
446 Microwave Engineering
the cathode passes through a hole in the anode to produce the beam. In some
of the tubes a grid is inserted between the cathode and anode. Itis main-
tained at an adjustable negative potential of few tens of volts with respect
to the cathode. The function of this grid is to control the beam current. The
electron beam travels down the tube to the collector, which is maintained at
a higher potential with respect to the cathode as well as the anode of the elec-
tron gun. The beam remains conned inside the helix, which is also held at
a high potential with respect to the cathode. The helix current is low because
of the beam ...