Power calculation from E and H field
The Poynting vector \$\bf S\$ is given by
$${\bf S} = {\bf E}\times{\bf H}$$
The magnitude of the Poynting vector gives the intensity of the electromagnetic wave. That is the, the power per unit area. 

To get the received power from this you must average over time and integrate \$\bf S\$ over the effective aperture area of your antenna, multiplying for the directive gain of the antenna at its orientation to the Poynting vector, if it is not aligned ideally.