QUESTION

+1 vote
Is there a disadvantage to using a smaller transmission line over a larger one?

The transmission line calculator shows that a 50 ohm impedance match can be achieved with two widely different widths and gaps. Is there any drawback to choosing the smaller transmission line over the larger one?

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2 Answers

+2 votes
answered by
I suspect with larger trace width variation in the dielectric will have a slightly greater effect on the impedance. Also at the smaller extreme you can run into manufacturing tolerance issues if the trace were to get too small. I would recommend to keep in mind the size of the other components that may be in the RF path. For instance if you have a pi matching network and are using 0402 size components it would be a good idea to make the trace width the same as the width of the pads of the components to avoid transitions in the trace size.
+3 votes
answered by
I concur with AB9TE regarding component size.  For example, you use 0402 parts in the matching network with a t-line 7 mil width and gap for a 50 ohm match, but the tradeoff requires a dielectric thickness between the signal layer and the ground plane on the order of about 4 mils.

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