhiu ti u vo b thu l : Pn = kT B F Trong : k :hng s Boltzmanns T:nhit my thu(Nhit Kelvin)B:Di thng ca nhiu my thu(c th xem nh bng di thng ca tn hiu)Noise Figure F ,s hng ln hn 1 so snh vi trng hp l tng =1 .Sau ta c th tnh c SNR = Pr/Pn.

Xung Radar(Pulse Radar)Xung Radar thng thng lm vic bng cch pht 1 xung RF ngn v o thi gian tr tr v.Di thng ca matched filter receiver xp x 1/ vi l rng xung cng xc nh phn gii tm xa(resolution range) ca Radar :

Xung RadarCc xung ngn hn yu cu di thng nhn l ln hn (nhiu nhiu hn) ,cung cp nng lng trung bnh thp hn (tn hiu yu hn) nhng cung cp phn gii tm xa (resolution range) tt hn.Matched filter c p ng xung ph hp vi xung pht iTm xa ti mc tiu s l : l thi gian tri qua gia pht v nhn xung.

Xung RadarCc xung thng c pht u n.Chu k ny c gi l PRI hoc PRT.Tn s pht li xung l: PRF = 1/ PRI.PRI m t tm xa r rng ln nht(range unambiguos maximum) ca h thng.

Xung RadarMt mc tiu ln xa gii hn r rng (unambigous range) c th hiu nh mc tiu ng (close target).

Xung Radar c bi s ln phn x tr li, RCS ca vt phn x xa thng phi ln.L tng chng ta mun R(unamb) cch xa khong d c ln nht ca Radar.Trong thc t c nhiu cch loi b hiu ng ca nhng ln quay tr li ny.

o tm xa(Range Measurement)Tm xa ca mc tiu c th c c lng chnh xc tt hn rng xung bng vic s dng b theo di chia cng(split-gate-tracker).Bng cch so snh nng lng gia Early Gate v Late Gate c lng c v tr ca mc tiu.

Radar clutter(Tp m- NhiuRadar )Clutter c nh ngha nh l s vng li Radar khng mong mun.S quay tr v mc tiu mt t s xut hin ground clutter (area clutter) S quay tr v mc tiu khng vn c th xut hin volume clutter

Area ClutterArea clutter c m t bi clutter cross-section trung bnh trn 1 n v din tch ,

Ci ny c gi l h s backscatter.S lng clutter nhn c ph thuc trn din tch mt t (ground area) c chiu sng l bao nhiu.

Area clutter rng ca clutter patch c nh ngha bi rng gc phng v ca ngten ( antenna azimuth beamwidth) v tm xa hoc khong cch ti clutter patch.Chiu di ca clutter patch c xc nh bi : The range gate size (shallow grazing angle-gc st qua nng ) Hoc rng gc nng (elevation beamwidth) cho cc gc st qua dc hn( steeper grazing angles) nh Radar khng vn chiu sng mc tiu di t.

Gc phng v

Gc nng

Area Clutter rng ca cc clutter cell l:

R l tm xa ti trung tm ca Clutter Cell v l rng gc phng v theo Radian.

Area Clutter su hoc chiu di ca clutter cell c xc nh bi phn nh hn ca :Range gate phng trn mt t. rng ca gc nng nhn vi The total range phng trn mt t.

Area clutterNh vy ,chiu di ca clutter cell c th c biu din nh sau :

Area ClutterV vy ,cc gc st qua nng (Shallow grazing angles ) ,khi xung b gii hn :

Area ClutterTi cc gc dc hn ,khi chm gii hn clutter area l gn ging din tch hnh elip.

Clutter Cross-sectionTit din ca Radar trn thc t ca clutter l clutter patch area nhn vi h s backscatter

Chng ta ch xem xt gii hn ca xung,cc pha m gc lt qua thp

Nng lng Clutter quay vNng lng phn x clutter quan st ti Radar l:

Nng lng Clutter quay vDo vy ,khi R tng ,nng lng Clutter gim theo 1/R^3 ,trong khi nng lng mc tiu gim theo 1/R^4.Bi v s tri rng sng Radio theo khong cch lm tng s lng clutter quan st c.Cho trng hp gii hn chm (beam-limited case),din tch clutter l hm ca R^2 v th nng lng clutter quay v t l vi 1/R^2 ,so vi 1/R^4 cho nng lng ca mc tiu.

