The space present between the anode and cathode is called as Interaction space. The
electric field is present radially while the magnetic field is present axially in the cavity
magnetron. This magnetic field is produced by a permanent magnet, which is placed such
that the magnetic lines are parallel to cathode and perpendicular to the electric field
present between the anode and the cathode.
The following figures show the constructional details of a cavity magnetron and the
magnetic lines of flux present, axially.
This Cavity Magnetron has 8 cavities tightly coupled to each other. An N-cavity magnetron
has N modes of operations. These operations depend upon the frequency and the phase
of oscillations. The total phase shift around the ring of this cavity resonators should be
2nπ where n is an integer.
If ! represents the relative phase change of the AC electric field across adjacent cavities,
Where n = 0, ±1, ±2, ± ( ( 1), ±
Which means that N/2 mode of resonance can exist if N is an even number.
""$ = " ""*+,$""
This mode of resonance is called as π-mode.
"""$ = 0""*+,$"""
This is called as the Zero mode, because there will be no RF electric field between the
anode and the cathode. This is also called as Fringing Field and this mode is not used in