What is the relationship of the microtrip's width?

What is the relationship of the microtrip's width to the spacing to ground? The bottom of PCB is copper.

a microstrip line between two ground line on the same surface becomes a coplanar wave guide. microstrip's width n its spacing to the ground will affect on its impedance

In CATV system, to get the impedance of 75 ohm, what are the microtrip's width and spacing to ground on the same surface? How to calculate them?

To get the most accurate answer, you should use a field solver such as the one offered by Polar http://www.polarinstruments.com/. The program is expensive to buy, but you can get a trial copy and/or rent time for as little as S20USD per hour.

There is a free web-based tool that can give you approximate results at:http://www.eecircle.com/applets/015/Gcpw.html

The CPW benefits you the small size with scarifying a little insertion loss.
For fixed impendence, wide line means large gap.

The relationship between the width and gap is complicated.
But you can calculate the impendence and loss very easily via line calculator which is available in ADS, if you know the physic parameters of the foundry material.
And you can get accurate characters via EM simulation.

Thanks all. I have a software as the attached. Can I get a exact width by using this software? but it don't come down to the gap.

Hi,

Download the next program (APPCAD)
You will find there what you need.
But you must know something else you can choise Coplanar WaveGuide WITH Ground plane ooooooooor WITHOUT this two they are not the same!


http://www.hp.woodshot.com/

David

In AppCAD software, why don't the Z0 change when i only change the frequency?

Z0 will not changed by frequency, because the CPW is a wide band element.
if you change the frequency, the skin depth and eletrical wave length will be changed.