Dual Band Planar Inverted-F antenna

Hi everyone,
I'm designing a Dual band Planar Inverted-F antenna that operates at 2 G Hz and 2.6 G Hz by using HFSS. I'm facing problem when designing the feeding pin. When I want to assign wave port, the software shows "all the faces selected to form a port source must lie on the same plane", what does it mean? Can any experts help with how to design a feeding pin for a pifa? Thanks.