GATE Electronics and Communications (EC) 2015 Shift 2 Solved Paper

An air – filled rectangular waveguide of internal dimensions $\mathit{a}\mathit{c}\mathit{m}\times \mathit{b}\mathit{c}\mathit{m}\left(\mathit{a}>\mathit{b}\right)$ has a cutoff frequency of $6\mathit{G}\mathit{H}\mathit{z}$ for the dominant $\mathit{T}{\mathit{E}}_{10}$ mode. For the same waveguide, if the frequency of the $\mathit{T}{\mathit{M}}_{11}$ mode is $15\mathit{G}\mathit{H}\mathit{z}$, the cutoff frequency of the $\mathit{T}{\mathit{E}}_{01}$ mode in GHz  is_________.