Microstrip Characteristic Impedance

[mbs4]

microstrip characteristic impedance

I have been looking at three equations to calculate the characteristic impedance of a microstrip line. The three I am interested in are the Wheeler, Schneider, and Hammerstad and Jensen equations seen at this website:

http://qucs.sourceforge.net/tech/node75.html

I am just looking at the equations that assume an infinitely thin strip. When I plot the three equations for z0 vs. w/h, the Hammerstad and Jensen equation gives a significantly different plot for epsilon_r not equal to 1. I was wondering if someone could explain to me the difference between that equation and the other two.

Thanks

 

[imodelit_moderator]

microstrip+characteristic impedance

Dear mbs4,

The most accurate model is that of "Hammerstad and Jensen". However the equations written on the website has a small problem in defining Zc (final Zc should be divided by √εeff and not √εr). Also, Hammerstad model is valid for narrow and wide strips. By the way, for more accuracy, you have to take the dispersion effect in your calculations. Thanks.

Best Regards,
imodelit Moderator

 

[mbs4]

wheeler microstrip

Ah, thank you for pointing out that error, helped alot.

Thanks

Added after 3 hours 12 minutes:

I am trying to write a matlab program to calculate the characteristic impedance using method of moments, if anyone has any info about that, that would be great.

Thanks

Added after 3 hours 7 minutes:

Also, does Wheeler have a different formula for two parallel strips or is it that same equation as for a microstrip line?