Two spacecrafts are separated by 3000 km. Each has a paraboloidal reflector antenna of 0.85 m diameter operating at a frequency of 2 GHz with an aperture efficiency of 64%. If the space crafts A's receiver requires 1pW for a 20 dB signal-to-noise ratio, what transmitter power is required on the spacecraft B to achieve this signal-to-noise ratio?

Consider an array of two non-directional radiators with spacing $$d\,\, = \,\,0.5\,\,\lambda $$. Determine the directions of maximum radiation when the radiators are excited as shown in Fig.. Calculate the phase shift required for turning the direction of the maximum radiation by $${90^ \circ }$$ keeping the separation d unchanged.