Why are the electric and magnetic fields in phase in EM waves?
Consider a radio wave emanating from a dipole antenna. Close to the antenna, I would think the electric and magnetic fields would be 90 degrees out of phase (i.e. if the strength of the magnetic field is due to the rate of change in electric field, the maximum magnetic field strength should be between the peaks of the electric field when current flow is ). But as the wave radiates, the electric and magnetic field are thought to be in phase. How and why does this transition come about? Is it due to the inductance/capacitance of free space?
The electric field is the driver of the EM wave power. The source of the EM wave makes a sinusoidal electric field continuously then the changing electric field makes a magnetic field instantly in all paths of its propagation, so the magnetic field is sinusoidal also with a delay phase.