Study of a Dual-Mode Multibeam Interaction Circuit With Coaxial Structure for Ka-Band High-Power EIK

A dual-mode five-beam extended interaction klystron (EIK) with a coaxial structure is proposed that can stably obtain high output power. The TM
$_{\textit {mn}}$
mode with uniform angular distribution in the coaxial cavity can effectively interact with beams located at the peaks of the axial electric field. However, when the center radius of the cavity is enlarged to meet the cathode area requirements of high-power devices at high frequency, the interval between adjacent modes will rapidly decrease. Especially when combined with a multigap structure, the circuit will suffer from mode competition. This article describes a study of the beam–wave interaction characteristics of the multigap coaxial cavity driven by multiple beams, contributing to a stable circuit design. The results show that the appropriate mode selection for each cavity can increase the stability and efficiency of this device. A
Ka
-band EIK with four cavities has been designed to show the circuit capability. The output cavity operates in the TM
₅₁
-
$2\pi $
mode, but the other cavities operate in the TM
₀₁
-
$2\pi $
mode. The 3-D particle-in-cell (PIC) simulation predicts a power of 211.6 kW at 35.19 GHz with the beam parameters of a voltage of 42 kV and a total current of 15 A (3 A
$\times5$
). The corresponding gain, electronic efficiency, and 3-dB bandwidth are 53.26 dB, 33.5%, and 50 MHz.