[SI-LIST] Re: resonance in insertion loss
- From: Gustavo Blando <gustavo.blando@xxxxxxxxxx>
- To: si-list <si-list@xxxxxxxxxxxxx>
- Date: Mon, 26 Nov 2012 10:39:39 -0500
Do a simple test:
- Plot your S21 and also S11
- Then renormalize your S-param to another impedance (let's say 45Ohms),
see if your S11 goes down. If S11 goes down I'll expect the
oscillations on you Insertion loss to get smaller until eventually,
if you find the right impedance, it'll go away.
Alternatively
- You can try to do a TDR on your S-parameters (you can do it yourself
by "ifft" or using any commercial software, and look at
the impedance of the line, as close as possible to your initial step.
- Then you can grab that impedance (from above) and use it to
re-normalize the Spar, and the weave should go away.
Reason:
If this is what is going on in your situation, what you are seeing is
1/2 wave resonance (dependent of the length and propagation of your line),
since the impedance at both ends (renormalization impedance) is the
same but different than the Zc of your transmission line.
If you concatenate this s-parameter twice, you'll see your resonance
increasing in frequency (you can try this too to prove it)
Hope this helps.
Thanks
Gus
On 11/26/2012 9:54 AM, 黄涛 wrote:
> hi si experts:
> When I test s-parameters of trace at PCB,the s21 does not show straight
> line but a dip or up/down ripple when freqency upto some point
> Who can help to explain how this produce or advise me some paper
> Thanks a lot.
>
> ���� Windows �ʼ�
>
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