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

  • From: sunil bharadwaz <sunil_bharadwaz@xxxxxxxxx>
  • To: SI LIST <si-list@xxxxxxxxxxxxx>
  • Date: Sat, 23 Nov 2013 04:59:12 -0800 (PST)

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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