# What does the current distribution look like on an antenna?

This is more of a conceptual question, but I am struggling with understanding the current distribution on a radiating antenna.

I understand how it travels, but how do we know? Is there some paper or textbook I could read that proves where the current is on a radiating antenna?

Reason I am asking is because maxwell's equations include a current distribution term that I am curious about.

• What type of antenna are we talking about here? Aperture? Wired? etc.?
– user103380
Dec 21, 2018 at 17:51
• Dipole antenna. To analyze an ideal dipole antenna with maxwell's equations, the diameter of the antenna is assumed to be infinitely thin. But with a real-world antenna, the diameter is obviously not infinitely thin. How do we account for this in maxwells equations? We need to know the current distribution right? Dec 21, 2018 at 18:02
• In the far field, the infinitely-thin approximation is a good one. Is that not sufficient? I'd recommend Balanis' book Antenna Theory: Analysis and Design. Dec 21, 2018 at 18:27
• It is sufficient to analyze a problem but I am trying to understand things on a deeper level Dec 21, 2018 at 19:31
• The current is obviously highest near the base and zero at the tip. assuming that the antenna is uniform the current profile will follow he integral of the voltage profile (starting at the tip), if you can solve this differential equation things like impedance and SWR should just come out of the maths. Dec 21, 2018 at 20:10

Think of the electrons moving along the dipole.

At the ends the current must always be zero because there is no place for the charge carriers to flow to.*

The maximum current must happen in the middle because the electrons going from one end of the dipole to the other must flow though the center to get from one side to the other.

Here is a nice animation from another Stack question.... If you want a deep intuitive understanding of this stuff I recommend you take a look at Matter and Interactions...

https://matterandinteractions.org/

This book changed how I think about electromagnetics and resolved many long standing confusions I had.

*Assuming the tips are isolated in a vacuum and the voltage at the tips does not exceed the work function of the wire, which is a fair approximation for our purposes.

Current (and voltage) distribution in antenna depend upon type of antenna. For example in a half wavelength dipole and microstrip antenna, current has maximum value at center while current is zero at the edge. The feed point on a resonant center-fed half-wave dipole occurs at the point of minimum voltage and maximum current, which enables the most efficient power transfer from the transmitter. • But how do you know? How can this be experimentally verified? Dec 24, 2018 at 16:37
• You can measure current distribution at any point of patch antenna using electromagnetic numerical technique like Method of Moment. Experimentally also this can be verified but you need proper setup and feed mechanism to do that. Dec 25, 2018 at 4:38