How does an antenna work with harmonics?

In summary: If so, then no, feeding a rectangular waves into an antenna will not produce radio waves. Radio waves are created when a rectangular wave is turned into a sine wave by inserting a loading coil between the output of the generator and the antenna.
  • #1
David lopez
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if you fed a rectangular waves to a radio antenna, would it still produce radio waves? does it have to be a sine wave?
 
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  • #2
No, it does not have to be a sine wave. In fact, a rectangular wave can be thought of as a specific sum of sine (and cosine) waves of various frequencies. That is the basis of the Fourier series. The antenna will respond to each sine wave as though it was not part of a rectangular wave, then all the responses to the sine waves can be summed to get the total antenna response to the rectangular wave.

Shown below is a sequence of better approximations of a square wave using more terms in the Fourier series. Each line is plotted a little higher so that you can see them separately. Clearly, the more terms there are, the closer it gets to a square wave. An antenna will respond to each sine wave as though it is alone. Then the individual responses can be summed to get the total response.
1575655092095.png
 
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  • #3
David lopez said:
if you fed a rectangular waves to a radio antenna, would it still produce radio waves? does it have to be a sine wave?
Of course, it would produce radio waves but true broad-spectrum mess. Square wave can be simply turned into decent sine wave by inserting a loading coil between output of generator and an antenna.
The principle is same as in this video. This would make antenna more or less electrically short though.
 
  • #4
zoki85 said:
Of course, it would produce radio waves but true broad-spectrum mess. Square wave can be simply turned into decent sine wave by inserting a loading coil between output of generator and an antenna.
The principle is same as in this video. This would make antenna more or less electrically short though.
A single square wave contains several sine waves of different frequencies and amplitudes. It would be possible to tune to anyone of those and tune out the others (although not completely). The amount of power lost by tuning out the other frequencies depends on the response of the filter to the other frequencies.
 
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  • #5
FactChecker said:
A single square wave contains several sine waves of different frequencies and amplitudes. It would be possible to tune to anyone of those and tune out the others (although not completely). The amount of power lost by tuning out the other frequencies depends on the response of the filter to the other frequencies.
It also depends on the frequency of square wave. For example if that frequncy is 3x higher than quarter wave resonant frequency system with loading coil, than the response of the system to the 3rd harmonic is particularly strong
 
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  • #6
Most radio antennae are not designed (it's very hard!) to operate over even a single octave of frequency range. Moreover, Transmitting amplifiers seldom handle a huge range of frequencies. About an Octave is about as much as you will ever get. A UHF Broadcast Travelling Wave Tube (a typical 'wide band' amplifier) has a wide enough bandwidth to handle a number of separate UHF channels but not over an octave frequency range. Even matching a transmitter to an antenna for a number of different channels is difficult. Most systems use a small Fractional Bandwidth.

So the question in the OP doesn't make a lot of sense in the practical world. However, RF antennae are usually capable of handling a Modulated RF signal which can carry a good looking square wave where the sharpness is limited by the Bandwidth allocated to the channel. An analogue TV transmitter can send 'good' black / white / black/white patterns that will satisfy the requirements of highish quality TV. The Sideband structure of the transmitted signal will consist of a fundamental and a number of (enough) harmonics within the channel width.

Perhaps that was what the OP really meant.
 
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Related to How does an antenna work with harmonics?

1. How does an antenna produce harmonics?

An antenna produces harmonics through a process called nonlinear distortion. This occurs when the antenna is subjected to high frequency signals, causing the antenna to vibrate and produce multiple frequencies.

2. What is the role of harmonics in antenna design?

Harmonics play a crucial role in antenna design as they determine the bandwidth and efficiency of the antenna. By understanding the harmonics produced by an antenna, scientists can optimize its design for better performance.

3. How do harmonics affect the transmission and reception of signals?

Harmonics can cause interference in the transmission and reception of signals. This is because the harmonics produced by the antenna can overlap with the desired frequency, resulting in distortion or attenuation of the signal.

4. Can harmonics be controlled or eliminated in antenna design?

Yes, harmonics can be controlled or eliminated in antenna design by using filters and tuning circuits. These components can help to suppress unwanted harmonics and improve the overall performance of the antenna.

5. Are harmonics always undesirable in antenna design?

No, harmonics can be desirable in certain cases, such as in frequency multiplication or frequency mixing applications. In these cases, the harmonics are intentionally produced and used for specific purposes.

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