Vacuum Tube Electronics at Ultra-high Frequencies

T HE art of producing, detecting, and modulating ultra-high-frequency electric oscillations has reached the same state of development which was attained in early work on lower frequency oscillations when experiment had outstripped theory. The experimenters were able to produce oscillations by using vacuum tubes, but were not able to explain why. They were able to make improvements by the long and tedious process of cut and try, but did not have the powerful tools of theoretical analysis at their command. In particular, the advantage of the theoretical attack may be illustrated by the rapid advance in technique which followed the theoretical concept of the internal cathode-plate impedance of three-element vacuum tubes. The work of van der Bijl and Nichols showed that for purposes of circuit analysis this path could be replaced by a fictitious generator of voltage, fj.e0, having an internal impedance whose magnitude is given by the reciprocal of the slope of the static Vv -- Ip characteristic. Development of commercially reliable vacuum tube circuits began forthwith. In a similar, yet less complicated manner, the internal network of two-element tubes may be replaced by an equivalent resistance when relatively low frequencies only are considered. In these concepts where the vacuum tube is replaced by its equiva* Presented in brief summary before U. R. S. I., Washington, D. C., April, 1932. Proc. I. R. £ . , Vol. 21, No. 11, November, 1933.