[HFSS] - Extracting Input Impedance from a Lumped Port

[vannik]

lumped port impedance calculation

Is there a straight forward way of extracting what the input impedance of a device (i.e. an antenna fed with a lumped port) is? An impedance for the lumped port must be specified, so is it normally done by computing the real and imaginary components of S11 and backing out the device impedance since you know the reference impedance?

Is there an easier way than this (something built into HFSS)?

Thanks

 

[shameemkabir]

plotting input impedance hfss

Is there an easier way than this (something built into HFSS)?

draw the relection (S11) on smith chart. Put the marker on the interesting points and you know the impedances.

 

[vannik]

it appears that the Z parameter plot (not port Zo) gives the same values that you can calculate from the s-parameters for this 1 port case, FYI.

 

[shameemkabir]

it appears that the Z parameter plot (not port Zo) gives the same values that you can calculate from the s-parameters for this 1 port case.

you are right. However, you can also see from the S-parameter plot the impedances. Please take a look at the two figues where I put the markers at the same frequency. From the S-parameter plot you can see that RX=1.4106+0.0248i. Since this value is normalized to 50 ohm you need to multiply with this value to get the absolute value.

Now if you take a look at the Z parameter plot, you see the same value (a little bit different in some cases). Therefore, you can know the impedance from both the plots.

 

[Mantas]

Hi,
Im a little confused. As I look into your plots I can't see the same values... I understand that shmit chart is correct and understandable to me. You just multiply RX to 50 ohm and in your example you got RX=1.4106+0.0248i so RX50ohm=70.53+1.24i ohm So I hope to see these values in your first plot, but I only see ~68 ohm. My question is how it is possible to see those RX values in your first plot??

 

[shameemkabir]

sorry, I couldn't find the same simulation. Putting the result from CST MWS (you get the same in HFSS). Real, imaginary part of Z and smith chart.