Bai Thuc Hanh HFSS

Bo Co Thc Hnh Chuyn Ngnh in T Vin Thng

THIT K, M PHNGV KHO ST CC THNG S K THUT CA ANTEN VI DI

I.MC CHGip cho sinh vin hiu c vai tr,v tr ca anten trong cc h thng

truyn thng v tuyn. Sinh vin c tin hnh m phng kho st cc thng s k thut ca anten bng phn mm m phng HFSS, tnh ton thit k v ch to anten vi di hot ng di tn yu cu, s dng my phn tch mng (network analyzer) o c kho st cc thng s k thut ca mt s anten mu.II. C S L THUYT

Anten l thit b quan trng khng th thiu trong mi h thng truyn thng khng dy. N l thit b chuyn i sng in t rng buc trong cc h nh hng thnh sng in t lan truyn trong khng gian t do v ngc li. Anten v ng dy dn (feeder) ng vai tr l thit b ghp gia cc mch in t v khng gian t do, feeder l b phn giao tip gia anten v mch in t. Ng vo ca feeder phi phi hp tr khng vi my pht, cn antenna pht nhn nng lng t my pht qua feeder v bc x ra khng gian. Ngoi vic phi hp tr khng yu cu i vi anten cn phi p ng v li v phng hng bc x.

Hin nay, ty thuc vo mc ch s dng ca cc h thng truyn thng v tuyn ngi ta s dng rt nhiu loi anten khc nhau, nh anten parabol vi li v tnh nh hng cao thng c s dng trong truyn hnh, thng tin vi ba, thng tin v tinh... cn u cui thng s dng cc loi anten nh nh anten Yagi,anten dy,... v c bit cng vi s pht trin mnh m v cng ngh ca cc u cui di ng th anten vi di ngy cng c s dng rng ri v khng ngng ci tin p ng nhu cu ca ngi s dng.

Anten vi di (hay anten mch in) c kch thc rt nh c cu to gm mt lp kim loi l mt bc x, mt lp kim loi khc gi l mt t (mn chn kim loi ), mt lp in mi gia hai lp kim loi trn v b phn tip in. Anten vi di c nhiu hnh dng nh hnh trn,hnh tam gic, hnh vung, hnh ch nht... trong , loi ph bin nht c kt cu hnh ch nht v c hng tnh, li cao ng thi d kt hp vi cc mch in t trn cng mt mch in.

Gio vin hng dn: TH.S L Th Kiu Nga TH.S Nguyn Th Minh

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Cc thng s k thut c bn ca anten- Tn s cng tc ca anten l tn s cng hng ca anten. Anten lun lm

vic ch cng hng v khi cng sut bc x ca anten l ln nht.- H s nh hng ca anten theo hng cc i c nh ngha bng t

s cng trng bc x ti mt v tr trn hng v cng trng bc x ca mt anten chun cng v tr tng ng (D). H s tng ch ( li) ca anten (G=e.D), trong e l hiu sut bc x ca anten;

- Tr khng vo ca anten : ZA = RA + jXAKhi kt ni anten vi feeder cn ch ti iu kin phi hp tr khng,Thng thng tr khng c tnh ca feeder l R0 ph hp tr khng th ZA = R0

- H s tn hao RL (dB) nh gi mc phn x ca sng ti im kt ni anten vi feeder

- H s sng ng SWR nh gi mc khng phi hp tr khng gia anten v feeder.

Trong :W l chiu rng mt bc x;L l chiu di mt bc x;h l b dy ca lp in mi;Wg l chiu rng ca mt phng t;Lg l chiu di ca mt phng t.

III. TNH TON, M PHNG V KHO ST CC THNG S K THUT CA ANTEN

Anten vi di hnh ch nht c cu to gm mt bc x, mt phng t v lp in mi gia 2 mt kim loi trn. Kch thc ca mt bc x, chiu cao v h s in mi l nhng thng s quyt nh tn s cng hng ca anten, nn chng phi c la chn v tnh ton chnh xc.

