Backup of Truyen Song Va Anten Sua

HC VIN CNG NGH BU CHNH VIN THNG

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Ging vin: Nguyn Vit Minh

in thoi/E-mail: (090) 406-2112/[email protected]

B mn: V tuyn Khoa Vin thng 1

Hc k/Nm bin son: II/2010

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www.ptit.edu.vn GING VIN: NGUYN VIT MINH

B MN: V TUYN KHOA VIN THNG 1 Trang 2

Tn hc phn:

Truyn sng v anten (Radiowave Propagation and Antenna )

Tng lng kin thc:

60 tit + L thuyt: 50 tit; Thc hnh: 6 tit; Bi tp: 4 tit

Mc tiu hc phn:

Gii thiu cc khi nim, cc biu thc ca qu trnh truyn lan sng v tuyn.Nghin cu s truyn lan ca sng cc ngn trong mi trng thc

Gii thiu l thuyt chung v anten, cc anten nguyn t. Nghin cu hot ngca chn t i xng, cc loi anten trong thng tin v tuyn

GII THIU MN HC

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Ni dung hc phn:

Chng 1: Cc vn chung v truyn sng + Tnh cht ca sng in t; Cc phng php truyn lan sng; Qu trnh

truyn lan sng trong khng gian t do

Chng 2: Truyn lan sng cc ngn + Truyn lan trong iu kin l tng; Truyn lan trong iu kin thc; Phadinh

v bin php chng

Chng 3: Truyn lan sng trong thng tin di ng + c tnh knh truyn sng di ng; Cc m hnh knh v tuyn di ng; nh

gi c tnh knh

Chng 4: L thuyt chung v anten + Cc tham s ca anten; Cc ngun bc x nguyn t; Nguyn l ca anten

thu

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Ni dung hc phn:

Chng 5: Anten chn t + Bc x ca chn t i xng, anten chn t n, cc loi anten s dng

nhiu chn t

Chng 6: Anten gc m + Nguyn l bc x mt, anten loa, anten gng parabol, anten khe , anten vi

di

Chng 7: K thut anten + Tng hp th phng hng anten, m rng di tn lm vic, cp in v

phi hp tr khng anten

Chng 8: Anten trong thng tin v tuyn tin tin + Anten thng minh, k thut a anten, anten cho h thng v tuyn bng siu

rng.

GII THIU MN HC

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Ti liu tham kho:

[1] Nguyn Vit Minh, Truyn sng v Anten, Bi ging, Hc vin cng ngh BCVT, 6/2010

[2] Phan Anh, Trng in t v truyn sng, NXB i hc Quc gia, 2002

[3] Phan Anh, L thuyt v k thut anten, NXB KHKT, 2004

[4] Robert E.Collin, Antennas and Radio wave propagation, McGraw Hill

[5] N. Blaunstein, Radio propagation in cellular network, Artech House

[6] Frank Gross, Smart antenna for wireless communication, McGraw Hill

GII THIU MN HC

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nh gi hc phn

Chuyn cn: 10% (ngh 2 tit tr 1 im) (Ngh t 16 tit tr ln khng c d thi ht mn)

Kim tra: 15% (2 bi, vng nhn im 0)

Thc hnh: 15% (1 bi, vng nhn im 0) (Vng thc hnh khng c d thi ht mn)

Thi kt thc hc phn: 60%

GII THIU MN HC

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CC VN CHUNG V TRUYN SNG

CHNG 1

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Ni dung chng 1: (6)

1.1 Gii thiu

1.2 Tnh cht c bn ca sng in t

1.3 Phn loi sng in t

1.4 Phng thc truyn lan sng in t

1.5 Biu thc truyn lan sng trong khng gian t do

1.6 H s suy gim

1.7 Cu hi v bi tp

NI DUNG

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H thng vin thng

1.1 Gii thiu

Hnh 1.1. M hnh h thng vin thng

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Truyn dn v tuyn (Radio Transmission)

Mi trng truyn dn + Khng gian (bu kh quyn)

Phng tin truyn dn + Sng in t

1.1 Gii thiu

Hnh 1.2. Mi trng truyn dn v tuyn

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Khi nim

Sng in t l qu trnh bin i nng lng tun hon gia in trng v t trng lm cho nng lng in t lan truyn trong khng gian.

c im

Sng in t c hai thnh phn: + in trng : E (V/m)

+ T trng : H (A/m)

y l hai i lng vect (c phng, chiu, ln), c quan h mt thit vi nhau trong qu trnh sng truyn lan trong khng gian

Cc ngun bc x sng in t thng c dng sng cu hoc sng tr, khi nghin cu ta chuyn v dng sng phng

1.2 Tnh cht c bn ca ST

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Biu thc quan h gia cc thnh phn

Nghin cu vi sng in t phng, truyn lan trong mi trng in mi ng nht v ng hng

Biu din sng in t bng h phng trnh Maxoel dng vi phn:

+ Gii h


yx

yx

HE

t z

HE

z t

: H s in mi

: H s t thm

z: C ly truyn sng

t: Thi gian

(1.1)

x 1 2

y 1 2

E F

G

z zt F t

v v

z zH t G t

v v

F, G: Cc hm sng

v: Vn tc truyn lan ca sng (m/s)

vz 1

t .

(1.2)

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Tr khng sng, Z: Biu th nh hng ca mi trng ti qu trnh truyn sng

+ Vi khng gian t do


(1.3)

(1.4)

ZE

H

97

0 0

8

0 0

00

0

v

104 .10 H / m ; F/ m36

13.10 m /s c

Z 120

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Bin i Fourier biu din sng in t di dng tn hiu iu ha

+ Nhn xt: Khi sng truyn lan, ti mi im thnh phn t trng v in

trng c pha nh nhau v bin lin h qua cng thc (1.5)


(1.5)

x m m

m my

E E

H

zcos t E cos t kzv

E Ezcos t cos t kzvZ Z

2 .f 2 .f 2k

v c f .

k: H s sng, c trng cho s thay i pha ca sng

BI




Thng lng nng lng ca sng in t, S

+ Thng lng nng lng trung bnh

Sng in t ngang, TEM


(1.6) [ ]S E H

2

m m mavg e

1 E .H ES R E H

2 2 2.Z

2W/m

Hnh 1.3. Sng TEM

(1.7)

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Mt sng + Sng in t lan ta trong khng gian, ti mi im sng in t c c

trng bi pha v cng

Mt sng: L qu tch nhng im trong khng gian ti sng in t c phanh nhau v cng bng nhau

Hai dng mt sng c bit: Mt sng phng, mt sng cu

Qu trnh truyn lan sng in t: Tnh cht sng + Sng in t bc x ra khng gian di dng v s cc mt sng lin tip + Ngun bc x sng in t ch ng vai tr l ngun bc x s cp + Qu trnh sng truyn lan, cc mt sng c to ra ng vai tr l ngun bc

x th cp to ra cc mt sng tip sau n


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Phn cc sng

KN: Trng phn cc l trng in t vi cc vecto E v H c th xc nhc hng ti thi im bt k (bin i c tnh quy lut)

Ngc li l trng khng phn cc (bin i ngu nhin trong khng gian)

Mt phng phn cc: L mt phng cha vec t E v phng truyn lan sng(vecto Z)

Phn loi + Phn cc ng thng: Mt phng phn cc c nh khi sng truyn lan

- Phn cc ng: Vecto E vung gc vi mt phng nm ngang - Phn cc ngang: Vecto E song song vi mt phng nm ngang

+ Phn cc quay: Mt phng phn cc quay xung quanh trc ca phng truyn lan - Phn vc trn: Khi vecto E quay, bin khng thay i (v ln ng trn) - Phn cc elip: Khi vecto E quay, bin thay i lin tc v ln ng elip Quayphi: Quay thun chiu kim ng h Quay tri: Quay ngc chiu kim ng h


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Phn cc sng


Hnh 1.4. Cc dng phn cc sng

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Phn chia sng in t + Da vo tnh cht vt l, c im truyn lan: Chia thnh cc bng sng


Hnh 1.5. Cc bng sng

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Phn chia sng in t + Da vo tnh cht vt l, c im truyn lan: Chia thnh cc bng sng


Bng 1.1. Cc bng sng

Tn bng tn (Bng sng) K hiu Phm vi tn s

Tn s v cng thp ULF 30 - 300 Hz

Tn s cc thp ELF 300 - 3000 Hz

Tn s rt thp VLF 3 - 30 kHz

Tn s thp (sng di) LF 30 - 300 kHz

Tn s trung bnh (sng trung) MF 300 - 3000 kHz

Tn s cao (sng ngn) HF 3 - 30 MHz

Tn s rt cao (sng mt) VHF 30 - 300 MHz

Tn s cc cao (sng decimet) UHF 300 - 3000 MHz

Tn s siu cao (sng centimet) SHF 3 - 30 GHz

Tn s v cng (sng milimet) EHF 30 - 300 GHz

Di milimet 300 - 3000 GHz

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Phn chia sng in t

Tnh cht quang hc + Sng nh sng cng l sng in t, bng tn th gic cm nhn c, khi

nghin cu sng in t thng s dng sng nh sng cho trc quan

+ Cc tnh cht quang ca sng nh sng cng ng cho sng in t - Truyn thng

- Phn x, khc x

-

ng dng cc bng sng + LF, MF: Pht thanh iu bin ni a, thng tin hng hi

+ HF: Pht thanh iu bin c ly xa

+ VHF, UHF: Pht thanh iu tn (66 108 MHz), truyn hnh, viba s bng hp, h thng thng tin di ng mt t

+ SHF: Viba s bng rng, thng tin v tinh

+ EHF: Thng tin v tr


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Bu kh quyn


Hnh 1.6. Phn tng bu kh quyn

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Sng t

Nguyn l + B mt tri t l mi trng dn khp kn ng sc in trng

+ Ngun bc x nm thng ng trn mt t, sng in t truyn lan dc theo mt t n im thu

c im + Nng lng sng b hp th t i vi tn s thp, c bit vi mt t m,

mt bin ( dn ln)

