FreeLists / si-list / [SI-LIST] Re: Reference plane resonance

[Istvan Novak <istvan.novak@xxxxxxx>]

Joe,

Assuming rectangular outlines of the planes, you will end up getting a 
double infinite
series of modal resonances from the structure.  Depending on where you 
are on
the rectangular planes, some resonances may coincide in frequency and 
they may
add up or may cancel.  The more symmetry you have in the structure, 
chances are
getting higher that resonances will line up.  Since this depends also on 
the location on
the planes, unless you know that you DO NOT use the planes other than at 
a selected
location, counting on the cancellation becomes tricky.  Cancellation that
may work at your selected location will not necessarily work at other 
locations.  Also
keep in mind that the components on the boards will have a tendency to 
shift the
resonance frequencies around, making it harder in practice to achieve 
cancellation.

Regards,
Istvan


Joe Paul wrote:

>I have a query on resonance of reference planes, (referring to 
>http://www.sigcon.com/Pubs/edn/ppresonance.htm)
>
>I under stand that resonance freq corresponds to the time, a disturbance in 
>reference plane ,take 
>to return to its origin after reflecting from edges of the board. I have also 
>read in a different 
>article that , symmetric board shapes like Square should be avoided as far as 
>possible for reducing 
>problems with resonance of reference planes .
>
>My doubt is
>  
>Is the shape concern due to chance of noise originating at center of board 
>after reflecting from 
>all four sides , reaching the center at same phase and adding up  ? or is 
>there any other reason ? 
>or is the shape concern a myth ?
>
>Regards
>Joe
>  
>

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