\begin{tikzpicture} 
\begin{axis}[
name=ideal_lpf_td,
anchor=origin,
axis lines*=middle,
enlargelimits = false,
ymin=-0.2,
ymax=1.2,
xmin=-2.5,
xmax=2.5,
axis line style={->,>=stealth},
xlabel={$t$},
ylabel={$h_{lin}(t)$},
yticklabel style = {yshift=0.2cm},
xticklabel style = {yshift=-0.1cm},
every axis x label/.style={
	at={(ticklabel* cs:1)},
	anchor=north,
},
every axis y label/.style={
	at={(ticklabel* cs:1)},
	anchor=south,
},
ytick=1,
xtick={-2,2},
xticklabels={$-T$, $T$},
every outer y axis line/.append style={white!15!black},
every y tick label/.append style={font=\color{white!15!black}},
legend style={draw=white!15!black,fill=white,legend cell align=left}]

\addplot[line width=1pt] coordinates {(-10, 0) (-2, 0) (0, 1) (2, 0) (10, 0)};
\end{axis}

\begin{axis}[
name=ideal_lpf_fd,
at=(ideal_lpf_td.right of south east), anchor=left of south west,
axis lines*=middle,
enlargelimits = false,
xmax=2.5,
xmin=-2.5,
ymin=-0.2,
ymax=1.2,
axis line style={->,>=stealth},
xlabel={$\Omega$},
ylabel={$|H_{lin}(j\Omega)|$},
yticklabel style = {yshift=0.2cm},
xticklabel style = {yshift=-0.3cm},
every axis x label/.style={
    at={(ticklabel* cs:1)},
    anchor=north,
},
every axis y label/.style={
    at={(ticklabel* cs:1)},
    anchor=south,
},
xtick=\empty,
ytick={1},
yticklabels={$T$},
xtick={-2, -1, 1, 2},
xticklabels={$-\frac{2\pi}{T}$, $-\frac{\pi}{T}$, $\frac{\pi}{T}$, $\frac{2\pi}{T}$},
every outer y axis line/.append style={white!15!black},
every y tick label/.append style={font=\color{white!15!black}},
legend style={draw=white!15!black,fill=white,legend cell align=left}]

\addplot[black!50, line width=1pt] coordinates {(-10, 0) (-1, 0) (-1, 1) (1, 1) (1, 0) (10, 0)} node[pos=0.55, black!50, pin={[pin edge={black!50, thick}]-70:{Ideal LPF}}, inner sep=0pt] {};
\addplot[smooth, line width=1pt, domain=-3:3, samples=101] {abs(sinc(x/2))^2};
\end{axis}

\end{tikzpicture}