+ Kh nng nhiu x mnh, cho php truyn lan qua cc vt chn

+ S dng cho bng sng di v trung vi phn cc ng


Thu Pht

A B

Hnh 1.7: Qu trnh truyn lan sng t (sng b mt)

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Sng khng gian

Nguyn l + Anten t cao trn mt t t nht vi bc sng

+ Sng in t n im thu theo 2 cch - Sng trc tip: i thng t im pht n im thu

- Sng phn x: n im thu sau khi phn x trn mt t (tha mn L PX)

c im + Chu nh hng nhiu ca iu kin mi trng

+ Ph hp cho bng sng cc ngn, l phng thc truyn sng chnh trong thng tin v tuyn


Hnh 1.8: Truyn lan sng khng gian

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Sng tng in ly (sng tri)

Nguyn l + Li dng c tnh phn x sng ca tng in ly vi cc bng sng ngn

+ Sng in t phn x s quay tr v tri t

c im + Khng n nh do s thay i iu kin phn x ca tng in ly


Hnh 1.9: Truyn lan sng tng in ly

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Sng t do (sng thng)

Nguyn l + Mi trng truyn sng l tng (ng tnh, ng hng, khng hp th)

+ Sng truyn lan trc tip n im thu theo mt ng thng

c im + Mi trng ch tn ti trong v tr, s dng cho thng tin v tr

+ Bu kh quyn tri t trong mt s iu kin nht nh c coi l khng gian t do


Hnh 1.10: Truyn lan sng t do

Mc tiu trong v tr

Trm trn mt t

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Tng kt:


Hnh 1.11: Cc phng thc truyn lan sng v tuyn

Sng t do

Sng tri

Sng t Mt t

Khng gian t do

Tng in ly

Tng bnh lu

Tng i lu

Sng khng gian

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Mt cng sut, cng in trng

Bi ton + Khng gian t do

+ Ngun bc x v hng, cng sut bc x P1 (W), t ti im T

+ Xt trng ti im R cch T mt khong r (m)

Gii quyt + Ngun bc x s bc x v s mt sng cu lin tip c tm ti T

+ Xt mt cu i qua R c bn knh l r. Thng lng nng lng (mt cng sut) ti mt cu:


12 2SP

4 .r

2W/m

1 m2 r

T R

(P1-W)

(1.8)

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Mt cng sut, cng in trng Theo l thuyt trng

+ Cng in trng ti im thu


(1.9) h h2 h h h

0

2

h2

E ES E

ES

.H ; HZ 120

120

Eh, Hh: Cng in trng, t trng hiu dng

Z0: Tr khng sng ca khng gian t do

1h 2

1h

E30P

r

60.PE E . 2.cos t kr .cos t kr

r

V/m

V/m

(1.10)

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Mt cng sut, cng in trng + S dng anten c hng

- Tp chung nng lng gip tng cng sut ti im thu

- c trng bi h s tnh hng D1


(1.11)

'

1 21 2 1 1'

1 2

1 11 12 2

( constant); ( constant)

60. ... . .

4 .

P PD P D P

P P

P DP DS E cos t k r

r r

Hnh1.13: Ngun bc x c hng

R; P2

bc x v hng

T; P1

(P1)

R; P2

(P2)

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Cng sut bc x ng hng tng ng (Equivalent Isotropic Radiated Power - EIRP)

L cng sut bc x tng ng ca mt anten v hng c th t c cng trng ti im thu bng vi khi dng anten c hng


G1: H s tng ch anten pht (GT)

1: Hiu sut anten pht (T)

P1: Cng sut bc x anten pht (P)

Pa1: Cng sut a vo anten pht (PT)

(1.12)

1 1

1 1

11 1 1 1

1

1 1

.

; .

. .

dB dB

a

a T T

EIRP P D

EIRP P D dB

GD P P

EIRP P G P G

(1.13)

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Cng sut nhn c trn anten thu, P2 + L tch gia mt cng sut ti im thu, S2 v din tch lm vic ca anten

thu, A

+ Trng hp s dng anten gng parabol trn xoay vi h s tnh hng D2

+ Cng sut thc t u ra anten thu


Ah: Din tch hiu dng ca anten thu

2: Hiu sut anten thu

(1.15)

2 2.P S A

2 22

22

22

2 1 12 1 1 22

.. .;

4 4.

. .. . . . W

4. 4. . 4. .

Dd dA D A

D P DP P D D

r r

2 2 2. ; .a h hP S A A A (1.16)

(1.14)

d: ng knh ming anten

: Bc sng cng tc

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Tn hao truyn sng, L + Xc nh bng t s gia cng sut bc x ca my pht vi cng sut anten

thu nhn c

+ Tn hao truyn sng trong khng gian t do gy ra bi s khuch tn tt yu ca sng theo mi phng, cng sut thu c ch l mt phn nh. Tn hao ny gi l Tn hao khng gian t do, Ltd

+ Trng hp s dng anten v hng, gi l tn hao c bn trong khng gian t do, L0


1

2

PL

P

2

1 2

4 . 1.

.td

rL

D D

(1.17)

(1.19)

(1.18)

2

0

0

1 2

4 .

20lg 20lg 92,45

20lg 20lg 92,45 10lg 10lg

GHz km

td GHz km

rL

L f r dB

L f r D D dB

(1.20)

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H s suy gim, F

Mi trng thc t c nhiu yu t nh hng ti qu trnh truyn sng, nh hng ti cng sut thu

Cc nh hng ca mi trng thc ln qu trnh truyn sng c biu din qua h s suy gim: F

Trong mi trng thc

1.6 H s suy gim

2

1 2

4 . 1.

. .td

rL

F D D

(1.24) 1 220lg 20lg 92,45 10lg 10lg 20lgtd GHz kmL f r D D F dB

21 12 2

..

4 .

P DS F

r 1hE

30P.F

rV/m

(1.23)

(1.22) (1.21)

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Bi tp chng 1

1.7 Cu hi v bi tp

6. Mt tri c cng sut bc x theo mi hng khong 3,85.1020 W, khong cch nh nht t qu

t n mt tri l 147.098.090 km (vo thng ging) v ln nht l 152.097.650 km. Tnh:

- Mt cng sut bc x cc tiu v cc i ca mt tri ln b mt qu t?

- Mt cng sut bc x mt tri khong cch trung bnh v t l phn trm sai s ca

bc x cc i v cc tiu so vi gi tr trung bnh?

7. Mt my pht c cng sut 3 W, anten pht c h s khuch i l 30 dBi. c ly 40 km t

mt anten thu c din tch hiu dng l 3,5 m2, hiu sut lm vic 100%. Tnh cng sut sng

mang nhn c anten thu.

(a) 0,164.10-5 W; (b) 0,164.10-4 W; (c) 0,154.10-5 W ; (d) 0,154.10-4 W

8. Xc nh cng sut my pht cn thit thc hin tuyn thng tin c cc iu kin: c ly

thng tin 50 km, tn s cng tc 2GHz, h s khuych i ca anten thu v anten pht l 30 dBi,

cng sut anten thu nhn c l 10-6W.

(a) 1,63W; (b) 2,63W; (c) 3,63W; (d) 4,63W

9. Mt my pht c cng sut 50 W. Biu din cng sut my pht sang n v dBm v dBW?

(a) 15 dBW v 45 dBm; (b) 16 dBW v 46 dBm; (c) 17 dBW v 47 dBm; (d) 18dBW v 48 dBm

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Bi tp chng 1

1.7 Cu hi v bi tp

10. Cng sut bi 9 c cp cho anten v hng lm vic vi sng mang c tn s 900 MHz,

tm cng sut thu (tnh theo dBm) ti im cch anten pht mt khong 10 km. Gi s anten thu c

h s khuch i l 2 v sng truyn trong khng gian t do.

(a) - 45,5 dBm; (b) - 51,5 dBm; (c) - 55,5 dBm; (d) - 61,5 dBm

11. S liu nh bi 9 v 10, tnh bin cng in trng hiu dng ti im t anten thu.

(a) 2,9 mV/m; (b) 3,9 mV/m; (c) 4,9 mV/m; (d) 5,9 mV/m

12. Tnh tn hao khi truyn sng trong khng gian t do (theo dn v dB) bit c ly truyn sng 50

km, tn s cng tc 2 GHz, vi anten v hng.

(a) 132,5 dB; (b) 135,5 dB; (c) 142,5 dB; (d) 145,5 dB

13. S liu nh bi 12, nu c hai anten c h s khuych i l 30 dBi th tn hao l bao nhiu?

(a) 72,5 dB; (b) 75,5 dB; (c) 82,5 dB; (d) 85,5 dB

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Bi tp chng 1

1.7 Cu hi v bi tp

14. Mt ngun v hng c cng sut bc x 100W. Mi trng truyn sng l khng gian t do.

Hy xc nh:

a, Mt cng sut ti im cch xa ngun 1000 m.

(a) 6,96 W; (b) 6,96 mW; (c) 7,96 W; (d) 7,96 mW

b, Mt cng sut ti im cch xa ngun 20 km.

(a) 19,9 pW ; (b) 19,9 W ; (c) 20,9 pW; (d) 20,9 W

15. Xc nh cng in trng hiu dng ti im thu vi cc gi thit cho trong bi 14.

(a) 44,7 mV/m v 1,74 mV/m; (b) 44,7 mV/m v 2,74 mV/m; (c) 54,7 mV/m v 1,74 mV/m; (d)

54,7 mV/m v 2,74 mV/m

16. Xc nh mt cng sut ti im cch anten 30 km ca mt anten c cng sut bc x 5 W

v h s khuch i ca anten l 40 dBi.

(a) 4,42 pW; (b) 4,42 W; (c) 5,42 pW; (d) 5,42 W

17. Mt anten pht c h s khuych i 30 dBi, hiu sut lm vic 60%. c cng in

trng hiu dng ti im thu cch anten pht 100 km bng 3,46 mV/m th cn phi a vo anten

cng sut l bao nhiu? Vi iu kin sng truyn trong khng gian t do.

