harry_dresden
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b1=S11a1+S12a2 ---(1)
In all references (that I can find), says that as long as load impedance equal to characteristic impedance, ZL=Z0, a2 will be 0, from (1), we can then find S11.
1. Say for this two port device under test, [S], has an output impedance of Zout, note that this is not the load impedance, ZL. My question is, assuming the output of [S], Zout is not match to Z0, would there be a reflection? If yes, a2 is not 0, this means that the S11 for [S] could not be obtain from (1).
2. Another question on similar context, but from another angle: refer to the figure attached, looking back into the transmission line with characteristic impedance of Z0 from the load, do we really see Z0? Say if the transmission line is quarter wave length, in order to have match (no reflection), we should choose the Z0= root(ZoutZL*), where Zout is the output impedance of [S]. In other words, when we look into the transmission line from the load, we see ZL* not Z0. While most reference never mention that Z0 is observed from that point, it seems to imply it that way as there is no discussion on this equation (Z0= root(ZoutZL*)), which is the condition to achieve match. Sure, we can consider in terms of lump element and the transmission to be negligible short. In this case, the matching condition, should be just ZL*=Zout not ZL=Z0.
Can anybody with a good understanding on this fundamental please help explain these clearly to me?
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