Table 2.

Theoretical resonant peaks calculations for an empty cavity

Modes	Theoretical resonant frequency, fmnl (GHz), $f_{mnl}=\frac{c}{2\mathit{\pi }\sqrt{{\mathit{\mu }}_r{\mathit{\epsilon }}_r}}{\left[{\left(\frac{p_{nm}}{b}\right)}^2+{\left(\frac{l\mathit{\pi }}{d}\right)}^2\right]}^{1/2}$
TM220	6.1829
TM320	7.1699
TM420	8.1277