Chn vt liu ch to anten l tm mch in hai mt c h s in mi v dy l: r = 4.5; h = 1.6 mm;Tnh ton kch thc ca anten vi di lm vic tn s:Gii tn GSM: f0= 1900 MHz


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Chiu rng ca mt bc x c tnh theo cng thc:

W = 2

12 0+rf

c 48 (mm)

c = 3x108 m/sVi c = 3x108 m/s ( c l vn tc nh sng), f0 l tn s cng hng ca anten,

r l h s in mi ca lp in mi.H s in mi hiu dng reff ph thuc c vo cc kch thc (W , h) v n

c xc nh theo cng thc:

reff = 1

2r + +

12

r 1/2

1 12wh

+ Thay s vo ta c reff 4.22

di hiu dng ca anten c xc nh theo cng thc:

Leff e2 o r ff

cf

Thay s vo ta c Leff 0.038 tng di L c tnh theo cng thc:

L = e

e

w( 0.3)( 0.264)0.412 . w( 0.258)( 0.8)

r ff

r ff

hh

h

+ +

+ =

Thay s vo ta c L 0.76(mm) di thc ca mt bc x c tnh bi cng thc:

L = Leff - 2L =0.038 - 2x0.76x10-3 0.766 (mm)Kch thc ca mt phng t ( Wg v Lg ) c xc nh theo cng thc:

Wg 6h + W Wg 6x1.6 + 48 58(mm) Lg 6h + L

Lg 6x1.6 +36 46 (mm)3.1. Cc phng php tip in cho anten vi dia. Tip in bng cp ng trc (hnh 1)

Trong phng php tip in cho anten vi di bng cp ng trc th li cp c hn tip xc vi mt bc x, v cp tip xc vi mt phng t.V tr tip in tt nht c tnh ton v xc nh c ta ( L/4, W/2)


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Phng php tip in ny c cc u im l d thc hin v khng c bc x ph.b. Tip in bng ng truyn vi di

Trong k thut tip in ny, mt di dn c kt ni trc tip n cnh ca mt bc x anten vi di. Di dn c thit k trn cng b mt vi mt bc x.

Chiu rng ca di dn nh hn rt nhiu so vi kch thc ca mt bc x. V tr tip in c ta (L/2, 0).

Kch thc ca di dn (Wf ; Lf ) c xc nh nh sau:Tr khng c tnh ca ng truyn l: Zo = 50Chiu rng ca di dn c tnh theo cng thc sau:

Wf = 12 0.611 ln(2 1) ln( 1) 0.39

2r

r r

h B B B

+ +

Trong : B = 0377

2 rZ

= 5.58Mi quan h gia chiu di v chiu rng: Lf /Wf = 3.96

IV. HNG DN S DNG PHN MM M PHNG HFSSHFSS ( Hight Frequency Structure Simulator ) l phn mm m phng

trng in t theo phng php ton sng (full wave) m hnh ha bt k thit b th ng 3D no. u im ni bt ca HFSS l c dao din ngi dng ha,tch hp m phng, o ha, m hnh ha 3D v t ng ha (t ng tm li gii) trong mt mi trng d dng hc, trong li gii cho cc bi ton in t 3D thu c mt cch nhanh chng v chnh xc. Ansoft HFSS s dng phng php phn t hu hn (Finite Element Method,FEM ), k thut chia li thch nghi (adaptive meshing ) v k thut ha. Ansoft HFSS c th c s dng tnh ton cc tham s chng hn nh: h s tn hao, tn s cng hng,gin hng tnh,tr khng vo...HFSS l mt h thng m phng tng tc,trong phn t mt li c bn l mt t din. iu ny cho php bn c th tm li gii cho bt k vt th 3D no. c bit i vi cc cu trc dng cong phc tp. Ansoft l cng ty tin phong s dng phng php phn t hu hn (FEM ) m phng trng in t bng cc k thut nh: phn t hu hn,chia li thch nghi...Ansoft HFSS cung cp mt giao din trc gic v d dng s dng pht trin cc thit b RF th ng.


