Btl Anten- Vu Minh Hai DTV50
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Transcript of Btl Anten- Vu Minh Hai DTV50
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8/14/2019 Btl Anten- Vu Minh Hai DTV50
1/18
Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 1
LI M U
Trong nhng nm gn y, khoa hc cng ngh pht trin nh v bo trn
mi lnh vc vi hng lot nhng nghin cu, pht minh mi gp phn khngnh trong vic nng cao trnh sn xut v i sng ca con ngi. Mt trong
nhng lnh vc c nh gi l c trin vng nht v c coi l th mnh ca
Vit Nam hin nay phi k n vin thng, n lm cho con ngi xch li gn
nhau hn, lm cho khong cch a l khng cn ngha na.
ng gp vo s pht trin mnh m ni trn chng ta phi ni n s pht
trin ca cc thit b thu pht v kh nng truyn lan sng in t hin nay, bi l
hu ht cc h thng truyn dn thng tin, lin lc chng u s dng phng thctruyn lan sng in t l ch yu.
Cc thit b thu pht v chuyn tip sng in t gi chung l anten. Tu
theo iu kin cng tc, mc ch s dng cng nh kt cu ca cc h thng vin
thng m ta s dng nhiu loi anten khc nhau: anten chn t, anten khe, anten
mch di, anten gng, anten xon
Do nhu cu thng tin, lin lc, truyn ti d liu ngy cng cao nn cc
bng tn di sng di, sng trung dn dn b thay th bi cc bng tn di sngngn v cc ngn. Vi li th l kh nng bc x tt cc di sng ny cng vi
kt cu tng i n gin, d dng iu chnh v kt hp vi cc loi anten khc
to thnh mt h bc x m anten chn t l la chn ti u trong hu ht cc
thit b v tuyn in.
Trong bai t p l n nay, em xin c trnh bay v c tnh phng hng ca
chn t i xng nhm tm ra c gi tr gii hn di chn t sao cho hng
tnh ca n cn t cc i hng 090 .y l mt trong nhng hng bc
x quan trng ca anten trong vic thu pht sng in t.
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 2
Mc lc, bao gm IVphn :
I: GII THIU CHUNG V CHN T I XNG
c tnh phng hng ca anten chn t1.1. M hnh ton
1.2. Hm phng hng v th phng hng ca chn t i xng
II: T VN
III: GII QUYT VN
IV: A NH GIA , K T LUN VA H NG PHA T TRI N TI
1. anh gia , kt lun
2. H ng pha t trin tai
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 3
I. GII THIU CHUNG V CHN T I XNG
Chn t i xng l mt cu trc gm hai on vt dn c hnh dng tu
(hnh tr, hnh chp, elipsoit) c kch thc ging nhau, t thng hng trongkhng gian, v gia chng c ni vi ngun dao ng cao tn.
Chn t i xng l mt trong nhng ngun bc x c s dng kh ph bin
trong k thut anten.N c th xem nh l mt anten c lp hon chnh (anten
chn t i xng ),ng thi trong nhiu trng hp n cng l phn t kt cu
nhng anten phc tp.
1. c tnh phng hng ca anten chn t
1.1: M hnh ton
Coi chn t l tp hp ca nhiu dipol(I(z)=const) v kho xt trng vngxa.
Gi s chn t c di l, c t dc theo trc 0z, tm pha trng vi gc ta .
