RF - reallyyyyyy basic question about Antenna  - Page 1
Forum section: electronics / general

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 10, 2015, 12:03:23 am
content: So i had a basic question about how antenna work , so from wave physics point of view you should move current in the antenna with enough power in order to radiate, what i can't understand since a current need a voltage difference between two point in order to generate current that flow between them and an antenna is a simple piece of metal with one pole ( still considered when designed to be a 50R dipole load ) how the current is pushed and pulled in the antenna with that single connexion. anyone can explain that please

author: IanB
author_rank: Super Contributor
timestamp: January 10, 2015, 12:44:17 am
content: The antenna has a capacitance allowing it to accumulate charge. An AC excitation signal can move charge in and out of that capacitance.

author: Rory
author_rank: Frequent Contributor
timestamp: January 10, 2015, 03:10:25 am
content: Try reading some of the material presented here:http://www.arrl.org/how-antennas-work

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 10, 2015, 03:15:24 am
content: Current flows through free space, even when there is a complete lack of conductors as we know them. This is called the displacement current.One of the design goals for a good antenna is coupling into this displacement current using conventional (ohmic, within conductors) currents. A very small antenna cannot couple into very much of a wave, and therefore has lower efficiency than a large one which can couple into a large fraction of the wavelength (or multiple wavelengths).Tim

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2015, 02:22:50 pm
content: In a dipole the current is moved back and fourth between the two poles.In a monopole, the current is moved back and fourth between a ground plane and the antenna. It's important to have a good ground plane in order to provide enough capacitance to push and pull the electrons in and out of. At high frequencies a copper plane on the PCB and the batteries themselves are sufficient but at lower frequencies, a ground plane needs to be constructed underneath the antenna.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 10, 2015, 10:35:56 pm
content: So the current , is either pushed to the air or pulled to the ground ? is that it ?

author: IanB
author_rank: Super Contributor
timestamp: January 10, 2015, 10:46:08 pm
content: No, the current stays inside the wires, but the charged particles inside the wire (the electrons) that carry the current can surge backwards and forwards around their rest position. (For an analogy, you may have sloshed water back and forth inside a bathtub as a child. The water doesn't leave the bathtub but it oscillates back and forth.)When charged particles like electrons are made to oscillate back and forth inside a wire they cause power to be radiated away from the wire. (Note that what is radiated is power, not current. All the current stays inside the wire, all the time. If you did a charge balance you would find all charge accounted for and no electrons escaping.)

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: January 11, 2015, 12:22:29 am
content: Ah ok, i see now Thanks everyone