Distributed amplifiers: some new methods for controlling gain/frequency and transient responses of amplifiers having moderate bandwidths

The limitation (first shown by Wheeler) of the gain-bandwidth product of an amplifier stage can be overcome, as earlier proposed by Percival, by connecting valves so that their input and output capacitances form the shunt elements of low-pass ladder networks. The resulting distributed amplifier does not give constant gain or delay within the pass band if simple networks are used. Improved constancy of gain can be obtained without using dissipative networks, however, or relying on the input conductance of the valves. Dissipative networks can also give improved phase/frequency response, and a gain/frequency response approaching Gaussian within the useful portion of the pass band. Amplifiers using dissipative networks are reasonably simple to construct, but suffer from the limitation that the gain-bandwidth product increases only as the square root of the number of valves in the stage, making amplifiers with more than about five valves of limited advantage. The practical realization of inductors reasonably free from transmission-line effects at high frequencies has presented difficulties, which were solved by the use of air-cored solenoids of very small physical size.