IE3D warnings when simulating a grounded CPW structure

[abhi_kolkata]

hi,

i am trying to simulate a grounded CPW structure with the specs. given below, in IE3D upto 50 GHz. IE3D is giving some medium warnings - saying the port separation factor for the ports are too big and suggesting that i should reduce the distance between the positive and negative ports.

wat should i do?? in that case, should i ignore the warnings or that would cause severe inaccuracy in the results(i want the ckt. to operate upto that freq. accurately)

plz aslo mention the reason for this warning and its physical significance (so that i do not repeat the same mistake next time).

Grounded CPW specs.:

Signal line width: 50 micron
CPW finite ground plane width : 250 micron
Gap between signal and gnd line: 70 micron
the total cpw line length : 340 micron
Substrate : GaAs (12.9) of thickness 350 micron

Another question is that - should i use some extra line length (more than 340 micron) to reduce the port to port coupling and get actual results.

If anybody knows the answers Plz do reply with ur views

eagerly waiting

abhi

 

[jian]

Re: IE3D warnings!!!

Hi, Abhi: I believe you must have not defined differential ports between the center strip and the finite cpw grounds. The port you defined on the center strip is referencing the infinite ground. IE3D issues a warning message to you. If you define the ports correctly, it should cause such message. Attached are two models for your cpw structure. They yield almost identical results for this structure. However, I believe the narrower ports on gnd model is better in reality. Sometimes, if we define the port too wide (compared to wavelength), it may cause accuracy problem. It is not the simulator's problem. It is from the microwave network theory. Also, the models do not have true thickness built. In case your CPW is thick, you should consider the true thickness model for high accuracy. In case your CPW has very large ground planes, you can consider modeling it as infinite ground CPW using magnetic current modeling. They are documented in IE3D manual. Happy Holidays! Best regards.