# Obtaining input/out impedance from S-parameters for a L network

This L network intend to transform Z1 to 50ohms. The design was made using a smith chart:  The s-parameters plotted (S11 red - S22 green) in the smith chart is done sweeping the frequency from 200MHz to 5GHz for this L network. If the reflection parameters represents the input/output impedance of the network, looking to the markers we have:

m1: f=900MHz, Z1=29+j22.5 (~ as expected)

m2: f=900MHz, Z2=66-j43,5

Considering ideal components in simulation, why the marker 2 (m2) is not in 50ohms? Thanks!

• Hello Felipe, and welcome to this site! :-) Jan 8 at 22:10
• Figure one is a transformation. For a fixed frequency. Matching is only for a single frequency. Figure 2 is a sweep. For the operating frequency your assumption is right; not for a sweep. Jan 9 at 11:48
• Felipe, some anonymous person just tried to ask for clarifications by suggesting this edit: "Frequency? Actual values? The second figure is a sweep....." (which is not the way to do that, yes). But I copied it here since @F.Sessink's comment was similar. Jan 9 at 21:54
• You're not clear what the second chart is. Guessing, is it the fixed impedance (about 35-j25) transformed by actual parallel L and series C, as per the design in chart 1, and then this plotted over frequency, for a range of frequencies away from the frequency at which you chose L and C in the first place? Why do you expect anything else? Jan 10 at 4:59
• @FelipeKalinski Sorry it's still not clear what the question is, and what the second diagram actually is. "L network" is not enough. If both markers are 900 MHz, why aren't they at the same place? Why is part of the line red and part green? Add a legend. Is the line drawn as Frequency changes, or something else? Over what range? What is the value of the independent variable at m1 and m2. Also draw the full circuit showing where Z1 and Z2 are measured. Jan 11 at 13:56 