I am trying to simulate a coupled differential micrsostrip transmission line in CST to obtain the differential impedance. I used two (full plane) waveguide ports to obtain the even mode model, the port mode results I got only contained the wave impedance.
In an attempt to obtain the odd mode, I sliced the model into two halves, as shown in the figure, and used 4 waveguide ports. The s-parameters obtained and the field current did not follow the expectation, as I was getting current at the dielectric (Rogers RO3003). Is there a way I can obtain a line impedance for the structure? I tried the same procedure with a single microstrip and I only obtained the wave impedance.
If I understand correctly the question, to find the impedance of the odd mode, it is sufficient to put an electric wall in the symmetry plane. Strictly speaking, the height of the wall should be infinite. But in the simulation it is sufficient that its height is 3 -5 times larger than the thickness of the dielectric.
For Microstrip lines the port has ton include the area surrounding the microstrip, hence, the port dimensions need to be extended to include that.
In order to simulate the differential line approach mentioned is valid, a different method would be one waveguide port with multiple pins, which allows defining the direction of the current in each strip for odd mode. The calculate macro can be used for a single ended waveguide port to calculate differential imoedance and differential s-parameters
Hi,
Take a look at the attached file. it covers both the issue of correct port definition as well as differential ports.
For microstrip, as Jacob says, use a magnetic wall along the centre-line to get the common mode impedance, and an electric wall to get the differential mode impedance.
The solver allows you to choose just to solve the port modes, which is very quick, and the impedances and wavenumber are shown when you select the results files for the port modes.
- Badges
- Science topic
- Similar topics
- Computer Communications (Networks)
- Simulators