Now, an antenna will be placed on the top of the box in a fixed position. That means that only the box is moving. It may be useful to make a parametric study to find which is the optimal ground plane position for the antenna behaviour. Click on Source -> Primitive Antenna -> Coaxial Feed -> Helix -> Multi-filar Helix menu, as shown in the following figure.
Primitive Antenna menu
The Multi-filar Helix panel is open on right side. Set all parameters as shown in the next Figure. Then, this primitive provide four ports defined one in each Helix. Confirm the antenna definition by clicking on Add button. After that, close the Multi-filar Helix panel.
Quadri-filar helix definition
This antenna must be placed on a planar structure which acts as reference plane, so the box performs this function. The resulting geometry is represented in next figure.
Final geometric design