Help! Sonnet microstrip

Hi, I am new here and relatively new to RF.

I am trying to make a circuit in microstrip that will match a 50 ohm source to a 10 ohm load. I am trying to do it with 4 quarter-wave transformers (seems easy enough for a beginner like me)

i calculated lamda/4 to be 212.59 for the roggers 6006 laminant (dielectric constant of 6.15 and loss tangent of .0027)

i then used txline to find widths that would correspond to the desired impedence values.

so the source is 50 ohms and i found that that corresponds to a width (in mils) of 72.8ohms
load is 10 ohms which is a width of 660 mils(which is huge and over a quarter wave btw)
i then chose an arbitrary impedence value for one of the quarterwave transformers and calculated the rest of the impedences of the quarterwave transformers from that.

I assumed transformer #2 to be 40 ohms (width 106.5) and calculated that:
the first quarter wave transformer should be 44.72 ohms - this is a width of 88.7
the third quarter wave transformer should be 35.78 ohms - this is a width of 127
the fourth quarter wave transformer should be 32 ohms - this is a width of 150

i made a sonnet project to represent this and the s11 response is just horrible; i get loads of return power rather than having it be negated due to matching. I want it to be under -20dB for the range of 2-4Ghz

I dont see anything wrong with my Sonnet project but if someone could help me understand what is wrong with my project/approach then please let me know.

Hi,

in your model, you have an input port but the other end of the line is open. You must add a second port at the 10 Ohm end of the line. I have made that change and simulated your model again. For faster analysis, I used symmetry (Circuit > Box > Symmetry).

For the lambda/4 calculation, you should consider that effective epsilon depends on the line width. Sonnet will plot this as a side result of the port calibration and we get eps_eff=4.34 on the 50 Ohm side and eps_eff=5.55 on the 10 ohm side.

This document might be useful to you:
http://www.muehlhaus.com/files/Z0_diagrams.pdf


Best regards
Volker

Thank you very much for the help Volker. That is document is really nicely written; thanks a lot for writing it / sharing it.

I should be able to make some good designs now I think.

Thanks a lot for the help.