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That in near field both fields oscillating 90° displaced is obvious since in antenna rod a lot of electrons will be accelerated and and this oscillation of electric field is escorted by alignment of electrons magnetic dipole moments. Thus oscillation of magnetic field - if strong enough - produces the next oscillation of electric field and so on.

But somehow this two components of EM field were going over to a state - called far field - there both fields oscillation at the same time. In know that Hertz produces sparks and registered this modulation of EM radiation some meters away.

Does he or someone else measure the synchronicity of the two components with amplitudes not shifted 0° to each other and of course both perpendicular to the direction of propagation and not shifted by 90° like in the near field?

Near field https://upload.wikimedia.org/wikipedia/commons/e/e6/Photon_Spin_%2B1.PNG

Far field https://upload.wikimedia.org/wikipedia/commons/3/35/Onde_electromagnetique.svg

Edit because of the comment from KyleKanos: What I'm asking is, has someone measured, that at one moment of time the peak of magnetic component is in the same distance from source as the peak at the electric field. That should be not easy because this peaks are moving with c.

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  • $\begingroup$ The translation of this is a bit muddled. Are you asking "How do the EM fields know about when to switch from the alignment in the near field to their alignment in the far field?" $\endgroup$
    – Kyle Kanos
    Commented Apr 26, 2015 at 16:56
  • $\begingroup$ @KyleKanos: Please feel free to correct my bad English. What I'm asking is, have one measured, that at one moment of time the peak of magnetic component is in the same distance from source as the peak at the electric field. That should be not easy because this peaks are moving with c. $\endgroup$
    – HolgerFiedler
    Commented Apr 26, 2015 at 17:10
  • $\begingroup$ The experimental difficulty scales with frequency, not with speed of light. Today it's quite "easy" to measure the phase between electric and magnetic components directly well into the microwave regime with suitable antennas, a bunch of amplifiers and a phase measurement bridge (in practice even a simple mixer will do). $\endgroup$
    – CuriousOne
    Commented Apr 26, 2015 at 18:30
  • $\begingroup$ @CuriousOne: Nice. Could you give some sources to read about such experiments? $\endgroup$
    – HolgerFiedler
    Commented Apr 26, 2015 at 18:50
  • $\begingroup$ You mean you really want me to do a literature search for you? $\endgroup$
    – CuriousOne
    Commented Apr 26, 2015 at 18:51

2 Answers 2

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What I'm asking is, has someone measured, that at one moment of time the peak of magnetic component is in the same distance from source as the peak at the electric field. That should be not easy because this peaks are moving with c.

You're asking the wrong question. Scientists don't measure the differences in the locations of the peaks of two signals. They measure the phase differences between the two signals. The former is ridiculously hard while the latter is rather easy. In fact, adjusting and measuring the phase difference between two signals of the same frequency is the heart and soul of modern digital communications (it's called phase shift keying, or PSK for short).

With regard to the phase difference between the E and H (or B) fields, Heinrich Hertz did just this over a century ago. That the phase shift is about 90 degrees initially and 0 degrees in the far field is well-established science. It is so well-established and so well-measured that the near-field phase shift can be used as a stand-in for distance. There are cheap measuring devices that estimate the distance between a source and a near-field receiver based on the observed phase shift between the electrical and magnetic components of the electromagnetic field. This technique of course doesn't work for a far-field receiver; the phase shift is zero after a few wavelengths from the transmitter. But it works quite nicely in the near field.

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  • $\begingroup$ About near field I agree with you. Hertz located a metal plate 12 m away from the antenna, producing by this way standing waves. The result see here en.wikipedia.org/wiki/Heinrich_Hertz#/media/…. I'm interested in measurements of E an B in the far field. $\endgroup$
    – HolgerFiedler
    Commented Apr 26, 2015 at 19:31
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Google search for "antenna far field magnetic field measurement" does not match any result. Always the electric field is measured and from this is concluded about magnetic field. I could not see that there is any measurement of electric and magnetic fields at the same point to show that both fields in phase.

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