Hello ,I have a multilayer board it has sections of differential ports connected to VNA:
70 ohm layer 5, length 6 inches
70 ohm layer 10 , length 6 inches

90 ohm layer 5
90 ohm layer 10
etc..

So I have many SDD21 and I need to decide what is the best material to use for this board.
I know I can subtract two S21 plots of the 10 inches and 5 inches and get loss per inch.
Two questions:
What engineers do given this setup to decide what metrial is the best to use?
Thanks.

 

Follow what the PCB manufacturers recommend:
https://jlcpcb.com/blog/choose-fr4-or-rogers-pcb-material

 

Depending on the frequency, you can use Rogers for sure but there are several other materials that can work for you also, like Megtron 6 and others. What you need to be aware of also, is material availability, talk to your board vendor and ask them for what they would recommend and verify it will work for your application. Some materials can have very long lead times because a vendor doesn't stock that material. Main thing is to talk with your FAB shop, they can get you what you want and tell you if it's long lead or not. Good Luck.

 

Hello , I am testing signal integrity a PCB for 200GEL XDR.
I got some TDR results and SDD21 insertion loss.So I test the impedance value and loss of S21.
How can I know :
1.what is the frequency range ?
2.what levels of SDD21 are suitable?
3.what TDR value that the trace exsibits is proper?
4. Is there some document I could use to answer these questions?
Thanks.

 

Hello , I am testing signal integrity a PCB for 200GEL XDR.
I got some TDR results and SDD21 insertion loss.So I test the impedance value and loss of S21.
How can I know :
1.what is the frequency range ?
2.what levels of SDD21 are suitable?
3.what TDR value that the trace exsibits is proper?
4. Is there some document I could use to answer these questions?
Thanks.

first, you need to research a class on pcb design techniques.
The task is fairly basic , but critical, im surprised you dont have suport from your co workeres !
why do you think you need Rodgeres or other ?
whats it going to give you ?

Its well possible to use "better" materials, and endup with a terrible board that fails.

 

The subtraction method you're describing is called Delta-L in most SI labs. Once you have those loss/inch curves, pay attention to how loss scales with frequency. Linear growth means Df (dielectric loss) is the main driver; a √f shape means copper roughness is dominating. That distinction tells you which datasheet spec should carry the most weight in your comparison. More on the full material evaluation workflow at https://portandpatch.com/uncategorized/rf-pcb-material-selection-vna-insertion-loss/

 

Hello,this is very intresting,is there a rigorous way to find exactly by how much copper roughness is dominating?
Thanks.