Study of r-f cathode unbalance in zero-order interdigital magnetrons

The loading effect of the cathode and its support structure are analyzed insofar as they affect the circuit impedance. It is found that a series resonance occurs, heavily loading the anode cavity. Cold test measurements are presented which support this finding. The effect of the unbalance of the cathode potential with respect to the anode r-f potentials is analyzed in the space-charge-free case. Using rather general principles it is shown that the amplitude of the Hartree fundamental is unchanged, but that even Hartree harmonic components of the space field are introduced. The latter are (usually) unimportant since their phase velocities are quite different from that of the fundamental. Operating tests results are presented for a magnetron in which cathode potential was varied over the complete range of balance and unbalance. The only effect noticeable was that caused by impedance loading. Because of the lack of variation in electronic efficiency as cathode potential passed through balance, it is concluded that the unimportance of cathode potential unbalance is here demonstrated.