hfss radiation boundary clarification

I have some questions about radiation boundary I want to clarify,

1) How long should the radiation boundary extend?
I have heard it should be 1/4 of wavelength.

If so, which is the correct way to implement?

1/4 wavelength height and start at position 0 (bottom, ground plane)

This makes my radiation pattern like this:

you can see that the bottom of the radiation pattern is cut off, I think due to the radiation boundary assignment..

1/4 wavelength height above and below, start at position of -1/4 wavelength (i.e not from 0)
I notice that this option makes the resonant frequency lower than option 1..

2) Which sides of the radiation box to assign as radiation boundary?
is it: all faces except the bottom (ground plane) or all faces (including the bottom) except the face the port is on?

Hi,

lambda/4 distance should be applied to all sides of structure. this ensures absorption of signals at boundary with minimal reflection. you can always increase more than lambda/4 but simulation time increases as well.

there's a change in resonant frequency as the E-field could be disturbed by reflections off the boundary, since the port is directly placed at the same plane as boundary.

Increase all sides to at least lambda/4. Then try increasing further and there should be minimal or no change in resonant frequency.

Best of luck