[SI-LIST] Re: Inserion loss of fr4 , 50 ohm trace .

From: steve weir <weirsi@xxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Date: Sat, 23 Nov 2013 05:24:26 -0800
Unfortunately the problem can be in your simulation, your measurements 
or both.  A couple of dB for a 5cm run seems pretty reasonable in this 
frequency range.

The stock checklist includes ensuring that you deembedded your test 
instrumentation properly, that you don't have a modal resonance issue 
(usually more of a problem with low loss materials than FR-406 and 
similar), and that you don't have an unusual situation with your DUTs 
like too much absorbed moisture.   You can get hints as to what is wrong 
by looking at the shape of the VNA plots.

Steve.
On 11/23/2013 4:59 AM, sunil bharadwaz wrote:
> Hi friends ,
> We are designing a dual band receiver ( 2.4 Ghz & 5.5 Ghz ) on a Fr4 
> substrate .
>
> The length of the 50 ohm RF trace ( CPW - 15 mil trace width & 18 mil spacing 
> to ground ) ,
> is approximately 5 cms .We have simulated this 5 cms long CPW trace on HFSS 
> using DK of
>
> 4.4 & DF  of 0.018 . The loss reported was about 1.6 dB .
>
> We have received the actual board , which shows about 6 dB loss for the same 
> trace (actual measurement on VNA)
>
> Measured the 50 ohm trace with TDR . It shows about 53 to 54 ohms . The fab 
> report is also
> in sync with the measurement on the impedance front .The test coupon ( from 
> fab  )also shows
> the right impedance .
>
> Why are we seeing such a huge insertion loss ? The DF of 0.018 seems to be 
> correct .
> I have double checked this number , with the fab .
>
> Can some one ( pls ) explain the inconsistency between the simulated & actual 
> results  ?
>
> Best Regards
> Sunil.Bh
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References:
- [SI-LIST] Inserion loss of fr4 , 50 ohm trace .
  - From: sunil bharadwaz
[SI-LIST] Re: Inserion loss of fr4 , 50 ohm trace .

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