regarding UWB antenna

hello

currently i am designing a UWB antenna based on an ieee paper, i could not reproduce the results given in the paper, please provide suggestions to overcome this problem?

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A Compact Ultrawideband Antenna With 3.4/5.5 GHz Dual Band-Notched Characteristics
by:
Qing-Xin Chu, Member, IEEE, and Ying-Ying Yang

Hi,
first off all you need to understand the Radiation Boundary you use.
The thing you want to simulate is the far field characteristics of your antenna in an infinitly large air box. As this cannot be designed you put the radiation boundary at the end of a finite airbox. This boundary is shall absorb all incoming waves but to work well it must be placed at least lambda/4 away from any radiating element.

The airbox in your file is simply to small, it even touches your antenna at the sides.
Furthermore your simulation is set for a wider frequency range than in the cited paper. I think 3...11 GHz is sufficient to compare.
Finally you are plotting the results for the return loss (S11). In the cited paper the VSWR and gain a reported. So it might be good the plot VSWR instead of S11 in your porject.

What to do:
First decide about your lower cutoff simulation frequency (e.g. 3 GHz).
Calculate the wavelength of the lower cutoff frequency (e.g. ~100mm)
Modify your airbox size or simply delete it and create a region with a constant offset of at least 25mm and pad it to all directions. Don't forget to assign the radiation boundary to your new airbox.
Now your port is in the middle of the airbox and you need a PEC port cap (rectangular box of pec having the same size of your waveport sheet and a rather small thickness of say 1mm). Alternatively you can try a lumped port.
Simulate All
Crate a new modal solution results plot and select VSWR as a category.

If you want to analyze the antenna gain first create a far field setup.
Plotting the gain results make sure if you need the "gain" or "realized gain" plot in HFSS.

Thank you for your reply. Could you please elaborate on "defing the PEC cap" because getting the below message


Port '1': A Wave Port appears to contact multiple 3D objects so as to require solving inside on both sides of the port. If an internal wave port is desired, please add a PEC cap to one side of the port surface.