Oscillations of E/H inside a sphere bounded with a PML

Hello,

I have some results but I'm not confident if they are correct. I am simulating an antenna which should generate very strong electric field, and I want to test it at the frequency of 200MHz (which is in the range provided by the producer).

I have attached two screenshots from COMSOL, depicting ratio between the norms of E and H in the plane XY cutting the antenna in half. The whole sphere has 3m radius and a PML 0.5m which is thick. Antenna's dimensions are 1m x 1m x 0.05m.

You can see that E/H looks like waves in this plane, but I would expect it to converge to the value of the impedence of the free space (~377 Ohm). Do you have any idea why it is this way? Is it a matter of mesh quality? Or rather PML settings?

Thanks,
Bartek Chaber