Here is the information that goes a little deeper into the theory of how an antenna works. Although this is not a very intellectually intense site, I will warn those viewers on a lunch break or perhaps surfing the net while "between projects," that there are some concepts on this page that use what some people call "math," and other supposedly important "scientific information."
The explanation behind the operation of an antenna begins with the electromagnetic spectrum, shown below:
http://www.gigaant.com/antenna basics/basicknowhow/
As the diagram shows, the range of visible light is very small, explaining why humans cannot see many types of radiated energy. What defines the different types of waves is the wavelength, or the distance it takes for one period (one cycle) to propagate. One period of a wave is shown below:
http://www.kyes.com/antenna/dipole.html
The wavelength of a wave is related to its frequency through the equation:
wavelength = 3 x 10^8 / frequency
This equation explains why the higher the frequency, the smaller the wavelength. Additional explanation can be found in the comparison of the above waveform with the waveform below. If both diagrams represent the same time period, it is easy to see that the lower diagram repeats itself many times more than the upper, thus it has a higher frequency and a visibly smaller wavelength.
http://www.kyes.com/antenna/dipole.html
The reason the electromagnetic spectrum is important, is because antennas radiate or collect electromagnetic signals, depending on whether they are transmitting or receiving. This is accomplished through the process of magnetic fields building up and collapsing in the antenna. The equations that govern this are rather complex and will not be discussed on this site. However, to get a general idea as to how these fields work, think of waves formed by a swimmer paddling his/her foot in the water. The actual swell of the wave could be considered the building up of a field and the trough of the wave would be the collapse of the field. A good visual example is the following animation, which is a simple radiating antenna:
http://www.kyes.com/antenna/dipole.html
You are probably thinking, "Well, I get the spectrum stuff, and I get that the antenna radiates the waves, but I don't understand how." The answer to this lies in the fact that an alternating electrical signal (also known as AC current, which is slightly redundant because it stands for Alternating Current current) has the form of a sine wave, inducing both positive and negative currents in the element through which it passes. The periodic characteristic of the sine wave causes the positive and negative currents to alternate cyclically (think of the swimmer constantly kicking, producing a continuous wave). This in turn causes the magnetic field to periodically build up and collapse.
A transmitting antenna has a signal generator connected to it (ie, a microphone, a video camera, etc) which gets its audio or visual input converted into an AC signal. This signal is then fed into the transmitting antenna, causing it to radiate an electromagnetic wave with the same properties as the input signal. The receiving antenna, does the exact opposite. The radiated signal induces a current in the receiving antenna, which then gets translated into audio or visual information, completing the process.
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