Research On Broadband Reconfigurable Technology Of Electric Bias Frequency Selective Surface

As a new type of anisotropic tunable medium,the dielectric constant of the electrically biased liquid crystal material can change with the change of the external bias voltage,so that the application scenarios of the liquid crystal material are gradually expanded from the optical field to the microwave and millimeter wave field.Liquid crystal materials have the advantages of linearly adjustable dielectric constant,low bias voltage,easy integration with microwave substrates,and low high-frequency loss.When used as a substrate with a variable dielectric constant for microwave passive devices,it conforms to the development trend of modern wireless communication systems of multi-frequency,broadband,miniaturization,multi-function,and high integration.The main work of this thesis is summarized as follows:1.Based on the theory of electrical tuning of the dielectric constant of liquid crystals,a broadband band-pass 10×10 frequency selective surface array that works in the Ku band is designed.Based on the torus structure,a comprehensive use of structural loading,inductive surface and capacitive surface coupling technologies,to achieve a broadband miniaturized FSS unit,the unit size is 1/4 ?.The liquid crystal material directly contacts the metal resonant circuit,and the frequency tuning can be achieved by changing the bias voltage.The test results show that the center frequency of the FSS array is 15.47 GHz,and its-10 d B passband bandwidth is 1.88 GHz,and the relative bandwidth exceeds 12%,reaching 1.22GHz;the frequency response reconfigurable range during the voltage increase is 8.2%,and the frequency is reconfigurable In the process,the passband bandwidth is above 12% to maintain the relative stability of the passband bandwidth.2.Based on the experience of broadband band-pass frequency selection surface design,we continue to design an ultra-wideband band-stop 8×8 frequency selection surface array in the Ku band.Based on the annular groove structure,the ultra-wideband characteristics are realized in the form of double-screen cascade using air as the medium.Considering that the use of liquid crystal materials to achieve reconfigurable characteristics requires two layers of metal resonant circuits as upper and lower electrodes,respectively,and finally by adding an inductive grid resonant structure to replace the dual-screen cascade form,a relative bandwidth of more than 40% of the stop band is achieved.The test results show that when the bias voltage is changed,the center resonant frequency shifts from 16.3GHz to low frequency to 14.87 GHz,the moving range reaches 1.43 GHz,and the relative reconfigurable range is 9.2%.3.Based on the ultra-wideband band-resistance FSS designed in this thesis,a joint tuning technology using liquid crystal materials and varactor diodes is proposed to increase the frequency tuning range of the FSS,and different forms of FSS unit simulations have verified the feasibility of the joint tuning technology.The joint tuning technology has obtained the advantages of different frequency tuning technologies.Through the change of the capacitance value of the varactor diode and the dielectric constant of the liquid crystal,the FSS obtains a larger frequency tuning range.The simulation verified that the reconfigurable range of the joint tuning frequency is about different tunings.The sum of the frequency reconfigurable range when the technology is tuned independently.At the same time,a preliminary introduction to the feed network required for joint tuning is provided,which provides a certain theoretical basis for subsequent implementation,improves the performance of the reconfigurable FSS,and expands its application prospects.