Port Impedance in HFSS

- September 25, 2019 at 2:35 pm
  
  bamdadslr
  Subscriber
  
  Hi everyone,
  
  I want to define a lumped port in HFSS (driven terminal solution type) to model a voltage source with an internal resistance of 5 kohms. So, I am defining a sheet (which is assigned as the lumped port), and then after a short distance (which is modeled by a cylinder), I define another sheet to assign 5 kohms to it as the interal impedance of the source. Is it the right way of doing that?
  
  Thanks,
  
  Bamdad
- September 30, 2019 at 3:51 pm
  
  Sorceress Gia
  Ansys Employee
  
  That should work in theory but you can just set the port source impedance in the lumped port settings to be 5k ohms instead of 50 ohms...
- September 30, 2019 at 3:55 pm
  
  bamdadslr
  Subscriber
  
  Thanks for your answer Peter. Actually I have tried that before, changing the port impedance from 50 ohms to 5k, but in makes it very hard for HFSS to converge (I don't know the reason). When I change the port impedance in this way, the same structure takes (at least) twice of the mesh numbers and time to converge.
- October 1, 2019 at 5:02 pm
  
  Sorceress Gia
  Ansys Employee
  
  If the port impedance is not matched to the system then most of the energy will be reflected back - and there will be little energy to excite the structure you are trying to model - which is why the simulation is having trouble converging.
  
  So for whatever device you are trying to model, most likely if you had the same device in reality and tried to drive it with this source with 5k impedance, most likely your device will reflect back all the energy you put into it and it will not radiate.