Is it common to make microstrip bandpass filter elements thinner to overcome loose Er

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Terminator3

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Etching tolerances, temperature changes, loose Er of substrate - all this leads to wrong central frequency, and poor s21 for desired frequency.. Can we make flter elements thinner, what are drawbacks (lower Q, anything else?).
 

The etching tolerance can go +/- so starting thinner will be better when you are on the high side of the tolerance but will make things worse when nominal or on the low side. Yes lower Q. Optimise with montecarlo analysis to get the design within spec for the most cases with variation. Wh y do you think thinner would decrease effects of variation? etching tolerances are typically absolute regardless of width, so the thinner line is going to be more sensitive to those tolerances. i.e. 4mils +/-1milis a 25% change where 10mil +/- 1 mil is 10%.
 
Wh y do you think thinner would decrease effects of variation?
Variation will still exists. But i hope that thinner coupled lines have a wider passband. Simulation shows that with some etching errors of 0.1mm with a line width of 1mm gives more than -10..-20dBm s21 attenuation (beacuse out of passband), and 0.4mm coupled line gives -0.2..-3dBm, that is more acceptable. I still doubt is this right. For single element bandpass filter s21 curve for 1mm and 0.4mm line have a huge difference. 1mm line have very narrow peak, and 0.4mm is wide and not so sharp around resonant frequency.

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Here is simulation result:

blue - 1mm microstrip width, 0.3mm gap
red - 0.4mm microstrip width, 0.3mm gap
 

That much of a change is typically dictated by the specs you have for the filter as far as out of band rejection. Take a look at S11 as well to see what your return loss is for each case. The widerband case should be more stable against insertion loss variation just because the response is flatter.
 
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