(a) 3 W; (b) 3,5W; (c) 4 W; (d) 5 W

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TRUYN LAN SNG CC NGN

CHNG 2

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Ni dung chng 2: (5)

2.1 Tng Qut

2.2 Truyn lan trong gii hn nhn thy trc tip vi iu kin l tng

2.3 nh hng ca cong tri t

2.4 nh hng ca a hnh

2.5 nh hng ca tng i lu

2.6 Cu hi v bi tp

NI DUNG

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c im truyn lan sng cc ngn

Bc sng t 1mm n 10m (30MHz 300GHz): L sng siu cao tn (RF Radio Frequency)

Phng php truyn + Tn s cao nn khng th phn x trong tng in ly (i xuyn qua)

+ Bc sng ngn nn kh nng nhiu x km, b hp th mnh bi mt t

+ Phng php truyn sng khng gian: L ph hp nht - Tn x tng i lu

- Siu khc x tng i lu

- Truyn lan trong gii hn nhn thy trc tip

2.1 Tng qut

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Tn x tng i lu + Tn ti cc vng khng gian khng ng nht trong tng i lu

+ Sng i vo trong vng khng ng nht s khuych tn theo mi hng

Li dng truyn sng n im thu

+ c im: Khng n nh do vng khng ng nht lun thay i

2.1 Tng qut

Hnh 2.1: Tn x tng i lu

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Siu khc x tng i lu + Ch s chit sut N gim theo cao.

+ Khi tc gim t dN/dh < -0,157 (m-1

) Tia sng c bn knh cong ln hn cong tri t nn quay tr li mt t : Siu khc x

Li dng truyn sng n im thu sau khi phn x nhiu ln trn mt t

+ c im: Khng n nh do min siu khc x lun thay i

2.1 Tng qut

Hnh 2.2: Siu khc x tng i lu

1

2

3

4 5 4

5

4

gh

h0 A

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Truyn lan trong gii hn nhn thy trc tip + Hai anten thu v pht phi c t cao trn mt t trnh b che chn bi

cc vt cn trn ng truyn hay cong ca tri t

+ Sng truyn t pht n thu trong min khng gian nhn thy trc tip gia hai anten

+ c im: t ph thuc vo iu kin thin nhin, s dng ph bin

2.1 Tng qut

Hnh 2.3 Truyn lan trong gii hn nhn thy trc tip

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TRUYN SNG V ANTEN



S tuyn thng tin

Kho st qu trnh truyn lan sng vi iu kin l tng + Mt t l bng phng, khng c vt cn trn ng truyn

+ Kh quyn ng nht, ng hng v khng hp th

+ Anten t cao trn mt t t nht vi bc sng cng tc ()

S truyn lan sng


Tia 2

Tia 1

C

B

A

ht

hr

r

Hnh 2.4 M hnh truyn sng vi iu kin l tng

Sng n im thu theo hai ng:

+ Sng trc tip: i trc tip t pht

n thu

+ Sng phn x: n thu sau khi phn

x t mt t (ch c mt tia tha mn

nh lut phn x)

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TRUYN SNG V ANTEN



Cng in trng ti im thu

Tng hp cng trng hai sng thnh phn (giao thoa)

+ Cng trng do tia trc tip

+ Cng trng do tia phn x


R 1 2

T1T kW j t

1

1 km

T2T kW j t k r

2

2 km

E

E

E E E

245. P Ge

r

245. P GR e

r

mV/m

mV/m

r1 : on ng i ca tia ti trc tip; r2 : on ng i ca tia phn x

r: hiu s ng i ca hai tia r = r1-r2; k : h s sng (= 2/)

R : h s phn x phc t mt t: jR Re , R: m un, gc sai pha

GT1 v GT2: h s khuch i ca anten pht theo hng tia trc tip v tia phn x

(2.1)

(2.2)

(2.3)

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TRUYN SNG V ANTEN




Do chiu cao anten hT, hR

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TRUYN SNG V ANTEN



Cng in trng ti im thu + t = + k.r: Gc sai pha ton phn. Chuyn dng hm m sang hm

lng gic

+ Cng in trng tng ti im thu

+ H s suy gim trong trng hp mt t phng


21 . 1 .cos .sin 1 .cos .

.sin1 .cos

j jR e R jR R R e

RtgR

2

TT kW j t

km

TT kW 2

h

km

2

E

E

245. P G . 1 2R cos R.e

r

173. P G. 1 2R cos R

r

F 1 2R cos R F 1 R F 1 R

mV/m

mV/m

(2.7)

(2.8)

(2.9)

(2.10)

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TRUYN SNG V ANTEN




Vi tuyn xc nh: hT, hR, , , c th xc nh c ly thng tin r c h s suy gim t cc tr

+ Cc i ti ( + k.r) = 2n. vi n = 1,2,

+ Cc tiu ti ( + k.r) = (2n + 1). vi n = 1,2,


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TRUYN SNG V ANTEN



Cng in trng ti im thu + Hiu s ng i gia hai tia


B

B

hr -ht

Tia 2

Tia 1

C

A

ht

hr

hr +ht

r

hr

22 2 2

1 r t

2 22 ' 2

2 t r

2 22 2 2 12 1 2 1 2 1

2 1

t r

r AB h h r

r AB h h r

r rr r r r . r r r

r r

2h hr m

r

(2.11)

Hnh 2.5 Xc nh hiu s ng i gia hai tia

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TRUYN SNG V ANTEN




Do r >> hT, hR gc ti tia phn x rt ln ( 900) R 1; 180

0

+ Cng thc hp l ha

+ Cng thc giao thoa n gin


2

2T R

T R T R

T m R m

km m

TT kW T m R mh

km mkm

F 1 2R cos R

4 .h .hF 1 2R cos Rr.

4 .h .h 2 .h .hF 2 2cos 2. sinr. r.

0,36.h .hF 2. sin

r .

346. P .G 0,36.h .hE . sin mV / m

r .r

(2.12)

(2.13)

(2.14)

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TRUYN SNG V ANTEN




Xc nh im giao thoa t cc tr + Cc i

+ Cc tiu


T R T R

T R

T Rn _ max

2 .h .h 2 .h .hsin 1 sin 1r. r.

2 .h .h 2n 1 . n 0,1,2,...r. 2

4.h .hr m

2n 1 .

T R T R

T Rn _ min

2 .h .h 2 .h .hsin 0 n 1 . n 0,1,2,...r. r.

2.h .hr m

n 1 .

(2.15)

(2.16)

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TRUYN SNG V ANTEN




Cng thc Vvedensky + Vi sin() (rad) khi < 20

0, nn

+ Cng thc Vvedensky xc nh cng in trng ti c ly


T R

T R

TT kW T m R m

h 2

km m

r.h .h18

4 .h .hF.r

2,18. P .G .h .hE mV / m

r .

T R18.h .hr

(2.18)

(2.17)

(2.19)

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TRUYN SNG V ANTEN



S tuyn thng tin khi k n cong tri t

nh hng ca cong tri t + Hiu s ng i gia sng trc tip v sng phn x thay i

+ im phn x li nn c tnh tn x H s phn x nh + Hn ch tm nhn trc tip gia anten thu v pht


A

B

A1 B1 C

O

a

hr ht

ht hr

Hnh 2.7 M hnh truyn sng trn mt t cu

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TRUYN SNG V ANTEN



C ly nhn thy trc tip, cng in trng ti im thu

C ly nhn thy trc tip r0 + L c ly ln nht c th nhn thy c vi anten c cao ht, hr

+ Cng thc thc nghim

(r0 = r, c ly dc theo mt t)


O

hr ht

A B

a

ro

C

0

2 2 2

t t t t t

2 2

r r r

0 t r

0 t m r m

r AC CB

AC a h a 2a.h h 2a.h h a

CB a h a 2a.h h a

r 2a. h h m

r 3,57 h h km

(2.20)

(2.21)

Hnh 2.8 C ly nhn thy trc tip

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TRUYN SNG V ANTEN



C ly nhn thy trc tip, cng in trng ti im thu

Cng in trng + Qu trnh truyn sng c ly nh hn c ly nhn thy trc tip

- Tng t nh mt t phng, chiu cao anten xc nh bng chiu cao gi nh : ht, hr

- Gi tr chiu cao anten gi nh xc nh bng h s b m (tra theo bng hoc th - ph thuc h a l)


' '

t r t r

t r

t r

TT kW t m r m

h 2

km m

E

h .h m.h .h

2.m.h .hr m

r

4 .m.h .hF

.r

2,17 P G .m.h .hmV / m

r .

(2.22)

(2.23)

(2.24)

(2.25)

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TRUYN SNG V ANTEN



g gh ca tri t (tia phn x)

nh hng gh ca tri t + Hin tng tn x

+ Tiu chun Rayleigh

Khi tiu chun Rayleigh tha mn

s phn x sng khng c tnh tn x

Mt t coi l phng

2.4 nh hng ca a hnh

h m8sin

B

B

C

C

A

A

h

Tia B

Tia A Mt sng 1

Mt sng 2

h: cao ca mt t phng gi nh

so vi mt t thc

: Gc ti ti im phn x

(2.26)

Hnh 2.10 M hnh tiu chun Rayleigh

Hnh 2.9 Mt ct ngang a hnh thc

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TRUYN SNG V ANTEN



Nguyn l Huyghen, min Fresnel (tia trc tip)

Nguyn l Huyghen + Nhn xt

- Bn cht in t ca sng nh sng

- Tnh cht sng ca sng in t khi truyn lan

+ Nguyn l: Mi im nm trn mt mt sng do mt ngun bc x sng in t s cp gy ra s tr thnh ngun bc x th cp mi. Ngun bc x th cp mi ny li to ra cc mt sng th cp mi khc. Nh vy trng in t ti mt im trong khng gian do mt ngun bc x s cp sinh ra s do ton b vng khng gian bao quanh ngun bc x s cp gy ra.

