Hi Marco
Thanks for your answer. I share much of your opinions... and i think there is still something I´m missing. Rather than being a pure CST software question, my doubts are related to EM. May be it´s a matter of nomenclature. For me, "even" and "odd" refer to classic CPW, with "even" mode meaning E lines from strip to lateral grounds. Apart from that,when I say "microstrip" mode I mean E lines from strip to bottom conductor, with "CB-CPW mode" being a combination of these "even" and "microstrip" modes. And If I understood well, you call "even mode" this very mode with E lines from strip to lateral and ground planes... yes, this is also the normal propagation mode for me, but I think it remains being a combination of two modes, in some sense... If you make the gap wider and wider, there`s a point in which the E lines from the center strip leave the lateral grounds and end in the bottom conductor... But, If it were a combination of the other calculated two modes, CST wouldn´t show it, obviously... Yep... probably it´s a mode on it´s own.
Anyway, and specially if these 3 modes are "linearly independent", my main concern is if I have to consider (and define) the other two modes when simulating a CB-CPW in a multipin waveguide port. Of course, it will depend on whether the other two modes are or not excited in my structure... but i think this again depends on where you place the vias from top to bottom planes, the interface with wich you connect to the CB-CPW (coax, 2wire, microstrip, slotline...if you connect your coax external conductor only in one lateral ground). Whenever you have a transition, there are local higher order modes excited, and it seems factible for me that this modes excite the other two QTEM modes, apart from the "even" one.
As to my knowledge, considering only this "even"(E from strip to lateral and bottom planes) mode gives good results and I'll continue simulating this way, but I think there´s something with the other 2 modes that...mmmm... I still don´t understand it completely. May be I'm wrong and they are excited only occasionally...
And with regards to the line impedance, if your mode is TEM or QTEM (in TE and TM modes you can define your impedance in different ways) no matter how you calculate it, I think it MUST give the same value for a multipin port mode or a mode from the normal waveguide port, as long as field line distribution is the same (that is, the mode is the same). It´s a matter of the material properties and the geometric configuration of the waveguide. If we talk about input impedance, then, of course, position along the waveguide makes this impedance change. But line impedance is a characteristic of your waveguide structure, and that´s why I don`t understand why same modes give different line impedance values. This question remains unresolved for me.
But thanks again!!!
Iban