There are only few ways to build a circuit that would transform the transceiver impedance of 50 Ohm into the high impedance required, they are either transformers or resonant circuits.
As the antenna is not sold in Germany I made an attempt with a resonant circuit and was very much surprised with the results on 20m. Booming signals at S9+ all over Europe plus audible ones from VK, ZL, YB. EA, 7Z and others confirm 59 signals.
As sceptical as I was, this thing appears to work! Plus, it has an excellent form factor for portable ops. Once I have experimented more with this, I will post some more details.