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For a center fed dipole antenna when operated at resonance, the AC electric potential applied at the feed point results in traveling waves of AC current which emanate from the feed point out towards the two ends of the antenna. When the traveling waves reach the ends of the antenna they are reflected back towards the feed point where they arrive in phase with the applied AC wave form. At the feed point then the voltage and current are said to be in phase, there is zero reactance in the AC impedance presented at the feed point, and the antenna is resonant.

I am very confused about the relationship between the applied AC electric potential, the traveling wave of movement of charge, and the amplitude and phase in time and space of the current and voltage at the feed point and at each point on the antenna.

I have searched endlessly on the internet and have found it astonishingly difficult to find information on this subject.

I am not looking a for picture such as this :

https://en.wikipedia.org/wiki/Dipole_antenna#/media/File:Dipole_antenna_standing_waves_animation_461x217x150ms.gif

The explanation given in Wikipedia doesn't come close to answering my questions.

Can anyone please either explain to me without using extensive math the exact details of the traveling wave mentioned, in terms of phase in space and time and the exact relationship between the traveling wave of movement of charges, instantaneous current, voltage and phase in time and space with respect to each other and to the feed point, or point me in the right direction where i can find an explanation ?

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    \$\begingroup\$ If everything is balanced, then the phase angle between voltage and current is zero at all points along the dipole. \$\endgroup\$
    – Chu
    Jun 21, 2020 at 8:18
  • \$\begingroup\$ Hi Chu thanks for the comment, so you are saying that at resonance at every point on the antenna the voltage and current are in phase with respect to each other at each point on the antenna ? can you explain further ... \$\endgroup\$
    – Andrew
    Jun 21, 2020 at 8:20
  • \$\begingroup\$ The graphs you see on wikipedia etc. show the amplitudes of voltage and current along the transmission line/antenna, not the phase angle. \$\endgroup\$
    – Chu
    Jun 21, 2020 at 8:28
  • \$\begingroup\$ Yes i know that. \$\endgroup\$
    – Andrew
    Jun 21, 2020 at 8:46
  • \$\begingroup\$ You mentioned phase angle in your post, I was just commenting on that. \$\endgroup\$
    – Chu
    Jun 21, 2020 at 8:48

1 Answer 1

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There are only standing waves of voltage and current on a resonant dipole antenna, not travelling waves.

It is the current that reverses direction, after traversing the length of the antenna, every half cycle.

This phenomenon is well demonstrated in the Wikipedia animation.

Travelling waves of voltage and current exist only on a non-resonant dipole antenna.

Here's an animation of a travelling wave.

https://upload.wikimedia.org/wikipedia/commons/9/91/1D-Wave.gif

A standing wave of voltage or current shows the unchanging value of either along the length of the antenna.

A travelling wave, on the other hand, shows the constantly changing values along its length.

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