| Terahertz waves combine the characteristics of millimeter waves and infrared lights,and are widely used in the fields of communication,biomedicine,public safety and military.In the future,terahertz systems based on ground or space want the receiver to collect several pixels at the same time,which requires the antenna to provide multi-beam solution.One elegant way to generate multiple beams is placing antenna arrays on the focal plane of reflector.Focal plane feed arrays are required to have high directivity,clean rotational symmetry and wide bandwidth.This paper mainly focuses on the micro-lens element and array design,and application as feed for a single reflector.In the first part of this paper,the working principle of dielectric lens antenna and parabolic reflector antenna is described,the Gaussian beam in quasi-optical theory is introduced too.Combined with application of terahertz stacked receiver circuits,the micro-lens that is based on extended hemispherical lens is used as antenna element.The micro-lens is fed by leaky wave waveguide,which is easy to connect with terahertz receiving circuits using waveguide port.At the same time,silicon micro-machined lens has relatively small aperture,and can easily implement a large-scale array.The lens unit structure design research is specifically carried out,the influence of matching layer on reflection efficient and gain of lens antenna is analyzed,and the Gaussian beam coupling efficiency of micro-lens is also analyzed in this paper.In addition,in order to achieve polarization diversity,transmission and reception multiplexing,dual-polarized micro-lens antenna element is analyzed.This section concludes with a brief introduction to micro-mechanical process and discusses possible processing steps of micro-lens.In the second part of this paper,several kinds of antenna systems that generate multi-beams are introduced first.Here,a single parabolic reflector antenna is selected.By comparing the performance of two types,micro-lens and horn,we finally choose micro-lens to work as focal plane feed array for parabolic reflector.To solve the problem of feed-blocking for front-feeding reflector antenna,optical path design of an off-axis parabolic antenna with micro-lens array feed is carried out.The lens array is arranged in a honeycomb,and seven elements can produce seven independent beams.Gain of each beam is higher than 40 dB,and aperture efficiency of reflector antenna is greater than 50%.To obtain good far-field coverage,each beam can overlap at 3dB half power point by selecting an appropriate unit spacing and focal distance to diameter ratio of paraboloid.The simulation results prove that the design is correct.In the third part of this paper,as terahertz waveguide-based power-division network suffers a large loss,a reflection-type Fourier phase grating is designed to divide the local oscillator signal into several equal sub-beams,so as to achieve space power distution of oscillator signal.A one-dimensional Fourier phase grating structure is optimized using genetic algorithm,and the influence of phase grating period and element number on diffraction pattern is analyzed.The diffraction efficiency of one-dimensional phase grating which produces three sub-beams is 92.5%.Starting from a one-dimensional structure,a two-dimensional grating structure generating nine sub-beams in a 3×3 array form is completed.The simulation results are in good agreement with theoretical calculations. |
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