velocity modulation concept

                                  VELOCITY MODULATION
Velocity modulation is defined as that variation in the velocity of a beam of electrons caused
by the alternate speeding up and slowing down of the electrons in the beam. This variation is
usually caused by a voltage signal applied between the grids through which the beam must pass.
The direction of the electron beam and the static electrical field goes to each other parallelly
(linearly) into linear beam tubes. Against this the fields influencing the electron beam stand
vertically by the electron beam at the cross field tubes.
The following table compares with characteristic quantities of the velocity-modulated tubes used
in radar technology. Although the planar tube isn't a velocity-modulated tube, it was included into
this table for comparison purposes. The grid of the density controlled tube (like the planar triode)
regulates the number of electrons on the path to the anode. The different speeds of the electrons
by additional accelerating due the microwave voltage are annoying in this case. The cut-off

frequency of density controlled tubes is relatively low. Higher frequencies need the use of
velocity-modulated tubes, as shown in the table:
 
  Table:.

                           klystron       travelling      magnetron         carcinotron               EIK/EIO
                                              wave tube
freq.               up to 35Ghz     up to 95 Ghz   up to  95Ghz    up to 5Ghz              up to 230Ghz      

bandwidth       2-4%             10-20%          any mega hz    2Ghz                     0.5-1%

power i/o        50MW          1MW               10MW            1MW                     1kW

amplification    60db            50db                  -                   -                               40-50db