formulas.tex

\documentclass{article}
\begin{document}
    \begin{equation}
        E_{z}=\frac{-\frac{\mathrm{j}}{2} \eta  I_{a} \left(1-\cos \! \left(\frac{k l}{2}\right)\right) {\mathrm e}^{\mathrm{-j} k r}}{\mathrm{\pi} \sin \! \left(\frac{k l}{2}\right) r}
    \end{equation}
    \begin{equation}
        V_{\mathit{OC}}=\frac{\mathrm{j} \eta  I_{a} \tan \! \left(\frac{k l}{4}\right)^{2} {\mathrm e}^{\mathrm{-j} k r}}{\mathrm{\pi} k r}
    \end{equation}
    \begin{equation}
        P_{\mathit{load}}=\frac{V_{\mathit{OC}}^{2}}{8 R_{\mathit{rad}}}
    \end{equation}
    \begin{equation}
        P_{\mathit{rx}}=\frac{P_{\mathit{tx}} G_{\mathit{tx}} G_{\mathit{rx}} \lambda^{2}}{16 \mathrm{\pi}^{2} r^{2}}
    \end{equation}
\end{document}