% Author: Dr. Matthias Jung, DL9MJ
% Year: 2020
\begin{circuitikz}
    \draw[-Triangle](0,0) -- (5.0,0.0) 
        node[anchor=north east] () {$f$};
    \draw[-Triangle](0.0,0.0) -- (0.0,3.0)
        node[anchor=north east] () {$Z$};

    \draw [thick] plot [rounded corners=10mm] coordinates {
        (2.10,3.00)
        (2.50,0.00)
        (2.90,3.00)
    };
\end{circuitikz}