Metamaterial-based Sheet Beam Microwave Oscillator

Microwave oscillators are widely used in military and scientific research. With the emergence of new materials, new electromagnetic structures and new electromagnetic simulation softwares, the performance and reliability of microwave oscillators continue to reach new heights. Microwave oscillators are required to have high power and high efficiency in some important military and civilian systems, and sheet beam backward wave oscillators (BWO) are designed to meet this need. Metamaterials microwave oscillators have a great prospect, with the advantages such as miniaturization, high output power and high electron efficiency. Recently, a new type of metamaterial composed of planar complementary electric split ring resonators (CeSRRs) has been proposed, which has potential applications in microwave oscillators. In this paper, the square waveguide loaded by the CeSRRs is used as the slow-wave structure (SWS) in BWO which may contribute to the miniaturization of the device. At the same time, the sheet beam is used to improve the output power and efficiency of the device.This paper reports the research of an S-band sheet beam BWO using metamaterials.The new coupling structure for the BWO is designed and beam-wave interaction is studied. The main contents of this paper include the following aspects:1.The basic principle of the BWO and the SWS are studied. The waveguide loaded by CeSRRs operates below the cutoff frequency and the waveguide size is only 1/7 of the free-space wavelength at the operating frequency, which achieve the miniaturization of the device.2.We design two coupling structures for this microwave oscillator: coaxial coupling structure and the waveguide coupling structure. The transmission characteristics of the SWS under the two kinds of structures are studied. In the case of waveguide coupling, the transmission characteristics of the system are compared under two conditions: the standard waveguide coupling structure and the narrow waveguide coupling.3.When we use coaxial coupling structure in the microwave oscillator, the interaction between single sheet beam and metamaterial SWS is studied, and the interaction between double sheet beams and metamaterial SWS is studied.Particle-in-cell (PIC) simulations for this BWO using the computer simulation technology (CST) shows that the peak output power is 5 MW and the efficiency is 13.2%when the working voltage is 180 kV, the magnetic field is 1.3 T and the single sheet beam electron current is 210 A. When we use the double sheet beam electrons current of 210 A, we get the peak output power of 4.7 MW, the efficiency of 12.4%.4. When the microwave oscillator use waveguide coupling structure, the interaction between single sheet beam and metamaterial SWS is studied, and the interaction between double sheet beams and metamaterial SWS is studied. CST software simulation for this BWO shows that the peak output power is 8 MW and the efficiency is 20%when the working voltage is 200 kV, the magnetic field is 2 T and the single sheet beam electron current is 200 A. the peak output power is 9 MW and the efficiency is 22.5%when we use the double sheet beams.