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RF<br />
signal X<br />
RF<br />
signal X<br />
RF<br />
signal X<br />
5-2<br />
<strong>Impedance</strong> matching (or tuning) is important for the following reasons :<br />
incident<br />
(or input)<br />
reflection<br />
<br />
in<br />
Z0<br />
Zin<br />
Reflection<br />
<strong>Matching</strong><br />
Network<br />
coefficient<br />
Return<br />
( or S11) ( Zin<br />
Z0)<br />
/( Zin<br />
Z0)<br />
Loss) :<br />
2011-12 H.-R. Chuang EE NCKU<br />
(or<br />
Load<br />
minimum power loss in the feed line & maximum power delivery<br />
linearizing the frequency response of the circuit<br />
improving the S/N ratio of the system for sensitive receiver components (lownoise<br />
amplifier, etc.)<br />
reducing amplitude & phase errors in a power distribution network (such as<br />
antenna array-feed network)<br />
* Factors in the selection of matching networks<br />
- complexity -b<strong>and</strong>width requirement (such as broadb<strong>and</strong> design)<br />
- adjustability - implementation (transmission line, chip R/L/C elements ..)<br />
<br />
/4 microstrip RF Choke<br />
l<br />
Z0<br />
0.5 0.25<br />
Short-<br />
Cirucited<br />
(S.C.)<br />
* At high freq.,<br />
capacitance is like<br />
4 Short-cirucited<br />
2<br />
X sc / Z0<br />
-2<br />
-4<br />
ZL<br />
RF Choke<br />
扼流圈
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