FR-4 PCB Material used on Radio design

On the Element-14 website the following question was asked by Richard.

I would like to make a SWR meter working on 2.45 GHz with a 50 Ohm track designed on a PCB.

Do you think that the FR-4 PCB could fit this requirement ?

There is a “Epoxyd hard fibre FR4” for sale in FARNELL manufactured by “ROTH ELEKTRONIK” under “RE1001-LF” reference.

Do you know where I could find the exact drawing to make such 50 Ohm coupled tracks on the FR-4 PCB ?

I have  a 2.4 Ghz generator with a 2W output RF power and I would like to use this device to check a microwave cavity supposed to work at 2.4 Ghz. Hence the SWVR meter…

Hope you could help.

Chris Pinter Replied:

FR-4 Material is OK at 2.45GHz only if your radio can handle significant drift over temperature.  FR-4 is typically used for consumer applications only and the board stack must be tightly controlled.   You need to have expertise when working with FR-4 at 2.4GHz if you hope to get repeatable results.   You need to be careful to make sure your design is sound before you go into production.  You could develop a radio using 5 to 10 prototype boards and everything looks fine.  However you most likely will see a difference in performance in production.   FR-4 is not intended for radio products.

Since you are developing an SWVR meter you will need to use a different material in order to get any kind of accuracy in your SWVR measurements.    I would suggest you look at a ceramic material before you start.  Rogers corporation has been the standard for industrial and specialty designs for a very long time.    I would suggest you look at the RO4000 series.  It is the most cost effective product they have available.  However it will cost you 7 to 10 times that of FR-4 .   It is well worth the cost in order to get repeatable reliable results.

http://www.rogerscorp.com/acm/products/16/RO4000-Series-High-Frequency-Circuit-Materials-Woven-glass-reinforced-ceramic-filled-thermoset.aspx

I have been developing radio technology for the last 15 years.  It is not an easy task you are undertaking.   The design my well seem rather straight forward but you will see performance issues if you do not get the  transmission lines, PCB layout and grounding issues nailed.   In all radio design the PCB is a major part of the circuit.

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