% Author: Prof. Dr. Matthias Jung, DL9MJ
% Year: 2026
\begin{circuitikz}

    \draw[DARCred,thick] (0,6)
        sin ++(4, 1)
        cos ++(4,-1);
    \draw[DARCred] (0.25,6.5) node[](){$I$};

    \draw[very thick] (0,6) coordinate(start)
        to [short] ++( 3.9,   0)
        to [short] ++(   0,-0.8) node[anchor=south east](){$\downarrow \unit{\ohm}$};
    \draw[very thick] (8,6) coordinate(end)
        to [short] ++(-3.9,   0)
        to [short] ++(   0,-0.8) node[anchor=south west](){$f$};
    
    \draw(start) node [anchor=east] () {a.};
    \DARCmeasure{start}{end}{0,2}{0}{$\frac{\lambda}{2}$}

    \draw[DARCred,thick] (0,4)
        sin ++(2, 1)
        cos ++(2,-1)
        sin ++(2, 1)
        cos ++(2,-1);
    \draw[DARCred] (0.25,4.5);

    \draw[very thick] (0,4) coordinate(start)
        to [short] ++( 3.9,   0)
        to [short] ++(   0,-0.8) node[anchor=south east](){$\uparrow \unit{\ohm}$};
    \draw[very thick] (8,4) coordinate(end)
        to [short] ++(-3.9,   0)
        to [short] ++(   0,-0.8) node[anchor=south west](){$2\cdot f$};

    \draw(start) node [anchor=east] () {b.};

    \draw[DARCred,thick] (0,2)
        sin ++(1.333, 1)
        cos ++(1.333,-1)
        sin ++(1.333, 1)
        cos ++(1.333,-1)
        sin ++(1.333, 1)
        cos ++(1.333,-1);
    \draw[DARCred] (0.25,2.5);

    \draw[very thick] (0,2) coordinate(start)
        to [short] ++( 3.9,   0)
        to [short] ++(   0,-0.8) node[anchor=south east](){$\downarrow \unit{\ohm}$};
    \draw[very thick] (8,2) coordinate(end)
        to [short] ++(-3.9,   0)
        to [short] ++(   0,-0.8) node[anchor=south west](){$3\cdot f$};

    \draw(start) node [anchor=east] () {c.};

    \draw[DARCred,thick] (0,0)
        sin ++(1, 1)
        cos ++(1,-1)
        sin ++(1, 1)
        cos ++(1,-1)
        sin ++(1, 1)
        cos ++(1,-1)
        sin ++(1, 1)
        cos ++(1,-1);
    \draw[DARCred] (0.25,0.5);

    \draw[very thick] (0,0) coordinate(start)
        to [short] ++( 3.9,   0)
        to [short] ++(   0,-0.8) node[anchor=south east](){$\uparrow \unit{\ohm}$};
    \draw[very thick] (8,0) coordinate(end)
        to [short] ++(-3.9,   0)
        to [short] ++(   0,-0.8) node[anchor=south west](){$4\cdot f$};

    \draw(start) node [anchor=east] () {d.};
\end{circuitikz}