\documentclass[crop,border=3pt,tikz,convert={outext=.svg,command=\unexpanded{pdf2svg \infile\space\outfile}},multi=false]{standalone}
\usepackage{ifthen}
\usetikzlibrary{math}
\usetikzlibrary{calc,through,shapes}

\pgfdeclarelayer{background}
\pgfdeclarelayer{foreground}
\pgfsetlayers{background,main,foreground}

\def\lines{3}
\def\omegat{20}
\def\PhaseDiff{30}

\newcommand{\markangle}[6][0.25]{
  \begin{scope}
    \clip (#2)--(#3)--(#4);
    \node (ANG) [draw, circle, minimum size=#5] at (#3){};
  \end{scope}
  \coordinate (E1) at (intersection 0 of ANG and #3--#2);
  \coordinate (E2) at (intersection 0 of ANG and #3--#4);
  %\draw[thick] (E1) to [bend right=50] (E2);
  \coordinate (EM) at ($ (E1)!0.5!(E2) $);
  \coordinate (EM) at ($ (EM)!#1!(#3) $);
  \node at (EM) {#6};
}

\begin{document}
  \begin{tikzpicture}[>=latex]
    \tikzmath{\D=\PhaseDiff;}
    \draw[gray,->] (0,-4) -- (0,4) node[anchor=south]{$y$};
    \draw[gray,->] (-4,0) -- (4,0) node[anchor=west]{$x$};
    \coordinate (A) at (0,0);
    \tikzmath{\Amp=5/\lines;}
    \coordinate (B) at (\omegat:\Amp);
    \coordinate (B0) at (B);
    \foreach \a in {1,...,\lines}{
      \coordinate (Bext) at ($ (A)!1.8!(B) $);
      \coordinate (New) at ($ (B)+(\a*\D+\omegat:\Amp) $);
      \draw[ultra thick,->,blue] (A) -- (B);
      \ifthenelse{\a = \lines}{}{
        \draw[dotted,thick,blue] (B) -- (Bext);
        \markangle{New}{B}{Bext}{50}{$\delta$};
      }
      \coordinate (A) at (B);
      \coordinate (B) at (New);
    }

    \draw[ultra thick,red,->] (0,0) -- (A);
    %\node()[anchor=north east] at (5,5){\LARGE $\delta=\D^\circ$};
    \coordinate (C) at (\omegat:1.8*\Amp);
    \markangle{2,0}{0,0}{C}{75}{$\omega t$};
    \node[red,fill=white,anchor=north]() at (0,-1){$x=\cos(\omega t)+\cos(\omega t+\delta)+\cos(\omega t+2\delta)$};
    \node[red,fill=white,anchor=north]() at (0,-1.7){$y=\sin(\omega t)+\sin(\omega t+\delta)+\sin(\omega t+2\delta)$};
    \begin{pgfonlayer}{background}
      \draw[gray] (-5,-5) rectangle (5,5);
      \path[fill=red!30] let \p1=(A) in (0,0) circle ({veclen(\x1,\y1)});
    \end{pgfonlayer}
  \end{tikzpicture}
\end{document}