Right option is (b) 1.17m^2
The best explanation: The directivity of half-wave dipole is 1.64
The effective aperture of half-wave dipole is \(A_e=1.64\frac{\lambda^2}{4\pi}\)
\(\lambda=\frac{c}{f}=\frac{3×10^8}{100×10^6}=3m\)
\(A_e=1.64 \frac{\lambda^2}{4\pi} = 1.64 \frac{3^2}{4\pi}\)=1.17m^2.