Two parallel perfectly conducting planes of infinite extent are placed ‘b’ distance apart so that the cut-off frequency of the lowest order TE mode is 15 GHz. If additionally, two perfectly conducting planes are placed 10 mm_apart so as to form a rectangular wave guide as shown in figure. Find out the cutoff frequency of $$TE_{11}$$ mode.

A

30 GHz

B

$$\frac{15}{\sqrt{2}}$$ GHz

C

$${15}{\sqrt{2}}$$ GHz

D

$${10}{\sqrt{2}}$$ GHz