2.4 nh hng ca a hnh

S r

A

M

Hnh 2.11: Xc nh trng theo nguyn l Huyghen

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TRUYN SNG V ANTEN




Nguyn l Huyghen

+ ngha - Qu trnh truyn sng in t t im pht n im thu khng phi ch theo

mt tia m cng trng ti im thu l do ton b min khng gian bao quanh im pht gy ra

- C th xc nh cng trng ti mt im bt k trong khng gian khi bit mt trng ca mt sng to ra n.

2.4 nh hng ca a hnh

C

A

A

B

B

Hnh 2.12. Biu din nguyn l Huyghen trong khng gian t do

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TRUYN SNG V ANTEN




Min Fresnel + Xy dng min Fresnel

+ Khi nim

2.4 nh hng ca a hnh

Nn

r1

A B

Nn

N0

r2

N0

N1 N2

N4

+ + + + +

+ +

+ +

+

+

+ + +

+

+

+

+

+

+

+

+ +

+

+

+

+

-

- - -

-

-

- - -

- -

-

- -

-

-

-

-

N3

N1

N1

+ Ngun pht A, im thu B, AB = r

+ Dng mt sng i qua im N0 + Dng mt nn trn xoay trc BN0,

ng sinh l: (BN0 + n./2), ct mt

sng Nn (n = 1,2,3 )

+ Min Fresnel th n (Fn) l vng khng gian c

gii hn bi qu tch cc im m hiu s gia tng

khong cch t im ny n im pht v im thu

vi khong cch gia hai im thu pht l hng s c

gi tr bng n ln na bc sng cng tc.

n nAN N B AB n. 2 + Min Fresnel c dng elip trn xoay nhn hai im thu

v pht lm tiu im, c bn knh l bn

(2.27)

Hnh 2.13: Nguyn l cu to min Fresnel trn mt sng cu

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TRUYN SNG V ANTEN




Min Fresnel + Tnh bn knh min Fresnel n, bn

+ Cng thc hp l ha

2.4 nh hng ca a hnh

n n 1 2

2 22 2 n n

n 1 n 1 1 n 12

1 1

2 22 2 n n

n 2 n 2 2 n 22

2 2

2 2

n n1 2 1 2

1 2

1 2

1 2

1(km) 2(km)

1 2 GHzkm

AN BN r r n.2

b bAN r b r . 1 r b r

r 2r

b bBN r b r . 1 r b r

r 2r

b br r r r n.

2r 2r 2

r .rb .n. m

r r

r .r .nb m

r r .f

n

n

=

= 17,32.

(2.28)

(2.29)

Hnh 2.14: Xc nh bn knh min Fresnel

b1max

B A

Hnh 2.15: Vng tham gia vo qu trnh

truyn lan sng

B

Nn

A

bn

S0

N0

r1 r2

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TRUYN SNG V ANTEN




Min Fresnel + Chng minh c rng: Cng trng ti im thu ch yu c gy ra

bi vng khng gian nm trong khong mt na min Fresnel th nht (0,6b1). Tng cng trng do cc im nm ngoi min ny gy ra ti im thu s b tr cho nhau v trit tiu do pha ca chng ngc nhau. y l gii hn ca vng truyn sng trong phm vi nhn thy trc tip.

+ ngha - Qu trnh truyn sng v tuyn gia hai anten thu v pht khng phi ch theo

mt tia, cng khng phi do ton b min khng gian m ch l vng khng gian c dng elip trn xoay nm trong khong mt na min Fresnel th nht

- Qu trnh truyn sng v tuyn c bn tn ti khi vng khng gian gii hn bi 0,6 b1 khng b cn tr sut dc ng truyn.

- qu trnh pht v thu sng v tuyn t hiu qu cao, ta dng cc bin php k thut sng in t bc x ra ch tp chung trong min Fresnel th nht s dng anten c hng (anten parabol).

2.4 nh hng ca a hnh

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TRUYN SNG V ANTEN



Chit sut (n), ch s chit sut (N)

+ Chit sut, n, ca tng i lu xp x bng 1, trong tnh ton m bo

chnh xc cao ta s dng ch s chit sut N

+ Tng i lu khng ng nht, cc thng s thay i theo khng gian v thi gian chit sut thay i

+ Tc thay i ch s chit sut theo cao nh hng ti qu trnh sng truyn lan: Qu o sng b cong do hin tng khc x Hin tng khc x kh quyn

- Tc thay i:


''

6

c 1n 1

v 2

N 10 . n 1

dN

1/dh

m

A

B

C

(2.30)

Hnh 2.16 Qu o ca tia sng trc tip v tia phn x t mt t trong tng kh quyn thc

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TRUYN SNG V ANTEN



Bn knh cong ca sng + Nguyn tc

+ Bn knh cong

2.5 nh hng ca tng i lu Qu o sng

d

+ d

R

O

c

a

b

dh

n = const

n + dn = const

+ Chia tng i lu thnh cc lp

mng vi dy dh, chit sut thay

i mt lng dn

+ Cung AB nm trn ng trn bn

knh R, gc chn tm d

6

0

t r

abR

d

dh dh dhab d R

c c c .d

sin .dnn.sin n dn .sin d c .

n

n 1 10R R h ,h r 90 ;n 1

dn dNdnsin .

dh dhdh

os +d os os

os d

+ dN/dh > 0 R < 0; dN/dh < 0 R > 0; dN/dh = 0 R =

(2.31)

Hnh 2.17 tnh bn knh

cong tia sng

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TRUYN SNG V ANTEN



Phng php tnh cng in trng

Bn knh tng ng ca tri t, atd + Mt t thc bn knh a = 6.378 km, tia sng b khc x vi bn knh cong R

+ Mt t c bn knh atd, tia sng i thng (R = )

Bn knh atd phi tha mn iu kin: cong tng i gia mt t v tia sng khng i


Bn knh tri t

Bn knh cong qu o

a)

a

R

b)

at

td6td

2 1td

1 1 1 1 a aa

a dNa R a1 1 a .10

R dh

dN4.10 m a 8.500km

dh

(2.32)

Hnh 2.18 Cc qu o ca sng v tuyn a) Qu o thc vi tri t bn knh thc

b) Qu o ng thng vi tri t c bn knh tng ng

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TRUYN SNG V ANTEN



Phng php tnh cng in trng

H s cong tia sng, k

+ C ly nhn thy trc tip

+ li tri t


td

6

a 1k

dNa1 a .10

dh

'0 t rr 2k.a h h m

1 km 2 kmr .rB m

12,74.k

(2.33)

(2.34)

(2.35)

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TRUYN SNG V ANTEN



2.5 nh hng ca tng i lu Loi khc x

(1/m) R (m) at (m) Qu o sng thc t

Qu o sng tng

ng

Khc x m

>0

< 0

< 6,378.106

Khng khc x

0

6,378. 106

Khc x thng

- 0,04

2,5. 107

8,5. 106

Khc x ti hn

- 0,157

6,378. 106

Siu khc x

< - 0,157

< 6,378. 106

< 0

dN

dh

atd = a

a

atd = a

a

atd < 4a/3

a atd < a

a atd < 0

BI GING

TRUYN SNG V ANTEN



Hp th sng trong tng i lu + Nng lng sng b hp th do cc phn t kh, ma, sng m

+ Hp th ph thuc vo tn s, thay i theo khng gian, thi gian

Hp th phn t + Ch yu do phn t nc v xy

+ Ph thuc thiu vo tn s

c bit tng nhanh vi tn s trn 10GHz


3 6 15 30 60 150 300

10+2

10+1

100

10-1

10-2

10-3

Tn s GHz

Suy hao dB/km

f = 22 GHz

O2

H2 O

Hnh 2.19. S ph thuc ca h s hp th sng ca O2 v H2O vo tn s

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TRUYN SNG V ANTEN



Hp th sng trong tng i lu

Hp th trong ma v sng m + Hp th trong ma ph thuc vo cng ma tnh theo mm/h, v theo tn

s, tng nhanh vi tn s t 6GHz tr ln

+ Hp th do sng m ph thuc

theo tn s v tm nhn xa ca anten

+ Gy thay i phn cc sng


6

8 10 20 30 40 50 60 100

2

3

4

8

40

30

20

10

Tn s GHz

Hp th dB/km

41 m 150 m

Hp th dB/km

0,01

0,1

1

10

10 30 100 3 1 Tn s GHz

30 m

Hnh 2.21. S ph thuc ca h s hp th trong ma vi cng ma 100 mm/h vo tn s

Hnh 2.20. S ph thuc ca h s hp th trong sng m theo tm nhn xa v tn s

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TRUYN SNG V ANTEN



Bi tp chng 2

2.6 Cu hi v bi tp

9. Cho ng truyn c cc thng s sau: Cng sut bc x 15 W, bc sng cng tc 35 cm, h

s khuch i ca anten pht l 100, cao ca anten pht v anten thu ln lt l 80 m v 20 m,

c ly ng truyn l 10 km. Vi R = 0,91 v = 1800 khi sng phn cc ngang v R = 0,68; =

1800 khi sng phn cc ng. Xc nh h s suy gim?

(a) 0,42 v 0,44; (b) 0,52 v 0,54; (c) 0,62 v 0,64; (d) 0,72 v 0,74

10. S liu nh bi 9, xc nh cng in trng hiu dng ti im thu?

(a) 10 mV/m v 11,5 mV/m; (b) 11 mV/m v 10,5 mV/m; (c) 11 mV/m v 11,5 mV/m; (d) 10,5

mV/m v 11,5 mV/m

11. S liu nh bi 9, xc nh tn hao truyn sng bit h s khuch i ca anten thu l 100.

(a) 76,78 dB v 76,45 dB; (b) dB; (c) 76,78 dB v 80,45 dB; (d) 80,78 dB v 80,45 dB

12. Xc nh h s suy gim khi ng truyn c cc tham s: cng sut pht 50 W, bc sng

cng tc 10 cm, h s khuch i anten pht 60, cao anten pht 25 m, anten thu 10 m, c ly

truyn sng 10 km, h s phn x R = 1 v = 1800.

