Topic: Microwave Engineering
The transmit time in the repeller space of a reflex klystron must be $(n+3/4)$ cycles to ensure that,
- A. Electrons are accelerated by the gap voltage on their return
- B. Returning electrons give energy to the gap oscillations
- C. It is equal to the period of the cavity oscillations
- D. The repeller is not damaged by striking electrons
Answer: B. Returning electrons give energy to the gap oscillations
Explanation: In a reflex klystron, for sustained microwave oscillations to occur, the bunched electrons must return to the cavity gap precisely when the RF electric field provides maximum retardation. This ensures the kinetic energy of the electrons is transferred to the RF field. This optimal phase condition requires the transit time in the repeller space to be $n + 3/4$ cycles.