notes 5 - waveguides part 2 parallel plate
DESCRIPTION
parallel competionTRANSCRIPT
Prof. David R. JacksonDept. of ECE
Notes 5
ECE 5317‐6351 Microwave Engineering
Fall 2011
Waveguides Part 2:Parallel Plate Waveguide
1
2
2
2
2
z zx c z
c
z zy c z
c
z zx z
c
z zy z
c
E HjH kk y x
E HjH kk x y
E HjE kk x y
E HjE kk y x
ωε
ωε
ωμ
ωμ
⎛ ⎞∂ ∂= ⎜ ⎟∂ ∂⎝ ⎠
⎛ ⎞∂ ∂−= ±⎜ ⎟∂ ∂⎝ ⎠
⎛ ⎞∂ ∂−= ± +⎜ ⎟∂ ∂⎝ ⎠
⎛ ⎞∂ ∂= +⎜ ⎟∂ ∂⎝ ⎠
∓
∓
Summary
2 2ck ω με=
( )1/22 2c zk k k= −
Field Equations (from Notes 4)
These equations will be useful to us in the present discussion.
2
Parallel‐Plate Waveguide
Both plates assumed PECw >> d, λ
0x∂
⇒ =∂
Neglect x variation,edge effects
The parallel‐plate stricture is a good 1ST order model for a microstrip line.
,ε μ
3
Parallel‐plate waveguide2 conductors ⇒ 1 TEM mode
To solve for TEM mode:
2 0 00
t x wy d
∇ Φ = ≤ ≤≤ ≤
for
Boundary conditions:
0( ,0) 0 ; ( , )x x d VΦ = Φ =
2 22
2 2 0t x y⎛ ⎞∂ ∂
⇒∇ Φ = + Φ =⎜ ⎟∂ ∂⎝ ⎠
TEM Mode
z ck j k k jkβ α ω με ′ ′′= − = = = −
c jσε εω
= −
kk
βα
′=′′=
4
where
0
( , )
( , ) ; 0
0
Vx y
x y
y x w
y
A y
dd
B
⇒
⇒Φ =
Φ = ≤
≤
+
≤
≤
0ˆ( , , ) ( , ) jkz jkzt
Vx y z e x y e y eEd
= = −⇒ ∓ ∓
0
@ 0
0
@
y
A
y d
VBd
=
⇒ =
=
⇒ =
2
2 0y∂
Φ =∂
( ) ( ) 0,0 0 & ,x x d VΦ = Φ =
( ) ˆ ˆ, ot t
Ve x y y yy d∂
= −∇ Φ = − Φ = −∂
z ck k ω με= =
TEM Mode (cont.)
c jσε εω
= −
5
Recall
( ) 0ˆ, , jkzVH x y z x edη
⇒ = ± ∓
For a wave prop. in + z direction
Time‐ave. power flow in + z direction:
( )2
*
20 2
* 20 0
22
0 *
1 ˆRe ( )2
1 ˆ ˆRe
1 1 1Re
)
2
2
s
w dk z
k z
P E H z dS
Vz z
V w
e dy
dd
dxd
eη
η
+
′′−
′′−
⎧ ⎫= × ⋅⎨ ⎬
⎩ ⎭⎧ ⎫⎛ ⎞⎪ ⎪= ⎜ ⎟⋅⎨ ⎬⎜ ⎟⎪ ⎪⎝
⎛ ⎞⎛ ⎞⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠
⎠⎩ ⎭
=
∫∫
∫ ∫
1 ˆ( )H z Eη
= ± ×
y
x
V0
EH
0ˆ( , , ) jkzVE x y z y ed
= − ∓
2 20 *
1 1Re2
k zwP V ed η
′′+ −⎛ ⎞⎛ ⎞= ⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠
TEM Mode (cont.)
6
Transmission line voltage0
0
ˆ( )
( ) jd
z
kz
ck k
V z
V z E y d
V e
y ω με= ⋅ = =
=
∫∓
Transmission line current
( )
0
0
0
( )
ˆ( ) , ,w
k
I
j zI z
I z H x d z x d
V e
x
wdη
=
=
±
⋅∫
∓
Characteristic Impedance
00
0
jkz
jkz
V eZI e
−
−=
Phase Velocity (lossless case)
pr r
cv ω ωβ ω με μ ε
= = = c = 2.99792458 ×108 m/s
x
d
I
I+
‐V
y
z
C , ,ε μ σ
w
(Assume + z wave)
0dZw
η=
TEM Mode (cont.)
