Application Of Graphene In Microwave Circuits And Antennas

With the high development of communication systems,miniaturization,tunability,high performance and low power consumption have become the mainstream of future electronic devices.Production costs will increase exponentially if we want to use traditional technology and materials to realize the above indicators.In order to promote the continuous progress of the wireless communication industry,the exploration and application reaserch of new materials is urgently needed on the basis of continuing traditional techniques and materials.As a new two-dimensional carbon-based material,graphene has excellent electrical,thermal,optical and mechanical properties,providing a new solution for the design of traditional microwave devices.Graphene can excite surface plasmon waves in the THz frequency band,and both the real and imaginary parts of the conductivity can be adjusted by external bias.Therefore,graphene-based THz absorbers,modulators and leaky wave antennas have been extensively studied.In the microwave frequency band,the imaginary part of graphene conductivity is close to zero,and only the real part can be regulated by external bias,resulting in less research on the application of graphene in the microwave frequency band.In addition,the problem of low conductivity has always limited the application of graphene in the field of antennas.From the perspective of engineering application,this paper aims to explore the application potential of graphene in microwave and millimeter wave circuits and antennas,and to make full use of graphene' characteristics of adjustable conductivity,flexibility and high electron mobility to improve the performance of traditional microwave devices and antenna.The main work of this paper includes the following aspects:1.The electrical,thermal,optical and mechanical properties of graphene are introduced.The preparation processes of graphene materials and their advantages and disadvantages are summarized.The mathematical model of graphene is established based on Kubo formula,which provides theoretical support for the design of devices.2.The application of graphene on microwave planar circuits was studied.Based on graphene's characteristics of omnidirectional resistance,microstrip nine-way power divider and coplanar waveguide tunable attenuator were designed.The nine-way power divider realizes high isolation level between each output ports of planar multi-way power divider based on graphene's characteristic of omnidirectional resistance.The bonding of the isolation resistors is avoided and the double-layer structure realizes the miniaturization design of the power divider.The tunable attenuator realizes dynamic adjustment of the attenuation based on the tunable conductivity of graphene.The working frequency of the attenuator also can be adjusted by changing the loading position of graphene.Both the power divider and the attenuator have been physically processed and tested.The test results show that graphene can greatly improve the performance of traditional microwave devices.3.The application of graphene on microwave and millimeter wave antenna is studied.A 24 GHz millimeter wave microstrip array antenna and a 5.8 GHz wearable circularly polarized antenna were designed based on a kind of high conductivity graphene conductive film.The 24 GHz millimeter wave antenna is verified by simulation and measurement,which can achieve similar performance with the same structure metal antenna and shows certain advantages in working bandwidth.The 5.8 GHz wearable circularly polarized antenna utilizes the flexible properties of graphene to maintain antenna performance in the flat and bent state.It meets internationally required electromagnetic radiation safety standards and can be used in wearable devices.