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For the stability of any amplifier, it is desirable to suppress as many unnecessary circuit modes as possible. In this paper, the dispersion diagram for the Ka-band Cusp gun second-harmonic TE21 gyro-travelling-wave-tubes (TWT) amplifier is given. The dispersion diagram shows the grazing intersection of the second-harmonic cyclotron resonance and the TE21 mode of the circular waveguide circuit which represents the mode of operation. The diagram also shows other potential oscillating modes. The mode selective circuit is employed in the device to destroy the odd-order TEm1 modes is also given.
Date of Conference: 28-30 May 2003