Ta im kho st l R ( , ). Khi kho st trng vng xa ta lun c R
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8/14/2019 Btl Anten- Vu Minh Hai DTV50
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 4
Theo quy c nh hnh v trn, gc c xc nh bi hnh chiu ca R
trn mt phng x0y v 0x
, cn gc c xc nh bi gc gia R
v 0z
, tc l
mt phng x0y c 090
+ Cng thc tnh cng trng bc x ca chn t i xng:
Ta c: E=
/ 2
/ 2
l
l
dE =2
/ 2
0
l
dE (1)
M dE=W2
i 1
Re
-ikRI(z)
dz
sin( ) (2)
Thay (2) vo (1) ta c:
E= 2/ 2
0
l
W2
i 1
Re-ikR I(z)
dz
sin( ) (3)
(4)
(5)
lk lk os( cos )-cos( )
12 2W 2 sin
ikR
c
E iIbH eR
(6)
*Trong :W: tr khngsng (W=120 ( ))Ib:bin dng in im bng sng
k: h s sng (k=2
)
l: chiu di ca chn t:bc sng
1.2.Hm phng hng v th phng hng ca chn t i xng-p dng nguyn l nhn th hm phng hng ta c:
f( ,)=fd( ,).fk( ,) (7)
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 5
Trong :fd( ,)=sin() :hm phng hng thnh phn
fk( ,)=
2
cos cos cos
2 2sin
kl kl
:l hm phng hng t hp
*Hm phng hng dng chun ha bin c dng:
F( ,)=
,
max( , )
f
f
(8)
+Vi di tng i ca chn t so vi bc sng l
1.44
Khi =900=>f(max)=(1-cos
2
kl)
Suy ra ( , ) ( , ). ( , )d k
F F F =
2
cos cos cos2 2
sin
sin 1 cos2
kl kl
kl
(9)
+ Vi di tng i ca chn t so vi bc sng l
>1.44(hm phng hng
khng cn cc i gc =900)
f( ,)=2
cos cos cos2 2
sin
kl kl
+ V hm phng hng dng chun ha bin c dng
F( ,)=
,
max( , )
f
f
* th phng hngng vi cc trng hpl
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 6
+ Xt trong mt s trng hp:
0l
: dipol in
0.5l
: chn t na sng
1l
: chn t ton sng
l
=1.25 v
l
= 1.44 ;
l
=1.5 ;
l
=2
*Gin phng hng trong h ta cc ng vi cc gi tr ca l/ :
Hnh a:l
0 Hnh b:
l
=0.5
Hnh c:l
=1 Hnh d:
l
=1.25
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 7
Hnh e:l
=1.44 Hnh f:
l
=1.5
Hnh g:l
=2
*Nhn xt: Hm phng hng anten cng ch ph thuc vo gc ,ngha l bc x
ca anten c hng tnh trong mt phng E v v hng trong mt phngH.
Hm phng hng ca anten chn t ng hng vi mt phng vunggc vi trc ca chn t (mt phng ).
Hm phng hng bc x bng khng ti =00hoc =1800. c tnh hng ch xc nh trong mt phng cha trc ca chn t v ph
thuc vo chiu di l.
*T cc th phng hng ta nhn thy:
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 8
Khi anten c di l/ nh, th phng hng chun ha c dng gnging th phng hng ca dipol in (hnh b), ch khc l n c
rng hp hn (so snh a vi b).iu ny c gii thch nh sau: - V trng bc x ca dy dn ti im kho st bng tng vecto ca trng
to bi cc dipol thnh phn (anten l tp hp ca cc dipole). Khi di
l/ rt nh, dng in mi im trn anten ng pha nhau. ng thi v
c th coi khong cch t cc dipol n cc im kho st bng nhau nn
trng bc x ca cc dipol ring r s ng pha v c cng i s vi
nhau. Bin trng bc x ca dy dn cc im trong khng gian u
tng ln mt s ln ging nhau so vi cng trng bc x ca mtdipol in ring r. V vy m th phng hng ca anten khng khc
so vi th phng hng ca dipol in.
- th phng hng ca n hp hn l do sai pha khong cch gia ccdipol thnh phn.
Khi tng dn di anten (trong gii hn vn m bo ng pha dng intrn anten, ngha l l/ 1) th th phng hng s hp dn li (hnh b,
c)
- Tht vys tng di anten trong gii hn ni trn s tng ng vivic tng s dipol ng pha sp xp theo ng thng. Cng trng
khu xa theo hng vung gc vi anten s bng tng i s cng
trng ca cc dipole in ring r, v theo hng ny khng c sai pha
khong cch. Bc x c tng cng theo hng = 90. Khi dch
chuyn im kho st khi hng ny s xut hin sai pha khong cch.
Cng trng ti im kho st trong trng hp ny s nh hn
trng hng = 90. Tng vecto s gim nhanh nu im kho st
cng dch chuyn xa hng = 90.
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 9
Khi tng di anten qa gii hn mt bc sng (l>) s xut hin khuvc dng in ngc pha. th phng hng c xu th hp li nhng
ng thi s xut hin cc cc i ph (hnh d,e,f,g). S xut hin cc cci ph l do bc x theo hng vung gc vi trc dy dn ca cc dipol
thuc khu vc dng in ngc pha s b trit tiu bi bc x ca cc dipol
thuc khu vc dng in mang du dng, v theo hng ny khng c sai
pha khong cch nhng sai pha dng in bng . Nu dch chuyn im
kho st khi hng = 90 th s xut hin gc sai pha khong cch ca
trng to bi cc dipol thuc hai khu vc ni trn.Ta c th tm c
hng m theo hng sai pha khong cch ca trng to bi haikhu vc dng in s bng . Tng sai pha ca trng s bng2 , ngha
l trng bc x to bi cc dipol thuc hai khu vc dng in ngc pha
s tr nn ng pha nhau, v hng s xut hin cc i ph.
Tip tc tng di dy dn th cng trng theo hng = 90 sgim (do nh hng bc x ca cc dipol c dng in ngc pha gy ra),
ng thi bin cc i ph s tng.
