What's wrong simulation in CST changing material

I try simulate VHF antenna (Yagi) with changing differient material : Steel, Aluminum, Iron but All results the same (Gain, E-field).
I wonder what's wrong with my simulation? And how to simulate to see different material lead to differ Antenna's characteristic.
I'm using CST.
Tks

Have you set your boundary conditions and background properties?

Steel, Aluminium and Iron are all very good conductors. There is very little difference to be expected when changing between these materials.
In patch antennas (or similar) with a substrate, the properties of the substrate material can greatly affect performance of the antenna.
But, for a simple Yagi made of only metal, you do not expect much difference and you are better off simulating with just a PEC.