Measurement of impedance transformation on practical dipoles

The measured input impedance of a practical dipole antenna is shown to be related to the theoretical input impedance of a delta-gap cylindrical dipole through a bilinear transformation. In order to determine the three complex constants which specify the transformation, the impedance of a dipole in front of a ground plane is measured and compared with the theoretical impedance. The comparison is performed by a curve-fitting procedure for bilinear transformation on a complex plane. The same measurement yields also the receiving efficiency of the antenna and its feeding network. Experiments show that the input impedance of a practical folded dipole, incorporating a balun transformer, may be predicted with an accuracy of better than four percent.