| In recent years,with the rise of artificial electromagnetic media,a large number of functional devices based on metamaterials emerged,which provided new ideas and research methods for the dilemma of the relative lack of functional devices in the terahertz band.At present,the rapid development of heterodyne array receivers for radio telescopes has made phase grating beam splitters important application in the sub-millimeter wavelength range.It can transmit a single local oscillator source signal to the superconducting SIS/HEB mixer array receiver through split beam synchronization.Because the characteristic size of the phase grating in the terahertz band is in the sub-micron range,its processing accuracy directly affects the device performance,which brings great challenges to micromachining technology.Based on this,a new type of terahertz four-beam splitter is designed in this paper in combination with phase-coding metamaterial technology.The electromagnetic beam can be separated using only a single-layer metamaterial coding unit.The structure is simple and easy to process.The working frequency range is 0.85-1.45 THz,which can cover two astronomical observation windows of 0.78-0.95 THz and 1.25-1.4THz at the same time.The main contents of the paper are as follows:1.Research on Microwave Band Beam Separation.Based on the 1-bit coding metamaterials,the binary metamaterial structure of multi-beam separation in the microwave band is studied.By adjusting the width w of the metal patch,the reflection phase difference in the wide frequency band of 8.3-11.9 GHz is about 180 °.Using this unit structure,the array of coding sequences is arranged,and two different coding sequences are used to realize the beam separation of single beam,two beams and four beams.The beam separation characteristics of the coding metasurfaces at the incident angles of 30 °,45 ° and 60 ° were preliminarily studied.The results show that the greater the incident angle,the worse the beam separation effect.Finally,the coding metamaterial structure of 2bit and higher bits is discussed and analyzed.2.Research on Terahertz Beam Splitter.The expansion from microwave to terahertz frequency band has realized the design of four-beam splitter with two beam splitting modes in terahertz frequency band.According to the characteristics of the terahertz band,the artificial unit using polyimide film as the basic unit for coding metasurfaces,the reflection phase difference of the two unit structure in the 0.85-1.45 THz band is about 180 °.Numerical simulation studies the reflection characteristics of one-dimensional coding multi-beam and two-dimensional combined coding metasurfaces,and determines the four-beam coding sequences.According to the matching requirements of the array,two beam splitters(1×4 and 2×2)are designed.The frequency adjustable range of the 1×4 array beam splitter is up to 20%,the frequency adjustable range of the 2×2 beam splitter is up to 52%,and the power difference of the four beam signals does not exceed 10%,which realizes the regulation of broadband terahertz beam.In-depth study of the far-field pattern of coding metasurfaces beam separation under different incident angles of 10°,20°,30°,and 40° to determine the optimal oblique incidence angle(less than 30 °)3.Experimental test of terahertz beam splitter.The array structure of the 1 × 4 terahertz beam splitter was expanded by 20 times for experimental testing.Due to the change in the overall coding sequence of the expanded array,the four-beam separation is converted into a five-beam separation.When the incident angle is 20°,the maximum power difference between the two beams increases from 30% of the theoretical simulation to 34%.Compared with the maximum power difference of a single array not exceeding 10%,the uniformity of the power distribution becomes worse.The theoretical simulation and experimental test results after the array expansion are basically the same. |
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