why are the results of different port types different for the same structure in HFSS?

[afz23]

why results of different port types are different for same structure in HFSS?

I simulated a SIW resonator with wave ports first and got the expected results.But when I simulated the same structure with lumped ports results were very different.What could be the reason? I expected the results to be identical.

 

[MuroSamuro]

Re: why results of different port types are different for same structure in HFSS?

I've read about it,
from what i understand, in order to use lumped ports u must know the charectaristic impedance of the connecting feeding in order to get right results of s-parameters.
In the case u use wave ports, one port defining the reference impedance so u avoid that problem

 

[afz23]

Re: why results of different port types are different for same structure in HFSS?

Hi ,

Wave port assumes that ,it is connected to a long 50 ohm,(characteristic impedance) wave guide,so it
calculates s-parameters for a 50 ohm system.

If I choose ,50 ohm characteristic impedance of a lumped port,than its
like terminating the port with 50 ohms,I should get same results in both the cases.

 

[nomigoraya]

Re: why results of different port types are different for same structure in HFSS?

HFSS has different set of Ports and boundary conditions each with a unique set of characteristics and for a particular case to be use. Yes for sure there may be cases where we can use different ports and boundaries without affecting the results but results can be changes as well. Lets look at the definition of two types of ports under discussion from HFSS
Wave Port
HFSS assumes that each wave port you define is connected to a semi-infinitely long waveguide that has the same cross-section and material properties as the port. When solving for the S-parameters, HFSS assumes that the structure is excited by the natural field patterns (modes) associated with these cross-sections. The 2D field solutions generated for each wave port serve as boundary conditions at those ports for the 3D problem. In addition to serving as a boundary condition, a wave port also supplies port impedance and propagation constants that are useful in describing waveguides or transmission lines.
Lumped Port
Lumped ports resemble wave ports, but can be located internally and have a complex user-defined reference impedance. Lumped ports are restricted to single mode ports and the S-parameters are always based on the user defined reference impedance. This mainly because no transmission line is being modeled in the interior domain which suggests an interpretation of the lumped port as a measurement probe being connected to the surface of the lumped port with the reference impedance specified by the user.