Research On The Technique Of Antenna And Mode Conversion Based On Diffraction Periodic Structure

Antennas and mode converters are two important types of devices in the electromagnetic transmission links.Among them,the antenna mainly realizes the conversion between the guided?or spatial?electromagnetic wave and the spatial electromagnetic wave,and the mode converter is used for the mutual conversion between the guided electromagnetic wave and the spatial electromagnetic wave.Conventional antennas and mode converters mainly control electromagnetic wave transmission by adopting different macroscopic boundary conditions.Therefore,the design methods,steps,and macrostructures used in traditional devices are usually different,which increases the complexity and difficulty of the whole design.Diffraction periodic structure?DPS?is comprised of periodic?or quasi-periodic?elements and has special electromagnetic transmission characteristics.Its macrostructure is usually uniformity and its element can be customizable.Therefore,DPS can easily realize the wavefront conversion,polarization conversion and mode conversion,which has great application potentiality and important research value.Based on the physical mechanism of DPS,this dissertation firstly studies the shortcomings of the current antenna based on DPS and then uses the revised DPS to broaden the bandwidth of the antenna and apply for the monopulse system.Due to the theoretical consistency between antennas and mode converters,a generalized design methodology of mode conversion based on DPS is proposed and studied in this dissertation.The main contents and results of the dissertation are shown as follows:1.Due to the limited bandwidth of reflectarray antennas?usually 3%-5%?,the dissertation deeply analyzes and reveals the factors which affect the bandwidth of reflectarray antennas,and the promising solutions are also summarized.Based on that,two broadband reflectarray antennas that use the log-periodic DPS element and thin membrane DPS element are designed,manufactured,and tested.The experimental results show that the 1-dB gain bandwidths of the proposed reflectarray antennas are greater than 10%and the aperture efficiencies are also larger than 45%.2.The traditional monopulse antenna is usually rather heavy,bulky and high fabrication cost in the millimeter-wave bands.To overcome the above shortcomings,a compact Ka-band Cassegrain monopulse antenna is proposed in this dissertation:the main-and sub-reflectors of the antenna are designed with the DPS,the substrate integrated waveguide?SIW?technology is utilized to design monopulse comparator.The proposed compact monopulse antenna is designed and tested,the experimental results show that the measured gain of the sum beam is 29.4dB,the gain ratios between the sum beam and different beams are about 3dB and 5dB in azimuth and elevation plane,respectively.More importantly,compared with traditional Cassegrain monopulse antenna,the total length of the proposed antenna is shrinked to 67.85%.It is conducive to the compact design of the system and applies the millimeter-wave monopulse antenna into the system with the limited space.3.There require two widely separated frequencies to share the same aperture of monopulse antenna in some targeted applications.A conventional method is to adopt the dual-band monopulse feeds and comparators,whose structures are very complicated,even difficult to be fabricated.A novel Ku/Ka dual-band Cassegrain antenna based on DPS is designed,manufactured and tested.The experimental results show that the measured peak gains are 28.57dB at 35GHz and 24.3dB at 16GHz,respectively.The measured and simulated results indicate the good radiation performance of the antenna in both bands,which is a good candidate for dual-band monopulse antenna.4.Due to the limitations in technology,materials and manufacturing accuracy,the current mode conversion techniques are still difficult to satisfy simultaneously some requirements of systems,such as high performance,compact size,and low cost.To overcome these disadvantages,a novel move conversion technique based on the reflective DPS is studied in theoretically and experimentally,and the polarization conversion based on DPS are derived.Based on the geometrical optics method and vector diffraction theory,the parameter analysis program of the mode conversion technique is compiled,and then the W-band novel mode conversion based on reflective DPS is developed.The experimental results show that the polarization content of the Gaussian-like mode is larger than 96%from 90GHz to 98GHz,which effectively validates the correctness of the proposed mode conversion method based on the reflective DPS.5.In mode conversion based on the reflective DPS,the input-output beams are not aligned on the same axis and the blockage effect has still existed.Therefore,a novel mode-transducing antenna based on the transmissive DPS is proposed.The mode-transducing antenna can simultaneously realize the abilities of mode conversion and wave-front manipulation,and the generalized design methods and steps are also presented in detail.The proposed methodology is discussed in detail,including the mathematic formulations,the design criterion,and procedures.Four examples based on the proposed methodology are also presented.Subsequently,the proposed design methodology is evaluated experimentally through a sample which converts a circular waveguide TM_0,1 mode into a Gaussian-like mode.Furthermore,a measured gain of23.4dB at the center frequency of 10.3GHz is achieved and the measured polarization purity is 98.57%at 10.3GHz.