code class$=$"asciimath"$>$P$\mathrm{.}9-12$ The instantaneous expression for E$\_($z$)$ of a TM mode in an air$-$filled $5\mathrm{.}0($cm$)\backslash$times $2\mathrm{.}5($cm$)$ rectangular waveguide is E$\_($z$)=$E$\_(0)$sin$(100\backslash$pi x$)$sin$(100\backslash$pi y$)$cos$(2\backslash$pi $10^(10)$t$-\backslash$beta z$),(($V$)/($m$)).$ af$\_($c$),\backslash$beta $,$Z$\_($TM$),$ and $\backslash$lambda $\_($q$).$