thejim said:

I have concuded somewhere regarding Electricaly short antenna.

I just want to mention it to see if my conclusions are correct.

If the antenna is shorter than 0.25 of the wavelength then there will

be a phase angle as a result of disturbances and that is why there is

impendance rather just resistance

Am i saying it correctly?

I don't understand what you say. The outgoing wave bounces off the

end of the antenna and returns back toward the transmission line, with

some energy lost to radiation. Right at the end of the antenna, the

current of the outgoing and reflected wave must sum to zero, since

there is no other currents involved except the two waves. So the

returning wave is current inverted.

The thing that is hard to wrap your brain around is that you are

dealing with traveling waves, not lumped components (like capacitors

and inductors). So to understand how these two waves act at any point

on the antenna or transmission line, you have to deal with the time it

takes for any part of the wave to get from point A to point B.

If the antenna were electrically resonant (not too long or too short),

the outgoing wave would take a quarter of a cycle time to get to the

tip of the antenna and a quarter of a cycle time for its reflection to

get back to the feed point. But there is also the inversion at the

reflection, which adds another 180 degrees or one half cycle to the

total effect, so the returning wave meets the outgoing next cycle, in

phase.

If the antenna is short, the reflected wave gets back too soon, and

the next cycle sees the last one at an earlier phase in its cycle.

For instance, if the outgoing cycle is right at zero volts and going

positive, it meets the reflection at a negative voltage heading for

zero volts. This is a lot like how it would be if the outgoing wave

were driving a lumped capacitor. The capacitor voltage would always

be lagging the applied wave. Short antenna = capacitive reactance at

the feed point.

If the antenna were long, the reflection would have the (travel) time

to get ahead of the drive wave, so it would have a voltage that leads

the drive in phase, just as an inductive load would have a voltage

than leads its current.