Re: Difference between a two section tline and a single stub?
The whole concept of "Impedance Matching" was developed so that you could add arbitrary lengths of line at the input and output of a circuit component, and not see any performance degradation. But to do that the component, an LNA in this case, has to first be matched to the characteristic impedance of the line you want to use. Normally that is 50 ohms, so do your match at the input to 50 ohms, and the match at the output to 50 ohms, then you can add all the line length of 50 ohm microstrip you desire!
In some rare cases, you might not match to 50 ohms...like if the LNA is driving a bandpass filter, and the bandpass filter components are easier to realize in a 20 ohm system....