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

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From: Doug McKean (dmckean@corp.auspex.com)
Date: Mon Sep 25 2000 - 09:17:46 PDT


"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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