# Calculate the sparameters of a coplanar stripline structure

1. Feb 17, 2010

how to calculate the sparameters of a coplanar stripline structure with 434microns breath 45microns height and 1950microns length fed with 1Win TE10 mode at 35GHz...

can some one help me

regards..

2. Feb 17, 2010

### f95toli

Re: S-Parameters

That question makes no sense.
First of all, are you asking about a coplanar waveguide OR a stripline (they are different types of transmission lines)? since you haven't specified a gap to the groundplane I am guessing you mean the latter? Also, is the metal REALLY 45 microns thick? And what kind of substrate are you using?

Secondly, neither type will -as far as I know- support a TE10 mode...

Thirdly, how are you feeding the line? With some sort of waveguide-to-stripline transition?

3. Feb 18, 2010

Re: S-Parameters

Hi
thanx for the reply....... sorry for not putting the question clear enough...

i am trying to design a coplanar stripline structure in comsol multiphysics by importing the structure from the orcad pcb design tool the structure has 3 layers the dielectric as rogers 3003 with Er=3 of height 250 microns and above this is the 2 striplines of height 45microns and width of 434 microns with 366 microns apart..... above this is the air gap of 600microns, the length of the entire structure is 1950microns. Port one is fed with 1 watt. I annalysed the struct in comsol and obtained the results of s-para at 35GHz, now i wanna compute the s-parameters in theory... so as to verify the results......

regards

4. Feb 18, 2010

### f95toli

Re: S-Parameters

OK, now I understand what you mean. So it really is a coplanar stripline (a.k.a. a coupled MSLine), the fact that you did not specify the gap or the substrate me think that you really meant an ordinary stripline.

Anyway, I put your numbers into TxLine (freeware, you can download it) and I get that the impedance is 62 Ohm and the electrical length 131 degrees at 35 GHz.
From this you should be able to calculate the S parameters yourself. Note that I don't think you can expect analytical solutions to be very accurate here (meaning TXline will be off), especially with metal that thick.

Also, if you want to read about the theory and check the formulas yourself I would recommend "Coplanar waveguide circuits..." by Rainee Simons.

5. Feb 20, 2010

Re: S-Parameters

i refered the book u recomended. but could not find thwe formulas to compute the s-parameters with parameters i said before (dimentions and the input power).please help me in finding s-parameters

regards

6. Feb 20, 2010

### f95toli

Re: S-Parameters

I am pretty sure the formulas for calculating the impedance and electrical lenght of coupled MS can be found in that book, but I'll double check when I am back in my office on Monday.

Note that I am assuming you know how the compute the S-parameters once you have the impedance of the line. If you don't know how to do that I would (as usual) recommend "Microwave Engineering" by Pozar.
Although you should be able to find that information in just about any book on microwave engineering, it is pretty basic.

btw, note that I am assuming that you are interested in TEM modes here; not TE01 as in your orignal question. A coupled MS line will -as far as I know- not support a TE01 mode (for a TE01 mode you would use something like a circular waveguide, i.e. a pipe)

7. Feb 22, 2010