The traveling-wave linear antenna

It is shown experimentally that an essentially traveling-wave distribution of current can be produced on a linear antenna by inserting a resistance of suitable magnitude one-quarter wavelength from the end of the antenna. A theory for the resistively-loaded dipole antenna is formulated on the basis that the inserted resistors (one in each arm) can be replaced by equivalent generators and that the resulting triply-driven antenna can be solved by the superposition of singly- and doubly-driven dipoles. Approximately 50 per cent of the power is dissipated in these resistors. With a traveling-wave distribution of current on an antenna available, the properties of this antenna are then investigated and compared with those of the conventional linear antenna. It is found that the input impedance of the traveling-wave antenna remains essentially constant as a function of antenna length, whereas that of the conventional linear antenna varies considerably. It is also shown that the input impedance of the traveling-wave antenna varies only slightly over a 2 to 1 frequency band. The directional properties of the traveling-wave and conventional dipole are compared, and it is shown that a minor lobe does not appear in the radiation pattern of the traveling-wave dipole until it is much longer than the conventional dipole. Also, it is shown that where the directional properties of the conventional dipole are quite sensitive to a change in frequency, those of the traveling-wave dipole are not.