Problem with radiation efficiency>1 in HFSS...

[ifelix]

Hi,
I'm simulating a whip loaded by means of a bottom coil.I know that HFSS is not the best choice in this case but I need to simulate with it to compare results with another program. I've created a radiation boundary with a big sphere (probably is also unecessary big but anyway...) and then I've added a radiation to determine far field parameters like gain,radiation efficiency and so on...
I've seeded the mesh manually and I think it's enough looking the plot of the mesh on the boundary...but however when I simulate the model I obtain always a radiation efficiency >1...IMPOSSIBLE!!
In other words the power radiated by the antenna is major respect to the power accepted by it...
I would know if anyone knows why this happens and how I can solve my problem correctly...
I attach the model if anyone could gently look at it...
It's not necessary to solve for it but just solve the mesh to look if the seeding seems enough accurate (if you think this is the problem...)
P.S. I'm using a fast sweep and in this case when I plot the rad.eff. vs. frequency I note that rad.eff. goes over one near the resonance...so I've solved a one step discrete simulation for the resonance frequency thinking that the cause was of the kind of solve method(fast maybe inaccurate) but also with the discrete one I've found a radiation eff.>1...
Please help me!!!
Thanks a lot to everyone in adv...

 

[ifelix]

Please help me!

 

[savedadogs]

This question has been posted several times. Please you the search feature next time...you need to seed your radiation boundary, seed it about lambda/10.

 

[antennas321]

This is a common problem in HFSS. As the first post said, seeding the mesh down to 1/10*lambda will make sure the boundary is sufficient. Make sure the conductor has the finite conductivity (no PECs) and include the loss tangents of any substrates.

Also, the radiation boundary doesn't need to be spherical. A box is just as good. The mesh is the key.

Even with these considerations, HFSS may still give higher efficiencies than other codes. It is due to the way it solves for the E-field first, then the H-field and currents to get the far-field parameters. Some error is inherent in this method of obtaining far-field parameters due to small numerical error terms. Moment method codes solve directly for currents and can integrate to get far-field data.