How to find the width of a microstrip line?

[geft]

I'm only given the height and dielectric constant of the substrate, characteristic impedance, thickness of the conductor, and the operating frequency. How do I find the width? I can't solve through the impedance formula because it requires the effective dielectric constant, and I can't find the effective dielectric constant without finding the width.

 

[zebroo]

Hi,

Try with this link :

**broken link removed**

I have tested it and the results are corrects...
BR

 

[geft]

Thanks. I've used the tool but I was wondering if there is a specific formula I can work out.

 

[zebroo]

miracle of Wiki :

https://en.wikipedia.org/wiki/Microstrip

 

[geft]

That looks... impossible. Thanks anyway.

 

[DeboraHarry]

That looks... impossible. Thanks anyway.

There is no exact analytical equation for this - at least I've never come across one, and I think plenty of people have tried to derrive one. So you are relying on an empricial formula. You could take many approaches.

1) Try to invert it Wheeler's equation, perhaps using something like Mathematica to aid you. Good luck to you if you try that!!!
2) Write a small computer program (Excell would be fine) to just solve it itteratively for what you want.
3) If you only have one to do, not an endless number, use the free calculator

https://web.awrcorp.com/Usa/Products/Optional-Products/TX-Line/

set all the paramters that are fixed (Er, height), then adjust the width to get the Zo you know. If you first attempt has Zo of say 40 Ohms, and you want 60, then of course you know you need to adjust reduce the width to increase Zo. It should take you no more than a minute to do this.

 

[volker_muehlhaus]

set all the paramters that are fixed (Er, height), then adjust the width to get the Zo you know. If you first attempt has Zo of say 40 Ohms, and you want 60, then of course you know you need to adjust reduce the width to increase Zo. It should take you no more than a minute to do this.

You don't even need to iterate manually, because TXline can calculate both directions: calculate width from Z0, or calculate Z0 from width.

 

[Azulykit]

I find Simon and Waddel's books helpful. Polar 9000 is a good commercial software package too.

 

[bepsml]

or this one https://www.edaboard.com/threads/61954/

 

[mtwieg]

Related question: does anyone have any equations or calculators that account for the effect of having a ground plane on the microstrip layer?

 

[tony_lth]

HFSS can solve your prblem, but it is a little complex to set the model.