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7/28/2019 THIT K ANTEN VI DI CHO NG DNG GNSS
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THIT K ANTEN VI DI CHO
NG DNG GNSSNgy nay cc ng dng ca h thng GNSS (Global Navigation
Satellite System) v ang thm nhp vo i sng x hi ngy cng a
dng v phong ph. phc v cuc sng ngy mt tt hn, nhiu h thng
nh v dn ng trn th gii ra i nh: GPS (Global Positionting
System) ca M, GLONASS ca Nga v Galileo ca Chu u. Trong cc b
thu tn hiu nh v, thit b u cui anten ng vai tr quan trng, lm tng
nhy, gim mc tiu th nng lng. Trong phm vi bi bo ny s phn
tch v thit k mt anten vi di hot ng tn s 1565MHz sau:
1595MHz, phc v cho cc thit b tch hp ng dng ca GNSS trong
hin ti v tng lai.
I. Gii thiu chung v anten vi di
Nhng cu trc bc x vi di c a ra ln u tin vo nm 1953.
Tuy nhin phi gn hai mi nm sau, nhng anten thc t mi c sn
xut. K t , vic nghin cu, pht trin cc anten vi di v cc mng
anten vi di khng ngng c m rng, nhm khai thc trit nhng u
im, cng nh cch khc phc cc u nhc im ca loi anten ny.
Anten vi di vi cu hnh n gin nht bao gm mt patch pht x nm
trn mt mt ca mt lp in mi (lp ), mt kia lp in mi l mt
phng t, cht dn in l tng. Ming Patch l cht dn in, c th lbt k hnh dng no, nhng thng s dng hnh dng sao cho vic phn
tch, tnh ton thit k d dng, hiu qu. Tuy nhin vi s pht trin ca
cng ngh v s ra i ca cc chng trnh m phng thit k cho php c
th thit k patch bt k hnh dng no. Hng s in mi ca lp
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ng vai tr quan trng i vi hot ng ca anten, nh hng n tr
khng c tnh, tn s cng hng, bng thng v hiu sut ca anten.
II. Tnh ton kch thc v m phng
Anten thit k y l m hnh anten mt lp, in mi c s
dng l FR4_epoxy c hng s in mi = 4,4. Tnh ton xp x kch
thc ca anten theo cng thc sau: L = W 0,49.d = 0,49. Vi l bc
sng trong khng gian t do, d l bc sng trong cht in mi, l h s
in mi ca lp . Thng s v kch thc gn ng ca anten nh sau:
Wp = Lp = 43,91mm, L = 4,87mm, r1l = 27,09mm, w1l = 2,21mm, r2l =
10mm, w2l = 6,1mm, s dng lp in mi c = 4,4 b dy lp in mi h(h c th thay i tm c anten c ti u), kch thc lp in mi
v Ground: 90mmx104mm. Anten GNSS gm hai phn c bn: Mt bc x
(patch), ng truyn vi di tip in cho patch, cng l mch phi hp tr
khng dng b phi hp tr khng /4. Bng tn lm vic, bng thng ph
thuc vo kch thc tm patch v b dy lp in mi. Sau y s tin
hnh kho st mt vi trng hp thy c s ph thuc ny.
Hnh 1: Anten vi di
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Khi tng hoc gim b dy lp in mi trong mt gii hn cho php th
cc thng s k thut ca anten nh bng thng, t s trc (AR) thay i ng
k. Theo kt qu nh trn, m hnh anten vi h = 1,6mm v h =
3,2mm u t c S11 tt nhng bng thng li khc nhau, vi h =
1,6mm bng thng ca GPS 60MHz (3,8%), vi h = 3,2mm l ti u hn
c, tha mn c v S11, bng thng v t s trc. Vy m rng bng thng
cho anten l tng dy ca lp in mi.
Kho st anten khi thay i kch thc tm patchB dy lp in mi khng i c chn l h = 3,2mm, thng s thay i
y l kch thc tm patch, thc hin iu chnh di ca on ct vt thay i t s trc AR < 3dB. Khi thay i kch thc on ct vt ca tm
patch thu c kt qu t s trc (AR) nh hnh 4.
Hnh 4: AR khi delta_l thay i
Thay i kch thc tm patch lm thay i cc thng s k thut ca anten.
M hnh anten vi delta_l = 4,87mm c chn v cc thng s k thut tha
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mn yu cu v l ti u nht trong nhng m hnh trn.
III. Kt qu m phng v ch to anten tha mn yu cu
t ra
M hnh anten vi b dy lp in mi h = 3,2mm v delta_l = 4,87mm
chp nhn c vi yu cu t ra ca anten GNSS, di y l kt qu m
phng trn phn mm ANSYS HFSS vi thng s anten nh sau: Wp = Lp =
43,91mm, L = 4,87mm, r1l = 27,09mm, w1l = 2.21mm, r2l
= 10mm, w2l = 6,1mm, = 4,4, h = 3,2mm.
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Hnh 5: Phn b in trng
IV. Kt lun
Anten thit k nh trn tha mn yu cu ca anten GNSS, c th thy rt
n gin trong vic ch to. Cc thng s k thut ca anten c ti u t
c yu cu k thut.
Trong gii hn ca bi bo ny ch dng li vic thit k cc anten vi di
phn cc trn, tip in n dng ng truyn vi di. Mc d cc tham s
k thut t yu cu ca anten phc v cho ng dng GNSS, nhng t s
trc ca anten vn cn ln so vi yu cu t ra cho anten phn cc trn, hiu
sut s dng ca anten cha cao. ci thin cc tham s k thut anten, c
th thay i cch thc tip in, phi hp trkhng, to phn cc, s dng lp
c hng s in mi ln hn.
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