Impedance Matching

Impedance matching is a procedure for obtaining the maximum power transfer to a load. What is a goal for microwave design? If we can give maximum power to a load, we succeed in design. Impedance matching allows us to make that happen.

1. Impedance
Matching
Antenna EngineeringAntenna Engineering
CHO, Yong HeuiCHO, Yong Heui

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EM Wave LabEM Wave Lab2
1. Impedance Matching
Basic Concept
Voltage or Current Ratio is a key factor
→
Load
Wave

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EM Wave LabEM Wave Lab3
Maximum power transfer
1. Impedance matching
Condition for maximum power transfer
-
Matching network
- Usually source and load are fixed.
Reflection
- Conjugate matching doesn’t mean no reflection.
No reflection
-
 *
0
)(
L
ZZ=
L
ZZ=
0

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EM Wave LabEM Wave Lab4
출처: KAIST
1. Impedance Matching
Variable Phase Shifter

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EM Wave LabEM Wave Lab5
Matching with lumped elements
Compact size
Difficulties in finding the proper value of L or C
L-network, T-network, and -network

P
1. Impedance matching

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EM Wave LabEM Wave Lab6
Procedure: L-network
Define
Draw
Find to intersect the circle
Draw
Find to cancel out
 0
/ZZz
LL
=
LL
zy/1=
jxz
L
+=1
11 =++= jXjxz
in
jB
L
z
jX jx
1. Impedance matching

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EM Wave LabEM Wave Lab7
Example
Design the L section matching network to match
the transmission line,
where

[] [] MHzfZjZ
L
500,100,100200
0
=W=W-=
Smith chart
1. Impedance matching

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EM Wave LabEM Wave Lab8
Single-stub matching
Open stub and short stub
Short stub (L)
Open stub (C)
1. Impedance matching

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EM Wave LabEM Wave Lab9
Single-stub matching
Simple matching network
Smith chart
1. Impedance matching

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EM Wave LabEM Wave Lab10
Procedure: shunt stub
Define
Draw
Move to the direction of
generator
Find the intersection of the
circle
Adjust the length of a shunt
stub
 0
/ZZz
LL
=
LL
zy/1=
jby
L
+=1
jby
S
-=
11 =-+=
+=
jbjb
yyy
SLin
1. Impedance matching

11. Antenna EngineeringAntenna Engineering
EM Wave LabEM Wave Lab11
Example
Design the single-stub shunt tuning network to
match the transmission line,
where

[] [] GHzfZjZ
L
2,50,1015
0
=W=W+=
Smith chart
1. Impedance matching

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EM Wave LabEM Wave Lab12
Double-stub matching
Fixed length between the load and stub
Smith chart
1. Impedance matching

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EM Wave LabEM Wave Lab13
Quarter-wave transformer
Easy calculation of the matching network
Narrow bandwidth characteristics

4/,
01
l== lZZZ
L
1. Impedance matching

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EM Wave LabEM Wave Lab14
Transitions
Complicated design procedure
Broad bandwidth characteristics
The theory of small reflections

Binomial multisection line
Chebyshev multisection line
Tapered line

1. Impedance matching