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4.6 S-Parameters, Impedance and Smith Charts in MWO 197 Now, if we want to measure the values of the impedance we must first measure ( ) as seen by PORT 1 (Figure 4.6-4). To measure our reflection coefficient in MWO, we will use an S 11 measurement which, as we have seen in section 3.6 is the same as the reflection coefficient for a one-port network. We would then normally use equation (4.1-1) to convert this value into an impedance ( ) , however MWO allows us to carry out this conversion in several, simpler ways. The easiest one would entail plotting the reflection coefficient on a Smith Chart and reading the value of the impedance directly from the chart markings or by using a marker. Be careful though! This impedance is not ZL! It is the combination of a line, with electrical length EL and characteristic impedance Z0, and ZL!! Remember that the impedance seen at PORT 1 may be derived from the phase and magnitude of the reflection coefficient S11 ( eq.(3.5-3)). Now the magnitude of S11 is determined by ZL alone and hence is not affected by the length of the line EL (section 3.1), but its phase is. In a laboratory environment we would have apply a technique called de-embedding (section 3.8) in order to work out the phase of S11 right at the load terminals and then calculate ZL from the 'adjusted' S11. This may of course be done in MWO also, however the simulator also allows us to probe and measure impedances in many places in our circuit which in the real world would not be directly accessible. This is very useful! Now that we have illustrated some basic simulation concepts, we will delegate the teaching of the remainder of the material on passive circuits to our video tutorials. These will explain in great details how to analyse and design passive circuits at RF and Microwave frequencies. In particular the reader will learn how to design various types of matching networks which are essential building blocks of most high frequency circuits. Conquer Radio Frequency 197 www.cadence.com/go/awr

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