[SI-LIST] Re: Microstrip line loss on Rogers 4350
- From: Ming Tsai <ming.tsai@xxxxxxxxxx>
- To: Scott McMorrow <scott@xxxxxxxxxxxxx>
- Date: Mon, 21 Mar 2005 10:15:59 -0800
Hi Scott,
Thanks for your message.
I was measuring single-ended microstrip. My two SMA connectors were separ=
ated
about 2.75". All the traces (3", 5" and 7.5") had some curves and bends w=
hich
I can identify from TDR plots. The measured |S21| curves were pretty clea=
n up
to 15 GHz. The |S21| could be read as (including two SMA connectors)
Trace Length |S21| @ 5GHz |S21| @ 10GHz
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
3" -1.25 dB -1.98 dB
5" -1.92 dB -2.91 dB
7.5" -2.76 dB -4.35 dB
So I estimated the trace loss by taking the delta and draw a linear line =
on
the chart. The trace bending would have some effect, but I did not expect=
it
to me the major concern. (Plus the 3" line is pretty straight).
The return loss curves did show some deep resonance, but all below -20 dB
(for all three lengths from 0-13 GHz). |S11| @ 10 GHz are less than -25 d=
B. I
did not think any obvious concern there. If you wish, I can e-mail you th=
e
[S] data and plots separately.
Thanks!
Ming
Scott McMorrow wrote:
> Ming
>
> You didn't say whether you were measuring single-ended or differential
> microstrip. Are your insertion loss curves clean and free of resonance=
s
> out to beyond 10 GHz? What does your return loss curve look like.
> What's your return loss at 10 GHz.
>
> Something is obviously wrong, since your measurements imply a loss
> tangent of around .011 rather than .004. I'd suspect something
> structural in nature.
>
> scott
>
> Scott McMorrow
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
> (401) 284-1827 Business
> (401) 284-1840 Fax
>
> http://www.teraspeed.com
>
> Teraspeed=AE is the registered service mark of
> Teraspeed Consulting Group LLC
>
> Ming Tsai wrote:
>
> >Hi All,
> >
> >I am studying the microstrip line loss on 10 mil Rogers 4350 (Er =3D 3=
.48,
> >loss tangent =3D 0.004 @ 10 GHz). The trace width is 22 mils, with hal=
f oz
> >copper. From some transmission line calculator I expect to see 0.25dB
> >/inch loss @ 10 GHz. However I measured under network analyzer and I g=
ot
> >the loss up to 0.5dB/inch @ 10 GHz.
> >
> >I did not have well-setup TRL calibration on board, but I took 3
> >separate measurements from 3", 5" and 7.5" long microstrip lines, and
> >estimated the delta to get 0.5dB/in loss. So I assume the edge-mounted
> >SMA connector is not a factor. Also checked under TDR I saw 48 ohms of
> >line impedance, which is within the spec. I also scratched out the
> >solder mask which did not have any effect. I used full-wave tool to
> >verify the radiation as well as skin effect, but no surprise the
> >simulation showed that I should get about 0.25dB/in loss.
> >
> >Does anyone have similar experience or any suggestion? Thanks!
> >
> >Regards,
> >
> >Ming
> >--
> >Ming. Tsai
> >Staff Hardware Development Engineer
> >Product Technology - Hardware Design Group
> >XILINX
> >
> >
> >
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--
Ming J. Tsai, Ph.D.
Staff Hardware Development Engineer
Product Technology - Hardware Design Group
XILINX
Telephone: 408-626-6260
E-Mail: ming.tsai@xxxxxxxxxx
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