how does an antenna work
[looks so simple and silly question......which is not]
The definition below is from the Antenna Handbook MCRP 6-22D pg. 38.
http://www.armymars.net/ArmyMARS/Ant...antenna-hb.pdf
?When an alternating electric current flows through a conductor (wire), electric and magnetic fields are created around the conductor.
If the length of the conductor is very short compared to a wavelength, the electric and magnetic fields will generally die out within a distance of one or two wavelengths. However, as the conductor is lengthened, the intensity of the fields enlarge. Thus, an ever increasing amount of energy escapes into space. When the length of the wire approaches one-half of a wavelength at the frequency of the applied alternating current, most of the energy will escape in the form of electromagnetic radiation. For effective communications to occur, the following must exist: alternating electric energy in the form of a transmitter, a conductor or a wire, an electric current flowing through the wire, and the generation of both electric and magnetic fields in the space surrounding the wire.?
An antenna can be made out of any conducting material, usually metal.
Whereas waveguides/striplines/microstrips/etc. are built to confine the EM energy between conductors (by balancing the + and - closely spaced, so that at large distance no nett field is 'seen'), antennas are built to maximize the nett electric fiels 'seen' at a distance. That's why e.g. a dipole antenna can be made by bending outwards the conductors of twin-cable.
The electrons dance along the antenna wire!
How exactly are the electrons made to dance in the wire. Its not part of a closed circuit, so how is the alternating current passed through it?
I have similar problem understanding, accelerating electron in single metal stick like those in "el cheapo" AM FM radio.
If some how the antenna is connected to LC tank, which is also open circuit, I still don't understand how electron running up and down the length of that metal stick.
please some smart people to explain this.
thanks
Electromagnetic energy can be transferred in many types of medium, including air. The antenna in itself is a passive component, it works as a impedance transformer so EM energy can be transmitted/received with minimum impedance mismatch loss.
TX radio-> Antenna -> free space, is a closed circuit if nothing else picks up the EM waves and adding more branches in the closed circuit, such as a receiving antenna->radio or any else type of absorber.
If it is an open circuit, is also impedance infinite. Anyone measured a stick antenna that had infinite impedance? For EM waves do free space represents a media with 377 Ohm as characteristic impedance so not even space in it self is a open circuit. Other medias have other impedance properties which also affect length and speed of a the EM wave that travels in that medium.
Electrons do dance on the wire if they are charged with energy. As a result of this dance are fotons emitted. In the RX antenna is opposite happen, electrons are charged by fotons that the antenna picks up from space, resulting in a measurable antenna signal that can be amplified in the receiver circuit.
Hello Kafeman,
thank you for helping me understand it. so space has impedance, hmmm interesting. I only know now. thank you.
BTW you are Kafeman, are you prefer to have coffee than beer, any good beer from Sweden?
I feel like to buy you a big pitcher of beer as a way to say thanks.
Learning that space is limited by its impedance as any else medium and nothing feels real wireless any longer.
Yes we have good beer in Sweden. I travel regularly to Germany to import it as a Dunkel not last too long.
Local brewers makes soft drinks. Ok as table water.