A square waveguide carries $$TE_{11}$$ mode whose axial magnetic field is given by $$H_{Z}=H_{o} \times \cos (\frac{\pi x}{\sqrt{8}}) \times \cos (\frac{\pi y}{\sqrt{8}})$$ A/m where waveguide dimensions are in cm. What is the cut-off frequency of the mode?

A

5.5 GHz

B

6.5 GHz

C

7.5 GHz

D

8.5 GHz