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Tm tt qu trnh m phng bng phn mm HSFF m phng mt anten bt k v c bn ta thc hin cc bc sau:

Chn HFSS \ Solution Type \ Driven Terminal Chn n v: #D Modeler \Units, chn mm

Da vo cc cng c trn thanh cng c v cu trc ca anten vo giao din lm vic

To port cp ngunChn mt cp ngun, sau vo HFSS \ Excitation \ Assign - Nu cp ngun bng probe th chn Wave Port

- Nu cp ngun bng ng vi di th chn Lumped Port Khai bo cc mt bc x ( thng khai bo cho mt phng t ): Chn mt

bc x, sau vo HFSS \ Boundaries \ Assign \ Perfect E To khng gian bc x cho anten- V mt Box bao trm c anten, thng thng khong cch t ra anten n mt Box khong bc sng cng hng cn thit, sau vo:

HFSS \ Boundaries \ Assign \ Radiation- Chn cc mt ca Box pha m anten c bc x

- Chn HFSS \ Radiation \ nsert Far Field Setup \ Infinite Sphere- Mn hnh hin ln bng pha Far Field Radiation Sphere Setup- Nhp cc thng s mnh mun v nhn OK

Khai bo tn s cng hng mong mun, s bc lp v sai s ln nht chp nhn c: HFSS \ Analysis Setup \ Add Solution Setup

- Solution Frequency: nhp vo tn s cng hng mong mun- Maximum Number of Passed: s bc lp ti a ca m phng- Maximum Delta S Per Pass: sai s chp nhn c, cng nh cng chnh

xc. Chng trnh m phng s chy cho n khi sai s tnh ton nh hn hoc bng delta S. Khi xem nh m phng chnh xc v c hi t ( Converged). Nu chy ht tt c cc bc lp m vn khng c sai s no nh hn delta S, chng trnh cng s t ng dng li. Khi qu trnh m phng s khng hi t v cho kt qu khng chnh xc. Mun khc phc ta phi tng gi tr delta S ln hoc l tng s bc lp ln nhn c kt qu chnh xc. Tuy nhin nu sai s tnh ra ngay nhng bc lp u tin nh hn Delta S th kt qu nhn c


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cng khng ng tin. trnh hin tng ny ta phi gim Delta S tng s bc lp ca chng trnh. Thng thng nu chng trnh chy nhiu hn 5 bc lp v c hi t th s nhn c kt qu chnh xc.

Khai bo vng tn s kho st ( xung quanh tn s trung tm)Vo HFSS \ Analysis Setup \ Add Sweep

Sau khi thc hin tt c cng on trn, ta vo HFSS \ Validation check kim tra li thit k. Nu khng c li, vo HFSS \ Analyze v bt u chy m phng.

Hin th cc kt qu m phng- vo HFSS \ Results \

V. CC THNG S M PHNG TN S 1900Ghz5.1. Thit k ng ten vi di- Khi ng chng trnh: Program => Ansoft => HFSS11 => HFSS11

- Thit lp thng s:

+ Tool => Option => HFSS option

Ti khung General tch chn nh sau:

+ Tool => Options => Modeler options

Trong khung 3D Modele options mc Operation chn Automatically cover closed polylines

Trong mc Drawing chn edit properties of new primitivesGio vin hng dn: TH.S L Th Kiu Nga TH.S Nguyn Th Minh

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+ Moderler => units => Select units: mm

+ HFSS => Solution type => Chn Driven Terminal

y chn gi quyt bi ton tn s lm vic f0 = 1900 MHZ

- Thit k mt phng t: Draw => box ( t)

+ Thng s thit k lp t


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+ Thit lp mt phng t:

Edit => select => face

HFSS => Boundaries => Asign => Finite Conductivity Ok

- Thit k lp in mi: Draw => box ( in mi)

Thng s thit k lp in mi

- Thit k mt bc x => box ( bc x)


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Thng s thit k lp Mt bc x

- Thit k lp line => box ( line)

Thng s thit k lp Line

- Thit k im cp ngun cho ng vi di

v ngun ta vo Draw=>Rectangle (v hnh ch nht vung gc v tip xc mt ngoi Feed Line)


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Thng s thit k lp Ngun

Thit lp cp in: HFSS=>Excitations=>Asign=>Lumped Port (Nu thy Feed Line bn mc Conducting Objects c ngha c tip im, nhn Ok cp ngun)

- Thit k lp khng gian: Draw => box ( khng gian)

+ Thng s thit k lp Khng gian


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+ mt bc x: Kch chn ln lt 4 mt bn v mt trn ca mt bc x ri thc hin: HFSS=> Boundaries=>Assign=> Radiation

