\documentclass{article}
\usepackage{tikz,amsmath, amssymb,bm,color}
%\usepackage[margin=0cm,nohead]{geometry}
%\usepackage[active,tightpage]{preview}
\usetikzlibrary{shapes,arrows}
\usetikzlibrary{decorations.markings,math}
% needed for BB
\usetikzlibrary{calc}

\begin{document}

\begin{figure}
\begin{tikzpicture}
\tikzmath{\ang = 45;};
\begin{scope}[thick,decoration={
    markings,
    mark=at position 0.5 with {\arrow{latex}}}
]
\filldraw[red] (-1,0) circle (2pt)
node[anchor=east, font = \footnotesize] at (-1,-0.2) {$\mathrm{E_0}$};
\draw[dashed, red] (-1,0) --++({\ang+90}:1);
\filldraw[green] (1,0) circle (2pt)
node[anchor=west, font = \footnotesize] at (1,-0.2) {$\mathrm{E_0}$};
\draw[postaction={decorate}, red] (-1,0) --++ (\ang:2);
\draw[postaction={decorate}, green] (1,0) --++ (\ang:2);
\draw[<->, thick] (-1, -0.2) -- (1, -0.2);
\draw[dashed, green] (1,0) --++ ({\ang+90}:2.5);
\draw[<->, thick] (-1,0)++({\ang+90}:1) --++ (\ang:{2*cos(\ang)});
%       \draw[<->, thick] (-1,0)++({\ang+90}:1) --++ (\ang:{2*cos(\ang) });
\node[anchor=north, font = \footnotesize]  at  (0, -0.2) {d=$\lambda/2$};
\end{scope}
\draw[blue, thick, dash pattern= on 25 off 7 on 50 off 7 on 10] (-2,0) -- (2, 0);
\node[anchor=west, font = \footnotesize, blue] at (1.5,-0.05) {z}; node[near start, auto] {true}
\draw[thick,blue,->] ([shift=(0:1)]1,0) arc (0:\ang:1);
%   \draw[thick,blue,->] (2,0)  arc (0:\ang:1);
\draw (1,0)++({\ang/2}:1.2) node[rotate=\ang, anchor=base, blue, font=\normalsize]{$\theta$};
\draw ({\ang+90}:1.3) node[rotate=\ang, anchor=base, black, font=\normalsize]{$d\cos\theta$};
\end{tikzpicture}
\end{figure}
\end{document}