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An L-band high-power relativistic backward wave oscillator is designed. In the simulation, microwaves centered at 1.6 GHz are generated, with the power of 3.6 GW and the efficiency of 40%. In the preliminary experiment, the pulse duration of the device was only 45 ns, presenting a pulse-shortening phenomenon. Through the 3D particle-in-cell simulation analysis, it was found that the accelerating diode resonances significantly impact the operation of the L-band high power relativistic backward wave oscillator, and the resonance of a TE11 mode in the accelerating diode played the primary role in the pulse shortening. Moreover, we found that choosing the appropriate distance between the cathode baffle and the end of the annular cathode is beneficial to effectively suppress the starting oscillation of the parasitic TE11 mode. In the improved experiment, we changed the distance between the cathode baffle and the end of the annular cathode from previous 5.4 to 4.6 cm. Eventually, when the diode voltage is 650 kV and the diode current is 14 kA, microwaves centered at 1.58 GHz are generated with the power of 3.3 GW, the efficiency of 36%, and the pulse duration above 104 ns. [ABSTRACT FROM AUTHOR]

Compact is a significant research direction of low-frequency high-power microwave devices. In this paper, a compact S-band relativistic backward wave oscillator is presented. The radial dimension of the device is reduced by utilizing the characteristic that the cutoff frequency of the fundamental mode (quasi-TEM mode) of the coaxial Slow-Wave Structure (SWS) is zero. Moreover, a coaxial extraction structure is designed to enhance its resonance characteristics to reduce the number of slow-wave structures. In addition, a reflective structure with the phase difference between inner and outer conductors is used, which replaces the pre-reflection cavity and shortens the axial size of the device. A relativistic backward oscillator with a 2.5-period coaxial slow-wave structure is proposed through theoretical analysis, simulation calculation, and experiment. Its radial dimension is 160 mm (∼1.28λ), and its axial dimension is 320 mm (∼2.56λ). In the experiment, the results show that the output microwave has a center frequency of 2.41 GHz, a power of 1.5 GW, a pulse width of 92 ns, and continuous operation for 20 s at a repetition of 10 Hz. [ABSTRACT FROM AUTHOR]

An improved X-band coaxial transit time oscillator is proposed in this paper. First, the device uses a non-uniform three-gap modulation cavity to improve the clustering of electron beams under a low magnetic field and to increase the depth of the fundamental current modulation. The operating mode of the modulation cavity is the 2π/3 mode of TM01. Second, the dual-cavity extraction structure works in π mode, which can continuously and intensively extract the electron beam energy. The physical characteristics of the device are studied through simulation and experiment. The experimental results indicate that the high power microwave with a frequency of 8.38 GHz and a power of 1.78 GW is generated when the diode voltage is 520 kV and the guiding magnetic field is 0.65 T, yielding a pulse width of 27 ns and an efficiency of 32%. [ABSTRACT FROM AUTHOR]

The energy consumption of high-power microwave sources has attracted much attention in the research field of high-power microwaves. One way of decreasing the energy consumption is to reduce the guiding magnetic field. In this work, a high-efficiency transit-time oscillator is proposed with a low guiding magnetic field. In order to enhance the modulation depth of electrons and increase the conversion efficiency under a low guiding magnetic field, two bunchers are adopted to modulate the electron beam. 2.5D simulation results show that the proposed device generates microwaves with a power of 3.6 GW and a frequency of 4.31 GHz. The power conversion efficiency is 40% and the modulation depth is 125% when the guiding magnetic field is only 0.5 T. In addition, a 3D simulation verifies the results. [ABSTRACT FROM AUTHOR]

Frequency hopping is one of the most significant technological advancements in high power microwave (HPM) sources. Mechanical alteration is generally adopted in traditional cross-band microwave generation, but it has the detriments of a complex adjustment strategy. In this paper, a cross-band frequency hopping Cerenkov microwave generator with an advantageous adjustment strategy, high beam–wave interaction efficiency, and pure output mode is developed. Two-segment slow wave structures (SWSs), which work in C and X-bands separately, are adopted. Additionally, by utilizing the cyclotron resonance absorption phenomenon reasonably, only the relative band microwave is energized under different magnetic fields, which adequately represses mode competition and realizes cross-band frequency hopping. After the electron beam passes through the first SWS section, the bunching center is consistently at the acceleration or deceleration phase of the subsequent SWS section, which a guarantees high beam–wave interaction efficiency in the two bands. The preliminary results of the particle-in-cell (PIC) simulation are as follows: when the guiding magnetic field is 0.7 T, the microwave output comprising only the X-band is obtained, with an efficiency of 42%; when the guiding magnetic field is 1.5 T, the microwave output comprising only the C-band is obtained, with an efficiency of 30%. [ABSTRACT FROM AUTHOR]