This question appears at first glance to be almost identical with this one Antenna coupling via capacitor but I think that in the following case the involved coupling capacitor might play a different role than in the linked question and I would like to find out which role it has.
Consider the models of antenna + matching modules (I found them in: https://www.gsm-modem.de/M2M/m2m-faq/how-to-design-an-antenna-matching-circuit/)
Question: What is the job of the capacitor in first model? Unfortunately, the author waived any explanation on the function of this coupling capacitor, he just noted that a final matching circuit could be just one capacitor or inductor in row. Why?
Indeed I think that here the reason d'etre of this coupling capacitor might be another one than of that one from Antenna coupling via capacitor which was based on the circuit I found here: http://makearadio.com/misc-stuff/regennotes.php (but I don't know, it's just a conjecture of mine)
The reason for implementation of the coupling cap there was (see Andy aka's answer) that the author was dealing with a concrete regenerative receiver, where the (variable!) coupling capacitor's job was to set the right amount of the Q-factor which is roughly proportional to the quotient \$ Ctank/Ccou \$, where \$ Ctank \$ is the capacitor in the tank, and \$ Ccou \$ the coupling cap.
Now in https://www.gsm-modem.de/M2M/m2m-faq/how-to-design-an-antenna-matching-circuit/ the author not says to which kind of receiver the antenna is coupled. So it seems that the role of coupling capacitor which he introduces there is of more "universal" manner and not depends on concrete receiver type which sits at the other end.
So could somebody explain what the job of the coupling capacitor in first model is?