CHAPTER 5 Impedance Matching and Smith Chart

5-19
Microstrip Line Matching Networks (Ludwig P431)
In the mid-GHz and higher frequency range, the wavelength becomes
sufficiently small and the distributed components are widely used. Also, the
discrete R/L/C lumped elements will have more noticeable parasitic effects (see
chapter 2) and let to complicating the circuit design process
Distributed componenets (such as transmission line segments) can be used
to mix with lumped elements
From Discrete Components to Microstrip Lines
Avoid using inductors (if possible) due to higher resistive loss (& higher price)
In general, one shunt capacitor & two series transmission lines is
sufficiently to transform any load to any input impedance.
EX: transform load ZL to an input impedance Z in
Z
L 30 j10
Zin
60 j80
f 1.
5 GHz
zL
0.
6
zin
1.
2
Identify input & load SWR circles
j0.
2
Choose A (yA= 1-j0.6) & transform zL to
A by a series TL (l1)
=>Transform A to B (on the input SWR circle)
by a parallel C1
=> Transform B to zin by a series TL (l2)
zL + series-TL (l1)
=> A + shunt C1
=> B + series-TL (l2)
=> zin
j1.
6
2011-12 H.-R. Chuang EE NCKU