(a) 1,62 ; (b) 1,72; (c) 1,82; (d) 1,92

13. S liu nh bi 12, xc nh cng in trng ti im thu?

(a) 115,34 V/m; (b) 125,34 V/m; (c) 115,34 mV/m; (d) 125,34 mV/m

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TRUYN SNG V ANTEN



Bi tp chng 2

2.6 Cu hi v bi tp

14. S liu nh bi 12 nhng bc sng cng tc l 1m. Hy xc nh cng in trng ti

im thu?

(a) 15 mV/m; (b) 16 mV/m; (c) 17 mV/m; (d) 18 mV/m

15. Mt anten pht c t cao 49m v anten thu c t cao 25m. Khong cch tm

nhn thng ca hai anten ny l gi tr no di y?

(a) 35,8 km; (b) 42,8 km; (c) 45,8 km; (d) 50,8 km

16. Mt anten pht c t cao 30m v anten thu c t cao 15m. Khong cch tm

nhn thng ca hai anten ny l gi tr no di y?

(a) 27,4 km; (b) 30,4 km; (c) 33,4 km; (d) 35,4 km

17. Anten pht v tuyn truyn hnh t cao 64m. Tnh cao ca anten thu ti mt im t

cch xa i pht mt khong 50 km c th thu c tn hiu.

(a) 2 m; (b) 2,5 m; (c) 3 m; (d) 3,5 m

18. Xc nh bn knh cong ca tia sng khi i trong tng i lu i lu tiu chun?

(a) 2.106 m; (b) 2,5.106 m; (c) 2.107 m; (d) 2,5.107 m

BI GING

TRUYN SNG V ANTEN



TRUYN LAN SNG TRONG THNG TIN DI NG

CHNG 3

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TRUYN SNG V ANTEN



Ni dung chng 3: (6)

3.1 Gii thiu

3.2 c tnh knh trong cc min

3.3 Pha inh phm vi hp

3.4 Phn b Rayleigh v Rice

3.5 Cc m hnh knh

3.6 Phn tp

3.7 Cu hi v bi tp

NI DUNG

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TRUYN SNG V ANTEN



c tnh knh v tuyn di ng nh hng trc tip n cht lng

truyn dn v dung lng.

Tnh c bit

Tnh ngu nhin

3.1 Gii thiu

My pht

My thu

Hnh 3.0: Truyn sng v tuyn

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TRUYN SNG V ANTEN



Cc yu t hn ch t mi trng v tuyn

Suy hao: Tng theo khong cch, gi tr t 50 n 150dB

Che ti: Cc vt cn trn ng truyn lm suy gim tn hiu

Phainh a ng: Tn hiu trc tip, phn x, nhiu x, tn x giao thoa vi nhau gy mo tn hiu (thay i cng tn hiu; Nhiu giao thoa

gia cc k hiu ISI, InterSymbol Interferrence, do phn tn thi gian)

Nhiu: Trng tn s (CCI CoChannel Interference), knh ln cn (ACI Adjacent Channel Interference)

Knh v tuyn

Khng gian truyn dn gia anten pht v anten thu + u vo ca knh: Anten pht

+ u ra ca knh: Anten thu

3.1 Gii thiu

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Phn loi knh v tuyn

Theo phm vi khng gian + Phadinh phm vi rng

- Khong cch nh gi knh ln (vi km), phainh xy ra trong thi gian di

+ Phadinh phm vi hp - Khong cch nh gi knh nh, phainh xy ra trong thi gian ngn

(phainh nhanh, do hin tng a ng)

Theo c tnh knh + Phn tp khng gian: c tnh knh thay i theo khng gian (phadinh chn

lc khng gian)

+ Phn tp tn s: c tnh knh thay i theo tn s (phadinh chn lc tn s)

+ Phn tp thi gian: c tnh knh thay i theo thi gian (phadinh chn lc thi gian)

3.1 Gii thiu

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TRUYN SNG V ANTEN



Minh ha c tnh ca knh

3.1 Gii thiu

Tnh chn lc khng gian ca knh

Bin

Min khng gian

Tnh chn lc tn s ca knh

Bin

Min tn s

Tnh chn lc thi gian ca knh

Bin

Min thi gian

Hnh 3.1; 3.2; 3.3: Tnh cht knh trong min khng gian, min tn s, min thi gian

Hnh 3.1 Hnh 3.3 Hnh 3.2

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Min khng gian

Tn hao ng truyn: PL (Path Loss) hay Lp + L hm ph thuc khong cch

n = 2: Khng gian t do; n = 3 5: Mi trng di ng

d: Khong cch truyn dn

+ Cng sut thu trung bnh gim so vi khong cch theo hm logarit

+ M hnh tn hao ng truyn bao gm nhiu tham s, ti mt khong cch d xc nh th PL l mt qu trnh ngu nhin c phn b log chun quanh gi tr trung bnh

: Tn hao ng truyn trung bnh ti khong cch d

X: Bin ngu nhin phn b Gausse, trung bnh 0 vi lch chun

d0: Khong cch tham chun thu pht

n: M tn hao ng truyn


nPL d(3.1)

( )[dB] = PL(d) ( ) lg dB( )d

PL d X PL d n Xd

0

0

10 (3.2)

PL d

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TRUYN SNG V ANTEN



Min tn s

iu bin tn s + Gy ra do hiu ng Doppler: Dch tn s doppler, f

v : Tc my di ng (MS)

: Bc sng

: Gc gia phng chuyn ng ca MS v sng ti

fd: Tn s doppler cc i

+ Tn hiu a ng t cc phng khc nhau lm tng rng bng tn tn hiu, gi l tri ph doppler

Chn lc tn s + Mt s on ph ca tn hiu qua knh chn lc tn s b nh hng nhiu

hn (thay i theo tn s)

+ Phadinh chon lc tn s lm mo tn hiu


cos cos cos

c

Rx c

df f fc

f f f

(3.3)

S

A B

v

Hnh 3.4 Hiu ng Doppler

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Min thi gian + Cc knh v tuyn thay i theo thi gian (phadinh chn lc thi gian)

+ Biu din tn hiu thu

x(t): Tn hiu pht : Tr a ng

h(t,): p ng xung kim knh v tuyn vi tr

+ nh hng a ng knh v tuyn l tri tr (phn tn thi gian), nghim trng vi cc h thng tc cao


( ) ( ) ( , ) ( ) ( , )y t x h t d x t h t

(3.4)

"0"

"1"

"0" "1"

Hnh 3.5 nh hng ca tri tr

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Min thi gian

Tri tr trung bnh qun phng, RDS (Root mean square Delay Spread)

P(k): Cng sut trung bnh a ng vi tr k

+ RDS biu th tr so vi ng n sm nht (LOS Line Of Sight)

+ RDS nh gi nh hng ca ISI (InterSymbol Interference)


22

2

2( ) ( )

( ) ( )

k k k k

k k

k k

k k

P P

P P

(3.6)

(3.5)

(3.7)

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Min thi gian

Tr tri cc i + Tr tri cc i ti, X dB, l tr thi gian m nng lng a ng gim

X dB so vi nng lng cc i.

Thi gian nht qun, Tc + L thi gian knh tng quan rt mnh vi tn hiu thu

+ Tc xc nh tnh tnh ca knh, cc k hiu truyn qua knh chu nh hng ca phadinh nh nhau (khng ph thuc thi gian; knh phadinh chm)


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Quan h cc thng s trong cc min khc nhau

Bng thng nht qun v tri tr trung bnh qun phng + Bng thng nht qun, Bc, l di tn m knh c c tnh tnh theo tn s, tc

ng ca knh ln cc thnh phn ph trong di tn u nh nhau

+ Vi tng quan tn s l 0,5

Thi gian nht qun v tri doppler


c

1B

5(3.8)

C

d

Tf

1

(3.9)

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Min khng gian Min tn s Min thi gian

Thng s d;

Thng ging ngu nhin

fd;

;

Nhc im Chn lc khng gian Chn lc tn s Chn lc thi gian

Gii php MIMO OFDM Thch ng

Mc ch Li dng a ng Phainh phng

(T)

Phainh chm

(BS>>fd)

Ch thch d: khong cch thu pht; MIMO: Multile Input Multiple Output; fd:

tri Doppler; BC: rng bng nht qun ca knh xt cho trng

hp tng quan ln hn 90%; T: chu k k hiu; : tri tr trung

bnh qun phng; TC: thi gian nht qun ca knh; BS: rng

bng tn hiu pht

Tng kt c tnh knh


cB

1

50c

d

Tf

1

Bng 3.1 Cc c tnh knh ca ba min

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Phn loi phadinh phm vi hp

Tri tr a ng + L thng s min thi gian, lm mo tn hiu do tr v phadinh chn lc tn

s (nh hng ln c tnh knh min tn s) - Phainh phng

- Phainh chn lc tn s

Tri doppler + L thng s min tn s, dn n tn tn v phadinh chn lc thi gian (nh

hng ln c tnh knh min thi gian) - Phainh chm

- Phainh nhanh

ngha + iu kin phadinh ngoi ph thuc thng s knh l tri tr a ng v bng

thng nht qun, cn ph thuc c im ca tn hiu bao gm chu k k hiu v rng bng tn

+ La chn tn hiu ph hp s ci thin c hiu nng truyn dn

3.3 Phadinh phm vi hp

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Phn loi phadinh phm vi hp

B: rng bng tn tn hiu

Bc: Bng thng nht qun

fd: Tri doppler cc i

T: Chu k k hiu

: Tri tr trung bnh qun phng

3.3 Phadinh phm vi hp

C s phn loi Loi Phainh iu kin

Tri tr a ng Phainh phng B

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c s dng m t tnh cht thng k thay i theo thi gian ca tn hiu phadinh phng

