| Passive millimeter wave imaging radar detection technology can aim at stealth and non stealth targets in the air and detect them in the whole airspace.Its principle is to use millimeter wave radiometer to passively receive the brightness temperature radiated from the target and background,and detect the target according to the temperature difference.Millimeter wave radiation of the target is inherent and cannot be hidden.The better the stealth characteristics are,the easier it is to be found.Passive millimeter wave radar does not emit electromagnetic waves,and has good concealment,small size,light weight,and all-weather working ability.Focal plane array antenna system is one of the key components of passive millimeter wave radar,which uses the lateral defocusing characteristics of reflector focusing antenna.Based on the background of air target detection,the technology of passive millimeter wave passive radar front-end antenna is studied,and the quasi optical system of radar front-end focal plane array antenna is designed.In this paper,based on the theory of passive millimeter wave radiation detection,the relationship between temperature and power is analyzed theoretically,and the antenna efficiency is emphatically analyzed.The overall beam efficiency is the result of the joint influence of reflector antenna and feed.The edge illumination level plays a major role in the efficiency when the focal diameter ratio is large.Selecting the edge illumination level as-11 dB,the ideal aperture efficiency can be achieved.According to the design principle of quasi optical path,considering the field of view,working frequency,spatial resolution and other factors,a quasi optical system is designed,which can focus the electromagnetic wave radiated by the target to be detected on the receiving radiometer.According to the requirements of edge illumination level,the 35 GHz horn antenna and 94 GHz horn antenna are designed.Meanwhile,according to the layout requirements of one-dimensional linear array,the antenna array is designed according to the principle of lateral focus.The focusing performance of the reflector is simulated and analyzed.The focusing characteristics of the paraboloid and the offset paraboloid are studied and analyzed.At the same time,the influence of the bracket of the two kinds of reflector is simulated and analyzed.Considering the engineering practice,the offset paraboloid is determined as the reflector of the focal plane array antenna.In order to improve the defocusing performance of the biased paraboloid,Zernike polynomials are introduced to design the free-form surface.By changing the coefficients of Zernike polynomials,a Zernike polynomials free-form surface is designed,which improves the focal spot distortion of the reflector antenna beam and reduces the gain,The problem of beam broadening. |
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