Metamaterial Absorber Designing And Its Application In Planar TWT

With the rapid development of satellite communication services,the W band will be an expectable candidate for future satellite communication by virtue of tis large bandwidth and lack of interference.Vacuum device amplifier is an important device for satellite communication.Therefore,traveling wave tubes(TWTs)with high frequency,wide band,high gain and small size are the trend to meet requirements of satellite communications.Planar slow wave structures(SWS)which are suitable for microfabrication and integration in TWTs,have overcome some intrinsic defects of the miniaturization process of traditional three-dimensional SWSs,both in structure and performances.Meanwhile,metamaterials have become a research focus because of flexible high absorptivity bands.Metamaterial structures are suitalbe to replace traditional coating attenuators for application in TWTs because of their light weight and thin thickness,which are following the trends of miniaturization and integration of TWTs.Based on the above merits,this thesis is focused on metamaterial absorbers(MA)designing and their application in planar TWTs.MAs called connected rectangular resonators(CRR)are proposed.The CRRs have several absorption peaks when the wave is parallel incident to them,which meets the demands for circuit attenuation in planar TWTs.Absorption peaks of metamaterials on demand bands can be directly designed by acquiring their constitutive parameters.In this thesis,numerical methods to obtain the constitutive parameters were summarized,and the inversion algorithm based on equivalent transmission line theory was introduced.In this way,constitutive parameters are calculated by measuring(simulation)S parameters,including the ones of metamaterials when the wave transmit parallel to them in a plane wave guiding system.Therefore,it is convenience for designing MAs under circumstances of parallel incident waves.CRR absorbers were designed in this thesis.They are composed of a copper block set at the center of a CRR absorber unit which is braced with four connected rectanglular resonators.CRR absorbers can have suitable absorption peaks in particular bands by adjusting the structure parameters and forming composite ones with multiple parameters.Experiments were carried out in the low frequency band and the results were in good agreement with the simulation ones,which showed the correctness of the design and the practicability of the MAs.The application of MAs was studied based on the U-shaped microstrip meander line slow wave structure(MML-SWS)in this thesis.The SWS was modeled and optimized to obtain suitable cold parameters.Moreover,according to the cold parameters,CRR absorbers were designed,which have multi absorption peaks lie in the back wave and harmonic wave bands,to suppress frequency competition in TWT,ensuring that the input signal is fully amplified.Next,with the MAs and coating absorbers loaded onto the SWS respectively,PIC simulations of the whole structures were carried out.The effects of the MAs on performances of the whole structures were analyzed.The simulation results indicated that the half power band of the SWS with MAs rangs from 72 to 84 GHz,3GHz wider than that of the same SWS with traditional attenuators,and the output power gain is 42.5dB at centre frequency,2.85dB bigger than the latter.Finally,we give a conclusion and point out the future work of this thesis.