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Grounded Coplanar Microwave In Pcb Loyout

I have to develop a 6 layers PCB Layout for a ciruit.
In this circuit there is a Bluetooth Interface based on STM Module and an Antenova Antenna (external at the STM Module).
I must develop a connection from the Antenova Antenna to the STM Module. The user guide of the Antenova antenna describe that I have to use a Groundeed Coplanar Microwave and the guide show that I don't have any route near at the microwave and antenna.
I use to design the geometrical parameter of the Grounded Coplanar Microwave the tool Aglent AppCAD.
I Would like to know if in the gemetrical design of the Grounded Coplanar Microwave, I can consider to locate the grounded plane in the bottom of the circuit to obtain a dielectric thickness equal at the 5*signle layer dielectric thiskness becouse from a layer to other there isn't copper near at the antenna.
If I can suppose it, the error of the real characteristic impedance that I design is small compared to the AppCad or ideal value?
In addition, I'd like to know which is the most powerfull and simple tool that I use to simulate the Grounded Coplanar Microwave thath I have to design how Geometry for my loyout circuit with Cadence Allegro PCB Editor.

Thanks

redwire over 14 years ago

I think you are asking if it is ok to use a 6 layer board in a GCPW design assuming there is no signal copper nearby?
Yes.
There are many reasons why I would recommend you NOT use GCPW but that is a subject for another discussion.
For your case you would need to make sure that that only the outside layers have copper (as I think you said). For the dielectric, you need to look up the *exact* dielectric constant for *each* pre-preg and core material within the 6 layer stackup. The overall dielectric becomes the RMS value of the individual layers. You may have to contact the dielectric material provider to get the specific values.
With GCPW you need to be aware of via spacing between each via and between the antenna line. The wrong spacing can cause an unexpected resonance.
AppCAD is fine for getting close. Several other tools: Applied Wave Research (AWR) has a free tool and a full simulation tool Polar *might* have something available. Sonnet has a limited 2 layer tool which will allow you to compute the return loss over your frequency band of interest whereas the other tools do a simplified static 2D solution.
My personal choice is to design it using AWR and match the transmission line with the active circuit and antenna.
Other recommendations are to find a consultant who can do a true 3D solution in CST or HFSS.
Hint: Look at a simplified microstrip solution to get equivalent performance without all the headaches of GCPW.
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