The directivity of an antenna array can be increased by adding more antenna elements, as a larger number of elements

For an antenna radiating in free space, the electric field at a distance of 1 km is found to be 12 m V/m. Given that intrinsic impedance of the free space is 120$$\pi \Omega $$, the magnitude of average power density due to this antenna at a ditance of 2 km from the antenna (in n W/$${m^2}$$) is

Match column A with column B.

Column
1. Point electromagnetic source
2. Dish antenna
3. Yagi-Uda antenna

Column
P. Highly directional
Q. End fire
R. Isotropic

The radiation pattern of an antenna in spherical co-ordinates is given by $$$F\,(\theta )\, = {\cos ^4}\,\theta \,\,\,;\,\,0\,\, \le \,\,\theta \,\, \le \,\,\pi /2$$$ The directivity of the antenna is