How are RF harmonics affected by the shape of a waveform?

In summary, Fourier Analysis can be used to calculate the amplitude of each harmonic in a repetitive/periodic wave. A square wave has an infinite number of odd harmonics, with the n'th harmonic having an amplitude of 1/n compared with the fundamental. The propagation of high-frequency harmonics through electronic components depends on the frequency response of the system. There is no general way to calculate RF harmonics, as they can arise from different mechanisms and can be either odd or even multiples of the base frequency. In linear circuits, the output signal is the sum of all the differently shifted and scaled sinewave harmonics. The switching rate of a MOSFET is meaningless without qualification, and it is unlikely for a switching MOSFET
  • #1
Plat
48
2
How can the power/amplitude of a particular RF harmonic be calculated? I would assume it is some well-defined fraction of the amplitude of the main frequency?

Do RF harmonics from a square-wave drive appear only on the even, odd, or both, multiples of the base frequency?

How do high-frequency harmonics propagate through electronic components? For example, if a MOSFET can switch at 1MHz max, then can it convey harmonics from the source/signal frequency that are above 1MHz? I know I'm greatly simplifying things here.
 
Engineering news on Phys.org
  • #2
Fourier Analysis enables us to calculate the amplitude of each harmonic in a repetitive/periodic wave.
 
  • #3
Plat said:
Do RF harmonics from a square-wave drive appear only on the even, odd, or both, multiples of the base frequency?
A square wave has an infinite number of odd harmonics. The n'th harmonic has an amplitude of 1/n compared with the fundamental.
https://en.wikipedia.org/wiki/Square_wave#Fourier_analysis
 
  • #4
Plat said:
How can the power/amplitude of a particular RF harmonic be calculated? I would assume it is some well-defined fraction of the amplitude of the main frequency?
In general, RF harmonics are a bad thing, especially in communication systems. Quiz Question -- Why? :smile:

And there is no general way to calculate them. They arise from several different mechanisms, some generating odd harmonics some generating even harmonics, and some generating both.
 
  • #5
Plat said:
How do high-frequency harmonics propagate through electronic components?
A circuit has a transfer function that shows circuit gain and phase shift across frequency. In linear circuits, the fundamental and each harmonic must be treated separately as each passes through the circuit. The resultant signal will be the sum of all the differently shifted and scaled sinewave harmonics.
The spectrum of the output signal is the spectrum of the input signal multiplied by the transfer function.

Plat said:
For example, if a MOSFET can switch at 1MHz max, then can it convey harmonics from the source/signal frequency that are above 1MHz?
A MOSFET needs to be on or off most of the time to minimise both heating during each transition and the power needed to charge and discharge the gate. For that reason, switching rate is meaningless without qualification. It is unlikely that a switching MOSFET application would be driven by a sinewave alone.
 
  • #6
Plat said:
How do high-frequency harmonics propagate through electronic components?
It would depend entirely on the 'frequency response' of the system you are dealing with. There is nothing magic about harmonics. They are totally independent of the fundamental, once they have been created. Their frequencies will stay the same - that's all.
To find out more about the relationship between the shape of a waveform in time and its description in 'frequency space', try this wiki article. Frequency and time domain descriptions are just alternative ways of describing the same signal. It is not 'really' one or the other.
 

1. What are RF harmonics?

RF harmonics are the frequencies that are multiples of the fundamental frequency in a radio frequency (RF) signal. They are produced when an RF signal passes through a non-linear device, such as an amplifier or mixer.

2. How are RF harmonics generated?

RF harmonics are generated when a non-linear device, such as a diode or transistor, is used to amplify an RF signal. These devices produce harmonics by creating distortions in the original signal, resulting in additional frequencies being generated.

3. What are the characteristics of RF harmonics?

RF harmonics have lower amplitudes compared to the fundamental frequency and are spaced at regular intervals from the fundamental frequency. They also have the same phase as the fundamental frequency and can be either in-phase or out-of-phase with each other.

4. Why are RF harmonics important?

RF harmonics can cause interference in communication systems and can also affect the performance of electronic devices. In some cases, they may also be intentionally used for modulation or frequency-hopping techniques in wireless communication.

5. How can RF harmonics be minimized or eliminated?

There are several methods to minimize or eliminate RF harmonics, such as using filters, shielding, or using linear devices instead of non-linear ones. Proper design and testing techniques can also help to reduce the generation of harmonics in RF systems.

Similar threads

  • Electrical Engineering
Replies
28
Views
3K
  • Electrical Engineering
3
Replies
73
Views
7K
Replies
5
Views
2K
Replies
7
Views
3K
Replies
14
Views
1K
Replies
4
Views
6K
Replies
6
Views
17K
Replies
32
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
2
Views
11K
  • Advanced Physics Homework Help
Replies
6
Views
1K
Back
Top