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I've seen various "recommended" chamfers for 90 degree grounded coplanar and microstrip traces. For example, this paper from Georgia Tech or this RF/Microwave layout guide.

Is there a "rule of thumb" for which type of chamber and which geometries work best for RF layout? For my case I'm interested in 3 to 12 GHz with a grounded coplanar waveguide conductor of 10 mils with 6.5 mil air gaps on a 6.6 mil thick Rogers 4350B substrate. But my case aside, are there rules of thumb that I can follow to ensure I have a constant 50 ohm impedance without resorting to 3D EM simulators like CST Microwave or HFSS?

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Yes there are rules of thumb for designing chamfers. The slides you posted include 4 different ones.

Designing a chamfer that is absolutely optimized for your particular stackup and frequency band can't be done just from rules of thumb; you'll need to invest (time and money) in an EM simulator if you want that.

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  • \$\begingroup\$ Thanks for the answer. Makes sense that optimization requires EM simulation. \$\endgroup\$ – FullmetalEngineer Nov 5 '15 at 21:10

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