cancel coupling between two microstrip structure in hfss

hi all.
guys i am completely confused about this problem.

according to attached picture i want to cancel the coupling between balun and planar spiral(in hfss).
i want to place a material around balun to prevent coupling effect on radiating spiral. in experiment we'll use absorber to reach that goal. but now i want to do this in simulation. please help me solve this guys. thank you very much.

You may place a very thin and relatively large PEC layer between them.

hi BigBoss.
thank you for your reply.
if i place a PEC between them , the PEC affect the radiation of spiral and make it worse.
the green are in the above picture is dielectric material and the blue strips are PEC.

The easiest way to avoid coupling in simulation: split this into two separate EM models.

coupling? well the balun is driving the spiral, so they are pretty "coupled" already! Why not add a disk of metal to the back of the spiral. it will prevent rearward radiation (where the balun is).

In some antennas there are chokes to keep rf currents from going backward down the balun (which would make the balun part of the antenna radiation pattern).

thank you biff44.
in the CST for prevent unwantend radiation we can use eccosorbs . i want to build such a material(eccosorb) in HFSS.