The production of ultra-short electromagnetic waves by the retarding field method is analyzed.It is found that to generate oscillations of very short wave lengths, it is more effective to reduce the size of the electrodes of the vacuum tube and to design the tubes to oscillate higher orders than to increase the grid potential.
Experiments were made with the Pliotron FP-126 tubes as retarding field oscillators.These tubes generated strong normal and higher order oscillations.The wave length of the normal oscillations differed considerably from the values calculated from the Barkhausen and Scheibe equations.For the higher order oscillations, the observed wave lengths were approximately equal to values calculated according to Potapenko’s formula: n2λ2Eg=C.It was found that the predominating higher order oscillations were generated by the grid coil at its natural frequency.Its wave length agrees with that calculated from its dimensions.
Tubes with plate diameters as small as 0.05 cm. were made.They generated normal as well as higher order oscillations.They were designed so that the grid had a natural wave length of about 1 cm.The grid potentials calculated agree fairly well with the values observed.The energy of oscillations with these tubes was exceedingly small.The wave length of 1 cm. is about the shortest limit that can be obtained by the retarding field method.
