How are electromagnetic waves produced?

(N/A) Stationary charges or charges moving with constant velocity (steady current) cannot be the source of electromagnetic waves. This is because a stationary charge produces only an electric field,and charges moving with constant velocity produce both electric and magnetic fields,but these fields do not change with time.
According to Maxwell,accelerated charges produce electromagnetic waves.
An oscillating charge is an example of accelerated motion. When a charge oscillates with a certain frequency,it produces electric and magnetic fields that oscillate in space. As this phenomenon repeats,the oscillating electric and magnetic fields propagate through space,which are called electromagnetic waves.
These waves propagate in a direction perpendicular to both the electric and magnetic fields. The electric and magnetic fields oscillate perpendicular to each other.
The frequency of the electromagnetic waves is equal to the frequency of the oscillating charge. The energy of the accelerated charge is imparted to the propagating electromagnetic waves.
It is easy to imagine that light consists of electromagnetic waves,but it is difficult to test this in a laboratory because modern electronic circuits can typically produce frequencies up to $10^{11} \text{ Hz}$,whereas the frequency of yellow light in the visible spectrum is about $6 \times 10^{14} \text{ Hz}$. Hence,to provide experimental proof of electromagnetic waves,Hertz's experiment was performed in the lower range of radio waves.
After the success of Hertz's experiment,Jagdish Chandra Bose,working in Kolkata,succeeded in producing and observing electromagnetic waves of much shorter wavelengths ($25 \text{ mm}$ to $5 \text{ mm}$). His experiment was confined to the laboratory. During this time,the Italian scientist Marconi succeeded in sending electromagnetic waves over several miles.