\documentclass[tikz]{standalone}

\usepackage{pgfplots}

\pgfplotsset{compat=1.14}

\begin{document}

\begin{tikzpicture}
    \begin{axis}[xmin=0, xmax=10, width=12cm, height=5cm, xlabel={$f=2\pi\omega$}, ylabel={$|\underline H(f)|$}]
        \addplot [domain=0:10, mark=none, samples=100, smooth] {1/sqrt(1+(x)^2)};
    \end{axis}
\end{tikzpicture}

\end{document}
