Parametric Curve(s)
$$$
\forall\alpha\in\{0,2\pi\}\quad\;
0\leqslant\;k_{a}\;\leqslant2.8\quad\;$$$
$$$ \left \{ \begin{array}{r c l}
\theta(\alpha)& = &\alpha \\
r(\alpha)& = &0.1\times\left (\cos{\alpha}-k_{a}\right )
\end{array}\right .$$$