Research On Reconfigurable Millimeter Wave Antenna Based On Liquid Crystal

With its rich spectrum resources,millimeter-wave wireless communication system has been widely concerned in recent years.As an indispensable component of millimeter-wave wireless communication system,millimeter-wave antenna has naturally become a research hotspot.At the same time,due to the urgent demand for multi-functional and large capacity system in current application scenarios,reconfigurable antenna has become the development trend of future antenna.Therefore,reconfigurable millimeter-wave antenna has high research value.For the reconfigurable millimeter-wave antenna,the reconfigurable technologies have attracted much attention.As a kind of tunable material,liquid crystal has the advantages of being suitable for high frequency,low cost and low direct current power consumption.Therefore,the researches of reconfigurable millimeter-wave antenna based on liquid crystal have broad application prospects.In this paper,a series of innovative researches about the reconfigurable millimeter-wave antenna based on liquid crystal is proposed.Simultaneously,a solution is proposed to enlarge the small tuning range of liquid crystal,which lays a foundation for the further development of liquid crystal in reconfigurable millimeter-wave antenna.The main contents of this paper are as follows:(1)A novel liquid crystal reconfigurable antenna based on characteristic mode theory is proposed.Different from the traditional microstrip patch antenna,it has a bending slot in the middle.Owing to the introduction of the bending slot,this antenna can operate in two modes within the same frequency band,namely odd mode and even mode.The resonance and radiation characteristics of the two modes are obtained by using the characteristic mode analysis method.The results show that the two modes have different resonant frequencies and radiation patterns.Therefore,by selecting liquid crystal as the dielectric layer of the antenna,the operating mode of the antenna can be changed by changing the dielectric constant of the liquid crystal.Depending on different designs,E-plane beam scanning antenna,H-plane beam scanning antenna and mode reconfigurable antenna can be realized.(2)An electrically steerable parasitic array radiator in package based on liquid crystal is proposed.It consists of one main driven microstrip patch element and two parasitic microstrip patch elements.Liquid crystal is the dielectric layer of the patches.This antenna is an electrically steerable parasitic array radiator based on the induced voltage model,which works in the Ka band.By changing the dielectric constant of liquid crystal to vary the induced voltages on the parasitic elements,the main beam can be steered to the desired direction.The experimental results show that this antenna can achieve a 53° scanning range at 28 GHz.At the same time,it has 8.3% impedance bandwidth and avoids both large direct current power consumption and complex bias scheme,making it suitable for millimeter-wave 5G access point antenna.(3)An electrically steerable parasitic array radiator based on tunable high impedance surface with liquid crystal is proposed.This antenna utilizes three microstrip patches as the radiators and a tunable high impedance surface based on liquid crystal as the ground plane.In this design,liquid crystal is deliberately disposed under the two parasitic microstrip patches to reduce the effect of relatively large dielectric loss and improve the gain and radiation efficiency of the antenna.More importantly,this work explores a tunable high impedance surface based on liquid crystal,which has advantages of simple structure and biasing scheme as compared with other tunable high impedance surfaces based on solid-state devices.By changing the permittivity of liquid crystal,the high impedance surface is able to manipulating the propagation of TE surface wave,therefore contolling the mutual coupling strength between the main and parasitic microstrip patches.Consequently,the main lobe can be steered to the desired direction and the scanning range of the antenna is enlarged.Measured results show that the antenna not only has acceptable gain,but also keeps a satisfactory scanning range.(4)A pattern reconfigurable antenna based on meta-liquid crystal molecular structure is proposed.Liquid crystal plays an important role in the field of tunable materials.However,in the millimeter-wave band,the tunable range of liquid crystal is relatively small,which limits its application.This chapter introduces a design method utilizing metamaterials characteristics to enhance the tunability of liquid crystal.In this design method,metamaterials structures are embedded into liquid crystal,which forms a new tunable material,namely the meta-liquid crystal molecular structure.By properly designing the metamaterials structures to meet the derived conditions,the tuning range of the meta-liquid crystal can be larger than that of the original liquid crystal.We apply it to the pattern reconfigurable antenna.The results show that the beam scanning range of the pattern reconfigurable antenna based on the meta-liquid crystal molecular structure is much wider than that of pattern reconfigurable antenna based on the original liquid crystal,which confirms the enhancement of the tunability.Therefore,this work fills the research gap in improving the performance of liquid crystal in millimeter-wave band.At the same time,the relationship between tunable materials and metamaterials is established,which means that the characteristics of tunable materials can be manipulated by metamaterials.