# Is the phase difference between the voltage and current of the standing wave on a dipole antenna constant along the dipole's length?

Everyone knows that a 1/2 λ dipole antenna has on it a standing wave of RF energy the voltage and current of which are about 90° out of phase with each other. The standing wave is circulating reactive stored energy present due to the fact that the antenna is a resonant system.

Apparently there is a departure of phase difference away from 90° which is the in-phase component of the standing wave responsible for radiation, the out of phase energy of the standing wave remains in the antenna.

At the ends of the antenna where there is a complete open circuit, how can the phase difference between voltage and current of the standing wave be anything else other than exactly 90° ? But there must be some non-reactive component otherwise there will be no radiation !

So, does the phase difference between voltage and current of the standing wave start off as exactly 90° at the outer ends of the elements, and then gradually change to a lesser value along the antenna elements with a minimum value at the current maximum at the feed points, in which case the standing wave must not be a perfect sine wave ? or is the phase difference the same everywhere on the antenna, and so the reflection at the ends must not be exact ?

Moderator Note: The same question was asked here at Amateur Radio.SE so interested readers may want to visit that page too. To avoid any appearance that this situation is the norm, duplicating questions across different SE sites is generally strongly discouraged.

• Nice question. There is also a further question: if there is a 90 deg phase difference, how come the TEM wave has its E and H back in phase? Aug 24, 2021 at 9:47
• @MarkoBuršič Is that the question no one knows the answer to ? Aug 24, 2021 at 9:49
• Not me, I have asked myself this question many times. You have a generator, transmission line, antenna - all perfectly matched. The generator and line have V,I in phase, then antenna has them out of phase generating EH filed out of phase, after they become perfectly in phase, kind of black magic. The real knowledge would be a method to keep the EM wave out of phase for a long distance. Aug 24, 2021 at 10:15
• The standing waves represent the amplitudes of voltage and current at points along the antenna, they are not the voltage and current signals as functions of time. So referring to a phase angle between voltage and current standing waves is not correct.
– Chu
Aug 24, 2021 at 15:25
• @chu Thanks for your comment but what you just said is completely wrong, there is a absolutely a phase difference of a bit less than 90 deg between voltage and current of the standing wave on a dipole, this is explained in just about every antenna book in existence. [Edited by a moderator.] Aug 24, 2021 at 21:58