Radiating Boundary Condition

Hi,

After reading some patents and articles about the two method of simulation: Radiating Boundary Condition and PML( Perfectly Matched Layer).
I concluded that PML is better than RBC, because the PML have a property to absorb the incident wave from antenna, without reflecting energy into the antenna. While with the RBC we can have a small reflection into the interior.

So, Why we use the Radiating Boundary Condition if the PML is better?
What is the advantage of the RBC?

Thanks

The ABC is computationally cheaper as it is merely a boundary condition that terminates the tangential E field while ignoring the normal component (hence the angle of incidence effect) while the PML is a 3D object that must be meshed and solved inside. Also, ABC boundaries are fine as long as you have a single radiator and the fields incident upon it are near normal (say lambda/4 away from radiator). PMLs are certainly preferred fro most antenna simulations and especially for multiple antennas in a single model simulations, but they can be computationally more expensive.

I like to think of ABC boundaries as 'good' and PMLs as 'great'. If I need absolute accuracy...PML if I need quick simulations to understand trends...ABC. It is important to have the option.

Thanks for your attention.

But the ABC boundaries is also a 3D object because you must to select a air box . and the air box must be also meshed and solved.

You are incorrect. The air does indeed need to be meshed and solved, but that is simply due to the fact that HFSS solves explicitly for E and thus need to include fringing fields to correctly represent the electromagnetics of the problem. You can have an air box without a radiation boundary...however what do the fields do at the surfaces? You need a boundary condition applied to the surface of your air box to terminate the fields in a matched condition if you want to prevent fields from reflecting back into your domain. If there is no boundary assigned...something is still needed from a computational perspective and a PEC is applied.

Again...All boundary conditions are assigned to faces of a 3D objects. However the Boundary condition itself is only operated on the surface and the Radiation boundary works as I described above.

Hi
In addition to those discuused...

One more thing which I observed is that by using RBC simulations doesnot take long time for single radiators and simple antennas. But when u go for multiband antennas, more than one resonance PML seems to be much faster.

Otherwise usage of either PML or RBC is a just a matter of effient use of computational resource and the accuracy of ur result

I concur with the general comments above. PML's are more complex to create compared to an ABC. Another warning, If you are using a parametric model keep a close eye on any PML's. You may find that the parametric modeling does not adjust the PML as one would expect. It is sometimes necessary to re-create a PML after a model is parametrically adjusted. I have not seen similar failures when using ABC's.

Hi

Do u mean when using ABC conditions and try parametric modeling the ABC box resizes itself ( or the size itself is lambda/4 doesn't effect hugely while performing parametric modeling)....... can u make it clearer?

I haven't encountered this problem while performing parametric variables using PML....

Thanks
venu

I have occasionally had PML boundaries not resize themselves as I expected and intended. The ABC boundaries have resized more easily. I have not seen, nor have I looked, for this in version 13. I bring it up as something to keep an eye on as a potential pitfall. It does not happen in all cases. It is not a big deal to manually create a PML with an otherwise parametric model. As I said, I like to keep an eye on PML's so I am not surprised.

HFSS is an excellent tool, just keep an eye on this aspect.

Thanks amigos