Study Of High Order Mode Sheet Beam Extended Interaction Oscillator At Ka-band

Millimeter wave technology is widely applied in millimeter wave radar,millimeter wave imaging,electronic countermeasures and detection,etc.Millimeter wave source can be divided into two categories:vacuum electronic device and solid state semiconductor device.Vacuum electronic device mainly includes gyrotron,klystron,traveling wave tube（TWT）,magnetron,etc.As the electric vacuum device extends to higher frequency,the research will face new challenges in terms of high power,high frequency and miniaturization.Extended Interaction Oscillator（EIO）was proposed as a millimeter radiation source in the 1950s.It is an important high power source in the millimeter wave and even terahertz band.As a novel millimeter wave device,the sheet-beam extended interaction oscillator（SBEIO）has outstanding performance in high power,high efficiency and miniaturization.SBEIO combines the advantages of the extended interaction resonator and the sheet-beam device.The sheet-beam helps to improve the beam-wave interaction,and is conducive to the miniaturization of the device.The extended interaction device adopts a distributed structure,which has a large interaction area and R/Q value.In conclusion,SBEIO has important research value in high power and miniaturization.In this paper,a sheet-beam extended interaction oscillator with five interaction gaps working at Ka-band is designed.Firstly,by analyzing the principle of EIO,the structural parameters of SBEIO working at Ka-band is designed.The electromagnetic simulation software CST is used for resonate simulation of SBEIO operating at TM₁₁-2πmode,and the operating frequency is 35.15 GHz.Based on the SBEIO operating at TM₁₁-2πmode,the high-order mode cavity is designed.The resonance frequency of the cavity and the uniformity of the electric field distribution are analyzed.And the SBEIO operating at TM₃₁-2πmode has the same resonance frequency with the cavity operating at the fundamental mode.In order to prove that the high order mode SBEIO has more advantages than the traditional EIO,the cold cavity analysis results of the TM₃₁-2πmode and the TM₁₁-2πmode in the same cavity are compared.The results showed that the operating frequency of the high order mode(TM₃₁)is much larger than the fundamental mode in the same size,and the electric field amplitude corresponding to TM₃₁ mode is also higher.Accordingly,the EIO operating at high-order mode is significant to breaking through the frequency limit and supporting a larger cavity.Then the results of two SBEIO operating at the same frequency are compared.The SBEIO operating at TM₃₁-2πmode has higher the unloaded quality factor（Q₀）,which verity the high order mode EIO has great meaning in improving power capacity.Finally,in order to verify the feasibility of the TM₃₁ mode scheme,the improved high order mode SBEIO is simulated by the PIC solver of CST-PS.The simulation model has 5 interaction gaps,the size of the electron beam channel is 12mm×1.2mm,the size of the sheet beam is 8mm×1mm,and a 0.25T guided magnetic field is used for focusing.Under the condition that the beem voltage is 29kV and beem current is 6A,the output power is 38.01kW,and the frequency of the 2πoperating point is 35.25GHz.This paper reserach the advantages of SBEIO operating at TM₃₁-2πmode,and provide an important reference for the study of high-power,high-frequency millimeter wave radiation sources.