An experimental study of the disk-loaded folded monopole

Data is presented to show the reduction in size and increase in radiation resistance and bandwidth of the disk-loaded folded monopole as compared with a disk-loaded monopole of the same electrical length. The ratio of diameters of the folded part to the diameter of the driven part was varied for one series of impedance measurements and the axial spacing between the driven part and folded part was varied for another series. The resonant radiation resistance and resonant length may be varied almost independently. The radiation resistance depends upon the ratio of diameter of the folded part to the diameter of the driven part, and the resonant length depends upon axial spacing. The radiation resistance multiplication factor relative to a disk-loaded monopole of the same electrical length is approximately the same as the multiplication factor of a folded dipole relative to a dipole. The disk-loaded folded monopole has a greater bandwidth than an unloaded monopole of the same wavelength-to-diameter ratio. Where the effective diameter1 of the folded antenna is √2DdS, its radiation pattern is essentially that of an unloaded monopole.