Measurement of losses in multiconductor cable transmitting in the dipole-mode

A series of attenuation measurements on various kinds of multiconductor cable sample have been made in the frequency range 300 MHz to 3 GHz to investigate dipole-mode propagation. Two different approaches have been used. In the first, short lengths of cable, about 1m long, were resonated between two end-plates to determine the Q-factor, from which the attenuation was calculated after elimination of losses in the endplates, and in the coupling slots. In the other approach sample lengths of about 50m of cable were investigated by transmission measurements. Here high-efficiency launching devices were required instead of the weak-coupling probes used in the resonator measurements. For the transmission work a new type of launching device was examined, comprising an 8-way coaxial power divider whose output supplied the separate wires of the dipole-mode cable with currents of appropriate amplitude and phase. In the series of loss measurements, all the attenuation figures observed were in quite good agreement with theory. In the course of the work, it was shown by calculation that dipole-mode cable exhibited minimum values of attenuation which could be considerably smaller in magnitude than those of `corresponding TEM¿¿ coaxial cable, for which the outer remains unchanged while the inner comprised a copper rod of the same diameter as the outside diameter of the mjultiwire structure exployed in dipole-mode transmission.