Why do radio transmission harmonics occur?

[Tech2025]

What I understand about harmonics, is when something is transmitted at high power, the antenna resonates on other frequencies besides the desired one. But Why?

 

[sophiecentaur]

What I understand about harmonics, is when something is transmitted at high power, the antenna resonates on other frequencies besides the desired one. But Why?

We usually assume an antenna is linear - which is fine for a new one with no no rusty bolts.
The non linear products come from the active devices in the transmitter amplifier. For the sake of efficiency, most transmitter designs will have some compromise with regard to the linearity so there will be some inherent harmonic content.
Back to the antenna. It is unlikely that an antenna will happen to 'resonate' at an exact harmonic of the fundamental of the transmitted signal but you don't need resonance for a piece of metal to radiate. Harmonics will tend to get through if you do not filter them out somewhere along the chain. The regulations are pretty severe about out of band radiation and, in addition to limits on radiated harmonic levels, other non linear products such as the theoretically infinite sidebands of an FM signal may also be radiated.
It is worth asking you what your level of knowledge of this very nerdy topic and how deep you want to delve.
Edit: PS The basic stuff about dipoles tells you that there is a resonance when the wire is a half wavelength (approx) long. Just as with vibrating strings, you can get standing wave resonances at overtones of the basic length. At around those frequencies, the antenna will radiate 'better' in the same way that the half wave dipole does.

 

[Tech2025]

We usually assume an antenna is linear - which is fine for a new one with no no rusty bolts.
The non linear products come from the active devices in the transmitter amplifier. For the sake of efficiency, most transmitter designs will have some compromise with regard to the linearity so there will be some inherent harmonic content.
Back to the antenna. It is unlikely that an antenna will happen to 'resonate' at an exact harmonic of the fundamental of the transmitted signal but you don't need resonance for a piece of metal to radiate. Harmonics will tend to get through if you do not filter them out somewhere along the chain. The regulations are pretty severe about out of band radiation and, in addition to limits on radiated harmonic levels, other non linear products such as the theoretically infinite sidebands of an FM signal may also be radiated.
It is worth asking you what your level of knowledge of this very nerdy topic and how deep you want to delve.

Thanks for the explanation, Just getting started with learning antenna theory.

 

[sophiecentaur]

Thanks for the explanation, Just getting started with learning antenna theory.

I edited my post and added a bit.