Millimeter Wave And Sub-6GHz Antenna Designs Based On Transparent Materials

There has been a significant rise in the requirement for the communication rates in the wake of the mushroom growth of smart cities and the Internet of Things.The working frequency of future communication systems,especially for fifth（5G）communication systems,will increase,as well as the bandwidth.The millimeter-wave band provides a broader development space for 5G communication technology due to its valuable and rich spectrum resources.At the same time,antennas continue to play an increasingly important role in the field of 5G communication technology as an indispensable terminal device.However,although there are various reports about the design of the combination of the millimeter-wave technology with traditional antennas,the limitations of materials greatly affect the application scenarios of antennas,and thus people put forward higher requirements on antenna designs in terms of beauty,transparency,and easy integration.Therefore,transparent antennas have become a hot field in recent years,which have some potential applications in solar panels,car windshields,liquid crystal displays,etc.With its special advantages in light transmittance,transparent antennas can greatly expand the antenna application scopes into the military field,medical monitoring field,automotive communication field,satellite communication field and 5G communication fields.In this thesis,facing 5G communication development trends,transparent mesh film is employed to design two transparent antennas,i.e.,wideband transparent antenna in the 5G millimeter wave band and dual-polarized,high isolation transparent antenna in the sub-6GHz band.Specifically,Firstly,a transparent antenna based on substrate integrated waveguide（SIW）operating in the millimeter-wave band of 5G wireless communication has been designed.A kind of transparent conductive film with small square resistance is used as the conductor structure and transparent PET material is chosen as the dielectric substrate.Based on the materials mentioned above,the antenna can obtain a high transparency of about 71%.By removing a part of the metallic vias on both sides of the SIW,the TE₁₀₃ mode can be better excited in the cavity.Then,the hybrid multi-mode resonance of the antenna can be realized by introducing slots with different shapes at the special positions on the cavity surface.The eigenmode theory and the theory of characteristic mode are respectively used to elaborate the operation mechanism of the multiple modes caused by the slots on the top surface on the SIW cavity,thus resulting in a wide band.Then further optimization is conducted for the antenna structure,and the working bandwidth of 24.31-27.81GHz is obtained.The peak gain of the antenna at 26.5GHz is 7.8 d Bi,and the cross-polarization ratio and front-to-back ratio in the working band can achieve more than 20 d B.Finally,the actual fabrication and measurement of the antenna are performed.The results show that the simulation and measured results are in good agreement.Compared with the reported millimeter-wave transparent antennas,the designed transparent antenna is of broad band and high gain.Secondly,a sub-6GHz dual-polarized transparent antenna working in the n78 frequency band of 5G communication has been designed.The antenna is composed of a multi-layer microstrip structure,the transparent conductive film with small square resistance is used as the conductive material,and the dielectric material used in this thesis is chosen as PC transparent substrate with a smaller relative permittivity and higher chemical stability.By using a stacked structure composed of a few patches and parasitic strips over the patch,multiple resonant modes can be introduced to broaden the band.The theory of characteristic mode is used to analyze the corresponding mode and field distributions of the antenna,showing the operating states at different resonant frequencies.Then,in order to further improve the impedance matching.The slots are etched on the ground to form a defective ground structure（DGS）for improvement of the isolation between two ports.Four corners of the coupling patch are cut off to obtain a stable gain of the antenna in the operating band.Finally,with the geometric optimizations,the resulting antenna has a working bandwidth of 2.87-3.81GHz,with the isolation between ports better than 27.1d B and front-to-back ratio more than 10 d B.Good agreement between the simulation and measurement demonstrates that the proposed antenna has a wide band,high gain and good isolation,etc.