Wideband power amplifiers - 1948 to the present day

A team led by William R. Hewlett presented a new principle and circuit methodology for wideband amplifier design in 1948. The technology of the day was vacuum electron tubes. It was shown that by an appropriate distribution of tubes along artificial transmission lines it was possible to obtain amplification over much greater bandwidths than would be possible with reactively matched circuits. The concept of maximum gain-bandwidth product limitations introduced by Hendrik W. Bode and others did not apply to the distributed amplifier. The high frequency limit of the distributed amplifier was determined by the cutoff of the artificial transmission lines and the frequency response of the amplifying device. As technology changed, transistors and MMICs were introduced and new benchmarks were established. The theory of wideband design morphed to include circuit techniques such as capacitive gate coupling and non-uniformity. This paper will examine distributed power amplifiers that set new benchmarks in power, bandwidth, and efficiency implemented in technologies from vacuum electron devices to GaN HEMT MMICs.