Adding space before \hline inside table with equations and between rows

Question

I have a table with couple of equations and I'd like to add a small space between rows inside table and afer and before \hline. I already have the command \renewcommand{\arraystretch}{1.5} inside the preamble but it does not affect the space inside the table I want to modify. Would you know a solution to this? Red arrows indicate where I'd like to have some spacing. Thank you.

\documentclass[a4paper]{article} 
\usepackage{amsmath}
\usepackage{tabularx}
\usepackage{float}
\usepackage{siunitx}
\begin{document} 

\begin{table}[H]
\caption{Table}
\label{Tab:table}
\centering
\begin{tabular}{l | ll}
  \hline
  \hline
  First-order pole & $\frac{1}{\pi R_\text{load}C_\text{out}}$ & \SI{100}{\hertz}\\
  Second-order pole & $\frac{f_\text{sw}}{\pi}{\big(\frac{1}{D(1+\frac{V_\text{in}}{NV_\text{out}})}\big)}^2$ & \SI{100}{\hertz} \\
  Left half-plane zero & $\frac{1}{2\pi R_\text{ESR}C_\text{out}}$ & \SI{100}{\hertz}\\
  Right half-plane zero & $\frac{R_\text{load}}{2\pi \frac{V_\text{out}}{NV_\text{in}}\big(1+ \frac{NV_\text{out}}{V_\text{in}}\big)L_p}$ & \SI{100}{\hertz}\\
  DC gain & $\frac{V_\text{in}}{D_\text{iv}}\sqrt{\frac{R_\text{load}f_\text{sw}}{2L_p}}\frac{1}{S_e+S_n}$ & \SI{100}{\hertz}\\
  Duty cycle & $\frac{V_\text{out}}{V_\text{in}}\sqrt{\frac{2L_pf_\text{sw}}{R_\text{load}}}$  &\SI{100}{\hertz}  \\
  \hline
\end{tabular}
\end{table}

\end{document}

Answer 1

You can use \\[the_additional_space_you_want] instead of \\ between two lines. For example, \\[2mm] will add 2 mm of additional vertical space between the two lines.

Edit: and to insert more space between the two first rules and the first line, you can insert a "strut" (a rule of width 0 and of the height you desire) between \hline\hline and the beginning of the line: for example \rule{0mm}{5mm} (first argument is the width, here 0, second is the height).

Answer 2

for more vertical space in cells package makecell provide macro \makegapedcells:

\documentclass[a4paper]{article}
\usepackage{nccmath}
\usepackage{makecell, tabularx}
\setcellgapes{5pt}
\usepackage{siunitx}
\usepackage[skip=1ex]{caption}

\begin{document}
    \begin{table}[htb]
\caption{Table}
\label{Tab:table}
\makegapedcells
\centering
\begin{tabular}{l | >{$\displaystyle}l<{$} >{\SI{100}{\hertz}}l}
  \Xhline{1pt}
\makecell[l]{First-order pole}
    &   \frac{1}{\pi R_\mathrm{load}C_\mathrm{out}}                         &   \\
Second-order pole
    &   \frac{f_\mathrm{sw}}{\pi}{
        \left(\frac{1}{D\left(1+
                \mfrac{V_\mathrm{in}}{NV_\mathrm{out}}\right)}\right)}^2    &   \\
Left half-plane zero
    &   \frac{1}{2\pi R_\mathrm{ESR}C_\mathrm{out}}                         &   \\
Right half-plane zero
    &   \frac{R_\mathrm{load}}{2\pi\mfrac{V_\mathrm{out}}{NV_\mathrm{in}}
        \left(1+ \mfrac{NV_\mathrm{out}}{V_\mathrm{in}}\right)L_p}          &   \\
DC gain
    &   \frac{V_\mathrm{in}}{D_\mathrm{iv}}
        \sqrt{\frac{R_\mathrm{load}f_\mathrm{sw}}{2L_p}}\frac{1}{S_e+S_n}   &   \\
Duty cycle
    &   \frac{V_\mathrm{out}}{V_\mathrm{in}}
        \sqrt{\frac{2L_pf_\mathrm{sw}}{R_\mathrm{load}}}                    &   \\
  \Xhline{1pt}
\end{tabular}
    \end{table}
\end{document}

edit:

as pointed Bernard in his comment, use of \makegapedcell has some issues (specific to this table); first cell in the first column is not left aligned. as cure for this mismatch in this cell i use \makecel[l]{...}.

beside this table looks is improved by with use of \displaystyle, nccmath package (both stolen from Bernard answer), caption package and Xhline from makecell package. also typing of units is shortened.

Answer 3

A solution with cellspace, booktabs, caption for a decent spacing between caption and table, and a few other packages:

\documentclass[a4paper]{article}
\usepackage{amsmath, nccmath}
\usepackage{tabularx}
\usepackage{float, caption, booktabs, cellspace}
\setlength{\cellspacetoplimit}{6pt}
\setlength{\cellspacebottomlimit}{6pt}
\usepackage{siunitx}

\begin{document}

\begin{table}[H]
\caption{Table}
\label{Tab:table}
\centering
\begin{tabular}{l |>{$\displaystyle}Cl<{$}l}
 \toprule
 \midrule 
 First-order pole & \frac{1}{\pi R_\text{load}C_\text{out}} & \SI{100}{\hertz}\\
  Second-order pole & \frac{f_\text{sw}}{\pi}{\frac{1}{\Bigl(D\Bigl(1+\mfrac{V_\text{in}}{NV_\text{out}}\Bigr)\Bigr)^2} }& \SI{100}{\hertz} \\
  Left half-plane zero & \frac{1}{2\pi R_\text{ESR}C_\text{out}} & \SI{100}{\hertz}\\
  Right half-plane zero & \frac{R_\text{load}}{2\pi \mfrac{V_\text{out}}{NV_\text{in}}\Bigl(1+ \mfrac{NV_\text{out}}{V_\text{in}}\Bigr)^{\mathstrut}L_p} & \SI{100}{\hertz}\\
  DC gain & \frac{V_\text{in}}{D_\text{iv}}\sqrt{\frac{R_\text{load}f_\text{sw}}{2L_p}}\frac{1}{S_e+S_n} & \SI{100}{\hertz}\\
  Duty cycle & \frac{V_\text{out}}{V_\text{in}}\sqrt{\frac{2L_pf_\text{sw}}{R_\text{load}}} &\SI{100}{\hertz} \\
  \bottomrule
\end{tabular}
\end{table}

\end{document}