Hi,
I am trying to use COMSOL to simulate some lumped-element based transmission line structure (modified CPW line by increasing series inductance and shunt capacitance) by having lumped ports on both ends. While I could sweep the shunt capacitance and obtain a 50 Ohm transmission line with a certain configuration (a certain shunt capacitance for instance), I realize that if I simulate the same structure with a longer length by repeating the unit cell, I obtain a different result. That is, the shunt capacitance needed to give a 50 Ohm structure is different for different TL length.
My original goal was to obtain an equivalent LC-ladder for the lumped-element TL, it will be critical to obtain a consistent and accurate S11 from the simulation. Your advice will be much appreicated.
PS: More details on the structure: The lumped-element transmission line is formed by having series inductance along a CPW, and in between the lumped inductors, there are 1 to 2 open-ended stubs to provide shunting capacitance. By sweeping the shunt capacitance, I meant sweeping the length of these open stubs.