Q$3(20$P$)$: Assume that a walkie$-$talkie is operating at $446$ MHz $,$ and half$-$wave transmitting dipole antenna is going to be installed at the roof top of the police station. Backside of the tall building is covered by metallic plate. Calculate the directivity of proposed antenna in case where $d=25mm,d=100mm,d=200mm,d=400mm,d=1000mm.$ Hint: Assume that a distance of $\frac{}{10}$ is close enough to form unified body.