A compact S-band relativistic backward wave oscillator with a 2.5-period slow-wave structure

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.