Question about distance between microstrip and CPW
I have a little question?
I using in my design with microstrip,
To get Zo=50Ω: H=32mil, T=1.41mil=1oz, w=58mil, FR4 => ε=4.5 [F=800÷2200MHz]
What is intresting me how much I must to move from microstrip with ground plane so I wan't get CPW (Coplanar Wave Guide).
I thought that minimum distance is height of PCB (in my case 32mil),
But my colleague say that at least 2*width (2w) of the microstrip line.
Who is telling the truth?
David
I use substrate height. What if you had a very wide line of Z0=5 ohms. Would you still use 2*W spacing? Use a 2.5D EM simulator to draw your own conclusions.
Hi,
Tnx for applying,
yesterday i spoke with other colleague he said that I must move a FEW wavelength from microstrip!
David
If you don't currently have a 2.5D simulator you can use Sonnet Lite for free. It has enough capability to handle two coupled microstrips (4 ports). Just vary the spacing while observing return loss and coupling. I think you'll find that a spacing of 1*H to 2*H will get you between -20 dB to -30 dB of coupling depending on length. While this is too much for a high isolation switch it is probably for running traces next to a ground flood. You spacing shiould be determined by your needs and with a 2.5D simulator you can perform quick experiments in a few minutes.
http://www.sonnetusa.com/products/lite/index.asp
Added after 10 minutes:
I tried your configuration in a 0.5"x0.5" enclosure. The response with no ground on either side is |S11|=-40 dB.
With 1*H spacing to ground (with continous via) is |S11|=-32 dB.
2*H spacing yields |S11|=-50 dB.