Khi l
=1.44 th cc i chnh bng cc i ph.
Khi l
=1.5 th cc i ph ln t cc i chnh.
Khi l
=2 trng bc x theo hng = 90 s hon ton b trit tiu, cn
cc cc i ph s tr thnh cc cc i chnh ca anten (hnh g).
Nh vy rng bp sng chnh trong c tnh phng hng ca chn tph
thucvo thng s l/
II: t vn
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8/14/2019 Btl Anten- Vu Minh Hai DTV50
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 10
Gi 3(hay 21/2) l rng bp sng chnh - l gc to bi hai hng m ti
cng sut bc x suy gim mt na so vi hng bc x cc i. Theo hnh v
ta cng thy rng trong khong bin i ca l
, t rt nh ( 0 ) n gi tr gii
hn, rng bp sng chnh 3( hay 21/2) cng thay i theo. Vy quy lut bin
i ca 3 theol
nh th no?Bi ton t ra l chng ta phi tm -c mi lin
h ( tc l tm hm 3=f( l
) ).
III: GII QUYT VN
Vi bi ton ny chng ta c th gii quyt c theo ba cch sau:
Biu din di dng th (phng php ny rt trc quan, thhin r rngs ph thuc 3vo
l
).
Biu din di dng bng (ta c th tra cu cc gi tr c th ca 3ng vimi gi tr ca
l
).
S dng chng trnh trong Matlab tra cu nhanh chng gi tr 3 khinhp bt k gi tr
l
no.
Ta s s dng cng c phn mm Matlab v ng cong biu din s ph
thuc ca rng bp sng chnh trong c tnh phng hng ca anten chn
t vo di tng i ca chn t so vi bc sng(L= l
).
Ta s trnh by 2 hng gii bi ton ny:
+Hng 1:Theo hng F( )=-3dB( hm phng hng suy gim 3dB)
+Hng 2:Theo hng F()=0.7071(hm phng hng suy gim na
cng sut)
Lnh v hng 1 Lnh v hng 2
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8/14/2019 Btl Anten- Vu Minh Hai DTV50
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 11
th hm 3=f( l
) c dng nh hnh v:
clear
clc
for i=1:1:144L=0.01*i;
F=0;
teta=90;
b=1-cos(pi*L);
while F>-3.0102
teta=teta-0.01;
t=teta*pi/180;
a=(cos(pi*L*cos(t))-
cos(pi*L))./sin(t);
f=abs(a./b);
F=20*log10(f);
end
l(i)=L;
teta3(i)=2*(90-teta);
end
plot(l,teta3)
grid on
xlabel('do dai cua chan tu so voi buoc
song')
ylabel(' gia tri goc teta3')
title ('do thi cua ham teta3')
clear
clc
for i = 1:1:144L= 0.01*i;
b = 1-cos(pi*L);
F = 1;
teta = 90;
while F > 0.7071
teta=teta-0.01;
t = teta*pi/180;
a=(cos(pi*L*cos(t))-
cos(pi*L))./(sin(t));
F=abs(a./b);
end
l(i)=L;
teta3(i)=2*(90-teta);
end
plot(l,teta3)
grid on
xlabel('l/lamda')
ylabel(' gia tri goc teta3')
title (' do thi ham teta3 )')
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8/14/2019 Btl Anten- Vu Minh Hai DTV50
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 12
0 0.5 1 1.44 1.620
30
40
50
60
70
80
90
100
l/lamda
gia
trigoc
teta3
do thi ham teta3 )
Trong matlab guide, ta c th lp trnh yu cu matlab v th, giao din nh
sau:
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 13
Hnh 3.1: l p trnh trong matlab guide biu din s phu thuc cua go c 3vo l/
+Biu din s ph thuc ca gc 3theol
nh trong bng sau:
di
(l/)
Gc 3 di (l/) Gc 3 di (l/) Gc 3
0.01 90.00 0.50 78.08 0.94 51.72
0.04 89.94 0.52 77.12 0.98 49.14
0.08 89.70 0.54 76.12 1.00 47.84
0.10 89.54 0.56 75.10 1.04 45.30
0.12 89.34 0.60 72.94 1.08 42.78
0.14 89.08 0.62 71.82 1.10 41.54
0.16 88.80 0.64 70.68 1.12 40.30
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8/14/2019 Btl Anten- Vu Minh Hai DTV50
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 14
0.18 88.48 0.66 69.52 1.14 39.08
0.20 88.12 0.68 68.32 1.16 37.88
0.24 87.28 0.70 67.12 1.18 36.680.26 86.80 0.72 65.90 1.20 35.50
0.28 86.28 0.74 64.64 1.24 33.18
0.30 85.74 0.76 63.38 1.25 32.62
0.32 85.14 0.78 62.12 1.28 30.92
0.34 84.50 0.80 60.84 1.27 31.48
0.36 83.84 0.82 59.54 1.28 30.92
0.37 83.48 0.84 58.24 1.30 29.82
0.40 82.38 0.88 55.64 1.34 27.64
0.44 80.78 0.90 54.34 1.36 26.58
0.46 79.92 0.91 53.68 1.40 24.50
0.48 79.02 0.92 53.02 1.44 22.48
Bng 1: Cc gi tr ca 3ng vil
thay i t 01.44
+nh gi:
Gi tr l/ Gc 3theo l thuyt Gc 3theo thc t
0.5 800 78.08
0
1.0 44 47.84
1.25 31 32.62
Bng 2: So snh kt qu gia thc t v l thuyt gc 3
+Lnh trong Matlab tra cu nhanh chng gi tr 3khi nhp bt k gi tr l
no.
