Which scientist discovered radio waves experimentally in 1887?

Heinrich Hertz experimentally discovered radio waves in 1887.

Hertz built a spark-gap transmitter and a separate receiving loop with a tiny gap. Sparks appearing in the receiver showed that an electromagnetic disturbance had travelled through space from the transmitter.

James Clerk Maxwell had predicted electromagnetic waves mathematically in the 1860s, but Hertz’s experiments provided the first clear laboratory confirmation. Hertz also measured properties such as reflection, refraction and interference, showing that the waves behaved like light.

The unit of frequency, the hertz, was named after him. Marconi later developed practical wireless telegraphy, but Hertz’s work came first and established the physical reality of radio waves.