Phn b phadinh Rayleigh

L phn b ng bao ca tng hai tn hiu c phn b Gauss vung gc

Hm mt xc sut, PDF

: Bin ngu nhin ca in p ng bao tn hiu thu, r: gi tr ca

: Gi tr trung bnh qun phng ca tn hiu thu ca tng thnh phn Gauss

2: Cng sut trung bnh theo thi gian ca tn hiu thu

3.4 Cc phn b Rayleigh v Rice

,( )

,

r

re rf r p

r

r

2

22

20

0 0

(3.10)

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Phn b phadinh Rayleigh

Gi tr trung bnh ca phn b rayleigh

Phng sai ca phn b rayleigh (thnh phn cng sut xoay chiu)


(3.11) [ ] ( ) ,

tb E rp r dr

02

1 253

[ ] - [ ] ( ) ,r E E r p r dr

2

2

2 2 2 2

0

22

2 20 4292 (3.12)

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Phn b phadinh Rice

L phn b ng bao phadinh phm vi hp, nhn c khi tn hiu thu c thnh phn n nh vt tri, (LoS Line of Sight)

Thnh phn a ng xp chng ln tn hiu vt tri

Hm mt xc xut

A: Bin nh ca tn hiu vt tri

I0(.): Hm Bessel ci tin loi mt bc khng


(3.13)

( )

cos

, ,( )

,

( )

r A

y t

A rr Are If r

r

I y e dt

2

2 2

202 2

0

0 0

0 0

1

2

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Phn b phadinh Rice

Phn b Rice thng c m t bng tha s K

K 0: Suy thoi thnh knh Rayleigh

K : Knh ch c ng trc tip


(3.14)

2

2

Cng sut trong ng vt tri AK =

Cng sut trong cc ng tn x

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M hnh knh trong min thi gian

Nguyn tc: + Knh phadinh a ng: c trng ton hc bng b lc tuyn tnh thay i

theo thi gian (ng tr)

+ Knh c trng bng p ng xung kim knh

+ Tn hiu u ra bng tch chp tn hiu u vo knh vi p ng xung kim knh

3.5 M hnh knh

( )

( ; ) , , ....,( ) ( ) ,L

i th t Lt e t

1

0

0 1 1 (3.15)

Trong

l (t), l (t), l (t) biu th cho bin , pha v tr i vi xung thu th l (ng truyn l);

biu th cho tr, t biu th cho s thay i theo thi gian ca chnh cu trc xung kim

(.) biu th cho hm Delta Dirac, L biu th cho s ng truyn

( ) ( ) ( , ) ( ) ( , )y t x h t d x t h t

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M hnh knh trong min thi gian

3.5 M hnh knh

0

x(t)

0 1L 2

L 1

y(t)

0 0 1L 2 (L 2) L 1 (L 1)

1 L 2 L 1

Hnh 3.6 M hnh knh v tuyn di ng bng ng tr a nhnh

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M hnh knh trong min tn s

Nguyn tc: + S thay i thi gian tr dn n thay i tn s f, ngha l tn thi ca

knh khin knh mang tnh chn lc tn s

+ Thc hin bin i Fourier p ng xung kim knh trong min thi gian

3.5 M hnh knh

(3.16) '

-[ ' ( )]

( ', ) ( , ) ( , )j f

Lj f t

h f t h t e d h t e

2

12

0

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Phn tp

Thng tin c truyn ng thi trn nhiu ng c lp t c tin cy truyn dn cao (cc ng truyn khng tng quan nhau)

+ Phn tp thi gian: Cc k hiu c truyn phn tn trong cc khong thi gian khc nhau m bo tnh c lp (m ha v an xen)

+ Phn tp tn s: Cc k hiu c pht hai tn s c lp (cch nhau mt khong bng rng bng tn nht qun)

+ Phn tp phn cc: Cc k hiu c pht hai phn cc cho nhau m bo tnh c lp

+ Phn tp khng gian: Cc k hiu n im thu theo ng i c lp nhau (s dng nhiu anten pht hoc thu t khong cch xa)

SIMO: Single Input Multiple Output

MISO: Multiple Input Single Output

MIMO: Multiple Input Multiple Output

3.6 Phn tp

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Phn tp khng gian + S dng hai anten tr ln cho thu hoc pht

- B tr cch nhau > 5 theo phng thng ng

- Khong cch m bo tn hiu i trn hai knh khng tng quan nhau

+ ng thi cng truyn mt tn hiu trn hai knh - Do hai knh c lp nn khng b phadinh ng thi Kt hp tn hiu t cc

anten nhn c tn hiu tt

L phng php s dng ph bin, chng c c phadinh phng v phadinh la chn, thng s dng phn tp khng gian thu

3.6 Phn tp

f

f

Tx

Rx

Rx

Kt hp

S liu vo

S liu ra

Hnh 3.7 Phn tp khng gian

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Phn tp tn s + S dng hai cp my thu/pht lm vic hai tn s khc nhau

- Cc tn s phi c khong cch m bo khng tng quan phadinh vi nhau

- To nn hai knh v tuyn c lp

+ ng thi cng truyn mt tn hiu trn hai knh - Do hai knh c lp nn khng b phadinh ng thi Kt hp tn hiu t cc

my thu nhn c tn hiu tt

L phng php s dng khng hiu qu tn s, phc tp trong cu hnh, hiu qu trong chng phadinh la chn tn s

3.6 Phn tp

Hnh 3.8 Phn tp tn s

SW

f2

f1 Tx1 Rx1

Rx2

S liu vo S liu ra

Tx2

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Phn tp thi gian - Phadinh su xy ra trong thi gian ngn gy li cm

+ Phn tn thi gian tn hiu pht khc phc li cm - Phn tn cc li trong khong thi gian rng hn

Duy tr cht lng tuyn dn trung bnh gi tr m bo yu cu

+ Thc hin bng k thut an xen tn hiu trc khi pht

L phng php hiu qu trong vic chng li khi, c s dng ph bin

3.6 Phn tp

Hnh 3.9 Phn tp thi gian

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Bi tp chng 3

3.7 Cu hi v bi tp

15. Xt mt my pht pht x sng mang c tn s 1850 MHz. My di ng c

t trn xe t chy vn tc 80 km gi. Tnh tn s sng mang ti my thu khi

my di ng tin thng n my pht?

(a) 1850,000010 MHz; (b) 1850, 000120 MHz; (c) 1850,000137MHz

16. (Tip). Tnh tn s sng mang ti my thu khi my di ng ri xa my pht

(a) 1850,000118MHz; (b) 1850,000220MHz; (c)1849,999863MHz

17. (Tip). Tnh tn s sng mang ti my thu khi my di ng chuyn ng vung

gc vi phng sng ti.

(a) 1850,000118MHz; (b) 1850,000220MHz; (c)1849,999863MHz; (d) 1850 MHz

18. Gi thit p ng xung kim knh c s dng lp m hnh cho cc knh v

tuyn vi tr tri ln nht l100s. Nu s nhnh tr c c nh l 64. Tm

ca m hnh ng tr a nhnh.

(a) 1,3s; (b)1,56s; (c)1,5625s; (d)1,625s

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L THUYT CHUNG V ANTEN

CHNG 4

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Ni dung chng 4: (5)

4.1 Gii thiu

4.2 Cc tham s c bn ca anten

4.3 Cc ngun bc xa nguyn t

4.4 Nguyn l anten thu

4.5 Cu hi v bi tp

NI DUNG

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Vai tr ca anten

L thit b bc x sng in t ra khng gian v thu nhn sng in t t khng gian bn ngoi

+ Anten pht: Bin i tn hiu in cao tn t my pht thnh sng in t t do lan truyn trong khng gian

+ Anten thu: Tp trung nng lng sng in t trong khng gian thnh tn hiu in cao tn a n my thu.

4.1 Gii thiu

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Cc loi anten

4.1 Gii thiu

Hnh 4.2. Mt s loi anten

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Qu trnh vt l bc x sng in t

in trng xoy + L in trng c cc ng sc khng b rng buc vi cc in tch to ra

n m t bn thn chng khp kn.

iu kin to sng in t + Quy lut ca in t trng bin thin, in trng xoy bin thin s sinh ra

t trng bin i. Bn thn t trng bin i li sinh ra mt in trng xoy mi. Qu trnh lp li v sng in t c hnh thnh

4.1 Gii thiu

Hnh 4.3. Qu trnh truyn lan sng in t

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Qu trnh vt l bc x sng in t

Kho st qu trnh bc x

4.1 Gii thiu

a

b

M

c

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Hm tnh hng

Khi nim: L hm s biu th s ph thuc ca cng trng bc x bi anten theo hng kho st khi c ly kho st l khng i

, : Gc bc x ca anten (gc phng v v gc ngng)

Hm tnh hng bin : Biu th quan h ca bin trng bc x theo hng kho st vi c ly kho st khng i

Hm bin tng i (chun ha)

4.2 Cc tham s c bn

, , . , .f f i f i (4.1)

22

, , ,f f f (4.2)

ax

ax

,, ; 1

,m

m

fF F

f

(4.3)

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th tnh hng + L th khng gian biu th s bin i tng i ca bin trng bc x

theo hng kho st khi c ly kho st l khng i

+ c v t F(,) trn ta cc hoc ta cc - Mt phng chn v th l hai mt phng vung gc i qua hng bc x

cc i ca anten (,)

- Vi ta cc, trc chun ban u chn trng vi trc i xng ca th, bt u hng cc i

- Thang biu din c th theo thang thp phn hay thang logarit

4.2 Cc tham s c bn

-60 -30 30

o

0,25

0,50

0,75

1,0

0 90 -90 60

Hnh 4.5. th tnh hng

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rng th tnh hng

L gc gia hai hng m theo hng cng sut bc x gim + Gc bc x khng (20): Cng sut bc x hng cc i gim n 0

+ Gc bc x na cng sut (21/2 hay 3dB): Cng sut bc x gim mt na so vi hng cc i

Th hin tnh tp chung nng lng bc x theo hng lm vic

4.2 Cc tham s c bn

090

090

00

2/maxP

2/maxP

maxP

)(2 32

1 dB

02

0

0

Hnh 4.6. rng ca th tnh hng

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Cng sut bc x, in tr bc x, hiu sut + Cng sut bc x (P): L phn cng sut bc x thnh nng lng in t

