Why is the condition for length/lambda >= 0.01 in transmission lines?

Question

Why is the condition for length/lambda >= 0.01 in transmission lines?

Answer 1

Ahh you mean when deciding to use transmission line techniques, why does the ratio have to be greater than 0.01 to cause a designer to use those techniques?

That number will change depending on who you talk to, its just a value gained from experience that engineers use as a guide.  I have seen it vary from 0.05 to 0.1.  0.01 is now the lowest I have seen that ratio....100th of the wavelength.

When you go up in frequency a wire or PCB trace no longer looks like a resistive element as the inductive and capacitive elements have a larger effect.  The Tx line will look very electrically different when the line length starts getting close to the wavelength.  This is why transmission line design techniques are necessary.  This number just is a guide as to when to start using those techniques.

Answer 2

This means that the length of the transmission line is less than about 1/100 of the wavelength. The physical significance of this is that the transmission line can be ignored (i.e. treated as a wire) .