hello everyone! thank you for your visit.

I have been simulating coupled transmission lines for several days,i don't know the way to simulate it directly.i simulate the four ports single-ended S-parameters first and then use some equations to turn these data into mixed mode such as Sdd11.i have several problems.

problem 1:is there a direct way to simulate S-parameter of diff_pair signals through coupled transmission lines?

problem 2:when i use the ideal tclin,the results is much better than pclin2, i am wondering that the impedance doesn't match,have you ever use the linecal to calculate the impedance of PCB coupled lines?could you tell me how to calculate the impedance?

i'm a new one to use ads,and i think the question is a little bit low-level.thank you very much for your answer.and i attach the schematic and data display window.

I have been simulating coupled transmission lines for several days,i don't know the way to simulate it directly.i simulate the four ports single-ended S-parameters first and then use some equations to turn these data into mixed mode such as Sdd11.i have several problems.

problem 1:is there a direct way to simulate S-parameter of diff_pair signals through coupled transmission lines?

problem 2:when i use the ideal tclin,the results is much better than pclin2, i am wondering that the impedance doesn't match,have you ever use the linecal to calculate the impedance of PCB coupled lines?could you tell me how to calculate the impedance?

i'm a new one to use ads,and i think the question is a little bit low-level.thank you very much for your answer.and i attach the schematic and data display window.

Yes. The are two approaches. If you want to drive the differential mode, without defining/terminating the common mode, you can use 2 ports (instead of 4) and connect your port symbol (+) and (-) differentially *between* the line pins (instead of connecting to GND symbol)

If you have a more complex layout, where some mode conversion happens, the better approach is to insert a mode conversion block that splits the (+) and (-) signals into differential and common mode. In ADS, this mode conversion block is available in the System-Passive palette: Balun4. That element converts between the (+) and (-) pins and the c=common mode and d=differential mode ports. To get started, you can try it with a simple testcase.

> problem 2:when i use the ideal tclin,the results is much better than pclin2, i am wondering that the impedance doesn't match,have you ever use the linecal to calculate the impedance of PCB coupled lines?could you tell me how to calculate the impedance?

A typical misunderstanding for differential lines is the definition of even and odd modes. Linecalc uses even and odd mode impedance, which is defined with respect to a line of symmetry, and *not* between the (+) and (-) pin of the line. If you want to design for a 100 Ohm system with a differential line impedance of 100 Ohm, your required Zodd is 50 Ohm and not 100 Ohm. Maybe that is where you got lost?