| Because of its better environmental adaptability,observation ability and observation accuracy,the multi-band photoelectric detection systems,which is composed of two or three single-band photodetection systems,play an important role in photoelectric detection technology in the fields of aerospace,astronomical observation,and military reconnaissance.Among them,the visible light / infrared / microwave multi-band photoelectric detection system can integrate the advantages of each single-band photoelectric detection technology,realize all-day and all-weather work,and has the characteristics of anti-stealth and anti-electronic-interference.Considering the volume and weight of the system,the multi-band photoelectric detection system should use optical splitting devices to realize the common aperture collection and separation of multi-band signals.However,the current multi-band common aperture beam splitting method based on multilayer dielectric films has the problem of large microwave loss.For the external observation window of the multi-band photoelectric detection system,the existing materials cannot control the microwave scattering properties while maintaining high visible-infrared transmittance and without changing the substrate surface.Therefore,a new common aperture beam splitting method and a multi-band electromagnetic wave control technology that can take into account high visible-infrared transmittance and flexible control of microwave backscattering properties are urgently needed to improve the performance of multi-band photoelectric detection systems.In view of the above problems,this thesis aims to provide a new common aperture beam splitting method for multi-band photodetection technology and a multi-band electromagnetic wave control method,which is suitable for external observation windows to take into account high visible-infrared transmittance and flexible control of microwave backscattering properties.The proposed method is experimentally verified by preparing functional samples and building test platforms.The main research contents of this thesis are as follows:1.Research on the microwave scattering properties of electromagnetic metamaterial based on metal mesh(EMMM).Aiming at the problem that the effect mechanism of structural parameters on the microwave scattering properties in the existing EMMM complex equivalent refractive index model is unclear,the complex equivalent refractive index model and microwave scattering properties of EMMM are studied.Through quantitative analysis of the reflection and transmission properties of EMMM,the complex equivalent refractive index model was revised,the electrical characteristics analysis method of EMMM was improved,and the microwave scattering properties of EMMM were clarified.The conditions under which high transmittance EMMM can be equivalent to metal film in microwave range were obtained,and the theoretical basis and technical guidance for regulating the microwave backscattering properties of EMMMs were provided.2.The optical diffraction characteristics of EMMM were studied.Aiming at the problem that the existing methods for solving the optical diffraction characteristics of EMMM are not suitable for the situation that the structure is complex and the EMMM is inclined to the optical axis,a optical diffraction characteristics solving method based on coordinate transformation and discrete Fourier transform(OMCDFT),was proposed.Based on OMCDFT,the influence of the introduction of EMMM on the imaging performance of photodetection system was explored,and the comprehensive optical evaluation factor was defined to evaluate the diffraction field of the EMMM.Numerical calculation results show that when the randomness increased from(0,0)to(50%,50%),the comprehensive optical performance of the EMMM diffraction field got a significant improvement.The square EMMM and the cracked EMMM were prepared,and the experimental results showed that the optical performance of the cracked EMMM are better than that of the squared EMMM.The above research provides a theoretical basis and parameter selection guidance for reducing the impact of the introduction of EMMM on the optical performance of multi-band photodetection systems.3.Aiming at the problem of large microwave loss in the multi-band common aperture composite structure that uses the multi-layer dielectric film as beam splitter,a tri-band common aperture beam splitting method with rear-placed feed based on microwave backscattering from a curved EMMM was proposed.The influence of substrate thickness,incident angle and other parameters on the microwave backscattering properties of EMMM was analyzed,and the backscattered microwave from curved substrate EMMM was used to construct a tri-band common aperture composite with the short-wave infrared / long-wave infrared detector in front and the microwave feed behind.By preparing functional samples and building the test platform to test the performance of the structure,the feasibility of the proposed beam splitting method was verified.The experimental results show that the tri-band common aperture composite structure realizes the collection and separation of 10 μm,3 μm and 3.19 mm signals.The system built on the basis of the above composite structure has a gain of 35.72 d B for the 94 GHz microwave,and the microwave loss caused by the EMMM secondary mirror is 0.61 d B compared to the system based on the metal film secondary mirror.4.In order to control the microwave scattering properties without changing the substrate surface of the external observation window of the multi-band photodetector system,a method for regulating the microwave scattering properties of the optical window based on patterned EMMM was proposed.This method patterned the EMMM to construct an optically transparent microwave resonator unit with tunable equivalent impedance in the microwave section.By adjusting the structural parameters of the unit,the microwave reflection phase can be changed,and the microwave scattering properties of the optical window can be controlled under the condition of high visible-infrared transmittance and no change of the substrate surface.Based on this method,the virtual shaping at 19 GHz of the spherical-crowned curved optical window and the radar cross section(RCS)reduction in the frequency band of 19 GHz to 23 GHz of the planar optical window were respectively realized.The designed structure was processed on a plane optical window and the RCS reduction performance and light transmission performance of the sample were tested to verify the feasibility of the proposed method. |
PDF Full Text Request