Radio gain

The radio gain or power transfer between two short electric dipole antennas in free space is derived. When the antennas are above and parallel to a perfectly conducting plane, the radio gain approaches a constant as the antennas approach the ground. As the antennas are raised the radio gain is approximately proportional to the square of the product of the antenna heights. At greater heights the interference between the direct and reflected wave causes the radio gain to oscillate. At low antenna heights on vertical polarization the radio gain is the same as in free space. As the antennas are raised it increases and oscillates about four times its free space value. At greater heights the oscillation of the radio gain has greater amplitude. The maxima on vertical polarization occur at the same height as the minima on horizontal polarization and vice versa. For antennas above an imperfectly conducting plane, the radio gain decreases indefinitely as the antennas are lowered and depends upon the polarization and whether the antennas are electric or magnetic dipoles. Numerical values are given for . Vertical loop antennas give greater radio gain for ground wave propagation.