[SI-LIST] Re: Resonance on the pcb board
- From: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>
- To: "John Smith" <swagguy18@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 25 Mar 2011 11:51:19 -0600
John,
Cavity/waveguide resonances can be an issue. Power/ground planes act like
resonant cavities. Use the standard formulas found in any Emag text,
remembering that they are approximations and not a replacement for a 3D
solver. Plug in the dimensions of your power plane(s), and the permittivity
of the material used (core/prepreg). If the dominant mode(f(1,0) for
waveguide, f(1,0,1) for cavity) is close to 3.5GHz, it is possible that
cavity effects are contributing to your problem. The basic calculation will
probably produce a frequency higher than 3.5GHz since it does not take into
account the numerous sources of loss. These losses will downshift the
resonant frequency.
I don't know of any specific correlation between dielectric loss and
resonance at 25GHz. Dielectric loss dominates resistive loss at around
1GHz, and gets worse from there. Cavity/waveguide resonance occurs at any
frequency depending on the geometry and materials used. Permittivity,
permeability(magnetic material), loss tangent, surface roughness, metal
thickness, and length/width/height of the cavity/waveguide determine the
modal resonant frequencies.
Something to check anyway,
Ken
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of John Smith
Sent: Thursday, March 24, 2011 8:21 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Resonance on the pcb board
Hi, Experts,
I am new to signal integrity and I have some questions.
(1) I did some measurements on my pcb board and found resonances around
3.5GHz. Can you give me some hints on what causes the resonances?
(2) Could you please list some typical issues which can cause resonances and
at what frequency range? I know dielectric loss can cause resonance at
around 25GHz, what about the other effects?
Thanks in advance.
Regards,
John
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