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I understand that in a half-wave center-fed antenna current distribution has a sinusoidal wave approximately, so the current in the center has max value and it has to become zero at the ends of dipole which are open. But since we change the feed point from center to one of the end points, the current in feed point (the end of antenna) is not zero this time right? So it seems that moving feed point from center to end change the current distribution.

My question is how to calculate current distribution in theory in this new arrangement. I am familiar with Hallen integral equation and method of moment, but in this method we use boundary condition of current which is zero in both ends. However, in end-fed dipole it seems we do not have this boundary condition in one end.

So what should I do? Or in general how can I calculate current on dipole antenna?

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    $\begingroup$ Can you define more clearly what the feed is connected to? It can't actually be at the end, because no current can flow out of an unconnected end. A clear description of the whole structure is the first thing you need. $\endgroup$ – tomnexus Feb 12 at 18:08
  • $\begingroup$ EZNEC will feed an "end-fed" in the middle of the end segment or at the junction of any two wires. $\endgroup$ – Cecil - W5DXP Feb 12 at 21:20
  • $\begingroup$ I have not gotten EZNEC to feed at the junction nor at the end of a segment. Of course, I use the free version. $\endgroup$ – Baruch Atta Feb 12 at 21:48
  • $\begingroup$ @Baruch Atta The middle of a segment is as close as one can get to the end of the wire which IMO is close enough given many more segments than 20. $\endgroup$ – Cecil - W5DXP Feb 13 at 2:09
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    $\begingroup$ I would not be surprised if calculating a realistic current distribution in such an antenna requires including inductive coupling to the antenna from a non-ideal feed-line. $\endgroup$ – hotpaw2 Feb 13 at 17:06
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M-o-M software such as NEC (Numerical Electromagnetics Code) is capable of calculating the distribution and values of r-f currents along radiating conductors.

The graphic below shows the distribution of such current along the conductors of an "end-fed" antenna system, for the parameters and configuration described there.

The value of r-f current at each segment of the antenna conductors is available from the calculated results, but that data is omitted in this post.

enter image description here

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Perhaps the following graph based on EZNEC simulation data will allow the development of an empirical curve-fitting formula. Note that the current envelope is very similar to one half of a Double Zepp. Current Magnitude and Phase for an End Fed Dipole simulated in EZNEC

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