I have read about matching networks, authors usually will describe a target impedance to be presented, to say, the output of an amplifier, and then they design the matching network. To widen the bandwith they usually create a matching network with more sections, thus, lowering the general Q and presenting the same impedance to a wider range of frequencies.
But my question is this: What's the point on presenting the same impedance over a wide range of frequencies if the S-parameters (and thus the required load/source to be presented to the amp) change with frequency? For example the optimum source impedance for LNA design is not the same at different frequencies, in a power amplifier the optimum load varies with frequency, so whats the point on designing a matching network that presents the same load over a wide range of frequencies?, instead, shouldnt a network be designed to "track" those impedance changes, thus presenting the ideal source/load required for each frequency?, how is a network like that designed?
Best Answer
I've developed a tool (based on the algorithms described in [2]) for matching a frequency dependent complex source to a frequency dependent complex load impedance. It is still WIP, but I think it works a treat. You'll have to compile that from the source and provide the impedances to match as s1p files.
https://github.com/Qucs/qucs/pull/555
On the other hand, Keysight ADS comes with a similar tool based on the RFT and the analytic methods.
Some references:
[1] Wideband circuit design. H.J. Carlin. 1998. CRC Press
[2] http://ethw.org/images/a/a6/RF_Networks_OCR.pdf
Hope it helps