History of the Microwave-Tube Art

Many ideas important to microwave tubes, including the interaction of electrons with waves, occurred very early. An orderly understanding came much later. The RF diode equation (1933-1944) gave quantitative results concerning microwave tubes rather than insight. The klystron and the concept of velocity modulation and phase focusing (1938-1939) led to a clear picture of important phenomena as well as to powerful microwave devices. Insight and performance were extended by the traveling-wave tube and the wave analysis of its behavior (1946-1947). This led to explorations in terms of the behavior of coupled circuits (1951, 1954) and negative-energy waves (1951). Backward-wave oscillators provided further understanding and a new tool (1952-1953). This background of understanding which grew up concerning microwave tubes led to analysis of and improvement in noise behavior (1950-1959). Finally, the invention of the parametric amplifier led to very-low-noise microwave tubes (1959-1961). Crossed-field tubes have always been highly effective but difficult to analyze and design. Nonetheless, useful high-power amplifiers and oscillators have been built.