Research On Quasi-Optical Monopulse Network At THz

The monopulse technology can realize the purpose of beam pointing control and tracking in a single radar pulse,and is the most common tracking system in the microwave frequency band.In the microwave and millimeter-wave band,monopulse antennas are mostly implemented using transmission line structures such as waveguides,microstrip lines and substrate integrated waveguides.However,in the terahertz band,using the above-mentioned transmission line structure is bound to face problems such as large loss and difficult processing.At present,the proposed quasi-optical monopulse antenna feed scheme has preliminarily proved the feasibility of implementation,while the research on monopulse feed network based on quasi-optical technology is still in its infancy,and there are still technical defects in the issues of optical path compactness,bandwidth,sub-flap level and energy transmission efficiency.How to solve the above technical problems and propose a more excellent technical solution is the key to the practicalization of terahertz monopulse antena system,and the solution of these problems will certainly promote the development of China's technology in this field and truly realize its application in radar,communication and electronic countermeasures.The main work and contributions of the thesis are as follows:1.An in-depth study of the terahertz Gaussian feed horn and quasi-beam waist converter is carried out.A high-purity terahertz Gaussian feeder with a gradual change in optical wall radius designed using pattern matching theory is used to complete the primary radiation of the quasi-optical Gaussian beam;The ellipsoidal mirror is used to complete the transformation of the Gaussian beam waist radius 1.25mm-4.5mm and to achieve the feed matching from the Gaussian horn feed source to the quasi-optical and differential network,and the results show that the Gaussian beam distortion during its beam waist transform is small and satisfies the matching input.2.Analysis of the traditional quasi-optical sum-difference comparator narrow-band reasons,an improved broadband wide quasi-optical sum-difference comparator design scheme is proposed.Firstly,the beam splitting principle based on the dielectric sheet and grating is compared and analysed,and a grating with controllable polarisation direction is selected as the 3dB beam splitter of the quasi-optical sum-difference comparator;Then the single-stage quasi-optical sum-difference comparator is optimised by combining a Gaussian feed source and an ellipsoidal mirror,and the results verify the feasibility of its broadband width;Finally,a two-dimensional quasi-optical and differential network is realised by cascading multiple sum-difference comparators to complete the sum and difference beam generation.3.Based on the principle of phase correction,the research on the phase correction technology of double-reflection type sum-difference beam is carried out.By controlling and correcting the four-channel beam,the quality of the sum and difference beams can be effectively improved,and the sub-flap level of its sum beam is reduced from-0.5dB to below-14 dB.The reflection-based phase correction scheme can overcome the problems of large dielectric loss and high processing difficulty in the traditional transmission-based correction scheme,and effectively improve the transmission efficiency of the system.4.The terahertz quasi-optical monopulse network has been physically processed and the related experimental studies have been carried out.Experimental tests were conducted on the radiation and transmission characteristics of the sum beam,azimuthal difference beam and pitch difference beam of the terahertz quasi-optical single-pulse system,and the test results show that the sum beam sub-flap level is below-14 dB,the zero depth is below-20 dB and the transmission loss is below 4dB in the bandwidth range of 330GHz-350 GHz.