Volume Clutter(Th tch Clutter)Volume clutter ph thuc vo:Range gate lengthRange to range gate of interest rng gc nng v gc phng v ca ngtenTh tch ca clutter cell s xp x:

Volume ClutterTh tch clutter c m t bi tit din backscatter trn n v th tch, , c n v l

Tng clutter cross section l :

V vy ,phng trnh tm xa c p dng , chng ta s thy clutter return ch gim theo R^2 bi v s ph thuc th tch clutter theo R^2

Volume Clutter Cell

Kt lunH thng Radar chi tn hao ng truyn t l vi R^4 ln hn R^2 trong truyn dn 1 ng ca h thng thng tin.Phng trnh tm xa ca Radar cung cp 1 nng lng (power) ngha l d on cng tn hiu quay v.Clutter c th l din tch (mt t-ground) hoc th tch (thi tit weather).Din tch hoc th tch clutter tng theo R hoc R^2 ,Clutter khng gim theo khong cch nhanh nh cng tn hiu.Cng tn hiu t l vi 1 tham s -c gi l radar cross section ci c p dng vi clutter hoc cc mc tiu.

Mt s ng dng ca RadarRadar pht hin ra v tr ,vn tc ca vt th .Trong 1 s h thng tin tin cn xc nh c hnh dng ca chng .

Trong hng khng dn dng

My bay dn dng c trang b cc thit b Radar cnh bo chng ngi vt , thm d ng i v a ra cao chnh xc.My bay c th h cnh trong sng m ti cc sn bay c trang b h thng iu khin mt t c h tr bi Radar.Trong ng bay c theo di trn mn hnh RadarH thng Radar dn ng iu khin t xa cho my bay c pht trin vo nm 1960.

ng dng trong qun sRadar c s dng pht hin my bay v tu ca i phng.Radar iu khin ho lc tiu dit mc tiu.Radar dn ng cho khng qun tim kch , oanh tc cc mc tiu khng nhn thy c.

ng dng trong qun sCc h thng gim st v dn ng Radar c s dng cho nghin cu khoa hc v phng th.Cho h thng phng th pha Bc nc M chnh ph pht trin (c.1950-63) 1 h thng Radar c xem nh h thng cnh bo sm tn la n o-BMEWS(Ballistic Missile Early Warning System ) , c lp t Thule, Greenland; Clear, Alaska; and Yorkshire, England .

ng dng trong qun sMt h thng Radar c xem nh h thng dn ng v kim sot khng gian - Space Detention and Tracking System (SPADATS), hot ng cng tc gia Canada v M , dn ng v tinh nhn to quan st tri t.

ng dng ca Radarng dng Radar o khong cch , din tch a l ,tm v nh v ngoi khi.Radar cng c s dng nghin cu cc hnh tnh v tng in ly thuc h mt tri , pht hin cc tia sng v cc vt th di chuyn ngoi khng gian.

ng dng trong kh tng Ma l mc tiu l tng cho S-Band Radar (~10cm)n v Radar thi tit c thnh lp M vo thp k 60.(WSR-57)

Radar L band Radars 15-30 cm ,1-2 GHz. i tng l s chuyn ng ca khng kh. S band Radars 8-15 cm , 2-4 GHz Far range a ngten ln C band Radars 4-8 cm ,4-8 GHz Short range a ngten nh X band Radars 2.5-4 cm , 8-12GHzShorter rangeD cc phn t nh hn.

Hnh nh Radar WSD-88D Hnh nh cng hng t

CASA

Mt vi hnh nh Top view

Lc xoy

Hnh nh cc m my tch ma

Xin chn thnh cm n thy gio v cc bn.