FreeLists / si-list / [SI-LIST] Re: Question on EMI radiated power

["Andrew Burnside" <Andrew.Burnside@xxxxxxxxxxxxxxxxxxx>]

Chuck 
:My interpretation of a reactive component is energy storage in the near
:field surrounding the antenna, and of course there will be no power transfer
:due to this.  This is completely consistent with energy storage in
::capacitors and inductors.  Therefore, there is no such thing as a complex
::radiation impedance.


However, the reactive component may relate to any (partial) mutual 
inductance/capcitance there is to other structures in the near field. 
Therefore, we don't have an ideal antenna due to the near field loading. When 
considering EMI, we may well be within the near field range.

If we consider digital circuits only for a moment, then the majority of the 
emissions are likely to be due to clocks / and current dumped down the power 
supply network. Yes, there may be some direct emissions from interconnects, but 
these are usually fairly small compared to the PSN, as we aren't talking power 
electronics here. 

If we are considering the far field only, then yes it is possible to get away 
with a resistance only if we are only interested in power transfer. However, I 
would have thought though that the emission phase is becoming signficant, 
considering the rise times of some of the signals present.

Regards

Andrew


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