Novel coupling cavities for improving the performance of G-band ladder-type multigap extended interaction klystrons

A pair of ladder-type multigap cavities, namely, wide-coupling cavity and narrow-coupling cavity, were comparatively studied to improve the performance of G-band extended interaction klystrons (EIKs). It is found that the narrow-coupling cavity has higher effective characteristic impedance and stronger electric field distribution which lead to relatively stronger beam-wave interaction strength and obviously better output characteristics. Particle-in-cell (PIC) simulation confirmed this conclusion. Under an working voltage of 16.5 kV, current of 0.3 A, and operating mode of π mode, the narrow-coupling cavity structure has greater output power and wider bandwidth. Specifically, when the ratio of long and short slots is 1.13, 1.21, and 1.26, compared with the wide coupling cavity structure, the output power of the narrow coupling cavity structure is increased by 40, 90, and 50 W, and the bandwidth is significantly increased by 50, 100, and 200 MHz, respectively. Then a maximum output power of 400 W, a gain of 39 dB, a bandwidth of 500 MHz can be achieved with our narrow-coupling cavity structure EIK in G-band. Thus, such structures show potential performance improvement of millimeter-wave and terahertz EIK.