Parametric Manipulation Of Electromagnetic Characteristics Of Novel Sub-Wavelength Periodic Structures

With the rapid development of radar detection technology,the strategic advantages of information-based battlefield have increasingly relied on the excellent stealth performance of flight weapons and the complex electromagnetic environment compatibility of electronic equipment.As one of the most crucial cores to ensure the strategic strike and penetration in modern warfare,the research on the manipulation of electromagnetic characteristics based on the periodic structure has drawn great worldwide attention.Meanwhile,due to the complicated structures of the current electromagnetic control technology,the design flow lacks an explicit guidance,which brings great challenges to effective engineering applications.Thus,how to meet the miniaturized periodic structures with practical and flexible control of frequency/polarization features is still a major scientific and engineering problem to be solved.In this dissertation,based on the limitation of the current research on the electromagnetic manipulation of the periodic structures,the parametric synthesis procedures of the electromagnetic-field-coupled(J-type)miniaturized-element frequency selective surface(MEFSS)and the inductively-coupled(K-type)MEFSS are systematically studied,respectively.Compared to the J-type MEFSS coupled with the electromagnetic field,the superiority of the K-type MEFSS is demonstrated.On this basis,the main line of the study is unfolded based on their equivalent circuit models of the proposed periodic structures.A dual-band inductively-coupled MEFSS with higher-order bandpass response and a hybrid third-order bandpass MEFSS with high selectivity are designed in details,and their comprehensively parametric design flow and systematic synthesis procedure are developed as well.The design approaches of the proposed MEFSSs and the effectiveness of corresponding synthesis processes are all verified using the theoretical simulations and experimental characterizations.At the same time,a reflective polarization converter surface with sub-wavelength unit cell and ultra-wideband,high polarization conversion ratio is deeply studied.All of these designed periodic structures show the stable frequency responses in a wide-angle domain,and the proposed approaches provide a series of new ideas for the manipulation of electromagnetic characteristics of sub-wavelength periodic structures,and have a significantly theoretical guidance and engineering application value.The main contributions and innovations of this dissertation are as follows1.The parametric synthesis procedures of two resonator-coupled MEFSS are studied.Using the theoretical model of the coupled filters applied with the equivalent circuit analysis method,the corresponding synthesis processes for the J-type MEFSS and K-type MEFSS are established,respectively.Using these two parametric synthesis procedures,MEFSSs with different frequency responses were designed,which validate the effectiveness of two procedures very well.In addition,compared to J-type MEFSS,the K-type MEFSS consisting of inductively-coupled transmission-line resonators shows superiorities with a shorter design cycle,a stronger structural rigidity,a lower processing complexity,and an insensitiveness to the relative misalignment between adjacent metal layers,which provides a new technical approach for MEFSS design.2.A dual-band MEFSS with Nth-order bandpass response is proposed.The design enables dual-band MEFSS architecture with any center frequency,fractional bandwidth,and response type and meets the design requirements for independent control of the frequencies of operation of each band.Using the equivalent circuit model of this dual-band MEFSS,a parametric synthesis procedure is developed that can be used to synthesize the dual-band MEFSS from its system-level performance indicators.Additionally,the performance is verified by a design example of a dual-band second-order band-pass MEFSS with center frequencies of 16.5 GHz and 31 GHz.The theoretical simulation and experimental results prove the feasibility of the design idea and the validity of the proposed synthesis procedure.Meanwhile,the proposed structure shows a stable frequency response with respect to the angle of incidence up to ±45° for both TE and TM polarizations of incidence.This design method realizes the design flow from theory to practical engineering,which solves the shortcoming of complicated flow in the traditional methods,and provides a useful guidance for practical applications and a new direction for the research on designing dual-band FSS.3.A low-profile,highly selective,third-order bandpass MEFSS with hybrid resonator is proposed.Without increasing the number of transmission line resonators,the proposed design not only adds a transmission pole to the transfer function of MEFSS,but also cleverly introduces a transmission zero.Thus,a higher-order bandpass filter response with a low profile structure is realized,the selectivity of the frequency response is also greatly improved.Using the equivalent circuit model of the proposed third-order MEFSS,a parametric synthesis procedure that allows for designing the FSS from its desired system level performance indicators is developed,which can achieve a filter with any third-order bandpass response.The validity of this design concept and synthesis procedure is fully verified by presenting a design example of a hybrid third-order bandpass MEFSS with a center frequency of 8.5 GHz.The design results show that this type of MEFSS has a 30.3%reduction in the overall thickness compared to the K-type MEFSS,and its out-of-band transmission coefficient is as small as-101.7 dB.Moreover,the proposed structure has an extremely low sensitivity to the incident angle in the range of ±45°.Meanwhile,the proposed design method can be effectively applied to the MEFSS design with low-profile,high selectivity,higher-order bandpass response,which can greatly expand the application of the proposed approach.4.A reflective polarization converter surface(PCS)with sub-wavelength unit cells and ultra-wideband characteristics is proposed.From the perspective of physical mechanism and its equivalent circuity the polarization conversion principle of the proposed structure is qualitatively analyzed.The rationality of mechanism analysis is then well verified by the full-wave simulation.Also,the polarization rotation sensitivity with respect to the operation bandwidth is deeply studied in terms of geometrical parameters of the proposed architecture,And the full-wave numerical simulation shows that in an ultra-Wideband operation range of 5.2 GHz-12.7 GHz,the proposed PCS could rotate the polarization of the reflected wave with respect to that of incident wave by 90°,where its polarization conversion ratio(PCR)is always greater than 90%.Meanwhile,the proposed structure can maintain broadband,high PCR and stable polarization rotation response in a wide-angle domain of±45°.Compared with the existing studies,the proposed polarization converter surface has the advantages of simple structure,small size:,and low processing cost,and it also has a wider operational bandwidth and a more stable PCR p'erformance.These advantages allow for the proposed design more easily integrated into the relevant engineering applications.