Applications Of High-Conductivity Graphene Films In Microstrip Filters

In the communication system,the filters,as the frequency-selecting device,play a very important role.With the continuous updating of the communication technology,the development of the filter has encountered new challenges.It is necessary not only to meet the higher and higher system requirements,but also to have the new characteristics required for application such as corrosion resistance,flexibility and mechanical stability.Graphene films have excellent properties in these aspects.The development of RF microwave applications and devices for graphene films is an important direction in the field of microwave applications and graphene industry.In this paper,the innovative application of high conductivity graphene film in microstrip filter is studied.The following three aspects of research have been carried out,and the new results of graphene film application in microstrip filters have been obtained.Firstly,a lowpass filter based on high-conductivity graphene films is investigated.The graphene films with a conductivity of1.1×10~6 S/m developed by the research group are used to design the filter instead of the traditional metals.The fabrication of graphene microstrip filter combines laser engraving technology with the characteristics of graphene films,which has the advantages of economy,convenience,high efficiency and environmental protection,accurate and fast.The measured results of the graphene filter made by this method are in good agreement with the simulation results.The microwave sdignal can be effectively propagating through the graphene filter.The actual cut-off frequency of the filter is 2.4GHz.The in-band insertion loss is 0.68dB and 29.61dB at 4GHz in stopband.In addition,the graphene filter can reach the same performance of the traditional copper filter.Secondly,a hairpin-bandpass filter based graphene films of wide bandstop is investigated.The filter is designed with hairpin structure.Because the traditional hairpin filters are easy to produce parasitic pass bands,the method of increasing L-shaped branches in the design can suppress the parasitic pass bands.The S parameter and current density of graphene hairpin filter are simulated,and the inhibition of the number of branches on parasitic pass band of the filter is investigated.The simulation results show that the more the number of branches,the better the suppression,and the increase of branches does not affect the pass-band performance of the filter.After adding four branches to the filter,the stopband was successfully broadened 3.8GHz to 10.18GHz,which is 4.39GHz wider than the unbranched traditional hairpin filter.Finally,the flexible filter of high-conductivity graphene films is studied.The design,fabrication and test of the filter are completed.The experimental results of the flexible filter with flat state show that the cut-off frequency is 3.6GHz,in-band maximum insertion loss is 0.82dB and stopband insertion loss is 26.2dB at 5GHz,which the stopband is broadened to 12GHz.The measured results are basically consistent with the simulation.When the proposed filter is bent downward 10°,20°,30°,40°and 50°,the performance changes little compared with the flat state.In additon,the proposed flexible filter is fatiguedly tested for 20 times.The test results show that the graphene filter still maintains a good performance.But the copper filter of the same configuration is only tested once and failed because of the fracture of the copper conductor band.The investigations on these high conductivity graphene films in microstrip filters extends the application of graphene films in RF devices and provides basic research results for the development of novel filters based on graphene films.