A microwave transmission operating at 15 GHz has transmitting and receiver antennas separated by 100 m uses two identical antennas with radiation intensity \(U\left( {\theta ,\phi } \right) = 10{\cos ^8}\theta \;W/{m^2}\)  (θ is angle along z-axis). Assuming the antennas are lossless, if the power transmitted is 3 kW the power at receiver is ______ (in mW)