What cause EMI radiation?

[jw11396]

I am confused with two EMI radiation causes on PCB:
1. changing current
2. impedance discontinuity

Assume AC signal on a 50ohm microstrip transmission line with 50ohm termination at the end, is there going to be any radiation?

Thanks

 

[wchu01]

At different frequency, the impedance seen by the signal would differ, hence the transmission line model kicks in. In my view even with the impedance between device well taken care, I often see that device with high speed signals radiate.

 

[FvM]

A microstrip is a "leaking" transmission line and generally radiating to a certain extent. The effect is increased with a nonunity VWSR respectivly transmission line reflections and discontinuities in the geometry.

Radiated interferences are also caused by ground and power planes acting as antenna.

 

[AmirMohammad]

hi
These are two most important causes but not the all, I think everywhere we have current the potential vectors can exist and thus radiation will occur.