7
ˆs
sz z
J n H
J H+
= ×
⇒ =
PEC :Note:
For wave propagating in + z direction
Time‐ave. power flow in +z direction: { }*
200
2 20 *
1 1
1 Re *2
1
e
e2
2
R
R
k z
k zwP V ed
P VI
V wV edη
η
+
′′
′−
−
′+
=
⎧ ⎫⎛ ⎞⎪ ⎪= ⎨ ⎬⎜ ⎟⎝ ⎠⎪
⎛ ⎞⎛ ⎞= ⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠
⎪⎩ ⎭
Recall that we found from the fields that:
2 20 *
1 1Re2
k zwP V ed η
′′+ −⎛ ⎞⎛ ⎞= ⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠
same
TEM Mode (cont.)
(calculated using the voltage and current)
This is expected, since a TEM mode is a transmission‐line type of mode, which is described by voltage and current.
8
TEM Mode (cont.)
9
We can view the TEM mode in a parallel‐plate waveguide as a “piece” of a plane wave.
The PEC and PMS walls do not disturb the fields of the plane wave.
ˆ 0n E× =PEC : ˆ 0n H× =PMC :
y
PEC
PEC
PMCPMC , ,ε μ σ
x
E
H
Recall
( ), sin( ) cos( )
@ 0 0
@ 0,1,2,.... c
z c c
c
e x y A k y B k y
y B
y d k d n nkd
nπ π
= +
= ⇒ =
⇒= == ⇒ =
where12 2
2 2 2 22 2 0, [ ]c z c zk e k k k
x y⎛ ⎞∂ ∂
+ + = = −⎜ ⎟∂ ∂⎝ ⎠
subject to B.C.’s Ez = 0 @ y = 0, d
( , , ) ( , ) zjk zz zE x y z e x y e= ∓
TMz Modes (Hz = 0)
10
( ), sin 0,1,2,...zne x y A y ndπ⎛ ⎞= =⎜ ⎟
⎝ ⎠
sin zjk zz n
nE A y edπ⎛= ⎟
⎝ ⎠⇒ ⎞
⎜∓
Recall:
2 2
2 2
cos
cos
0 0 0
z
z
jk zc czx n
c c
jk zz z zy n
c c
x y z
j jE n nH A y ek y k d djk E jk n nE A y ek y k d d
E H H
ωε ωε π π
π π
∂ ⎛ ⎞ ⎛ ⎞= = ⎜ ⎟ ⎜ ⎟∂ ⎝ ⎠ ⎝ ⎠∂ ⎛ ⎞ ⎛ ⎞= = ⎜ ⎟ ⎜ ⎟∂ ⎝ ⎠ ⎝ ⎠
= = =
∓
∓∓ ∓
2 2
22
z ck k k
nkdπ
= −
⎛ ⎞= − ⎜ ⎟⎝ ⎠
2 2ck ω με=
TMz Modes (cont.)
11No x variation
sin zjk zz n
nE A y edπ⎛ ⎞= ⎜ ⎟
⎝ ⎠∓
Summary
22
2 2
cos
cos
0
; 0,1, 2,...
z
z
jk zzy n
c
jk zcx n
c
x y z
c
z
c
jk nE A y ek d
j nH A y ek d
E H H
nk nd
nk kd
k
π
ωε π
π
π
ω με
⎛ ⎞= ⎜ ⎟⎝ ⎠
⎛ ⎞= ⎜ ⎟⎝ ⎠
= = =
= =
⎛ ⎞= − ⎜ ⎟⎝ ⎠
=
∓
∓
∓
Each value of n corresponds to a unique TM field solution or “mode.”
⇒ TMn mode
Note:0
0TEM
zn k kTM= ⇒ =
⇒ =
12
TMz Modes (cont.)
(In this case, we absorb the An coefficient with the kc term.)
212
22
12 2 2
c
z
c
k
nk kd
k k
π⎡ ⎤⎢ ⎥
⎛ ⎞⎢ ⎥= − ⎜ ⎟⎢ ⎥⎝ ⎠⎢ ⎥⎣ ⎦
⎡ ⎤= −⎣ ⎦
0,1,2,...n =
2 2
2
2
2 2 2
2
z
z c z c
c
j z
c
k z
k k k k j k k j
e
k k k k
e α
β α− −
⇒ = = − ⇒ = − − = −
⇒
<
=
>
⇒propagating mode
for for
Fields decay exponentially⇒ evanescent fields⇒ “cutoff” mode
Lossless Casecε ε ε ′= =
2 2k ω με=
13
TMz Modes (cont.)
