How Are Electromagnetic Waves Produced?

please tell me how an EM wave is created

First about EM radiation. Charges under acceleration emit EM radiation. The emission happens perpendicular to the direction of acceleration. For example, the synchrotron radiation is around the tangent of the accelerator ring. Accelerating a charge upwards the photons get emitted horizontally (in 360° around the wire).

To get an EM wave you simply has to drive your wire with an alternating current. The current modulate the EM radiation to a sinusoidal wave. Much better of course is to use a open circuit.

Let us begin with a definition, because arguing things without definition may lead to confusion. An electromagnetic wave is defined as an energy wave that has a velocity in vacuum that coincides with the velocity of light in vacuum. According to this definition, gamma rays, X-rays, ultraviolet rays, visible light rays, infra red rays, radio waves, and gravitational waves are known electromagnetic waves. Microwaves, alpha rays, and beta rays are not em waves as per this definition. To produce electric field waves there should be a strain in electric fields, and to produce magnetic field waves there should be a strain in magnetic fields. If the voltage is increased in a resistance, two successive electrons in serial try to come closer because of voltage, and two electric fields of two electrons should repel each other. So, there is a strain in electric field as it is explained in second figure to produce electric field waves or light rays. If the current is increased in a conductor, two successive electrons in parallel try to come closer because of increased current, and two magnetic fields of moving electrons should repel each other. So, there is a strain in magnetic field, as it is explained in first figure. These are all only situations related with voltage and current in production of electric field waves and magnetic field waves. In practical situations one need not go for voltage and current. In a fire, electrons of two successive molecules may bring a strain in electric field and it may produce light (or electric field wave). When there is a flow of gases in sun, the moving electrons moving in parallel may bring a strain in magnetic field and it may produce radio waves (or magnetic field waves). I ask the questioner to assume the followings (for which a basic theory may be found in a book entitled “Planets and electromagnetic waves”). The followings are based on mathematical interpretations for solutions of Maxwell equations. (1) If current exceeds some limit (depending on source of production), then magnetic field waves are produced. These waves are called in general radio waves. (2) If voltage exceeds some limit (depending on source of production), then electric field waves are produced. These waves are called in general light waves. (3) If current exceeds the corresponding limit and the voltage also exceeds the corresponding limit then both magnetic field waves and electric field waves exist separately; not in combined form (that is, not as everyone gives a figure for em waves with two component waves). A peculiar situation for (3) is the Hertz’s experiment. It may also happen both types of waves may not produced, and only oscillations may happen when the limits are not reached.

P.S. When two self rotating neutron stars come closer, the magnetic fields of the stars are disturbed and energy waves are released from the magnetic fields. These waves are gravitational waves. Since they are from magnetic fields, they are of electromagnetic wave type. After 1.7 seconds collision happens. During this collision, gamma rays, X-rays, ultra-violet rays, visible light rays and infra red rays may be released. For example, the article https://doi.org/10.1007/s11467-019-0913-4 explains such a delay of 1.7 seconds. Microwaves mentioned above in the answer correspond only to microwaves generated in micro ovens.