Re: [SI-LIST] : Cavity Resonant frequecy and radiated EMI

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From: Bill Owsley (owsley@cisco.com)
Date: Mon Sep 25 2000 - 20:54:44 PDT


None of these seem to have anything to do with your problem at a somewhat
lower frequency. So, maybe box resonance has nothing to do with your
problem. Look for another source...

At 09:17 AM 09/25/2000 -0700, Doug McKean wrote:
>"KHOO,KENG-KOK (HP-Singapore,ex4)" wrote:
> >
> > Hi,
> >
> > Sorry for the mistake.
> >
> > The box demension is (L)70mm x (W)120mm x (H)140mm
> >
> > Thanks.
>
>
>No problem.
>
>Your actual problem may be as Mr. Weir explained.
>
>The various modes of TE resonance for those dimensions
>will give you the following frequencies:
>
> 1.25 GHz
> 1.07 GHz
> 2.14 GHz
> 1,64 GHz
> 2,48 GHz
> 2,39 GHz
> 2,70 GHz
>
>It operates on the fact that the length of one of the
>dimensions is one half wavelength for resonance. So, the
>1.25 GHz comes from a resonance along the 120mm width.
>The length is considered half wavelength because it
>sets up a standing wave. The 1.07 GHz comes from a
>resonance along 140mm height. The 2.14 GHz comes from
>a resonance along the 70mm length. Again, the actual
>lengths being considered half wavelengths.
>
>Assume for the moment that various combinations of the
>(height, width, depth) are different resonance modes at
>a fundamental frequency. It's easy to assign numbers
>so that (1,0,0) is the fundamental resonance along the
>height (between the top and bottom plates), or
>1,0,0 = 1.07 GHz.
>
>Likewise, the other modes turn out to be ...
>0,1,0 = 1.25 GHz (TE resonance between the side plates)
>0,0,1 = 2.14 GHz (TE resonance between the front and back plates).
>
>The other modes
>
>1,1,0 = 1.64 GHz
>1,0,1 = 2.48 GHz
>0,1,1 = 2.39 GHz
>1,1,1 = 2.70 GHz
>
>are more complex modes of resonance. 1,1,0 being a resonance
>between the top, bottom, and side plates, etc ...
>
>The calculation of these frequencies is simply
>by using the three dimensional distance formula.
>
>Regards, Doug
>
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----------------------------
Bill Owsley, owsley@cisco.com
919) 392-8341

TMBU Compliance
Cisco Systems
7025 Kit Creek Road
POB 14987
RTP. NC. 27709

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