An L-band radar \((1500 \mathrm{MHz})\) uses an antenna whose gain is \(G=30 \mathrm{~dB}\). Compute the aperture size. If the radar duty cycle is \(d_{t}=0.2\) and the average power is \(25 \mathrm{~kW}\), compute the power density at range \(R=50 \mathrm{~km}\).