| Because of their special electromagnetic characteristics such as narrow beam and large bandwidth,millimeter waves have received increasing attention among researchers over the past ten years.Millimeter-wave technology has potential applications in nondestructive testing,medical diagnosis,high-speed wireless communication,radar imaging,and others.In addition,the demand for different high-performance antennas is increasing.Because the reconfigurable reflectarray antenna shows high gain,beam scanning,beam forming,and other useful properties for the millimeter wave band,it has always been an important research topic.Liquid crystals are very suitable material that can be used as dielectric materials for reconfigurable reflectarray antenna.This is because they show excellent properties for millimeter waves and even higher frequency bands.In this paper,a liquid crystal-based millimeter-wave reflectarray was designed to realize two-dimensional beam scanning through electronic control.The specific research content can be summarized as follows:A W-band phase-shifter,which is based on liquid crystals,was designed.The basic operating principle of the phase-shifter is explained using transmission-line theory.The simulation results show that the device can accomplish a phase shift of 514.5° at 99.8GHz and a phase shift of more than 360° in the frequency range from 94.8 GHz to 102.1GHz.Vacuum sputtering technology was combined with UV lithography and wet etching to produce the double dipole patch structure of the phase-shifter samples.The test results show that a phase shift of more than 360° is achieved under a bias voltage of 5.4 V,and saturation is reached at 30 V,which represents a maximum phase shift of 395.6°.The frequency range for the 360° phase shift is from 90.6 GHz to 94.4 GHz,and the relative bandwidth is 4.11%.The reason for the difference in the test results is also analyzed through a simulation.To achieve two-dimensional beam-scanning,a novel two-dimensional feeding scheme was designed based on a liquid-crystal phase-shifter.Based on static driving technology of liquid-crystal displays,each unit is regarded as an independent "pixel" and fed independently through the feeder and the ground plate.In order to reduce the process complexity,every 3×3 elements are treated as a sub-array,and each sub-array is fed uniformly through a rectangular ring bias line.The feasibility of the scheme was analyzed using a simulation,and the specific size of the feeding line was determined.The experimental results show that,within a ±10 um process error,a phase shift of more than360° can be achieved at a voltage of 15 V,and the average operating frequency of the sample's maximum phase-shift is around 97 GHz.An antenna drive-circuit,based on multiple output voltage supply,was also designed.The DC boost module uses a step-down regulator(LTC3649)and a dual-channel,digitally controlled,variable resistor(VR)device(AD5242)to achieve a maximum output-voltage of 50 V and an adjustment accuracy of 2 m V.It is combined with a full-bridge shaping circuit to convert the DC signal into a square wave signal.The circuit is expanded to 40 voltage outputs to meet the needs of a phase-shifter and for antenna testing.Then,a liquid-crystal-based millimeter-wave two-dimensional beam-scanning reflectarray antenna was designed.The designed array size and diameter is 30×30 and32.7 mm×32.7 mm,respectively.The simulation results show that the maximum gain of the E-plane is 21.2 d Bi at 94 GHz with 9.6% bandwidth.The maximum electric scanning angle is 56°,the electric scanning angle of the H-plane is 43°,and the maximum gain under different angles changes from 20.5 d Bi to 21.2 d Bi.By simultaneously comparing the reflectarray antenna with the two-dimensional feed network,it was found that the performance of the E-plane and H-plane of the antenna degraded slightly.The reasons for the performance decrease were analyzed. |
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