Frequency that defines border between cutoff and propagation(lossless case): fc ≡ cutoff frequency
@ cnf f=c cn
nk kdπω με= ⇒ =
12cnnfd με
= cutoff frequency for TMn mode
3cf1cf 2cf
14
TMz Modes (cont.)
cε ε ε ′= =
Time average power flow in z direction (lossless case):
( )*
0 0
*
0 0
2 22
0
1 ˆRe2
1 Re2
Re{ } cos2
w d
TMn
w d
y x
d
z nc
P E H z dydx
E H dydx
nk A w y dyk dωε π
± ⎡ ⎤= × ⋅⎢ ⎥
⎣ ⎦⎡ ⎤
= − ⎢ ⎥⎣ ⎦
⎛ ⎞= ± ⎜ ⎟⎝ ⎠
∫ ∫
∫ ∫
∫
22
; 0Re{ } 2
2 ; 00,1, 2,...
TMn z nc
d nP k A w
k d nn
ωε±⎧ ⎫>⎪ ⎪= ± ⎨ ⎬⎪ ⎪=⎩ ⎭=
Real for f > fcImaginary for f < fc 15
TMz Modes (cont.)
cε ε ε ′= =
Recall ( , , ) ( , ) zjk zz zH x y z h x y e= ∓
where
( )12 2
2 2 2 22 2 , 0, [ ]c z c zk h x y k k k
x y⎛ ⎞∂ ∂
+ + = = −⎜ ⎟∂ ∂⎝ ⎠
subject to B.C.’s Ex = 0 @ y=0, d
1 yzx
c
HHEj y zωε
∂⎛ ⎞∂= −⎜ ⎟∂ ∂⎝ ⎠
sin( ) cos( )@ 0 0
@ , 1,2,3,...
z c c
c c
h A k y B k yy A
y d k d n n nkd
π π
⇒ = +
= ⇒ =
= ⇒ = = ⇒ =
TEz Modes
ˆ 0H n⋅ =PEC :
16
( ), cos 1,2,3,
co
.
s
..
zjk zz
n
n
z
nH
nh x y B y nd
B y ed
π
π
⎛
⎛ ⎞⇒ = ⎜ ⎟⎝ ⎠
⎞= =⎜ ⎟⎝ ⎠
∓
Recall:
2 2
2 2
sin
sin
0 0 0
z
z
jk zzx n
c c
jk zz z zy n
c c
x y z
Hj j n nE B y ek y k d djk H jk n nH B y ek y k d d
H E E
ωμ ωμ π π
π π
∂− ⎛ ⎞ ⎛ ⎞= = ⎜ ⎟ ⎜ ⎟∂ ⎝ ⎠ ⎝ ⎠∂ ⎛ ⎞ ⎛ ⎞= = ± ⎜ ⎟ ⎜ ⎟∂ ⎝ ⎠ ⎝ ⎠
= = =
∓
∓∓
2 2
22
z ck k k
nkdπ
= −
⎛ ⎞= − ⎜ ⎟⎝ ⎠
2 2ck ω με=
TEz Modes (cont.)
17No x variation
Summary
cos zjk zz n
nH B y edπ⎛ ⎞= ⎜ ⎟
⎝ ⎠∓
TEn mode
Cutoff frequency1
2cnnfd με
⎛ ⎞= ⎜ ⎟⎜ ⎟
⎝ ⎠
Each value of n corresponds to a unique TE field solution or “mode.”
22
2 2
sin
sin
0
; 1,2,...
z
z
jk zx n
c
jk zzy n
c
x y z
c
z
c
j nE B y ek d
jk nH B y ek d
H E E
nk nd
nk kd
k
ωμ π
π
π
π
ω με
⎛ ⎞= ⎜ ⎟⎝ ⎠
± ⎛ ⎞= ⎜ ⎟⎝ ⎠
= = =
= =
⎛ ⎞= − ⎜ ⎟⎝ ⎠
=
∓
∓
18
TEz Modes (cont.)
For all the modes of a parallel‐plate waveguide, we have
12cnnfd με
⎛ ⎞= ⎜ ⎟⎜ ⎟
⎝ ⎠
The mode with lowest cutoff frequency is called the “dominant” mode of the wave guide.
1 2 3
3cf1cf 2cf
321
All Modes
19
cε ε ε ′= =
( )*
0 0
*
0 0
2 22
0
1 ˆRe2
1 Re2
Re{ } sin2
w d
TEn
w d
x y
d
z nc
P E H z dydx
E H dydx
nk B W y dyk dωμ π
± ⎡ ⎤= × ⋅⎢ ⎥
⎣ ⎦⎡ ⎤
= ⎢ ⎥⎣ ⎦
⎛ ⎞= ± ⎜ ⎟⎝ ⎠
∫ ∫
∫ ∫
∫
{ } ( )22 Re
4TEn z nc
P k B Wdkωμ± =
n = 1,2,…..
Power in TEz ModeTime average power flow in z direction (lossless case):
Real for f > fcImaginary for f < fc 20
cε ε ε ′= =