Does the "frequency" of the photons emitted from an antenna match the RF frequency?

Question

For a continuous sine wave applied to an antenna, will the Planck's relation frequency v of all photons emitted match the oscillation frequency of the sine wave applied?

This is likely in some ways a duplicate of the whole general "wave / particle" or "quantum / classical" theme e.g.

And I think this is in some ways almost the very same as Relation between radio waves and photons generated by a classical current question. But I don't understand the answers (or what the question really is) on that one in this context. My question here is really just a hopefully much simpler yes/no (with any nuance still appreciated of course).

It seems like when we talk particle physics and stuff then "energy" (≈frequency) tends to involve voltage and the potential of electron gaps and stuff at the quantum-level. But when we talk "classical" RF then it doesn't really matter the voltage applied to an antenna so much as how rapidly that potential/voltage/current is changing at the macro-level.

But in the end, if I'm sending energy (whether at a rate of 1 mW or 1W or 1GW) into an antenna but always at a steady "radio frequency" f of 1 MHz in the classical sense, will each of the photons involved all happen to end up with their own "Planck frequencies" v of 1 MHz as well? Or do the photons emitted from electrons when those electrons are just getting "sloshed around in a wire" kind of play by their own rules (vs. the specific-frequency photons emitted when we're talking "band gaps" of lasers/LED or "MeVs" from nuclear decay) unrelated to the frequency of said macro-level sloshing — just random-energy (quantum frequency) photons coming out of the antenna whose overall flux density changing through time is what ends up getting picked back up at a receiver as (classical/RF) "frequency"?

score 1 · Answer 1 · answered Jan 09 '25 at 22:39

Frequency of a photon is defined as frequency of the EM field the photon is associated with. Thus there is no other frequency, in vacuum, to assign.

The whole antenna radiates, individual fields of its parts superpose to a net field, and photons are defined as changes of this net field. There is no "single electron emits single photon", radiation of 1MHz is a collective phenomenon where immense number of electrons participate.

If the 1MHz EM wave gets into a non-linear medium, then harmonic generation, or down-conversion can happen, and waves of different frequencies can appear. Then one can talk about photons of such different frequencies.

score 0 · Answer 2 · edited Jan 11 '25 at 08:32

From the point of view of the coarse grain observer (Contrubute to @Andrew), the EM wave could consist of a photon of the same wavelength. But even here the weakness of such a traction becomes apparent. For a rod antenna, one photon per radiation period means a cylindrical distribution with increasing ‘dilution’ in the direction of movement?

From emission to absorption

Emission

A radio wave is created when surface electrons are accelerated back and forth synchronously. In the process, the electrons emit photons. Their wavelength depends on a variety of circumstances: free path length for the electron, applied voltage and the effective potential difference, power of the wave generator.

Absorption

A small piece of conductive material - in relation to the transmitter rod - is sufficient for radio engineers to adjust the electronics to the wavelength of the transmitter and receive modulated information. This is possible because the incoming photons are polarised. They are polarised because of the synchronous acceleration phases on the transmitter rod: the electric field component of the photons is periodically parallel and antiparallel to the rod and the magnetic field component of the photons is perpendicular to it (and perpendicular to the direction of propagation, here too periodically with changing sign).
If such a number of photons now hit the surface of the receiver, its surface electrons are set in motion by the concerted field components of the incoming photons during absorption - ultimately reversing the emission mechanism.

TL;DR

Thermal sources

I can easily simulate the wave properties of EM radiation - for example from a thermal source or a laser (with beam expansion). To do this, I rotate a disc in the shape of a semicircle in front of a round opening. What comes out at the back is a sinusoidal intensity distribution. I can modulate information onto this wave-shaped radiation by changing the light intensity of the source. Using a photodiode, I can tune to the transmitter (fade out the background noise) and read out the information.

What I cannot do is use the technology of the receiving antenna for radio waves. Due to the chaotic alignment of the field components of the emitted photons, the surface electrons of the receiver do not move synchronously, but chaotically. No electric current is generated.

Receiving cosmic radiation from distant radio sources

Astronomers can deduce radio sources from the reception of single incoming photons through long-term observations. This means that the radio source is at such a final distance that instead of the zillions of photons of EM radiation, only individual photons fall on the detector.
In my opinion, this is a good argument in favour of the fine grain view of the radio wave as consisting of individual photons emitted by electrons.

Spectrum of EM radiation

This is only a nuance, but perhaps important for the methodology of looking at EM radiation.
We have the one area with the different wavelengths (and energy contents) due to different levels of excitation of electrons and protons. This occurs in the wave range from infrared to visible light to X-rays and beyond.

We also have the radio wave range, in which radio waves are generated by the synchronous and polarised emission of photons (with wavelengths as described in the previous paragraph).