I'm a little fuzzy on what you're asking. You can calculate the receive voltage on the antenna terminals based on the field strength of the incoming electromagnetic signal, for various antenna configurations and so on. Like for an ideal dipole or monopole antenna at resonance, you can express the output terminal voltage as a function of the Electric field strength of the incoming EM (in units of Volts/meter). You can convert the electric field strength to a power if you want (in watts), to go from incoming power to the output terminal voltage of the antenna. Is this what you are trying to do, or are you looking at more basic stuff? Is this for high school physics (mostly just forumulas) or for college physics (so you have a background in Maxwell's equations, etc.)?