effective permittivity and wavelength when using air gap

Hi all, When we use air gap(between the dielectric substrate and ground plane) technique to enhance the antenna parameters we use height h= substrate height + air gap height for calculation of patch and feedline dimensions. What about the effective permittivity and wavelength? How to calculate the effective permittivity and wavelength when using any dielectric material and airgap together in patch antenna?

I found the answer myself

Reference : http://nopr.niscair.res.in/bitstream...%20143-147.pdf

Are you using Air as substrate ? Interested of air you can also use low dielectric constant Foam materials.

I am using double layer (FR4 + air) as substrate...thnx for suggestion...