printed monopole antenna design

hello guys... I need your help and suggetions.. .please...

I am doing a project on UWB antenna and I have been trying to recreate the designs (for the past 2 month) of UWB rectangular /Cicular monopole on CST. Both my design and the journals were I took the dimention from are enclosed on the respective zip files, I have read the help files but i still can solve the problem, right now I don't know if it is the software or my design.
For both design I am simulating from 0 - 15Ghz frequency range.

For the case of the rectangular printed monopole: the following warning message keeps coming:
- Some PEC material is touching the boundary! This may lead to inaccurate farfield results.
And when I try to plot the farfield for (3Ghz) I have the following warning
-Warning: Distance to open boundary is smaller than lambda /8. Farfield dbi inacurate

For the case of CD printed monopole:
For this one It keep giving some error message until I have change the Line per wavelength for 10 to a value < 6. But the results S11 are far from what I expected, specially from 10Ghz above it seems to be well matched.

I have read the CST helps so many time I still cann't figure it out what the problem is... So you guys are my only hope... If you use CST can have look at my design and give some suggetion on where the problem might be...please.

Wainting for your replays.
thanks

Hi angolaX,

You structure is quite alright, however, you have defined wrong boundary. Just change all boundary to open (add space), everything would be fine. Moreover, it is better to define your waveport from the bottom of the ground plane (so, for rectangular monopole, it should start from z=-1 and for circular z=-2).

I've attached the return loss for both and radiation pattern of rectangular monopole at 3 GHz.

regards,
shameem

Hi shameem...

There is one thing I still confuse about...
Although by changing all boundary to open (add space) as removed all the warning message for both Circular / rectangular.
- Why has the S11 result still far from what has been reported on those paper?

- Another thing is on the definition of the waveguide port, you suggested it should start from the botton of the ground plane, but I have been reading the CST help file on microstrip line, it suggest that the botton height of the waveguide to be the size of the height of the substrate. If you any information (like pdf file) on the definition of waveport for microstrip and CPW line you post it or send to me please.

Thanks for your help

Hi angolaX,

I think your S11 result for rectangular antenna behave as the same way it is shown in the paper. However, the absolute values are not the same. You need exactly same setup as the author (like meshing, port size, accuracy level etc.). In your plot, you have two crest at the same frequency like the paper.

Since I cannot open your document of the circular antenna, I cannot tell anything about it. But I guess it also depends on the solution setup.

And you are right. It really does not matter whether you setup the port from the top or bottom of the ground plane. Both give the same results.

Regards,
Shameem