![]() ![]() I hope this question isn't too confusing. I worry I've missed an important point here. Normalized impedance, Z ZL/ Zo r+ jx, where r R / Z0 and x X / Z0. This is because the behavior of the transmission line depends on load impedance as well as characteristic impedance. But, it seems to me that the kind of impedance matching operation described above is simply using the impedance(conductance) map and its ability to express complex addition and subtraction to move from one point to another and each points relationship to reflection isn't really relevant. Normalized impedance is used for plotting on Smith chart. In other words, the charts "meaning" is related to reflection. Smith Chart 2 To move along line 1, we need to normalize with respect to Z01. What I don't understand is, where is the reflection coefficient in any of this? If I understand the chart correctly, it basically maps the reflection coefficient for a normalized characteristic impedance to every possible (within reason) impedance (or conductance). Then divide the resistance and reactive values by 50 : 1.2 + j0.8 Once you plot that value, draw the SWR circle through the. If you need to match one impedance to another (one would be a conjugate), you simply identify the two impedances on the chart (normalized if necessary) and track a path between the two using the rules above. Plot the load impedance on the Smith chart using the normalized value. If you use a combined impedance and conductance chart you can easily model ladder networks, which of course is exactly what you need for an L, Pi or T matching network. Likewise, adding reactive elements in shunt can be achieved with the conductance form of the Smith Chart again using a simple addition or subtraction. The text points out that adding reactive elements in series with a resistor is a simple matter of adding the appropriate imaginary quantity, thus moving you along the constant resistance circle. He uses some of the earlier matching examples (solved using equations) and shows how the same result can be obtained using the Smith Chart. I've been reading the impedance matching chapter of Bowick's excellent RF Circuit Design book and I have a question.įor those who haven't read this book (or have but can't remember!), the chapter discusses L and 3 element matching networks (very intuitively, I might add) with some helpful examples before moving to an introduction to the Smith Chart. ![]()
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