cpwg calculator

Hello ,everybody, In my antenna switch,in order to get more than 4 ampers carrying capacity,i have to use wider trace width >80 mil. In order to improve the isolation ,i am going to utilize coplanar waveguide construction. but according to the calculation of AppCAD,with 80 mil trace width,the gap may up to 350 mil,is it right for a 30mil substrate? Any help will be appreciated!
PS:Substrate Thickness,30mil;copper thickness,2.8mil,dielectric constant,3.5.

at the same time ,i use Txline to calculate,but have different result,i don't know why!

You cannot have CPW with 80 mil wide trace on 30 mil substrate with Er=3.5. It is possible on 37 or 38 mil substrate with 80 mil trace and 80 mil slot width. This was checked with Polar field solver. AppCAD is not good program for transmission line calculations. I assumed that you need 50 Ohm CPW.

Yes, I need a 50 ohm CPW. you mentioned AppCAD is not a good program for CPW, So what program is good? Would you offer one? Thanks!

Added after 7 minutes:

Dear RF-OM, i calculate a 50 ohm CPW with AppCAD or calculator(site:http://www.microwaves101.com/encyclopedia/calcpw.cfm), and can't get your result! Would you tell me the program you use! Thanks!

Hi,

Like I know u have a few rules with CPWG.
I assuming here that u are using Coplanar wave guide vs ground Plane.

Okay, u can see at help in ADS or Genesys u will find a few dumb rules.
In cases u could i will attach them.

IN:
"CPWG.jpg" u will find dump guide from Genesys (this one pretty similat to ADS)
"CPWG Microstrip Via and more.pdf" u will find an example from Hittite.

In jpg try to see:

[HEIGHT/(WIDTH +2*GAP)]>1

Regarding to APPCAD I am agree vs RFOM (how are u?) it's free but not so good prog!

David

To sitp_710,

I used Polar as I mentioned. It is EM field solver and this is the best program when you have unusual dimensions as in your case. For normal CPW cases I usually use Transmission Line Calculator into LINC2 and/or my own worksheets. This is the fastest way to design CPW. Then, if it is necessary Polar can be used to final check.

Unfortunately transmission line calculations are not easy and it is especially tedious for CPW (elliptic integrals solutions are involved). A lot of calculators use some simplifications and suggestions that makes trusted area of dimensions narrow and accuracy suffers. Among the worse are AppCAD and MWO.

Added after 1 minutes:

Hi DDavid,

I am okay, a lot of things to do and it keep me busy. How are you?

Thank you all for your help! i got so much from you!