Limitations of the Simple Model

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The simple model described above has a number of limitations; the major ones are:


Transmission lines are electrically short when their length is less than λ/10 where λ is the wavelength. λ is deduced from the relationship λ = c/f, where c is the speed of light (3×108m/s) and f is the frequency in Hz.

The main problem with the simple model described previously is that it is only valid whilst the transmission lines are electrically short. As frequency or line length increases, the lines will eventually become electrically long. Once this occurs, standing waves are set up on the lines making the simple model invalid.

To overcome these and other problems, full wave EMC modelling is required.

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  1. BS EN 55022:1998, “Information technology equipment - Radio disturbance characteristics - Limits and methods of measurement”

Last Updated: 2004-Oct-21