How does an antenna radiates if its current is zero at ends?

 

It current is zero at the ends when the voltage is max.
The current is max at the ends when voltage is zero.

Voltage and current are not in phase in the antenna.

Remember RF is an AC signal and will constantly vary in strength and polarity when viewed from a single position such as the end of an antenna dipole.

 

The moving current in the dipoles creates magnetic fields which expand then collapse then expand as the opposite polarity then collapse again. This happens as many times a second as the frequency of transmission.
The high voltage at the ends of the dipole are what drives the electrons back and forth.

As the ends of the dipoles change polarity the electrons leave one dipole and surge into the other. Back and forth, back and forth.

 

As the ends of the dipoles change polarity the electrons leave one dipole and surge into the other. Back and forth, back and forth.

I think electrons leaving and surging across dipoles goes a bit too far. The actual electron displacement in an antenna is minuscule when Quintillions of electrons vibrate at the RF frequency. The electromagnetic field travels at the speed of light but electrons travel at the drift velocity in a conductor and have very little momentum/kinetic energy usually.

http://www.nsarc.ca/hf/ant_rad.pdf

 

They TRUE physics of the phenomenon could create a lot more confusion than a simplistic explanation using freshman level vocabulary.

Honestly, there is still some disagreement with how RF energy moves from antenna to near field regions.
Understanding the quantum physics of the action is not necessary to becoming an excellent tech or engineer.

 

Honestly, there is still some disagreement with how RF energy moves from antenna to near field regions.
Understanding the quantum physics of the action is not necessary to becoming an excellent tech or engineer.

Nothing quantum or very mysterious about classical electromagnetics and drift velocities. I liked your explanation except for the scope of travel for electron movements.

 

A single capacitor plate is an open circuit. Does current flow into and out of a capacitor plate?

An antenna element is a single capacitor plate. It charges just like a capacitor. However, a regular capacitor discharges back into the circuit with it's mating plate. An antenna open capacitor plate discharges into space. The mating antenna element is NOT it's capacitor mating plate. The angle between cap plates is 90 degrees. The angle between antenna elements is 180 degrees.
The capacitance angle is out 90 degrees from normal on the antenna plates (elements).

Just like the inductance angle is out. An antenna is like a mouse trap. The out of phase capacitance (90 degrees)...cocks the trap half way.......and the out of phase inductance (90 degrees) cocks it the rest of the way to 180 degrees...like a mouse trap.

These two fields are now out of phase from where they need to be... to be re-absorbed by the antenna circuit. SO they radiate out into space. They are still COCKED 180 degrees out of normal phase.

When those radiated fields fine the proper length of free charge to be absorbed..... the fields will un-cock on that charge ....giving that length of charge a 180 degree torque. One pi of torque. At that frequency. It charges or turns the free charge that it finds.

A receiver amplifies.....the changing or turning charge on the antenna.

 

To be truthful it was only a few years ago I myself finally discovered the truth.
I had presumed all my life that electrons travelled at lightspeed in copper wire. Then to find out an individual electron only moves mere inches per second.
I was amazed.

 

To be truthful it was only a few years ago I myself finally discovered the truth.
I had presumed all my life that electrons travelled at lightspeed in copper wire. Then to find out an individual electron only moves mere inches per second.
I was amazed.

It's a convenient, logical but nonfactual (current or charge-flow as the energy-flow carrier) inference that works well in circuit theory, hydraulic/xyz analogies, etc ...

 

If you think that an antenna is the secondary of a transformer, that is the operation of the antenna. An antenna matches the impedance of the the transmission line to the impedance of air.