How to compare S-parameters between HFSS and Measurements

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hertz

Newbie level 5
hfss s(1:1, 2:2)

Hi,

I am looking at a simple rectangular waveguide and simulate in HFSS. I use waveport simulation for up to 3 modes from 1-20GHz. I think the number of modes are sufficient in this case. There are different combinations of S-parameters like S(waveport1:mode1,waveport2:mode1), S(1:2,2:2), S(1:2,2:3), etc.

How do you actually combine these S-parameters if you, for example, want to compare with network analyzer measurements? Should you just sum the square of all the S12, then do the same thing for S11, S21, S22.

I tried to do this for S12. I only sum the modes S(1:1,2:1), S(1:2,2:2) and S(1:3,2:3). But I started to get the results greater than 1 after the 2nd cutoff?

-Hertz

navuho

s(1:1,1:2)+hfss

How do you actually combine these S-parameters if you, for example, want to compare with network analyzer measurements?

Network analyzer works only with single-moded waveguid's components. In other case you will not be able to calibrate it.
So, to measure at high frequency band you need also change WG-calibration set. And the results of measurement are four S-params,
which describes two single-mode ports.
Why do you need to take into account 3 modes?

I started to get the results greater than 1 after the 2nd cutoff
It's OK
Modes bellow cut-offs don't transmit a power. Just realize that you have
a very short waveguide and defined 10 modes at the input. Because the length is
neglible and the attenuation due to cut-off also you will have the s12 close to 1 for each mode!
The power conservation's law will work only for modes which transmits the power.

yanal_ysf

Points: 2