Difference between GCPW and CPW

gcpw design

Dear Sir/Mdm,

Need to seek advice from you:

What will be the main advantages in using Conventional CPW (Coplanar Waveguide) as compared to CPW with underlying ground?

Your advice is needed !

Yours Sincerely with Best Regards,
Zesong

you can find the answer form the book
Coplanar Waveguide Circuits Components and Systems

zesong said:

Dear Sir/Mdm,

Need to seek advice from you:

What will be the main advantages in using Conventional CPW (Coplanar Waveguide) as compared to CPW with underlying ground?

Your advice is needed !

Yours Sincerely with Best Regards,
Zesong

Click to expand...

Hi,

there are some pros and cons on using these variants of CPW. Sometimes this is more dictated with technology available to you, less by taking the best choice.

Just to mention some of the aspects if you can choose:

Ordinary CPW is a open structure meaning that in vertical direction both half spaces are considered infinite. It has some inpact on your design, e.g. you will have to have to take care that the side of the substrate with no signal conductors have to be suspended over a bottom lid in a box. This require more complex (and expensive) box.

In CBCPW (conductor backed CPW) you have ground plane which allows you to consider only one half space. It can offer better isolation between the parts of the circuit if via walls are applied. On the other hand, this structure is supporting surface wave modes that must be taken into account and suppressed.

The ratio of line width/spacings and absolute dimensions are different depending on a variant chosen so sometimes you will prefer one solution from that point of view etc.

This is a very simplified story try to find the stated reference.

flyhigh

Dear FlyHigh,

What do you mean by half-space !

It will be great if you can further elaborate !

Best Regards,
Zesong

Hi,

well, maybe my terminology was not adequate, sorry if I confuse you. The essence is that in ordinary CPW is basically a 3 layer structure - you have a subtrate, a layer of air above the substrate and a layer of air below it. CBCPW is the 2 layer structure, you have a substrate, a layer of air above and a ground below the substrate.

In the past I did myself some work on analysis of idealized CPW structures where it was assumed that the air layers are infinite in hight (they should be called open CPW/CBCPW structures as there is no cover, so the structure is open). These infinite air layer can be called half-spaces as they are infinite in one direction (from substrate surface to infinity). In reality you got to have covers, so air layers will have finite hight and it might influence CPW and CBCPW performance.

Hope I cleared the confusion that I made. The other details from previous post are clear?

flyhigh

Hi ,

so GCPW ( Grounded CPW) is CBCPW written in Coplanar Waveguide Circuits, Components, and Systems ? right ?

Coz I used the equations in pp.88 in this book to calculate the effective dielectric constant and characteristic impedance,
but they were all different from the paper " Experimental models of series and shunt elements in coplanar MMICs " ....

I don't get where the problems are ....

Pls help me , thx .... :?: