What is Effective area for patch antennas?

[NewAlf]

Hi guys,
I'm new to the forum so please forgive me if i'm posting this at the wrong place.

I am currently using the forumula Aeff(effective area) = (lambda^2)*Gain / 4*pi to calculate the effective area of a patch antenna. From what i remember, the above formula works for a wire antenna but not sure if its the same for a patch antenna.

Any help will be greately appreciated.