The Research On The Quasi-optical Focal Plane Array System In Terahertz Band

Terahertz quasi-optical focusing system is an important part of terahertz focal plane array imaging system.The quality of the quasi-optical focusing system decides the field of view(FOV)and the resolution of the off-axis beam.The performance of the quasi-optical system still needs to be improved.The small FOV and the low resolution are two major problems that causes the noneffective use of large focal plane arrays.In order to enhance the FOV(field of view)and the off-axis resolution,we analyze the relative principle of the quasi-optical system.The near-field gain and resolution is calculated by diffraction integral equation.Firstly,the external parameters of the system are studied in this paper.The resolution is influenced by the distance between the adjacent feed sources,the diameter of the system,the F number and the field angle in image space.According to the research,it is required that the resolution of the off-axis beam should be less than 20% lower than that of near-axis beam.We purpose a method to design the dielectric rod antenna in terahertz band.The Chebyshev multistage waveguide matching transitions method is adopted.The VSWR is less than 1.2 in the 180-220 GHz band.the antenna has the advantage of high gain,low VSWR and low cross mutual crossing.It is regareded as the feed source in the quasi-optical imaging system.A method to design the terahertz lens antenna is purposed in this paper.In this method,the fact that the diffraction and aberration commonly influence the focusing effect of the terahertz lens antenna is considered.To optimize the aberrational spot radius regardless of the diffraction effect is the first step in the new design method.Using the diffraction integral equation to calculate the resolution and the near-field gain is the second step.In this paper,we point out that the terahertz lens antenna is regareded as a small aberration system to be designed regardless of the FOV in order to improve the off-axis resolution.Under the condition the half-FOV less than 10°,the GO method in FEKO is adopted.Under the condition the half-FOV more than 10°,the MLFMM method is used to calculate the near-field gain and resolution of the lens antenna.We design a single lens antenna whose half-FOV is 10° in this method.For the first time,the cooke triplet lens antenna is applied in the terahertz band,and a cooke triplet lens antenna group with a half-angle of FOV(field of view)of 18° and a resolution of less than 5 mm at a distance of 400 mm is designed and developed.The feasibility of the design is verified by the measured results.The experimental error is analyzed in this paper.We first introduce a varifocus lens antenna system in terahertz band.The variable group,compensation group and fixed group are adopted to complete the design.The focal length can be reached 80 mm,100 mm and 120 mm.The resolution and near-field gain are calculated...