Improved bandwidth and efficiency of short antennas by the use of radials

Design equations are given for the radius of a disc radial, in terms of the antenna diameter and antenna length, and it is shown how the size of spoked radials is simply related to this disc radius. Radials increase the radiation resistance of a short antenna and can resonate it at the frequency of interest. These two improvements together considerably increase the efficiency of the antenna system by reducing the losses in the matching circuits. Further increases in input resistance may be possible by feeding the antenna within one of its radial spokes. The bandwidth is considerably increased over that of the same antenna without radials, and for short antennas is proportional to the radius of the radial. However, the bandwidth is always less than that of a half wave dipole of the same antenna diameter. The radiation pattern of a short antenna is essentially the same as a half wave dipole no matter how short it is, and this is unaffected by the addition of radials.