coplanar waveguide design

I have two quick questions on CPW.

Different set of (W, G) values for a CPW can give the same impedance. If the conduction loss is the main concern, one could increase W and correspondingly G to reduce the loss due to not-infinite conductance (worsen by skin effect) of copper. What's the limit as one simply increases W and G, if board area is not yet a concern? What typical W people typically use, say 1 oz copper on two sheets of 2116 FR4 at 2GHz for 50 Ohm?

Another question. Is there a way to make Agilent ADS automatically generate layout with bended CPW from schematics?

Thank you very much!

One more question. Since I do not know how to get ADS to generate bended CPW in layout automatically, if I have manually drawn the layout without a corresponding schematics, how do I let the Momentum simulator know which polygons are grounds? Thank you!

Hello,

The free TX-Line Transmission Line Calculator from AWR is helpfull in
calculating Coplanar waveguide /Grounded coplanar WG parameters & seeing effect on loss..

The Txline calculator available freely on AWR website...
http://web.awrcorp.com/Usa/Products/...ducts/TX-Line/

Also AWR Microwave Office (MWO) has good CPW models which provides automatic layout generation & simulation model...

Also good routing/trace models available to draw complex CPW traces in layout
& the same can be extracted as EM model & you can select the EM simulators such as Sonnet, EMSight, AXIEM, etc with a simple setp...

http://www.sonnetsoftware.com/suppor...r_waveguid.htm

http://www.sonnetsoftware.com/produc.../apps_cpw.html

Also you can do the same or similar work with ADS & using Momentum, but it takes little effort..


---manju---

Hi zhipeng!

If the size of the design is not a corcern, then excitation of a higher-order mode limits your choice of W and G for a given characteristic impedance. Typically, cut-off frequency of that next higher-order mode is quantified with the relation

lambda_0/(a*sqrt(epsilon_r))=(2*G+W)

where

lambda_0: the free-space wavelength at the corresponding cut-off frequency,

a: A scaling factor, 8 or 10 is provided in the literature

epsilon_r: Relative permittivity of the substrate being employed

2*G+W: Pitch of the CPW line

When the next higher-order mode is excited, CPW line is said to radiate significantly into the substrate, that is why epsilon_r is provided in the formulation instead of epsilon_effective.

Then, what you would do is to select a cut-off frequency that is sufficiently away from your operating frequency and subsequently determine the maximum pitch dimension of your CPW. Next, determine W and G to satisfy a given characteristic impedance.

Hope this helps!

I think so, that the TXLine is the best