LY THUYET DÚaNG DAY GHEP VA PHAT TRI^N
3.2 Dae tinh lua chon tan so ciia duong day ghep |2|
l + {s/f,j (3.27)
3.2 Dae tinh lua chon tan so ciia duong day ghep | 2 |
Cae dang duong day truyen sc')ng trong Hinh 3-1 co the duc;c dung de lam thanh nhieu loai bg Igc. Viec che lao cae bg Igc thong dai hay chan dai su dung duong day ghep thirc sir rat de dang khi ma do rong bang dugc \cu cau cho bg Igc nho hon 20%. De che tao eac bg Igc dcM hoi do rong bang Ion htm thi \cu cau khoang each giúa cae duong day dan dien cua doan ducmg da\ ghep la rat nho (luan
di8m nay duac dua ra trong tap sach Microwave Hngineering cua I)a\ id Po/a
nhung c)ng chua chung minh, trong luan van nay luan diem d(') sc dugc chung minh), day la viec rdt khc) thuc hien. Dau licMi chiing la sc nghien cuu dae linh cua
bg Igc tao boi cae doan dirong da> eo chieu dai mgl phan ur hucre song, vix sau dc)
se chi ra lam ih^ nao ma nhung dudng day na\ co the dugc su dung de che tao be) igc thong daị
(») <b) <b) ( c ) ^ z •- z ỌC.
Hinh 3-6. Bi^u dien dien ap va dong dicn tren doan duong da\ ghep co cau iriic microstrip
Mot cap dircyng day song song trong Hinh 3-6. \cVi cae cdng thuc xac dinh
dien ap va dong dien tai cong. Ta sc rut ra ma Iran tro khang ho mach cho mang 4 c6ng nay bang viec xem set sir chc^ng chat ciia cae mode kich thich chan \ a le duac
chi trong Hinh 3-6. Do vaỵ eac nguOn dong i, va \y, di vao duong day trong mode chan va mode le, trong khi i: va ị, di vao ducmg da> a mode chan. Do tinh ehdng
chat dien lir irucmg, la thdy rang dong dien tc^ng . 1, co the duc^c bieu dien duai dang cong thuc ciia dong dicMi mode chfin \ a mode le nhu sau:
I,=ị+i:, »--8^^) l:=i,-i:. *--^t^'
1 - i i (-^ -^^^
Dau tien ta coi dong dien i, dang di vao mode chin cua duong daỵ N^u cae c6ng khac la ha mach, tro khang nhin vao tai c6ng 1 va 2 la:
Z° =-/Z„^,coty9/ . (3.29) Dien ap tren ca hai dau cua doan day dan dien la:
e-""-"+e- I0(:'I)1
v:(-)-;,(z)=r
= 2rcosyg(/-.-), Vi vay dien ap tai cong 1 va 2 la
V : ( O ) = V : ( O ) = 2 F ; C O S / ? / = / , Z : ,
Ket qua nay va (3.29) co the dugc su dung de viCn lai (3.30) duoi dang hieu ihiic cua dong /| nhu sau:
(3.30) (3.31)
(3.32)
, , , , , , cospll-z)
Tuong tu nhu vay, dien ap do dong /^ dua vao duong da\ trong mode chan la
(3.32)
(3.33)
Bay gio nghien ciai duong day ghep khi co mot nguon dong /: o nu)dc Ic dua \ aọ
Neu eac c6ng khac la ho mach. tro khang nhin vao tai cong 1 \ a 2 lạ
z : = -/Z,„ col/i/. (3.34) Dien ap tren ca hai dau cua ducmg da\- dan dicn co the dugc bieu dien nhu sau:
,,2 (.) ^ _,,:(,) ^ ,;; f, '/'(--'I +,/'/'<--"] = 2i;,ros/^(/ - r) (3.35) dicn ap tai cong va 2 la
V-; (0) = -v; (0) = 2V: cos^/ = i:Z:„. (3.36) Ket qua nay va (3.34) co thC^ dugc su dung di y\k lai (3.35) duoi dang bicu thuc
cua '\2 nhu sau:
v]{z)=-vl[:) = -jZ„. cos/?(/---)
/?/
/, (3.37)
, 4 / \ 4 / Y --7 COS PZ sin pi sin pi
Bay gio long dien ap tai cong 1 la :
^^,=v:(0) + v,:(0)^v:(0) + ;-:(0)
= -7(2o,/, + Z„„/, )cot6' - y(Z„.,/, + ZJ, )csc^, (3.39)
trong do cae ket qua (3.32). (3.33). (3.37). va (3.38) dugc sir dung, va ^ = /?/. Sau do ta se giai (3.28) cho dong /j duoi dang bieu thirc cua /, la:
/, = ^ ( / , + / : ) , (3.4()a)
/, = ^ ( / , - A ) , (3.40b)
/, = i ( / 3 + / , ) , (3.400
>,--{!:.-IA- (^-^"J
va sir dung cae kcl qua (3.39)
V^=-l{Z,J,+ZJ, +ZJ,-ZJMoUi (3.41)
= -^(Z.,./.+2„7,+Z„„/,-Z.„7.,)csc^^. (3.42)
Ket qua (3.42) cho la hang diu lien cua mo\ ma Iran iro khang ho mach \/.\ JUCTC SU
dung de mieu ta mot doan duang da> ghep. Ihco linh chat doi xung. tat ca cae phan tu khac ciia ma Iran ccS the ducTc xac dinh mgl khi hang dau lien dugc biet.
Z„ - ^:: - ^--•. = 2,, = ^ t Z . , +Z,„)coi6^. (3.43a)
7 = Z = Z = Z , - = — ( Z „ -Z„ )col^. (3.43b)
Z „ = Z „ = Z , . = Z , = ^ ( Z . „ - Z , „ ) c s c ^ ^ . (3.43c)
Mgt mang hai cong co th^ dugc tao ra tir cae doan duang da> ghep b4ng each dk ho mach hoae ngan mach 2 trong 4 c6ng cua mach. Co tk ca 10 su phoi hgp nhu thẹ
trong so do co nhirng mach co dap irng thong dai, chan daị thong thSp. hoac la toan
daị De co mot dap irng thong daị nguoi ta hku nhu chi quan tam den truang hgp trong Hinh 3-6e, vi cau triie nhu the dugc che tao de dang nhk trong thuc tẹ Trong
truang hgp nay, A = /4 = 0. vi vay tro khang mang 4 cong chi con la:
V,i = Zi,I, + Ziih. (3.44) Vii= Zsili+Zssh. (3.45)
trong do Z,j da cho trong (3.43).
Ta CO the phan tich dae tinh kic cua mach nay bang viec tinh tro khang anh tai cong 1 va cong 3 va hang so truyen song. Tuy nhien ta chi can tinh tro khang tai mot cong bai vi chiing bang nhau do mang la dc"-)i xirng \a ihuan nghieh. lu bang 2.2. bieu thirc tra khang anh ciia mach duong day ghep eo cau triic nhu llinh 3-6c theo cae tham so ciia ma tran tra khiing Z la:
" z „
^ ^ ( Z , , . . -Z„„rcsc-^^^-(Z,,+Z.J-'cot^^ (3.46)
Khi duong day truyen song co dc) dai la h'4 khi dcS 6=71 2. tro khang anh chi con la
Z, =(Zoc-Zoo)/2, (3.47)
Phuang trinh nay la thuc va ducmg. \ i Zoc> Z,,,,. Nhung khi ^^ -> U ha\ ,T. Z ^ ±j-^- thi bg Igc trtV thanh chan daị Phdn ihuc cua tro khang anh duoc \c trong Hinh 3-7. trong do tcin s6 ck ccS th(j ducic xac dinh lir phucrng irinh (3.47) nhu sau:
cos0^=-cos0.=^^^^. (3.48)
I irmg sc^ truyen song ccS thC cung duoc linh lir Bang 2.2. nhu sau:
,,,;,= E S = ^ = | ^ c o s ^ . (3.49)
COSO, = ( Z o e - Z o o ) / (Zoe + Zoo) . (3.50)
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Hinh 3-7. Phan thuc ciia iro khang anh doi vai mach thong dai