+ Thit lp hng bc x: HFSS=>Radiation=>Insert Far Field Setup=>Infinte=>Ok

+ Thit lp tn s lm vic: HFSS=> Analysis Setup=>Add Solution Setup

y ta thit lp tn s lm vic nh chn l : 1900 MHZAdd Frequency Sweep

Ta c Star: 1.5GHZ, Stop : 2.4 GHZ , cn Step Sto

+ Thit lp gii hn tn s qut: HFSS=>Analysis Setup=>p l : 10 MHZ

Sau Sweep Type chn: Fast > chn Ok To

5.3. Thng s thit k ng ten cp ngun bng cp ng trc- Thng s thit k lp t (tng t nh trn)- Thng s thit k lp in mi (tng t nh trn)- Thng s thit k lp Mt bc x (tng t nh trn)- Thng s tip in trn


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- Thng s tip in di

- Thng s vng ngoi

- Thng s thit k lp Cp ngunGio vin hng dn: TH.S L Th Kiu Nga TH.S Nguyn Th Minh

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- Thit k lp khng gian: Draw => box ( khng gian)

+ Thng s thit k lp Khng gian

+ mt bc x: Kch chn ln lt 4 mt bn v mt trn ca mt bc x ri thc hin: HFSS=> Boundaries=>Assign=> Radiation

- Thit lp cc thng s


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+ Thit lp hng bc x: HFSS=>Radiation=>Insert Far Field Setup=>Infinte=>Ok

+ Thit lp tn s lm vic: HFSS=> Analysis Setup=>Add Solution Setup

y ta thit lp tn s lm vic nh chn l : 1900 MHZAdd Frequency Sweep

Ta c Star: 1.5GHZ, Stop : 2.4 GHZ , cn Step Sto

+ Thit lp gii hn tn s qut: HFSS=>Analysis Setup=>p l : 10 MHZ

Sau Sweep Type chn: Fast > chn Ok To

VI . Kt qu m phng6.1. Kt qu m phng thit k ng ten vi di tn s 900Hnh m phng 3D


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Tn s cng hng:

th smith:

li:


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nh gi v qu trnh v kt qu m phng:- suy hao khng ln- Kt qu m phng t c kt qu gn st vi tn s 900- Hnh dng th t vi yu cu ra- Qua nhiu ln cn chnh cho thy: vi tn s kh cao l 900 th kt qu kh chnh xc,cn tnh ton t m, chnh sa hp l mi c th t kt qu tt nht6.2. Kt qu m phng thit k ng ten cp ngun bng cp ng trc tn s 1900GhzHnh m phng 3D

Tn s cng hng:

th smith:


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th 3D Polar Plot

nh gi kt qu m phng thit k ng ten cp ngun bng cp ng trc:- Tnh ton ta t phc tp v t cn sa hn so vi thit k ng ten vi di- Cho hnh dng m phng t chun t cn chnh hn- Tn s t c kh st vi tn s 1900khz- Trn kt qu ta thy suy hao vn cn kh lnVII. KT QU S DNG MY PHN TCH MANG CHO ANTEN VI DI7.1.Cung cp ngun v nhn nt khi ng cho my phn tch mng E5061A7.2. Kt ni ph kin cao tn chun MSA Port 1 ca my phn tch mng E5061 A Agilent E5061 RF Network Analyzer7.3. H s phn x ( S11):


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H s suy hao im phn x S11 = -13.437dB

Tn s cng hng im phn x f=970.30464MHz

7.4. th Smith Chart uc hin th:

Tr khng o uc trn th l =47.41

7.5. H s sng ng SWR:

Ti im S11 xc nh tn f= 969.31MHz

H s sng ng =1.52


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7.6. Bng thng:

Ta xc nh uc 2 im S11 v S12 trn th vi h s =9.5dB trn th

y ta c tn s f1,f2 tung ng l:

f1=980.352MHz

f2=961.589MHz

Bng thng uc tnh = f1-f2=980.352-961.589 = 18.763MHz

7.7. li:

tnh li ta da vo cng thc:

Gain=1/2 (Pr(dB)-Pt(dB)+20 log(d)+20log(f)-27.56)

Trong Pr,Pt l h s dB hin th trn my:

pr=-14dB Pt=-22dB

d l khang cch gia 2 anten:

d=15cm

f la tn s dao ng ca anten:

f=900MHz

Nh vy: Gain =1/2 ( -14-(-22))+20 log(15)+20log(950)-27.56)=23.775


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VIII. SO SNH KT QU VI YU CU BI V KT LUNH s tn hao =-13.437dB

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