Hello every body.
I'm studying for the antenna's radiation. Antena antena is connected to the generator through a transmition line.
I have a question: Does a Transmition line radiate along it?
if no then Why?
and another question is : How electron accelerate on the line? and velocity of it on the line?
Thank you every one

 

Rf radiation is emitted by transmission lines.
It is one of the 3 loss mechanisms.
Resistive- copper losses
Inductive-dielectric losses
Radiant-RF energy escape from transmission lines

 

Hello every body.
I'm studying for the antenna's radiation. Antena antena is connected to the generator through a transmition line.
I have a question: Does a Transmition line radiate along it?
if no then Why?
and another question is : How electron accelerate on the line? and velocity of it on the line?
Thank you every one

Usually you want to minimize radiation on a transmitting line unless it's designed to be a active part of the antenna. The typical methods are with shielding in a coax or with balanced currents that cancel (equal and opposite) with a open two-wire line.

The conductor electrons operate as a conduction current in the transmission line and antenna. This means they only move very small distances back and forth in response to the electric field of the time-varying RF energy. The electrons 'phase velocity' is very high(and can even be FTL), but the motion of the electrons in the conductors is very slow. Electrons have mass, they can't move at light speed because their mass would become infinite at this speed.

 

Short answer: Usually not if you do things correctly.

The EH antenna is through to rely on radiation from the transmission line for its miraculous performance.
http://www.eh-antenna.com/Ham_intro.html

 

Usually you want to minimize radiation on a transmitting line unless it's designed to be a active part of the antenna. The typical methods are with shielding in a coax or with balanced currents that cancel (equal and opposite) with a open two-wire line.

The conductor electrons operate as a conduction current in the transmission line and antenna. This means they only move very small distances back and forth in response to the electric field of the time-varying RF energy. The electrons 'phase velocity' is very high(and can even be FTL), but the motion of the electrons in the conductors is very slow. Electrons have mass, they can't move at light speed because their mass would become infinite at this speed.

thank for your explain.but
I do not understand why the acceleration of the electrons on the transmition line is different from that of the electrons on the antenna. While antennas and transmition line are connected to each othe.

 

thank for your explain.but
I do not understand why the acceleration of the electrons on the transmition line is different from that of the electrons on the antenna. While antennas and transmition line are connected to each othe.

Using open wire feedlines to illustrate this, I think that is easy to explain -for each electron going to the antenna on one conductor there is exactly one electron (on average) going away from the antenna on the other conductor. The field disturbances from the electrons going in opposite directions cancel out.

 

thank for your explain.but
I do not understand why the acceleration of the electrons on the transmition line is different from that of the electrons on the antenna. While antennas and transmition line are connected to each othe.

Using open wire feedlines to illustrate this, I think that is easy to explain -for each electron going to the antenna on one conductor there is exactly one electron (on average) going away from the antenna on the other conductor. The field disturbances from the electrons going in opposite directions cancel out.

What Dick says is exactly right. An electron is an electron but how they are physically separated is what matters with the fields that are generated from that acceleration. First consider that no power leaves the physical antenna. It might seem strange at first to say that but the little power that's dissipated as heat in the physical antenna comes from the space around it. All the power that's radiated plus the ohmic losses are transferred directly from the generator to space. So where moving charges cancel (by design in the transmission line) there is no radiation into far-field space and where moving charges are uncanceled (by design at the antenna) there is radiation into far-field space as the energy moves away from the antenna.

Sometimes the antenna system is a combination of transmission lines effects and radiation line effects like in a Bruce Array (a type of old school Curtain_array).

Here we have currents that cancel and add depending on what section of the antenna we look at.