Doesn't no one here know what determines the strength of EM waves radiated by antenna, voltage, current or both and how?

Ah-ha. Need to explore the difference between near field and far field. In all cases, the power is the product of the voltage times the current. For the near field, the ratio of voltage to current is affected by the type of antenna. A short wire will radiate a mostly electric field, and a loop will radiate a mostly magnetic field.

But as the wave front propagates, it takes on the characteristic impedance of free space, about 377 ohms. This will define the voltage to current ratio in the far field.

To add to what's said. Most antennas are tuned (their length is some factor of the wavelength. E.g. a dipole has two 1/4 wavelength elements).

In a tuned antenna, a standing wave is set up. The feedpoint impedance is low, typically 70 to 300 ohms. At the feed point the currents are high and the voltages low. At the ends of the dipole the current is zero but the voltages are high.

The strength is determined by the POWER radiated. Power = Voltage times current. If the antenna resistance is constant, then Power = (Vrms)^2 / R = (Irms)^2 * R.

rms = root mean square.