we usually dont design PIFA with coaxial and it have common reason
because we used PIFA in cell phone and laptop and we dont use it in array systems and other application
if u seen kin LU WONG papers u can see it clearly
thankyou dear ferdows,,,,what is the type of feeding you had in your previous uoloaded pifa design,,,can you advice me about a main reference a bout pifa theory and mathematical ...thanks