ABSTRACT
The potential of traveling-wave or distributed amplication for obtaining power gains over very wide frequency bands was recognized in the mid-1930s when it was found that the gain-bandwidth performance is greatly affected by the capacitance and transconductance of the conventional vacuum tube [1]. However, the rst theoretical analysis and its practical verication were obtained for broadband vacuum-tube ampliers more than a decade later [2,3]. The basic concept was based on the idea of combining the interelectrode capacitances of the amplifying vacuum tubes with series wire inductors to form two lumped-element articial transmission lines coupled by the tube transconductances. As a result, the distributed amplier overcomes the difculty of a conventional ampli-er, whose frequency limit is determined by the factor that is proportional to the ratio of the transconductance of the tube to the square root of the product of its input grid-cathode and output anode-cathode capacitances, by paralleling the tubes in a special way, in which the capacitances of the tubes can be separated while the transconductances may be added almost without limit and not affect the input and the output of the device. Since the grid-cathode and anode-cathode capacitances form part of low-pass lters that can be made to have a substantially uniform response up to lter cutoff frequencies, whose value can be conveniently set within a wide range by suitable choice of the values of the external inductor coils, it became possible to provide amplication over much wider bandwidths than was achievable with conventional ampliers.
