No, you change the primary sweep as frequency. So, it results x-axis as frequency.

Make sure that solution is sweep but not last adaptive.........

Thanks! in "Results/create far fields report" I only have "last adaptive" in my "Solution" option; how would I add "sweep" to Solution option?

In the Analysis->Sweep-> enable save fields option.........

Be careful in HFSS simulation. HFSS (and CST also) give 102% efficiency (or sometime 103%-105%) for DRA. Therefore, if you simulate microstrip antenna, you may get 95% efficiency but practically, you will get 78-80%. Therefore, simulate your design properly.

In Analysis--->Setup1--->right click and add frequency sweep. there you can give the sweep range and click save fields.

Then in solution you can change the "last Adaptive" to your sweep and get the results accordingly.

Thanks everyone! I could plot efficiency versus freq.

Now as you mentioned efficiency goes above 1 - or is very close to 1 at some frequencies. why does this happen? Indeed the main purpose of my sim is to figure out how much power is going to be radiated from the antenna under test. Do you know of any other method which the amount of radiated power could be examined? I know we can plot accepted/radiated power in Results/far field/recatngle/antenna parameter/ - what do you recommend?

Thanks for your help!

During my work, I faced that problem (efficiency > 100%). To overcome that problem, design your antenna structure as per the fabricated design i.e. include thickness of ground plane, use proper coaxial probe to excite the antenna, give at least 4-5 times larger (than max dim of antenna) ground plane, try to avoid hypothetical inputs (these are designed for simulation purpose only such as wave-port, lumped port etc) etc. After incorporating all those corrections, we got excellent results in HFSS. Experimentally, we got similar results. After performing several experiments for the same sample, we got the correct procedure for designing antenna geometry in HFSS (as given above).

HFSS (or other simulators) is a tool only. We have to use it properly in research. All the best for your work.

It is better to design at least one published geometry in HFSS (or CST) and verify those results. Then go for your work using similar design procedure.

Thanks very much. Appreciate your help!