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HFSS simulation of a multiport network

nikosnte

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Hi all,
i am new to HFSS software and i'm trying to simulate a ten port network. After i simulated it first time, i received all the s-parameters and i checked at fields->edit sources that only port 1 had excitation power amplitude of 1W and all the others had zero. From what i understood when i saw it, i thought that only port 1 should excite the structure and the other ports should act as matced loads during the entire simulation, but the simulation gave me all the s parameters, as all ports were excited. These power amplitudes are just scaling factors or they are the actual power that stimulates each port? Because it didn't make sense to me. Thank you
 

PlanarMetamaterials

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From what i understood when i saw it, i thought that only port 1 should excite the structure and the other ports should act as matced loads during the entire simulation, but the simulation gave me all the s parameters, as all ports were excited.
S-Parameters are always defined, regardless of what fields you are exciting in the model.
 

nikosnte

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Yes, but if i don't excite port number two for instance, how is S22 defined? Where does the incident wave at port two come from?
 

PlanarMetamaterials

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Another way to phrase my previous comment could be something like: the excitation you specify in the ports editor has nothing to do with the computation of the S-parameters.
 

nikosnte

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Ok got it, so what difference does it make for my results if i leave it as it is by default (only port 1 is excited with 1W of power amplitude) and if i specify amplitudes for the other ports as well?
 

PlanarMetamaterials

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Changing the port excitations only changes the post-processed results, such as displayed fields, computed field-based quantities such as SAR, far-field radiation patterns, etc.
 

nikosnte

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Ok thanks. Do you know if there is any way that i can only use 6 of my 10 ports? In cst i know this is possible but regarding HFSS i searched the web but didn't find something useful about how to do this. The reason is that i would like to treat these 4 ports as matched loads without exciting them at the entire simulation
 

PlanarMetamaterials

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Ok thanks. Do you know if there is any way that i can only use 6 of my 10 ports?
I'm not sure what you mean by this. Are you wanting to visualize the fields when you've excited six of the ports? In this case, just set the power magnitudes at these ports to a nonzero value, and reload the field plots. The power represents the power incident into the domain from the port; any amount of power can be absorbed by the port.
 

nikosnte

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I actually want to terminate some ports with a matched loads but i do not know how to do this in HFSS. So i thought that when a waveport is excited all other waveports behave like matched loads. So, i wanted a number of ports to behave as matched loadswithout exciting the structure at all so i can save computational time. In other words, i want these ports to just absorb power not give power to my structure.
 

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Yes, that's what the ports will do by default. The power specified under sources is the incident power into the domain from the ports.

I'm not sure why you would expect this to save computation time, however. If you just want a "load" object; use an impedance surface or lumped RLC surface.
 

nikosnte

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Yes, that's what the ports will do by default. The power specified under sources is the incident power into the domain from the ports.

I'm not sure why you would expect this to save computation time, however. If you just want a "load" object; use an impedance surface or lumped RLC surface.
How can i use an impedance surface or lumped RLC surface in HFSS?
 

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Yes, i meant i couldn't find a way to do this in hfss
If you're using microstrip, draw a surface between the strip and the conductor backing, making sure it contacts both metals. Select the surface and the select from the menuL "HFSS"->"Boundary"->"Assign...", and select the boundary of your choosing.

FYI I never do this, I just use wave ports -- doing so gives more accurate solutions, IMO.
 

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