S11 calculation in HFSS?

1. What is the equation for calculating S11 in HFSS? Is it S11 = Power reflected/Power incident, or S11 = Power reflected/Power accepted?

2. Does S11 value account for reflections from the antenna structure or just the adjacent object(s) or both?

3. Do reflections from adjacent objects get reflected to antenna or radiated in far field?

I would appreciate answers straight to the point to each of the 3 questions.

Thank you.

S11 is the same definition as used anywhere else, it is voltage (not power) ratio of reflected/incident wave.

isn't S11 same as return loss which is 10 log Preflected/Pincident?

Yes, S11 is return loss. If you look at the definition of S-parameters, or the linear scale values, or Smith chart, you can see that it is wave (voltage) and not power.

And thus you have S11 = 20 log Vreflecred/Vincident

Thanks, guys.

How about the second and third questions in my top post? Anybody?

2. Does S11 value account for reflections from the antenna structure or just the adjacent object(s) or both?

3. Do reflections from adjacent objects get reflected to antenna or radiated in far field?


Thanks.

Both

Both. Depending on the target geometry, some part of the signal will be reflected back. This is how radar works ....

The S11 value is defined at the port, thus everything that reflect a signal into it influences it. And nearly every material in the surrounding of the antenna reflect something back to the antenna and so to your port. You can check this easily by placing a PEC object near the antenna and look how your S11 changes.