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Everyone knows that a 1/2 λ dipole has on the elements a standing wave the voltage and current of which are a bit less than 90° out of phase with each other, and the departure of this phase difference away from exactly 90° is the non-reactive component of the standing wave which results in radiation.

My understanding is that the out of phase component of the standing wave is reactive circulating energy never to leave the antenna due to the antenna being a resonant system, and the in phase component of the standing wave results in real work being done which produces radiation.

At the tips of the antenna elements, for an ideal dipole, voltage and current must be precisely 90° out of phase, how can it be any other way ? and apparently this phase difference between voltage and current changes along the length of the elements as a function of the distance from the ends.

This occurs because every part of the antenna has coupling to every other part of the antenna and because the antenna has ends with boundary conditions, and is one of the reasons why the equations for feed point impedance are so complicated and an approximation only.

If a perfect sine wave was applied at the center feed points of an ideal resonant 1/2 λ dipole, then because the phase difference between voltage and current of the standing wave is only exact at the end of the elements, and changes along the length of the elements, then the standing wave can't be a perfect sine wave and must have some distortion as it is "twisted" in accordance with the change in phase along the elements.

Does this departure of the standing wave from a sine wave cause distortion ? and if so then the distortion must increase as the Q increases.

Obviously there is no distortion otherwise everyone would know about this so does the antenna at the receiving end have the reverse effect and undo the distortion ?

Or is there something else going on ?

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  • $\begingroup$ I do not understand most what you wrote but to the title question yes if the bandwidth of the signal to be transmitted/received is larger than $\omega_c/Q$ you will have substantial distortion in both amplitude and phase of the signal. $\endgroup$
    – hyportnex
    Aug 31, 2021 at 0:27
  • $\begingroup$ @Hyportnex Is the reason you don't understand most of the question because i have made assumptions which are incorrect ? If so is it possible to tell me which bits are wrong ? $\endgroup$
    – Andrew
    Aug 31, 2021 at 0:36
  • $\begingroup$ "At the tips of the antenna elements, for an ideal dipole, voltage and current must be precisely 90° out of phase, how can it be any other way ?" As far as I know the current at the tip is zero, so its phase has not much meaning there; after this I got totally lost in your description but I hope my comment above answers some of your question. $\endgroup$
    – hyportnex
    Aug 31, 2021 at 12:29

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