文档介绍：Chapter 3Matching and Tuning
By
Professor Syed Idris Syed Hassan
Sch of Elect. & Electron Eng
Engineering Campus USM
Nibong Tebal 14300
SPS Penang
©Prof Syed Idris Syed Hassan
Why matching or tuning is important?
To maximize power delivery and minimize power loss.
To improve signal to noise ratio as in sensitive ponents such as LNA, antenna, etc.
To reduce amplitude and phase error as in work such as antenna array.
Basic idea of impedance matching
Concept of maximum power transfer
Power maximum whence ZL = Zo
Power deliver at ZL is
In lump circuit
continue
In transmission line
No reflection whence ZL = Zo , hence
The load ZL can be matched as long as ZL not equal to zero (short-circuit) or infinity (open-circuit)
The important parameter is reflection coefficient
Factors in selecting work
Complexity: simpler, cheaper, more reliable and low loss circuit is preferred.
Bandwidth: match over a desirable bandwidth.
Implementation: depend on types of transmission line either cable, stripline, microstripline, waveguide, lump circuit etc.
Adjustability:work may need adjustment to match a variable load.
Matching with lumped elements
The simplest work is an L-section using two reactive elements
Configuration 1
Whence RL>Zo
Configuration 2
Whence RL<Zo
ZL=RL+jXL
continue
Configuration 1
Configuration 2
If the load impedance (normalized) lies in unity circle, configuration 1 is configuration 2 is used.
The reactive elements are either inductors or capacitors. So there are 8 possibilities for matching circuit for various load impedances.
Matching by lumped elements are possible for frequency below 1 GHz or for higher frequency in integrated circuit(MIC, MEM).
Impedances for serial lumped elements
Serial circuit
Reactance relationship values
+ve X=2pfL L=X/(2pf)
-ve X=1/(2pfC) C=1/(2pfX)
Impedances for parallel lumped elements
Parallel circuit
Susceptance relationship values
+ve B=2pfC C=B/(2pf)
-ve B=1/(2pfL) L=1/(2pfB)
Lumpe