Fig. 1. Schematic of the new nested device based on two relativistic klystron oscillator (RKOs)

Fig. 2. Normalized electric field distribution and electron conductivity

Fig. 3. Resonance characteristics of the modulation cavity

Fig. 4. Leakage power from outer and inner RKO

Fig. 5. Output power of the outer RKO and the spectra of the generated microwave

Fig. 6. Output power of the inner RKO and the spectrum of the generated microwave

Fig. 7. Operation frequency for the two RKOs

Fig. 8. Operation phase for the two RKOs

Fig. 9. Output power varies with the operating parameters

Fig. 10. Profile of the power combiner

Fig. 11. Transmission coefficient and relative phase of the power combiner

Fig. 12. Schematic of the whole system

Fig. 13. Output power of the system and the spectra of the generated microwave