antenna-theory.com

[nnomme]

Hi all
first time here

Got to this forum while searching for some information on how antennas work.

So, i know antennas are made of conductors that accelerate an electrical charge along the conductor, thus creating EM waves.
Antennas receive information when the EMW apply a force on the said electrical charge thus moving it up and down, and creating current.

So for example when tuning a radio
I cant understand how can antennas be sensible only to a certain frequency of EMW when all frequencies of EMW are passing by it, so the movement of the electrical charge inside the antenna, should be a mix of all the EMW it is receiving.

Can anyone explain this to me?

thanks

[bigSteve]

Antennas do disturb the E- and H- fields at all frequencies.

However, you have to be able to deliver the energy from the antenna to a receiver. The receiver has some impedance (typically 50 Ohms). If the antenna is very small, the antenna impedance will be something like 0.003 - j*4000 Ohms. You won't transfer any power in that case.

So the point to understand is that you can induce current on the antenna at all frequencies, but you can't deliver it unless the impedance is correct.

[R. Fry]