the value of the first term on the right side of equation 2-3 is determined by the wavelength of the RF carrier ,and this term become larger as A decreases In fact looking back at equation 2-1, we notice that P , is proportional to the square of the wavelength. This means that if other factors remain unchanged , doubling the carrier frequency (halving the wavelength) increases PL by 6 dB, which is equivalent to a factor of 4. that seems counterintuitive ; isn't the RF power density on the surface of a sphere with radius d from the transmit antenna independent of frequency?