| Microwave and millimeter wave phased array antennas have important application value in wireless systems such as military/civil radar,satellite communications.Low-orbit satellite internet has become the main way for 6G communication deployment,and the demand for beam scanning is increasing.Conventional active phased array antennas are limited in many application scenarios due to their high cost,bulky size,limited operating frequency,and high power consumption.Low-cost,miniaturized microwave and millimeter-wave phased array solutions are urgently needed.Liquid crystal is a dielectric anisotropic material,and the dielectric constant of liquid crystal will change continuously under the action of an external electric field;with the increase of operating frequency,the loss of liquid crystal to microwaves does not change significantly.Using liquid crystal as an electrical modulation medium in an antenna can realize a low-cost,low-power,miniaturized reconfigurable antenna working in high frequency bands.In this work,the microwave and millimeter wave liquid crystal phased array antenna is studied.The main contributions of this thesis are listed as follows.1.Aiming at the basic characteristics and tunability mechanism of nematic liquid crystals in the Ka band,the non-uniformity,anisotropy,and electromagnetic properties of the dielectric constant of liquid crystals are studied;under the application of different bias voltages,the molecular structure,microwave loss,dielectric properties of liquid crystals are studied.We propose an equivalent dielectric constant modeling and extraction method,and establish the relationship model between liquid crystal dielectric constant and bias voltage.Finally,the theory of microstrip patch phased array antenna based on aperture coupling is studied.2.Due to high cost,difficult heat dissipation and low phase-shifting accuracy of the conventional semiconductor phase shifters,developling low cost and low power consumption phase shifter is needed.In this work,an inverted microstrip delay line phase shifter in Ka-band with liquid crystal as the substrate was designed and processed.The bias voltage was applied to the liquid crystal to change its dielectric.The tunability of dielectric constant can achieve continuous phase shifting of more than 360°.The engineering feasibility of the phase shifter is verified through theoretical derivation,numerical simulation and experimental testing.3.Using glass as the substrate and encapsulating liquid crystal in the middle,a multi-layer slot-coupled antenna unit with integrated liquid crystal phase shifter is designed to realize the integration of phase-shifting function and radiation function.The unit is arrayed,and the feed network,bias network and DC blocking structure are designed and integrated in cascade.Using liquid crystal display technology,a Ka-band8×8 linearly polarized liquid crystal phased array antenna is designed and processed.The effectiveness of the phased array is verified by numerical simulation and experimental tests.The phased array beam control algorithm and controlling circuit based on FPGA are developed to supply bias voltage,and the phasor of each unit is independently controlled to achieve ±42° two-dimensional beam scanning.The antenna thickness of the entire integrated phased array is within 1.5mm,which realizes the low cost and miniaturized structure characteristics.4.According to the needs of the 6th generation mobile communication and K-band satellite communication field,a K-band phased array antenna with a new topology of high gain circular polarization has been developed.The circular polarization is achieved by cutting the corners of the rectangular patch.The feeding layer and the phase-shifting layer are separated to different layers to facilitate the layout of the bias network.The waveguide power divider and the microstrip power divider are cascaded.The low-loss feeder network,large-scale array design,and high-isolation bias network were designed.Finally,a 16×16 two-dimensional planar phased array was designed and processed.With the wave control algorithm combined with FPGA,circularly polarized beam scanning in the range of ±50° in elevation and 0～360°in azimuth is demonstrated.The results validate that liquid crystal phased array is a kind of low-cost,high-gain,high-reliability K-band phased array antenna,which has great application value in mobile terminals and satellite communications. |
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