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

\pgfkeys{/tikz/savelength/.code 2 args={\global\edef#1{#2}}}

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

\def\lines{40}
\def\omegat{20}
\def\PhaseDiff{359}

\newcommand{\mypicture}{
  \tikzmath{\D=\PhaseDiff;}
  \draw[gray,->] (0,-4) -- (0,4);
  \draw[gray,->] (-4,0) -- (4,0);
  \coordinate (A) at (0,0);
  \tikzmath{\Amp=5/\lines;}
  \coordinate (B) at (\omegat:\Amp);
  \foreach \a in {1,...,\lines}{
    \draw[->,blue] (A) -- (B);
    \coordinate (A) at (B);
    \coordinate (F) at (B);
    \coordinate (B) at ($ (B)+(\a*\D+\omegat:\Amp) $);
  }
  \node at (-4,4){\large $N=\lines$};

  \path let \p1=(F), \n1={veclen(\x1,\y1)} in [savelength={\n}{\n1}];

  \ifthenelse{\lengthtest{\n < 8 pt}}{
    \draw[ultra thick,red,tips=proper] (0,0) -- (F);
    \ifthenelse{\lengthtest{\n < 1 pt}}{
      \draw[ultra thick] (0,0) circle (1);
      % \node at (-1.5,-1.5){Minimum};
    }{}
  }{
    \draw[ultra thick,red,->,tips=proper] (0,0) -- (F);
  }

  \begin{pgfonlayer}{background}
    \draw[fill=white] (-5.1,-5.1) rectangle (5.1,5.1);
    \path[fill=red!30] let \p1=(F), \n1={veclen(\x1,\y1)}  in (0,0) circle[radius=\n1];
  \end{pgfonlayer}
}

\begin{document}
\begin{tikzpicture}[>=latex]
  \tikzmath{\lines=2;}
  \mypicture
  \node()[fill=white, inner sep=10] at (5.1,-5.1){\Huge $\delta=\PhaseDiff^\circ$};
  \begin{scope}[shift={(10.2,0)}]
    \tikzmath{\lines=5;}
    \mypicture
  \end{scope}
  \begin{scope}[shift={(0,-10.2)}]
    \tikzmath{\lines=10;}
    \mypicture
  \end{scope}
  \begin{scope}[shift={(10.2,-10.2)}]
    \tikzmath{\lines=40;}
    \mypicture
  \end{scope}
\end{tikzpicture}
\end{document}