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Tuning Technology Researches On Microwave Key Passive Component Based On Liquid Crystal Material

Posted on:2018-03-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y P LiuFull Text:PDF
GTID:1318330512988098Subject:Electromagnetic field and microwave technology
Abstract/Summary:PDF Full Text Request
Liquid crystal material is organic compounds between liquid and crystalline state,which has some advantages of both liquid and crystal.Based on the electro-optic effect,liquid crystal materials have birefringence and dielectric anisotropy in the microwave frequency band and have wide application prospects in microwave radar,precision guidance and wireless broadband communications and other fields.The liquid crystal material is applied to the microwave key passive components,which can realize the control of the center frequency broadband tuning,realize the dynamic frequency selection,expand the tuning range and bandwidth,and realize the miniaturization and light weight of the electronic system.It can be widely used in microwave systems such as communication,radar,tracking receiver and electronic countermeasures equipment.It is one of the focus directions in microwave field.In the aspect of the tuning properties of liquid crystal materials,miniaturized resonance units and microwave key passive components,this paper thoroughly studies the physical properties of liquid crystal materials in the microwave frequency band,the liquid crystal tunable filters with open-loop resonant structure,the liquid crystal tunable filter integrated power divider with split-ring resonant structure,the liquid crystal tunable corrugated substrate integrated waveguide filters with complementary split-ring resonator and the liquid crystal tunable half-mode corrugated substrate integrated waveguide filters with complementary split-ring resonator.The research contents include as following:1)Study on dielectric properties of liquid crystal materials in microwave frequencys.Based on the mathematical model analysis of the physical characteristics such as the electric field effect,the birefringence property and the dielectric anisotropy of liquid crystals,The electrically tuning dielectric properties of liquid crystal materials are precisely modeled by using the continuum elastic deformation theory.The numerical simulation shows that the continuous distribution curve of rotation angle of director of the liquid crystal molecules at different positions increases with the applied bias.The dielectric constant of the liquid crystal in the microwave band is measured and calculated by using the improved resonance method with the correction factor,and to get extremes of the dielectric constant of the liquid crystal in the microwave frequency band,the electronic tuning dielectric characteristic model of the liquid crystal were measured and the microwave frequency continuous variation curve of liquid crystal dielectric parameters with external bias.The voltage-controlled characteristics of the loss tangent of the liquid crystal materials in the microwave band are obtained by using the iterative method in combination with the measured dielectric constant.In this paper,the pattern matching condition in the adjacent interface of the liquid crystal layer is analyzed by the eigenvalue.The transmission of the incident uniform plane wave in the liquid crystal is carried out by the Maxwell equations to obtain the corresponding electromagnetic field transmission characteristic.The experiment results show that the permittivityof sample liquid crystal ranges from(2.73,2.32,2.32)to(2.32,2.32,2.73)at microwave frequencies.The above researches have laid a foundation for applications of liquid crystal materials in microwave tunable devices;2)Based on the dielectric properties of liquid crystal materials at microwave frequencies,simulation and design methods of a tunable filter based on liquid crystal material are proposed.This method comprises the following steps: the liquid crystal material is encapsulated in the inner layer of the multilayer substrate;the inverted microstrip circuit structure is effectively contacted with the liquid crystal material;the tunable characteristic of the circuit is realized by the electrical tunable dielectric anisotropy of the liquid crystal material;the high-Q SRR magnetic resonant structure is cascaded to expand the broadband and produce stop-band suppression performance,the gradient impedance transformation structure is used to solve the port impedance matching and tunable stability problems caused by electronically controlled dielectric anisotropy of liquid crystal material.Then,a high performance microwave tunable filter is designed.Finally,the liquid crystal tunable filter is simulated and realized.The experiment result shows that the center frequency tuning range of this type of liquid crystal tunable filter can be greater than 430 MHz.The obtained circuit has the characteristics of wide bandwidth,small size,good transmission response,wide tunable pass band and good high-frequency selectivity;3)In order to achieve low loss transmission of the signal and strong suppression of the signal at the same time,a liquid crystal tunable filter integrated power divider with split-ring resonant(SRR)structure is proposed.The circular/polygon SRR structure is used instead of the quarter-wavelength converter of the Wilkinson power divider to integrate the filtering function in the power divider.The dynamic frequency selection and power distribution of the filter integrated power divider are realized by changing the bias voltage value and effectively controlling the effective dielectric distribution of the liquid crystal by using the inverted microstrip circuit structure and filling the liquid crystal material inside the power divider.Simulation and experiment results show that the center frequency tuning range of this type of tunable filter integrated power divider can be greater than 510 MHz and can effectively avoid the coupling of multiple resonators and the inter-stage impedance mismatching during tuning.The experimental design shows that one device effectively complete the function of two devices,it effectively reduce the energy loss in the circuit,and it meet the electronic system on the microwave components miniaturization,lightweight,easy integration,low loss,high Q value and other requirements;4)For the new waveguide filter,a novel microwave liquid crystal tunable corrugated substrate integrated waveguide(CSIW)filters with complementary split-ring resonator is proposed.The quarter microstrip branch of CSIW is used to replace the metal through hole of the substrate integrated waveguide(SIW)to solve the short-circuit problem between the two vertical and horizontal planes caused by the metal through holes with the bias voltage added in the SIW.According to the working principle and transmission characteristics of the CSIW transmission structure,the electromagnetic scattering characteristics of the complementary split-ring resonator(CSRR)the electrical tunable dielectric anisotropy of the liquid crystal material and the high tuning efficiency of the inverted microstrip line,the CSRR-CSIW filter based on the electric control liquid crystal material is realized.This waveguide filter has the advantages of high tuning efficiency,high quality factor and low transmission loss.In order to realize the miniaturization of the component,a novel half-mode corrugated substrate integrated waveguide(HMCSIW)tunable filter with CSRR structure is proposed.The novel microwave CSIW/HMCSIW tunable filter is analysed by transmission line theory and equivalent circuit principle.The experiment results show that the tunable frequency range of this novel filter can be expanded to 1.33 GHz,the in-band insertion loss is less than 5.3dB,the in-band return loss is more than 15 dB.The structure size is 18.5mm×17.2mm.The novel CSIW/HMCSIW-CSRR liquid crystal tunable filter is designed and realized with good frequency selection.
Keywords/Search Tags:nematic liquid crystal, microwave passive component, electric tuning dielectric characteristics, resonant metamaterial, liquid crystal planar waveguide filter
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