Investigation On Dual-band Complex MILO's Radiation System

In the past few decades,with the development of pulse power technology and high-current electron beam generation technology,the research of high-power microwave technology has made great achievements,and a variety of microwave sources have been developed.Among these microwave sources,the magnetically insulated line oscillator?MILO?has the advantages of high microwave radiation power,stable operation,no external magnetic field,compact structure and so on.It is one of the most promising HPM devices.However,the power efficiency of MILO is not high because some intense electron beams are used to produce an insulating magnetic field to confine another part of the electrons.To solve this problem,the dual-band MILO uses an electron beam that generates an insulating magnetic field to another MILO,which improves the utilization efficiency of the electron beam and greatly improves the overall efficiency of MILO and the output microwave power.Dual-band MILO produces a dual coaxial TEM mode microwave.If it is radiated directly,it will produce a far-field pattern with zero axial direction.The sidelobe level is high and the energy is dispersed,so it can't work effectively on the target.Therefore,it is necessary to use mode converter to convert the mode first,and then radiate it.In this paper,two kinds of dual-band mode converters and two kinds of dual-band mode-transducing antennas are designed to solve the radiation problem of dual-band MILO.The research contents of this paper include the following two aspects:1.Design and simulation of dual-way coaxial plate-insert mode converter and dual band power combiner.The dual-band MILO's radiation system is composed of a dual-way coaxial plate-insert mode converter and a dual-band power combiner.Firstly,a dual-band coaxial plate-insert mode converter is designed.The center frequencies are 1.775 GHz and 3.175 GHz,respectively.The conversion efficiency from the two-way coaxial TEM mode to the two-way TE₁₁ mode are 98.3%and 99.2%respectively.The dual-band power combiner combines the dual TE₁₁ mode microwave into a single microwave.The transmission efficiency at the central frequency are 99.6%and 99.0%respectively,and the high-order modes are suppressed.Finally,a dual-band radiation system is constructed with the horn antenna.The far-field gain of 17.8dB and18.9dB are achieved at the central frequency,respectively.The far-field pattern sidelobe level is low.2.Design of dual band mode conversion antenna.In order to further compact the dual-band radiation system,the dual-band power combiner and the horn antenna are integrated to design the dual-band plate-insert mode conversion antenna and the dual-band cross mode conversion antenna,respectively.The dual-way coaxial plate-insert mode converter and a dual-band conical horn nested by two conical horns can form a dual-band plate-insert mode conversion antenna with center frequencies of 1.717 GHz and 4.167 GHz respectively.The far-field gain of 19.7dB and 20.8 d B are achieved.The overall return loss are 1.90%and 1.36%respectively,and the power capacity are 5.6GW and 1.9GW.The whole system size is 554mm?828mm.Because of the inherent limitations of the working principle,the two-way coaxial plate-insert mode converter can't further reduce the size in the axial direction.The cross mode converter can make full use of radial space to shorten the axial dimension,so a dual-band cross mode conversion antenna is designed.At the center frequency,the far-field gain are 17.9dB and 19.4dB respectively,and the total reflection is 1.25%and1.18%respectively.The power capacity is 5.1GW and 2.0GW respectively.The whole system size is 554mm?564mm.The axial length is reduced by 31.9%compared with the dual band plate type mode conversion antenna.