+ Cng sut tn hao (Pth): Cng sut b tiu tn do nhit bi vt dn, trong cc lp in mi

+ Cng sut a vo anten: Pa = P + Pth

Hiu sut anten

in tr bc x: L gi tr in tr tng ng tiu hao cng sut bng cng sut bc x khi c dng in cao tn vi bin nh trn anten chy

qua

+ in tr bc x c trng cho kh nng bc x ca anten

4.2 Cc tham s c bn

1

1a

tha

P

PPP

21 .2

mP I R

(4.4)

(4.5)

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H s tnh hng, h s tng ch

H s tnh hng + L t s gia mt cng sut ca anten ti mt hng xc nh vi mt

cng sut ca mt anten chun khi hai anten t cng v tr v cng sut bc x nh nhau. Anten chun thng chn anten v hng

H s khuych i anten (tng ch) + nh ngha nh h s tnh hng nhng hai anten c cng sut a vo

anten nh nhau v anten chun c hiu sut bng 1

- H s tng ch va biu hin tnh hng, va biu th tn hao trn anten

4.2 Cc tham s c bn

2

2

0 0

2

ax ax

, ,, ; , ;

, . , , . ,m m

S ED D

S E

E E F D D F

0

,, . . ,a a

SG D

S

(4.6)

(4.7)

(4.8)

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Tr khng vo

Anten l ti ca my pht, tr s ti c trng bi tr khng vo ca anten + Thun tr R c trng cho thnh phn nng lng bc x thnh sng in t

+ in khng X l do phn trng gn, b rng buc vi anten (v cng)

Tr khng vo nh hng ti ch lm vic ca cc thit b ni ti anten

4.2 Cc tham s c bn

ava va va

a

UZ R jX

I

Hnh 4.7. Mch tr khng tng ng ca anten

(4.9)

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Chn t in (dipol in) + L phn t dn in thng, rt mnh, c di l rt nh hn bc sng. Dng

in phn b u c v bin v pha

4.3 Ngun bc x nguyn t

H

E

Ie Ie

Ie

l E

H Ie

Hnh 4.9. Bc x ca chn t in trong khng gian t do Hnh 4.8. Phn b dng in trong chn t

x

z

Ie

r

k

H

E

y

M

O

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Chn t in (dipol in)

Kho st trng ti im M + Tn ti vecto in trng trong mt phng in trng ()

+ Tn ti vecto t trng trong mt phng t trng ()


sin ( / )4

0

0

sin4

ikre

ikre

ikZ eE I l i V m

r

E

H

ik eH I l i

r

Trong : k = 2/ l h s sng

Z: l tr khng sng ca mi trng truyn lan. Trong khng gian t do Z = 120 ()

Ie : l dng in trong dipol in

r: l khong cch t tm O dn im kho st M

l : chiu di ca dipol

,: l cc gc ca h ta cu

(4.10)

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Chn t in (dipol in)

Kho st trng ti im M + Nhn xt

- Trng bc x ca dipol in l trng phn cc ng thng, in trng ch c thnh phn E v t trng ch c thnh phn H

- Mt phng E trng vi mt phng kinh tuyn cha trc chn t, mt phng H trng vi mt phng v tuyn vung vi trc chn t

- Ti mi im vecto E v H c pha ging nhau nn nng lng bc x l nng lng thc

+ Hm tnh hng

- Trng bc x c hng trong mt phng E, v hng trong mt phng H


, . . .sin .

, . . . sin

sin onst

onst onst

e

e

f Z I l i

f Z I l

F c

F c c

(4.11)

(4.12)

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Chn t in (dipol in)

Kho st trng ti im M + th tnh hng


c) Ta vung gc

1,0

0,8

0,6

0,4

0,2

1,0

0,8

0,6

0,4

0,2

3600 00 1800 3600 00 1800

0 0

F() F()

a) Trong khng gian

x

y

z

b) Ta cc

E

F(); = const

F() = 1; = const Hnh 4.10. th tnh hng ca dipol in

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Chn t in (dipol in)

Kho st trng ti im M + Cng sut bc x

+ in tr bc x

+ H s tnh hng


222

2 3

0 0 0

1 1E x H . sin sin

2 2 4

e

e

s

Z I lEP ds d r d d

Z

22

3

e Z lR

22

3

e

eZ I l

P

2 2 2

ax

, .4 .1 3, . sin

2 . 2

3/ 2

h

m

E rD

Z P

D

(4.13)

(4.14)

(4.15)

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Chn t t (dipol t) + L phn t dn t thng, rt mnh, c di l rt nh hn bc sng. Dng

t phn b u c v bin v pha


Hnh 4.12. Bc x ca chn t t trong khng gian t do Hnh 4.11. Phn b dng t trong chn t

Im

l

E

H

Im a)

H

E Im

x

z

Im

r

k

E

H

y

M

O

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Chn t t (dipol t)

Kho st trng ti im M + Tn ti vecto in trng trong mt phng in trng ()

+ Tn ti vecto t trng trong mt phng t trng ()


sin ( / )4

0

0

sin4 .

ikrm

ikrm

ik eE I l i V m

r

E

H

ik eH I l i

Z r

Trong : k = 2/ l h s sng

Z: l tr khng sng ca mi trng truyn lan. Trong khng gian t do Z = 120 ()

Im

: l dng t trong dipol t

r: l khong cch t tm O dn im kho st M

l : chiu di ca dipol

,: l cc gc ca h ta cu

(4.16)

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Chn t t (dipol t)

Kho st trng ti im M + Nhn xt

- Trng bc x ca dipol t l trng phn cc ng thng, in trng ch c thnh phn E v t trng ch c thnh phn H

- Mt phng H trng vi mt phng kinh tuyn cha trc chn t, mt phng E trng vi mt phng v tuyn vung vi trc chn t

+ Hm tnh hng

- Trng bc x c hng trong mt phng H, v hng trong mt phng E


, . .sin .

, . . sin

sin onst

onst onst

m

m

f I l i

f I l

F c

F c c

(4.17)

(4.18)

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Chn t t (dipol t)



c) Ta vung gc

1,0

0,8

0,6

0,4

0,2

1,0

0,8

0,6

0,4

0,2

3600 00 1800 3600 00 1800

0 0

F() F()

a) Trong khng gian

x

y

z

b) Ta cc

E

F(); = const

F() = 1; = const Hnh 4.13. th tnh hng ca dipol t

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Chn t t (dipol t)

Kho st trng ti im M + Cng sut bc x

+ in dn bc x

+ H s tnh hng


2

21/

3

m lGZ

22

3

m

mI l

PZ

2 2 2

ax

, .4 .1 3, . sin

2 . 2

3/ 2

h

m

E rD

Z P

D

m eI ZI (4.19)

(4.20)

(4.21)

(4.22)

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Nguyn t bc x hn hp

Cu to: Phn t bc x gm mt dipol in t vung gc vi mt dipol t

+ Dipol in t theo ox, dng Ie

x ; Dipol t t theo oy, dng Im

y

+ di bng nhau: l;

+ Quan h dng in v dng t:


.

m

y

e

x

Ia Z

I

M(,)

Iex

x

z

Imy

r

y

Hnh 4.14. Nguyn t bc x hn hp

(4.23)

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Nguyn t bc x hn hp

Kho st trng ti im M + Trng bc x gm 4 thnh phn E, E, H, H.

+ Trng ti vng xa:


os os +a4

sin 1 os4

os os +a4

sin 1 os4

ikre

x

ikre

x

ikre

x

ikre

x

ikZ eE I lc c i

r

ikZ eE I l ac i

r

ik eH I lc c i

r

ik eH I l ac i

r

(4.24)

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Nguyn t bc x hn hp

Kho st trng ti im M + Hm tnh hng

+ Hm tnh hng bin chun ha

Max: = 0; Min: =

+ H s tnh hng (a = 1)


, os os +a

, sin 1 os

e

x

e

x

f ZI lc c i

f ZI l ac i

os os +a,

1

sin 1 os,

1

c cF

a

acF

a

2

ax

3 os +1, ; 3

4m

cD D

(4.27)

(4.26)

(4.25)

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Nguyn t bc x hn hp


- th hnh cardioit trn xoay,

- Nng lng bc x cc i v mt hng, l hng ca tch vc t (Ie xI

m)


z

y

x

z

Hnh 4.15. th phng hng ca nguyn t bc x hn hp

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Kho st

Hai anten t cch nhau trong mi trng ng hng

Tr khng tng l Z1 v Z2

Nguyn l tng h


1 1 1

2 2 2

t v

t v

Z Z Z

Z Z Z

x1

y1

z1

x2

y2

z2

R1

2

Hnh 4.12. M t tng h hai anten

1 2

2 1thu thu

e e

I I

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Xc nh S trn anten thu

Trng bc x v dng u vo

S trn anten


21 1 01 1 1 1,4

ikR

h

ik eE L I F

R

Z

21

01

1 01 1 1 1

.4

, ikRh

E RI

ik L I F e

Z

21 11

1 1 1 1

12 22

2 2 2 2

.4 .

,

.4 .

,

ikR

h

ikR

h

E R Ze

ik L F e

E R Ze

ik L F e

Z

Z

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Xc nh dng trong ti anten

Tng qut:

Do cc anten l bt k nn dng trong ti anten l

S nhn c trn anten thu


1 1 1 2 2 2

12 1 1 1 1 21 2 2 2 2, ,

thu t v thu t v

h h

I Z Z I Z Z

E L F E L F

0 ,h

thu

t v

E L FI C

Z Z

0 0 ,he CE L F

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Bi tp chng 4

4.5 Cu hi v bi tp

10. Xc nh h s hng tnh (theo dBi) ca mt anten c tnh hng to nn mt cng sut ti im xem xt l

3mW/m2 khi m anten v hng to nn mt cng sut cng ti im l 0,5W/m2.

