The solid angle subtended by the sun as viewed from the earth is Ω =$$4 \times 10^{-5}$$ steradian.
A microwave antenna designed to be used for studying the microwave radiation from the
sun has a very narrow beam whose equivalent solid angle is approximately equal to that
subtended by the sun. What is the approximate directivity, D?

A

$$10^{5}$$

B

$$\pi \times 10^{5}$$

C

$$\pi \times 10^{6}$$

D

$$10^{6}$$