Format figure caption when using minipage

Question

I am using minipage within figure environment, and I want to maintain only the figure name, and sort of "sub caption" to the minipage.

MWE:

Currently, this is how I plot the figure:

\documentclass[conference]{IEEEtran}
\usepackage[demo]{graphicx}
\usepackage{lipsum}


\begin{document}

\begin{figure}
  \centering
  \begin{minipage}{0.48\linewidth}
       \centering
        \includegraphics[width=\linewidth]{a}
        \caption{a part }
    \end{minipage}
    \hfill
   \begin{minipage}{0.48\linewidth}
        \centering
         \includegraphics[width=\linewidth]{b}
          \caption{b part}
    \end{minipage}
\end{figure}

\lipsum[1]
\end{document}

Which produces:

Require figure title format:

Answer 1

Since you don't need to cross-reference the subfigures individually, you don't need custom \caption directives for them.

Aside: As the subcaption package isn't fully compatible with the IEEEtran document class, this answer deliberately doesn't make use of the that package.

\documentclass[conference]{IEEEtran}
\usepackage[demo]{graphicx}
\usepackage{lipsum}

\begin{document}

\begin{figure}[h]
  \begin{minipage}[b]{0.48\linewidth}
  \includegraphics[width=\linewidth]{a}
  
  \medskip\footnotesize\centering (a) part 
  \end{minipage}
  \hfill
  \begin{minipage}[b]{0.48\linewidth}
  \includegraphics[width=\linewidth]{b}
  
  \medskip\footnotesize\centering (b) part
  \end{minipage}

\caption{Required output format} \label{fig:required}
\end{figure}

A cross-reference to Figure \ref{fig:required}.

\lipsum[1]

\end{document}

Answer 2

Edit:

• Use of the subcaption package in ˙IEEEtrandocumentclass throw warning, thatcaptionpackage (which is loaded bysubcaption` package) will not be used but default document class caption settings.
• However, if instead of it is used older subfig package, there is not problems (warning, error) at compilation, since it is compatible with IEEEtra document class. So the posible simple solution for your problem can be:

\documentclass[conference]{IEEEtran}
\usepackage{graphicx}
%\usepackage{subcaption}   it givers warning that instead `caption` is used default caption setup.
\usepackage{subfig}% works without any problem
\usepackage{lipsum}


\begin{document}
\lipsum[1]
\begin{figure}[ht]
    \centering
\setkeys{Gin}{width=0.48\linewidth}
\subfloat[part]{\includegraphics{example-image-a}}
\hfill 
\subfloat[part]{\includegraphics{example-image-b}}
    \caption{Required output format} 
    \label{fig:required}
\end{figure}

A cross-reference to Figure \ref{fig:required}.

\lipsum[2-7]
\end{document}