How may I plot S parameter curves in dB unit ?

[wsteffe]

Let consider the annexed test case.

monoliticOnLTCC_qucs.zip

As you may see the S parameters are not plotted in dB units as usual for this kind of data.

I have tried to put dB(S[1,1]) instead of S[1,1] into the trace expression but it does'nt work. Any hint ?

Thanks

[ra3xdh]

I cannot reproduce the plotting issue. I guess you are simulating in Qucsator mode. The attached schematic doesn't contain the equations. I guess you didn't use the equations or using the equations wrong. Refer to the examples in the share/qucs-s/examples/qucsator subdirectory. It contains an example of dB plotting with S-parameters. Keep in mind that Nutmeg equation will not work in SPICE mode.

Also the archive doesn't contain the s2p file. The schematic will not work without it.

[andresmmera]

@wsteffe You can try with the example attached. Simply replace the S2P file as needed.

As @ra3xdh said, the equation block is missing.

Plot_S2P_prj.zip

[wsteffe]

Hello ra3xdh. Many thanks for help.
In fact using qucsator and variables dBS11, dBS12 defined in equations it works.

I had already tried a similar approach before (using both nutmag or qucsator equations) but it gave me an error (indefinite variable or something similar) I do not know what has changed but now it is fixed.

Many thanks

[ra3xdh]

I had already tried a similar approach before (using both nutmag or qucsator equations)

I guess you have used qucsator syntax with SPICE or SPICE syntax with Qucsator. Different simulation kernels require different S-parameter equation syntax. Qucsator equations supports only limited syntax subset in SPICE mode. Refer to the examples shipped with Qucs-S distribution for S-parameters simulation examples with equations. It contains examples for both Ngspice and Qucsator.

Closing this issue as resolved and transferring to Discussions/Q&A