\begin{table}%t7
\caption{\label{tab7}RF requirements on the waveguides.}
%\centering
\par
\begin{tabular}{p{5.5cm}ccc}
\hline\hline\noalign{\smallskip}
 &30 GHz&44 GHz&70 GHz \\
\hline 
Insertion loss [dB] \dotfill &$-$2.5&$-$3&$-$5 \\
Return loss [dB] \dotfill &$<$25&$<$25&$<$25 \\
Isolation [dB] \dotfill &$<$30&$<$30&$<$30 \\
Waveguide size \dotfill &WR28&WR22&WR12 \\
Waveguide internal section [mm] \dotfill &7.112 $\times$ 3.556&5.690 $\times$ 2.845&3.099 $\times$ 1.549 \\
\hline
\end{tabular}
\end{table}