CHAPTER 4 - Impedance Matching
186
Figure 4.4-5 Constant normalised resistance circles and normalised reactance lines form the Impedance Smith chart grid
The mathematics behind the creation of this plot are beyond the scope of this treatment but
what you MUST remember when you look at a Smith chart, is that it is a polar plot of the reflection
coefficient upon which we have superimposed (Figure 3.6-2) a very cleverly designed mask to read
out impedance values directly without having to use conversion formulae!
Bearing in mind how the impedance chart is constructed (Figure 4.4-3 and Figure 4.4-4), it is
apparent that its top half represents impedances with inductive reactances and the bottom half
represents impedances with capacitive reactances (Figure 4.4-6).
Note that all points on the outer circle represent impedances which are purely reactive:
purely inductive in the upper half and purely capacitive in the bottom half.
Figure 4.4-6 Inductive and capacitive halves of the impedance Smith chart
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