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 15
Lnh v hng 1 Lnh v hng 2
clear
clcdisp('day la bai toan tim goc teta3 theo
huong suy giam 3 dB')
L=input('nhap L=')
F=0;
teta=90;
b=1-cos(pi*L);
while F>-3.0102
teta=teta-0.01;
t=teta*pi/180;
a=(cos(pi*L*cos(t))-
cos(pi*L))./sin(t);
f=abs(a./b);
F=20*log10(f);
end
disp('goc teta3 can tim la:')
disp(2*(90-teta))
clear
clcdisp('nhap vao gia tri do dai chan tu
theo buoc song :');
L= input('nhap gia tri L=');
b= 1-cos(pi*L);
F=1;
teta=90;
while F> 0.7071
teta= teta-0.01;
t=teta*pi/180;
a= (cos(pi*L*cos(t))- cos(pi*L))./sin(t);
F= abs(a/b);
end
disp('goc teta 3 can tim la=');
disp(2*(90-teta));
Tuy nhin, nu s dung matlab thng thng , mi khi cn xac i nh 1 gi tr 3ta
phi copy dng lnh v paste vo ca s comman , ho c phai n F 5 chy li m-
file o 1 ln. iu o khng c tin l i khi ta c n tra c u nhanh cac gia tricu a
gc 3.Matlab guide acho ta l p trnh giao din tnh toan 1 cch d dng hn.
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 16
Hnh 3.2: l p trnh trong matlab guide tnh goc 3khi nh p vao l/
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 17
IV: a nh gia , kt lun va h ng pha t trin ta i:
1. anh gia , kt lun:
T th biu din s ph thuc 3= lf
ta c th nhn thy mt cch
trc quan rng khi gi trl
tng th rng bp sng chnh gim.
Kt qu cngtng t khi ta biu din bng bng , hay mt hm . Vi bngtra c u lp c vaham l p trnh trong matlab guide ta c th tra cu
mt cch d dng cc gi tr ca 3khil
thay i t 0 n gi tr ti hn.
So snh vi cc s liu c vi kt qu tnh ton c ta nhn thy giachng c s sai lch. R rng l kt qu tnh ton c trn c
chnh xc cao hn. Mc d kt qu a ra trong cc ti liu c sai s l
khng ng k.
Vi vic tm ra gi tr ti hn ( l
)gh c tnh hng ca chn t vn t
cc i gc = 90 th vic thit k ra cc anten chn t c kh nng bc
x tt s tr nn thun tin, d dng hn.
Vic phi ghp anten chn t vi nhau s cho hiu qu cao nht khita bitc hng tnh ca mi anten, ta s to ra mt h thng thu pht sng in
t p ng yu cu ngy cng cao ca k thut anten.
2. H ng pha t trin bi tp ln:
- Vi ti ny chng ta c th xy dng c tp hp cc anten chn t vi
di thch hp, sao cho n c kh nng bc x tt nht sng in t.
- V thi gian lm bi tp ln c hn nn em ch tm hiu c 1phn rt nho
trong l p trnh matlab guide nn ban l p trnh matlab guide con rt th s ,cha
thhin c ht tnh trc quan ca bi tp ln . hoan thin hn v mang
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Bi Tp Ln Mn L Thuyt V K Thut Anten
Sinh vin: V Minh Hi Lp: TV50-H 18
l p trnh , h ng pha t trin cu a bai t p l n nay lal p trnh bng matlab guide
ho c bng cc ngn ng khc nh Visual basic , C+. v i hoa e p hn, trc
quan hn, kt h p thc hin c nhiu vi c m t lu c nh v a xac i nh cgc 3khi nh p vao L t ban phm, v a vera vachra c goc 3 o trong toa
cc cung nh trong khng gian 3D.