How to add a substrate to an antenna pattern

I am a bleeding newbie to Matlab and found the example below to simulate RFID tag antennas, BUT do not see in the description how to add the influence of the substrate below the metallic atenna pattern ( In the case of the example PET approx. 90µm thick - Dielectricity constant between 3 and 4).

Can anybody help me with pointing the right way ?

Thanks in advance !!

RFID Antenna Design

This example uses:

• Antenna Toolbox
• Partial Differential Equation Toolbox

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This example creates a commercially available RFID tag operating at 915 MHz. The planar antenna is drawn and meshed using PDE Toolbox™. The meshed structure is then imported into Antenna Toolbox and solved for its EM properties.

This example requires the following product:

• Partial Differential Equation Toolbox™