(a) 30,8 dBi; (b) 33,8 dBi; (c) 35,8 dBi; (d) 37,8 dBi

11. Xc nh h s khuch i (theo dBi) ca anten c h s hng tnh l 40 v hiu sut lm vic 60%.

(a) 13,8 dBi; (b) 15,8 dBi; (c) 17,8 dBi; (d) 20,8 dBi

12. Xc nh cng sut bc x ng hng tng ng (theo dBW v dBm) ca mt anten c h s hng tnh 43 dBi,

hiu sut 70% v cng sut u vo anten l 5 W.

(a) 45,44 dBW v 75,44 dBm; (b) 48,44 dBW v 78,44 dBm; (c) 45,44 dBW v 78,44 dBm; (d) 48,44 dBW v 75,44 dBm

13. Mt anten c in tr bc x 20, in tr tn hao 0,5 v h s hng tnh l 200.

a, Xc nh hiu sut ca anten: (a) 87,56 %; (b) 90,56 %; (c) 95,56 %; (d) 97,56 %

b, Xc nh h s khuch i: (a) 22,4 dBi; (b) 22,6 dBi; (c) 22,8 dBi; (d) 22,9 dBi

14. Mt anten c cng sut bc x 65W, cng sut tn hao 5W v h s hng tnh l 500.

a, Xc nh hiu sut ca anten: (a) 90,86 %; (b) 92,86 %; (c) 95,86 %; (d) 97,86 %

b, Xc nh h s khuch i: (a) 26,6 dBi; (b) 26,7 dBi; (c) 26,8 dBi; (d) 26,9 dBi

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ANTEN CHN T

CHNG 5

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Ni dung chng 5: (5)

5.1 Gii thiu

5.2 Anten chn t i xng

5.3 Anten chn t n

5.4 Anten nhiu chn t

5.5 Cu hi v bi tp

NI DUNG

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Khi qut

Anten chn t cn c gi l anten dipol, s dng chn t lm phn t bc x trc tip sng in t

Anten chn t c kt cu n gin, c tnh tng t ng y dn mt u h mch

Cc loi anten chn t in hnh + Anten chn t i xng

+ Anten chn t n

+ Anten nhiu chn t

5.1 Gii thiu

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Khi nim

L mt cu trc gm hai vt dn hnh dng ty + Kch thc ging nhau, t thng hng trong khng gian

+ gia ni vi ngun in cao tn

S dng nh anten hon chnh, hay cu to nn anten phc tp

Phn b dng in

Tng quan chn t i xng v ng dy song hnh


l

z

a) b)

Hnh 5.1 S tng quan gia chn t i xng v ng dy song hnh

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Phn b dng in

Tng quan chn t i xng v ng dy song hnh + Khc bit: Chn t i xng c

- Thng s phn b L, C thay i dc theo chn t

- Nng lng bc x ra khng gian di dng sng in t

+ Vi chn t mnh (d > ): Coi l tng quan. Phn b dng in trn chn t i xng c dng sng ng

+ Phn b in tch


.sinz bI z I k l z

Ib l bin dng in im bng .

l: l di mt nhnh chn t

..cos . , 0

.

..cos . , 0

.

b

z

b

k Ik l z z

iQ

k Ik l z z

i

(5.1)

(5.2)

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Phn b dng in


Q I

a) l = 0,25

Q I

c) l = 0,675

Q I

b) l = 0,5

Hnh 5.2 Phn b dng in v in tch trn chn t i xng

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Bc x ca chn t i xng trong khng gian t do

Bi ton + Chn t i xng chiu di 2l t trong khng gian t do

+ Kho st trng ti M cch chn t r0 >> , lp vi trc chn t gc

Xc nh cng trng + Chia chn t thnh cc phn t rt nh dz >> . Mi phn t tng ng vi

mt chn t in - Chiu di dz

- Khong cch r

- Mt dng khng i Iz


r dz

dz M

ro

r1

r2

l z

Hnh 5.3 M t cc thng s tnh trng bc x ca chn t i xng trong khng gian t do

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Xc nh cng trng + Trng do phn t dz nhnh 1 v 2 gy ra ti M

+ Tng hp cng trng do hai phn t


1

2

1

1

2

2

60sin

60sin

ikrz

ikrz

I dzdE i e i

r

I dzdE i e i

r

1 0

2 0

os

os

do r

r r zc

r r zc

0

0

1 2

os os

0

0

; .sin .

60 . ..sin .sin . .

.

60 . .sin .sin . .2cos kz.cos

.

z b

ikr ikzc ikzcb

ikrb

dE dE dE I I k l z

I dzdE i k l z e e e i

r

I dzdE i k l z e i

r

(5.3)

(5.5)

(5.4)

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Xc nh cng trng + in trng do ton b chn t gy ra ti M


0

0

0

0

0

0

cos klcos coskl60. . .

sin

60. . ,

60.. ,

l

ikrb

ikrb

b

E d E

IE i e i

r

IE i e f

r

IE f

r

(5.7)

(5.6)

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Tham s ca chn t i xng

Hm tnh hng v th tnh hng

Hm tnh hng bin

Trong mt phng H vung gc vi trc chn t c l hng s, hm tnh hng ch ph thuc vo k.l, (hay chiu di tng i l/)

+ Chn t ngn: l < /4

- Tng t chn t in: C hng mt phng E cha trc chn t, v hng mt phng H vung gc vi trc chn t, cc i hng vung vi trc


cos klcos cos kl

,sin

f f

22 k.lxcosx 1 sin

2 2

sin

x f

F

(5.10)

(5.9)

(5.8)

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Hm tnh hng bin + Chn t na sng : l = /4

+ Chn t c sng: l = /2

- th hp hn


.2

cos cos cos cos .cos2 2 2

sin sin

k l

f

2

.

2cos .coscos .cos 1 2

sin sin

k l

f

(5.11)

(5.12)

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Hm tnh hng bin + Chn t di: l > /2

Trn mi nhnh xut hin dng in ngc pha, do - Ti hng vung gc, khng c sai pha v ng i nhng dng in ngc

pha nn cng trng tng gim (bp chnh thu hp li)

- Ti hng c sai pha v ng i th sai pha c b tr nh sai pha v dng in nn xut hin cc bp ph (bp ph ln dn). Khi l = , bn bp ph tr thnh bn bp chnh.

Tnh hng ca chn t i xng ph thuc vo chiu di in:


l

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th tnh hng ca chn t i xng trong mt phng E


90o

0o 180o

c) l 0,5

90o

0o 180o

a) l 0,1

90o

0o 180o

b) l 0,25

90o

0o 180o

d) l 0,75

90o

0o 180o

e) l

Hnh 5.4 th phng hng ca chn t i xng trong mt phng E

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Tr khng sng, tr khng vo

Tr khng sng + Tr khng sng dy song hnh

D: Khong cch tm hai dy dn

r: Bn knh dy dn

+ Chn t i xng thng s in dung phn tn thay i - Vi l

- Vi l > (cng thc Kesenich)

E: Hng s le (= 0,577)


276.lgfD

Zr

2120 ln 1

120 ln.

A

A

lZ

r

Z Er

(5.13)

(5.14)

(5.15)

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Tr khng sng, tr khng vo

Tr khng vo + Vi ng dy song hnh h mch u cui c tr khng vo

+ Chn t i xng nng lng bc x ra khng gian nn c thnh phn in tr bc x u vo ng vai tr thun tr

+ Tr khng vo ca chn t

(Vi l < 0,75)


cotg .vA AX iZ k l

2

2

sin

.cotgsin

bvA

bvA vA vA A

RR

kl

RZ R jX iZ kl

lk

(5.17)

(5.18)

(5.16)

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Tr khng vo


- 300

- 400

- 200

- 100

0

100

200

300

400

0 0,2 0,4 0,6 0,8 1,0 1,2

XVA()

l/r=40

l/r=20

l/r=60

100

-100

200

300

400

500

600

700

800

0 0,2 0,4 0,6 0,7 1,0 1,2

RVA()

l/r =40

l/r =20

l/r =60

0

Hnh 5.5. S ph thuc ca ZvA vo l

Nhn xt:

- Chn t ngn (l < /4): cotg l (+) nn ZVA l (-) Tr khng vo mang tnh dung

- Chn t na sng (l = /4): cotg = 0 nn ZVA = RVA = 73,1 Mch cng hng ni tip

- Chn t c (/4 < l < /2): cotg l (-) nn ZVA l (+) Tr khng vo mang tnh cm

- Chn t ton sng (l = /2): cotg = 0, sin = 0, nn ZVA = Mch cng hng song song

l

l

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Cng sut bc x, in tr bc x, h s tnh hng

Cng sut bc x + Cng sut bc x qua din tch ds

+ Cng sut bc x ca chn t


x

d

ds = r2sindd

z

r

y

Hnh 5.6. Xc nh cng sut bc x ca chn t i xng

2

22 2

2

2 2

0 0

2

2

0

. . . .2

cos klcos cos klsin

8 sin

cos klcos cos kl30 .

sin

b

b

tb h h

EdP S ds E H ds ds

Z

ZIP r d d

r

P I d

(5.20)

(5.19)

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in tr bc x + Xc nh ti im bng

Nhn xt

- Khi l/ nh, ging dipol in, tng l lm cho dng ng pha tng Tng R - Khi l > /2, xut hin dng in ngc pha Gim R - in tr bc x dao ng cc i di l bi s chn ln /4, cc tiu

di l bi s l ln /4


2

2

0

1.

2

cos klcos cos kl60 .

sin

b b

b

P I R

R d

(5.21)

0

50

100

150

200

250

0,25 0,5 0,75 1,0

Rbxb()

Hnh 5.7. Quan h gia in tr bc xv di tng i

l

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H s tnh hng


2 2

2

ax

b

, .2 .,

Z.P

Z1 cos kl

2 .m

E rD

D DR

Nhn xt:

- Khi l/ 0,675: Bc x anten cc i hng = /2, tng l D tng

- Khi l/ > 0,675: Tng l D gim do cc i chnh gim

(5.22)

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