Question about multiple-layer structure simulated by HFSS

[tang76]

Dear all,

I attached 3 models RX_J4RX.hfss, RXRX_J4.hfss and RXRX_J4RX.hfss about multiple-layer structure simulated by HFSS. I need to calculate the S parameters of these models.

The third model RXRX_J4RX.hfss, is exactly the combining of models RX_J4RX.hfss and RXRX_J4.hfss, therefore, the transmission matrix of third model should be the product of matrices of former two models. i.e., T3 = T1 * T2

On the other hand, the transmission matrix can be transformed by S parameter matrix:
T(1,1)=1/S(2,1)
T(1,2)=-S(2,2)/S(2,1)
T(2,1)=S(1,1)/S(2,1)
T(2,2)=(S(1,2)*S(2,1)-S(1,1)*S(2,2))/S(2,1)

therefore, I calculated S parameters of three models S1, S2, and S3, and then transform S1 and S2 to transmission matrix T1 and T2, then the transmission matrix of third model should be T3 = T1 * T2, and then the S parameter matrix of third model by the other method is also got:
S(1,1)=T(2,1)/T(1,1)
S(1,2)=(T(2,2)*T(1,1)-T(1,2)*T(2,1))/T(1,1)
S(2,1)=1/T(1,1)
S(2,2)=-T(1,2)/T(1,1)
Two S parameter matrices by two different methods should be agree with each other.

However, now there are very large difference between these two methods, could anyone help me to take a look at it?

Thanks

 

[volker@muehlhaus]

I don't have HFSS and I have not looked at your files, but here is a general comment on this topic:

If you cascade EM models that have been simulated separately, the signal flow is only through the ports that you have defined, with the modes that you have defined. If you simulate everything in one big model, there could be additional EM coupling between the pieces, or maybe some mode that couldn't propagate because of your port definitions (e.g. common mode signal if you defined differential ports).

 

[tang76]

Dear volker,

Thank you very much for your kindly reply.

But how to 'find' the addition EM coupling between the pieces? Can I add more Floquet modes in HFSS simulation? I can simulate with multiple modes excited in Floquet port and the S parameters of multiple modes are calculated, but how to understand the S parameters of multiple modes and how to calculate the global S parameters?

On the other hand, do you mean that this method is impossible, since simulate two models separately always can't consider additional EM coupling between the pieces?

Thanks,
Tang Laoya