One simple method would be to use tikzpackage. You can draw each line of the rectangle. It may be tedious at first to use tikz, but it is so much more convenient when you need to modify your image.
\usepackage{tikz}
\begin{document}
\maketitle
S
\begin{tikzpicture}[font=\small\sffamily\bfseries, node distance = 0.5cm]
\tikzset{
mynode/.style={rectangle,rounded corners,draw=black, top color=white, bottom color=yellow!50,very thick, inner sep=1em, minimum size=3em, text centered},
myarrow/.style={->, >=latex', shorten >=1pt, thick},
mylabel/.style={text width=7em, text centered}
}
\tikzstyle{block} = [rectangle, draw,
text width=11em, text centered]
\tikzstyle{decision} = [diamond, draw, text width=4em, text badly centered, inner sep=0pt]
\node[block] (rectangle) [text width=13em] {text_inside_rectangle};
\end{tikzpicture}
Here, I draw a node. you can specify the dimensions of the rectangle accordingly. And if you want more such rectangles you just have to repeat the '\node[block] (rectangle) [text width=13em] {text_inside_rectangle}; '
statement. Hope this helps.
\square
fromamssymb
. or$s\sqsubset\!\sqsupset$