After watching many double-stub matching tutorials, yours is by far the best. You started with a good, concise Smith chart review which was helpful for those of us who don't use these charts often. You explained how the auxiliary unit circle is simply a translation of the original to a different line location. In the step-by-step examples, you constantly cross-referenced points on the circuit diagram with corresponding points on the Smith chart to show why the geometric transformation you were doing were justified by the distances involved. (Many other tutorials present the "compass work" without sufficient justificaton.) My only quibble is that you were using a Smith chart with only an impedance grid while doing a problem in admittance, so it wasn't immediately clear where some susceptance values were coming from without stopping the video to reference a paper chart that had the missing admittance circles. Thank you for pointing out that the solution with shorter stubs yields wider bandwidth. It's clear to me that this is because longer stubs accumulate phase errors more quickly, but it might be advisable to say so explicitly. Overall, an excellent lecture! Thank you for making the effort to produce it.
David, thank you so much for your complement and useful comments. As an FYI, the students in the Intro to Transmission Lines class I recorded this for have just been recently introduced to a Smith chart by the time they watch this video. I chose to keep it simple and not get into the admittance format. The students will eventually get to it. Thanks again.
Two questions: 1) I have noticed that you have used short-circuit stubs in all examples. Is there a difference between short and open circuit stubs aside for starting 0.25 wavelengths apart? 2) For the second example you state that the preferable solution is the second solution because it uses less length and therefore less material? Are there designs where a longer stub would be preferable? Besides that awesome video!
